JP2008197535A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device for an image forming apparatus, in which paper separation performance is secured over a long period of time. <P>SOLUTION: The fixing device 2 for the image forming apparatus, which passes a recording medium through a nip portion 18 formed between a fixing member 20 having a metal core 22, an elastic layer 24 and a heat generating layer and a pressure member 10 brought into press-contact with the fixing member 20, to heat and fix-process an unfixed image formed on the recording medium is provided with an external heating member 30 which heats the heat generating layer of the fixing member 20 from the outside, a separation member 42 which is oppositely arranged near the fixing member 20 and separates the recording medium after fix processing from the fixing member 20 and gap maintaining means 24 and 40 for maintaining the gap G between the surface of the fixing member 20 and the separation member 42 constant. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device used in an image forming apparatus such as an electrophotographic copying machine or a printer.

  In image forming apparatuses such as electrophotographic copying machines and printers, a charging device is used to uniformly charge the surface of a member to be charged (photosensitive member), and an image is exposed thereon to form an image latent image. Has been. The formed image latent image is developed with toner to form a toner image, which is transferred to a recording medium, or transferred to an intermediate transfer member, for example, an intermediate transfer belt, and further transferred to a recording medium and transferred. Image formation is performed by heat-fixing the toner image with a fixing device.

  As a fixing device used in such an image forming apparatus, a heat roller type fixing device having a nip portion in which a fixing roller and a pressure roller are disposed in pressure contact is widely used. A separation claw for separating the toner-fixed paper after passing through the nip portion from the roller is disposed on at least one surface of the fixing roller and the pressure roller. In this type of fixing device, a halogen lamp as a heat source is arranged inside the fixing roller, and this halogen lamp is connected to an energization control device so that the surface temperature of the fixing roller is maintained at a predetermined fixing temperature. Has been.

  The above heat roller type fixing device has a long track record of use and excellent fixing performance, but it has a long rise time from turning on the power to reach the fixing processable temperature, low thermal efficiency, etc. Have a problem.

  As a heating method that shortens the rise time and has high thermal efficiency, an external heating method in which heating is performed from the outside of the fixing roller by a heating means such as induction heating, resistance heating, or lamp heating has been proposed.

  In the induction heating method as an example of the external heating method, an elastic layer and a release layer are formed on a heating thin plate made of a ferromagnetic material such as iron on the surface of a rotating roller provided with an elastic material around a fixing roller core. For a fixing roller with a laminated arrangement, or for a fixing belt with an elastic layer and a release layer laminated on a heating thin plate made of a ferromagnetic material such as iron, which is rotatably mounted on the surface of the fixing roller. The coil unit is arranged. Then, the fixing roller and the fixing belt are heated by Joule heat generated from the eddy current flowing through the heating thin plate leave provided in the fixing roller and the fixing belt by passing a high frequency current through the coil unit.

As a conventional elastic layer used for the fixing roller, silicone rubber or a silicone sponge having a low rebound resilience with a rebound resilience of about 30 to 50% is generally used (see, for example, Patent Document 1). When the belt is heated by the above-described external heating method, it is advantageous for the temperature raising performance of the belt that the elastic layer is made of a silicone sponge having higher heat insulation. However, with silicone sponge, due to endurance deterioration due to long-term use, the resilience of the elastic layer decreases as the elastic layer shrinks, and the gap between the outermost surface of the fixing belt or fixing roller and the separation claw increases. As a result, the conventional type fixing device composed of an elastic layer having low rebound resilience has a problem of occurrence of separation failure in which the recording medium attached to the fixing roller and the pressure roller is hardly peeled off by the separation claw.
JP-A-7-334024.

  Therefore, a technical problem to be solved by the present invention is to provide a fixing device of an image forming apparatus that can ensure sheet separation performance over a long period of time.

Means and actions / effects for solving the problem

In order to solve the above technical problem, according to the present invention,
An unfixed image formed on a recording medium by passing through a nip formed between a fixing member having a metal core, an elastic layer, and a heat generating layer and a pressure member pressed against the fixing member. In a fixing device of an image forming apparatus that heats and performs a fixing process,
An external heating member for heating the heat generating layer of the fixing member from the outside;
A separating member that is disposed opposite to the fixing member and separates the fixed recording medium from the fixing member;
Gap maintaining means for maintaining a gap between the surface of the fixing member and the separation member below a certain level;
A fixing device for an image forming apparatus is provided.

  As described in the prior art, the gap between the surface of the fixing member and the separation member tends to increase due to the durability deterioration of the elastic layer of the fixing member. According to the above configuration, the gap maintaining means for maintaining a constant gap between the surface of the fixing member and the separation member is provided, thereby forming between the fixing member heated by the external heating member and the pressure member. The fixing-processed recording medium discharged from the nip portion can be stably separated from the fixing member over a long period of time by the separating member.

  Such a gap maintaining means is configured to actively maintain a constant gap, that is, the gap between the surface of the fixing member and the separating member is measured by a gap sensor, and the gap is measured. Then, the separating member is corrected to a predetermined position.

  Alternatively, the gap maintaining means is configured to maintain the gap constant by the component itself, that is, a configuration using a sponge-like elastic body having a rebound elastic modulus of 50% or more as the elastic layer of the fixing member. It is.

  The fixing member may be configured such that the heat generating layer is fixedly disposed on the elastic layer. However, the fixing belt including the heat generating layer has a feature that it is easily externally heated on the outer peripheral surface of the elastic layer. It is the structure inserted in.

  The external heating member can be used for resistance heating, lamp heating, or the like, but is preferably induction heating with a short rise time and high thermal efficiency.

  Hereinafter, a fixing device 2 of an image forming apparatus according to an embodiment of the present invention will be described in detail with reference to FIG.

  FIG. 1 is a schematic explanatory view of a fixing device 2 of an image forming apparatus according to an embodiment of the present invention. The fixing device 2 forms a latent image on an electrophotographic image forming apparatus (for example, a copying machine, a printer, etc.), that is, an image carrier (for example, a photosensitive drum), and visualizes the latent image with toner. Thus, it is detachably incorporated in a device for forming a toner image and subsequently transferring the toner image onto a sheet.

  As shown in FIG. 1, the fixing device 2 is in pressure contact with the fixing roller 20 to form a nip portion 18 through which a sheet passes, a pressure roller 10 (pressure member), a fixing roller 20 (fixing member), An induction heating coil unit 30 (external heating member), a separation claw 42 (separation member), and a separation claw control unit 40 (gap maintaining means) are provided.

  The pressure roller 10 is connected to a rotary drive motor, for example, and an elastic layer 14 made of a silicone sponge having a thickness of about 2 to 5 mm is formed on a cored bar 12 made of aluminum, steel or the like, and the surface thereof is made thick. The structure is covered with a release layer made of PFA (perfluoroalkoxy) of about 30 μm. The pressure roller 10 is pressed against the fixing roller 20 by being biased toward the fixing roller 20 by a spring (not shown). A contact portion between the fixing roller 20 and the pressure roller 10 forms a nip portion 18 by elastic deformation of the elastic layer 14 and the elastic layer 24.

  The fixing roller 20 has a configuration in which a sponge-like elastic layer 24 obtained by foaming silicon rubber is disposed on a core metal 22 such as aluminum or steel, and a fixing belt 26 is fitted on the outer peripheral surface of the elastic layer 24. The fixing belt 26 and the fixing roller 20 are driven to rotate as the pressure roller 10 rotates.

  The fixing belt 26 is formed, for example, by forming an elastic layer made of silicon rubber with a thickness of about 300 μm on a heat generating layer made of iron or SUS430 stainless steel with a thickness of about 50 μm, and the surface thereof is made of PFA (with a thickness of about 20 μm). The belt is formed by coating with a release layer made of perfluoroalkoxy), and is a flexible belt capable of induction heating.

  Around the fixing roller 20, an induction heating coil unit 30 is arranged at a position far from the nip portion 18 (in the drawing, a position approximately 180 degrees from the nip portion 18) on the upstream side in the rotation direction of the fixing roller 20.

  The induction heating coil unit 30 includes a main core made of ferrite, a hem core disposed on both sides thereof, a main coil 36, and an induction heating coil drive power source (not shown). When a high-frequency current is passed through the main coil 36 of the induction heating coil unit 30, an eddy current flows through a portion of the heat generation layer of the fixing belt 26 facing the induction heating coil unit 30 to generate heat due to Joule heat. 20 is heated.

  At the downstream side of the nip portion 18 in the paper conveyance direction, at least one separation claw 42 for separating the paper is provided on the fixing roller 20 side so as not to be in contact with the fixing roller 20. When the toner image formed on the paper is heat-fixed, the fixing roller 20 is disposed on the print surface side. However, since the toner-fixed paper is easily wound around the fixing roller 20, the separation claw 42 is provided on the fixing roller 20 side. It has been.

  A tapered tip end portion of the separation claw 42 is disposed in the vicinity of the fixing belt 26 of the fixing roller 20. The gap G (for example, 1 mm) between the surface of the fixing belt 26 of the fixing roller 20 and the separation claw 42 is made constant by moving the front end portion of the separation claw 42 forward or backward toward the fixing belt 26 of the fixing roller 20. A separation claw control unit 40 is provided for maintenance. The separation claw control unit 40 as a gap maintaining means includes a drive motor 48 that drives the separation claw 42, a gap sensor 46 that detects a gap G between the surface of the fixing belt 26 of the fixing roller 20 and the separation claw 42, And a control circuit 44 that controls the forward / backward movement of the separation claw 42 based on information from the gap sensor 46.

  As the gap sensor 46, for example, a transmission type laser measuring device is used. Since the separation claw 42 is for separating the toner-fixed paper from the fixing roller 20 in the nip portion 18, laser measurement cannot be performed because the pressure roller 10 in the nip portion 18 is in the way. Accordingly, the roll length of the pressure roller 10 is configured to be shorter than the roll length of the fixing roller 20, and a dummy claw having the same shape as the separation claw 42 is provided in a region where the pressure roller 10 is not present in the axial non-sheet passing region. A transmission type laser measuring device is arranged, and a gap G between the surface of the fixing belt 26 of the fixing roller 20 and the dummy claw is measured, so that the gap between the surface of the fixing belt 26 of the fixing roller 20 and the separation claw 42 is measured. Can be measured in a pseudo manner.

  Alternatively, the absolute position of the surface of the fixing belt 26 of the fixing roller 20 is measured by a laser-type, eddy current-type, or ultrasonic-type position displacement sensor, and the fluctuation between the surface position of the fixing belt 26 and the separation claw 42 is measured. By estimating the gap G, the fluctuation of the gap G can be known.

  A gap between the surface of the fixing belt 26 of the fixing roller 20 and the separation claw 42 by advancing or retreating the separation claw 42 by the drive motor 48 based on the information regarding the fluctuation of the gap G obtained from the gap sensor 46. G is kept constant.

  In the above-described configuration, a high-frequency current is passed through the induction heating coil unit 30 to heat the fixing roller 20, and an unfixed sheet (recording medium) on which a toner image has been transferred by an image forming apparatus of an image forming apparatus (not shown) is nipped. The toner image is fixed by passing through the section 18. The toner-fixed paper that has passed through the nip portion 18 is separated from the fixing roller 20 by the separation claw 42 and then conveyed to a paper discharge portion (not shown).

  Even if the rebound resilience of the fixing roller 20 is lost due to long-term use, the gap G between the surface of the fixing belt 26 of the fixing roller 20 and the separation claw 42 is kept constant. Predetermined paper separation performance can be ensured.

  Next, a fixing device 2 of an image forming apparatus according to another embodiment of the present invention will be described with reference to FIGS. 2 to 6, but portions that overlap with the above-described embodiment are omitted, and differences are described. The explanation will be centered.

  FIG. 2 is a schematic explanatory view of a fixing device 2 of an image forming apparatus according to another embodiment of the present invention. FIG. 3 is a diagram showing the relationship between the rebound resilience of the sponge-like elastic body used in the fixing device 2 and the durability time. FIG. 4 is a diagram illustrating the relationship between the belt position displacement and the durability time in the fixing device 2 according to the comparative example. FIG. 5 is a diagram showing the relationship between the belt position displacement and the durability time in the fixing device 2 according to the present invention. FIG. 6 is a diagram for explaining that the belt position displacement in the fixing device 2 varies depending on the elastic layer to be used.

  In the embodiment shown in FIG. 1, the separation claw 42 is configured to maintain the gap G constant by actively displacing, whereas in this embodiment, as shown in FIG. It is characterized in that the separation claw 42 is in a fixed position and the elastic layer 24 of the fixing roller 20 is made of a material that hardly deteriorates in durability. That is, the elastic layer 24 of the fixing roller 20 that is not easily deteriorated in durability is characterized in that it is composed of a sponge-like elastic body having a rebound resilience of 50% or more as a gap maintaining means.

  The elastic layer 24 disposed on the cored bar 22 of the fixing roller 20 is made of a silicone sponge body having a specific gravity of 0.4 to 0.6. It has been found that the rebound resilience of the silicone sponge body being 50% or more is extremely effective when used for the elastic layer 24 of the fixing roller 20. That is, various silicone sponge bodies having different rebound resilience are prepared, and the silicone sponge bodies having the rebound resilience shown in Table 1 are incorporated in the elastic layer 24 of the fixing roller 20 of the fixing test apparatus to obtain 300,000 sheets. Table 1 shows the test results.

  As is apparent from Table 1, when the rebound resilience of the silicone sponge body is 45% or less, separation failure occurred, whereas when the resilience resilience of the silicone sponge body was 50% or more. There was no problem in the 300,000 sheet passing test.

  FIG. 3 shows a conventional sponge having a rebound resilience of about 45% (dotted line) for the silicone sponge of Table 1 and a repellent resilience of about 57% for the silicone sponge of Table 1. The endurance test result of (solid line) is shown. The rebound resilience of the silicone sponge body incorporated in the fixing roller 20 of the test fixing device was measured with a Trypson rebound resilience test device defined in JIS K6255.

  As is clear from FIG. 3, the rebound resilience according to the present invention has a rebound resilience of about 45% (dotted line), while the rebound resilience decreases over time. About 57% (solid line) shows that the rebound resilience has hardly changed over time.

  By the way, as shown in FIGS. 4 to 6, the position of the fixing belt 26 constantly fluctuates due to the warming condition of the fixing belt 26 and the sponge-like elastic layer 24. 4 and 5 show the relationship between the operation time (heating time) and the displacement of the fixing belt 26 when the rebound resilience according to the prior art is about 45% and the rebound resilience according to the present invention is about 57%. Showing the relationship.

  As shown in state A of FIG. 4 (dotted line in FIG. 5), a new product having a rebound resilience of about 45% according to the prior art and a new product having a rebound resilience of about 57% according to the present invention are respectively sponged. The fixing belt 26 was fitted into the sponge-like elastic layer 24, and the relationship between the operation time (heating time) and the displacement of the fixing belt 26 was examined. As a result, none of the fixing belts 26 fitted to the sponge-like elastic layer 24 was almost deformed.

  Next, the relationship between the operation time (heating time) and the displacement of the fixing belt 26 was examined for the fixing belt 26 fitted to the sponge-like elastic layer 24 subjected to a paper passing test for a predetermined time.

  As shown in state B of FIG. 4 (thick line in FIG. 5), a sponge having a rebound resilience of about 45% according to the prior art immediately after heating when power is turned on and after an endurance test (after 382 hours) The fixing belt 26 fitted to the elastic layer 24 is recessed by about −0.8 mm. As the time elapses, the sponge-like elastic layer 24 that has been deformed by contraction expands by heating, so that the fixing belt 26 recovers to a position of about 0 mm.

  As shown in state C of FIG. 4 (thin line in FIG. 5), immediately after heating when the power is turned on, the rebound resilience according to the present invention is about 57% and after a durability test (after 258 hours or 405 hours). Since the fixing belt 26 fitted in the sponge-like elastic layer 24 has rebound resilience, the fixing belt 26 rises instantaneously by being pressed and is displaced to a position of about +0.8 mm. Then, the fixing belt 26 is gradually stabilized at a position of about 0 mm.

  Therefore, the elastic layer 24 of the fixing roller 20 that is not easily deteriorated in durability is made of a sponge-like elastic body having a rebound resilience of 50% or more, so that the surface of the fixing belt 26 of the fixing roller 20 and the separation claw 42 are separated. Since the gap G is maintained below a certain level, a predetermined sheet separation performance can be ensured over a long period of time.

  The above description is disclosed for explaining one embodiment of the present invention, and the present invention is not limited to this, and various modifications are possible. For example, in the above embodiment, the fixing roller 20 is of a type that includes the fixing belt 26, but may be of a type that includes only a roller body that does not have the fixing belt 26. That is, the fixing roller 20 includes a cored bar 22 provided with a sponge-like elastic layer 24 in which silicon rubber is foamed, and a heat generation layer formed thereon. The heat generating layer has a structure in which an elastic layer made of silicon rubber having a thickness of about 300 μm is formed on a thin iron plate having a thickness of about 400 μm, and the surface thereof is covered with a PFA layer having a thickness of about 20 μm. Further, as an external heating unit for heating the fixing roller 20 from the outside, a heating unit such as resistance heating or lamp heating can be used. Furthermore, in the above embodiment, the separation claw 42 is provided on the fixing roller 20 side, but the separation claw 42 may be provided on the pressure roller 10 side instead of or in addition to this.

1 is a schematic explanatory diagram of a fixing device of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a schematic explanatory diagram of a fixing device of an image forming apparatus according to another embodiment of the present invention. It is a figure which shows the relationship between the rebound resilience of a sponge-like elastic body used for a fixing device, and durable time. FIG. 6 is a diagram illustrating a relationship between belt position displacement and durability time in a fixing device according to a comparative example. FIG. 7 is a diagram illustrating a relationship between belt position displacement and durability time in the fixing device according to the present invention. FIG. 6 is a diagram illustrating that the belt position displacement in the fixing device varies depending on the elastic layer used.

Explanation of symbols

2 fixing device 10 pressure roller 12 core metal 14 elastic layer 18 nip portion 20 fixing roller 22 core metal 24 elastic layer 26 fixing belt 30 induction heating coil unit 32 main core 34 hem core 36 main coil 40 separation claw control unit 42 separation claw 44 Control circuit 46 Gap sensor 48 Drive motor G Gap

Claims (5)

An unfixed image formed on a recording medium by passing through a nip formed between a fixing member having a metal core, an elastic layer, and a heat generating layer and a pressure member pressed against the fixing member. In a fixing device of an image forming apparatus that heats and performs a fixing process,
An external heating member for heating the heat generating layer of the fixing member from the outside;
A separating member that is disposed opposite to the fixing member and separates the fixed recording medium from the fixing member;
A gap maintaining means for maintaining a constant gap between the surface of the fixing member and the separating member;
A fixing device for an image forming apparatus.   The gap maintaining means measures the gap between the surface of the fixing member and the separation member with a gap sensor, and corrects the separation member to a predetermined position based on the measured gap. Fixing apparatus for image forming apparatus.   2. The fixing device for an image forming apparatus according to claim 1, wherein the gap maintaining means uses a sponge-like elastic body having a rebound resilience of 50% or more as an elastic layer of the fixing member.   4. The fixing device for an image forming apparatus according to claim 1, wherein the fixing member has a configuration in which a fixing belt including a heat generating layer is fitted on the outer peripheral surface of the elastic layer.   The fixing device for an image forming apparatus according to claim 1, wherein the external heating member is induction heating.

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