JP2006084805A - Thermal fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device that is free from image failure resulting from hot offset of a paper non-passage part or a wrinkle caused by a fixing roller, even if narrow papers (i.e., small-sized paper), such as envelopes are printed in a large quantity. <P>SOLUTION: A heater for heating the fixing roller is in the form of a plate with a low heat capacity and has a plurality of heating elements of different lengths. This restrains the temperature rise of the paper non-passage area of the thermal fixing device. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat fixing device used in an electrophotographic printer, a copying machine, and an electrostatic recording apparatus.

  2. Description of the Related Art Conventionally, in a fixing device provided in an image forming apparatus that employs an electrophotographic system, an electrostatic recording system, etc., a fixing roller and a pressure roller that rotate a recording material carrying an unfixed toner image in pressure contact with each other. A so-called heat roller type heat fixing device is widely used in which a nip portion formed by the above method is fixed on a recording material as a permanent image. FIG. 10A shows a schematic configuration of the heat roller type heat fixing device. The fixing roller 60 is provided with a heating element 62 such as a halogen lamp in a hollow core bar 61 made of aluminum or stainless steel, and a release layer 63 such as a fluororesin for preventing toner offset on the outer surface. It is a thing. Further, the pressure roller 50 is formed with an elastic layer formed of silicone rubber or the like on the outside of the core metal 51 or a sponge elastic layer 52 formed by foaming silicone rubber or the like, and the outer layer is similar to the fixing roller 60. A releasable layer 53 such as a fluororesin is formed. Further, in the case of an image forming apparatus using a high-speed machine or color toner, in order to sufficiently satisfy the toner fixing property, as shown in FIG. By providing the elastic layer 64 of the degree, the toner is wrapped around the soft fixing roller surface, thereby improving the efficiency of heat transfer to the recording material and the toner.

  However, while reduction of power consumption is strongly desired as one of the environmental problems in recent years, high-quality and high-speed image output is desired from market needs. Therefore, in order to meet such demands for reduction of power consumption and high speed and high image quality, various improvements have been attempted on the heat roller type heat fixing apparatus.

  One is to arrange the heating body 62 on the outer surface of the fixing roller 60 or the pressure roller 50 as shown in FIG. 11 for the purpose of shortening the heating time of the fixing roller 60 and reducing the power consumption, and only the outer surface. JP-A-10-301417, JP-A-11-073050, and the like have proposed an example of a heat-fixing device with low power consumption and high thermal efficiency by heating the toner. The heating element 62 arranged on the outer surface of the fixing roller 60 is roughly classified into a contact state with respect to the fixing roller 60 and a non-contact state, but the contact type is more heated. High propagation efficiency. The heating element 62 is of a type in which a halogen lamp 66 is provided in the hollow core metal 65, or an inner surface of the hollow core metal 65 as shown in FIG. 9 with an insulating layer 67 such as an organic resin such as polyimide or glass. There is also a heat roller type provided with a heating resistance layer 68.

  On the other hand, in particular, a method for suppressing power consumption as much as possible without supplying power to the heat-fixing device during standby, specifically, a toner on a recording material through a thin film having a small heat capacity between the heater unit and the pressure roller. An example of a heat fixing method by a film heating method for fixing an image is proposed in Japanese Patent Laid-Open No. 63-313182, Japanese Patent Laid-Open No. 2-157878, Japanese Patent Laid-Open No. 4-44075, Japanese Patent Laid-Open No. 4-204980, etc. Yes. FIG. 8 shows a schematic configuration of an example of the film heating method. That is, in FIG. 7, a heater 71 in which a heating resistance layer is formed on a ceramic plate such as alumina or aluminum nitride is fixed to a stay holder (support) 72, and a heat-resistant thin wall such as polyimide that is in close contact with the heater 71. A film (hereinafter, referred to as a fixing film) 73 and a pressure roller 50 that is in pressure contact with the film interposed therebetween. The fixing film 73 is conveyed and moved in the direction of the arrow by the rotational force of the pressure roller 50 while closely contacting and sliding on the surface of the heater 71 at the fixing nip portion. The temperature of the heater 71 is detected by a temperature detection means 74 installed on the back surface of the heater and fed back to an energization control unit (not shown), and is heated and adjusted so that the heater temperature becomes a constant temperature (fixing temperature). Various image forming apparatuses such as printers and copiers that use such a film heating type fixing device eliminate the need for preheating during standby and shorten the wait time due to high heating efficiency and rapid start-up. There are many advantages over the conventional method of heat fixing using a heat roller or the like.

  However, even with the above-described conventional heat fixing device, it is very difficult to achieve both excellent performance in all of the shortening of the temperature rising time at the time of startup, the reduction of power consumption, and the high speed and high image quality. For example, when considering a film heating method, the shortening of the rise time and the reduction of the power consumption are very excellent, but there are the following problems when the speed is increased. First, since an organic heat resistant resin such as polyimide is used for the fixing film, the thermal conductivity is poor, and it is impossible to supply a sufficient amount of heat to the recording material when the speed is increased. That is, even if as much heat as possible is generated by the heater without causing any practical problems, the heat is insulated by the thin film and cannot be efficiently transferred onto the recording material and toner.

  In addition, image deterioration is a problem that appears prominently when speeding up. Even if the unfixed toner image formed on the recording material has high image quality, the image is often deteriorated by the heat fixing device. In particular, in the above-described film heating method, since the fixing film is driven and rotated by the rotational drive of the pressure roller, there is a problem that the speed of the film is delayed with respect to the rotational speed of the pressure roller as the speed increases. It leads to deterioration. In addition, when heat-fixing a recording material with rough surface irregularities, the surface of the toner image is not smooth because the metal tube has a hard surface and the contact with the concave portions of the paper is poor and sufficient heat cannot be transmitted to the recording material. To do. Such a problem also occurs in a heat roller type heat fixing device, and does not have an elastic layer on the surface as shown in FIG. 10 (a), only a release layer is provided on a metal core. In the fixing roller (hard roller), image roughness becomes more noticeable as the speed increases.

  In view of the above problems, it is essential to have an elastic layer as a fixing roller in order to cope with high speed. Based on this condition, if a heat fixing device that can cope with high speed is selected, the heat roller type heat fixing device with a conventional elastic layer has an overwhelmingly long heating time of the fixing roller, and power is supplied even during standby. Power consumption increases, which is a disadvantageous configuration for environmental and market needs.

Further, in the method of heating the surface of the fixing roller from the outside as shown in FIG. 11, the heating time is shortened and the power saving is improved as compared with the conventional heat roller method. Compared to performance. One reason for this is that when the heating member for heating the surface of the fixing roller (hereinafter referred to as a heat roller) has a halogen heater or the like in a hollow metal core as shown in FIG. 11, the metal core is a halogen heater. Since the temperature is raised by the radiant heat, it takes time to heat the heat roller itself. Further, as shown in FIG. 9, the heat roller having the heat generating resistance layer 68 on the inner surface of the metal pipe 65 via the insulating layer 67 rises faster than the type in which the temperature is raised by the halogen heater. With this heating member, heat can be supplied to the fixing roller only at the nip portion formed by pressure contact between the heat roller 62 and the fixing roller 60, and the portions other than the portion in contact with the nip are heated to the outside air. The heat supply becomes inefficient. If the heat fixing process speed is slow, the heat on the surface of the fixing roller taken away by the passage of the recording material can be compensated by the heat supply from the heat roller, but the heat supply from the heat roller as the speed increases. It is thought that it will not be in time alone. Therefore, it is considered that there is a limit to the speed increase in the system in which the fixing roller is externally heated with a roller-shaped heater. Further, the pressure roller 50 shown in FIG. 10 also accumulates heat via the fixing roller 60, which causes a rise in the rising temperature rise time.
JP-A-10-301417 Japanese Patent Laid-Open No. 11-73050 JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980 JP 2002-236426 A

  As explained in the prior art, a heat fixing device capable of outputting images with high speed and high image quality while maintaining low power consumption and shortening the heating time has a configuration as proposed in the past. Impossible.

  In order to solve the above problems, the applicants have filed an invention characterized by the following (see Patent Document 7).

  A fixing roller having an elastic layer; a heating member that contacts the fixing roller from an outer surface to form a heating nip portion; and a pressure member that presses the fixing roller to form a fixing nip portion. The recording material on which the unfixed toner image is formed is conveyed by nipping and heating fixing. The heater provided in the heating member has a plate shape with a low heat capacity, and generates heat by sliding on the heating nip portion. The pressure member includes a thin film having a low heat capacity and a stay holder for externally fitting the thin film.

  In the above application, there is no problem when printing a so-called large size close to the heating width of the heater, but when printing an envelope or narrow paper (small size), the temperature rises at a non-sheet passing portion where the paper does not pass. Is a problem. In particular, this type of fuser has an on-demand property that immediately rises to the fixing temperature without preheating, so it has a small heat capacity and heat insulation, so excess heat from the non-sheet-passing part flows to the sheet-passing part. Hateful. For this reason, if large size paper is printed after flowing a large amount of small size paper, hot offset image defects may occur in the small size non-sheet passing area, or the non-sheet passing area of the fixing roller will thermally expand and print. Later, when the image was cooled, the image was wrinkled, and fixing the large size paper caused a problem that image defects occurred due to the fixing roller wrinkles.

  Therefore, in the present invention, a fixing device is provided in which even when a large amount of narrow paper (so-called small size paper) such as an envelope is printed, image defect due to hot offset of a non-sheet passing portion or fixing roller wrinkle does not occur. With the goal.

  In order to solve the above problems, the invention according to the present application is characterized by the following.

  A fixing roller having an elastic layer; a heating member that contacts the fixing roller from the outer surface to form a heating nip portion; and a pressure member that presses the fixing roller to form a fixing nip portion. In the heat fixing apparatus for performing heat fixing by sandwiching and transporting a recording material on which an unfixed toner image is formed, the heater provided in the heating member has a plate shape with a low heat capacity, and the paper to be fixed on the heater is fixed. A plurality of heating elements having different lengths depending on the width of the heating element.

  The heating member provided in the heating member has a plate shape with a low heat capacity, and the heating heater has a heating element divided into a plurality of portions according to the width of the paper to be fixed.

  This prevents the on-demand performance of this fuser from being lost and prevents non-sheet-passing temperature rise when fixing narrow paper, and prevents flaws caused by hot offset and fixing roller wrinkles, resulting in good fixing. Sex can be obtained.

  As described above, according to the present invention, a plurality of heater heating elements are provided or divided into a plurality of heaters so that a heating element having an appropriate width according to the paper width can be used. Since the temperature could be suppressed, the occurrence of hot offset did not occur and good fixability could be obtained.

(First embodiment)
Examples according to the present invention are shown below. FIG. 1 is a block diagram of an image forming apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes a photosensitive drum, in which a photosensitive material such as OPC, amorphous Se, or amorphous Si is formed on a cylindrical substrate such as aluminum or nickel. The photosensitive drum 1 is rotationally driven in the direction of the arrow, and first, the surface thereof is uniformly charged by a charging roller 2 as a charging device. Next, scanning exposure is performed by the laser beam 3 which is ON / OFF controlled according to the image information, and an electrostatic latent image is formed. This electrostatic latent image is developed and visualized by the developing device 4. As a development method, a jumping development method, a two-component development method, a FEED development method, or the like is used, and image exposure and reversal development are often used in combination.

  The visualized toner image is transferred from the photosensitive drum 1 onto the recording material P conveyed at a predetermined timing by a transfer roller 5 as a transfer device. Here, the leading edge of the recording material is detected by eight sensors so that the image forming position of the toner image on the photosensitive drum 1 matches the writing position of the leading edge of the recording material, and the timing is adjusted. The recording material P conveyed at a predetermined timing is nipped and conveyed between the photosensitive drum 1 and the transfer roller 5 with a constant pressure. The recording material P to which the toner image has been transferred is conveyed to the fixing device 6 and fixed as a permanent image. On the other hand, residual toner remaining on the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the cleaning device 7.

  FIG. 2 shows the configuration of the heat fixing device 6 according to the present invention. In FIG. 2, the fixing roller 10 is composed of the following members. An elastic layer (solid rubber layer) formed of silicone rubber on the outer side of the aluminum or iron core 11, or an elastic layer (sponge rubber layer) formed by foaming silicone rubber in order to have a more heat insulating effect, Alternatively, it is composed of an elastic layer (bubble rubber layer) 12 in which bubbles are dispersed in the silicone rubber layer by some method to enhance the heat insulating action. However, if the heat capacity of the fixing roller 10 is large and the thermal conductivity is as large as possible, the heat received from the outer surface is easily absorbed, and the surface temperature is unlikely to rise. A material having as low a heat capacity as possible, a low thermal conductivity, and a high heat insulating effect is advantageous for the rise time of the fixing roller surface temperature. Here, the silicone rubber solid rubber has a thermal conductivity of 0.25 to 0.29 W / m · K, and the sponge rubber and bubble rubber have 0.11 to 0.16 W / m · K. Half the value. The specific gravity related to the heat capacity is about 1.05 to 1.30 for solid rubber and about 0.75 to 0.85 for sponge rubber / bubble rubber. Therefore, a preferable form of the elastic layer is preferably a sponge rubber layer or a bubble rubber layer having a thermal conductivity of about 0.15 W / m · K or less and a specific gravity of 0.85 or less and a high heat insulating effect. The smaller the outer diameter of the fixing roller 10, the smaller the heat capacity. However, if the fixing roller 10 is too small, the heating nip is difficult to earn, so an appropriate diameter is required. Regarding the wall thickness of the elastic layer, if it is too thin, heat will escape to the metal core, so an appropriate thickness is required. In consideration of the above, in this embodiment, in order to form an appropriate heating nip and to suppress the heat capacity, an elastic layer is formed using a foam rubber having a wall thickness of 4 mm, and a fixing roller having an outer diameter of φ20 mm is used. did. Further, the cored bar 11 may be a hollow cored bar as described in the conventional example of FIG. A fluororesin release layer 13 such as perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene resin (FEP) or the like is formed on the elastic layer described above. The release layer 13 may be either a tube coated or a surface coated with a paint.

The heating member 20 is composed of the following members. 21 is a heater for heating the surface of the fixing roller 10. Heating heater 21 is screen-printed with a conductive heating resistance layer such as Ag / Pd (silver palladium), RuO ₂ or Ta ₂ N along the longitudinal direction on the surface of a highly insulating ceramic substrate such as alumina or aluminum nitride. Is a member for current heating formed by coating in a linear or thin strip shape having a thickness of about 10 μm and a width of about 1 to 5 mm. In this embodiment, a heat generation pattern of Ag / Pd (silver palladium) is screen printed on an alumina substrate.

  A protective sliding layer is preferably provided on the surface of the heater 21 so that the release layer of the fixing roller 10 is not worn by rubbing. Examples include perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene resin (FEP), ethylenetetrafluoroethylene resin (ETFE), polychlorotrifluoroethylene resin ( CTEF), polyvinylidene fluoride (PVDF) and other fluororesin layers, either alone or mixed, or a dry film lubricant or glass coat made of graphite, diamond-like carbon (DLC), molybdenum disulfide, etc. A protective layer such as Reference numeral 22 denotes a heat insulating stay holder for holding the heater 21 for heating. The fixing roller 10 is pressurized by a pressing means (not shown), and a heating nip N is formed between the heater 21 and the fixing roller 10 by the applied pressure. The heat insulating stay holder 22 has a role of preventing heat radiation in the direction opposite to the heating nip N, and is formed of liquid crystal polymer, phenol resin, PPS, PEEK, or the like.

  A temperature detection element 23 such as a thermistor for detecting the temperature of the fixing roller 10 is disposed in contact with the fixing roller 10 and downstream of the heater 22 and upstream of the fixing nip M. By appropriately controlling the duty ratio, wave number, etc. of the voltage applied to the energization heating resistor layer from the electrode portion (not shown) at the longitudinal end of the heater 21 in accordance with the signal of the temperature detection element 23, The heater 21 generates heat, and the surface of the fixing roller 10 is heated and temperature-controlled. The thermistor is appropriately pressed by a heat resistant elastic material ceramic paper, a leaf spring or the like, and is contacted and pressed to the fixing roller 10. DC energization from the temperature detecting element 23 to a temperature control unit (not shown) is achieved by a connector (not shown) via a DC energization unit and a DC electrode unit (not shown).

  The pressure member 30 has the following configuration. Reference numeral 33 denotes a sliding film, which is a resin film based on heat-resistant and thermoplastic polyimide, polyamideimide, PEEK, PES, PPS, PFA, PTFE, FEP and the like. The film thickness is in a suitable range of 20 μm or more and less than 150 μm in consideration of strength and the like. Further, in order to prevent the offset toner adhering to the fixing roller 10 from accumulating, the surface layer is mixed or singly coated with a heat-resistant resin having good releasability such as PFA, PTFE, FEP, and silicone resin. Reference numeral 31 denotes a sliding plate provided inside the sliding film, and reference numeral 32 denotes a heat insulating stay holder that holds the sliding plate 31. The heat insulating stay holder 32 is pressed against the fixing roller by a pressing means (not shown) to form a nip M necessary for fixing between the sliding plate 31 and the fixing roller 10 via the sliding film 33. Yes. The heat insulating stay holder 32 is formed of liquid crystal polymer, phenol resin, PPS, PEEK, or the like as a resin having heat insulating properties and heat resistance, like the stay holder 22 of the heating member. The sliding plate 31 is formed of the same liquid crystal polymer, phenolic resin, PPS, PEEK, etc. as the stay holder 32 as a material having low friction with the sliding film 33 and heat insulation. It is desirable to coat the sliding layer to reduce The example is the same as the sliding layer provided on the surface of the heater 21 and will not be described. Here, the sliding plate 31 and the heat insulating stay holder 32 are handled as separate members, but they may be formed by integral molding, and the sliding layer may be coated on the sliding portion, thereby further reducing the cost. Is possible. Further, a small amount of lubricant such as grease is interposed between the sliding film 33 and the sliding plate 31 in order to keep the frictional resistance small.

  In such a configuration, the fixing roller 10 is rotationally driven in the direction of the arrow by a rotational drive (not shown) from the end in the longitudinal direction through the cored bar 11. As a result, the sliding film 33 is driven to rotate on the outside of the stay holder 32 in the direction of the arrow in the figure. The above is the configuration of the heat fixing apparatus of the present embodiment. The recording material P is appropriately supplied by a supply unit (not shown) and is formed by the fixing roller 10 and the pressure member 30 along the heat-resistant fixing inlet guide 15. It is conveyed into the fixing nip M. Thereafter, the recording material P discharged from the fixing nip is guided by a heat-resistant fixing paper discharge guide 16 and is nipped and conveyed by a paper discharge roller 17 and a paper discharge roller 18 to be discharged onto a discharge tray (not shown).

  FIG. 3 shows a diagram of a heater according to the present invention. Reference numeral 22 denotes an alumina substrate having a thickness of about 1 mm, on which heating elements (resistors) indicated by 35 and 36 are formed. The heating element 35 is 222 mm, which is slightly wider than the LTR width, so that the LTR size (width of about 216 mm), which is the maximum width in this apparatus, can be fixed. The heating element 36 is a heating element for handling narrow paper such as envelopes, and is 120mm wider than the commonly used COM10 envelope width (width of about 105mm) and DL envelope width (width of about 114mm). It is as. Although not shown in the figure, electrodes made of a power feeding conductor are formed from both ends of the heating element, and power controlled by a power source is applied.

  In this apparatus, a sensor for detecting the paper width is provided at a position 8 in FIG. This is because a sensor is provided at a position 122 mm from the paper passing reference position (center). When this paper crosses the paper, it is recognized as a wide paper and the heating element 35 is energized and fixed. Is not crossed, the paper is recognized as being narrow and the heating element 36 is energized.

  Further, the apparatus of this embodiment can process 25 sheets per minute at a process speed of 150 mm / sec. The resistance value of the heating element 35 of the heater is 12.5Ω, and the power when operated at a voltage of 100 V is 800 W. This is a fully energized state, and the duty is set to 0, 2.5, 5, 7.5, 10, ..., 95, 97.5, 100% every 2.5% by known wave number control or phase control. By controlling, the energization power to the heater is controlled. In this embodiment, the surface temperature of the fixing roller for fixing is 200 ° C. Start up the fixing device from room temperature to reach 200 ℃. When starting up the fixing device, there is no paper in the fixing device, and the heating element 35 is energized to uniformly warm the entire length of the fixing device.

  It took about 8 seconds for the thermistor temperature to reach 200 ° C. In the fixing device of the present invention, the fixing operation can be started about 8 seconds after the fixing device is started up, and the paper is actually fed at such a timing that the paper enters the fixing nip at this moment.

The paper width is detected by the paper width sensor at the position 8 in FIG. 1. When the paper is wide, the heating element 35 is continuously energized. When the paper is narrow, the heating element is switched to 36. To fix. Incidentally, since the heating element 36 is short in length, it is set to 23.1Ω (12.5 × 222 ÷ 120) in order to align the heat generation amount per unit length with 35.
A paper passing test was performed using the above apparatus.

(1) Alternate feeding of envelope and LTR paper
Print COM10 envelopes and LTR size plain paper one after another alternately. Printed at a speed of 25 sheets per envelope and LTR. The COM10 envelope was a Mail-Well COM10 # 582 envelope, and the LTR paper was Xerox 4024 paper (LTR 75 g / m ² ). Paper passing experiments were conducted with the apparatus of the present invention and the conventional apparatus, respectively, and the results are shown in Table 1.

表の通り本実施例の装置では交互連続プリントを実施しても特に問題は発生しなかった。これは前述の通り、封筒を定着するときは短い発熱体35を使用するため封筒の非通紙部分では発熱しないため、非通紙部分が異常に昇温することがないからである。

As shown in the table, in the apparatus of this example, no problem occurred even when alternating continuous printing was performed. This is because, as described above, when the envelope is fixed, a short heating element 35 is used, so that heat is not generated in the non-sheet passing portion of the envelope, and the non-sheet passing portion does not rise abnormally.

  On the other hand, in the comparative conventional example, hot offset has occurred on both sides of the LTR paper from around the 22nd sheet. This is shown in FIG. In the conventional example, since the heating element 35 in the entire longitudinal direction is used for fixing the COM10, the temperature of the non-sheet passing portion on both sides of the heater is raised at the time of fixing the envelope, and the LTR paper is fixed at 37 in FIG. As a result, a hot offset occurs at the position.

(2) Envelope continuous paper passing A comparative experiment was conducted by passing the paper with the present invention and the conventional device in a mode in which LTR size paper was fixed immediately after fixing several tens of envelopes. The paper type used is the same as (1). The results are shown in Table 2.

表のようにCOM10封筒の枚数が多いほど、従来例では次のLTRサイズ紙のホットオフセット発生枚数が多くなっている。発生したホットオフセットは、図４に示したものと同様である。

As shown in the table, the larger the number of COM10 envelopes, the greater the number of hot offset occurrences of the next LTR size paper in the conventional example. The generated hot offset is the same as that shown in FIG.

  Thus, the effect of the present invention was shown. In order to investigate the reason, the result of measuring the fixing roller temperature immediately after the heater using a non-contact thermometer is shown in the graph of FIG. This graph shows the 10th temperature when 10 COM10 envelopes are printed continuously. In the present invention, since the short heating element 36 is energized, the temperature is not increased outside the envelope sheet passing region, but in the comparative conventional example, the temperature is increased outside the envelope sheet passing region and reached 250 ° C. In both cases, the temperature inside the envelope sheet feeding area was controlled to 200 ° C.

  As described above, it was shown that by providing the heating elements of the heaters for each paper size, it is possible to suppress the temperature rise of the non-sheet passing portion by using the heating elements having appropriate lengths.

  In this example, the length of the heating element was optimized for envelopes where the temperature rise at the non-sheet passing part was severe, but this is not limited to this, and it is optimized for other narrow paper sizes such as A5 and Executive size. It is also possible to provide a heated element. Further, the number of heating elements is not limited to two, and a plurality of heating elements can be provided according to the required paper width.

  Furthermore, in the present embodiment, the description has been given with the apparatus in which the reference position of each paper size is the center. However, for example, when the reference position is at one end, the present invention is provided by providing a heating element at a position corresponding to the reference position. Is valid.

  Furthermore, according to the present invention, it is possible to heat only the necessary width corresponding to the paper width to be fixed. Therefore, not only hot offset is prevented, but also when fixing narrow paper, power is saved by not heating unnecessary portions. We were able to plan. In this embodiment, since the heat generation amount per unit length is aligned, the power consumption is roughly determined by the ratio of the length of the heating element. When the heating element 36 is used for fixing a narrow paper, it is about 0.6 times (120 / 222) has the effect of reducing power.

  It is also possible to energize a long heating element 35 as appropriate in order to avoid the non-sheet passing portion of the fixing roller from being cooled due to a large number of envelopes being fixed. If the temperature difference of the fixing roller is excessively large in the longitudinal direction, there is a concern that roller wrinkles may occur due to the difference in thermal expansion of the fixing roller. Therefore, it is effective to select an energization heating element as appropriate.

(Second embodiment)
This embodiment is characterized in that the heating element of the heater is divided in the longitudinal direction. FIG. 6 shows a heating element arrangement of the heater of this embodiment. The heating elements 37, 38 and 39 are arranged in a straight line, and a gap of 0.5 mm is provided between them. When fixing a wide range of paper such as LTR, all the heating elements 37, 38 and 39 are energized. When fixing the COM10 envelope, only the heating element 38 is energized. The combined length of the heating elements 37, 38 and 39 is 222 mm, and the length of the heating element 38 is 120 mm, which is the same as in the first embodiment.

  Also in this example, when the same experiment as described in (1) and (2) of Example 1 was performed, the same effect could be confirmed. Although the arrangement of the heating elements is different, the heat generation distribution in the longitudinal direction is exactly the same as in Example 1, so the same effect was obtained.

  As a feature of the present embodiment, since the heating elements are arranged in a straight line, the number of divisions of the heating elements can be increased according to the paper size without increasing the substrate width of the heater. In the second embodiment, the COM10 envelope and the LTR size have been described. However, the number of heating element divisions can be increased according to the size of A5, Executive, and the like.

  In addition, a gap of about 0.5 mm is generated between the divided heating elements as in this embodiment, and when this heater is used in the film type fixing device described in the prior art, the fixability of the gap portion is deteriorated. In some cases, in this configuration, the heater transmits heat to the fixing roller, and until the fixing roller rotates and fixes the paper, heat is also transferred to the portion corresponding to the gap between the heating elements on the fixing roller. Uniform fixability could be obtained.

(Third embodiment)
This embodiment is characterized in that the heating element of the heater is divided in the longitudinal direction. FIG. 7 shows a heating element arrangement diagram of the heater of this embodiment. The heating element 40 has a length of 222 mm corresponding to the maximum sheet passing width LTR size, and is provided with conductor electrodes 41 and 42 in the middle. The distance between the electrodes 41 and 42 is 120 mm. In this configuration, when fixing a wide paper such as LTR size, the entire heating element is energized, and when fixing a narrow paper such as a COM10 envelope, the current is applied between the electrodes 41 and.

  With this configuration, the heat generation distribution in the longitudinal direction similar to that in Example 1 can be obtained also in this example. Therefore, when the same test as (1) and (2) described in Example 1 was performed, the same effect was obtained. Could get.

  When the heater having the heating element of the present embodiment is used in the film type fixing device described in the conventional example, when the entire longitudinal area is energized to fix a wide range of paper, the current is applied to the portions of the conductive electrodes 41 and 42. There was a concern that the amount of heat generated via the heat transfer decreased and the fixing property was partially deteriorated. In the case of the fixing device of this configuration, heat is transmitted on the fixing roller, so that the fixing property on paper is uniform.

  Also in this embodiment, the number of divisions is not limited to this, and can be provided according to the number of types of required paper width.

1 is a schematic view of an image forming apparatus according to the present invention. 1 is a schematic view of a fixing device according to the present invention. The figure of the relationship between the heat generating body and paper width by this invention. The figure of the hot offset by a comparative prior art example. The graph of the temperature distribution of the fixing roller at the time of envelope fixing. The figure of the relationship between the heat generating body and paper width by this invention. The figure of the relationship between the heat generating body and paper width by this invention. Schematic of a fixing device according to a conventional example. Schematic of a fixing roller according to a conventional example. Schematic of a fixing device according to a conventional example. Schematic of a fixing device according to a conventional example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Image exposure 4 Developing device 5 Transfer roller 6 Fixing device

Claims (4)

  A fixing roller having an elastic layer; a fixedly arranged heating member that contacts the fixing roller from the outer surface to form a heating nip portion; and a pressure member that presses the fixing roller to form a fixing nip portion; In a heat fixing apparatus that performs heat fixing by sandwiching and transporting a recording material on which an unfixed toner image is formed in a fixing nip portion, the heater provided in the heating member has a plate shape with a low heat capacity and a different length. A heat fixing device comprising a plurality of heating elements.   The fixing device according to claim 1, wherein the heating element corresponds to a paper passing area to be fixed.   A fixing roller having an elastic layer; a fixedly arranged heating member that contacts the fixing roller from the outer surface to form a heating nip portion; and a pressure member that presses the fixing roller to form a fixing nip portion; In a heat fixing apparatus that performs heat fixing by sandwiching and transporting a recording material on which an unfixed toner image is formed in a fixing nip portion, the heater provided in the heating member has a plate shape with a low heat capacity and a plurality of heaters in the longitudinal direction. A heat-fixing device having a heating element divided into two.   4. The fixing device according to claim 3, wherein the heating element corresponds to a paper passing area to be fixed.

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