JP2008299314A - Image heating apparatus and rotatable heating member used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image heating apparatus including a rotatable heating member 30 for heating an image T on a recording material P in a nip portion Nt, and a heating unit 21 for heating the heating member 30 from the outside thereof, in which a warm-up time period or a first print-out time period can be reduced, low power consumption can be accomplished and further, satisfactory image quality can be achieved with no heating (fixing) irregularity. <P>SOLUTION: The heating member has a low thermal conductive elastic layer 32, and a heat storage layer 33 outside the low thermal conductive elastic layer 32 to have a volume heat capacity larger than that of the low thermal conductive elastic layer. A heat capacity of the heat storage layer 33 per unit surface area of a fixing member is in the range of 100 J/m2K to 600 J/m2K. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image heating apparatus suitable for use as a heat fixing apparatus mounted on an image forming apparatus such as a printer or a copying machine using electrophotographic technology or electrostatic recording technology.

  The present invention also relates to a rotatable heating member incorporated in the image heating apparatus.

  Examples of the image heating device include a fixing device that fixes an unfixed image on a recording material, and a gloss increasing device that increases the glossiness of an image by heating the image fixed on the recording material.

  2. Description of the Related Art Conventionally, in an image forming apparatus, a contact heating type apparatus is widely used as an apparatus for heating and fixing an unfixed toner image formed and supported on a recording material on the recording material. In this contact heating type fixing device, a rotatable heating member (hereinafter referred to as a fixing roller) heated to a predetermined temperature is brought into contact with a recording material at a nip portion, and unfixed toner on the recording material. The image is heat-fixed as a fixed image.

  As the heating method of the fixing roller, there are an internal heating method and an external heating method (surface heating method). In the internal heating method, a heating means (heating source: heater) is disposed inside the fixing roller, and the fixing roller is heated from the inside to heat the surface of the fixing roller to a predetermined fixing temperature. In the external heating method, a heating unit is provided outside the fixing roller, and the fixing roller is heated from the outside to heat the surface of the fixing roller to a predetermined fixing temperature.

  The external heating system heats the fixing roller from the outside by a low heat capacity heating means such as a ceramic heater or a small-diameter heating roller with a built-in halogen heater. It is. Therefore, the warm-up time is shortened as compared with the internal heating type apparatus.

  Patent Document 1 describes a configuration of an external heating fixing roller (heat roller) that can shorten the time required to reach a fixable temperature. That is, a cored bar, an elastic heat insulating layer made of silicone rubber formed on the outer periphery thereof, a heat conductive layer made of metal material formed on the outer periphery thereof and having a thickness of 5 to 100 μm, and a thickness formed on the outer periphery thereof. It is a roller having a surface layer (toner release type layer) of 5 to 30 μm fluororesin.

  Since the fixing roller has elasticity, it is possible to form a high-quality image without fixing unevenness. Further, since the surface of the fixing roller is heated, the surface of the fixing roller can be rapidly heated even if an elastic layer is provided below the surface of the fixing roller.

  Further, Patent Documents 2 and 3 propose a configuration in which a high thermal conductive silicone rubber layer is interposed between the heat insulating elastic layer and the release layer.

  By increasing the thermal conductivity in the vicinity of the fixing roller surface layer, heat from the external heating means can be easily transmitted, the temperature rise of the fixing roller surface can be accelerated, and the warm-up time can be shortened.

  In Patent Document 2, a fixing member and a pressing member pressed against the fixing member are provided, and the recording material is heated at the pressing nip portion. A heat insulating elastic layer and a high thermal conductive silicone are provided on both the fixing member and the pressing member. A rubber layer and a release layer with high thermal conductivity are provided. Then, a heat roller is brought into contact with each other as an external heating means, and a surface (hereinafter, this surface is referred to as a paper front side and the back side as a paper back side) carrying unfixed toner on the recording material, The structure which heats from both sides is proposed.

This proposal also specifies the thermal conductivity of a solid rubber layer and a heat-insulating elastic layer with high thermal conductivity for shortening the warm-up time, and it is disclosed that the warm-up time can be reduced to 60 seconds or less. Yes.
JP-A-6-75491 JP 2002-123117 A JP 2004-317788 A JP 2004-101865 A

  However, in an external heating method that does not have a heating means inside, particularly an external heating method that has a heating means only in the fixing roller, the warm-up time is shortened, and the heat capacity of the fixing roller and the pressure member is reduced. The following problem arises.

  That is, in the fixing roller having no heat source inside, the temperature of the surface of the fixing roller is lowered when the heat is transmitted in contact with the recording material. Therefore, a sufficient amount of heat cannot be applied to the recording material unless the surface temperature of the fixing roller is heated to a considerably high temperature by the heating means.

  The usable temperature on the surface of the fixing roller is limited to a predetermined temperature or less in consideration of heat resistance of the fixing roller, the temperature detecting element, the safety element, and the like. For example, even when silicone rubber having high heat resistance is used for the elastic layer of the fixing roller, the rubber may deteriorate and be destroyed when continuously used at a high temperature of 230 ° C. or higher. It is necessary for the fixing roller to secure a sufficient amount of heat necessary for heat fixing at the fixing nip portion below this temperature.

  Even if a high heat conduction layer is provided near the surface of the fixing roller and the temperature near the surface of the fixing roller can be increased efficiently by the heating means, it is safe and stable if the temperature of the surface of the fixing roller necessary for heat fixing is too high. Can not be used.

  For this reason, the fixing roller not only has internal heat insulation and high thermal conductivity in the vicinity of the surface, but if the heat capacity in the vicinity of the surface is not appropriate, the amount of heat necessary to heat and fix the toner on the recording material. Cannot be stored.

  In proposals related to conventional external heating type fixing devices, no proposal has been made for an appropriate heat capacity near the surface of the fixing roller.

  Further, a proposal relating to a conventional external heating type fixing device relates to a heating device having a warm-up time of about 60 seconds. Currently, there is a demand for an image heating apparatus that does not consume power during standby and that has a sufficiently short time from when a print signal is received until the recording material on which an unfixed toner image is formed is heated and fixed. . This time is generally 20 seconds or less.

  Although the fixing roller has a layer with low thermal conductivity and is heated from the surface, the assumed warm-up time is actually long enough to be transmitted not only near the surface but also to the inside. . It was not considered to heat and fix with the amount of heat stored only in the vicinity of the surface of the fixing roller with a short warm-up time of 20 seconds or less.

  As described above, the conventional external heating type heat fixing device does not consume power during standby, and sufficiently reduces the time from receiving a print signal to fixing the recording material on which an unfixed toner image is formed. However, an apparatus that achieves sufficient fixing performance for the recording material has not been realized.

  In the above, the time from when the print signal is received to when the recording material on which the unfixed toner image is formed is heated and fixed is hereinafter referred to as a first printout time.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an image heating apparatus capable of shortening the first printout time and a heating member used in the apparatus.

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

In order to achieve the above object, a typical configuration of the image heating apparatus according to the present invention includes an elastic layer having heat insulation properties and a heat storage layer that is provided outside the elastic layer and includes at least one layer. A rotatable heating member whose surface is in contact with the toner image, a nip forming member that forms a nip portion that sandwiches and conveys the recording material together with the heating member, and a heater that heats the heating member from the outside. In the image heating apparatus for heating the toner image formed on the recording material, the heat capacity C / S per unit surface area of the heat storage layer is:
100 J / (m ² · K) ≦ C / S ≦ 600 J / (m ² · K)
It is characterized by satisfying.

In order to achieve the above object, a representative configuration of the heating member according to the present invention includes a rotatable heating member whose surface is in contact with a toner image on the recording material, and the conveyance of the recording material together with the heating member. A heating member used in an image heating apparatus having a nip forming member for forming a nip portion to be heated and a heater for heating the heating member from the outside, and provided with an elastic layer having heat insulation properties and an outer side than the elastic layer. And a heat capacity C / S per unit surface area of the heat storage layer is 100 J / (m ² · K) ≦ C / S ≦ 600 J / (m ² · K ).
It is characterized by satisfying.

  ADVANTAGE OF THE INVENTION According to this invention, the image heating apparatus which can shorten a first printout time, and the heating member used for this apparatus can be provided.

Example 1
(1) Example of Image Forming Apparatus FIG. 2 is a schematic cross-sectional view showing a schematic configuration of a laser beam printer (hereinafter abbreviated as a printer) 1 as an example that suitably illustrates the image forming apparatus of the present embodiment.

  Image information is input to the printer 1 from an image information providing device (not shown) such as a host computer provided outside the printer. The printer 1 performs a series of image forming processes in which an image corresponding to the input image information is formed and recorded on a sheet-like recording material (recording medium) P according to a known electrophotographic system.

  The printer 1 includes a process cartridge 4 that holds a drum-like rotatable electrophotographic photosensitive member (hereinafter abbreviated as a photosensitive member) 2 as a latent image carrier, a primary charging mechanism 8, and a developing device 3. I have. Further, a laser scanner unit (hereinafter abbreviated as “scanner”) 5 for forming an electrostatic latent image corresponding to the image information on the outer peripheral surface of the photoreceptor 2 by an exposure processing step corresponding to the image information input from the image information providing apparatus. It has. Further, a roll-shaped rotatable transfer body 6 that performs a process of transferring an image to the recording material P, and a fixing device 7 as an image heating apparatus that performs a fixing process on the recording material P that has undergone the image transfer process by heating and pressing. It has.

  The process cartridge 4 is detachably supported with respect to the printer body. The printer body is an image forming apparatus portion other than the process cartridge. When maintenance such as repair of the photosensitive member 2 and replenishment of developer to the developing device 3 is necessary, the cover 9 that is supported by the printer body so as to be opened and closed is opened, and then the entire process cartridge 4 is replaced. Speeding up and simplification.

  The primary charging mechanism 8 charges the outer peripheral surface of the rotating photoreceptor 2 to a specified potential distribution by applying a specified bias from a commercial power source or the like before the exposure processing step by the scanner 5. .

  The scanner 5 outputs a laser La that is modulated in accordance with a time-series electrical digital pixel signal of image information from the image information providing apparatus. The laser La scans and exposes the charged portion of the outer peripheral surface of the photoreceptor 2 through the window 4a provided in the process cartridge. As a result, an electrostatic latent image corresponding to the image information is formed on the outer peripheral surface of the photoreceptor 2.

  Next, a series of image forming processes in the printer 1 will be described. When the start button or the like (not shown) provided on the printer is pressed, the rotation of the photosensitive member 2 is started. The photoreceptor 2 is driven to rotate at a specified peripheral speed in the clockwise direction indicated by the arrow K1. At the same time, the outer peripheral surface of the photoreceptor 2 is charged to a specified potential distribution by the primary charging mechanism 8 to which a specified bias is applied.

  Next, according to the image information from the image information providing apparatus, the charged portion of the outer peripheral surface of the photoreceptor 2 is scanned and exposed by the scanner 5. Thereby, an electrostatic latent image corresponding to the image information is formed on the portion of the photoreceptor 2. The electrostatic latent image is developed by the developer of the developing device 3 to be visualized as a toner image (toner image).

  On the other hand, the recording material P is separated and fed from the paper feed cassette 11 by the paper feed roller 12 driven at a predetermined timing. A plurality of recording materials P are stacked and accommodated in the paper feed cassette 11. The paper feed cassette 11 is detachably supported by the printer. The recording material P fed from the paper feed cassette 11 is fed to a transfer nip portion formed between the photosensitive member 2 and the transfer member 6 by a registration roller pair 12a at a predetermined control timing, and the transfer nip portion. Is being nipped and conveyed. In this nipping and conveying process, the toner image on the photosensitive member 2 side is sequentially transferred to the recording material P side by the transfer member 6.

  The recording material P that has been subjected to the transfer process is subjected to a heat fixing process of the toner image by the fixing device 7, and then passes through the fixing paper discharge unit 10 that is rotatably supported by the paper discharge unit 13. Is ejected. The discharged recording material P is stacked on a tray 14 attached to the upper surface of the printer. As described above, a series of image forming processes is completed.

(2) Fixing device 7
FIG. 1 is a schematic cross-sectional view of a fixing device 7 which is an external heating type image heating device in this embodiment.

  Reference numeral 30 denotes a fixing roller (fixing rotator) as a rotatable heating member that is heated from the outside and heats the image on the recording material at the nip portion. Reference numeral 63 denotes a rotatable pressure roller as a pressure member.

  The fixing roller 30 and the pressure roller 63 are arranged substantially in parallel in the vertical direction and are pressed against each other by a pressure spring (not shown) at the end. Thus, a fixing nip portion (pressure nip portion) Nt having a predetermined width is formed between them in the recording material conveyance direction.

  The fixing roller 30 is rotationally driven by a driving means (not shown) in a clockwise direction indicated by an arrow at a predetermined peripheral speed. The pressure roller 63 rotates following the rotation of the fixing roller 30. Note that the fixing roller 30 and the pressure roller 63 may be separately rotated.

  Reference numeral 21 denotes a heating means (heating source) for heating the fixing roller 30 from the outside thereof. In this embodiment, the heating means 21 is a plate heater (hereinafter abbreviated as a heater). The heater 21 is fixedly held on the heater holder 24 and is arranged on the upper side of the fixing roller 30 in parallel with the axis of the fixing roller 30. The holder 24 is urged by a pressure mechanism (not shown) so that the heater 21 is pressed against the upper surface of the fixing roller 30 with a predetermined pressure. That is, the heater 21 is always in contact with the fixing roller 30 at the same portion, and forms a heating contact region Nh having a predetermined width in the rotational direction of the fixing roller 30 with the fixing roller 30.

  The length of the roller portions of the fixing roller 30 and the pressure roller 63 (in the direction perpendicular to the drawing) and the length of the effective heat generating portion of the heater 21 (the same) are larger than the maximum sheet passing width of the fixing device.

  The rotating fixing roller 30 is heated from the outside by the heater 21 in the heating contact area Nh, and gives a necessary and sufficient amount of heat to fix the unfixed toner image T on the recording material P at the fixing nip Nt. It is done.

  As described above, after the toner image T is formed in the image forming portion, the recording material P is sent to the fixing device 7 and introduced into the fixing nip portion Nt formed by the fixing roller 30 and the pressure roller 63. It is nipped and conveyed. The recording material P is heated by the fixing roller 30 and receives the nip pressure in the process of being nipped and conveyed through the fixing nip portion Nt. As a result, the unfixed toner image T is fixed by heat and pressure as a fixed image on the recording material P surface.

  The heating contact area Nh and the fixing nip Nt are formed at different positions on the circumference of the fixing roller 30. The shorter the distance between the heating contact area Nh and the fixing nip Nt around the fixing roller in the rotation direction of the fixing roller, the less heat is released into the air and the heat escapes into the fixing roller, and the heating contact area Nh Heat can be more efficiently conveyed from the toner to the fixing nip Nt.

  On the other hand, when the positions of the fixing nip portion Nt and the heating contact region portion Nh are shifted from each other by 180 ° by a half circumference of the fixing roller, as shown in FIG. The pressure applied to the fixing roller 30 cancels each other out. Therefore, the bending of the fixing roller 30 can be suppressed to a low level, and the strength required for the cored bar is reduced, so that there is an advantage that the diameter can be easily reduced and the heat capacity can be easily reduced.

  If the diameter of the fixing roller 30 is reduced, as a result, the distance between the heating contact area Nh and the fixing nip Nt can be shortened. Therefore, when there is no need for a large difference in the pressure applied to the fixing roller 30 between the heater 21 and the pressure roller 63, the fixing nip portion Nt and the heating contact region portion Nh should be arranged to face each other as shown in FIG. good.

(3) Fixing roller (rotatable heating member) 30
FIG. 3 is a schematic diagram of the fixing roller 30 in the present embodiment. The fixing roller 30 includes a cored bar 31, a first layer 32 formed on the outer periphery thereof, and a second layer 33 formed on the outer side thereof. The first layer 32 is an inner layer with respect to the second layer 33, and the second layer 33 is an outer layer with respect to the first layer 32.

  The first layer 32 is a low thermal conductive elastic layer, has lower thermal conductivity than the second layer 33, and has elasticity. Hereinafter, the first layer 32 is referred to as a heat insulating elastic layer.

The second layer 33 is a heat storage layer, and the heat capacity per unit surface area of the fixing roller 30 as a heating member is 100 J / (m ² · K) or more and 600 J / (m ² · K) or less. Hereinafter, the second layer 33 is referred to as a heat storage layer.

  The cored bar 31 is made of, for example, a metal material such as aluminum, iron, or SUM material, or another rigid material such as ceramic. Since the core 31 is thermally insulated from the surface of the fixing roller by the heat insulating elastic layer 32, even if it has a lower thermal conductivity and a lower heat capacity than the heat storage layer 33, its effect is less. Therefore, it may have higher thermal conductivity and higher heat capacity than the heat storage layer 33, and the form thereof may be solid or hollow and the form is not limited.

  As described above, the fixing roller (rotatable heating member) 30 includes the heat-insulating elastic layer 32 and the heat storage layer 33 that is provided outside the elastic layer and includes at least one layer. The heat conductivity of the heat insulating elastic layer 32 is preferably 0.20 W / (m · k) or less.

The heat storage layer 33 may, for example, a highly heat conductive silicone rubber, 100 J / per unit surface area of the total heat capacity fixing roller ^(m 2 · K) or more, are blended adjusted 600J / ^(m 2 · K) or less and so as.

  The heat capacity per unit surface area of the fixing roller is a value (C / S) obtained by dividing the heat capacity C of the heat storage layer 33 by the surface area S of the outer peripheral surface of the fixing roller. This is related to the amount of heat stored under the unit surface area of the fixing roller when the fixing roller surface temperature is kept at a predetermined temperature.

Further, “heat capacity C / S per unit surface area of the heat storage layer 33” and “time t when the fixing roller 30 contacts the recording material per rotation at the fixing nip Nt when the recording material P is passed through”. (That is, the time t required for one point of the surface of the fixing roller (heating member) to pass through the fixing nip portion).
C / S [J / (m ² · K)] ≦ 10000 [J / (s · m ² · K)] × t [s]
And

  When the time t when the recording material P and the fixing roller 30 are in contact is short, a large temperature difference is required between the fixing roller 30 and the recording material P in order to transmit heat to the recording material P in a short time. When the fixing roller temperature must be increased, the heat capacity of the heat storage layer 33 needs to be reduced.

  The characteristics required for this heat capacity will be described later based on experimental results.

It is desirable that the volume heat capacity of the heat storage layer 33 (volume heat capacity of the second layer) is larger than the volume heat capacity of the heat insulating elastic layer 32 (volume heat capacity of the first layer). Preferably, the volumetric heat capacity is larger than that of a general solid rubber, and it is desirable to set it to 1.25 × 10 ⁶ J / (m ³ · K) or more. By making the heat capacity of the heat storage layer 33 higher than that of the heat insulating elastic layer 32 inside, the heat stored in the fixing roller 30 is unevenly distributed in the heat storage layer 33 in the vicinity of the surface, and heat is transferred to the recording material P. Easy to do.

  The thermal conductivity of the heat storage layer 33 is preferably higher than that of the heat insulating elastic layer 32. Preferably, the thermal conductivity is higher than that of a general solid rubber, and is 0.3 W / (m · K) or more.

  By making the thermal conductivity of the internal heat insulating elastic layer 32 lower than the thermal conductivity of the heat storage layer 33, the heat transferred from the surface of the fixing roller is unevenly distributed on the heat storage layer 33 in the vicinity of the surface, thereby making it easy to maintain. Further, by making the thermal conductivity of the heat storage layer 33 higher than that of the heat insulating elastic layer 32, heat can be absorbed and released by the heat storage layer 33 quickly.

  The thermal conductivity, volumetric heat capacity, and heat capacity per unit surface area of the heat storage layer 33 are measured by the following methods.

  That is, as shown in FIG. 4, a test piece A having a length of 5 mm and a width of 5 mm is cut out from the heat storage layer 33 of the fixing roller 30.

  The mass density is obtained by measuring the test piece A with a dry automatic densimeter (model number AccuPyc1330, Shimadzu Corporation).

  The specific heat is obtained by measuring the test piece A with a differential scanning calorimeter (model number DSC8240, manufactured by Rigaku Corporation).

  The volumetric heat capacity and the heat capacity per unit surface area of the fixing roller are obtained from the following equations.

1) Volume heat capacity = mass density × specific heat capacity 2) Heat capacity per unit surface area of fixing roller = Volume of test piece A × volume heat capacity / surface area of test piece A
Or
= Volumetric heat capacity x Specific heat capacity x Heat storage layer thickness Thermal conductivity of specimen A is measured by Fourier transform type thermal thermal diffusivity measuring device (model number FTC-1, ULVAC-RIKO, Inc.). Measure. And the heat conductivity of the thickness direction of the thermal storage layer 33 is calculated | required from the following formula.

3) Thermal conductivity = thermal diffusivity × mass density × specific heat capacity The heat storage layer 33 is formed by the following method, for example. For example, a solid rubber layer in which a layer in which powdery filler is mixed in an amount of 10 mass% or more and 50 mass% or less in a rubber material such as silicone rubber or fluorine rubber is formed on the heat insulating elastic layer 32.

  By blending 10% by mass or more of the filler, the heat capacity can be increased as compared with a normal solid rubber. Further, when the filler to be blended is large, the heat storage layer 33 becomes hard and the surface of the fixing roller 30 becomes hard. If the blending amount is 50% by mass or less, the surface of the fixing roller 30 can have sufficient elasticity.

The powdery filler has a volumetric heat capacity of at least 1.25 × 10 ⁶ J / (m ³ · K) or more (filler with a high volumetric heat capacity), and a thermal conductivity of at least 10 [W / (m · K)] or more ( It is made of a filler material having a high thermal conductivity.

  Thus, by dispersing the filler having a high volumetric heat capacity, the volumetric heat capacity of the heat storage layer 33 can be increased while suppressing the blending amount. Moreover, by dispersing the filler having a high thermal conductivity, the thermal conductivity can be increased while suppressing the amount of blending.

  Examples thereof include metal oxides such as AlN, graphite, and alumina, metals such as carbon nanotubes, diamond, aluminum, titanium alloys, and copper alloys, and powdery fillers such as boron nitride, silicon nitride, and crystalline silica.

  Moreover, as long as it is a means for achieving a desired heat capacity and thermal conductivity, the type of filler material is not limited, and the shape of the filler may be any shape. It is not constrained to achieve.

  The thickness of the heat storage layer 33 (the thickness of the second layer) is preferably 30 μm or more and 400 μm or less. The heat storage layer 33 in which the filler is dispersed and the heat capacity is increased has elasticity but has high hardness. For this reason, if the heat storage layer 33 is too thick, the surface of the fixing roller becomes hard, and the adhesion to the recording material P is changed. Adhesiveness to the recording material P deteriorates, and it becomes difficult to perform uniform toner image fixing. Therefore, the heat storage layer 33 is desirably 400 μm or less. On the other hand, if the heat storage layer 33 is too thin, it is difficult to uniformly disperse the filler and to obtain a uniform heat capacity and heat conductivity, which may cause uneven fixing. Therefore, even if the heat storage layer 33 is thin, it is preferably 30 μm or more.

  The heat insulating elastic layer 32 is a rubber layer having a low thermal conductivity, and is blended and adjusted so that the thermal conductivity is smaller than that of the heat storage layer 33. As described above, the thermal conductivity of the heat insulating elastic layer 32 is preferably 0.20 W / (m · k) or less.

  The thermal conductivity and volumetric heat capacity of the heat insulating elastic layer 32 are measured by the following methods. As shown in FIG. 4, a test piece B having a thickness of 500 μm, a length of 5 mm, and a width of 5 mm is cut out from the heat insulating elastic layer 32 of the fixing roller 30. The thermal conductivity and volumetric heat capacity in the thickness direction are obtained by the same method as that for the test piece A of the heat storage layer 33.

  The thickness of the heat insulating elastic layer 32 formed on the outer periphery of the cored bar 31 is not particularly limited. However, in order to form the fixing roller 30 having a small diameter without having an effective heat insulating property and an excessive heat capacity. 0.0-5.0 mm, preferably 2.0-4.0 mm.

  Unlike the conventional internal heating type heat roller fixing device, the external heating type fixing device 7 in this embodiment does not have a built-in object such as a heating source inside the fixing roller, so that the outer diameter of the fixing roller 30 is reduced. Can do.

  If the direction in which the heater 21 serving as the heating means and the pressure roller 63 serving as the pressure member abut on the fixing roller 30 are horizontally opposed, and the pressures that contact each other are equal, the pressure on the fixing roller 30 is offset. Even if the diameter is reduced, there is no fear of bending due to insufficient strength.

  The fixing roller 30 preferably has a small diameter and a low heat capacity, and preferably has an outer diameter in the range of 10 to 20 mm.

  The heat insulating elastic layer 32 is formed by the following method, for example. It is formed by firing and curing after forming a blend in which a hollow filler is blended with an organopolysiloxane composition, or a blend in which a water-absorbing polymer and water are blended in an organopolysiloxane composition.

  For example, a silicone rubber composition, which is a silicone rubber composition obtained by blending 0.1 to 200% by mass of a hollow filler having an average particle size of 500 μm or less with 100 parts by weight of a thermosetting organopolysiloxane composition, is heated and cured. The balloon rubber layer is formed.

  Here, as the hollow filler, there is a microballoon material or the like that lowers the thermal conductivity like sponge rubber by having a gas portion in the cured product. Such materials may be any glass balloon, silica balloon, carbon balloon, phenol balloon, acrylonitrile balloon, vinylidene chloride balloon, alumina balloon, zirconia balloon, shirasu balloon and the like.

  The amount of the hollow filler is 0.1 to 200 parts by weight, preferably 0.2 to 150 parts by weight, more preferably 0.5 to 100 parts per 100 parts by weight of the thermosetting organopolysiloxane composition. Parts by weight. In this case, it is preferable to blend so that the content of the hollow filler in the silicone rubber composition for a fixing roller is 10 to 80%, particularly 15 to 75% by volume. If the volume ratio is too small, the decrease in thermal conductivity is insufficient, and if it is too large, molding and blending are difficult, and the molded product may be brittle without rubber elasticity.

Alternatively, for example, the silicone rubber heat insulating layer 32 may be formed by a method of adding a water-absorbing polymer and water.

  Such silicone rubber compositions include 0.1 to 50 parts by weight of a water-absorbing polymer, 10 to 200 parts by weight of water, 100 parts by weight of an organopolysiloxane composition, a curing catalyst such as a platinum compound catalyst, and a SiH polymer. The composition which added the crosslinking agent like this is formed. Thereafter, this may be thermoformed to form the heat insulating elastic layer 32.

  In this case, heating is performed in the following three or two stages. That is, in the first stage, the silicone base polymer is not substantially cured and moisture is not evaporated, and the mold is formed by heating at 100 ° C. or lower, preferably 50 to 80 ° C. for 10 to 30 hours. Next, in the second stage, the molded product is heated at 120 to 250 ° C., preferably 120 to 180 ° C. for 1 to 5 hours to evaporate water contained therein and water-containing impurities. Depending on the heating conditions when the moisture evaporates, the independent bubbles may be converted into an open cell structure or may not be converted. If the curing speed is high, the number of independent bubbles increases without conversion, and if controlled so that substantial curing due to crosslinking does not occur, the structure is converted to an open cell structure. In the final third stage, the obtained foam is heated at 180 to 300 ° C., preferably at 200 to 250 ° C. for 2 to 8 hours, to proceed with curing, so that a desired porous rubber-like elastic body is obtained. Complete the silicone rubber layer.

  A sponge-like silicone rubber layer obtained by foaming silicone rubber can also be used in this embodiment. Examples of the foamed silicone rubber include a method of adding a pyrolytic foaming agent and a method of molding a foam using hydrogen gas by-produced during curing as a foaming agent.

  However, in molding such as injection molding, there is a problem that it is difficult to obtain a foamed silicone rubber having fine and uniform cells, and the cell diameter in the foamed silicone rubber is not uniform. It is easy, the cell wall thickness is not uniform, and the strength varies greatly.

  From this, it has been confirmed that when the fixing roller 30 is formed with a small diameter, if the tension is continuously applied to the fixing roller with a small radius of curvature, the weak cell wall is broken and bubbles are broken. In addition, it has been difficult to achieve both durability and heat insulation with foamed silicone rubber. In other words, in the case of foamed silicone rubber having a non-uniform foam diameter, the cell wall constituting the elastic layer becomes thinner when the foaming ratio is increased in order to increase the heat insulation, and bubbles are more likely to break due to durability. It tends to occur.

  Even a solid rubber layer made of silicone rubber can be used in this embodiment. Low heat conduction of 0.20 W / (m · K) or less can be achieved by extremely reducing the mixing amount of the compound having high thermal conductivity such as a reinforcing filler into the silicone rubber.

  However, low thermal conductive solid rubber has a large thermal expansion. When used as the fixing roller 30 directly heated by the heater 21, the outer diameter changes greatly due to thermal expansion, and when used in the fixing device in the image forming apparatus, the conveyance speed of the recording material P changes, and the recording material P It becomes difficult to maintain image printing accuracy.

  Therefore, it is desirable that the heat insulating elastic layer 32 is formed of a liquid silicone composition mainly composed of a balloon such as a microballoon or an organopolysiloxane containing a water-absorbing polymer. A uniform cell that is open-celled is obtained. Therefore, compared with a sponge silicone rubber heat insulation layer and a solid rubber heat insulation layer, it is excellent in heat insulation and durability, and has little thermal expansion.

The manufacturing method of the fixing roller 30 is not particularly limited. The heat insulating elastic layer 32 is formed on the metal core 31, and the outermost layer is formed by the heat storage layer 33 having a higher thermal conductivity than the heat insulating elastic layer 32. And the heat storage layer 33 heat capacity fixing roller unit surface area per 100J / ^{m 2} · K or more, and be formed to be equal to or less than 600J / ^{m 2} · K, but may be any method.

(4) Configuration other than fixing roller (4-1) Heater 21
FIG. 5 is a schematic cross-sectional view of the heater 21. Reference numeral 21a denotes a heater substrate, which is a heat-resistant and electrically insulating member formed of an insulating ceramic such as alumina or aluminum nitride, or a heat-resistant resin such as polyimide, PPS, or liquid crystal polymer. The substrate 21a is an elongated member whose longitudinal direction is the vertical direction of the drawing, and the length dimension is larger than the maximum sheet passing width of the fixing device.

Along the longitudinal direction on the surface of the substrate 21a (fixing roller facing surface), for example, an energization heating resistance layer 21b such as Ag / Pd (silver palladium), RuO ₂ , Ta ₂ N, etc. is formed by screen printing or the like with a thickness of about 10 μm. It is formed by coating in the form of a line or a thin strip of about 1 to 5 mm.

  An insulating protective layer 21c made of, for example, glass, polyimide (PI) resin, or the like having a thickness of about 10 μm to 100 μm is formed on the energization heat generating resistance layer 21b for the purpose of protecting this layer and ensuring insulation.

  Further, for the purpose of improving the slidability with the fixing roller 30 and preventing adhesion of toner or the like, for example, a sliding layer 21d made of a material having good slidability and releasability such as a fluororesin is formed to a thickness of 10 μm. To a thickness of about 30 μm.

  Alternatively, a protective layer made of a fluororesin or the like and having a thickness of about 10 μm to 100 μm may be directly formed on the energization heat generating resistance layer 21b, and the insulating protective layer and the sliding layer may be used as a structure.

The insulating protective layer 21c, the sliding layer 21d, or a combination layer of both is formed as thin as possible within a range where durability, smoothness, releasability, and the like can be secured. Further, it is desirable to improve the thermal conductivity by mixing a high thermal conductive filler or the like as long as the releasability can be maintained.

  The heater holder 24 that fixes and holds the heater 21 is formed of a heat-resistant resin such as liquid crystal polymer, phenol resin, PPS, or PEEK. The lower the thermal conductivity, the higher the heat efficiency when heating the fixing roller 30. Therefore, a hollow filler such as a glass balloon or a silica balloon may be included in the resin layer.

  On the opposite side of the heater 21 from the fixing roller 30, a temperature detection means 22 such as a thermistor for detecting the temperature of the substrate 21 a raised in accordance with the heat generation of the energization heat generation resistance layer 21 b is disposed. This temperature detection means 22 is provided for the purpose of controlling the temperature of the heater 21.

  As the temperature control method, the duty ratio, wave number, etc. of the voltage applied to the energization heating resistor layer 21b from the electrode part (not shown) at the longitudinal end of the heater 21 according to the signal of the temperature detection means 22 are set. By appropriately controlling, the heater 21 generates heat and the temperature is controlled. The effective heat generation area width in the longitudinal direction of the heater 21 is larger than the maximum sheet passing width of the fixing device. The detected temperature information from the temperature detecting element 22 is sent via the temperature control unit 100 to the triac element 101 as an energization driver. Based on the energization signal from the temperature control unit 100, the triac element 101 performs energization ON / OFF of the AC power supply 102 that supplies power to the energization heating resistor layer 21b.

  As a temperature control method, a temperature control is performed so that the temperature of the heater 21 is a predetermined temperature, and a temperature detection element is also brought into contact with the surface of the fixing roller so that the temperature of the fixing roller surface is a predetermined temperature. There is a method to control the power to the.

  By controlling the temperature so that the surface temperature of the fixing roller is a predetermined temperature, it is possible to keep the fixing property constant and prevent image defects such as hot offset due to excessive application of heat.

  The continuous usable temperature of the silicone rubber and the fluororesin used for the fixing roller 30, the heater 21, and its peripheral parts is generally about 230 ° C, preferably about 200 ° C. When used at a higher temperature than this, the silicone rubber deteriorates or the wear resistance of the fluororesin deteriorates.

  The temperature of the surface of the fixing roller or the temperature of the heater 21 is desirably controlled to be 230 ° C. or lower, preferably about 200 ° C. to 230 ° C. at the highest.

  The heater 21 has been described in the form in which the energized heat generating resistance layer 21b is formed on the fixing roller side of the substrate 21a. However, when aluminum nitride or the like having good thermal conductivity is used as the heater substrate 21a, as shown in FIG. Also, a back surface (back surface) heating type heater 21 can be used. That is, the energization heat generating resistance layer 21b is formed on the back surface of the substrate 21a (on the side opposite to the fixing roller facing surface side), and the insulating protective layer 21c is provided on the heating element energization heat generation resistance layer 21b. The sliding layer 21d may be provided on the surface of the substrate 21a (on the side facing the fixing roller).

  As shown in FIG. 7, the substrate 21 a of the heater 21 may have a curved shape in which the fixing roller facing surface corresponds to the outer surface of the fixing roller 30. The heater 21 is easy to follow along the surface of the fixing roller, and the fixing nip portion Nh having a wide width in the rotation direction of the fixing roller 30 can be secured with a lighter pressing force.

  Further, as shown in FIG. 8, a flexible heater 21 may be used. For example, a heat-resistant resin made of polyimide, polyamideimide, or the like is formed into a sheet shape having a thickness of 50 μm to 300 μm, and this is used as a heat-resistant / insulating heater substrate 21 g having flexibility. An energization heating resistor 21b made of, for example, a SUS thin film is formed thereon. An insulating protective layer 21c made of polyimide (PI) resin or the like and having a thickness of about 10 μm to 100 μm is formed thereon. Further, a sliding layer 21d made of a fluororesin having a thickness of about 10 μm to 30 μm is formed to form a sheet-like heater 21 having flexibility as a whole.

  The heater 21 is fixedly supported at both ends on the upstream side and the downstream side in the rotation direction of the fixing roller by support members 26 on that side, and is arranged in pressure contact with the surface of the fixing roller 30. Since this sheet-like heater 21 has flexibility, it can easily follow the surface of the fixing roller 30 and can secure a wide fixing nip portion Nh in the rotation direction of the fixing roller 30 with a light pressure.

  Instead of the sliding protection layer 21e of the heater 21, a fixing nip is provided between the heater 21 and the fixing roller 30 with a protective sheet 21e-a interposed on the fixing roller side (front side) of the heater 21 as shown in FIG. It is good also as a structure which forms the part Nh.

  The protective sheet 21e-a is formed, for example, by forming a sheet base layer and a release layer made of, for example, a fluororesin with a thickness of 10 to 30 μm on the surface of the sheet base layer on the fixing roller side. The sheet base layer is a metal member such as stainless steel (SUS), nickel (Ni), titanium (Ti), or copper (Cu). Alternatively, it is a sheet having a thickness of 30 to 100 μm in which a high heat conductive filler made of metal particles, metal oxide, artificial diamond, graphite or the like is mixed in a heat resistant resin such as polyimide (PI). Further, the protective sheet 21e-a is, for example, a fluororesin alone formed in a sheet shape with a thickness of 30 to 100 μm.

(4-2) Pressure roller (nip forming member) 63
In this embodiment, the pressure roller 63 is formed by forming an elastic layer 42 and a releasable layer 43 on the outermost layer outside the cored bar 41 made of aluminum, iron, SUM, or the like.

  The pressure roller 63 forms a fixing nip portion Nt by contact pressure with the fixing roller 30. In the fixing nip portion Nt, when the heat flow from the surface of the fixing roller 30 to the pressure roller 63 is suppressed as much as possible, the temperature increase speed of the surface of the fixing roller 30 in the heating contact region portion Nh is increased.

  Therefore, the elastic layer 42 is a balloon rubber layer in which a hollow filler such as a microballoon is blended with silicone rubber or the like, like the heat insulating elastic layer 32 of the fixing roller 30. Alternatively, a silicone rubber layer containing a water-absorbing polymer or a sponge rubber layer obtained by hydrogen foaming silicone rubber is used. If the thermal conductivity is low, a solid rubber layer may be used.

  Examples of the release layer 43 include polytetrafluoroethylene resin (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA), and fluorinated ethylene polypropylene copolymer resin (FEP). Can do. Furthermore, a polyvinylidene fluoride resin (PVDF), a polyvinyl fluoride resin (PVF), etc. can be mentioned.

  The coating can be formed by latex, Daiel latex (Daikin Kogyo Co., Ltd., fluorine-based latex), dipping coating using a dispersion, spray coating, or the like. Unlike the outermost layer of the fixing roller 30 described above, it is preferable that the thermal conductivity is low, and it is more appropriate not to mix a high thermal conductive filler or the like.

  As shown in FIG. 10, the pressure roller 63 may be a rigid cylindrical member formed by forming the releasable layer 43 directly on the outside of the cored bar 45. Since the fixing roller 30 has an elastic layer, the fixing roller nip portion Nt can be formed even if the pressure roller 63 is not an elastic body. Since there is no heat insulating elastic layer between the cored bar 45 and the releasable layer 43, the heat insulating property is insufficient, and the heat of the fixing roller 30 can easily escape to the pressure roller 63. It is desirable to reduce the heat capacity of the hollow cored bar.

(5) Drive Description With the above configuration, the energization of the heater 21 is started in a state where the fixing roller 30 is rotationally driven and the pressure roller 63 is driven to rotate, and the surface temperatures of the heater 21 and the fixing roller 30 are set to the recording material. Start up to the temperature required for heat fixing.

  Since the heater itself has a low heat capacity, the temperature of the heater 21 rises quickly.

  The fixing roller 30 has a heat insulating elastic layer 32 formed on a core metal 31 and has a sufficient heat capacity only near the surface, and the heat insulating elastic layer 32 inside has a small heat capacity. Further, a heat storage layer 33 having a high thermal conductivity is formed on the surface, and heat can be efficiently transferred from the heater 21 to the heat storage layer 33 near the surface of the fixing roller. Therefore, the surface temperature of the fixing roller 30 rises quickly.

  The unfixed toner image T on the recording material P is heated and fixed by introducing the recording material P on which the unfixed toner image T is formed in the fixing nip portion Nt with the surface of the fixing roller kept at a predetermined temperature. A fixed image.

  Since the surface of the fixing roller 30 has a heat storage layer 33 having a high thermal conductivity and a sufficient heat capacity, the toner image T on the recording material P can be heated and fixed with a sufficient amount of heat. Is possible.

  The state of the toner image T and the fixing roller 30 in the fixing nip Nt at this time will be described with reference to FIG. In FIG. 11, when the recording material P on which the unfixed toner image T is formed is introduced into the fixing nip portion Nt, the toner image T is pressed by the surface of the fixing roller 30 and is crushed. At this time, since the fixing roller 30 has elasticity, the surface of the fixing roller 30 is slightly deformed corresponding to the unevenness of the toner image T. As a result, the outermost high heat conductive layer 33 of the fixing roller 30 is recessed so as to wrap the toner image T. As a result, the contact area of the fixing roller 30 increases with respect to the toner image T, and heat is efficiently transferred from the fixing roller 30 to the toner image T on the recording material P. In particular, since the fixing roller 30 is an elastic member as shown in the present embodiment, even if the toner image is on a recording material having a large surface roughness, the surface of the fixing roller 30 follows the unevenness of the recording material P. The fixing property on the recording material P can be obtained.

Since the recording material moves following the surface of the fixing roller, although the surface of the fixing roller is slightly deformed, the heat received by the toner image on the unit area on the recording material is the surface of the unit area on the surface of the fixing roller 30 and The heat q stored in the inner region oozes out. That is, the amount of heat q stored under the unit surface area of the fixing roller is a main heat source for heating and fixing the toner image T per unit area. In the present invention, the heat storage layer of the fixing roller is formed to have a heat capacity of 100 J / m ² · K or more per unit surface area, and a sufficient amount of heat is stored in the heat storage layer of the fixing roller. T can be fixed.

  The fixing device 7 in this embodiment can obtain a good image without fixing unevenness in a short first printout time. Because the warm-up time is short, standby temperature control is not performed. Since there is no wasteful power consumption during standby, energy saving is achieved.

(6) Other examples of heating means As described above, the fixing roller 30 is used as a heating means for heating from the outside, the plate heater 21 is used, and this is pressed against the surface of the fixing roller 30 while being rubbed against the rotating fixing roller 30. The description has been made by taking the configuration of contact as an example.

  However, the heating means for heating the fixing roller 30 from the outside itself has a low heat capacity and can quickly rise in temperature, and can form a heating nip Nh with the fixing roller 30 to heat the fixing roller. If it is, it is not limited to said structure.

  For example, as shown in FIG. 12, a heating film 21 f that is a flexible member is externally fitted to the heater 21 so as to be slidably rotatable on the outside of the heater holder 24 that supports the heater 21. The heating contact area portion Nh may be formed by interposing the heating film 21f between the heater 21 and the fixing roller 30.

  The heating film 21 f is rotated by the rotation of the fixing roller 30 and rotates outside the heater holder 24 while sliding on the surface of the heater 21 to protect the heater 21.

  The heating film 21f is a film-like member in which, for example, a sheet base layer and a release layer made of, for example, a fluororesin are formed on the fixing roller side of the sheet base layer with a thickness of 10 to 30 μm. The sheet base layer is a metal member such as stainless steel (SUS), nickel (Ni), titanium (Ti), or copper (Cu). Alternatively, it is a sheet member base layer having a thickness of 30 to 100 μm in which a high heat conductive filler made of metal particles, metal oxide, artificial diamond, graphite or the like is mixed in a heat resistant resin such as polyimide (PI). Further, the heating film 21f is a film-like member formed of a single fluororesin and formed into a sheet shape having a thickness of 30 to 100 μm.

  In order to suppress the heat capacity of the heating film 2f itself and to suppress heat radiation to the air, it is desirable that the outer diameter of the heating film 21f be, for example, a small diameter of about φ18 to φ10.

  Further, the heating means for heating the fixing roller 30 from the outside can be a heat roller 21A as shown in FIG. The heat roller 21 </ b> A is provided with a heating source 51 such as a halogen heater inside the hollow core metal 53.

  It is desirable that the heat roller 21A achieve a rapid temperature rise by reducing the heat capacity. For example, a small-diameter cylindrical member is formed in which a release layer 54 made of, for example, a fluororesin is formed on a hollow core metal 53 having an outer diameter of about φ18 to φ10 and a thickness of 1 to 0.3 mm with a thickness of 10 to 30 μm.

(7) Confirmation by experiment The above was confirmed by conducting an experiment using the image forming apparatus provided with the fixing device 7 in this embodiment.

  First, the basic configuration of the fixing device 7 used in this experiment will be described below.

  The process speed of the image forming apparatus used was 100 mm / sec, and an experiment was performed using a laser beam printer that performed 16 prints per minute.

  In the fixing device 7, a heating means for heating the fixing roller 30 from the outside is a ceramic heater (plate heater) 21 in which a heat generating paste of silver and palladium is formed on a ceramic substrate 21 a having a thickness of 1.0 mm with a thickness of 10 μm. It was used. The ceramic heater 21 is held by a heat insulating liquid crystal polymer member (heater holder) 24 containing a hollow resin.

  An insulating glass layer 21c having a thickness of 30 μm is formed on the surface of the ceramic heater to protect the heating element, and a sliding layer 21d made of a PFA resin having a thickness of 10 μm is further provided.

  As the pressure roller 63, a silicone rubber layer 42 having a thermal conductivity of 0.12 W / (m · K) and a thickness of 2.0 mm is provided on a SUM cored bar 41 having an outer diameter of 8 mm, and on the outer side thereof. What provided the fluororesin layer 43 was used.

  With the above configuration, a heating contact area Nh having a width of 7 mm was formed by applying a pressure of 49 N between the ceramic heater 21 and the fixing roller 30. Further, a pressure of 49 N was applied between the fixing roller 30 and the pressure roller 63 to form a fixing nip portion Nt with a width of 7 mm. The ceramic heater 21 and the pressure roller 63 are arranged to face each other by 180 ° with the fixing roller 30 as the center.

(Experiment 1)
In the fixing roller 30 used in the experiment, a 2.0 mm thick silicone rubber layer was formed as a heat insulating elastic layer 32 on a SUM cored bar 31 having an outer diameter of 8 mm. The silicone rubber of the heat insulating elastic layer 32 is a balloon rubber in which an acrylonitrile balloon having a particle size of 80 μm, which is a hollow resin, is contained in a silicone rubber, and a small amount of triethylene glycol is blended so that bubbles are connected. This heat insulating elastic layer 32 had a thermal conductivity of 0.12 [W / (m · K)] and a volumetric heat capacity of 1.1 × 10 ⁶ [J / (m ³ · K)].

  Further, a silicone solid rubber layer was formed as a heat storage layer 33 outside the heat insulating elastic layer 32.

In other words, the fixing roller 30 used in the experiment is a two-layer silicone rubber 32/33 fixing roller in which the surface layer of the fixing roller is a heat storage layer. The outer diameter of the fixing roller 30 is 12 mm, the length L of the rubber portion is 230 mm, and the surface area S of the outer peripheral surface is 8671 mm ² .

  For the heat storage layer 33, five types of silicone rubbers 1 to 5 having different heat capacities are used, and the thicknesses are changed to 50, 150, and 400 μm, respectively, and a total of 15 types of rollers A1 to A15 having different heat capacities of the heat storage layer 33 are used. It was created. The outline of the created rollers A1 to A15 is as shown in Table 1.

  The rubbers 1 to 5 are prepared by blending silica having a particle diameter of 4 to 6 μm and alumina having a particle diameter of 4 to 6 μm as a filler in a silicone rubber in a total amount of 10% by mass or more and 50% by mass or less. A solid rubber compounded and adjusted to achieve heat capacity and thermal conductivity.

  The recording material P on which the unfixed toner image T was formed was passed through the fixing device 7 and the fixing performance was evaluated.

  The experiment is started from a state in which the temperature of the heater 21, the fixing roller 30, and the entire fixing device is adapted to the ambient temperature (hereinafter, this condition is referred to as a cold start). The environment during the experiment was a temperature of 25 ° C. and a humidity of 60%.

  As shown in FIG. 14, the surface temperature of the fixing roller 30 is equal to the surface temperature of the fixing roller 30 at the intermediate position D from the heating contact area Nh to the fixing nip Nt in the rotation direction of the fixing roller 30. Measurement is performed using a total of 103.

  At the same time as the start of rotation of the fixing roller 30 from the cold start, 500 W of electric power is supplied to the ceramic heater 21 to heat the ceramic heater 21 to heat the fixing roller 30 and to raise the fixing roller 30 to a target temperature. .

  The temperature of the fixing roller 30 is controlled using the radiation thermometer 103, and after reaching the desired fixing roller temperature, the electric power of the ceramic heater 30 is controlled so as to maintain the target temperature.

  After a warm-up time of 20 seconds, the recording material P on which the unfixed toner image T is formed is passed. The experiment was performed by changing the target temperature of the fixing roller 30 and the target temperature adjustment temperature of the ceramic heater 21, and the temperature of the fixing roller 30 at which the fixability of the image on the heat-fixed recording material P was good was obtained. .

As a method for evaluating the fixing performance of the unfixed toner image T on the recording material P, a cellophane tape is stuck on the toner image of the recording material P after heat fixing, and a surface of 0.49 N / cm ² (50 g / cm ² ). Remove the cellophane tape after pressing for 1 minute under pressure. Then, evaluation was performed based on the degree of image defects (defects peeled off by the tape) in the toner image at that time.

The case where the image defect exceeded 5% of the original toner image was determined as NG (defect). As the recording material P, 4024 manufactured by XEROX, basis weight 75 g / mm ² paper was used.

  This experiment was performed with an experimental apparatus using 15 types of rollers A1 to A15 having different heat capacities of the heat storage layer 33, and the relationship between the heat capacity and the fixing roller temperature was compared.

  The results are shown in FIG. The horizontal axis is the heat capacity of the heat storage layer per unit surface area of the fixing roller, and the vertical axis is the surface temperature of the fixing roller when the recording material is passed so that the fixing performance is OK. Even if the heat storage layers have the same thickness, those made of rubber having a small volumetric heat capacity have a small heat capacity. When the heat capacity / surface area (C / S) decreases, the surface temperature of the fixing roller at which the fixing performance is good increases.

This is generally
Amount of heat Q = heat capacity C × temperature T
It is because it becomes.

  It can be seen that the smaller the heat capacity of the heat storage layer 33, the higher the surface of the fixing roller must be, in order to accumulate the amount of heat for fusing and fixing the toner placed on the unit surface area of the recording material P.

When the heat capacity / surface area was smaller than 100 J / (m ² · K), the surface temperature of the fixing roller necessary for fixing the toner exceeded 230 ° C. This exceeds the heat-resistant temperature which can be continuously used, such as silicone rubber used for the heat storage layer 33 and the heat insulating elastic layer 32. If it continues to be heated above the heat-resistant temperature, the rubber crosslinks break or recombine, causing a change in hardness, leading to rubber breakage. Therefore, in order to stably operate without failure while obtaining good fixability, it is necessary to use the fixing roller 30 including the heat storage layer 33 having a heat capacity / surface area of 100 J / (m ² · K) or more. .

As the heat capacity / surface area increased, the fixing roller surface temperature at which the fixing performance was good decreased. However, even when the heat capacity / surface area was larger than 600 J / (m ² · K), the fixing roller surface temperature at which the fixing performance was good did not change. That is, when the heat capacity / surface area is larger than 600 J / (m ² · K), the heat storage layer stores an excessive amount of heat. In addition, since the heat storage layer stores a large amount of heat, the energy for heating the fixing roller with the heater also increases.

  As described above, the fixing roller 30 needs to be used at a temperature of 230 ° C. or lower. As the temperature required for the surface of the fixing roller increases, the heater needs to be heated to a higher temperature. In addition, a large amount of electric power is required for the temperature rise of the heater itself. In addition, high heat resistance is required for the heater and peripheral components, leading to an increase in cost. The temperature of the entire image forming apparatus also rises due to heat radiation from the fixing device. For example, when the temperature in the vicinity of the developing device 3 rises, unused developer stored in the developing device 3 melts or deteriorates. Problems occur. In order to use the fixing roller 30 at as low a temperature as possible, it is effective to increase the heat capacity.

  However, if the temperature of the fixing roller (the temperature of the heat storage layer) becomes too low, the toner fixability becomes insufficient even if the amount of heat necessary for fixing the toner is stored. This is because if the temperature of the fixing roller is low, the temperature gradient between the fixing roller and the recording material becomes small, and the thermal conductivity from the fixing roller to the recording material (toner) decreases.

When the heat capacity of the heat storage layer is too large ((a) and (b): the heat capacity C / S per unit surface area is larger than 600 J / (m ² · K)) and when it is moderate ((c): C / FIG. 27 shows an image in which S is 600 J / (m ² · K) or less).

  The vertical axis in FIG. 27 indicates the temperature of the heat storage layer of the fixing roller. (A) in FIG. 27 is a model in which a wasteful amount of heat is stored because the heat capacity is large (C2) and the amount of stored heat is large (Q2). (B) is a model in which only the heat quantity Q1 necessary for fixing the toner is stored in the heat storage layer having a large heat capacity. In this case, since the temperature of the fixing roller is lowered, the temperature gradient between the fixing roller and the recording material is reduced, and it is difficult to transfer the stored heat amount (to the toner) to the recording material. (C) is a model in which only the heat quantity Q1 necessary for fixing the toner is stored in a heat storage layer having a moderate heat capacity (C1). In this case, there is little excess heat in addition to the amount of heat necessary for fixing the toner, and the temperature of the fixing roller is reasonably high, so the temperature gradient between the fixing roller and the recording material increases, and the stored heat amount is stored in the recording material. Easy to convey (to toner). The present invention provides an apparatus close to the model (c) or the model (c).

The amount of heat stored under the unit surface area of the fixing roller is the [heat capacity / surface area x fixing roller temperature] of the fixing roller.
Can be estimated.

  The result of Experiment 1 was converted as the relationship between the fixing roller temperature necessary for securing the toner fixability and the heat storage amount necessary for ensuring the toner fixability. As shown in FIG. The vertical axis represents the temperature required for fixing, and the horizontal axis represents the amount of heat stored per unit surface area of the fixing roller.

  Here, it is shown that the fixing rollers A13, A14, and A15 need the same fixing temperature as the fixing roller A12, that is, have an excessive heat storage amount.

These fixing rollers uselessly have a large heat capacity, perform wasteful heat storage that does not contribute to toner fixing, and waste energy. The fixing rollers A13, A14, A15 are fixing rollers having a heat capacity / surface area larger than 600 J / (m ² · K).

That is, in order to reduce the waste of energy in the fixing operation, it is necessary to use a fixing roller having a heat storage layer 33 having a heat capacity / surface area of 600 J / (m ² · K) or less.

(Experiment 2)
Next, a heat storage layer was formed by changing only the thickness of the heat storage layer 33 of the fixing roller 30, and a comparative experiment was performed.

In the fixing roller 30 used in the experiment, a 2.0 mm thick silicone rubber layer was formed as a heat insulating elastic layer 32 on a SUM cored bar 31 having an outer diameter of 8 mm. The silicone rubber of the heat insulating elastic layer 32 is a balloon rubber in which an acrylonitrile balloon having a particle size of 80 μm, which is a hollow resin, is contained in a silicone rubber, and a small amount of triethylene glycol is blended so that bubbles are connected. The heat insulating elastic layer 32 had a thermal conductivity of 0.12 [W / (m · K)] and a volumetric heat capacity of 1.1 × 10 ⁶ [J / (m ³ · K)].

Further, on the outside of the heat insulating elastic layer 32, as a heat storage layer 33, a silicone solid rubber having a thermal conductivity of 0.3 W / (m · K) and a volumetric heat capacity of 1.5 × 10 ⁶ J / (m ³ · K). A layer was formed.

  By changing the thickness of the heat storage layer 33, seven types of fixing rollers A16 to A22 having different heat capacities of the heat storage layer 33 were created. The outline of the heat storage layer 33 of the prepared fixing rollers A16 to A22 is shown in Table 2.

  The same experiment as Experiment 1 was performed, and the fixing roller temperature at which the fixing property was OK was measured for each fixing roller. The results are shown in FIG. The horizontal axis is the heat capacity of the heat storage layer per unit surface area of the fixing roller, and the vertical axis is the surface temperature of the fixing roller when the recording material P is fed so that the fixing performance is good.

Similar to Experiment 1, when the heat capacity / surface area is decreased, the surface temperature of the fixing roller at which good fixing performance is obtained increases. When the heat capacity / surface area was smaller than 100 J / (m ² · K), the necessary fixing roller surface temperature exceeded 230 ° C. Further, even when the heat capacity / surface area was larger than 600 J / (m ² · K), the fixing roller surface temperature at which the fixing performance was good did not change.

In order to stably operate without failure while obtaining good fixability, it is necessary to use a fixing roller having a heat storage layer having a heat capacity / surface area of 100 J / (m ² · K) or more. In order to reduce waste of energy in the fixing operation, it is necessary to use the fixing roller 30 including the heat storage layer 33 having a heat capacity / surface area of 600 J / (m ² · K) or less.

(Experiment 3)
From Experiments 1 and 2, the heat storage layer 33 having a heat capacity C / S of 100 J / (m ² · K) or more and 600 J / (m ² · K) or less is provided to prevent breakage and heat fixing the recording material without waste. It was found that the amount of heat required for the heat can be stored.

  Next, it is explained that the heat quantity necessary for heating and fixing the recording material can be stored without waste by providing the heat storage layer 33 having an appropriate heat capacity C / S for the contact time between the fixing roller 30 and the recording material P. To do.

  The experiment was performed by changing the time for which the fixing roller 30 and the recording material contact each other. The process speed of the image forming apparatus used was 100 mm / sec, and an experiment was performed using a laser beam printer that performed 16 prints per minute.

  In the image forming apparatus used in the experiment, the pressure between the fixing roller 30 and the pressure roller 63 is changed, and the width of the fixing nip Nt (width in the recording material conveyance direction) is 6.0 mm, 5.0 mm, and 4. There are five types of experimental devices that are changed to 0 mm, 3.0 mm, and 2.0 mm.

  The fixing nip time t in which the recording material contacts the fixing roller 30 at the fixing nip portion Nt in these experimental apparatuses is 0.06, 0.05, 0.04, 0.03 per rotation of the fixing roller. 0.02 [seconds]. In other words, the time t required for one point on the surface of the fixing roller to pass through the fixing nip is 0.06, 0.05, 0.04, 0.03, and 0.02 [seconds].

  Experiments similar to Experiment 1 were performed using the fixing rollers A17 to A21 used in Experiment 2.

  The result is shown in FIG. The vertical axis represents the fixing roller temperature necessary for fixing, and the horizontal axis represents the heat capacity C / S per unit surface area of the fixing roller used. The relationship between the fixing temperature and the heat capacity of the heat storage layer is shown for each experimental device with different contact time between the fixing roller and the recording material used in the experiment.

  In the experimental apparatus in which the contact time between the fixing roller and the recording material was 0.06 [seconds], the fixing roller having a large heat capacity C / S had a low fixing roller temperature required for fixing. For example, with the fixing roller A21, the fixing roller can be fixed at about 120 ° C. However, even if the same fixing roller is used, about 190 ° C. is necessary for fixing in an experimental apparatus having a fixing nip time of 0.02 [second]. For the same fixing roller, naturally, the higher the fixing roller temperature, the more heat storage. In the combination of the fixing roller A21 and the experimental apparatus with a fixing nip time of 0.02 seconds, the amount of heat storage required for fixing becomes large.

As described above, the amount of heat stored under the unit surface area of the fixing roller is
[Heat capacity / surface area of fixing roller × fixing roller temperature]
Can be estimated.

  The result of Experiment 3 is converted into the relationship between the fixing roller temperature necessary for fixing and the heat storage amount necessary for fixing, and is shown in FIG. The vertical axis represents the temperature required for fixing, and the horizontal axis represents the amount of heat per unit surface area of the fixing roller. The results of each experimental apparatus used in the experiment with different fixing nip times are shown. As can be understood with reference to FIG. 19, in order to ensure good fixability, the shorter the time required for one point of the fixing roller surface to pass through the fixing nip portion, the more it is necessary to accumulate per unit surface area. The amount of heat is increasing. That is, the higher the processing speed, the greater the amount of heat that needs to be stored per unit surface area.

  Here, in an experimental apparatus in which the contact time between the fixing roller and the recording material is 0.02 [seconds], the fixing rollers A19, A20, and A21 require the same fixing temperature as the fixing roller A18, and energy saving is achieved. Inferior. Similarly, in the experimental device of 0.03 [seconds], the fixing rollers A20 and A21 are rollers inferior in energy saving in the experimental device of 0.05 [seconds].

  In FIG. 19, the combination of the fixing roller and the device on which the fixing device is mounted in the region shown in the lower left of the broken line (circled region) is the best combination in terms of energy saving.

  As described above, in the combination of the fixing roller and the apparatus, it was possible to separate the combination excellent in energy saving and the combination not.

The results are shown as a graph in FIG. The horizontal axis represents the contact time between the fixing roller and the recording material in the experimental apparatus used for the experiment, the vertical axis represents the C / S of the fixing roller, the efficient combination is ◯, and the inefficient combination is ×. In FIG. 20, the ◯ and X regions could be separated by straight lines. ○ area
C / S ≦ 10000 [J / (s · m ² · K)] × t [s]
It was possible to express it. Here, t is the contact time of the fixing roller with the recording material in the fixing device, in other words, the time required for one point on the surface of the fixing roller to pass through the fixing nip portion. That is,
100 [J / (m ² · K)] ≦ C / S ≦ 600 [J / (m ² · K)]
Within the range, the relationship between the heat capacity C / S of the heat storage layer 33 of the fixing roller 30 and the time t of the fixing device to be used is
C / S ≦ 10000 [J / (s · m ² · K)] × t [s]
If so, it is possible to make a combination of an efficient fixing device and a fixing roller capable of effectively using the stored heat quantity.

(Experiment 4)
As described above, with a fixing roller having a large heat capacity, the fixing roller temperature required for fixing becomes lower as it is combined with an experimental apparatus having a longer contact time between the fixing roller and the recording material. However, when combined with an experimental apparatus in which the contact time between the fixing roller and the recording material is short, the effect is not exhibited, and the fixing roller temperature required for fixing is high. As a result, this combination is an inefficient combination that cannot be fixed at low temperature even though the amount of heat storage is large.

  The mechanism of this phenomenon is explained by the following experimental results.

  A thermocouple was attached on the recording material, and the temperature rise of the recording material was measured while the fixing roller and the recording material were in contact at the fixing nip. As an example, the fixing roller A19 and the fixing roller A20 were used to adjust the temperature of the fixing roller at 165 ° C. and warmed up in the same manner as in Experiment 3 to pass the paper.

  The results are shown in FIG. The vertical axis represents the temperature of the thermocouple attached on the recording material, and the horizontal axis represents the elapsed time since the recording material entered the fixing nip.

  In the roller A19 and the roller A20, the temperature of the thermocouple on the recording material similarly increased until 0.02 [seconds] after entering the fixing nip, but in the roller A19, the temperature increase gradually decreased to 0.05 [ Seconds], a difference in the temperature of the thermocouple occurred between the roller A19 and the roller A20.

  Since the heat capacity of the heat storage layer of the fixing roller is small and the heat storage amount is small compared with the roller A20, the roller A19 loses heat to the recording material at the fixing nip, and the heat transfer to the recording material is slow. With the roller 20 having a large heat capacity, the heat supply to the recording material is continued.

  Thus, a fixing roller having a large heat capacity and a large amount of heat storage exhibits a great effect during a long contact time.

  However, if the fixing nip is narrow and the contact time from the fixing roller to the recording material is only 0.02 [seconds], the effect is the same as that of a roller having a small heat capacity.

  A fixing roller having a large heat capacity requires more energy to start up to a predetermined temperature, consumes more power, and has a longer warm-up time than a fixing roller having a small heat capacity. In an experimental apparatus in which the contact time with the recording material is short, a fixing roller having a large heat storage amount is a wasteful roller that stores heat even to a heat amount that cannot be used up.

As described above, in the heat-fixing apparatus that heats from the outside, a heat storage layer is provided in the vicinity of the surface of the fixing roller having a low heat capacity inside, and the heat capacity / surface area of the heat storage layer 33 of the fixing roller 30 is 100 [J / (m ² · K)] to 600 [J / (m ² · K)]. As a result, it is possible to provide a fixing roller that has a low heat capacity, can store a sufficient amount of heat for heat-fixing the recording material, can use the stored heat amount effectively, and can be used stably without failure.

Further, the relationship between the heat capacity / surface area of the heat storage layer 33 of the fixing roller 30 and the time t at which the recording material contacts the fixing roller 30 per one rotation of the fixing roller,
C / S ≦ 10000 [J / (s · m ² · K)] × t [s]
And As a result, the amount of heat that can be transferred to the recording material within a specified contact time can be stored only in the vicinity of the surface of the fixing roller where the heat capacity is reduced, providing a heat-fixing device that consumes less energy and has a short warm-up time. it can.

Further, when the heat fixing device has a plurality of heating modes having different contact times with the recording material per rotation of the fixing roller 30, that is, a plurality of heating modes having different peripheral speeds of the fixing roller (heating member) are set. In the case of a device that can be used, the following settings may be made. That is, when the time required for one point of the surface of the fixing roller to pass through the fixing nip portion in the heating mode in which the contact time between the fixing roller and the recording material is the shortest (the peripheral speed of the fixing roller is the fastest) is t. The heat capacity C / S per unit surface area of the fixing roller of the heat storage layer 33 is
C / S [J / (m ² · K)] ≦ 10000 [J / (s · m ² · K)] × t [s]
It is desirable that

For example, a heating mode 1 in which the fixing roller and the recording material are in contact time t1 at a process speed of 100 mm / sec, and a heating mode 2 in which the fixing speed and the recording material are in contact time t2 at a process speed of 50 mm / sec. Suppose that there is a printer with two heating modes. If the width of the fixing nip portion is the same in any mode, t1 is shorter than t2. Therefore,
C / S ≦ 10000 [J / (s · m ² · K)] × t1 [s]
It is desirable to mount a fixing roller that satisfies the above.

  When the heat capacity / surface area of the heat storage layer 33 is increased so as to be suitable for the contact time t2 of the heating mode 1 having a long contact time with the recording material, the amount of heat stored in the heat mode 1 during the t1 when the contact time is short is heated. I can not communicate. When heat is stored in the heat storage layer 33 so as to be suitable for t1, the heat quantity of the heat storage layer 33 can be used effectively in both the heating mode 1 and the heating mode 2, and the heat fixing with less waste of energy and short warm-up time. Equipment can be provided.

Example 2
FIG. 22 is a schematic cross-sectional view illustrating the configuration of the fixing roller 30 in this embodiment.

  The embodiment in this example is substantially the same as that in Example 1, but the fixing roller 30 in this example has a heat insulating elastic layer 32 formed on a cored bar 31 and a solid heat storage elastic layer formed on the outside thereof. 33 is formed, and a release layer 34 is formed on the outermost layer (outermost layer).

Heat storage elastic layer 33 and the release layer 34 together forms a heat storage layer 33A, the heat capacity of the heat storage layer 33A is, per unit surface area of the fixing roller 100J / ^(m 2 · K) or more, 600 J / ^{(m 2} -K) It is formed to be the following.

  The thermal conductivity of the thermal storage elastic layer 33 and the release layer 34 of the thermal storage layer 33 </ b> A is formed so as to be higher than the thermal conductivity of the heat insulating elastic layer 32. The thermal conductivity of the heat insulating elastic layer 32 is 0.20 W / (m · k) or less.

Further, as shown in FIG. 23, on the outside of the heat insulating elastic layer 32, the heat capacity per unit surface area of the fixing roller 100J / ^(m 2 · K) or more, are formed 600J / ^(m 2 · K) or less and so as Only the release layer 34 may be formed as the heat storage layer 33B.

  The thermal conductivity and heat capacity of the heat storage layers 33A and 33B are measured by the following methods. A test piece of 5 mm in length and 5 mm in width including the surface of the fixing roller was cut out from the heat storage layers 33A and 33B on the surface of the fixing roller, and the heat capacity of the surface layers 33A and 33B was measured by the same measurement method (FIG. 4) as the heat storage layer 33 described above. Then, the thermal conductivity in the thickness direction is obtained.

  The release layer 34 is preferably a layer in which a high thermal conductive filler is mixed in a rubber material such as silicone rubber or fluororubber, or a base resin material such as a fluorine compound. Specifically, a layer in which 10% by mass or more and 50% by mass or less of a powdery high thermal conductive filler made of a material having a thermal conductivity of at least 10 W / (m · K) or more is mixed in the base resin material. It is desirable to form a release layer with high thermal conductivity.

  Examples of the base resin material include fluororesin, polyphenylene sulfide, polysulfone, polyetherimide, polyethersulfone, polyetherketone, liquid crystal polyester, polyamideimide, and polyimide.

  In the above, examples of the fluorine-based resin include polytetrafluoroethylene resin (PTFE) and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA). Moreover, a fluoroethylene polypropylene copolymer resin (FEP), a polyvinylidene fluoride resin (PVDF), a polyvinyl fluoride resin (PVF), etc. can be mentioned.

  The high thermal conductive release layer 34 using a fluorine resin is formed of a fluorine resin coating agent, a fluorine resin tube, or the like.

  The coating may be any method such as latex, Daiel latex (made by Daikin Industries, Ltd., fluorine latex), dipping coating using a dispersion, spray coating, or the like.

  Examples of the high thermal conductive filler include diamond, graphite, carbon, carbon nanotube, boron nitride, metal oxide, various alloys, AlN, crystalline silica, and the like.

  Moreover, as long as it is a means to achieve high thermal conductivity, the type of filler material is not limited, and the shape of the filler may be any shape, and in order to achieve the purpose of this embodiment There are no restrictions.

  As in the present embodiment, the outermost layer of the fixing roller 30 is a blend formed by blending a fluorine compound with a high thermal conductive filler. As a result, the thermal conductivity necessary for the outermost surface layer of the heating member 30 can be achieved, and the outermost surface of the heating member can be provided with releasability, whereby an image forming apparatus capable of more stable operation can be obtained. .

  When an adhesive layer is required between the high thermal conductive solid rubber layer 33 and the high thermal conductive release layer 34, it is desirable to disperse the high thermal conductive filler in the adhesive layer to form a high thermal conductive adhesive layer.

  With the above-described configuration, a fixing device is provided that achieves a reduction in warm-up time, a short first print time, and energy saving even when the release layer 34 is provided on the outermost surface of the fixing roller 30. Is possible.

(Experiment 5)
In order to confirm the above effects, an experiment was conducted in the case where a release layer 34 made of a fluororesin was provided on the surface of the fixing roller.

  The configuration other than the fixing roller is the same as in Experiment 1, the process speed of the used image forming apparatus is 100 mm / sec, and a laser beam printer that performs printing of 16 sheets per minute is used. Further, the heating contact region Nh is formed with a width of 7 mm, and the fixing nip portion Nt is formed with a width of 7 mm.

  The fixing roller 30 used in the experiment has a configuration in which a fluororesin layer having a thickness of 15 μm is formed as a release layer 34 on the outermost layer of the configuration of the fixing rollers 16 to 22 used in Experiment 1.

That is, silicone having a thermal conductivity of 0.12 W / (m · K) and a volumetric heat capacity of 1.1 × 10 ⁶ J / (m ³ · K) is formed on the SUM metal core 31 having an outer diameter of 8 mm as the heat insulating elastic layer 32. A rubber layer is formed with a thickness of 2 mm. Further, a silicone solid rubber layer having a thermal conductivity of 0.3 W / (m · K) and a volumetric heat capacity of 1.5 × 10 ⁶ J / (m ³ · K) is formed on the outside as the heat storage layer 33, and the thickness thereof is changed. Further, a release layer 34 is provided on the outer side.

As for the fluororesin layer as the release layer 34, pure fluororesin generally has a low thermal conductivity of about 0.2 W / (m · K). In this experiment, PFA was used as the fluororesin. In this PFA, 10 to 50 parts by weight of alumina having a particle size of 4 to 6 μm was contained as a heat conductive filler, a volumetric heat capacity of 2.0 × 10 ³ (J / m ³ · K), a heat conductivity of 0. 3 (W / (m · K)) high thermal conductivity fluororesin was used.

  Table 3 shows the outline that was created.

  An experiment similar to Experiment 1 was performed using the above fixing rollers A23 to A29. The experimental results are shown in FIG. The horizontal axis is the heat capacity C / S of the heat storage layer per unit surface area of the fixing roller, and the vertical axis is the surface temperature of the fixing roller when the recording material is passed and the fixing performance is OK.

As in Experiment 1 of Example 1, when the heat capacity / surface area was 100 J / (m ² · K) or less, the necessary fixing roller surface temperature exceeded 230 ° C. Further, even when the heat capacity / surface area was 600 J / (m ² · K) or more, the fixing roller surface temperature at which the fixing performance was OK did not change.

  As described above, in this embodiment, the high heat conductive release layer 34 is provided on the outermost layer of the fixing roller 30 to obtain a fixing roller having good release property and slipperiness.

Even if there is a fluororesin layer as the outermost layer, the heat capacity / surface area of the heat storage layer of the fixing roller is set to 100 J / (m ² · K) or more and 600 J / (m ² · K) or less as in Example 1. As a result, it is possible to provide a fixing roller that can prevent destruction, stably perform fixing operation, and can effectively use the amount of heat stored.

Example 3
The embodiment in the present example is almost the same as that in the first example. However, as shown in FIG. 25, the pressure member 95 that forms the fixing nip portion Nt with the fixing roller 30 is externally fitted to the plate-shaped pressure members 90 and 91, and the plate-like member is added according to the rotation of the fixing roller 30. And a film 93 that rotates around the pressure members 90 and 91.

  The plate-like pressure members 90 and 91 are formed by forming a heat insulating member or a heat insulating layer 91 on a support 90 made of, for example, a SUM material. A film 93 having a low heat capacity and low heat conductivity is fitted on the outer periphery.

  The pressure member 95 and the fixing roller 30 are brought into contact with each other with a predetermined pressure to form the fixing nip portion Nt. At the fixing nip portion Nt, the recording material P is nipped and conveyed while the surface of the fixing roller and the film 93 are rotated, and heat and pressure are applied to the recording material to fix the toner image on the recording material.

  The heat insulating layer 91 may be an elastic member made of, for example, silicone rubber or fluorine rubber. However, since the surface of the fixing roller is an elastic body, the fixing nip portion Nt is secured even if the heat insulating layer 91 is a rigid body member. it can. That is, the heat insulating layer 91 may be a rigid member formed of a heat resistant resin such as a liquid crystal polymer, a phenol resin, PPS, PEEK, polyimide, polyamideimide, or a fluorine resin.

  The lower the thermal conductivity of the pressure member 95, the faster the temperature of the fixing roller surface rises. Therefore, the lower the thermal conductivity of the heat insulating layer 91, the better.

  When the heat insulating layer 91 is an elastic heat insulating layer, for example, a balloon-containing silicone elastic layer manufactured from an organopolysiloxane composition mixed with a hollow filler or an organopolysiloxane composition containing a water-absorbing polymer and water is suitable. ing. Alternatively, a bubble-containing silicone elastic layer or a silicone sponge elastic layer formed by foaming silicone rubber is suitable.

  In the case where the heat insulating layer 91 is a rigid heat insulating layer, if the contact surface with the fixing roller 30 is a smooth surface, the fixing nip portion Nt can be made smooth and the recording material can be transported excellently. A resin material that includes a hollow filler, such as a glass balloon or a silica balloon and has a low thermal conductivity, is also suitable for the rigid heat insulating layer.

  For example, the film 93 is formed on a base layer made of a resin material having a high heat resistance such as PPS, polyimide, or polyamideimide having a thickness of about 30 μm to 100 μm and having a low thermal conductivity. Formed by providing a mold layer.

  Since the film 93 has a low heat capacity and a low heat conduction, the heat to the film 93 and the heat radiation from the film surface to the atmosphere are small. A lubricant such as silicone oil is interposed between the plate-like pressure members 90 and 91 and the film 93 to improve the slidability of the film.

  The effect of the present embodiment is the same as that of the first embodiment, but the fixing device using the plate-like pressure member in the present embodiment has a simple configuration and can be downsized and have a low heat capacity. In addition, compared to the pressure roller, heat loss due to heat radiation to the atmosphere is small, which is suitable for shortening the warm-up time and saving energy.

  As described above, according to the configuration of the present embodiment, it is possible to provide a fixing device that achieves shortening of the warm-up time, realization of a short first print time, energy saving, and excellent image quality.

Example 4
The embodiment in the present embodiment is substantially the same as that in the fourth embodiment. However, as shown in FIG. 26, the pressure member 96 is a plate-shaped pressure member 90, 91, or 92 that is brought into sliding contact with the fixing roller 30. . The film 93 provided in Example 4 is not provided.

  The plate-like pressure members 90, 91, and 92 are formed by, for example, forming a heat insulating member or heat insulating layer 91 on a support 90 made of a SUM material, and further forming a sliding release layer 92. It is.

  The sliding release layer 92 is preferably made of a material having excellent slidability so as not to hinder the conveyance of the recording material P, and is preferably made of a material having excellent release properties so that toner transferred onto the fixing roller does not adhere. . For example, a sheet formed by bonding or coating a fluororesin sheet to form a sliding release layer is suitable.

  As the surface layer 33 of the fixing roller 33 in this embodiment, for example, a high thermal conductive elastic layer in which a high thermal conductive filler is blended with silicone rubber or fluoro rubber is suitable. A high thermal conductivity and a frictional force necessary for conveying the recording material can be obtained.

  By configuring the surface of the fixing roller to have a high coefficient of friction, the recording material can be conveyed.

  The fixing roller 30 and the pressure member 96 are brought into contact with each other with a predetermined pressure to form a fixing nip portion Nt. In the fixing nip portion Nt, the recording material is conveyed by the surface of the fixing roller due to the difference between the frictional force on the surface of the fixing roller and the frictional force of the plate-like pressure members 90, 91, and 92, and heat and pressure are applied to the recording material. Then, the toner image on the recording material is fixed.

  The effect of the present embodiment is the same as that of the first embodiment. However, the fixing device according to the present embodiment has a simple configuration and can be reduced in size and heat capacity. The fixing roller 30 and the plate-like pressure members 90, 91, and 92 are in contact with each other only at the fixing nip portion Nt and are thermally insulated. Therefore, heat loss due to heat transfer to the pressure member 96 and heat radiation to the atmosphere is extremely small, which is suitable for shortening the warm-up time and saving energy.

  As described above, according to the configuration of the present embodiment, it is possible to provide a fixing device that achieves shortening of the warm-up time, realization of a short first print time, energy saving, and excellent image quality.

  As in Example 4, the pressure member is a plate-like member that is always in contact with the heating member at the same location, thereby suppressing heat dissipation from the pressure member, reducing the heat capacity of the device, and reducing power consumption. A short first printout time can be achieved.

As described above, as described in each embodiment, it is possible to shorten the warm-up time and the first printout time while suppressing the occurrence of heating unevenness (fixing unevenness). In addition, power consumption can be reduced. That is, the inside of the heating member is a low thermal conductive elastic layer, and the outer and outermost surface has a heat capacity per unit surface area of the fixing member of 100 [J / (m ² · K)] or more and 600 [J / (m ^2). · K)] The following heat storage layer. As a result, the heat transferred from the external heating means to the surface of the heating member can be stored in a quantity of heat that can sufficiently heat and fix the image on the recording material only in the vicinity of the surface of the heating member.

  Appropriate heat capacity is provided near the surface of the heating member. Therefore, the surface temperature of the heating member necessary for heating the image on the recording material does not exceed the heat resistance temperature for continuous use such as an elastic layer made of silicone rubber constituting the fixing roller, and is higher than the toner on the recording material. It can be made the range. It is possible to provide a fixing roller that can store a sufficient amount of heat for heat-fixing a recording material, can use the stored heat amount effectively, and can be used stably without failure even though it has a low heat capacity.

Further, the relationship between the heat capacity / surface area of the heat storage layer of the fixing roller and the time t during which the recording material contacts the fixing roller 30 per rotation of the fixing roller is expressed as follows:
C / S [J / (m ² · K)] ≦ 10000 [J / (s · m ² · K)] × t [s]
And As a result, the amount of heat that can be transferred to the recording material within a specified contact time can be stored only in the vicinity of the surface of the fixing roller where the heat capacity is reduced, providing a heat-fixing device that consumes less energy and has a short warm-up time. it can.

  By providing a low thermal conductivity elastic layer having a low thermal conductivity in the lower layer of the heat storage layer, the escape of heat to the core of the heating member can be suppressed and the heating rate on the surface of the heating member can be increased. The time for raising the surface temperature of the heating member to the temperature required for fixing can be shortened. Further, by using the low thermal conductive layer as an elastic body, the adhesion of the surface of the heating member to the image can be improved, and a good image quality without heating unevenness can be obtained.

  Each of the above examples is an example of the best mode of the present invention, but the present invention is not limited to the configurations shown in these examples. That is, various modified configurations are possible within the scope of the idea of the present invention.

  1) For example, the heating means and the pressure member can be brought into pressure contact with and separated from the fixing roller by a contact / separation mechanism, and are brought into pressure contact with the fixing roller at a predetermined control timing when the fixing device is in operation. Sometimes, it can be configured to be separated from the fixing roller. Accordingly, it is possible to prevent the fixing roller elastic layer from being sagged due to the heating means and the pressure member always being in pressure contact with the fixing roller.

  2) The rotatable heating member for heating the image on the recording material at the nip portion is not limited to the roller form of the embodiment, and may be a flexible endless belt form.

  3) The heating means for heating the heating member from the outside can be a non-contact type such as an infrared lamp or electromagnetic induction heating means arranged in non-contact with the heating member.

  4) The image heating apparatus of the present invention is not limited to the heat fixing apparatus of the embodiment, but an image heating apparatus that modifies the surface properties such as gloss by heating a recording material carrying an image, an image heating apparatus that is supposed to be worn, etc. It can be used as an apparatus for heat-treating a recording material carrying an image.

2 is a schematic cross-sectional view of a fixing device in Embodiment 1. FIG. 1 is a schematic sectional view of an image forming apparatus in Embodiment 1. FIG. 3 is a schematic diagram of a fixing roller in Embodiment 1. FIG. FIG. 6 is a schematic diagram illustrating a method for measuring the thermal conductivity of a fixing roller constituent layer. It is typical sectional drawing of a plate-shaped heater. It is a structure typical sectional view of the plate heater of other composition. It is a structure typical sectional view of the plate heater of other composition. It is a structure typical sectional view of the plate heater of other composition. It is a structure typical sectional view of the plate heater of other composition. FIG. 10 is a schematic cross-sectional view of a fixing device having another configuration. It is a schematic diagram explaining the behavior in a fixing nip. FIG. 10 is a schematic cross-sectional view of a fixing device having another configuration. FIG. 10 is a schematic cross-sectional view of a fixing device having another configuration. FIG. 10 is an explanatory diagram of a temperature measurement procedure on the surface of the fixing roller. 6 is a graph showing a relationship between a heat capacity per unit surface area of a heat storage layer of a fixing roller and a fixing roller temperature necessary for heat fixing. 6 is a graph showing the relationship between the amount of heat per unit surface area of the heat storage layer of the fixing roller and the fixing roller temperature necessary for heat fixing. 6 is a graph showing a relationship between a heat capacity per unit surface area of a heat storage layer of a fixing roller and a fixing roller temperature necessary for heat fixing. 6 is a graph showing the relationship between the heat capacity per unit surface area of the heat storage layer of the fixing roller and the fixing roller temperature necessary for heat fixing, for each contact time between the fixing roller and the recording material. 6 is a graph showing the relationship between the amount of heat per unit surface area of the heat storage layer of the fixing roller and the temperature of the fixing roller necessary for heat fixing, for each contact time between the fixing roller and the recording material. 6 is a graph showing an efficient combination and a bad combination of the heat storage amount per unit surface area of the heat storage layer of the fixing roller and the contact time of the recording material. 6 is a graph showing a temperature rise of a thermocouple on a recording material that is in contact with a fixing roller. FIG. 3 is a schematic cross-sectional view (part 1) illustrating a layer configuration of a fixing roller of Example 2. FIG. 6 is a schematic cross-sectional view (No. 2) showing a layer configuration of a fixing roller of Example 2. 6 is a graph showing a relationship between a heat capacity per unit surface area of a heat storage layer of a fixing roller and a fixing roller temperature necessary for heat fixing. FIG. 6 is a schematic cross-sectional view of a fixing device of Example 3. FIG. 6 is a schematic cross-sectional view of a fixing device of Example 4. When the heat capacity of the heat storage layer is too large ((a) and (b): the heat capacity C / S per unit surface area is larger than 600 J / (m ² · K)) and when it is moderate ((c): C / An image comparing S with 600 J / (m ² · K) or less).

Explanation of symbols

  1 .. Image forming device 2. ..Sliding layer 22 ..Thermistor 24 ..Heater holder 30 ..Fixing roller 31 ..Core metal 32 ..Low thermal conductive elastic layer 33. Layer, 41 .. core metal, 42 .. elastic layer, 43 .. release layer, 63 .. pressure roller, Nh .. heating nip, Nt .. fixing nip, P .. recording material, T. toner

Claims (8)

A rotatable heating member having a heat insulating elastic layer and a heat storage layer comprising at least one layer provided outside the elastic layer, the surface of which is in contact with the toner image, and a recording material together with the heating member In an image heating apparatus that includes a nip forming member that forms a nip portion that sandwiches and conveys the toner, and a heater that heats the heating member from the outside, and that heats a toner image formed on a recording material,
The heat capacity C / S per unit surface area of the heat storage layer is
100 J / (m ² · K) ≦ C / S ≦ 600 J / (m ² · K)
An image heating apparatus characterized by satisfying the above. When the time required for one point of the surface of the heating member to pass through the nip portion is t, the heat capacity C / S per unit surface area of the heat storage layer is
C / S [J / (m ² · K)] ≦ 10000 [J / (s · m ² · K)] × t [s]
The image heating apparatus according to claim 1, wherein: The heating member has a plurality of heating modes having different peripheral speeds, and the time required for one point of the surface of the heating member to pass through the nip portion is t in the heating mode in which the peripheral speed of the heating member is the fastest. Then, the heat capacity C / S per unit surface area of the heat storage layer is
C / S [J / (m ² · K)] ≦ 10000 [J / (s · m ² · K)] × t [s]
The image heating apparatus according to claim 1, wherein:   The image heating apparatus according to claim 1, wherein the elastic layer has a thermal conductivity of 0.20 W / (m · K) or less.   The image heating apparatus according to claim 1, wherein a thickness of the heat storage layer is 30 μm or more and 400 μm or less. A rotatable heating member whose surface is in contact with the toner image on the recording material; a nip forming member that forms a nip portion that sandwiches and conveys the recording material together with the heating member; and a heater that heats the heating member from the outside. In the heating member used in the image heating apparatus having,
An elastic layer having heat insulation properties, and a heat storage layer that is provided outside the elastic layer and includes at least one layer, and a heat capacity C / S per unit surface area of the heat storage layer is 100 J / (m ² · K) ≦ C / S ≦ 600 J / (m ² · K).
A heating member characterized by satisfying   The heating member according to claim 6, wherein the elastic layer has a thermal conductivity of 0.20 W / (m · K) or less.   The heating member according to claim 6 or 7, wherein the heat storage layer has a thickness of 30 µm or more and 400 µm or less.