JP2008026677A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device including the configuration in which the generation of the abnormal image due to the generation of contact marks is prevented in the case where a temperature detecting member of a contact system is used, and temperature detection accuracy can be assured without entailing a cost increase. <P>SOLUTION: The fixing device is equipped with the contact type temperature detecting member 76 disposed contactually on the surface of the fixing member 74 as a temperature detecting member of a heat source 73A used for heat fixing. The contact type temperature detecting member 76 is previously provided with an oil layer 75B provided with a width (W1) narrower than the width (W0) of the contact surface on the side coming into contact with the fixing member 74, and is incorporated into the fixing member 74 so as to come into contact therewith. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly to a temperature detection mechanism.

  In an image forming apparatus such as a copying machine, a facsimile machine, a printer, or a printing machine, it is undetermined by being transferred and carried on a sheet-like recording medium such as recording paper or an OHP film (hereinafter, described for recording paper). A fixed image is heated and fixed to obtain a copy or a printed output.

  The configuration of the fixing device uses a heat roller fixing system in which a fixing roller having a built-in heating source and a pressure roller capable of forming a nip portion that is a nipping / conveying portion of a recording sheet by contacting the fixing roller. Is known (for example, Patent Document 1).

  On the other hand, in the fixing device, a separation claw for separation and a temperature detection member used for temperature management are generally provided in contact with the roller surface, but there are rubbing marks on the roller surface. There are problems such as the occurrence of streaks in the image.

  Therefore, conventionally, a configuration for applying oil to reduce friction and preventing toner offset on the roller surface (for example, Patent Document 2) and a configuration for reducing contact pressure of the contact member (for example, Patent Documents 3 and 4). ) Has been proposed.

  Patent Document 2 discloses a configuration in which oil having different viscosities is applied in accordance with the sheet passing width region corresponding to the size of the recording paper in the heating roller, and Patent Document 3 discloses a state in which the thermistor element is wrapped. A configuration is disclosed in which silicon grease for enhancing thermal conductivity is filled inside a tape with an adhesive material such as a polyimide film integrated with a leaf spring, that is, between the thermistor element. Patent Document 4 discloses a cantilever beam. Discloses a two-layer structure in which a foam material is provided at the tip of a thermistor supporting leaf spring that is supported in a shape and a fluorine film is provided on the surface thereof.

Japanese Patent No. 3153732 (paragraph “0015” column, FIG. 1) JP-A-7-181546 (paragraph "0020" column) Patent 3519855 (paragraph "0007" column) Japanese Patent No. 3756017 (paragraph "0011" column)

  In order to reduce the load on the surface of a roller or the like used as a fixing member, as disclosed in Patent Documents 3 and 4, reduction of the contact pressure is one method. There is a risk that the temperature cannot be detected.

  Therefore, it is conceivable to use a member that does not use contact. For example, it is conceivable to use a temperature detection member by a non-contact method such as an infrared absorption type thermopile instead of a thermistor as a temperature detection member, but a large installation space is required to secure an area necessary for infrared absorption. Therefore, a new problem in cost such as high cost and high price arises, and installation may be difficult when a small image forming apparatus is targeted.

  Therefore, when temperature management control using a contact-type temperature detection member is unavoidable from the viewpoint of cost or the like, it is possible to reliably prevent the occurrence of contact marks on the surface of the mating member to be contacted. It is desirable to be able to prevent the occurrence of an image, ensure temperature detection accuracy, and prevent an increase in cost.

  In view of the above problems in the conventional fixing device, the object of the present invention is to prevent the occurrence of abnormal images due to the occurrence of contact marks when using a contact-type temperature detection member, and to increase the temperature detection accuracy without causing an increase in cost. An object of the present invention is to provide a fixing device and an image forming apparatus having a configuration that can be secured.

In order to solve the above problems, the present invention comprises the following arrangement.

(1) In a fixing device provided with a contact-type temperature detection member provided in contact with the surface of a fixing member as a temperature detection member of a heat source used for heat fixing,
The fixing device according to claim 1, wherein the contact-type temperature detecting member is incorporated in such a manner that an oil layer is provided in advance on a surface in contact with the fixing member so as to contact the fixing member.

  (2) The fixing device according to (1), wherein a thermistor is used as the contact-type temperature detecting member, and oil is applied in advance to a contact surface side of the thermistor with the fixing member.

  (3) The fixing device according to (1) or (2), wherein the oil layer is provided in a range narrower than a width of a contact surface of the contact-type temperature detecting member with respect to the fixing member.

  (4) The fixing device according to any one of (1) to (3), wherein the amount of oil used in the oil layer is set to 100 mg or less.

  (5) An image forming apparatus using the fixing device according to any one of (1) to (4).

  (6) In the fixing device using the thermistor in which the oil amount is set, the waiting time from the power-on to the first printing start after the thermistor is installed is longer than the waiting time from the first printing to the start of printing. The image forming apparatus according to (5), wherein the image forming apparatus is also long.

  According to the present invention, when a contact-type temperature detection member is used, an oil layer is provided in advance on the surface that comes into contact with the fixing member, and installation is not required unlike oil application, In addition, it is possible to suppress wear on the surface of the fixing member and generation of contact marks by reducing contact resistance with oil. As a result, it is possible to prevent the occurrence of streaky contact marks in the image and to prevent the occurrence of abnormal images.

  In particular, when a thermistor is used as the contact-type temperature detection member, an oil layer can be provided in advance when the thermistor is manufactured. Therefore, unlike the case where the oil layer is provided after being incorporated in the fixing device, the oil layer As a result, it is not necessary to adjust the position and amount of application of the oil layer, as in the case where the oil layer is provided after installation. .

  In the invention described in claim 3, the oil layer is provided in a range narrower than the temperature detection region in the thermistor, so that the facing surface between the thermistor and the fixing member is left, so that the thermistor and the fixing member are left between them. It is possible to prevent the temperature detection accuracy from being lowered by preventing the temperature detection sensitivity from being lowered due to the presence of an oil layer which is a different substance from the quantity member. In particular, it is desirable to consider shortening the warm-up time when the temperature is raised, and to prevent the detection sensitivity from being reduced in consideration of overheating prevention except during the warm-up. In the invention according to claim 3, the thermistor and Since there remains a range where the fixing member is directly opposed to the fixing member, it is possible to reliably prevent the occurrence of the above-described problem by accurately detecting the temperature of the fixing member.

  In the invention described in claim 4, it is possible to prevent an increase in detection error by defining the amount of oil used in the oil layer.

  In the inventions according to claims 5 and 6, the oil layer of the incorporated thermistor is set by making the waiting time from when the power is turned on after installation into the first printing to be longer than the waiting time at the printing shell island after the first time. The oil is scraped off following the movement of the surface of the fixing member, and can be spread over the entire surface of the fixing member, so that the detection error when the oil layer is interposed is suppressed and the error is suppressed. It is possible to prevent the occurrence of hot offset due to overheating, which is one of the phenomena that occurs when the value of the value increases.

  The best mode for carrying out the present invention will be described below with reference to the illustrated embodiments.

  FIG. 1 shows an image forming apparatus to which a fixing device according to an embodiment of the present invention is applied. The image forming apparatus shown in FIG. 1 is a color printer having a plurality of color image forming units. In addition to this, the present invention includes a copying machine, a printing machine, a facsimile machine, or a combination of these functions.

In FIG. 1, a color printer 1 includes image forming units 71a and 71b in which a photosensitive member used as a latent image carrier and a device that performs a charging process, a developing process, and a cleaning process are collected in each process cartridge and stored in a process cartridge. , 71c, 71d.
The color printer 1 mentioned as the present embodiment is configured so that each image forming unit is arranged along the extending direction of an intermediate transfer belt 28 as an intermediate transfer member used for sequentially transferring images of different colors formed for each image forming unit. A tandem method in which 71a, 71b, 71c, 71d are arranged in parallel is used.

The color printer 1 includes a housing main body 1A that can store the image forming unit 100, and the image forming unit 100 is disposed at substantially the center in the height direction of the housing main body 1A.
An optical scanning device 72 is provided above the image forming unit 100, and a sheet feeding cassette serving as a stacking unit capable of stacking and storing sheet-like recording media such as transfer paper (hereinafter referred to as transfer paper) below the image forming unit 100. Each of the paper feed units 4 equipped with is arranged.

  Image forming unit 71 a. Reference numerals 71b, 71c, and 71d correspond to latent image carriers, respectively, and are drum-shaped photosensitive members (hereinafter referred to as photosensitive drums) 22a, 22b, 22c, and 22d that can rotate clockwise in the figure, and are arranged around the photosensitive members. Charging rollers 21a, 21b, 21c, and 21d that are in contact with the photosensitive drum, and a developing sleeve 32a that performs visible image processing of the electrostatic latent images formed on the photosensitive drums 22a, 22b, 22c, and 22d, Cleaning devices 23a, 23b, 23c, and 23d having developing devices 31a, 31b, 31c, and 31d having 32b, 32c, and 32d and blades that contact the photosensitive drums 22a, 22b, 22c, and 22d and scrape residual toner. Are constituted by process cartridges 20a, 20b, 20c, and 20d.

In the process cartridges 20a, 20b, 20c, and 20d, the photosensitive drums 22a, 22b, 22c, and 22d that are uniformly charged at a high potential by the charging rollers 21a, 21b, 21c, and 21d in the dark are optical scanning devices. The laser beam 36a, 36b, 36c, 36d from the beam 72 is selectively exposed and scanned based on the image data, and an electrostatic latent image comprising a low potential portion where the potential is attenuated by this exposure and a high potential portion resulting from the initialization. An image is formed.
The developing devices 31a, 31b, 31c, and 31d form (develop) toner images by transferring toner to the low potential portion (or high potential portion) of the electrostatic latent image and performing visible image processing.

The process cartridges 20a, 20b, 20c, and 20d are configured such that the developing devices 31a, 31b, 31c, and 31d can be built in the housings that constitute the process cartridges. The photosensitive drums 22a to 22d rotate in the clockwise direction to rotate the toner images. Can be moved along the circumferential direction and conveyed toward a primary transfer position described later.
These latent image formation and toner image formation by development are performed at sequential timings in the process cartridges 20a, 20b, 20c, and 20d. As described later, cyan, magenta, yellow, and black 1 are sequentially primary-transferred from the image carrier onto the intermediate transfer belt 28 in which the upper extended surface facing the process cartridges 20a, 20b, 20c, and 20d in FIG. 1 moves in the direction indicated by the arrow P. A full-color superimposed image is carried.

  That is, the toner image transferred onto the intermediate transfer belt 28 in the image forming unit 71a is a contact portion between the intermediate transfer belt 28 as the next primary transfer portion and the photosensitive drum 22a (the intermediate transfer belt 28 in the corresponding contact portion). The photosensitive drum 20b of the adjacent image forming unit 71b operates in the same manner as in the image forming unit 71a, and the developing device 31b operates on the photosensitive drum 22b. The upper electrostatic latent image is subjected to visible image processing to form a toner image (development), and the toner image is rotationally conveyed and transferred onto the toner image already formed on the intermediate transfer belt 28. Similar operations are sequentially performed in the image forming units 71c and 71d.

  For electrostatic development, a negative bias voltage in which alternating current and direct current are superimposed is applied to a cored bar of each of the developing rollers 32a, 32b, 32c, and 32d from a bias power source (not shown). . In addition, a DC negative potential bias voltage is applied to each charging roller 21a, 21b, 21c, 21d from another bias power source to charge the photosensitive drum. For primary transfer, primary transfer rollers 29a, 29b, 29c, and 29d are disposed on the back side of the intermediate transfer belt 28 that is in contact with the photosensitive drums 22a, 22b, 22c, and 22d.

  The difference between the process cartridges 20a, 20b, 20c, and 20d is the developer used in the developing device, and toners of different colors such as cyan, yellow, magenta, and black are used as the developer. In this example, the process cartridges 20a, 20b, 20c, and 20d are arranged side by side along the intermediate transfer belt 28 stretched in the lateral direction, and the photosensitive drums 22a, 22b, 22c, and 22d are also in contact with the intermediate transfer belt 28. It is arranged side by side.

The intermediate transfer belt 28 used as one of the primary transfer members has a stretching surface in the horizontal direction in FIG. 1, and four photosensitive drums 22a, 22b, 22c, and 22d are arranged along the stretching surface, respectively. ing.
The upper extended surface of the intermediate transfer belt 28 is pressed by primary transfer rollers 29a, 29b, 29c, and 29d so as to be in contact with the photosensitive drums 22a, 22b, 22c, and 22d. The intermediate transfer belt 28 circulates in contact with the photosensitive drums 22a, 22b, 22c, and 22d, and the photosensitive drum 22a provided in the four image forming units 71a, 71b, 71c, and 71d as described above during this movement. , 22b, 22c, and 22d, the toner images are transferred in order, and a full-color toner image is formed as a four-layer superimposed image. The full-color toner image is batch-transferred onto the transfer sheet via the secondary transfer roller 39 by the secondary transfer unit 50.

  The toner image after being transferred onto the transfer paper is fixed by a fixing device 70, which will be described in detail with reference to FIG. 2, and is directly discharged from a tray-like discharge storage portion 5 via a discharge conveyance path 81 by a discharge means 80 constituted by a pair of rollers. The case where the sheet is discharged toward the second position and the case where the sheet is circulated again toward the secondary transfer unit 50 are selected. In the former case, image recording on one side of the transfer paper is targeted, and in the latter case, image recording on both sides of the transfer paper is targeted.

  When performing double-sided recording, which is the latter case, the transfer sheet is transported toward a recirculation transport path RP, which will be described later, and the recording surface is reversed when it reaches the secondary transfer unit 50 again. ing.

FIG. 2 is a schematic diagram showing the configuration of the fixing device 70. In FIG. 2, the fixing device 70 includes a fixing roller 71, a pressure roller 72, and a heating roller 73 including a heating source 73A that face each other and a fixing belt 74. And is configured.
The fixing belt 74 is wound around the fixing roller 71 and the heating roller 73 and is brought into close contact with the fixing roller 71 and the heating roller 73 by being given a constant tension by a tension roller 75 that is in contact with the expansion surface. Yes.

  A fixing nip is configured by pressing the pressure roller 72 against a portion corresponding to the fixing roller 71 of the fixing belt loop configured as described above.

The fixing belt 74 is composed of a PI (polyimide) belt which is an endless film of heat-resistant resin, and in this embodiment, the thickness is set to about 50 to 90 μm.
On the belt substrate, there is an elastic layer such as silicone rubber or fluororubber in order to maintain the flexibility of the image, and this thickness is suitably 100 to 300 μm. Further, a release layer such as PFA or PTFE is provided on the surface layer, and the thickness is about 20 to 50 μm. The release layer may be covered with a tube type or may be formed by coating or baking liquid or powder PFA or PTFE.

Inside the heating roller 73, a heat source 73A (halogen heater, infrared heater, or other thermal resistance is also possible) is provided, and a contact-type temperature detecting element 76 such as a thermistor through a control mechanism (not shown). The flashing of the heater used for the heat source 73A is controlled, and the surface temperature of the heating roller 73 or the fixing belt 74 is controlled. The heating roller 73 is made of a metal such as aluminum or iron. The thinner the thickness, the better. However, since it receives bending stress due to the belt tension, the thickness of aluminum is 0.4 mm or more, and the thickness of iron is 0.2 mm or more. It becomes.
The inside of the heating roller 73 is coated with a paint that promotes heat absorption such as black so that heat from the heat source 73A can be easily absorbed.

The fixing roller 71 has a surface layer covered with an elastic body such as silicone rubber and is made of a highly rigid core material such as metal. Iron and aluminum are suitable for the core material. Apart from this, it is also possible to use a high-strength resin.
As the elastic body of the surface layer, sponge rubber is most suitable, and since it can be configured with low hardness (50 HS or less: Asker C), not only the load on the fixing belt is small, but also the heat conduction is low compared to ordinary rubber, There is an advantage that heat of the fixing belt is difficult to escape.

  The tension roller 75 is provided at a substantially intermediate position of the extending surface formed by the fixing belt 74 being hung on the heating roller 73 and the fixing roller 71. In FIG. 2, a pressing member such as a spring 77 is provided from the outside of the belt loop. Is pressurized.

The tension roller 75 uses a highly rigid material such as metal for the core material, and covers the surface layer with a material having a certain degree of elasticity such as heat-resistant felt or silicone rubber. These surface materials do not damage the fixing belt 74 at the time of pressurization, and can ensure a uniform pressing force even in a setting lacking a certain degree of accuracy, and since heat conduction is not so fast, heat dissipation from the fixing belt 74 is prevented. It also helps to prevent.
The tension roller 75 may be applied from the inside of the fixing belt 74, or may be used instead of the tension roller 75 so that the heating roller 73 and the fixing roller 71 can be moved so as to change the distance between the axes.

  The pressure roller 72 has a configuration in which an elastic body such as silicone rubber is disposed on a rigid core material such as metal. It is effective to wind a member having good releasability such as a PFA tube on the surface layer.

At this time, if the hardness of the pressure roller 72 is set higher than that of the fixing roller 71 (such as reducing the rubber thickness or increasing the rubber hardness), the fixing nip becomes concave on the fixing roller 71 side. Also in this example, since the heating roller 73 and the heat source 73A are arranged on the fixing roller 71 (fixing belt 74) side, the temperature control on the fixing roller 71 side is easy, and therefore the fixing roller 71 side is used as the image surface. .
Accordingly, the fixing nip is concave on the image side. Since the color image has a larger amount of toner than monochrome, it is difficult to peel off from the fixing belt, and the concave nip on the fixing roller 2 side makes it easy to separate the curvature of the transfer paper that moves after fixing so that the post-fixing It has a feature that an image can be easily peeled off from the fixing belt 74.

  On the other hand, FIG. 3 is a view showing the peripheral portion of the fixing device 70. In FIG. 3, the unfixed image T carried on the transfer sheet S after transfer is provided on the transfer paper inlet side of the fixing device 70. The fixing roller 71 and the pressure roller 72 are brought into contact with the fixing nip formed along the entrance guide 78.

  In the fixing nip, the toner image T is fixed to the transfer paper S by melting and permeation by applying predetermined heat and pressure.

A separation plate 79 is disposed on the image carrying surface side of the transfer sheet S at the outlet of the fixing device 70. The separation plate 79 is made of metal and has a size that covers the entire conveyance width, and the tip end 79A located on the entry side of the transfer paper S is made as thin as possible (for example, within 0.2 mm). Since the tip is thin, it can be installed as close as possible to the fixing nip, and the heat capacity is low, so that the temperature can easily rise to a temperature at which water vapor cannot adhere.
The distal end 79A of the separation plate 79 may be crushed thinner than the plate thickness, or another thin plate of 0.2 mm or less may be attached. The separation plate 79 can be an advantageous member because it can reduce damage to the fixing belt 74 by not contacting the fixing belt 74 within the image range. In general, the gap (Gap) between the tip of the separation plate 79 and the fixing belt 74 is set to about 1 mm or less.
If the gap (Gap) is too far, the transfer paper S discharged from the fixing nip is easily caught by the separation plate 79 and is likely to be jammed. On the other hand, if the gap is too close, the transfer paper S comes into contact with the fixing belt 74. The gap dimension is set in consideration of scratching. In this embodiment, in order to keep the gap size accurate, positioning members 79B that are lightly abutted against the fixing belt 74 are provided at both ends of the separation plate 98 outside the image.

  By the way, when the transfer sheet S exiting the fixing nip is wound around the fixing belt 74 and conveyed along the fixing belt 74 for a longer time than the target time, unevenness may occur in the image. For this reason, in this embodiment, the tip position of the separation plate 79 is set as close as possible to the nip.

  The transfer sheet S fed out from the fixing device 70 is transported along the separation plate 79, is sandwiched between downstream transport rollers 80, and is transported further downstream (discharge port of the image forming apparatus).

Next, the characteristic part of a present Example is demonstrated.
The present embodiment is characterized in the configuration of a contact-type temperature detection member 76 such as a thermistor that detects temperature by contacting the fixing belt 74.
FIG. 4 is a schematic diagram showing an arrangement configuration of the fixing belt 74 and a contact-type temperature detection member (hereinafter referred to as a thermistor for convenience) 76, in which the thermistor 76 is wound around the heating roller 73. A flexible support member 76A having a cantilever-like shape that comes into contact with the fixing belt 74 at a position where the fixing belt 74 is in contact, and an oil layer 76B is provided in advance on the surface that comes into contact with the fixing belt 74. Accordingly, the thermistor 76 is assembled into the fixing device 70 as a finished product.

  That is, the thermistor 76 is assembled so that the surface of the thermistor 76 that comes into contact with the fixing belt 74 is preliminarily coated with oil and then contacts the fixing belt 74 when the fixing device 70 is assembled. The oil layer 76B may be configured not only to apply oil, but also to have a result similar to that obtained when a solid oil film (pasted) is pasted and crushed by contact pressure. Is possible.

  Since the present embodiment is configured as described above, the thermistor 76 in which the oil layer 76B is provided by applying oil on the surface in contact with the fixing belt 74 in advance when the fixing device 70 is assembled is used as the fixing belt. 74 under the predetermined contact conditions.

  This reduces the frictional resistance between the fixing belt 74 and the thermistor 76 that are in contact with each other without applying treatment such as oil application to the fixing belt 74 and prevents wear on the fixing belt 74 side.

  Therefore, contact marks generated by frictional resistance are prevented, and the occurrence of uneven gloss due to streaky unevenness on the image can be prevented. In particular, when a solid image with a large amount of toner adhesion is output, the influence of contact traces becomes significant. However, in this embodiment, the occurrence of contact traces is suppressed so that the glossiness of solid images is reduced. Generation of unevenness can be reliably prevented. Moreover, by providing an oil layer in advance, it is not only necessary to adjust the oil amount after installation, but also because the oil layer is formed when the thermistor is installed. Unlike the formation of, an oil layer with the same conditions can be obtained for each thermistor and productivity can be improved.

Next, the details of the oil layer 76B will be described.
The role of the thermistor 76 is to accurately detect the temperature on the fixing member 74 side of the heating unit and to perform optimum temperature control. An oil layer 76B is provided on the contact surface between the fixing member 74 and the thermistor 76. In this case, since a layer of another substance is formed between the contact portions of the two, there is a concern that the detection accuracy of the thermistor 76 that detects the temperature of the fixing member of the heating unit is lowered.

  Specifically, there is a deterioration in responsiveness when the temperature is suddenly raised to the fixing set temperature when the power is turned on, or a temperature erroneous detection during normal printing. Furthermore, temperature detection varies due to differences in the state of oil application amount and oil layer formation.

  When starting up, the fixing device 70 performs from about room temperature to about 150 ° C. in about 10 seconds. Therefore, if the thermistor 76 has deteriorated responsiveness, the actual temperature may instantaneously increase to 200 ° C. or higher. Is also possible. In that case, the fixing belt 74 may be altered or deformed due to overheating, which may cause not only image defects but also damage to the apparatus.

  Further, since the temperature of the fixing belt 74 is detected via the oil layer 76 </ b> B even during normal printing, the detection accuracy is deteriorated, and it is considered that the actual temperature is higher than the detected temperature of the thermistor 76. In that case, depending on the type of transfer material used, hot offset due to excessive heat may occur, which may cause image defects.

  Therefore, in this embodiment, as shown in FIG. 5, the oil layer 76B provided on the contact surface of the thermistor 76 with the fixing belt 74 is narrower than the width (W0) of the contact surface of the thermistor 76 with the fixing belt 74. A relationship (W0> W1) that is within the range (W1) is set.

  Since the present embodiment is configured as described above, the entire contact surface of the thermistor 76 is not covered with the oil layer, and therefore, the region where the thermistor 76 and the fixing belt 74 are in direct contact with each other unlike the case of the entire area application. Therefore, it is possible to alleviate the deterioration over time due to the rubbing of the fixing member 74 while maintaining the detection accuracy of the fixing member temperature without any extreme responsive deterioration.

Furthermore, the amount of oil applied is set to 100 mg or less. The reason is as follows.
FIG. 6 shows temperature rise data when the amount of oil to be applied is changed. In addition to the thermistor 76, a probe (not shown) for measuring the temperature of the fixing member 74 is provided, and the detected temperature of the probe and the detected temperature of the thermistor 76 are graphed.
As shown in FIG. 6A, when the oil application amount is 120 mg, the effect of reducing the frictional resistance is obtained, but the detection error at the start-up is large, and the measured temperature at the probe during printing is also the value of the thermistor. There are places where the detected temperature is higher by 20 ° C. or more, and it can be seen that the thermistor cannot accurately detect the temperature.

  On the other hand, as shown in FIG. 6B, in the case of an oil application amount of 100 mg, although a slight detection error is seen at the start-up, the actual temperature measured by the probe and the thermistor detection temperature are almost the same during printing. It ’s okay. That is, it can be seen that the amount of oil applied must also be controlled below a certain amount.

  As described above, by setting the formation conditions of the oil layer 76B, it is possible to detect the temperature with less error while suppressing deterioration with time caused by the frictional resistance to the fixing member 74 due to the contact of the thermistor 76.

Next, another embodiment of the present invention will be described.
In this embodiment, for a fixing device using a thermistor having an oil layer, after the thermistor is incorporated, the waiting time from the power-on to the first printing start is determined from the waiting time from the first printing to the first printing start. Is also characterized by a long setting.

  When the thermistor 76 having the oil layer 76B is used in the above-described embodiment, if the amount of oil is excessively large, the detection accuracy may be deteriorated, and as a result, overheating may occur during printing and hot offset may occur. .

  In this embodiment, in order to prevent hot offset during printing regardless of the amount of oil applied to form the oil layer, the fixing device after the thermistor 76 is incorporated, that is, the fixing device 70 is a color printer. After the arrival corresponding to immediately after being incorporated in 1, the power is turned on only for the first printing. The waiting time from power-on to the start of the first printing is longer than the waiting time until the other printing starts. is doing.

  FIG. 7 is a graph showing the change in temperature (measured temperature of the fixing belt 74 due to the temperature women's lobe) when printing is started after a set of 5 to 3 minutes after the power is turned on. When the amount of oil applied is 120 mg, the temperature immediately after start-up is 20 ° C. or more higher than that without the oil layer, and when printing is started as it is, hot offset occurs.

  Therefore, it can be seen that when waiting for about 2 minutes, the difference in detected temperature gradually disappears in the course of this time, and it becomes 10 ° C. or less.

  This is because the fixing belt 74 that continues to move (rotate) during standby deprives the oil applied to the contact surface of the thermistor 76 and makes the oil evenly distributed in the circumferential direction of the fixing belt 74. This is because the detection error is reduced by spreading. Therefore, when printing is started after this waiting time, the detected temperature accuracy during printing is also suppressed to within 10 ° C., and it is possible to avoid the occurrence of hot offset.

  As described above, by setting the waiting time from the power-on to the start of printing in the first printing after the thermistor 76 is incorporated in the fixing device, regardless of the amount of oil applied to the oil layer. The oil can be spread evenly over the entire fixing belt 74 within the waiting time to reduce the thickness of the oil layer and reduce the thickness of a different layer called the oil layer at the contact surface with the fixing belt 74. In this state, the temperature detection sensitivity can be increased by reducing the thickness and reducing the temperature detection error, thereby preventing the occurrence of adverse effects such as overheating and preventing hot offset.

1 is a schematic diagram illustrating an example of an image forming apparatus to which a fixing device according to an embodiment of the present invention is applied. FIG. 2 is a schematic diagram for explaining a main configuration of a fixing device according to an embodiment of the present invention. FIG. 3 is a schematic diagram for explaining a peripheral structure of the fixing device shown in FIG. 2. FIG. 3 is a schematic diagram for explaining an arrangement configuration of a fixing member, a pressure member, and a contact-type temperature detecting member used in the fixing device shown in FIG. 2. It is a top view for demonstrating the principal part structure of the contact-type temperature detection member shown in FIG. FIG. 6 is a diagram for explaining the relationship between the amount of oil used in the oil layer provided in the contact-type temperature detection member shown in FIG. 5 and the change in the temperature rising state of the fixing member; (B) shows the case where the amount of oil applied is 100 mg. It is a diagram for demonstrating the relationship between the standby time after power activation, and the change of a temperature rising state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color printer 70 Fixing apparatus 71 Fixing roller 72 Pressing roller 73 Heating roller 73A as a heating member 73A Heating source 74 Fixing belt as a fixing member 76 Thermistor 76A as a contact-type temperature detection member Support member 76B Oil layer

Claims (6)

In a fixing device provided with a contact-type temperature detection member provided in contact with the surface of a fixing member as a temperature detection member of a heat source used for heat fixing,
The fixing device according to claim 1, wherein the contact-type temperature detecting member is incorporated in such a manner that an oil layer is provided in advance on a surface in contact with the fixing member so as to contact the fixing member.   The fixing device according to claim 1, wherein a thermistor is used as the contact-type temperature detecting member, and oil is previously applied to a contact surface side of the thermistor with the fixing member.   The fixing device according to claim 1, wherein the oil layer is provided in a range narrower than a width of a contact surface of the contact-type temperature detecting member with respect to the fixing member.   The fixing device according to claim 1, wherein the amount of oil used in the oil layer is set to 100 mg or less.   An image forming apparatus using the fixing device according to claim 1. In the fixing device using the thermistor with the oil amount set, the waiting time from when the power is turned on until the first printing starts after the thermistor is incorporated is longer than the waiting time from the first printing to the beginning of printing. The image forming apparatus according to claim 5, wherein:

Images