JP4355751B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device mounted on a copying machine or a printer, and more particularly to a fixing device that heats an image via a rotating body having a low heat capacity such as a film (or belt).

  In recent years, copying machines and printers that consume less power and have a short apparatus start-up time have been desired. One of the factors that greatly influences power consumption and start-up time is a heat fixing device, and there is a technical trend to achieve both reduction of power consumption and shortening of start-up time by reducing the heat capacity of the heat fixing device.

  As an example of such a low heat capacity fixing device, a ceramic heater on which a heating resistor is formed, a fixing belt that rotates while in contact with the heater, and a pressure roller that forms a nip portion with the heater via the fixing belt And a fixing device that heats and fixes an unfixed image by passing a recording material carrying an unfixed image between a fixing belt and a pressure roller (see, for example, Patent Documents 1 to 3).

  Such a low heat capacity fixing device has been used in a mono-color image forming apparatus, but may be used in a full-color image forming apparatus. A full-color image is obtained by superimposing three or four layers of toners of a plurality of colors, and it is necessary to heat and fix so as to wrap around the toner layer for good fixing. However, a monocolor fixing belt has a high surface hardness only by having a resin base layer such as polyimide and a surface release layer such as a fluororesin. For this reason, problems such as a problem that the toner particles are crushed due to the rigidity of the surface layer and the resolution of the image is lowered, and problems such as poor color mixing are pointed out.

As a means for solving these problems, a method using a fixing belt in which an elastic layer is provided between a base layer and a surface layer has been proposed (for example, see Patent Document 4).
Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980 Japanese Patent Laid-Open No. 10-10893

  However, due to the presence of the elastic layer, the thermal conductivity is lower than that of a monocolor fixing belt. The above-described fixing device having a low heat capacity is normally temperature-controlled by controlling energization of the heater so that the heater temperature is maintained at a predetermined target temperature (fixing temperature). However, the thermal conductivity of the belt is low. Then, even if the belt surface does not reach the fixing temperature, the heater reaches the fixing temperature, and heat generation of the heater is restricted (that is, energization to the heater is restricted). In order to quickly start up the apparatus from the standby state in which the image forming apparatus waits for the input of a print signal until printing is started, a sufficient amount of current is required to the heater. As a result, the energization amount to the heater is restricted, and it is impossible to start up quickly.

  In addition, in a fixing device using an elastic belt in which an elastic layer such as a heat-resistant elastomer is provided on the base layer, when a large electric power is applied to the heating element, the elastic layer has a lower thermal conductivity than the base layer. Before the temperature reaches a predetermined temperature, heat escapes to the support member that supports the heating element, resulting in poor thermal efficiency, and repeated use in this state causes the support member to exceed the heat resistance temperature and break. It was.

  Thus, it is conceivable to increase the thermal conductivity of the fixing belt by making the base layer of the fixing belt metal, but this method alone does not secure a sufficient startup speed.

  The present invention has been made in view of the above-described problems, and an object thereof is to enable high-speed startup even when a fixing belt having an elastic layer is used, that is, to shorten the time required for startup of the heater. An object of the present invention is to provide a fixing device that can be used.

  Another object of the present invention is to provide a fixing device that can be used in an image forming apparatus capable of forming a full-color image.

  Further objects of the present invention will become apparent upon reading the following detailed description with reference to the accompanying drawings.

  The present invention is a fixing device having the following configuration.

An endless belt having a metal layer and a rubber layer; a heater that contacts the inner surface of the endless belt; a belt guide member that supports the heater and contacts the inner surface of the endless belt to guide rotation of the endless belt; A pressure roller that is in contact with the outer surface of the endless belt and forms a nip portion with the heater via the endless belt, and a control means for controlling the power supplied to the heater. In a fixing device that heats and fixes a recording material carrying a toner image while sandwiching and conveying the recording material,
A temperature detecting element that detects the temperature of the endless belt downstream of the nip portion in the rotational direction of the endless belt, and the control means is configured to maintain the detected temperature of the temperature detecting element at a predetermined temperature. The electric power supplied to the heater is controlled , and when the electric power is started to be supplied from the standby state to the heater and the apparatus is started up to a fixable state, the temperature detecting element for detecting the temperature of the endless belt. A fixing device, wherein power is continuously supplied to the heater until a detected temperature reaches the predetermined temperature .

  According to the present invention, the time required for starting up the heater can be shortened.

[1] Overall Schematic Configuration of Fixing Device FIG. 1 is a schematic sectional view of an example of a heating device to which the present invention is applied as a fixing device. In FIG. 1, 1 is an endless belt (rotating body: end level) having a metal base layer and an elastic layer (rubber layer), 2 is a heating element (heater) in which a heating resistor is formed on a ceramic substrate, A resin-made belt guide member that supports the heating element 2 and contacts the inner surface of the belt 1 to guide the rotation of the belt 1, and is formed of heat-resistant liquid crystal polymer, phenol resin, PPS, PEEK, or the like. . The belt 1 is externally fitted to the assembly of the heating element 2 and the support member 3 with a margin. Since the inner surface of the belt 1 rotates while rubbing against the heating element 2 and the support member 3 inside, it is necessary to keep the frictional resistance between the heating element 2 and the support member 3 small. Therefore, a small amount of a lubricant such as heat resistant grease is interposed between the heating element 2 and the support member 3 and the belt 1.

  A pressure roller 4 is rotatably supported and is in contact with the outer surface of the belt 1 and is pressed against the heating element 2 via the belt 1. The pressure roller 4 is rotated by driving means (not shown). It also functions as a driving roller for driving the belt 1. The pressure roller 4 is provided with a heat-resistant elastic layer 4b formed by foaming silicone rubber, fluorine rubber, or silicone rubber on a metal core 4a such as aluminum, and a release layer on the outer periphery of the rubber layer 4b. A layer 4c of fluorine resin or the like is provided.

  The belt 1 receives power by rotating the pressure roller 4 counterclockwise at least at the time of image fixing, and slides on the lower surface of the heating element 2 in the clockwise direction while carrying a predetermined peripheral speed, that is, a non-fixed toner image 6 bearing member. The recording material 5 that is a heating material is driven to rotate at substantially the same speed as the conveyance speed. The belt surface temperature is detected by the temperature detecting element 8, and the detected temperature is fed back to the temperature control circuit (control means for controlling the power supplied to the heater) 11 via the A / D converter 10, The AC driver 12 is controlled so that the surface temperature is maintained at a predetermined temperature, and the energization of the heating element 2 is controlled.

  In a state where the belt 1 is rotationally driven, a recording material 5 is introduced between the belt 1 and the pressure roller 4 in the pressure nip portion 7 formed by the heating element 2 and the pressure roller 4, and the recording is performed. The material 5 is brought into close contact with the outer peripheral surface of the belt 1 and passed through the pressure nip portion 7 while being overlapped with the belt, and the heat generated by the heating body 2 is applied to the recording material 5 through the belt 1 and pressure is applied together with it. The unfixed toner image 6 on the recording material 5 is heated and melted and fixed. That is, the fixing device heats and fixes the recording material carrying the toner image 6 at the nip portion 7 while nipping and conveying the recording material. The recording material 5 subjected to the fixing process is separated from the belt 1 after passing through the press-contact nip portion 7 and discharged outside the apparatus.

  As shown in FIG. 1, the temperature detection element 8 detects the temperature of the belt 1 on the downstream side of the nip portion 7 in the rotation direction of the belt 1. And the temperature control circuit 11 controls the electric power supplied to the heat generating body 2 so that the detection temperature of the temperature detection element 8 may maintain predetermined temperature.

  Although the formation of the unfixed toner image 6 on the recording material 5 is omitted in the drawing, an indirect (transfer) method or a direct method is used in an appropriate image forming mechanism such as an electrophotographic process, an electrostatic recording process, or a magnetic recording process. Formed with.

  Next, each component of the fixing device will be described in detail.

[2] Belt 1
FIG. 2 is a cross-sectional model diagram showing the layer structure of the belt 1. The belt 1 used in the apparatus of this embodiment is an endless belt having a multilayer structure including at least a metal base layer 1a and an elastic layer 1b.

a) Metal base layer 1a
As the metal base layer 1a, a metal having good thermal conductivity such as nickel, stainless steel or aluminum, or an alloy containing them can be used. Is used.

  Conventionally used resin base layers such as polyimide (PI) have a low thermal conductivity, so that the heat generated by the heater when the elastic layer is provided is less likely to be transmitted to the material to be heated. As in this example, by using a metal as the base layer of the belt, the thermal conductivity of the belt can be increased.

  The metal base layer 1a is made of a material that can be manufactured by an electroforming method such as nickel, and a cylindrical matrix such as SUS (stainless steel) or copper is used in an electroforming liquid such as nickel sulfamate, nickel sulfate, or nickel acetate. A thin metal base layer can be obtained by forming a nickel layer having a predetermined thickness by electroplating and demolding.

  The thickness of the metal base layer 1a is preferably 10 μm or more from the viewpoint of the strength of the belt 1. On the other hand, if the thickness is too large, the heat capacity is increased, so it takes time to raise the surface temperature of the belt 1 to a temperature at which the fixing property can be ensured. For example, it is preferable to set the thickness to 60 μm or less because it is difficult to ensure a good contact state. Therefore, the thickness of the metal base layer is preferably 10 μm or more and 60 μm or less. Similarly, the inner diameter of the metal base layer 1a is desirably 15 mm or more from the viewpoint of securing a contact state with the heating element 2.

  According to the study by the present inventors, heat transfer from the heating element to the belt is excellent in order to quickly raise the temperature of the belt surface to the fixing possible temperature after energization of the heating element is started. I knew I needed to be. For example, in order to reduce the time from the start of energization to the heating element to the output of the first recording material within 30 seconds, the heating amount of the heating element for at least 15 seconds after the start of energization to the heating element is at least If it is not more than 7.5 KJ, it is difficult to reach the temperature range sufficient for fixing the belt surface. Thus, in order to secure a sufficient calorific value in a short time, it has been found that it is necessary that the belt itself has excellent thermal conductivity and that the degree of adhesion between the heater and the belt is high. Therefore, in this example, the base layer of the belt is made of metal, and the thickness of the metal base layer is designed to be not less than 10 μm and not more than 60 μm, so that the flexibility of the belt can be secured and the belt can be in close contact with the heater. Furthermore, it is desirable that the inner diameter of the metal base layer is 15 mm or more in terms of ensuring flexibility.

b) Elastic layer 1b
As the elastic layer 1b, a heat-resistant elastomer layer such as fluorine rubber or silicone rubber is used. As an elastic layer forming method, an unvulcanized rubber member is applied on a nickel electroformed base layer using a coating means such as a spray coating method so that the thickness is substantially uniform within a range of about ± 20 μm. Then, it is crosslinked and cured using a heating means such as an oven. These rubbers may contain a filler for improving the thermal conductivity such as silica, alumina, boron nitride and the like.

  The thickness of the elastic layer 1b can be determined as appropriate in consideration of thermal conductivity and elasticity. However, in order to ensure sufficient resolution without crushing the toner image, it is better to have a thickness of 50 μm or more. However, if it is too thick, it takes time to raise the belt surface temperature. More preferably, it is 100 μm or more and 300 μm or less.

c) Releaseable layer 1c
Also, a silicone rubber layer or a release layer 1c such as a fluororesin such as PFA, PTFE, FEP or the like is formed on the outermost surface of the belt 1 by a method such as coating or tube coating in order to ensure toner release properties. It is preferable to do this.

  A heat resistant resin such as polyimide may be provided on the inner surface of the metal base layer 1a for the purpose of preventing deterioration due to rubbing against the heating element 2 and the support member 3.

  Further, layers other than those described above may exist in each of the layers 1a-1b and 1b-1c for the purpose of adhesion between layers.

[3] Heating element 2
FIG. 3 is a partially cutaway plan view of the heating element 2. The heating element 2 is formed on the front or back surface of a highly insulating ceramic substrate 2a formed of alumina, aluminum nitride, silicon carbide, or the like along the longitudinal direction (direction perpendicular to the moving direction of the material to be heated), for example, Ag. / Pd (silver palladium), RuO ₂ , Ta ₂ N, and other energization heating resistor layer 2b is formed by applying a linear or narrow strip with a thickness of about 10 μm and a width of about 1 to 5 mm by screen printing or the like. is there. On the surface of the heating element 2, an insulating protective layer 2c such as a thin glass coat that is electrically insulated and can withstand sliding against the belt 1 is provided. Electric power is supplied to the energization heating resistor layer 2b from a power supply means (not shown) via electrode portions 2d and 2d provided at the end of the energization heating resistance layer 2b.

  As described above, in this example, the fixing belt (rotating body) 1 has the metal layer and the elastic layer (rubber layer). Further, the energization control means 11 controls the energization to the heating resistor layer 2b so that the temperature detected by the temperature detecting element 8 that detects the temperature of the fixing belt 1 maintains the target temperature (fixing temperature). That is, as shown in FIG. 1, the temperature of the belt 1 is detected downstream of the nip portion 7, and the power supplied to the heating element (heater) 2 is controlled so that this temperature maintains a predetermined temperature. The time required for starting up the heating element 2 is shortened.

[4] Pressure roller 4
The pressure roller 4 is provided with an elastic layer 4b formed of a heat-resistant rubber such as silicone rubber or fluorine rubber, or a foam of silicone rubber on the outside of a metal core 4a such as iron or aluminum. On this layer, a release layer 4c such as PFA, PTFE, FEP or the like is formed.

  The pressure roller 4 has a diameter of about 20 mm. The pressure roller 4 is pressed in the direction of the belt 1 so as to form a pressure nip portion 7 required for heat fixing from both ends in the longitudinal direction. It is pressed. If the applied pressure is too small at this time, sufficient heat cannot be given to the toner, and sufficient adhesion of the belt to the heating element cannot be secured. It is better to have a pressing force of 0.39 N / mm or more per unit length in the direction perpendicular to it, but if the pressing force is too large, the pressure applied between the belt 1 and the heating element 2 or the support member 3 also increases. As a result, the frictional resistance during sliding rotation increases, and the torque applied to the pressure roller 4 increases more than necessary. Further, since the stress applied to the belt 1 increases, the fatigue of the metal base layer 1a leads to a decrease in durability. Therefore, the applied pressure is desirably 0.98 N / mm or less.

  The pressing force is set by pressing against both ends of the pressure roller or both ends of the support member using a spring (not shown) having an arbitrary spring constant and setting the spring length to an arbitrary value.

[Example 1]
By providing a silicone rubber elastic layer (200 μm) by spray coating on a metal base layer (thickness 30 μm) containing nickel (Ni) as a main component, and further providing a fluororesin release layer (20 μm) on the outermost surface, A belt 1 for a heat fixing device having a belt inner diameter of 24 mm was produced. This was incorporated in an external fixing device having a pressure applied from the pressure roller per unit length of 0.49 N / mm and a heating element input power of 550 W, and evaluated by the following evaluation method.

[Evaluation methods]
A recording material on which a line pattern (color overlap) is formed with “color toner exhibiting good fixability at a process speed of 120 mm / sec and a fixing temperature of 180 ° C.” is prepared. The controller of the fixing device controls the electric power supplied to the heating element 2 so that the detected temperature of the belt surface is maintained at 180 ° C. The belt 1 is driven by the rotation of the pressure roller, and the control unit controls the rotation speed of the pressure roller 4 so that the rotation speed of the belt 1 is 120 mm / sec.

  Using such a fixing device, first, energization of the heating element 2 was started simultaneously with the start of rotation of the belt, and the amount of heat generated by the heating element 1 in 15 seconds after the start of energization was measured. Further, when the belt temperature reaches 180 ° C. after 15 seconds, after 15 seconds, if it takes longer, the recording medium carrying an unfixed image is passed after the belt surface reaches 180 ° C., and the fixing property is evaluated. did. The belt surface temperature was measured by contacting a thermocouple.

  As a result, if the belt of Example 1 is used and the applied pressure is set to the value of Example 1, the heating element 1 generates 7.6 KJ of heat in 15 seconds from the start of energization. It was found that the belt surface temperature reached a fixing temperature of 180 ° C. in 5 seconds. In addition, the resolution of the unfixed image was secured, and good fixability was exhibited. The results are shown in Table 1.

[Image Evaluation Criteria]
○: The image is not crushed after fixing, and maintains almost the same resolution as that of the unfixed image. ×: The image is crushed after fixing and is greatly reduced from the resolution of the unfixed image [Example 2]
A belt 2 for a heat-fixing device was produced in the same manner as in Example 1 except that the thickness of the elastic layer was 400 μm. When evaluated in the same manner as in Example 1, it was possible to achieve both good prevention of overheating of the heater back surface and on-demand, and a good resolution. The startup time was satisfactory. The results are shown in Table 1.

[Example 3]
A belt 3 for a heat fixing device was produced in the same manner as in Example 1 except that the thickness of the base layer was 50 μm. When evaluated in the same manner as in Example 1, it was possible to achieve both good prevention of overheating of the heater back surface and on-demand, and a good resolution. The durability of the belt was satisfactory. The results are shown in Table 1.

[Example 4]
Evaluation was made in the same manner as in Example 1 except that the heating and fixing device belt 1 of Example 1 was used and the pressure per unit length from the pressure roller of the external fixing device was 0.74 N / mm. Both the prevention of overheating on the back side and on-demand performance were achieved, and good resolution could be secured. The torque applied to the pressure roller was at a level with no problem. The results are shown in Table 1.

[Comparative Example 1]
A heat fixing belt 4 was produced in the same manner as in Example 1 except that the elastic layer was not applied. When evaluated in the same manner as in Example 1, the resolution was lowered when an unfixed image was passed, and sufficient fixability could not be obtained. The results are shown in Table 1.

[Comparative Example 2]
A heat fixing belt 5 was produced in the same manner as in Example 3 except that the base layer was polyimide (PI) resin. As a result of evaluation in the same manner as in Example 1, good results were obtained in terms of increase in belt surface temperature and image fixability. However, after several studies, the heat generated by the heating element 1 in the support member 3 was obtained. It was melted and damaged because of heat up. The results are shown in Table 1.

  The present invention is not limited to the above-described embodiments, but includes modifications within the technical concept.

  As described above, it is possible to provide a fixing device that can be started up at high speed even when a belt having an elastic layer (rubber layer) is used as a rotating body. Further, it is possible to provide a fixing device that can be used in an image forming apparatus capable of forming a full-color image.

  By using a rotating body having a metal base layer and an elastic layer and appropriately controlling the heating value of the heater, the thickness and inner diameter / material of the metal layer, the pressing force of the pressure member, and the thickness of the elastic layer, for example, In the heat fixing device, it is possible to shorten the time until first printing, alleviate the excessive temperature rise of the heater, and ensure the resolution of the color image.

FIG. 3 is a schematic cross-sectional view of a heat fixing apparatus according to an embodiment of the present invention. Cross-sectional model diagram showing the layer structure of a belt mounted on the heat fixing device Partially cutaway plan view of a heating element provided in the heat fixing device

Explanation of symbols

  1 .... belt, 1a ... metal base layer, 1b ... elastic layer, 1c ... release layer, 2. heating element, 2a ... ceramic substrate, 2b ... energization heating resistance layer, 2c ... insulation protection Layer 2d ··· Electrode 3 ·· Support member 4 Pressure roller 4a · · Metal cored bar 4b · · Elastic layer 4c · · Release layer 5 · · Material to be heated (recording material) 6, Unfixed toner image, 7 ... Pressure nip, 8 ... Temperature detector

Claims (1)

An endless belt having a metal layer and a rubber layer; a heater that contacts the inner surface of the endless belt; a belt guide member that supports the heater and contacts the inner surface of the endless belt to guide rotation of the endless belt; A pressure roller that is in contact with the outer surface of the endless belt and forms a nip portion with the heater via the endless belt, and a control means for controlling the power supplied to the heater. In a fixing device that heats and fixes a recording material carrying a toner image while sandwiching and conveying the recording material,
A temperature detecting element that detects the temperature of the endless belt downstream of the nip portion in the rotational direction of the endless belt, and the control means is configured to maintain the detected temperature of the temperature detecting element at a predetermined temperature. The electric power supplied to the heater is controlled , and when the electric power is started to be supplied from the standby state to the heater and the apparatus is started up to a fixable state, the temperature detecting element for detecting the temperature of the endless belt. A fixing device, wherein power is continuously supplied to the heater until a detected temperature reaches the predetermined temperature .