JP2009093039A - Fixing device, image forming apparatus using the same, and an image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device configured to remove a carrier in accordance with the paper type of a recording medium, and prevent a defective image due to offset upon normal fixation from occurring. <P>SOLUTION: The fixing device includes: a pair of first rollers 71 and 72 for preheating the recording medium to which a toner image is transferred together with the carrier; a pair of carrier removing rollers 81 and 82 disposed on the downstream side of the pair of first rollers 71 and 72, for removing the carrier from the toner image on the preheated recording medium; a pair of second rollers 91 and 92 disposed on the downstream side of the pair of carrier removing rollers 81 and 82, for fusing the toner image on the recording medium. The pair of first rollers 71 and 72 and the pair of carrier removing rollers 81 and 82 are made movable with respect to the recording medium conveying path. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  In the present invention, a latent image formed on an image carrier is developed with a liquid developer composed of toner and carrier, the toner image composed of toner and carrier is further transferred to a recording medium, and the transferred toner image is fused. The present invention relates to a fixing device, an image forming apparatus, and an image forming method for fixing and fixing.

  Various wet image forming apparatuses that develop a latent image using a high-viscosity liquid developer in which a toner composed of a solid component is dispersed in a liquid solvent and visualize the electrostatic latent image have been proposed. The developer used in this wet image forming apparatus suspends solids (toner particles) in a highly viscous organic solvent (carrier liquid) having electrical insulation properties such as silicon oil, mineral oil, and edible oil. The toner particles are extremely fine with a particle diameter of around 1 μm. By using such fine toner particles, the wet image forming apparatus can achieve higher image quality than a dry image forming apparatus using powder toner particles having a particle diameter of about 7 μm.

For example, Patent Document 1 (Japanese Patent Laid-Open No. 2003-99864) discloses a liquid developer obtained by dispersing toner in a solvent that is partly or entirely non-volatile. An image fixing apparatus for heating and fixing an unfixed image on a recording medium formed using an agent, wherein the non-fixed image is heated in a non-contact manner with respect to the unfixed image on the recording medium. There is disclosed an image fixing apparatus provided with a means and a solvent removing means for removing the solvent to be deposited deposited by heating by the non-contact heating means from the image surface.
JP 2003-99864 A

  By the way, the image forming apparatus described in Patent Document 1 uses a fixing device that separates a solvent from an unfixed toner image by heating, and removes a carrier solvent that has emerged by heating with a non-contact heating means. However, non-contact heating is inefficient, and when excessive power is required, the device configuration of the non-contact heating means and power to the non-contact heating means are supplied. Therefore, there is a problem that a power source for the operation is required and the apparatus is enlarged.

  Further, since the non-fixed image is heated in a non-contact manner, temperature unevenness is likely to occur, unevenness occurs in the rising carrier, and unevenness occurs in the carrier removed by the carrier solvent removing means. Such a non-uniformity of the removed carrier has a problem that it may eventually cause a non-uniform image quality of the image fixed on the recording medium.

  Also, the absorbability of the carrier varies depending on the paper type of the recording medium (high quality paper, coated paper, etc.), and a paper with good carrier absorbency such as high quality paper may cause image defects due to offset during heat fixing. There was a problem.

  The present invention is to solve the above-mentioned problems, and a fixing device according to the present invention is provided downstream of the first roller pair for preheating the recording medium on which the toner image is transferred together with the carrier. A carrier removing means for removing the carrier from the toner image on the preheated recording medium, and a second roller pair provided downstream of the carrier removing means for fusing the toner image on the recording medium. One roller pair and the carrier removing means are configured to be movable with respect to the conveyance path of the recording medium.

  Further, the fixing device according to the present invention is characterized in that the carrier removing means comprises a pair of rollers.

  Further, the fixing device according to the present invention is characterized in that the carrier removing means includes a paper guide and a roller.

  Further, the fixing device according to the present invention is characterized in that a voltage for preventing offset is applied between the respective rollers constituting the first roller pair.

In the fixing device according to the present invention, the first nip pressure in the first roller pair and the second nip pressure in the second roller pair are
(Second nip pressure)> (first nip pressure)
It has the relationship of these.

In the fixing device according to the present invention, between the first nip temperature in the first roller pair and the second nip temperature in the second roller pair,
(Second nip temperature)> (first nip temperature)
It has the relationship of these.

  The image forming apparatus according to the present invention further includes a paper type determining unit that determines the type of the recording medium to be fixed by the fixing device, and the first roller pair and the first roller pair based on the determination result of the paper type determining unit. 8. The fixing device according to claim 1, wherein the carrier removing unit is moved with respect to a conveyance path of the recording medium.

Further, the image forming method according to the present invention determines the type of the recording medium to be fixed,
According to a result of the determination, upstream of the main fixing, it is determined whether to preheat the recording medium on which the toner image is transferred together with the carrier and to remove the carrier.

  According to the present invention, the carrier solvent that has been lifted by the contact-type heating means is removed, so that it is possible to realize power saving and efficient apparatus compaction by efficient heat transfer.

  Further, the contact-type heating means can uniformly heat the unfixed image and uniformly lift the carrier, so that image quality unevenness during fixing does not occur.

  In addition, contact-type heating is performed in a biased state, and the carrier is lifted, so that the carrier can be removed without offset and image quality is not disturbed.

  In addition, since the carrier is removed according to the paper type of the recording medium (quality paper, coated paper, etc.), there is no possibility of causing image defects due to offset during the main fixing.

  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 body 40 and the secondary transfer section (secondary transfer section (secondary transfer section) are arranged for the image forming sections of the respective colors arranged at the center of the image forming apparatus. The transfer unit 60 is disposed on the upper part 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, anilox rollers 32Y for supplying liquid developers of these colors from the developer containers 31Y, 31M, 31C, 31K to the developing rollers 20Y, 20M, 20C, 20K, 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 member 40 is an endless belt, and is stretched between the driving roller 41 and the tension roller 42, and is contacted with the image carriers 10Y, 10M, 10C, and 10K by the primary transfer portions 50Y, 50M, 50C, and 50K. It is rotationally driven by the driving roller 41 while in contact. The primary transfer units 50Y, 50M, 50C, and 50K are arranged such that the primary transfer rollers 51Y, 51M, 51C, and 51K are opposed to each other with the image transfer bodies 10Y, 10M, 10C, and 10K sandwiched between the intermediate transfer body 40 and the image transfer bodies 10Y, 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. Form an image.

  In the secondary transfer unit 60, a secondary transfer roller 61 is disposed opposite to the belt drive roller 41 with the intermediate transfer member 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, a single color toner image or a full color toner image formed on the intermediate transfer body 40 is conveyed on the sheet material conveyance path L such as paper, film, cloth, etc. Transfer to recording medium.

  Further, a fixing unit 90 is disposed in front of the path sheet material conveyance path L, and a single-color toner image or a full-color toner image transferred onto a recording medium such as paper is fused and fixed on the recording medium such as paper. Let

  Further, the tension roller 42 exceeds the intermediate transfer body 40 together with the belt driving roller 41, and the intermediate transfer body cleaning blade 46, the developer recovery unit, and the tension roller 42 are stretched around the tension roller 42 of the intermediate transfer body 40. A cleaning device 47 is abutted and arranged.

  The fixing unit 90 according to the present invention will be described with reference to FIG. FIG. 3 is a diagram showing the configuration of the fixing unit of the image forming apparatus according to the embodiment of the present invention. In the fixing unit 90, a first roller pair 71, 72, a carrier removing roller pair 81, 82, and a second roller pair 91, 92 are arranged from upstream to downstream. The first roller pair 71, 72 is provided with halogen lamps 73, 74 as heating sources, and the second roller pair 91, 92 is provided with halogen lamps 93, 94 as heating sources. Heating / pressing by the second roller pair 91, 92 is a main fixing in a normal image forming process, and heating / pressing by the first roller pair 71, 72 configured in the preceding stage is preheating (preheating). This is a pre-process for removing the carrier. The first roller pair 71 and 72 heats the toner image on the recording medium immediately after being transferred by the secondary transfer roller 61.

  The carrier removing roller pair 81 and 82 is a carrier removing device, and a pair of foamed urethane rolls is used. In addition to this, the carrier removing roller pair 81, 82 may be made of an elastic material capable of absorbing and swelling the carrier, or a porous material such as a nonwoven fabric, a foamed elastic body, or a foamed metal. Carrier removal roller pairs 81 and 82 such as a foamed urethane roll pair come into contact with the toner image and suck and remove the carrier from the toner image.

  The first roller pair 71 and 72 and the carrier removal roller pair 81 and 82 are formed to be movable from the paper transport path L by a mechanism (not shown). FIG. 3A shows a state in which the first roller pair 71 and 72 and the carrier removal roller pair 81 and 82 are closest to the paper transport path L and can contact the recording medium transported in the paper transport path. FIG. 3B shows that the first roller pair 71 and 72 and the carrier removal roller pair 81 and 82 are separated from the paper transport path L and are not in contact with the recording medium transported through the paper transport path. Yes. In this embodiment, whether to remove the carrier in the state of FIG. 3A or not to remove the carrier in the state of FIG. 3B is selected according to the type of the recording medium.

  In the present embodiment, a paper type determination sensor 5 is provided to detect the type of the recording medium. This paper type determination sensor 5 is formed of a light emitting element 6 that irradiates light to a recording medium conveyed through the conveying path, and a light receiving element 7 that detects reflection of reflected light from the recording medium. In this embodiment, a signal such as the reflectance of reflected light from the light receiving element 7 is input to a control unit such as a CPU (not shown), and the paper type of the recording medium (type of high-quality paper, coated paper, etc.) is determined. Is.

  Note that, from the beginning to the end of the image forming process, the configuration of the rollers and the like arranged in the preceding stage is defined as being upstream of the configuration of the rollers and the like arranged in the subsequent stage.

  The nip portion formed between the first roller pair 71 and 72 is referred to as a “first nip”, and the nip portion formed between the second roller pair 91 and 92 is referred to as a “second nip”. And

  Here, functions of the first roller pair 71 and 72 and the carrier removal roller pair 81 and 82 will be described. FIG. 8 is a diagram schematically showing the state of the toner particles and the carrier transferred onto the recording medium. FIG. 8A shows a state immediately after the toner image is transferred by the secondary transfer roller 61, and FIG. 8B shows a state immediately after the toner image on the recording medium is heated by the first roller pair 71 and 72. FIG. 8C shows a state immediately after the carrier is removed from the toner image by the carrier removal roller pair 81 and 82. FIG. 8 shows a case where coated paper is used as a recording medium.

  In a liquid developer using a carrier, the solvent does not volatilize at the time of image fixing. Therefore, the presence of the solvent at the time of fixing greatly affects the fixability. That is, in the method of heat-fixing a toner image, the toner that forms the developed toner image on the recording medium is softened or melted by heating, and a carrier enters between the toner and the recording medium so that the toner and the recording medium May interfere with the binding. For this reason, at the time of image fixing, it is necessary to either absorb the carrier remaining on the recording medium into the recording medium or to remove the solvent from the image surface side of the recording medium. In addition, the higher the residual ratio of the solvent in the toner image, the larger the heat capacity in the toner image, and the longer the time required for heat fixing.

  By the way, the amount of carriers remaining on the recording medium varies greatly depending on the type of the recording medium. That is, there is a recording medium with good carrier absorbability such as fine paper, and a recording medium with poor carrier absorbency such as coated paper, and the former recording medium has a toner image formed by the secondary transfer roller 61. Immediately after the toner is transferred, the carrier is quickly absorbed, and the carrier removal roller pair 81 and 82 do not need to remove the carrier, and the state shown in FIG. In contrast, the latter recording medium has a carrier-rich surface state as shown in FIG. 8A immediately after the toner image is transferred by the secondary transfer roller 61.

  In this embodiment, a movable first roller pair 71 and 72 and carrier removal roller pair 81 and 82 are provided as a configuration for efficiently removing the carrier from the toner image in the fixing process.

  When the paper type determination unit including the paper type determination sensor 5 determines that the recording medium to be fixed is coated paper that requires carrier removal from the toner image before the main fixing, the first type is determined. The roller pair 71 and 72 and the carrier removal roller pair 81 and 82 are arranged at positions where they can contact the recording medium.

  Immediately after the toner image is transferred onto the recording medium by the secondary transfer roller 61, the toner image is heated by the first roller pair 71 and 72 provided downstream of the secondary transfer roller 61. When the toner image is heated, the carrier is lifted from between the toner particles as shown in FIG. Such a phenomenon is considered to be caused by the toner particles being connected by heating and the carrier being pushed out due to the narrow space between the toner particles.

  Next, the lifted carrier is removed from the toner image by the carrier removing roller pair 81 and 82 provided downstream of the first roller pair 71 and 72 as shown in FIG. Such carrier removal is caused by a tearing phenomenon between the carrier of the toner image and the carrier on the carrier removal roller.

In addition, when the paper type determination unit including the paper type determination sensor 5 determines that the recording medium to be fixed is high-quality paper that does not require carrier removal from the toner image before the main fixing, The first roller pair 71 and 72 and the carrier removal roller pair 81 and 82 are arranged at positions away from the recording medium. Then, the carrier fixing operation is omitted and the main fixing process by the second roller pair 91 and 92 is carried out as it is. Thus, in the present invention, the carrier solvent floated by the contact type first roller pair 71 and 72 is removed. Since it is to be removed, it is possible to realize power saving and compact equipment by efficient heat transfer. In addition, the contact type first roller pair 71 and 72 can uniformly heat the unfixed image and can evenly lift the carrier, so that image quality unevenness during fixing does not occur.

  Further, since the carrier removal process is performed according to the paper type of the recording medium (quality paper, coated paper, etc.), there is no possibility of causing image defects due to offset during the main fixing.

  Next, control of the transfer-fixing process in the image forming apparatus of the present invention will be described. FIG. 4 is a diagram showing a flow of a transfer-fixing process of the image forming apparatus according to the embodiment of the present invention. Such a flow is executed by a controller of an image forming apparatus (not shown).

  Hereinafter, a recording medium having good carrier absorbency such as high-quality paper will be referred to as S2, and a recording medium having carrier absorption such as coated paper being worse than that of high-quality paper as S1.

  In FIG. 4, steps S104 to S107 and steps S108 to S110 show operations in the transfer process.

In FIG. 4, when the transfer-fixing process is started in step S100, the process advances to step S101, and the paper type determination sensor 5 detects the type of the recording medium. Next, in step S <b> 102, the toner image is transferred from the intermediate transfer body 40 to the recording medium in the secondary transfer unit 60.

  In step S103, it is determined based on the signal acquired by the paper type determination sensor 5 whether the recording medium is S1. When the result of determination in step S103 is YES, the process proceeds to step S104, and when the result of determination in step S103 is NO, the process proceeds to step S108.

  Proceeding to step S104 means that the recording medium is coated paper that does not absorb well. Therefore, in step S104, the halogen lamps 73 and 74 in the first roller pair are turned on. The halogen lamps 93 and 94 in the two-roller pair are turned on.

  In step S106, the contact state of the first roller pair 71, 72 is maintained, and in step S107, the contact state of the carrier removal roller pair 81, 82 is maintained.

  In step S111, the carrier is removed under the contact state as described above, and then the toner image is fixed on the recording medium S1 by the fixing unit 90. In step S112, the transfer-fixing process is terminated.

  Further, the process proceeds to step S108 because the recording medium is a high-quality paper having good absorbability. In step S108, the halogen lamps 93 and 94 in the second fixing roller pair are turned on.

  In step S109, the first roller pair 71, 72 is separated, and in step S110, the carrier removal roller pair 81, 82 is separated. In the separated state as described above, the fixing operation in the fixing unit 90 is executed in step S111 without removing the carrier. In step S112, the transfer-fixing process is terminated.

  By such control, in the image forming apparatus of the present invention, the carrier removal process is performed by the fixing unit 90 according to the paper type such as the recording media S1 and S2, so that there is a possibility of causing an image defect due to offset during the main fixing. Absent.

Further, in the present embodiment, between the first nip pressure in the first roller pair 71 and 72 and the second nip pressure in the second roller pair 91 and 92,
(Second nip pressure)> (first nip pressure)
Set so that. This is because the fixing in the second roller pair 91 and 92 is the main fixing and a large pressure is required, whereas in the first roller pair 71 and 72, the first roller pair 71 and 72 is efficiently transferred to the recording medium. This is due to the fact that there should be a minimum pressure that can be adhered well.

Similarly, in this embodiment, between the first nip temperature in the first roller pair 71 and 72 and the second nip temperature in the second roller pair 91 and 92,
(Second nip temperature)> (first nip temperature)
Set so that. This is because the fixing at the second roller pair 91 and 92 is the main fixing and a high temperature is required, whereas the second roller pair 91 and 92 is such that the carrier is lifted for the carrier removal process at the subsequent stage. This is due to the fact that temperature is sufficient.

  Next, examples will be described. In the present embodiment, Mitsubishi Paper: Pearl coated paper (trade name) is used as the coated paper (coated paper) of the recording medium S1, and Mitsubishi Paper: Kinryo (product) as the high quality paper of the recording medium S2. Name).

  When the paper type is determined by the paper type determination sensor 5 and the paper type is the recording medium S2 (Kinryo (Mitsubishi Paper)), the first roller pair 71 and 72 and the carrier removal roller pair 81 and 82 are separated from each other. After that, the recording medium is conveyed, and heat fixing is performed by the second roller pair 91 and 92. When the paper type is the recording medium S1 (pearl coated paper (manufactured by Mitsubishi Paper Industries)), the first roller pair 71, 72 and the carrier removing means are brought into contact with each other, and then the recording medium is transported to form the first roller pair 71. 72, after the recording medium was preheated by 72 and the carrier that floated up was removed by a pair of carrier removal rollers 81 and 82, heat fixing was performed by a second pair of rollers 91 and 92. Conditions relating to the temperature and linear pressure in the first roller pair 71 and 72 and the second roller pair 91 and 92 are shown in FIG.

  Although the recording medium has different carrier absorbency depending on the state of its surface layer, in the recording medium S1 (pearl coated paper (manufactured by Mitsubishi Paper Industries)) having low carrier absorbency, excess carrier remains on the paper at the time of entry into the fixing medium. The carrier may be interposed between the solid content and the paper to cause poor fixing. In order to obtain a high fixing rate in such a recording medium, it is necessary to remove the carrier on the paper. On the other hand, in the recording medium S2 (Kinryo (Mitsubishi Paper)) having a high carrier absorbability, the carrier absorption is almost finished when entering the fixing after transfer, and the carrier has almost no influence on the fixing rate. No. If the carrier is removed with such a carrier-absorbing paper, the image will be distorted or the carrier acting as a release agent will be lost due to excessive carrier removal, resulting in an offset. there is a possibility.

  According to the present invention, according to the carrier absorbability of the recording medium, it is possible to switch the application of the process of removing the carrier after the preheating, and there is no image disturbance regardless of the type of the recording medium, and good fixing. Rate images can be obtained.

  Next, bias application in the fixing unit 90 will be described. FIG. 6 is a diagram showing bias application in a fixing unit of an image forming apparatus according to another embodiment of the present invention. This embodiment is the same as the previous embodiment except that a bias voltage is applied by the fixing unit 90.

  As shown in FIG. 6, a bias voltage is applied to the first roller 71, and the first roller 72 is grounded. This bias voltage urges the toner particles on the recording medium in the direction of the first roller 72, and can prevent the toner particles from being offset to the first roller 71.

  According to such an embodiment, the first roller pair 71, 72 is heated in a contact manner with a bias applied to lift the carrier, so that the carrier can be removed without offset and the image quality is disturbed. There is no.

  Next, an image forming apparatus according to another embodiment of the present invention will be described. FIG. 7 is a diagram showing a configuration of a fixing unit of an image forming apparatus according to another embodiment of the present invention. The embodiment of FIG. 7 differs from the previous embodiment in the configuration of the carrier removing means, and the other configuration is the same as the previous embodiment.

  In the present embodiment, the carrier removing means includes a paper guide 83 and a carrier removing roller 84 that presses the recording medium against the paper guide 83 to remove the carrier. As shown in FIG. 7, the first roller pair 71 and 72 and the carrier removal roller 84 are formed to be movable from the paper transport path L by a mechanism (not shown).

  FIG. 7A shows a state in which the first roller pair 71 and 72 and the carrier removal roller 84 are closest to the paper transport path L and can come into contact with the recording medium transported by the paper transport path. b) shows that the first roller pair 71 and 72 and the carrier removal roller 84 are separated from the paper transport path L and are not in contact with the recording medium transported through the paper transport path.

  Also in such an embodiment, the carrier removal process can be performed according to the paper type of the recording medium (quality paper, coated paper, etc.), and there is no possibility of causing an image defect due to offset during the main fixing.

  Next, the image forming unit and the developing unit of the image forming apparatus according to the embodiment of the present invention 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, an anilox roller 32Y, and a toner compression roller 22Y are arranged on the outer periphery of the developing roller 20Y. A carrier amount adjusting blade 23Y is provided on the outer periphery of the toner compression roller 22Y. Further, a liquid developer supply roller 34Y and an anilox roller 32Y are accommodated in the liquid developer container 31Y.

  A primary transfer roller 51Y of the primary transfer portion is disposed along the intermediate transfer body 40 at a position facing the image carrier 10Y, and an intermediate transfer body squeeze roller 53Y, a backup roller 54Y, and an intermediate transfer are disposed downstream in the moving direction. An intermediate transfer body squeeze device 52Y comprising a body 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 toner compression roller 22Y, a developer container 31Y that stores a liquid developer in which toner is dispersed in a carrier at a weight ratio of approximately 20%, a developing roller 20Y that carries the liquid developer, a liquid developer, and the like. Toner compression for bringing the liquid developer carried on the developing roller 20Y into a compaction state by stirring the agent to maintain a uniform dispersed state and supplying it to the developing roller 20Y, the regulating blade 33Y, the supply roller 34Y, and the liquid developer carried on the developing roller 20Y A developing roller cleaning blade 21Y for cleaning the roller 22Y and the developing roller 20Y is provided.

  The liquid developer accommodated in the developer container 31Y is a low concentration (about 1 to 2 wt%) and low viscosity with Isopar (trademark: exon) as a carrier, which is generally used, and is volatile at room temperature. It is not a volatile liquid developer having a property, but a non-volatile liquid developer having a high concentration and a high viscosity and having a non-volatile property at room temperature. That is, in the liquid developer in the present invention, a solid having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a thermoplastic resin is introduced into a liquid solvent such as an organic solvent, silicon oil, mineral oil, or edible oil. It is a liquid developer having a high viscosity (about 30 to 10,000 mPa · s) which is added together with a dispersant and has a toner solid content concentration of about 20%.

  The anilox roller 32Y is a cylindrical member, and is a roller in which a concave and convex surface by a spiral groove is formed finely and uniformly on the surface so that the developer can be easily carried on the surface. As for the dimensions of the groove, the groove pitch is about 130 μm and the groove depth is about 30 μm. The anilox roller 32Y supplies the liquid developer from the developer container 31Y to the developing roller 20Y. In order to maximize the effect of the AC bias described later, it is desirable that the anilox roller 32Y and the supply roller 34Y are in contact with each other in the same rotational direction.

  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 comes into contact with the surface of the anilox roller 32Y, and a plate made of metal or the like that supports the rubber portion. Then, the film thickness and amount of the liquid developer carried and conveyed by the anilox roller 32Y made of an anilox roller are regulated and adjusted, and the amount of the liquid developer supplied to the developing roller 20Y is adjusted.

  The developing roller 20Y is a cylindrical member having a width of about 320 mm, 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 toner compression roller 22Y is a cylindrical member and is in the form of an elastic roller formed by covering an elastic body in the same manner as the developing roller 20Y. The toner compression roller 22Y includes a conductive resin layer or rubber layer on the surface layer of the metal roller base material. For example, as shown in FIG. 2, it rotates clockwise in the direction opposite to the developing roller 20Y. The toner compression roller 22Y has means for increasing the charging bias on the surface of the developing roller 20Y, and the developer conveyed by the developing roller 20Y is brought into sliding contact with the toner compression roller 22Y to form a nip as shown in FIG. An electric field is applied from the toner compression roller 22Y side toward the developing roller 20Y at the toner compression site. The electric field applying means for toner compression may be corona discharge from a corona discharger instead of the roller shown in FIG. A part of the carrier and some of the toner that has not been compressed are scraped off by the carrier amount adjusting blade 23Y, and merged with the developer in the reservoir 31Y and reused.

  On the other hand, the developer compressed by toner carried on the developing roller 20Y corresponds to the latent image on the image carrier 10Y by applying a desired electric field at the development nip where the developing roller 20Y contacts the image carrier 10Y. Developed. The developer remaining after development is scraped off and removed by the developing roller cleaning blade 21Y, joined to the developer in the reservoir 31Y, and reused. Note that the merged carrier and toner are not in a mixed color state.

  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. In this way, the image carrier squeeze roller 13Y is formed of an elastic roller member that covers the surface with an elastic body and rotates in sliding contact with the image carrier 10Y, and cleaning that presses and slides against the image carrier squeeze roller 13Y. The blade 14Y has a function of collecting excess carrier and originally unwanted fog toner from the developer developed on the image carrier 10Y and increasing the ratio of toner particles in the visible image.

  In the primary transfer unit 50Y, the developer image developed on the image carrier 10Y is transferred to the intermediate transfer member 40 by the primary transfer roller 51Y. Here, the image carrier 10Y and the intermediate transfer member 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 intermediate transfer member squeeze device 52Y is disposed on the downstream side of the primary transfer unit 50Y, and removes excess carrier liquid from the intermediate transfer member 40 to increase the toner particle ratio in the visible image.

  Similar to the image carrier squeeze device 52, the intermediate transfer member squeeze device 52Y has an intermediate transfer member squeeze roller 53Y composed of an elastic roller member that covers the surface of the elastic member and rotates in contact with the image carrier 40, and the image carrier 40 The intermediate transfer body 40 includes a backup roller 54Y disposed opposite to the intermediate transfer body squeeze roller 53Y, a cleaning blade 55Y that presses and slides against the intermediate transfer body squeeze roller 53Y to clean the surface, and a developer recovery unit 56Y. And a function of recovering excess carrier and originally unnecessary fog toner from the developer transferred to the primary. 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.

  As described above, according to the present invention, since the carrier solvent that has been lifted by the contact-type heating means is removed, it is possible to realize power saving and efficient device compaction by efficient heat transfer.

  Further, the contact-type heating means can uniformly heat the unfixed image and uniformly lift the carrier, so that image quality unevenness during fixing does not occur.

  In addition, contact-type heating is performed in a biased state, and the carrier is lifted, so that the carrier can be removed without offset and image quality is not disturbed.

  In addition, since the carrier is removed according to the paper type of the recording medium (quality paper, coated paper, etc.), there is no possibility of causing image defects due to offset during the main fixing.

  Note that although various embodiments have been described in this specification, embodiments configured by appropriately combining the configurations of the respective embodiments are also included in the scope of the present invention.

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. FIG. 2 is a diagram illustrating a configuration of a fixing unit of the image forming apparatus according to the embodiment of the present invention. FIG. 4 is a diagram illustrating a flow of a transfer fixing process of the image forming apparatus according to the embodiment of the present invention. It is a figure which shows the conditions concerning each temperature and linear pressure in a 1st roller pair and a 2nd roller pair. FIG. 5 is a diagram illustrating bias application in a fixing unit of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a diagram illustrating a configuration of a fixing unit of an image forming apparatus according to another embodiment of the present invention. FIG. 3 is a diagram schematically illustrating a state of toner particles and a carrier transferred onto a recording medium.

Explanation of symbols

5 ... paper type determination sensor, 6 ... light emitting element, 7 ... light receiving element, 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 ... toner compression roller , 23Y ... Carrier amount adjusting blade, 24Y ... Carrier amount adjusting roller, 25Y ... Carrier amount adjusting air knife, 30Y, 30M, 0C, 30K: Development unit, 31Y, 31M, 31C, 31K ... Developer container, 32Y, 32M, 32C, 32K ... Anilox roller, 31Y, 31M, 31C, 31K ... Developer container, 33Y: restriction blade, 34Y: supply roller, 40 ... intermediate transfer member, 41 ... belt drive roller, 42 ... tension roller, 45 ... developer recovery unit, 46 ... Intermediate transfer member 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 member squeeze unit, 53Y: Intermediate transfer member squeeze roller, 54Y: Intermediate transfer member squeeze backup 55Y ... Intermediate transfer member squeeze roller cleaning blade, 56Y ... Developer recovery unit, 60 ... Secondary transfer unit, 61 ... Secondary transfer roller, 62 ... Secondary transfer roller Cleaning blade, 63... Developer collecting unit, 71 and 72... First roller pair, 73 and 74... Halogen lamp, 81 and 82. 84 ... Carrier removal roller, 91, 92 ... Second roller pair, 93, 94 ... Halogen lamp

Claims (8)

A first roller pair for preheating the recording medium on which the toner image is transferred together with the carrier;
Carrier removing means for removing the carrier from the toner image on the preheated recording medium provided downstream of the first roller pair;
A second roller pair provided downstream of the carrier removing means for fusing the toner image on the recording medium,
The fixing device according to claim 1, wherein the first roller pair and the carrier removing unit are configured to be movable with respect to a conveyance path of the recording medium. The fixing device according to claim 1, wherein the carrier removing unit includes a roller pair. The fixing device according to claim 1, wherein the carrier removing unit includes a paper guide and a roller. 4. The fixing device according to claim 1, wherein a voltage for preventing offset is applied between the rollers constituting the first roller pair. 5. Between the first nip pressure in the first roller pair and the second nip pressure in the second roller pair,
(Second nip pressure)> (first nip pressure)
The fixing device according to claim 1, wherein the fixing device has the following relationship. Between the first nip temperature in the first roller pair and the second nip temperature in the second roller pair,
(Second nip temperature)> (first nip temperature)
The fixing device according to claim 1, wherein the fixing device has the following relationship. A paper type determining means for determining the type of recording medium to be fixed by the fixing device;
7. The method according to claim 1, wherein the first roller pair and the carrier removal unit are moved with respect to the conveyance path of the recording medium based on a determination result of the paper type determination unit. An image forming apparatus using a fixing device. Determine the type of recording medium to be fixed,
An image forming method comprising: preheating a recording medium on which a toner image has been transferred together with a carrier and determining whether or not to remove the carrier upstream of the main fixing in accordance with a determination result.

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