JP2004170690A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device and an image forming apparatus capable of fixing a toner image formed by liquid developer constituted by dispersing toner in liquid carrier on a recording medium with an improved fixing performance. <P>SOLUTION: A nip pressure at the entrance side of the nip part 69 is made higher than that at the exit side of the nip part 69. By applying the comparatively high nip pressure on the recording medium 4 on the entrance side of the nip part 69, the liquid carrier L is squeezed out of a gap between the toner T and the toner T and out of a gap between the recording medium 4 and the toner T, then, the quantity of the liquid carrier L remaining in the gap between them is drastically reduced. And, the recording medium 4 carrying the small quantity of the remaining liquid carrier is shifted toward the exit side of the nip part 69, and then, the toner T and one side S1 of the recording medium 4 are pressurized and brought into contact with each other so as to fix the toner T on the recording medium 4. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for fixing an unfixed toner image formed using a liquid developer in which a toner is dispersed in a liquid carrier to a recording medium.
[0002]
[Prior art]
Conventionally, a toner image is formed on a recording medium such as copy paper, transfer paper or paper by an image forming process using a liquid developer in which toner is dispersed in a liquid carrier, and the unfixed toner image is formed by a fixing device. 2. Related Art An image forming apparatus for fixing a recording medium is known. A fixing device in such an image forming apparatus of the wet developing system includes a heating roller, and a plurality of supporting rollers provided in a circumferential direction opposite to the heating roller, and a nip portion between the heating roller and the supporting roller is provided. There is known a method in which an unfixed toner image on a recording medium is fixed to the recording medium by passing the recording medium through the recording medium (see Patent Document 1).
[0003]
In the fixing device described in Patent Document 1, while a heating roller contacts a surface of a recording medium carrying an unfixed toner image, each supporting roller presses the recording medium from the back side of the recording medium toward the heating roller. However, in this case, the pressing force of the support roller is set to 50 g / cm or less per unit length in the axial direction of the support roller. As a result, the contact pressure of the recording medium with respect to the heating roller is sufficiently reduced, and the amount of offset of the toner adhering to the heating roller after fixing is reduced.
[0004]
[Patent Document 1]
JP-A-2000-112269 (page 3, FIG. 1, FIG. 2)
[0005]
[Problems to be solved by the invention]
By the way, in a wet development type image forming apparatus, since a liquid developer obtained by dispersing a toner in a liquid carrier is used as a developer, when the toner image formed by the development process is transferred to the recording medium, A liquid carrier as well as a solid toner exists on the surface, and the fixing process is performed in a state where these are mixed. That is, while passing through the nip portion between the heating roller and the plurality of support rollers, that is, while moving the nip width, the surface of the recording medium and the heating roller are pressed against each other to fix the toner on the recording medium. Is performed. Therefore, it can be easily estimated that the pressure distribution in the nip greatly affects the fixing characteristics. In particular, when a volatile carrier is used as the liquid carrier, the amount of the liquid carrier is relatively small because a part of the liquid carrier evaporates due to heat given to the fixing process. The liquid carrier hardly evaporates, and is more susceptible to the pressure distribution than when a liquid developer using a volatile carrier is used.
[0006]
However, in the conventional wet development type image forming apparatus, although the pressure value itself in the nip portion is sufficiently considered as described above, the pressure distribution in the nip portion is not considered at all. Therefore, there is much room for improvement in fixability.
[0007]
The present invention has been made in view of the above problems, and has a fixing device capable of fixing a toner image formed using a liquid developer obtained by dispersing a toner in a liquid carrier to a recording medium with excellent fixability. It is an object to provide an image forming apparatus.
[0008]
[Means for Solving the Problems]
The fixing device according to the present invention includes a contact device that is arranged so as to be able to contact one surface carrying an unfixed toner image formed by using a liquid developer in which a toner is dispersed in a liquid carrier, on both surfaces of a recording medium. Member, and a pressure member for pressing the recording medium against the contact member from the opposite surface of the recording medium, and the unfixed toner image is formed on the recording medium by passing the recording medium through a nip portion between the contact member and the pressure member. In order to achieve the above object, a fixing device for fixing to one surface is set such that a nip pressure at an inlet side of a nip portion is higher than a nip pressure at an outlet side of the nip portion.
[0009]
In the invention configured as described above, the unfixed toner image formed using the liquid developer is carried on one surface of the recording medium, and the solid toner and the liquid carrier are formed on one surface of the recording medium before fixing. Exist in a mixed state. Here, when the recording medium passes through the nip portion in this mixed state, first, the unfixed toner image receives a higher nip pressure on the entrance side than on the exit side. At this time, since the liquid carrier has higher fluidity than the solid toner, the liquid carrier is extruded from between the toners, and the remaining amount of the liquid carrier between the toners is greatly reduced. Also, the remaining amount of the liquid carrier between the recording medium and the toner is extremely small as in the case between the toners. Then, the recording medium moves through the nip with the low remaining amount, and the toner and one surface of the recording medium are pressed against each other to fix the toner on the recording medium. As described above, since the fixing process is performed with the liquid carrier removed between the toner and between the recording medium and the toner, the fixing strength can be increased, and excellent fixability can be obtained.
[0010]
Here, for example, a heating roller can be used as the contact member. Further, a belt nip type or a roller nip type can be used as the pressing member. As the former method, for example, a pressure member is constituted by a plurality of rollers including two nip rollers disposed in the vicinity of a heating roller, and an endless belt which can be wound around the plurality of rollers and run around. One in which a part of the outer peripheral surface of the endless belt is brought into pressure contact with the heating roller by two nip rollers to form a nip portion can be used. When the belt nip type is used as the pressing member, the width of the nip portion in the transport direction of the recording medium, that is, the nip width can be set wide. As a result, it is possible to set a longer time for the recording medium to pass through the nip portion, to secure a sufficient fixing time, and to obtain a good fixing property. Also, by adjusting the pressing force of the nip roller on the inlet side, the nip pressure on the inlet side of the nip portion can be accurately set, and also on the outlet side, the pressing force of the nip roller on the outlet side is adjusted. Thus, the nip pressure can be set accurately, and the fixability can be controlled well.
[0011]
Further, instead of using a nip roller, a pressure pad may be provided as a belt nip method. The pressure pad is arranged inside the endless belt in a non-rotating state, and presses the endless belt against the heating roller over the entire nip portion to form a nip portion. In this way, the endless belt can be pressed over a wider area than the nip roller, that is, the pressing force can be applied over the entire nip, and the nip pressure at the inlet side of the nip and the nip pressure at the outlet side are uniform. Can be adjusted. Therefore, the following operation and effect can be obtained, and the fixing property can be further improved. That is, if the nip pressure is not uniform on the entrance side or the exit side of the nip, the speed of the recording medium fluctuates while the recording medium passes through the nip. Therefore, slippage occurs between the endless belt and the recording medium, and the toner image may be disturbed. On the other hand, in the present invention, since the nip pressure can be made uniform by using the pressure pad, the occurrence of slip can be suppressed and a good fixed toner image can be obtained.
[0012]
Further, as the roller nip method, for example, a pressing member having a plurality of rollers that are in pressure contact with a heating roller, and a nip portion formed by the plurality of rollers and the heating roller can be used. In this case, the pressing force of the inlet-side roller of the nip portion with respect to the heating roller may be set to be higher than the pressing force of the outlet-side roller of the nip portion, and the nip pressure is adjusted by adjusting the pressing force of each roller. Can be controlled. Further, by further providing a heating means for heating the outlet roller, the fixing strength of the toner on the recording medium can be increased, and the fixing property can be further improved.
[0013]
Further, the nip portion may further include an electric field generating means for generating an electric field in a direction in which the toner in the liquid developer moves toward the recording medium. In this case, the toner is concentrated on the recording medium, It is possible to efficiently remove the liquid carrier from between the recording medium and the toner. As a result, the fixability can be further improved.
[0014]
In order to achieve the above object, an image forming apparatus according to the present invention includes: an image forming unit that forms a toner image on an image carrier using a liquid developer obtained by dispersing a toner in a liquid carrier; and an image forming unit. A transfer unit for transferring the formed toner image to one surface of the recording medium, and has the same configuration as the fixing device according to any one of claims 1 to 6, and is transferred to one surface of the recording medium by the transfer unit. Fixing means for fixing the unfixed toner image on the recording medium.
[0015]
In the invention configured as described above, at the time when the image is transferred to one surface of the recording medium, the solid toner and the liquid carrier exist in a mixed state on one surface of the recording medium. However, similar to the above-described invention (fixing device), since a higher nip pressure is applied to the recording medium at the entrance side of the nip portion than at the exit side, the liquid carrier between the toner and between the recording medium and the toner is applied. The remaining amount has been reduced. Then, the recording medium passes through the nip portion and the toner is fixed on the recording medium with the low remaining amount, so that the fixing strength can be increased and excellent fixing properties can be obtained.
[0016]
In the above-described image forming apparatus, the fixing process is performed after the transfer. However, the present invention can be applied to an image forming apparatus that performs the transfer and the fixing simultaneously. That is, the image forming apparatus according to the present invention, in order to achieve the above object, an image forming unit that forms a toner image on the surface of an image carrier using a liquid developer obtained by dispersing a toner in a liquid carrier; Transfer fixing means for transferring and fixing the toner image to one surface of the recording medium at the same time, the transfer fixing means comprising: a contact member arranged so as to be able to contact the back surface of the image carrier; And a pressure member for pressing the recording medium and the image carrier through the nip portion between the contact member and the pressure member to perform the transfer and fixation. The nip pressure on the outlet side of the nip portion is set higher than the nip pressure on the outlet side of the nip portion.
[0017]
In the image forming apparatus configured as described above, the transfer process and the fixing process are simultaneously performed by passing the recording medium and the image carrier through the nip portion between the contact member and the pressing member. When passing through the nip portion, the toner image is transferred to the recording medium at the entrance side, and at the same time, the liquid carrier existing between the toners transferred to the recording medium is pushed out from between the toners to form the liquid carrier between the toners. The remaining amount is greatly reduced. Also, the remaining amount of the liquid carrier between the recording medium and the toner is extremely small as in the case between the toners. Then, the recording medium moves along the exit side of the nip portion with the low remaining amount, and the toner and one surface of the recording medium are pressed against each other to fix the toner on the recording medium. As described above, since the fixing process is performed with the liquid carrier removed between the toner and between the recording medium and the toner, the fixing strength can be increased, and excellent fixability can be obtained.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a diagram showing an internal configuration of a printer which is an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the printer. This printer is a wet development type image forming apparatus that forms a single color image using a black (K) liquid developer. In this printer, when a print command signal including an image signal is given to the main control unit 100 from an external device such as a host computer, the engine control unit 110 responds to the control signal from the main control unit 100 to control each unit of the engine unit 1. And prints out an image corresponding to the image signal on transfer paper, copy paper, and paper (hereinafter, referred to as a “recording medium”) 4 transported from a paper feed cassette 3 disposed below the apparatus main body 2. .
[0019]
The engine unit 1 includes a photoreceptor unit 10, an exposure unit 20, a developing unit 30, a transfer unit 40, a fixing unit 60, and the like. In the photoconductor unit 10 among these units, the photoconductor 11 is provided rotatably in the arrow direction 15 (clockwise direction in the figure) of FIG. Around the photosensitive member 11, a charging unit 12, a developing roller 31, a transfer unit 40, a charge removing unit 13, and a cleaning unit 14 are arranged along a rotation direction 15. In the present embodiment, the charging unit 12 includes a charging roller, and a charging bias is applied from a charging bias generation unit 111 to uniformly charge the outer peripheral surface of the photoconductor 11 to a predetermined surface potential Vd (for example, Vd = DC + 600 V). And has a function as a charging unit.
[0020]
A surface area between the charging unit 12 and the developing roller 31 is an irradiation area of the light beam 21 from the exposure unit 20, and an electrostatic latent image is formed in this irradiation area. That is, the exposure unit 20 exposes the photoconductor 11 with the light beam 21 in accordance with a control command given from the exposure control unit 112, and forms an electrostatic latent image on the photoconductor 11 corresponding to an image signal. For example, when a print command signal including an image signal is provided from an external device such as a host computer to the CPU 101 of the main control unit 100 via the interface 102, the CPU 113 responds to a command from the CPU 101 of the main control unit 100 to cause the exposure control unit to execute. A control signal corresponding to the image signal is output to the device 112 at a predetermined timing. Then, a light beam 21 is emitted from the exposure unit 20 to the photoconductor 11 in response to a control command from the exposure control unit 112, and an electrostatic latent image corresponding to an image signal is formed on the photoconductor 11. When forming a patch image as necessary, a control signal corresponding to a patch image signal of a predetermined pattern (for example, a solid image, a thin line image, or a thin white line image) is sent from the CPU 113 to the exposure control unit. The electrostatic latent image corresponding to the pattern is formed on the photoconductor 11.
[0021]
The electrostatic latent image thus formed is visualized by toner supplied from the developing roller 31 of the developing unit 30. The developing unit 30 includes, in addition to the developing roller 31, a tank 33 for storing a liquid developer 32, an application roller 34 for drawing up the liquid developer 32 stored in the tank 33 and applying the liquid developer 32 to the developing roller 31. A regulating blade 35 for uniformly regulating the thickness of the developer layer on the application roller 34 and a cleaning blade 36 for removing the developer remaining on the developing roller 31 after supplying the toner to the photoconductor 11 are provided. The developing roller 31 rotates at a peripheral speed equal to that of the photoconductor 11 in a direction (counterclockwise in FIG. 1) that follows the photoconductor 11. On the other hand, the application roller 34 rotates at a peripheral speed of about twice the same direction as the developing roller 31 (counterclockwise in the figure).
[0022]
In the present embodiment, the liquid developer 32 includes a toner including a color pigment, a resin that adheres the color pigment, a charge control agent that gives a predetermined charge to the toner, a dispersant that uniformly disperses the color pigment, and a liquid carrier. And the toner is dispersed in the liquid carrier. Here, in the present embodiment, a non-volatile carrier such as a silicone oil such as polydimethylsiloxane oil is used as the liquid carrier, the toner concentration is 5 to 40% by weight, and a low-concentration developer often used in a wet development method. (The toner concentration is 1 to 2% by weight). Note that the type of the liquid carrier is not limited to silicone oil, and the viscosity of the liquid developer 32 is determined by the liquid carrier used, each material constituting the toner, the toner concentration, and the like. For example, the viscosity is set to 50 to 6000 mPa · s, which is higher than that of a low concentration developer.
[0023]
In the developing unit 30 having such a configuration, the liquid developer 32 stored in the tank 33 is pumped up by the application roller 34, and the thickness of the developer layer on the application roller 34 is uniformly regulated by the regulating blade 35. Then, the uniform liquid developer 32 adheres to the surface of the developing roller 31 and is conveyed to the developing position 16 facing the photoconductor 11 as the developing roller 31 rotates. The toner is positively charged, for example, by the action of a charge control agent or the like. At the developing position 16, the toner moves from the developing roller 31 to the photoconductor 11 by the developing bias Vb applied from the developing bias generator 114 to the developing roller 31. Thus, the electrostatic latent image is visualized. The developing bias Vb is determined by an optimization process using a patch image, and for example, about Vb = DC + 400 V is used.
[0024]
The toner image formed on the photoconductor 11 as described above is conveyed to a primary transfer position 42 facing the intermediate transfer belt 41 as the photoconductor 11 rotates. The intermediate transfer belt 41 is stretched around a plurality of rollers 43 to 46, and has a peripheral speed equal to that of the photoconductor 11 in a direction (counterclockwise in FIG. 1) 47 driven by the photoconductor 11 by a drive motor (not shown). And run around. Then, when a primary transfer bias (for example, DC-400 V) is applied from the transfer bias generator 115, the toner image on the photoconductor 11 is primarily transferred to the intermediate transfer belt 41. As described above, the toner image is formed on the intermediate transfer belt 41 corresponding to the “image carrier” of the present invention, and the photoreceptor unit 10, the exposure unit 20, and the developing unit 30 constitute the “image forming unit” of the present invention. Functioning as Note that the residual charge on the photoconductor 11 after the primary transfer is removed by the charge removing unit 13 composed of an LED or the like, and the residual developing solution is removed by the cleaning unit 14.
[0025]
A roller 48 is disposed so as to face the lowermost roller 45 of the rollers 43 to 46 stretched over the intermediate transfer belt 41, and the primary transfer toner image primarily transferred to the intermediate transfer belt 41 is Is transported to a secondary transfer position 49 sandwiched between rollers 45 and 48 with the rotation of. On the other hand, the recording medium 4 stored in the paper feed cassette 3 is conveyed to a secondary transfer position 49 by a conveyance drive unit (not shown) in synchronization with the conveyance of the primary transfer toner image. The roller 48 rotates at a peripheral speed equal to that of the intermediate transfer belt 41 in a direction (clockwise in FIG. 1) that follows the intermediate transfer belt 41. When (−100 μA) is applied in the control, the primary transfer toner image on the intermediate transfer belt 41 is secondarily transferred to the recording medium 4. As described above, in this embodiment, the transfer unit 4 functions as the “transfer unit” of the present invention, and temporarily holds the toner image on the intermediate transfer belt 41 corresponding to the “image carrier” of the present invention. Although the toner image is transferred to the recording medium 4 later, it goes without saying that the toner image formed on the photoconductor 11 may be directly transferred to the recording medium 4. Image carrier ".
[0026]
The recording medium 4 onto which the toner image has been secondarily transferred is conveyed along a predetermined conveyance path 5 (indicated by a dashed line in FIG. 1), and a fixing unit corresponding to a “fixing unit” or a “fixing device” of the present invention. The toner image is fixed on the recording medium 4 by 60 and is discharged to a discharge tray provided on the upper part of the apparatus main body 2. The configuration and operation of the fixing unit 60 will be described later in detail.
[0027]
Reference numeral 51 in FIG. 1 denotes a cleaning unit that removes a residual developer on the intermediate transfer belt 41 after the secondary transfer, and reference numeral 52 denotes a patch sensor including a reflection-type optical sensor. The density of the patch image formed above is detected. 2, the main control unit 100 includes an image memory 103 for storing an image signal given from an external device via the interface 102. When the CPU 101 receives a print command signal including an image signal from an external device via the interface 102, the CPU 101 converts the print command signal into job data in a format suitable for an operation instruction of the engine unit 1 and sends the job data to the engine control unit 110. The memory 117 of the engine control unit 110 includes a ROM for storing a control program of the CPU 113 including fixed data set in advance, and a RAM for temporarily storing control data of the engine unit 1 and calculation results by the CPU 113.
[0028]
FIG. 3 is a diagram showing a fixing unit as an embodiment of the fixing device according to the present invention. FIG. 4 is a graph showing a nip pressure distribution in a nip portion of the fixing unit in FIG. Hereinafter, the configuration and operation of the fixing unit 60 will be described in detail with reference to these drawings. The fixing unit 60 includes a heating roller (contact member) 61 arranged so as to be able to contact one surface S1 (FIG. 3) of the recording medium 4, and applies a rotational driving force from a motor (not shown) to the heating roller 61. To rotate the heating roller 61 in the arrow direction P in FIG. The heating roller 61 has a built-in heating heater 61h. By controlling the operation of the heating heater 61h based on a control signal from the heater control unit 116, the fixing temperature in the fixing unit 60 can be set to an arbitrary temperature. It is adjustable.
[0029]
Further, in the fixing unit 60, the nip roller 62 is pressed against the heating roller 61 by the compression coil spring 63. Further, a nip roller 64 is pressed toward the heating roller 61. Rollers 65 to 67 are arranged around the nip rollers 62 and 64, and an endless belt 68 is wound around these rollers 62, 64 to 67. Then, a rotational driving force from a motor is applied to a part of the roller, and the operation of the motor causes the endless belt 68 to travel around in the arrow direction Q in FIG. For this reason, the outer peripheral surface of the endless belt 68 contacts the heating roller 61 between the nip rollers 62 and 64 to form a nip 69, and the recording medium 4 conveyed from the transfer unit 40 passes through the nip 69. Then, the fixing process is executed. Thus, in this embodiment, the “pressing member” of the present invention is constituted by the plurality of rollers 62, 64 to 67, and the endless belt 68 stretched over the rollers 62, 65 to 67. A portion of the outer peripheral surface of the endless belt 68 is brought into pressure contact with the heating roller 61 by the two nip rollers 62 and 64 to form a nip portion 69.
[0030]
In this embodiment, the nip roller 64 corresponding to the exit side of the nip portion 69 is merely disposed so as to be pressed toward the heating roller 61, whereas the nip portion corresponding to the entrance side of the nip portion 69 is arranged. Since the pressure roller 62 is strongly pressed toward the heating roller 61 by the compression coil spring 63, the length of the nip portion 69 along the transport direction P and Q of the recording medium 4, that is, the nip pressure in the nip width is as shown in FIG. Has a pressure distribution as shown in FIG. That is, the nip pressure on the inlet side of the nip 69 is higher than the nip pressure on the outlet side of the nip 69. Therefore, when the recording medium 4 is conveyed from the transfer unit 40 to the fixing unit 60 thus configured, the fixing process proceeds due to the following phenomenon.
[0031]
First, in the recording medium 4 conveyed to the fixing unit 60, the unfixed toner image TI formed using the liquid developer is carried on one surface (the surface in this embodiment) S1 (FIG. 3) of the recording medium 4. Before the fixing, the solid toner T and the liquid carrier L exist on one surface of the recording medium 4 in a mixed state. Then, when the recording medium 4 reaches the entrance side of the nip portion 69 in this mixed state, it receives a relatively high nip pressure. Here, “relatively high nip pressure” means a nip pressure suitable for fixing the toner T in the liquid developer to the recording medium 4, that is, a pressure higher than the nip pressure on the outlet side. What is necessary is just to set according to the component of a liquid developer, an apparatus structure, the material of the recording medium 4, etc.
[0032]
When a relatively high nip pressure is applied to the recording medium 4 on the entrance side of the nip portion 69, the liquid carriers L are pushed out from between the toners T, and the remaining amount of the liquid carriers L between the toners T is greatly reduced. This is because the liquid carrier L has higher fluidity than the solid toner T, so that the liquid carrier L moves preferentially by the application of the nip pressure. For the same reason, the remaining amount of the liquid carrier L between the recording medium 4 and the toner T is extremely small as in the case of the toner T.
[0033]
Then, the recording medium 4 moves to the exit side of the nip portion 69 with the low remaining amount, and the toner T and one surface S1 of the recording medium 4 are pressed against each other to fix the toner T on the recording medium 4. Is performed. A nip pressure suitable for fixing is set at the outlet side, so that the fixing process can be performed satisfactorily. Moreover, since the fixing process is performed in a state where the liquid carrier L is positively removed from between the toner T and between the recording medium 4 and the toner T as described above, the fixing strength can be increased, and excellent fixing can be achieved. Property is obtained.
[0034]
As described above, according to this embodiment, the nip pressure at the inlet side of the nip portion 69 is set to be higher than the nip pressure at the outlet side of the nip portion 69. Can be fixed onto the recording medium 4 with excellent fixability by using a liquid developer obtained by dispersing the toner image TI.
[0035]
The present invention is not limited to the above-described embodiment, and various changes other than those described above can be made without departing from the gist of the present invention. Hereinafter, (1) to (6) will be described in detail.
[0036]
(1) In the above embodiment, the nip portion 69 is formed by pressing a part of the outer peripheral surface of the endless belt 68 against the heating roller 61, but as in the other embodiment shown in FIG. A configuration may be employed in which a part of the outer peripheral surface of the endless belt 68 is brought into pressure contact with the heating roller 61 by using a pressure pad instead of the use rollers 62 and 64.
[0037]
FIG. 5 is a view showing a fixing unit as another embodiment of the fixing device according to the present invention. FIG. 6 is a graph showing a nip pressure distribution in a nip portion of the fixing unit in FIG. Hereinafter, the configuration and operation of the fixing unit 60 according to this embodiment will be described in detail with reference to these drawings, focusing on differences from the previous embodiment. In this fixing unit 60, a pressure pad 71 is arranged instead of the nip roller. That is, three rollers 65 to 67 are provided, and an endless belt 68 is wound around them. Then, a rotational driving force from a motor is applied to a part of the roller, and the operation of the motor causes the endless belt 68 to travel around in the arrow direction Q in FIG. In addition, a pressure pad 71 is arranged inside the endless belt 68 in a non-rotating state, and the endless belt 68 is brought into pressure contact with the heating roller 61 over the entire nip portion to form a nip portion 69. Therefore, the outer peripheral surface of the endless belt 68 contacts the heating roller 61 at the position where the pressure pad 71 is provided to form a nip 69, and the recording medium 4 conveyed from the transfer unit 40 passes through the nip 69. Thus, the fixing process is executed. As described above, in this embodiment, the “pressing member” of the present invention is constituted by the plurality of rollers 65 to 67, the endless belt 68 stretched over the rollers 65 to 67, and the pressure pad 71. I have.
[0038]
The pressure pad 71 has two pad portions 711 and 712 as shown in FIG. The pad portion 711 is disposed on the entrance side of the nip portion 69 and is pressed against the heating roller 61 by the compression coil spring 72. On the other hand, the remaining pad portion 712 is merely arranged so as to be pressed toward the heating roller 61 at the exit side of the nip portion 69. For this reason, the length of the nip 69 along the transport direction P, Q of the recording medium 4, that is, the nip pressure in the nip width has a pressure distribution as shown in FIG. That is, the nip pressure on the inlet side of the nip 69 is higher than the nip pressure on the outlet side of the nip 69.
[0039]
Then, when the recording medium 4 is transported from the transfer unit 40 to the fixing unit 60 configured as described above, the fixing process proceeds in the same manner as in the above-described embodiment. That is, when the recording medium 4 conveyed to the fixing unit 60 reaches the entrance side of the nip portion 69, the liquid carrier L is pushed out from between the toners T by receiving a relatively high nip pressure, and the liquid carrier L between the toners T is pressed. The remaining amount of the liquid carrier L is greatly reduced, and the remaining amount of the liquid carrier L between the recording medium 4 and the toner T is extremely small as in the case of the toner T. Further, the recording medium 4 moves to the exit side of the nip portion 69 with the low remaining amount, and the toner T and one surface S1 of the recording medium 4 are pressed against each other to fix the toner T on the recording medium 4. Is performed. Therefore, the fixing process can be performed in a nip pressure state suitable for fixing, and in a state in which the liquid carrier L is positively removed from between the toner T and between the recording medium 4 and the toner T. Can be increased, and excellent fixability can be obtained.
[0040]
In this embodiment, since the nip 69 is formed by using the pressure pad 71, the following operation and effect can be obtained. That is, according to this embodiment, as shown in FIG. 6, the nip pressure on the outlet side of the nip portion 69 can be made uniform, and while the recording medium 4 passes through the nip portion 69, the recording medium 4 It is possible to reliably prevent the speed fluctuation from occurring. As a result, it is possible to suppress the occurrence of slip and obtain a good fixed toner image.
[0041]
(2) The above two embodiments both employ a so-called belt nip system, but the nip system is not limited to this, and for example, a roller nip system as shown in FIG. 7 may be employed. .
[0042]
FIG. 7 is a view showing a fixing unit as another embodiment of the fixing device according to the present invention. The fixing unit 60 includes a heating roller 61 corresponding to the “contact member” of the present invention, and a plurality of pressure rollers 73 to 75 corresponding to the “pressing member” of the present invention. The heating roller 61 is driven to rotate in a direction indicated by an arrow P in FIG. The rollers 73 to 75 are adjacent to each other along the rotation direction P of the heating roller 61, and are pressed against the heating roller 61 to form a nip portion 69.
[0043]
The pressing force of the inlet roller 73 of the nip 69 among these rollers 73 to 75 is set to be higher than the pressing force of the outlet roller 75 of the nip 69. Therefore, the length of the nip 69 along the transport direction P of the recording medium 4, that is, the nip pressure in the nip width has a pressure distribution similar to that in FIG. For this reason, even when the recording medium 4 is conveyed from the transfer unit 40 to the fixing unit 60 thus configured, similarly to the above-described embodiment, the gap between the toner T and the recording medium 4 The liquid carrier L is extruded from between the liquid carrier L and the toner T, and the recording medium 4 is fixed to the recording medium 4 while moving the recording medium 4 to the exit side of the nip portion 69 while keeping the low residual amount. Therefore, the fixing process can be performed in a nip pressure state suitable for fixing, and in a state in which the liquid carrier L is positively removed from between the toner T and between the recording medium 4 and the toner T. Can be increased, and excellent fixability can be obtained.
[0044]
Here, a heating unit such as a heater may be further provided at least on the outlet side roller 75, and by heating the roller 75, the fixing strength of the toner T to the recording medium 4 is increased to further improve the fixing property. it can.
[0045]
(3) In the above embodiment, the fixing process by the fixing unit 60 is performed after the toner image is transferred to the recording medium 4. However, the present invention is also applied to an image forming apparatus that performs the transfer process and the fixing process at the same time. Can be applied. Hereinafter, description will be made with reference to FIG.
[0046]
FIG. 8 is a diagram showing a transfer fixing unit as still another embodiment of the fixing device according to the present invention. The transfer and fixing unit 80 is a unit that performs not only the transfer processing but also the fixing processing at the secondary transfer position at the same time, and is significantly different from the above-described embodiment. The point is that the heating roller 61 is provided as the "contact member", and the rollers 62, 64-67, the compression coil spring 63, and the endless belt 68 are provided as the "pressing member" of the present invention instead of the roller 48. That is, in the transfer fixing unit 80, the heating roller 61 is disposed so as to be able to contact the back surface of the intermediate transfer belt 41, which is the "image carrier" of the present invention. The heating roller 61 has a built-in heating heater 61h. By controlling the operation of the heating heater 61h based on a control signal from the heater control unit 116, the fixing temperature in the transfer fixing unit 80 can be set to an arbitrary temperature. It is adjustable. Since other configurations are the same as those of the image forming apparatus of FIG. 1, only the main part of the transfer and fixing unit 80 will be described here, and the description of the other configurations will be omitted.
[0047]
Further, similarly to the embodiment of FIG. 3, the outer peripheral surface of the endless belt 68 is pressed between the nip rollers 62 and 64 against the surface S41 of the intermediate transfer belt 41 wound around the heating roller 61 so that the nip portion 81 is moved. Has formed. Therefore, when the recording medium 4 is conveyed to the transfer / fixing unit 80, the recording medium 4 passes between the nip portions 81, so that the transfer processing and the fixing processing can be performed simultaneously.
[0048]
Also in this embodiment, the nip roller 64 corresponding to the exit side of the nip portion 81 is merely arranged so as to be pressed toward the heating roller 61, whereas the nip roller 64 corresponds to the entrance side of the nip portion 81. Since the nip roller 62 is strongly pressed toward the heating roller 61 by the compression coil spring 63, the length of the nip 81 along the transport direction P of the recording medium 4, that is, the nip pressure in the nip width is shown in FIG. It has a pressure distribution as shown. Therefore, not only can the transfer and fixing be performed, but also the liquid carrier L is positively applied between the toner T and between the recording medium 4 and the toner T in a nip pressure state suitable for the transfer and fixing as in the above embodiment. Since the fixing process can be performed in a state where the toner is removed, the fixing strength can be increased, and excellent fixing properties can be obtained.
[0049]
In this embodiment, the same belt nip method as that shown in FIG. 3 is employed. However, the nip method is not limited to this. For example, the same belt nip method as that shown in FIG. 5 and the roller nip method shown in FIG. May be adopted.
[0050]
(4) In the above embodiment, the fixing process is performed simply by passing the recording medium 4 through the nip 69, and the transfer fixing process is performed simply by passing the intermediate transfer belt 41 and the recording medium 4 through the nip 81. An electric field generating means for generating an electric field in a direction in which the toner T in the liquid developer 32 moves toward the recording medium 4 may be further provided for each of the nip portions 69 and 81. In this case, the toner T is concentrated on the recording medium 4 side, so that the liquid carrier can be efficiently removed from between the toner T and between the recording medium 4 and the toner T, and the fixing property can be further improved. it can.
[0051]
(5) In the above embodiment, the nonvolatile carrier is used as the liquid carrier of the liquid developer, but the present invention can be applied to a liquid developer using a volatile carrier.
[0052]
(6) In the above-described embodiment, the printer that prints an image given from an external device such as a host computer on a recording medium is described. However, the present invention is not limited to this. The present invention can be applied to all image forming apparatuses that form an image on a recording medium. In the above-described embodiment, the present invention is applied to a monochrome image forming apparatus. However, the present invention is not limited to this, and the present invention can be applied to a color image forming apparatus. .
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an internal configuration of a printer which is an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a block diagram illustrating an electrical configuration of the printer of FIG.
FIG. 3 is a diagram showing a fixing unit as an embodiment of the fixing device according to the present invention.
4 is a graph showing a nip pressure distribution in a nip portion of the fixing unit in FIG.
FIG. 5 is a view showing a fixing unit as another embodiment of the fixing device according to the present invention.
6 is a graph showing a nip pressure distribution in a nip portion of the fixing unit in FIG.
FIG. 7 is a diagram showing a fixing unit as another embodiment of the fixing device according to the present invention.
FIG. 8 is a diagram showing a transfer fixing unit as still another embodiment of the fixing device according to the present invention.
[Explanation of symbols]
4 recording medium, 10 photoconductor unit (image forming means), 20 exposure unit (image forming means), 30 developing unit (image forming means), 32 liquid developer, 40 transferring unit (transfer means) , 60: fixing unit (fixing means) 80: transfer / fixing unit (transfer fixing means), 61: heating roller (contact member), 62: nip roller (on the inlet side), 64 ... nip roller (on the outlet side) , 65 to 67: roller (pressing member), 68: endless belt (pressing member), 69, 81: nip portion, 71: pressure pad (pressing member), 73: inlet side roller, 75: outlet side roller , S1... (One side of the recording medium), TI... Unfixed toner image, T.

Claims (8)

A contact member disposed so as to be able to contact one surface carrying an unfixed toner image formed using a liquid developer in which a toner is dispersed in a liquid carrier, on both surfaces of the recording medium; A pressure member for pressing the recording medium against the contact member from the surface, and passing the unfixed toner image on the recording medium by passing the recording medium through a nip between the contact member and the pressure member. In a fixing device for fixing on one side,
The nip pressure on the inlet side of the nip portion is set to be higher than the nip pressure on the outlet side of the nip portion. The contact member includes a heating roller,
The pressure member includes a plurality of rollers including two nip rollers disposed in proximity to the heating roller, and an endless belt that can be looped around the plurality of rollers and run around. A part of the outer peripheral surface of the endless belt is pressed against the heating roller by a roller to form the nip portion, and
The pressing force of pressing the endless belt against the heating roller by the nip roller on the entrance side of the nip portion of the two nip rollers is such that the endless belt is heated by the nip roller on the exit side of the nip portion. The fixing device according to claim 1, wherein the fixing device is set to be higher than a pressing force applied to the roller. The contact member is a heating roller,
The pressure member includes the plurality of rollers, an endless belt that is stretched around the plurality of rollers, and is capable of traveling around the endless belt. The fixing device according to claim 1, further comprising: a pressure pad that forms the nip portion by bringing the pressure roller into contact with the heating roller. The contact member includes a heating roller,
The pressure member includes a plurality of rollers that are in pressure contact with the heating roller, and the plurality of rollers and the heating roller form the nip portion.
2. The fixing device according to claim 1, wherein a pressing force of an inlet-side roller of the nip portion against the heating roller is set to be higher than a pressing force of an outlet-side roller of the nip portion. 3. The fixing device according to claim 4, further comprising a heating unit that heats the outlet roller. The fixing device according to claim 1, further comprising an electric field generation unit that generates an electric field in a direction in which the toner in the liquid developer moves toward the recording medium in the nip portion. Image forming means for forming a toner image on an image carrier using a liquid developer obtained by dispersing a toner in a liquid carrier,
Transfer means for transferring the toner image formed by the image forming means to one surface of a recording medium;
7. A fixing device having the same configuration as the fixing device according to claim 1 and fixing the unfixed toner image transferred onto one surface of the recording medium by the transfer device to the recording medium. An image forming apparatus. Image forming means for forming a toner image on the surface of the image carrier using a liquid developer obtained by dispersing a toner in a liquid carrier,
A transfer fixing unit that transfers the toner image to one surface of the recording medium and simultaneously fixes the toner image,
The transfer / fixing unit has a contact member arranged so as to be able to contact the back surface of the image carrier, and a pressing member that presses the recording medium against the surface of the image carrier from the opposite surface of the recording medium. Performing the transfer and fixing by passing the recording medium and the image carrier through a nip portion between the contact member and the pressing member, and
An image forming apparatus, wherein a nip pressure on an inlet side of the nip portion is set to be higher than a nip pressure on an outlet side of the nip portion.

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