JP2008090116A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can form a high-quality image for a long period and is provided with a plurality of heat fixing members. <P>SOLUTION: The image forming apparatus that uses a liquid developer including a carrier and toner particles includes an image carrier which carries the image formed from the liquid developer, an intermediate transfer member which is an endless belt stretched by a drive roller and a tension roller, a squeeze means which recovers the carrier from a portion formed with the image primarily transferred on the intermediate transfer member, a secondary transfer roller which secondarily transfers the image on the intermediate transfer member to the transfer member, a first fixing unit which heats the image secondarily transferred to the transfer material by coming into contact with the transfer material, and a second fixing unit which is arranged nearer the downstream in the conveyance direction of the transfer material than the first fixing device and heats the image secondarily transferred to the transfer material by coming into contact with the transfer material. According to transfer material kind information, the amount of recovery of the carrier by a squeeze means and the heating temperature of the first fixing unit can be adjusted,. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus in which secondary transfer of an image from a secondary transfer roller to a transfer material is satisfactorily performed and separation of carrier and toner particles on the transfer material is promoted when the image is fixed on the transfer material. And an image forming method.

An image carrier that carries an image, an intermediate transfer member, a secondary transfer roller that secondarily transfers an image on the intermediate transfer member onto which the image has been primarily transferred from the image carrier to a transfer agent material, and a heat fixing member When the image on the intermediate transfer member is secondarily transferred to the transfer material, the secondary transfer roller uses an image forming apparatus that presses the transfer material against the intermediate transfer member, and the image is transferred to the transfer material. Forming is widely done.
In order to improve the quality of the image formed on the transfer material, there is provided an image forming apparatus in which a plurality of heat fixing members are provided, and the heating temperature of the transfer material by the heat fixing member located most downstream in the transfer material conveyance direction is highest. (For example, refer to Patent Document 1 and Patent Document 2).
Japanese Patent Laid-Open No. 2005-78084 Japanese Patent Laid-Open No. 11-202675

  Recently, there has been a demand for improvement in the quality of an image formed by an image forming apparatus, and the quality of an image formed by the image forming apparatus provided with a plurality of heat fixing members is not sufficient. An object of the present invention is to provide an image forming apparatus and an image forming method capable of forming a high-quality image over a long period of time.

The present invention is an image forming apparatus in which a liquid developer containing a carrier and toner particles is used, and is stretched by an image carrier that carries an image formed from the liquid developer, a drive roller, and a tension roller. An intermediate transfer member that is an endless belt, squeeze means for recovering a carrier from a portion on which the primary transferred image is formed on the intermediate transfer member, and secondary transfer of the image on the intermediate transfer member to a transfer material A secondary transfer roller that contacts the transfer material, a first fixing device that heats the image secondarily transferred to the transfer material, and a transfer material that is disposed downstream of the first fixing device in the conveying direction of the transfer material. A second fixing device that heats the image secondarily transferred to the transfer material in contact with the material is provided, and the carrier recovery amount by the squeeze means and the heating temperature of the first fixing device are adjusted according to the transfer material type information The image forming apparatus.
In a preferred embodiment of the present invention, the first fixing device and the second fixing device of the image forming apparatus are rollers.
The present invention relates to an image forming method in which a liquid developer containing a carrier and toner particles is used, the step of carrying an image formed from the liquid developer on an image carrier, and a tension between a drive roller and a tension roller. A step of primary transfer of an image from an image carrier to an intermediate transfer member, which is an endless belt, a step of recovering a carrier by a squeeze means from a portion on which the primary transfer image is formed on the intermediate transfer member, a secondary transfer Secondary transfer of the image on the intermediate transfer member to the transfer material by the roller, heating of the image secondarily transferred to the transfer material by the first fixing device in contact with the transfer material, and secondary transfer to the transfer material Image forming method including a step of heating the transferred image by a second fixing device in contact with the transfer material, and adjusting the carrier recovery amount by the squeeze means and the heating temperature of the first fixing device according to the transfer material type information It is.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing main components constituting the image forming apparatus according to the embodiment of the present invention.
Development units 30Y, 30M, 30C, and 30K are arranged at the lower part of the image forming apparatus, and the intermediate transfer belt 40 and the secondary transfer unit 60 are arranged for the image forming unit of each color arranged in the center of the image forming apparatus. Arranged at the top of the image forming apparatus.

  The image forming unit includes image carriers 10Y, 10M, 10C, and 10K, charging rollers 11Y, 11M, 11C, and 11K, and exposure units 12Y, 12M, 12C, and 12K (not shown). The exposure units 12Y, 12M, 12C, and 12K have an optical system such as a semiconductor laser, a polygon mirror, and an F-θ lens. The image bearing members 10Y, 10M, 10C, and 10K are provided by charging rollers 11Y, 11M, 11C, and 11K. Are uniformly charged and irradiated with a modulated laser beam based on the input image signal by the exposure units 12Y, 12M, 12C, and 12K, and charged image carriers 10Y, 10M, 10C, and 10K. An electrostatic latent image is formed thereon.

  The developing units 30Y, 30M, 30C, and 30K generally include liquid developers of respective colors including the developing rollers 20Y, 20M, 20C, and 20K, yellow (Y), magenta (M), cyan (C), and black (K). Developer containers (reservoirs) 31Y, 31M, 31C, 31K to be stored, and developer supply rollers for supplying liquid developers of these colors from the developer containers 31Y, 31M, 31C, 31K to the developing rollers 20Y, 20M, 20C, 20K 32Y, 32M, 32C, 32K and the like, and the electrostatic latent images formed on the image carriers 10Y, 10M, 10C, and 10K are developed with liquid developers of respective colors.

  The intermediate transfer belt 40 is an endless belt, is stretched between a belt driving roller 41 and a tension roller 42, and is contacted with the image carriers 10Y, 10M, 10C, and 10K by primary transfer portions 50Y, 50M, 50C, and 50K. It is rotationally driven by the driving roller 41 while in contact. The primary transfer portions 50Y, 50M, 50C, and 50K are arranged such that the primary transfer backup rollers 51Y, 51M, 51C, and 51K are opposed to each other with the image transfer bodies 10Y, 10M, 10C, and 10K interposed between the intermediate transfer belt 40 and the image transfer body 10Y. 10M, 10C, and 10K are used as transfer positions, and the developed toner images of the respective colors on the image carriers 10Y, 10M, 10C, and 10K are sequentially transferred onto the intermediate transfer belt 40 and transferred. A toner image is formed.

  In the secondary transfer unit 60, a secondary transfer roller 61 is disposed opposite to the belt driving roller 41 with the intermediate transfer belt 40 interposed therebetween, and a cleaning device including a secondary transfer roller cleaning blade 62 and a developer recovery unit 63 is disposed. The Then, at the transfer position where the secondary transfer roller 61 is disposed, art paper, coated paper, fine paper, or the like, on which the single-color toner image or full-color toner image formed on the intermediate transfer belt 40 is transported through the transfer material transport path L. Transfer to a transfer material such as coated paper, fine paper, OHP film (plastic film). The belt driving roller 41 has a configuration in which an elastic layer is disposed on the surface of the roller core, and a preheating heater 70 made of a halogen lamp or the like is built in along the axial direction of the belt driving roller 41. This preheating heater 70 is used for preheating before the toner image on the transfer material is fixed by the fixing unit 80. Further, the length of the preheating heater 70 in the roller axis direction is configured to be equal to or greater than the width of the widest transfer material handled by the image forming apparatus. In the present invention, since the secondary transfer unit 60 is provided with such preliminary heating, “secondary transfer” may be referred to as “heated secondary transfer” or the like. Details of the secondary heating transfer of the present invention will be described later.

  Downstream of the transfer material conveyance path L, a transfer material squeeze unit 75 and a fixing unit 80 are sequentially arranged. The transfer material squeeze unit 75 is disposed so as to face the transfer material squeeze roller 76 with an elastic body coated on the surface thereof and a transfer material squeeze roller 76 made of an elastic roller member that rotates in sliding contact with the transfer material. A transfer material backup roller 77, a cleaning blade 78 that slides on the transfer material squeeze roller 76 to clean the surface, and a carrier recovery unit 79 are configured. In the transfer material squeeze unit 75, excess carrier is collected so that the toner particles are optimally fixed to the transfer material in the fixing unit 80.

Next, in the fixing unit 80, the single color toner image or the full color toner image transferred onto the transfer material is fused and fixed to the transfer material. The fixing unit 80 includes a first fixing roller 81 that preheats a transfer material that passes through, a first pressure roller 82 that presses the transfer material against the first fixing roller 81, a first fixing roller 81, and a first pressure roller. The second fixing roller 83 is provided downstream of the roller 82 and heats the passing transfer material to a temperature higher than the softening temperature of the toner particles. The second pressure roller 84 presses the transfer material against the second fixing roller 83. ing. The first fixing roller 81 and the second fixing roller 83 are formed of a metal core having an elastic layer on the surface, and a heater (not shown) is built in the first fixing roller 81 and the second fixing roller 83. A corona charger 85 and a transfer material are sandwiched between a roller pair consisting of the first fixing roller 81 and the first pressure roller 82 and a roller pair consisting of the second fixing roller 83 and the second pressure roller 84. A counter electrode 86 disposed to face the corona charger 85 may be provided. Depending on the type of the transfer material passing between the corona charger 85 and the counter electrode 86, the strength and direction of electric field application are changed, and the fixing of the toner particles to the transfer material is optimized.
On the side of the tension roller 42 that stretches the secondary transfer unit 60 together with the belt driving roller 41, a cleaning device including an intermediate transfer belt cleaning blade 46 and a developer recovery unit 47 is disposed along the outer periphery thereof.

Next, the image forming unit and the developing unit will be described. FIG. 2 is a cross-sectional view showing main components of the image forming unit and the developing unit. Since the configurations of the image forming unit and the developing unit for each color are the same, the following description will be made based on the yellow (Y) image forming unit and the developing unit.
The image forming unit includes a cleaning device including a latent image eraser 16Y, an image carrier cleaning blade 17Y, and a developer recovery unit 18Y along the rotation direction of the outer periphery of the image carrier 10Y, a charging roller 11Y, an exposure unit 12Y, and a development unit. A cleaning device including a developing roller 20Y of 30Y, an image carrier squeeze roller 13Y, an image carrier squeeze roller cleaning blade 14Y, and a developer recovery unit 15Y, which are associated with the development roller 20Y, is provided. In the developing unit 30Y, a cleaning blade 21Y, a developer supply roller 32Y using an anilox roller, and a developer compression roller 22Y are arranged on the outer periphery of the developing roller 20Y, and the liquid developer agitation is placed in the liquid developer container 31Y. A roller 34Y and a developer supply roller 32Y are accommodated. A primary transfer roller 51Y of the primary transfer portion is disposed along the intermediate transfer belt 40 at a position facing the image carrier 10Y, and an intermediate transfer belt squeeze roller 53Y, a backup roller 54Y, an intermediate transfer belt are disposed downstream of the moving direction. An intermediate transfer belt squeeze device 52Y including a belt squeeze roller cleaning blade 55Y and a developer recovery unit 56Y is disposed.

The image carrier 10Y is a photosensitive drum made of a cylindrical member that is wider than the developing roller 20Y and has a photosensitive layer formed on the outer peripheral surface thereof. For example, the image carrier 10Y rotates in a clockwise direction as shown in FIG. The photosensitive layer of the image carrier 10Y is composed of an organic image carrier or an amorphous silicon image carrier. The charging roller 11Y is disposed upstream of the nip portion between the image carrier 10Y and the developing roller 20Y in the rotation direction of the image carrier 10Y, and a bias having the same polarity as the toner charging polarity is applied from a power supply device (not shown) to The carrier 10Y is charged. The exposure unit 12Y irradiates laser light onto the image carrier 10Y charged by the charging roller 11Y on the downstream side in the rotation direction of the image carrier 10Y with respect to the charging roller 11Y, thereby forming a latent image on the image carrier 10Y. To do.
The developing unit 30Y includes a developer compression roller 22Y, a developer container 31Y that stores a liquid developer in a state where toner is dispersed in a carrier at an approximate mass ratio of about 25%, a developing roller 20Y that carries the liquid developer, a liquid The developer supply roller 32Y, the regulating blade 33Y, the stirring roller 34Y, and the liquid developer carried on the developing roller 20Y for maintaining the developer in a uniform dispersed state by stirring the developer are brought into a compacted state. And a developing roller cleaning blade 21Y for cleaning the developing roller 22Y and the developing roller 20Y.

The liquid developer contained in the developer container 31Y is a low-concentration (about 1 to 2% by mass) and low-viscosity room temperature that uses Isopar (registered trademark: exon) as a carrier. It is not a volatile liquid developer having volatility, but a non-volatile liquid developer having a high concentration and high viscosity and having non-volatility at room temperature. That is, the liquid developer in the present invention has a volume average particle diameter in which a colorant such as a pigment is dispersed in an epoxy resin, a polyester resin, a polyurethane resin, or a mixture thereof, and is 0.5 μm to 6 μm, preferably 1.5 to A liquid developer having a high viscosity (about 30 to 10,000 mPa · s) in which toner particles of 3.5 μm are added to a carrier together with a dispersant so that the toner particle concentration is 10 to 35% by mass, preferably 15 to 25% by mass. It is.
Carriers are a) paraffinic, isoparaffinic or cycloparaffinic hydrocarbons, b) linear, branched or cyclic silicones, c) fluorinated hydrocarbons containing fluorinated ethers, d) refined vegetable oils, e) refined Selected from esterified vegetable oils. The carrier has a viscosity of 0.5 to 1000 mPa · s.
The dispersant is not particularly limited. Dispersants include polyesteramine dispersant Solsperse 13940 (registered trademark, manufactured by Avecia), aminosilicone dispersant Finisch WR1600 (produced by Wacker Chemicals), Plexol (produced by Rohm and Haas), FOA- 2 (manufactured by Du Pont), Antaron AV220 (manufactured by ISP Technologies), which is an alkylated polyvinylpyrrolidone, and Disperse Ayd1 (manufactured by Elementis DCP Inc.). The content of the dispersant is 0.1 to 20% by mass with respect to the liquid developer.

The developer supply roller 32Y is a cylindrical member that rotates in a clockwise direction as shown in FIG. 2, for example, and has a fine and uniform spiral groove on the surface so that the developer can be easily carried on the surface. It is an anilox roller which formed the uneven surface by. The groove dimensions are such that the groove pitch is about 130 μm and the groove depth is about 30 μm. The developer supply roller 32Y supplies the liquid developer from the developer container 31Y to the developing roller 20Y. The stirring roller 34Y and the developer supply roller 32Y may be in sliding contact with each other, but may be arranged in a distant relationship.
The regulating blade 33Y is composed of an elastic blade whose surface is covered with an elastic body, a rubber portion made of urethane rubber or the like that contacts the surface of the developer supply roller 32Y, and a metal plate or the like that supports the rubber portion. The Then, the film thickness and amount of the liquid developer carried and conveyed by the developer supply roller 32Y composed of an anilox roller are regulated and adjusted, and the amount of liquid developer supplied to the developing roller 20Y is adjusted. Note that the rotation direction of the developer supply roller 32Y may be the opposite direction instead of the arrow direction shown in FIG. 2, and the regulating blade 33Y at that time requires an arrangement corresponding to the rotation direction.

The developing roller 20Y is a cylindrical member, and rotates counterclockwise around the rotation axis as shown in FIG. The developing roller 20Y is provided with an elastic layer made of polyurethane rubber, silicon rubber, NBR or the like on the outer periphery of an inner core made of metal such as iron. The developing roller cleaning blade 21Y is made of rubber or the like that comes into contact with the surface of the developing roller 20Y. The developing roller 20Y is arranged downstream of the developing nip portion where the developing roller 20Y comes into contact with the image carrier 10Y in the rotation direction of the developing roller 20Y. The liquid developer remaining on the developing roller 20Y is scraped off and removed.
The developer compression roller 22Y is a cylindrical member having a structure in which a conductive resin layer or a rubber layer is provided on the surface layer of a metal roller base. For example, as shown in FIG. Rotate around. The developer compression roller 22Y has means for increasing the charging bias on the surface of the development roller 20Y, and the developer conveyed by the development roller 20Y is brought into sliding contact with the developer compression roller 22Y as shown in FIG. An electric field is applied from the developer compression roller 22Y side toward the developing roller 20Y at a compaction site to be formed. The electric field applying means for compaction may be corona discharge from a corona discharger instead of the roller shown in FIG. Some of the toner that has not been compacted by the developer compression roller 22Y is scraped off by the developer compression roller cleaning blade 23Y, merged with the developer in the reservoir 31Y, and reused.

The image carrier squeeze device is disposed on the downstream side of the developing device 20Y so as to face the image carrier 10Y and collects the excess developer of the toner image developed on the image carrier 10Y, as shown in FIG. As described above, the image carrier squeeze roller 13Y made of an elastic roller member that is slidably contacted with the image carrier 10Y, the cleaning blade 14Y that presses and slidably contacts the image carrier squeeze roller 13Y, and the surface of the developer collecting unit 15Y. It consists of.
In the primary transfer unit 50Y, the developer image developed on the image carrier 10Y is transferred to the intermediate transfer belt 40 by the primary transfer roller 51Y. Here, the image carrier 10Y and the intermediate transfer belt 40 are configured to move at a constant speed, reducing the driving load of rotation and movement, and suppressing the disturbance effect on the visible toner image of the image carrier 10Y. Yes. The primary transfer portion 50Y for the first color does not cause a color mixing phenomenon because it is the first primary transfer, but since the second and subsequent colors transfer different color toner images onto the already transferred primary toner image portions, the intermediate transfer belt 40 is overlapped. Due to the so-called reverse transfer phenomenon in which the toner moves from the image carrier 10 (M, C, K) to the image carrier 10 (M, C, K), the reverse transfer toner and the untransferred toner are mixed and are carried on the image carrier 10 (M, C, K) together with the excess carrier. Moved from the image carrier by the action of the cleaning blade 17 (M, C, K) and pooled.

  The intermediate transfer belt squeeze device 52Y is disposed on the downstream side of the primary transfer unit 50Y, and removes excess carriers from the intermediate transfer belt 40 to increase the toner particle ratio in the visible image. Preferred secondary transfer at a stage where the carrier amount of the developer (toner dispersed in the carrier) transferred to the intermediate transfer belt 40 in the section 50Y is secondarily transferred to the final transfer material and proceeds to the fixing process. In order to exhibit the function and the fixing function, it is provided as means for further removing excess carrier from the intermediate transfer belt 40 when the toner in the liquid developer has not reached the desired dispersion state. Similar to the image carrier squeeze device 52Y, the intermediate transfer belt squeeze device 52Y includes an intermediate transfer belt squeeze roller 53Y composed of an elastic roller member that is covered with an elastic body and is in sliding contact with the image carrier 40, and the image carrier 40. A backup roller 54Y disposed opposite to the intermediate transfer belt squeeze roller 53Y, a cleaning blade 55Y for pressing and slidingly contacting the intermediate transfer belt squeeze roller 53Y, and a developer collecting unit 56Y. The developer recovery unit 56Y also serves as a recovery mechanism for the carrier liquid recovered by the magenta image carrier squeeze roller cleaning blade 14M disposed on the downstream side thereof.

  The surplus carrier collecting ability can be set to a desired collecting ability according to the rotational direction of the intermediate transfer belt squeeze roller 53Y and the relative peripheral speed difference of the surface of the intermediate transfer belt squeeze roller 53Y with respect to the moving speed of the intermediate transfer belt 40. Thus, when the intermediate transfer belt 40 is rotated in the counter direction, the recovery capability is increased, and even if the peripheral speed difference is set to be large, the recovery capability is increased, and this synergistic action is also possible. In this embodiment, as an example, the intermediate transfer belt squeeze roller 53Y rotates with the intermediate transfer belt 40 at substantially the same peripheral speed, and excess carrier and fog toner are collected from the developer primarily transferred to the intermediate transfer belt 40. Therefore, both rotational driving loads are reduced, and the disturbance effect on the toner image of the intermediate transfer belt 40 is suppressed.

The intermediate transfer belt 40 of the present embodiment is not particularly limited as long as it has good heat resistance, but in the present embodiment, polyimide, polyamideimide, polyetherimide, polyester, polyacrylate, polyethersulfur is used. An endless belt was formed by dispersing fine powders with excellent thermal conductivity such as carbon black that imparts conductivity to resin materials with excellent heat resistance and mechanical strength such as von, polyetherketone and polybaravanic acid. The thing was comprised as a base material. The fine powder excellent in thermal conductivity imparting conductivity is not limited to carbon black, and is a fine powder excellent in thermal conductivity such as magnesium oxide, silica, alumina, silicon nitride, zinc oxide, and the like. Also good.
A material having good heat resistance and releasability, such as fluorine resin such as PFA and PTFE, fluorine rubber, etc., is imparted to the outer peripheral surface of the endless belt base material having the above structure by the same means as described above, and 2 μm. The surface layer is covered with a means such as a coating with a thickness of 10 μm to increase the transfer efficiency of transferring the developer in the heat transfer nip onto the transfer material.

Although it is desirable that the intermediate transfer belt 40 has a small heat capacity as much as possible in order to increase the preheating efficiency of the carried developer, in this embodiment, the thickness including the surface layer is set to 80 μm in consideration of mechanical strength. . The intermediate transfer belt 40 may be configured to have a thickness of 30 μm or less as long as the intermediate transfer belt 40 has a regulation configuration in which stress is not generated at the end in the meandering control of the intermediate transfer belt 40. For example, it may be configured with a thickness of 120 μm or more, but it is not very advantageous in consideration of cost.
The belt driving roller 41 is configured to drive and convey the intermediate transfer belt 40 and to have a preheating heater 70 such as a halogen lamp inside as a heating unit, and the temperature is controlled by a control unit (not shown). The toner images that are primarily transferred from the plurality of image carriers 10Y, 10M, 10C, and 10K and overlaid with color are carried on the intermediate transfer belt 40 and conveyed to the secondary transfer site, and a preheater heater 70 is provided inside. Then, the belt drive roller 41 that is heated is wound around and heated.
The belt driving roller 41 of the present embodiment has a heat resistant and conductive elastic layer 72 formed on the outer periphery of a cored bar 71 made of a thin pipe material in order to reduce the heat capacity, and a halogen as a heating source inside. A preheating heater 70 such as a lamp is built in, and is configured to be rotatable by being driven by a drive source (not shown).

  The secondary transfer roller 61 is a structure that is disposed facing the belt driving roller 41 and presses the belt driving roller 41 toward the belt driving roller 41 side with a desired pressure. However, it may be driven and rotated by a drive source (not shown).

In the above configuration, when a trouble occurs in feeding the transfer material to the nip (common name: jam) in the secondary transfer unit 60, the transfer material is not interposed in the nip. Therefore, a secondary transfer roller cleaning blade 62 that is in sliding contact with the surface of the secondary transfer roller 61 is provided to remove this and prepare for the next secondary transfer. In order to effectively perform this cleaning function, it is desirable to have a structure in which the developer is easily peeled off from the surface of the secondary transfer roller 61. The specific configuration of the secondary transfer roller 61 is a thin wall to reduce the heat capacity. Coating or tube coating on the outer periphery of the cored bar made of pipe material with heat-resistant and conductive properties, such as PFA resin and other fluorine-based resins, such as PFA resin, with excellent developer release characteristics. It is preferable to configure the same. As described above, the secondary transfer roller 61 has a surface hardness higher than that of the elastic layer 72 of the belt driving roller 41, presses toward the belt driving roller 41, is fed, and enters the heating secondary transfer nip. The structure is such that a heated secondary transfer nip is formed in which the elastic layer 72 of the belt driving roller 41 is recessed with the material and the intermediate transfer belt 40 interposed therebetween. On the surface of the outer periphery of the cored bar made of a thin pipe material to reduce the heat capacity, an elastic layer higher than the elastic layer 72 of the belt drive roller 41 made of heat-resistant and conductive silicon rubber or the like is formed. A developer in which carbon is dispersed in a PFA resin or the like having excellent developer release characteristics may be coated or covered with a tube or the like. Forming effect a state in which modeled after the surface of the recording medium for the further improved.

A state when the transfer material passes through the secondary transfer unit 60 configured as described above will be described. FIG. 3 is a diagram schematically showing an enlarged view of a cross section during secondary transfer in the secondary transfer unit 60 according to the embodiment of the present invention.
The secondary transfer roller 61 has a surface hardness higher than that of the elastic layer 72 of the belt driving roller 41, and is fed when pressed toward the belt driving roller 41 side. As shown in FIG. 3 with the transfer belt interposed, a heated secondary transfer nip is formed in which the elastic layer 72 of the belt driving roller 41 is recessed. When the leading edge of the transfer material 100 is discharged from the heating secondary transfer nip in which the elastic layer 72 of the belt driving roller 41 is recessed, the transfer material 100 itself has an elastic force (commonly referred to as the waist strength of the transfer material). Due to the deformation behavior of the transfer material 100, the front end of the transfer material 100 is smoothly separated without being wound around the intermediate transfer belt 40 to which a transfer bias is applied, and is discharged.
The secondary transfer roller 61 is required to have a conductive surface in order to effectively apply the transfer bias, and preferable transfer of the developer from the intermediate transfer belt 40 wound around the belt driving roller 41. In order to achieve the above, the surface of the recording medium 100 is made as smooth as possible by using the elasticity of the belt driving roller 41 with respect to the developer carried on the intermediate transfer belt 40. It is desirable to form a state. Specifically, it is preferable that the ten-point average roughness (Rz) is 0.5 to 10 times the volume average particle diameter of the toner particles 101.

  On the other hand, in the scene where the belt driving roller 41 forms a state in which the developer carried on the intermediate transfer belt 40 is made to follow the surface of the transfer material 100 using the elasticity of the belt driving roller 41 as described above. The elastic layer 72 having a low hardness is more suitable for the purpose. On the other hand, for the purpose of regularly driving the intermediate transfer belt 40, the elastic layer 72 has a high hardness and a heat resistance. In order to suppress a change in diameter due to expansion as small as possible, it is desirable to make the thickness of the elastic layer 72 small. The specific configuration in the present embodiment is that the elastic layer 72 including the surface layer has a thickness of 0.4 mm and a hardness of JIS A 30 degrees, but a thickness of 0.3 mm and a hardness of JIS A 20 degrees level, or Even if the thickness is 1 mm and the hardness is JIS A 60 degree level, the purpose can be achieved.

The toner images that are primary-transferred from a plurality of image carriers 10Y, 10M, 10C, and 10K and overlaid are carried on the intermediate transfer belt 40, conveyed to the secondary transfer unit 60, and heated by the preheating heater 70. The belt drive roller 41 is wound around and heated. As described above, when the intermediate transfer belt 40 configured to have a very small heat capacity is wound around the belt drive roller 41, the intermediate transfer belt 40 is preheated together with the developer in a very short time due to the temperature of the heated belt drive roller 41. To the secondary transfer nip.
The heating secondary transfer process of the present embodiment does not completely fix the toner by the secondary transfer unit 60, but improves the secondary transfer efficiency and the fixing by the fixing unit 80 disposed on the downstream side. A heating temperature that improves the ability and achieves the object is sufficient.

Next, the heating secondary transfer resistance value and the bias application relationship will be described. The belt driving roller 41 of the present embodiment has a heat resistant and conductive elastic layer 72 formed on the outer periphery of a cored bar made of a thin pipe material in order to reduce the heat capacity, and a halogen lamp as a heating source inside. A (preheating heater 70) is built in, and is configured to be rotatable by being driven by a drive source (not shown). The elastic layer 72 is obtained by dispersing conductive fine powder such as carbon black fine powder in rubber having excellent heat resistance such as silicon rubber and urethane rubber.
Further, rubbers having excellent heat resistance such as silicon rubber and urethane rubber generally have strong tackiness and a strong frictional force with the intermediate transfer belt 40, so that the intermediate transfer belt 40 moves in a direction perpendicular to the moving direction. Since this is not preferable for the meandering regulation, it is necessary to reduce the frictional force between the surface of the elastic layer 72 and the intermediate transfer belt 40. Therefore, fine particles made of a fluorine material that has high heat resistance and reduces frictional force, such as fluororubber and fluororesin, are dispersed in the rubber having excellent heat resistance. Alternatively, the outer layer of the conductive rubber with excellent heat resistance may be coated with a conductive fluorine material or the like to reduce frictional force, or the tube may be covered to form a surface layer, or the conductive rubber with excellent heat resistance. Further, a lubricant such as heat-resistant conductive grease may be interposed on the contact surface of the intermediate transfer belt 40. The volume resistance value of the portion of the elastic layer 72 in contact with the intermediate transfer belt 40 is configured with a low resistance of 10 ⁵ Ω or less.

On the other hand, the intermediate transfer belt 40 is an endless belt obtained by dispersing fine powders having excellent thermal conductivity such as carbon black which imparts conductivity to a resin material having excellent heat resistance and mechanical strength such as polyimide and polyamideimide. The base material is formed on the outer peripheral surface of the endless belt base material and is made of a material having good heat resistance and releasability such as PFA and PTFE fluorine resin, and the like. And having a thickness of 2 μm to 10 μm and covering the surface layer by means such as coating, the volume resistance value including the belt base material and the surface layer is 10 ⁶ larger than the volume resistance value of the belt driving roller 41. It is composed of a medium resistance region of Ω to ^{10 10} Ω. The secondary transfer roller 61 is composed of a PFA resin or the like that has heat resistance and conductivity on the outer periphery of a cored bar made of a thin pipe material in order to reduce heat capacity, and has excellent developer release characteristics. It is constructed by coating or tube coating or the like in which black fine powder is dispersed, and the volume resistance value of the surface layer portion is constituted by a low resistance of 10 ⁵ Ω or less which is smaller than the volume resistance value of the intermediate transfer belt 40. It is.

  In the relationship between the belt driving roller 41, the intermediate transfer belt 40, and the secondary transfer roller 61, when a secondary transfer bias is applied in a direction in which the toner particles move toward the transfer material that has entered the heating secondary transfer nip, In particular, the transfer mechanism is developed based on the volume resistance value of the intermediate transfer belt 40, and as shown in FIG. 3, the toner carried on the intermediate transfer belt and conveyed is aggregated with the toner particles 101 on the intermediate transfer belt 40 side. Thus, the toner particles 101 in the aggregated state move to the transfer material 100 side in the heated secondary transfer nip, and good secondary transfer of the toner particles 101 can be obtained. On the other hand, the carrier 102 remaining on the intermediate transfer belt 40 side is transported and removed by the intermediate transfer belt cleaning blade 46 at the tension roller 42 portion disposed on the other side of the belt driving roller 41.

Next, recovery of excess carriers by the intermediate transfer belt squeeze roller 53Y before the secondary heating transfer will be described in detail. The amount of carrier required at the time of secondary heating transfer varies depending on the transfer material. Art paper, coated paper and fine coated paper have a coating layer on the surface. The amount of art paper coating is the largest, then the amount of coated paper coating is the largest, and the amount of fine coated paper coating is the smallest. Then, the carrier of the liquid developer is rapidly sucked by the coating layer, and the toner particles in the liquid developer move to the surface of the art paper, the coated paper or the fine coated paper by the suction force. Therefore, when the transfer material is art paper, coated paper, or fine coated paper (case a), the squeeze strength by the intermediate transfer belt squeeze roller 53Y before the secondary transfer by heating is such that a certain amount of carrier is present on the intermediate transfer belt 40. Adjusted to remain.
The fine paper does not have a coating layer on the surface. The carrier of the liquid developer is not attracted to the high quality paper, and the toner particles move to the surface of the high quality paper through the carrier by the secondary transfer bias. Therefore, when the transfer material is high-quality paper, the squeeze strength by the intermediate transfer belt squeeze roller 53Y before the secondary heating transfer is such that the amount of carrier remaining on the intermediate transfer belt 40 is larger than the carrier amount in case a. Adjusted to

  The OHP film also has no coating layer on the surface. The liquid developer carrier is not attracted to the OHP film, and the toner particles do not move to the OHP film surface together with the carrier. However, since the affinity between the OHP film and the toner particles is higher than the affinity between the carrier and the toner particles, and the surface of the OHP film is smooth, the toner particles move in a small amount of the carrier to the surface of the OHP film. Therefore, when the transfer material is an OHP film, the squeeze strength by the intermediate transfer belt squeeze roller 53Y before the secondary heating transfer is such that the amount of carrier remaining on the intermediate transfer belt 40 is smaller than the carrier amount in case a. Adjusted to

  Next, squeeze after heating secondary transfer will be described. At the time of main fixing after the secondary heating transfer, the toner particle concentration on the transfer material needs to be 70 to 85% by mass. When the toner particle concentration is less than 70% by mass, the binding of the toner particles is inhibited by the carrier. When the toner particle concentration exceeds 85% by mass, the carrier release action does not work, and offset to the fixing roller is likely to occur. Therefore, in this embodiment, after the secondary transfer by heating and before the main fixing, excess carrier is collected in the transfer material squeeze unit 75 and the toner particle concentration on the transfer material is adjusted to a range of 70 to 80% by mass. Can do. The squeeze strength in the transfer material squeeze unit 75 is set by a) the rotational direction of the squeeze roller 76, b) the relative peripheral speed difference of the surface of the squeeze roller 76 with respect to the transfer material moving speed, and c) the bias applied to the squeeze roller 76. The As the amount of coating on the surface of the transfer material increases, the carrier is more easily absorbed by the transfer material, and the squeeze strength by the squeeze roller 76 is adjusted to be weak. Therefore, the squeeze strength by the squeeze roller 76 increases in the order of OHP film, fine paper> fine coated paper, coated paper> art paper.

  Next, a fixing process in the fixing unit 80 after the secondary heating transfer will be described. After the excess carrier is collected in the transfer material squeeze unit 75, the fixing unit 80 performs the main fixing. In the main fixing process, first, preheating is performed by the first fixing roller 81 in order to separate the carrier and the toner particles. By preheating, the function of the dispersant in the liquid developer is weakened. Further, when the transfer material is paper, the carrier is easily absorbed into the paper by preheating. If the preheating temperature is too high, the toner particles are softened and offset occurs. The appropriate preheating temperature varies depending on the type of transfer material. As the amount of coating on the surface of the transfer material increases, the carrier is more easily absorbed by the transfer material, and the preheat temperature may be lower. When the transfer material is an OHP film, the carrier is not absorbed by the OHP film, so it is necessary to increase the preheat temperature to weaken the function of the dispersant and promote separation of the carrier and toner particles.

In addition, after preheating, an electric field can be applied to promote separation of the carrier and the toner particles. A specific example of the means for applying the electric field is provided between a roller pair composed of the first fixing roller 81 and the first pressure roller 82 and a roller pair composed of the second fixing roller 83 and the second pressure roller 84. A corona charger 85. A positive or negative electric field of 4 to 6 kV is applied to the corona wire of the corona charger 85. The carrier is absorbed by art paper, coated paper, finely coated paper and fine paper. The toner particles are positively charged. Therefore, when the transfer material is art paper, coated paper, fine coated paper, or high-quality paper, an electric field is applied by the corona charger 85 so that a negative corona falls on the toner particles, and the toner particles are removed from the art paper or coated paper. Then, the carrier is separated from the surface of the fine coated paper or fine paper, and the carrier is absorbed by the art paper, coated paper, fine coated paper or fine paper. On the other hand, when the transfer material is an OHP film, an electric field is applied by the corona charger 85 so that a positive corona falls on the toner particles, and the toner particles are pressed against the OHP film.
A second fixing roller 83 is provided downstream of the first fixing roller 81. The toner particles are heated by the second fixing roller 83 to a temperature equal to or higher than the softening temperature of the toner particles and fixed to the transfer material.

(Example 1)
For each transfer material type, the squeeze strength by the intermediate transfer belt squeeze roller 53Y and the heating temperature of the first fixing roller 81 were adjusted as shown in Table 1 to perform a fixing test. As a result, the toner particles were satisfactorily fixed on the transfer material.

1 is a diagram illustrating main components constituting an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating main components of an image forming unit and a developing unit. The figure which expanded the mode of the section at the time of the secondary transfer in the secondary transfer unit 60 which is an embodiment of the present invention, and was shown typically.

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 recovery unit, 16Y: Latent image eraser, 17Y: Image carrier cleaning blade, 18Y ... Developer recovery unit, 20Y, 20M, 20C, 20K ... developing roller, 21Y ... developing roller cleaning blade, 22Y ... developer compression roller, 23Y ... developer compression roller cleaning blade, 30Y, 30M, 30C, 30K ... Developing unit, 31Y, 31M, 31C, 31K ... Developer container, 32Y, 32M, 32C, 32K ... Image supply roller, 31Y, 31M, 31C, 31K ... developer container, 33Y ... regulating blade, 21Y, 34Y ... stirring roller, 40 ... intermediate transfer belt, 41 ... belt drive roller 42 ... tension roller, 46 ... intermediate transfer belt cleaning blade, 47 ... developer recovery unit, 50Y, 50M, 50C, 50K ... primary transfer unit, 51Y, 51M, 51C, 51K,. Primary transfer backup roller, 52Y, 52M, 52C, 52K ... Intermediate transfer belt squeeze unit, 53Y ... Intermediate transfer belt squeeze roller, 54Y ... Intermediate transfer belt squeeze backup roller, 55Y ... Intermediate transfer belt Squeeze roller cleaning blade, 56Y ... developer recovery unit, 60 ... secondary transfer Knit, 61 ... Secondary transfer roller, 62 ... Secondary transfer roller cleaning blade, 63 ... Developer recovery unit, 70 ... Pre-heating heater, 71 ... Core metal, 72 ... Elastic layer, 75 ... transfer material squeeze unit, 76 ... transfer material squeeze roller, 77 ... transfer material squeeze backup roller, 78 ... cleaning blade, 79 ... carrier recovery unit, 80 ... Fixing unit, 81 ... first fixing roller, 82 ... first pressure roller, 83 ... second fixing roller, 84 ... second pressure roller, 85 ... corona charger, 86: counter electrode, 100: transfer material, 101: toner particles, 102: carrier

Claims (3)

An image carrier that carries an image formed from a liquid developer containing carrier and toner particles, an intermediate transfer member that is an endless belt stretched by a driving roller and a tension roller, and primary transfer on the intermediate transfer member Squeeze means for recovering the carrier from the portion where the formed image is formed, a secondary transfer roller for secondary transfer of the image on the intermediate transfer member to the transfer material, and secondary transfer to the transfer material in contact with the transfer material A first fixing device that heats the transferred image, and a second fixing device that is disposed downstream of the first fixing device in the conveyance direction of the transfer material, and that heats the image secondarily transferred to the transfer material in contact with the transfer material An image forming apparatus that includes a fixing device and adjusts a carrier recovery amount by a squeeze means and a heating temperature of the first fixing device according to transfer material type information. The image forming apparatus according to claim 1, wherein the first fixing device and the second fixing device are rollers. A step of carrying an image formed from a liquid developer containing carrier and toner particles on an image carrier, and primary transfer of the image from the image carrier to an intermediate transfer member which is an endless belt stretched by a driving roller and a tension roller A step of recovering the carrier by a squeeze means from a portion where the primary transferred image on the intermediate transfer member is formed, a step of secondarily transferring the image on the intermediate transfer member to a transfer material by a secondary transfer roller, and a transfer A step of heating the image secondarily transferred to the material by a first fixing device contacting the transfer material, and a step of heating the image secondarily transferred to the transfer material by a second fixing device contacting the transfer material. An image forming method for adjusting the amount of carrier recovered by the squeeze means and the heating temperature of the first fixing device according to the transfer material type information.

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