JP2012013864A - Image heating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-quality image by suppressing a temperature drop of a longitudinal end of a heating rotor in an image heating apparatus of external heating type.SOLUTION: A fixation device 10 allows a contact unit 6 to clamp and convey a recording material 4 and heats the recording material with the heat of a fixation roller 1 that is heated by heating means 3. In the fixation device 10, at least either one of the fixation roller 1 and a pressurizing roller 2 is provided with, in a rotation axis direction, an elastic layer (a low heat-conductive layer 12) which has parts whose thermal conductivity is lower than the thermal conductivity of a central part, at both sides of the central part.

Description

  The present invention relates to an image heating apparatus applied to an image forming apparatus having a function of forming an image on a recording material such as a sheet.

An image forming apparatus employing an electrophotographic system such as a copying machine, a printer, or a facsimile is equipped with a heat fixing device that fixes an unfixed toner image transferred onto a recording material such as transfer paper or OHP onto the recording material. It is provided as a device. As the heat fixing device, a pressure roller is brought into pressure contact with a fixing roller as a heated heating rotator, and the unfixed toner image is fixed by heating and melting an unfixed toner image while nipping and conveying the recording material between both rollers. The heat roller type used has been widely used. In recent years, a heating film type fixing device has been proposed as a heat fixing device excellent in terms of power consumption and waiting time in order to save energy and reduce waiting time. The heating film type is a film heating type fixing device that fixes a toner image on a recording material through a thin fixing film having a small heat capacity between a heating unit and a pressure roller. However, in the heating film method, since the fixing film is driven and rotated by the rotational drive of the pressure roller, the pressure is generally set lower than that in the heat roller method, and there is a slight disadvantage in increasing the speed.
Therefore, an external heating method has been newly proposed as a fixing method that can maintain the advantages of low power consumption and short wait time, and can easily cope with high speed.

In the external heating type fixing device, an external heating means for heating the surface (outer peripheral surface) of the fixing roller from the outside is provided, and the pressure roller is pressed against the surface of the fixing roller other than the portion heated by the external heating means. As a result, a nip portion is formed. The unfixed toner image is heated and melted and fixed while the recording material is nipped and conveyed at the nip portion (see Patent Document 1).
According to this method, by providing a high heat conductive layer made of an elastic body in the vicinity of the surface of the fixing roller, the amount of heat stored in the vicinity of the surface of the fixing roller can be increased, so that a fixing operation with higher thermal efficiency can be performed. Is possible. Specifically, the heat from the external heating means is sufficiently accumulated in the high heat conductive layer, and the heat is prevented from diffusing to the inner peripheral side of the fixing roller until it enters the nip portion. In the nip portion, the heat stored in the recording material is released. This process continues without interruption during the fixing process.
Furthermore, when a high thermal conductive layer is provided in the vicinity of the surface of the fixing roller, even if a difference in temperature occurs between the paper passing portion and the non-paper passing portion in the longitudinal direction of the fixing roller due to the passing of a small size recording material. As a result, the amount of heat in the longitudinal direction can be made uniform instantly with the high heat conductive layer. For this reason, the temperature distribution in the longitudinal direction is likely to be uniform, and the temperature increase at the non-sheet passing portion of the fixing roller hardly occurs.
As described above, by using an external heating type fixing device, it is possible to increase the speed while accommodating low power consumption and a short wait time.

JP 2002-123117 A

However, in the above-described external heating type fixing device, since heat conduction in the longitudinal direction of the fixing member is good, heat radiation from the longitudinal end portion of the fixing member is active, and the temperature of the fixing member is increased at the longitudinal end portion of the fixing member. There is a concern that a decrease will occur. After the fixing member has risen to a predetermined temperature, the heating element is controlled so as to reduce the amount of heat generated. For this reason, after the fixing member rises to a predetermined temperature, the heat radiation from the longitudinal end of the fixing member becomes relatively large with respect to the amount of heat supplied to the fixing member, and the longitudinal end of the fixing member There is a concern that the temperature drop will become increasingly noticeable.
When printing (image formation) proceeds, the temperature at the longitudinal end of the fixing member decreases as printing proceeds, and the unfixed toner image is fixed to the recording material at the longitudinal end of the recording material. There is concern about the occurrence of defects.

  The present invention has been made in view of the circumstances as described above, and obtains a high-quality image by suppressing a temperature drop at the end in the longitudinal direction of the heating rotator in an external heating type image heating apparatus. With the goal.

In order to achieve the above object, the present invention provides:
A heating rotator and a pressure rotator that are pressed against each other to form a nip portion;
A heating unit disposed on an outer peripheral side of the heating rotator, and heating at a position excluding the nip portion on an outer peripheral surface of the heating rotator;
In the image heating apparatus that sandwiches and conveys the recording material at the nip portion and heats the recording material with the heat of the heating rotating body heated by the heating unit,
At least one of the heating rotator and the pressurizing rotator is provided with portions having thermal conductivity lower than that of the central portion on both sides of the central portion in the rotation axis direction. It has one elastic layer.

  According to the present invention, in an external heating type image heating apparatus, it is possible to obtain a high-quality image by suppressing a temperature drop at the longitudinal end of the heating rotator.

Sectional drawing which shows schematic structure of the fixing apparatus of Example 1. FIG. FIG. 6 is a diagram for explaining a fixing roller according to a first embodiment. The figure for demonstrating formation of the low heat conductive layer of Example 1. FIG. The figure which shows the temperature distribution of the fixing roller after 1st sheet printing of Example 1, and 20th sheet printing The figure for demonstrating the fixing roller of a comparative example The figure which shows the temperature distribution of the fixing roller after the 1st sheet and 20th sheet printing of a comparative example FIG. 6 is a diagram for explaining a fixing roller according to a second embodiment. The figure which shows the temperature distribution of the fixing roller after the 1st sheet of Example 2, and 20th sheet printing. FIG. 6 is a diagram for explaining a fixing roller according to a third embodiment. The figure which shows the temperature distribution of the fixing roller after the 1st sheet of Example 3, and the 20th sheet printing FIG. 6 is a diagram for explaining a fixing roller according to a fourth embodiment. Sectional drawing which shows schematic structure of image forming apparatus

  DETAILED DESCRIPTION Exemplary embodiments for carrying out the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

Example 1 will be described below. FIG. 12 is a cross-sectional view showing a schematic configuration of an image forming apparatus employing an electrophotographic image forming process in the present embodiment.
As shown in FIG. 12, the photosensitive drum 51 is rotationally driven in the direction of the arrow, and first, the surface thereof is uniformly charged by the charging roller 52. Next, the laser scanner 53 performs scanning exposure with a laser beam L that is ON / OFF controlled according to image information, and an electrostatic latent image is formed on the photosensitive drum 51. This electrostatic latent image is developed and visualized by the developing device 54 using toner (developer). The visualized toner image (developer image) is transferred from the photosensitive drum 51 onto the recording material 4 conveyed at a predetermined timing by the transfer roller 55.
The recording material 4 conveyed at a predetermined timing is nipped and conveyed by the photosensitive drum 51 and the transfer roller 55 with a constant pressure. The recording material 4 onto which the toner image has been transferred is conveyed to a fixing device 10 as an image heating device and fixed as a permanent image. On the other hand, the transfer residual toner remaining on the photosensitive drum 51 is removed from the surface of the photosensitive drum 51 by the cleaning device 56.

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a fixing device 10 according to the present exemplary embodiment.
The fixing device 10 includes a fixing roller 1 as a heating rotator and a pressure roller 2 as a pressure rotator that are in pressure contact with each other to form a contact portion (nip portion) 6. 3 is an external heating system. The fixing device 10 records the toner image 5 by heating the recording material with the heat of the fixing roller 1 heated by the heating unit 3 while sandwiching and conveying the recording material 4 carrying the toner image 5 at the contact portion 6. It is fixed to the material 4.
The fixing roller 1 has an outer diameter of about 14 mm, and includes a low thermal conductive layer 12 as a first elastic layer formed of a low thermal conductive silicone rubber having a thickness of about 3 mm on the outside of a stainless steel core 11 having a diameter of 8 mm. ing. The fixing roller 1 further includes a high heat conductive layer 13 as a second elastic layer made of a high heat conductive silicone rubber having a thickness of 100 μm on the surface layer (outer peripheral side) of the low heat conductive layer 12, and a release made of a fluororesin having a thickness of 10 μm. Layer 14 is sequentially provided. In the fixing roller 1, the width in the longitudinal direction of all the layers on the core bar excluding the core bar 11 is 230 mm. Here, in the present embodiment, the longitudinal direction refers to the rotation axis direction of the fixing roller 1 or the pressure roller 2, and this is also the width direction of the recording material orthogonal to the recording material conveyance direction.

FIG. 2A is a schematic sectional view of the fixing roller 1 taken along the line AB in FIG. FIG. 2B is a diagram showing the thermal conductivity in the longitudinal direction of the low thermal conductive layer 12 in the fixing roller 1. FIG. 2C is a plan view showing a schematic configuration of the ceramic heater 31 provided in the heating means 3, and FIG. 2D is a schematic cross section of the ceramic heater 31 taken along the EF cross section of FIG. FIG.
As shown in FIG. 2A, in the low thermal conductive layer 12 in this embodiment, the glass balloon 122 is dispersed as a hollow filler (filler) in the silicone rubber 121, and as the dispersion amount of the glass balloon 122 increases, the glass balloon 122 increases. The thermal conductivity of the low thermal conductive layer 12 is reduced.
As shown in FIG. 2B, the thermal conductivity in the longitudinal direction of the low thermal conductive layer 12 is substantially constant in the longitudinal central portion (hereinafter referred to as the longitudinal central portion) of the recording material passage (paper passing) region X. . The thermal conductivity in the longitudinal direction of the low thermal conductive layer 12 is the longitudinal direction end face (edge) of the low thermal conductive layer 12 from the vicinity of the portion 40 mm from the longitudinal edge of the recording material passage region X toward the longitudinal center. It gradually gets smaller as you go to. The thermal conductivity of the low thermal conductive layer 12 is about 0.15 W / m · K at the longitudinal center, and is about 0.12 W / m at both ends in the longitudinal direction of the recording material passage region X provided so as to sandwich the longitudinal center. It is about 0.12 W / m · K in the recording material non-passing area Y. The thermal conductivity in the circumferential direction of the low thermal conductive layer 12 is substantially constant at each position in the longitudinal direction.

Although the details will be described later, since the longitudinal width of the recording material used in this embodiment is 210 mm, the relationship between the recording material passing area X and the recording material non-passing area Y in the longitudinal direction of the fixing roller 1 is shown in FIG. 2 (a) and (b). In addition, the longitudinal width of the heating energization resistor layer of the ceramic heater 31 used as a heating element in the present embodiment is 210 mm. For this reason, as shown in FIGS. 2A to 2C, the longitudinal position of the recording material passage region X of the fixing roller 1 and the longitudinal position of the energization heating resistor layer 312 of the ceramic heater 31 substantially overlap each other. ing.

FIG. 3 is a schematic diagram for explaining the application (formation) of the low thermal conductive layer 12 in the present embodiment. The metal core 11 is attached to the coating table 91 so that the center line of the cylindrical metal core 11 faces the vertical direction. The cored bar 11 is arranged inside a ring-shaped coating head 92 having an inner diameter substantially the same as the outer diameter of the cored bar 11 after the low thermal conductive layer 12 is applied to the surface thereof.
The low thermal conductive layer 12 is supplied to the gap between the inner peripheral surface of the coating head 92 and the cored bar 11, and the cored bar 11 is moved coaxially with the axis of the coating head 92 in the axial direction thereof. A low thermal conductive layer 12 having a thickness t is applied.
The supply path 94 and the supply path 95 supply solid silicone rubber 121 that does not include the glass balloon 122 and silicone rubber 121 in which many glass balloons 122 are dispersed to the relay tank 93. By changing these two types of supply ratios during coating, the dispersion amount of the glass balloon 122 of the low thermal conductive layer 12 is controlled in the longitudinal direction.

  The low thermal conductive elastic layer of the low thermal conductive layer 12 is a silicone rubber composition, and 0.1 to 200 parts by weight of a hollow filler having an average particle size of 500 μm or less is blended with 100 parts by weight of the thermosetting organopolysiloxane composition. It is formed by heating and curing a silicone rubber composition. Here, as the hollow filler, there is a microballoon material or the like that has a gas portion in the cured product and reduces the thermal conductivity like sponge rubber. As such a material, any glass balloon, silica balloon, carbon balloon, phenol balloon, acrylonitrile balloon, vinylidene chloride balloon, alumina balloon, zirconia balloon, shirasu balloon, etc. may be used.

The high thermal conductive layer 13 is made of solid (unfoamed) solid silicone rubber, and is added with high thermal conductive particles (alumina, aluminum nitride, quartz, etc.) in order to increase the thermal conductivity. In this embodiment, alumina particles are used. The thermal conductivity of the high thermal conductive layer 13 is higher than the thermal conductivity of the longitudinal central portion of the low thermal conductive layer 12, and the higher the thermal conductivity of the high thermal conductive layer 13, the better, and the high thermal conductivity used in this example. The layer 13 has a thermal conductivity of 1.5 W / m · K. In addition, the heat storage effect is obtained as the thickness of the high thermal conductive layer 13 is increased. However, if the thickness is too large, the heat capacity is large, so that the fixing roller temperature cannot be increased and the fixing efficiency may be deteriorated.
Further, it is desirable that the thickness of the high thermal conductive layer 13 is changed depending on the conveyance speed of the recording material 4. This is because the thickness of the layer where heat is exchanged varies depending on the conveyance speed of the recording material 4.

  According to the examination results of the present inventors, when the conveyance speed is slow, the heat existing from the surface of the high heat conductive layer 13 to a deeper part contributes to fixing, but as the conveyance speed increases, the high heat conductive layer It has been found that only the heat stored in the shallow part 13 contributes to fixing. That is, when the conveyance speed of the recording material 4 is high, the thickness of the high heat conductive layer 13 may be relatively thin. When a layer thicker than necessary is provided, the heat capacity increases, and the fixing efficiency may be deteriorated. Concerned. The recording material conveyance speed in this embodiment is about 100 mm / sec, and the optimum thickness at this speed is about 100 μm according to numerical calculation.

  In this embodiment, the release layer 14 is made of PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer) having no additive. PFA was mixed with an aqueous dispersion, and this was applied onto the high thermal conductive layer 13 and baked at a high temperature of 320 ° C. or higher to form a film. In this embodiment, PFA having no additive is used for the release layer 14, but PFA containing BN (boron nitride) particles of a heat conductive filler may be used as an additive. Further, the material of the release layer 14 is not limited to PFA, and other fluororesin materials such as PTFE (polytetrafluoroethylene) may be used. Further, since the silicone rubber itself used for the high thermal conductive layer 13 is excellent in releasability, a fixing roller configuration without the release layer 14 may be used.

The pressure roller 2 is formed by forming an elastic layer 22 of silicone rubber having a thickness of about 2.5 mm on the outside of a core metal 21 made of stainless steel having an outer diameter of 13 mm, and a release layer made of PFA having a thickness of about 30 μm on the surface layer. 23, and the width of the elastic layer in the longitudinal direction is about 230 mm. The elastic layer 22 used in this example is of a type in which hollow fillers are not dispersed. However, the hollow fillers may be dispersed as in the low heat conductive layer 12 of the fixing roller.
The fixing roller 1 and the pressure roller 2 are arranged so as to be parallel to each other in the axial direction, and are brought into pressure contact with a total pressure of 15 kgf (147 N). At this time, a contact portion 6 is formed between the fixing roller 1 and the pressure roller 2. The width of the contact portion 6 in this example was about 6 mm.
The fixing roller 1 is rotationally driven in a clockwise direction indicated by an arrow shown in FIG. 1 by a drive system (not shown), and the pressure roller 2 rotates following the rotation direction of the fixing roller 1, and an unfixed toner image is formed on the contact portion 6. When the recording material 4 loaded with 5 is introduced, the recording material 4 is nipped and conveyed in cooperation with the fixing roller 1.

The heating unit 3 is a unit that heats the fixing roller 1 from the outside of the fixing roller, that is, a unit that is disposed on the outer peripheral side of the fixing roller 1 and performs heating at a position excluding the contact portion 6 on the outer peripheral surface of the fixing roller 1. It is. The heating means 3 includes a ceramic heater 31 as a heating body, a stay 32 which is a support body that supports and heats the ceramic heater 31, and a thin cylindrical film 8 wound around the stay 32 that supports the ceramic heater 31. .
Here, the ceramic heater 31 will be described with reference to FIGS. The ceramic heater 31 has an alumina substrate 311 having a length of about 250 mm in the longitudinal direction and a width (length in the recording material conveyance direction) of about 6 mm. The ceramic heater 31 is a thin strip having a thickness of about 10 μm, a longitudinal length of about 210 mm, and a width of about 2.0 mm by screen printing an energization heating resistor layer 312 such as Ag / Pd (silver palladium) on an alumina substrate 311. The structure is applied in a folded pattern. The energization heating resistor layer 312 is applied so as to be line-symmetric with respect to the center of the substrate with respect to the width direction.
In the alumina substrate 311, two Ag / Pt electrodes 313 are formed in the vicinity of one of the longitudinal ends, and the conductive heating resistor layer 312 and the electrode 313 are made of the same material as the electrode 30. Are connected and are in a conductive state.

As shown in FIG. 2D, the energization heating resistor layer 312 is protected by a protective layer 315 made of glass having a thickness of about 50 μm, and the surface of the protective layer 315 slides on the film 8.
The film 8 is an endless film having a diameter of 18 mm in which a fluorine substrate having a thickness of about 10 μm is applied on a polyimide base material having a thickness of about 60 μm, and the width in the longitudinal direction is about 230 mm. When the fixing roller 1 is driven to rotate, it is driven to rotate.
In the heating means 3, the ceramic heater 31 is disposed so as to be parallel to the fixing roller 1 in the axial direction, and is in pressure contact with the fixing roller 1 with a total pressure of 15 kgf (147 N). At this time, a contact portion (nip portion) 7 is formed by the fixing roller 1 and the ceramic heater 31. The width of the contact portion 7 in this example was about 6 mm.

  When the fixing roller 1 is rotationally driven, the fixing roller 1 is rotated while sliding and friction with the ceramic heater 31 of the heating unit 3. Thereafter, the ceramic heater 31 is energized to generate heat, and the surface of the fixing roller 1 is heated. A temperature detecting means 33, specifically, an NTC (negative temperature coefficient) thermistor is in contact with the surface of the ceramic heater 31 on the alumina substrate 311 side, and the temperature of the ceramic heater 31 is monitored. The temperature detection means 33 inputs temperature information of the ceramic heater 31 to a control circuit (not shown). The control circuit controls power supply to the ceramic heater 31 so that the detected temperature of the ceramic heater 31 input from the temperature detecting means 33 is maintained at a predetermined temperature (fixing temperature). Thereby, the temperature of the ceramic heater 31 is adjusted to a predetermined temperature.

In this embodiment, the heating means for the fixing roller 1 is an external heating means for pressing the ceramic heater 31 to the fixing roller 1 through a film. However, the ceramic heater 31 is directly attached to the fixing roller 1 without using a film. You may use the heating means from the outside made to press-contact. Further, the heating unit of the fixing roller 1 is not limited to a contact type heating unit, and may be a non-contact external heating unit such as a halogen heater.

With the configuration in this embodiment, the temperature distribution in the longitudinal direction of the fixing roller 1 and the fixability of the unfixed toner image 5 on the recording material 4 were measured. The temperature distribution in the longitudinal direction of the fixing roller 1 was measured using a thermo viewer (manufactured by NEC Corporation).
The fixability indicates how much the toner image after fixing is fixed on the recording material 4 and is expressed as a density reduction rate (unit:%). The method for measuring the concentration reduction rate is as follows. As the recording material 4, A4 size plain paper (CANON EXTRA80 manufactured by Canon Inc.) having a basis weight of 80 g was used. The width of the recording material 4 in the longitudinal direction is 224 mm, and the width in the recording material conveyance direction is 296 mm. The unfixed toner image 5 on the recording material 4 has a half-tone (gray) 5 mm square image in the longitudinal direction both ends of the recording material at the leading end, the center, and the trailing end in the recording material transport direction. It is drawn in nine places in the center. The halftone pattern of the unfixed image is a pattern in which a pixel density of 600 dpi is formed by a 3 × 3 matrix, and this is formed in a staggered pattern with one dot and one space.

After measuring the halftone density of the image after passing through the fixing device with a density measuring device (manufactured by Macbeth), scrape the image with a dedicated rubbing tester and measure the halftone density after rubbing again to reduce the density. Calculate the rate.
The rubbing tester has a structure in which a metal weight of 200 g is placed on a table on which a recording material is fixed by static electricity in accordance with black and halftone patterns of 5 mm square disposed at nine locations on the recording material. Silbon C paper (manufactured by Ozu Sangyo Co., Ltd.) is sandwiched between the recording material and the weight. The table for fixing the recording material can reciprocate in the longitudinal direction of the recording material. At this time, the image is rubbed against the Sylbon C paper and is lost. In this example, the image was rubbed with 5 reciprocations.
The density reduction rate is calculated for all nine halftone images on the recording material, an average value is calculated, and this is used as an index representing the fixing strength under the conditions.

This measurement was performed in a laboratory maintained at a room temperature of 23 ° C. and a humidity of 50%. The recording material was loaded into the fixing device every 4 seconds, and the unfixed toner image 5 was fixed. The total number of printed sheets is 20. The temperature of the ceramic heater 31 was controlled so that the density reduction rate at the longitudinal center of the recording material was always around 20%.
4A is a diagram showing a temperature distribution in the longitudinal direction of the fixing roller 1 after printing the first sheet, and FIG. 4B is a temperature distribution in the longitudinal direction of the fixing roller 1 after printing the 20th sheet. FIG. Table 1 shows the results of measuring the fixability of the first sheet and the 20th sheet.

  Next, the structure of the comparative example 1 performed for the comparison with Example 1 is demonstrated. Here, the configuration and characteristics at both ends in the longitudinal direction are the same, and in the following description, one end side of both ends in the longitudinal direction will be described.

[Comparative Example 1]
FIG. 5A is a schematic cross-sectional view of the fixing roller used in this comparative example, and this cross section corresponds to the cross section AB in FIG. FIG. 5B is a diagram showing the thermal conductivity in the longitudinal direction of the low thermal conductive layer in the fixing roller of this comparative example. FIG. 6A is a diagram showing the temperature distribution in the longitudinal direction of the fixing roller after printing the first sheet, and FIG. 6B is the temperature distribution in the longitudinal direction of the fixing roller after printing the 20th sheet. FIG. Since the members constituting the fixing roller of this comparative example are the same as those in the first embodiment, the same reference numerals are used for convenience of explanation.
In the low thermal conductive layer 12 in this comparative example, the glass balloon 122 is dispersed in the silicone rubber 121, and the dispersion amount of the glass balloon is constant in both the longitudinal direction and the circumferential direction. Therefore, as shown in FIG. 5B, the thermal conductivity of the low thermal conductive layer 12 is approximately 0.15 W / m · k, which is substantially constant in the longitudinal direction and the circumferential direction. Other configurations are the same as those of the first embodiment.
In the configuration of this comparative example, the temperature distribution measurement in the longitudinal direction of the fixing roller 1 and the fixability measurement were performed in the same manner as in Example 1. The results of fixing property measurement are shown in Table 1.

In Example 1, as shown in FIG. 4, the temperature distribution in the longitudinal direction of the fixing roller 1 is substantially uniform in the recording material passage region X both after printing the first sheet and after printing the 20th sheet. In addition, as shown in Table 1, the fixability of the longitudinal end portion (hereinafter referred to as the longitudinal end portion) and the longitudinal center portion of the recording material 4 becomes substantially uniform after printing the first sheet and after printing the 20th sheet. Yes.
In Comparative Example 1, as shown in FIGS. 6 (a) and 6 (b), after printing the first sheet and after printing the 20th sheet, from the longitudinal edge of the recording material passage region X toward the longitudinal center side of 40 mm. The temperature of the fixing roller 1 starts to greatly decrease from the vicinity of the spot toward the end face in the longitudinal direction. In particular, the temperature drop at the longitudinal end is remarkable after printing the 20th sheet.
Further, as shown in Table 1, the fixability of the longitudinal end portion of the recording material 4 is 5% or more worse than the fixability of the longitudinal center portion after printing the first sheet and after printing the 20th sheet. In particular, after printing the 20th sheet, the fixability of the longitudinal end portion of the recording material 4 is 10% or more worse than the fixability of the longitudinal center portion.
A heat fixing device is widely used as a fixing device for fixing an unfixed toner image on a recording material. However, in the conventional fixing device of the heat fixing system, there is a concern that the temperature at the longitudinal end portion of the fixing member is lowered mainly due to heat radiation from the longitudinal end surface of the fixing member (fixing roller). In particular, after the temperature of the fixing member or the temperature of the heating element that supplies heat to the fixing member reaches a predetermined temperature, the heat generation amount of the heating element is controlled to be small. The amount of heat supplied is relatively small compared to the amount of heat released from the end surface in the longitudinal direction of the fixing member. For this reason, as the printing proceeds, the temperature drop at the longitudinal end of the fixing member becomes remarkable, and there is a concern that the fixing of the toner image to the recording material at the longitudinal end of the recording material may occur.
As shown in the result of Comparative Example 1, even in the external heating method, heat radiation is mainly generated from the longitudinal end surface of the fixing roller 1 and the core metal 11, and from the longitudinal end surface of the pressure roller 2 and the core metal 21. Therefore, the temperature of the longitudinal end portions of the fixing roller 1 and the pressure roller 2 gradually decreases, and as the result of the comparative example 1 shows, the fixing failure of the toner image occurs at the longitudinal end portion of the recording material 4 as the second half of printing. May occur.

However, in the configuration of the first exemplary embodiment, the thermal conductivity of the low thermal conductive layer 12 of the fixing roller 1 is decreased in the recording material passage region X from the longitudinal center to the longitudinal end surface. Therefore, when the heat flow in the radial direction of the fixing roller 1 is considered in the recording material passage region X, the amount of heat transferred from the high heat conductive layer 13 to the low heat conductive layer 12 is smaller toward the end surface in the longitudinal direction.
On the other hand, in the recording material passage region X, the amount of heat transferred from the ceramic heater 31 to the high thermal conductive layer 13 via the film 8 and the release layer 14 is substantially the same at the longitudinal end portion and the longitudinal central portion of the fixing roller 1. For this reason, in the recording material passage region X, the high thermal conductive layer 13 is more likely to store heat at the longitudinal end portion.
Further, in the configuration of Example 1, since the thermal conductivity of the low thermal conductive layer 12 at the longitudinal end portion of the fixing roller 1 is smaller than that in Comparative Example 1, when considering the heat flow in the radial direction, The amount of heat transferred from the low thermal conductive layer 12 to the core metal 11 is smaller at the longitudinal end than in the first comparative example.

The heat transmitted from the low thermal conductive layer 12 to the cored bar 11 is transmitted toward the longitudinal end of the cored bar 11 and is radiated from the surface of the cored bar 11 protruding from the longitudinal end face of the fixing roller 1.
As described above, in Example 1, since the amount of heat transferred from the low thermal conductive layer 12 at the longitudinal end portion to the core metal 11 is smaller than that in Comparative Example 1, heat dissipation through the core metal 11 at the longitudinal end portion of the low thermal conductive layer 12 is performed. Is getting smaller. Therefore, in Example 1, the low thermal conductive layer 12 at the longitudinal end portion is kept at a higher temperature than in Comparative Example 1, and at the same time, the high thermal conductive layer 13 at the longitudinal end portion is kept at a high temperature.

  In Example 1, since the thermal conductivity of the low thermal conductive layer 12 in the recording material non-passing region Y is reduced, heat is applied from the low thermal conductive layer 12 at the longitudinal end of the recording material passing region X toward the longitudinal end surface. The escape of is suppressed. For this reason, the influence of heat radiation on the end surface in the longitudinal direction of the low thermal conductive layer 12 cannot reach the low thermal conductive layer 12 at the longitudinal end of the recording material passage region X. Therefore, in Example 1, the temperature drop at the longitudinal end portion of the low thermal conductive layer 12 due to heat radiation from the longitudinal end surface of the low thermal conductive layer 12 is smaller than in Comparative Example 1. And since the temperature fall of the longitudinal end part of the low thermal conductive layer 12 is small, the temperature fall of the high thermal conductive layer 13 of a longitudinal end part also becomes small.

  As described above, according to this embodiment, the longitudinal end portion of the high thermal conductive layer 13 can be easily stored, and the high thermal conductive layer by heat radiation from the longitudinal end surfaces of the core metal 11 and the low thermal conductive layer 12 can be used. 13 can be suppressed. For this reason, in the recording material passage region X, the temperature of the longitudinal end portion of the high thermal conductive layer 13 is not extremely lowered than the temperature of the longitudinal center portion, and the surface temperature distribution of the fixing roller 1 is spread over the entire longitudinal direction. It can be made substantially uniform. In addition, the surface temperature distribution of the fixing roller 1 becomes substantially uniform over the entire length direction, thereby preventing defective fixing of the unfixed toner image 5 to the recording material 4 at the longitudinal end portion of the recording material 4. Can do. This makes it possible to obtain a high quality image.

  In this example, the thermal conductivity in the longitudinal direction of the low thermal conductive layer 12 was gradually reduced from the position toward the longitudinal central portion side from the longitudinal edge of the recording material passage region X toward the longitudinal end surface by 40 mm. The reason is as follows. As shown in the result of Comparative Example 1, in the external heating type fixing device of Example 1, when the low thermal conductive layer 12 having substantially constant thermal conductivity in the longitudinal direction and the circumferential direction is used for the fixing roller 1, This is because the temperature in the longitudinal direction of the fixing roller has started to decrease from the vicinity of the aforementioned portion. That is, the temperature in the longitudinal direction of the fixing roller has started to decrease from the vicinity of the portion from the longitudinal edge of the recording material passage region X toward the longitudinal center of 40 mm.

  As a result of this embodiment, by starting to lower the thermal conductivity of the elastic member (elastic layer) constituting the fixing roller 1 from the vicinity of the position where the temperature of the fixing roller 1 starts to decrease in the longitudinal direction, the longitudinal direction is increased. It can be seen that a uniform temperature distribution of the fixing roller 1 can be obtained. However, since the position at which the temperature of the fixing roller 1 begins to decrease in the longitudinal direction differs depending on the configuration of the fixing device and the fixing roller 1, the temperature distribution in the longitudinal direction of the fixing roller is confirmed for each of the fixing device and the fixing roller. It is better to determine the position in the longitudinal direction where the thermal conductivity of the material starts to decrease.

As described above, in this embodiment, the thermal conductivity of the low thermal conductive layer 12 of the fixing roller 1 is gradually decreased from the vicinity of the position where the temperature decrease at the end portion of the fixing roller 1 is significant in the longitudinal direction toward the end surface. The thermal conductivity of the longitudinal end portion of the low thermal conductive layer 12 is made smaller than that of the longitudinal center portion. As a result, it can be seen that the temperature drop at the longitudinal end portion of the fixing roller 1 is suppressed and the fixing failure of the unfixed toner image 5 at the longitudinal end portion of the recording material 4 to the recording material 4 is suppressed. .
Here, in this embodiment, the low thermal conductive layer 12 of the fixing roller 1 is configured by one elastic layer, but is not limited thereto. Similarly to the present embodiment, if the longitudinal end portion is a low thermal conductive layer having a lower thermal conductivity than the longitudinal central portion, even if the low thermal conductive layer is composed of two or more elastic layers, the present embodiment The same effect can be obtained.
Further, in this embodiment, the thermal conductivity of the low thermal conductive layer 12 of the fixing roller 1 is gradually decreased from the vicinity of the position where the temperature decrease at the end of the fixing roller 1 becomes significant in the longitudinal direction toward the end surface. However, it is not limited to this. For example, it is sufficient that at least a part of the thermal conductivity of the longitudinal end portion of the elastic layer constituting the fixing roller 1 is smaller than the thermal conductivity of the longitudinal central portion. Further, at least a part of the longitudinal end portion of the elastic layer constituting the pressure roller 2 may have a thermal conductivity smaller than that of the longitudinal central portion. That is, an elastic layer in which at least one of the fixing roller 1 and the pressure roller 2 has portions having thermal conductivity lower than that of the central portion in the longitudinal direction on both sides of the central portion. What is necessary is just to have. Such a form will be described in detail in the following examples.

  Example 2 will be described below. FIG. 7A is a schematic sectional view of the fixing roller used in this embodiment, and this section corresponds to the section AB in FIG. FIG. 7B is a diagram showing the thermal conductivity in the longitudinal direction of the low thermal conductive layer in the fixing roller. FIG. 8A is a diagram showing the temperature distribution in the longitudinal direction of the fixing roller after printing the first sheet, and FIG. 8B is the temperature distribution in the longitudinal direction of the fixing roller after printing the 20th sheet. FIG. The members constituting the fixing roller of this embodiment are the same as those of the first embodiment, and the same reference numerals as those of the first embodiment are used. The configuration and characteristics at both ends in the longitudinal direction are the same. In this embodiment, one end side of the both ends in the longitudinal direction will be described.

In the fixing roller 1 of this embodiment, as shown in FIG. 7B, the thermal conductivity in the longitudinal direction of the low thermal conductive layer 12 is 40 mm long from the longitudinal edge of the recording material passage region X in the recording material passage region X. It gradually decreases as it goes from the portion toward the center side toward the longitudinal edge. In the fixing roller 1 of this embodiment, the thermal conductivity of the low thermal conductive layer 12 is about 0.15 W / m · K at the longitudinal center and about 0.12 W / m · K at the longitudinal edge of the recording material passage region X. It is. However, in the recording material non-passing area Y, the thermal conductivity of the low thermal conductive layer 12 increases toward the edge in the longitudinal direction, and about 0.15 W / m · K at the longitudinal edge of the recording material non-passing area Y. It is. The thermal conductivity in the circumferential direction of the low thermal conductive layer 12 is substantially constant at each position in the longitudinal direction.
With the configuration in this example, fixability measurement was performed in the same manner as in Example 1. The results of fixing property measurement are shown in Table 1.

  In this embodiment, as shown in FIGS. 8A and 8B, the temperature distribution in the longitudinal direction of the fixing roller 1 is higher than that of the comparative example 1 after printing the first sheet and after printing the 20th sheet. In the passing region X, the region is nearly uniform. Further, as shown in Table 1, the fixability of the longitudinal end portion and the longitudinal center portion of the first recording material 4 is substantially the same, and the fixability of the longitudinal end portion and the longitudinal center portion is also the 20th sheet. The difference is as small as 3%.

  In this embodiment, unlike the first embodiment, the thermal conductivity of the low thermal conductive layer 12 in the vicinity of the edge in the longitudinal direction of the recording material non-passing region Y is large. Even large heat dissipation occurs. However, since the thermal conductivity of the low thermal conductive layer 12 in the recording material non-passing region Y on the side close to the longitudinal edge of the recording material passage region X is small, heat radiation occurs from the longitudinal edge of the recording material passage region X. The escape of heat to the longitudinal end face of the low thermal conductive layer 12 is suppressed. Therefore, as in the first embodiment, in the recording material passage region X, the temperature of the longitudinal end portion of the high thermal conductive layer 13 is not extremely lowered than the temperature of the longitudinal center portion, and the surface temperature distribution of the fixing roller 1 is It becomes substantially uniform over the entire length direction. Therefore, it is possible to suppress fixing failure of the unfixed toner image 5 on the recording material 4 at the longitudinal end portion of the recording material 4.

  As described above, in the present embodiment, the thermal conductivity in the longitudinal direction of the low thermal conductive layer 12 of the fixing roller 1 is gradually reduced from the vicinity of the position where the temperature decrease of the fixing roller 1 becomes remarkable toward the longitudinal end surface, The thermal conductivity of a part of the longitudinal end portion of the low thermal conductive layer 12 is made smaller than that of the longitudinal central portion. Even in this case, the same effects as those of the first embodiment can be sufficiently obtained.

  Example 3 will be described below. FIG. 9A is a schematic cross-sectional view of the fixing roller used in this embodiment, and this cross-section corresponds to a cross section AB in FIG. FIG. 9B is a diagram showing the thermal conductivity in the longitudinal direction of the low thermal conductive layer in the fixing roller. FIG. 10A is a diagram showing the temperature distribution in the longitudinal direction of the fixing roller after printing the first sheet, and FIG. 10B is the temperature distribution in the longitudinal direction of the fixing roller after printing the 20th sheet. FIG. The members constituting the fixing roller of this embodiment are the same as those of the first embodiment, and the same reference numerals as those of the first embodiment are used. The configuration and characteristics at both ends in the longitudinal direction are the same. In this embodiment, one end side of the both ends in the longitudinal direction will be described.

In the fixing roller 1 of the present embodiment, as shown in FIG. 9B, the thermal conductivity in the longitudinal direction of the low thermal conductive layer 12 is abruptly changed at a portion where the longitudinal central portion is shifted to the longitudinal end portion. . The thermal conductivity of the low thermal conductive layer 12 is 0.13 W / m · K in the range of 40 mm from the longitudinal edge of the recording material passage region X to the longitudinal central portion, and 0.15 W / m · K in the longitudinal central portion. is there.
With the configuration in this example, fixability measurement was performed in the same manner as in Example 1. The results of fixing property measurement are shown in Table 1.

  In Example 3, as shown in FIGS. 10A and 10B, the temperature distribution in the longitudinal direction of the fixing roller 1 is higher than that of Comparative Example 1 after printing the first sheet and after printing the 20th sheet. In the passing region X, the region is nearly uniform. Further, as shown in Table 1, the fixability of the first sheet is about 2% better at the longitudinal end portion of the recording material 4 than the longitudinal central portion, and at the 20th sheet, the longitudinal central portion is longer at the longitudinal end portion. However, the difference in fixability between the longitudinal center portion and the longitudinal end portion is small in both the first and twentieth sheets.

In the present embodiment, the thermal conductivity of the low thermal conductive layer 12 is made smaller than that of the longitudinal central portion in the longitudinal end portion of the recording material passage region X and the recording material non-passage region Y. For this reason, in addition to the fact that the longitudinal end portion of the high thermal conductive layer 13 is easy to store heat as in the first embodiment, the high thermal conductive layer 13 of the core metal 11 and the low thermal conductive layer 12 is radiated from the longitudinal end surfaces. The temperature drop is suppressed.
Therefore, in the recording material passage region X, the temperature of the longitudinal end portion of the high thermal conductive layer 13 is not extremely lowered than the temperature of the longitudinal central portion, and the recording of the unfixed toner image 5 at the longitudinal end portion of the recording material 4 is performed. Fixing defects on the material 4 can be suppressed.

However, unlike the first embodiment, this embodiment has a sharp decrease in the thermal conductivity of the low thermal conductive layer 12 from the longitudinal center to the longitudinal end.
A large amount of heat escapes from the high thermal conductive layer 13 to the low thermal conductive layer 12 at the location where the thermal conductivity of the low thermal conductive layer 12 is large, and from the high thermal conductive layer 13 to the low thermal conductive layer 12 where the thermal conductivity of the low thermal conductive layer 12 is small. The amount of heat that escapes is small. For this reason, at the boundary where the thermal conductivity of the low thermal conductive layer 12 changes suddenly, a sudden temperature gradient in the longitudinal direction is instantaneously formed in the high thermal conductive layer 13.
However, the high thermal conductive layer 13 has a high thermal conductivity. For this reason, even if there is an instantaneously steep temperature gradient on the inner peripheral surface side of the high thermal conductive layer 13, the temperature gradient is immediately leveled, and the temperature distribution in the longitudinal direction of the fixing roller shown in FIGS. 10 (a) and 10 (b). As described above, in the recording material passage region X of the fixing roller 1, a substantially uniform temperature distribution is obtained over the entire longitudinal direction.

As described above, in this embodiment, the thermal conductivity in the longitudinal direction of the low thermal conductive layer 12 of the fixing roller 1 is abruptly decreased from the vicinity of the position where the temperature decrease of the fixing roller 1 becomes significant toward the longitudinal edge. ,
The thermal conductivity of a part of the longitudinal end portion of the low thermal conductive layer 12 is made smaller than that of the longitudinal central portion. Even in this case, the same effects as those of the first embodiment can be sufficiently obtained.

  Hereinafter, Example 4 will be described. FIG. 11A is a schematic sectional view of the pressure roller used in this embodiment, and this section corresponds to the CD section of FIG. FIG. 11B is a diagram showing the thermal conductivity in the longitudinal direction of the low thermal conductive layer in the fixing roller. The members constituting the fixing roller of this embodiment are the same as those of the first embodiment, and the same reference numerals as those of the first embodiment are used. The configuration and characteristics at both ends in the longitudinal direction are the same. In this embodiment, one end side of the both ends in the longitudinal direction will be described.

In the low heat conductive layer 12 of the fixing roller 1 of this embodiment, the glass balloon 122 is dispersed in the silicone rubber 121, and the dispersion amount of the glass balloon 122 is constant in both the longitudinal direction and the circumferential direction. Therefore, the thermal conductivity of the low thermal conductive layer 12 is substantially constant in the longitudinal direction and the circumferential direction and is about 0.15 W / m · K.
In the pressure roller 2 of this embodiment, as shown in FIG. 11A, the elastic layer 22 has a glass balloon 222 dispersed as a hollow filler in a silicone rubber 221. Here, as described above, the thermal conductivity of the elastic layer 22 decreases as the dispersion amount of the glass balloon 222 increases.
As shown in FIG. 11B, the thermal conductivity in the longitudinal direction of the elastic layer 22 is substantially constant at the longitudinal central portion of the recording material passage region X, and is long from the longitudinal edge of the recording material passage region X. It gradually decreases as it goes from the location 40 mm toward the center to the edge in the longitudinal direction. The thermal conductivity of the elastic layer 22 is about 0.15 W / m · K at the longitudinal center, about 0.12 W / m · K at the longitudinal edge of the recording material passage region X, and about about the recording material non-passing region Y. 0.12 W / m · K. The thermal conductivity in the circumferential direction of the elastic layer 22 is substantially constant at each position in the longitudinal direction. With the configuration in this example, the same fixing property as in Example 1 was measured. The results are shown in Table 1.

In this embodiment, the fixability of the longitudinal center portion and the longitudinal end portion of the recording material 4 was about 3% for the first sheet and about 5% for the 20th sheet, and the longitudinal end portion was worse than the longitudinal center portion. . However, as compared with Comparative Example 1, it can be seen that the difference in fixability between the longitudinal center portion and the longitudinal end portion of the recording material 4 is small for both the first and twentieth sheets.
Since the thermal conductivity of the longitudinal end portion of the elastic layer 22 of the pressure roller 2 is lower than the longitudinal center portion, the amount of heat transferred from the fixing roller 1 to the pressure roller 2 is longer at the longitudinal end portion of the fixing roller 1. Smaller than part. Therefore, the high heat conductive layer 13 at the longitudinal end of the fixing roller 1 stores more heat than the longitudinal central portion. For this reason, even if heat escapes from the longitudinal end portion of the fixing roller 1 due to heat radiation from the longitudinal end surface of the fixing roller 1, the temperature of the longitudinal end portion of the fixing roller 1 is not significantly lower than the temperature of the longitudinal central portion. No. For this reason, the temperature distribution in the longitudinal direction of the fixing roller 1 becomes nearly uniform, and defective fixing of the unfixed toner image 5 to the recording material 4 at the longitudinal end portion of the recording material 4 is suppressed.

As described above, in this embodiment, the pressure roller 2 is constituted by the core metal 21 and the one elastic layer 22 on the core metal 21, and the thermal conductivity of the longitudinal end portion of the elastic layer 22 is the longitudinal center part. A roller smaller than the thermal conductivity is used. As a result, it can be seen that the temperature drop at the longitudinal end of the fixing roller 1 can be suppressed, and the fixing failure of the unfixed toner image 5 at the longitudinal end of the recording material 4 to the recording material 4 can be suppressed.
Further, as the pressure roller 2, the elastic layer 22 is composed of two layers of a high heat conductive layer and a low heat conductive layer, and at least a part of the thermal conductivity of the longitudinal end portion of the low thermal conductive layer has a thermal conductivity of the longitudinal central portion. A roller having a lower rate may be used. Further, at least one of the fixing roller 1 and the pressure roller 2 is constituted by a cored bar and a single elastic layer on the cored bar, and at least a part of the thermal end of the elastic layer is heated. A roller having a smaller conductivity than the thermal conductivity of the central portion in the longitudinal direction may be used. This also suppresses a temperature drop at the longitudinal end portion of the fixing roller and suppresses the fixing failure of the unfixed toner image 5 to the recording material 4 at the longitudinal end portion of the recording material.
Note that the image heating apparatus according to the present invention is not limited to the example in the case of functioning as the above-described fixing device, and can also be applied as an apparatus for giving gloss to a toner image fixed on a sheet. .

DESCRIPTION OF SYMBOLS 1 Fixing roller; 2 Pressure roller; 3 Heating means; 6 Contact part; 10 Fixing device; 12 Low heat conductive layer

Claims (2)

A heating rotator and a pressure rotator that are pressed against each other to form a nip portion;
A heating unit disposed on an outer peripheral side of the heating rotator, and heating at a position excluding the nip portion on an outer peripheral surface of the heating rotator;
In the image heating apparatus that sandwiches and conveys the recording material at the nip portion and heats the recording material with the heat of the heating rotating body heated by the heating unit,
At least one of the heating rotator and the pressurizing rotator is provided with portions having thermal conductivity lower than that of the central portion on both sides of the central portion in the rotation axis direction. An image heating apparatus having one elastic layer.   The second elastic layer having a thermal conductivity higher than that of the central portion of the first elastic layer is provided on the outer peripheral side of the first elastic layer. The image heating apparatus described.

Images