JP5196804B2 - Image heating device - Google Patents

Description

The present invention relates to an image heating apparatus, and is suitable for use in an image heating fixing apparatus (fixing device) mounted on an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer.

  As an image heating fixing device (fixing device) mounted on an image forming apparatus such as an electrophotographic copying machine or a printer, there is a film heating type. A film heating type fixing device forms a heater and a nip portion via a fixing film, a heater having a resistance heating element on a ceramic substrate, a flexible fixing film that moves while contacting the heater, and the fixing film. And a pressure roller. Patent Documents 1 to 4 describe this type of fixing device. The recording material carrying the unfixed toner image is heated while being nipped and conveyed by the nip portion of the fixing device, whereby the toner image on the recording material is heated and fixed to the recording material. This fixing device has an advantage that the time required for starting energization of the heater and raising the temperature to the fixable temperature is short. Therefore, a printer equipped with this fixing device can shorten the time (FPOT: First printout time) until the first image is output after a print command is input. This fixing device also has an advantage that power consumption during standby for waiting for a print command is small.

  Since the above-described fixing device has the above-described advantages, it has been mounted on a high-speed image forming apparatus from a low-speed image forming apparatus. When mounted in a high-speed image forming apparatus, it is necessary to supply sufficient thermal energy to the recording material whose passing time through the nip portion is shortened, and a metal such as SUS (stainless steel) excellent in heat conduction as a fixing film. It has been proposed to use a fixing sleeve having a base layer made of metal. In this fixing sleeve, an elastic layer such as silicone rubber is provided on the outer periphery of the base layer, and a fluororesin layer is provided on the outer periphery of the elastic layer as a release layer (outermost layer) in order to improve releasability from the toner. Yes. Also for the pressure roller, an elastic layer made of sponge or solid rubber formed from silicone rubber or the like is provided on the outer periphery of the core metal, and a release layer (outermost layer) for preventing toner adhesion on the outer periphery of the elastic layer. It has been proposed to provide a fluororesin layer.

  In addition, in such a fixing device, the toner forming an unfixed toner image on the recording material is adsorbed to the recording material by electrostatic force. Therefore, in order to prevent the toner from adhering to the outer peripheral surface (surface) of the fixing sleeve (flexible sleeve) at the nip portion, the electric potential of the fixing sleeve surface and the electric potential of the outer peripheral surface (surface) of the pressure roller (pressing member) are set. An absolute potential difference is provided. That is, a configuration is adopted in which the negatively charged toner is transferred to the surface of the fixing sleeve and no offset occurs. More specifically, the fluororesin layer is negatively charged by applying a negative voltage having the same polarity as the toner to the fixing sleeve. At the same time, the pressure roller applies a positive voltage having a polarity opposite to that of the toner to the core metal, and similarly charges the release layer of the pressure roller to a positive potential or a negative potential lower than that of the fixing sleeve. As a result, a potential difference that prevents offset is maintained between the fixing sleeve and the pressure roller, and a good fixed image is output.

Here, when the release layer of the fixing sleeve and the pressure roller is used alone with an insulating fluororesin layer of PFA or PTFE, the surface resistance value is 23 ± 3 ° C. in a measurement environment of 50 ± 5% RH. 1.0 × 10 ¹⁶ (Ω / □) (DC 1000 V applied) or more.

When a conductive fluororesin layer is used, the surface resistance value is 1.0 × 10 ⁵ to 1 in the above measurement environment in order to maintain the releasability of the outermost layer and prevent adhesion of toner, paper powder, and the like. Generally, the range is about 0.0 × 10 ¹² (Ω / □) (DC 1000 V applied). This is because as the content of conductive particles (conductive material) such as carbon increases, the surface roughness increases and toner, paper powder, and the like are likely to adhere.

In the measurement of the surface resistance described above, the measurement environment is defined for the following reason. That is, the measurement resistance range is a high resistance region, and it becomes difficult to perform accurate surface resistance measurement according to a subtle change in temperature / humidity in the air, that is, a change in the amount of saturated water vapor. In other words, since saturated water vapor is involved as a current path in the application of DC 1000 V during resistance measurement, the surface resistance is measured low in the case of high humidity and high in the case of high humidity. In addition, since the saturated water vapor amount is also affected by temperature, the temperature and humidity are regulated to regulate the moisture amount in the measurement environment to improve the measurement accuracy of the surface resistance. In this surface resistance measurement, DC 1000 V was applied for at least 10 seconds in a measurement environment: 23 ± 3 ° C. and 50 ± 5% RH, and the Max value was measured. Furthermore, when the conductive particles such as carbon are made conductive, the resistance value tends to decrease when the amount of voltage applied during surface measurement increases. Therefore, in this application, the applied voltage in the surface resistance measurement is fixed at 1000 V, and the standard of the surface resistance is determined.
JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980

  In recent years, neutral paper has been used as a recording material used in image forming apparatuses. This is a recording material filled with calcium carbonate. The reason why calcium carbonate is used in place of talc as a filler is that it is easy to increase the whiteness of the recording material, does not cause image flow, and is cheaper than other fillers used. Therefore, depending on the recording material, it may be contained by about 25% by weight.

  However, when a recording material containing calcium carbonate (hereinafter referred to as charcoal paper) is used in the fixing device as described above, the following problems occur.

Since calcium carbonate has insulating properties, charcoal paper containing a large amount thereof tends to have a relatively high resistance as a recording material. For this reason, as the speed of the image forming apparatus increases, if such a large amount of charcoal paper is used continuously, the surface potential of the pressure roller becomes excessively negative due to friction between the recording material and the pressure roller surface. Charge (charge up). For example, when a fluororesin layer is used as the release layer of the pressure roller, the surface resistance value of the pressure roller is as high as 1.0 × 10 ¹⁶ (Ω / □) (when DC 1000 V is applied) or higher. The surface potential is excessively negatively charged up. For this reason, even when a voltage having a polarity opposite to that of the toner is applied to the core of the pressure roller as in the fixing device described in the conventional example, the negative potential is higher than that of the fixing sleeve to which the voltage having the same polarity as that of the toner is applied. Thus, the toner is transferred to the fixing sleeve, and an offset is generated. This phenomenon is remarkable because the pressure roller surface layer is excessively negatively charged especially when the paper is continuously passed, that is, when the fixing sleeve and the pressure roller surface layer are in direct contact (sliding). Thus, in order to eliminate the charge-up of the pressure roller surface layer, it is conceivable to increase the voltage applied to the core of the pressure roller. However, there are problems such as an increase in cost and a leak of bias.

  Further, when a fluorine resin containing conductive particles which is difficult to be charged is used for the release layer of the pressure roller, although it is slight, a charge-up phenomenon occurs and becomes noticeable as the speed of the apparatus increases. In order to avoid this, when the content of the conductive particles is increased, the releasability of the surface layer of the pressure roller is deteriorated, so that paper dust and toner are applied to the surface of the pressure roller when the carbonized paper is continuously fed. It becomes easy to adhere and recording material stains due to contamination occur. First of all, when charcoal calcareous paper is used, paper dust is generated by rubbing against a metal or plastic member used in the recording material conveyance path. Calcium carbonate or paper dust containing calcium carbonate has a characteristic that it easily becomes positively charged by friction with the conveyance path member of the recording material. Therefore, the fixing sleeve is configured not to have a positive surface potential in order to prevent the negatively charged toner from being offset to the fixing sleeve. Therefore, positively charged calcium carbonate or paper powder containing calcium carbonate is first electrostatically adsorbed on the surface of the fixing sleeve. Subsequently, when positively charged calcium carbonate or the like adheres to the fixing sleeve, the negative potential on the surface of the fixing sleeve is offset, and the toner is easily offset. The toner offset to the fixing sleeve is added in a very small amount until the recording material is discharged from the nip portion and the next recording material enters the nip portion (no recording material in the nip portion). It will also transfer to the surface of the pressure roller.

  Even if the amount of offset toner generated from one sheet of recording material is extremely small, the toner adhering to the pressure roller surface grows as a lump by passing several thousand to several tens of thousands of charcoal cal paper. It adheres to the image surface and the opposite surface of the recording material and causes image smearing.

  In addition, if the content of the conductive particles is increased, the resistance of the pressure roller surface layer is low, the negatively charged toner leaks, the image is distorted, toner scattering occurs, and the tailing may be deteriorated. Is done.

An object of the present invention is to provide an image heating apparatus having a pressure roller that can reduce toner offset and toner adhesion.

Configuration of the image heating apparatus according to the present invention for achieving the above object, a sleeve having a flexible, a heating element for heating the pre-kissing sleeve, a core metal, provided outside the metal core includes an elastic layer, and a pressure roller to form a nip portion in contact with said sleeve has a fluororesin tube or a fluororesin coating and release layer formed by the outer peripheral surface of the elastic layer, in an image heating apparatus for heating while feeding transportable recording material carrying the toner image by the nip, the surface resistivity of the releasing layer, 23 ± 3 ° C., and have you to 50 ± 5% RH in the measurement environment 2 . ^{0 × 10 13 ~8.0 × 10 15} (Ω / □) in the range of (1000V DC applied), a DC voltage having a polarity opposite to that of toner on the pressure roller, before kiss leave the same polarity as the toner of A direct current voltage is applied, respectively.

According to the present invention, it is possible to provide an image heating apparatus having a pressure roller that can reduce toner offset and toner adhesion.

  The present invention will be described with reference to the drawings.

(1) Example of Image Forming Apparatus FIG. 1 is a structural model diagram of an example of an image forming apparatus in which the image heating apparatus according to the present invention can be mounted as an image heating fixing apparatus. This image forming apparatus is an electrophotographic laser beam printer.

In the image forming apparatus shown in this embodiment, when a print signal is input, a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 11 as an image carrier rotates in the direction of an arrow. The outer peripheral surface (surface) of the photosensitive drum 11 is uniformly charged to a predetermined polarity and potential by a charging roller 12 as a charging means. A laser exposure apparatus 10 as an exposure unit irradiates a charged surface on the surface of the photosensitive drum 11 with laser light L generated based on image information from an external apparatus (not shown) such as an image scanner or a computer to perform scanning exposure. . As a result, an electrostatic latent image (electrostatic image) corresponding to the image information is formed on the surface of the photosensitive drum 11. The electrostatic latent image is developed (visualized) as a toner image (developed image) using toner (developer) by a developing roller 13a of a developing device 13 as a developing unit.

  On the other hand, the recording material P stored in the feeding cassette 17 is separated and fed one by one by the feeding roller 18 and conveyed to the registration roller 21 through the sheet path 20 by the conveying roller 19. The registration roller 21 sends the recording material P to the transfer portion T between the photosensitive drum 11 and the transfer roller 16 at a predetermined control timing. The recording material P is nipped and conveyed by the transfer portion T, and the toner image on the surface of the photosensitive drum 11 is sequentially electrostatically transferred onto the recording material P surface in the conveyance process. The recording material P that has received the transfer of the toner image at the transfer portion T is conveyed to the fixing device 22, and the toner image is heated and fixed to the recording material P by the fixing device 22. Then, the recording material P exiting the fixing device 22 is discharged to a discharge tray 25 at the upper part of the printer main body by discharge rollers 23 and 24.

  The surface of the photosensitive drum 11 after the transfer of the toner image is subjected to repeated image formation by removing deposits such as transfer residual toner and paper dust by a cleaning blade 14 a of the cleaning device 14.

  In the printer of this embodiment, the photosensitive drum 11, the charging roller 12, the developing device 13, and the cleaning device 14 are integrated into a cartridge. The process cartridge 15 is detachably attached to the printer body.

(2) Fixing Device FIG. 2 is a schematic cross-sectional view of an example of the fixing device 22. FIG. 3 is a schematic longitudinal sectional view of the fixing device 22 shown in FIG. 4 is a view of the fixing device 22 shown in FIG. 2 as viewed from the recording material introduction side. This fixing device is a film heating type device.

  In the following description, with respect to the fixing device or the members constituting the fixing device, the longitudinal direction is a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The short side direction is a direction parallel to the recording material conveyance direction on the surface of the recording material. The width is a dimension in the short direction.

  The fixing device 22 shown in this embodiment includes a heater 31 as a heating body, a stay holder 32 as a guide member, a rigid stay 34 as a support member, a fixing sleeve 33 as a flexible sleeve, and a roller or roll. And a pressure member 40 in the form of The pressure member 40 shown in this embodiment is in the form of a roller. The heater 31, the stay holder 32, the rigid stay 34, the fixing sleeve 33, and the pressure member 40 are all elongated in the longitudinal direction.

The holder 32 is for holding the heater 31 and preventing heat radiation to the side opposite to a nip portion N described later. The holder 32 is formed in a saddle shape having a substantially semicircular cross section using a material such as liquid crystal polymer, phenol resin, PPS resin, or PEEK resin. Both ends of the holder 32 in the longitudinal direction are supported by an apparatus frame (not shown). A groove 32a is provided along the longitudinal direction on the lower surface of the holder 32, and the heater 31 is held in the groove 32a .

FIG. 5 is an explanatory diagram showing an example of the configuration of the heater 31 and a temperature control system. The heater 31 includes a substrate 31a, an energization heating resistor layer 31b, a protective layer 31c, and the like. The substrate 31a is a member made of ceramic, such as alumina (JIS A1203), which has an electrically insulating property, high thermal conductivity, and low heat capacity and is elongated in the longitudinal direction. The resistance layer 31b is formed on the surface of the substrate 31a facing the sleeve 33 (surface on the surface side) at the approximate center in the short direction along the longitudinal direction of the substrate 31a. The resistance layer 31a itself has a thickness of about 10 μm and is formed by screen-printing silver palladium (Ag / Pd) on the substrate 31a in a narrow strip shape having a width of about 4 mm. The protective layer 31c is made of a thin glass that can withstand sliding friction with the fixing sleeve 33, and is coated on the surface (surface) on which the resistance layer 31b is formed on the substrate 31a. 31d is an electrode part and is electrically connected to the resistance layer 31b. Reference numeral 34 denotes a thermistor as temperature detecting means, which is provided on the back surface of the substrate 31a (the surface opposite to the surface on which the resistance layer 31b is formed). The thermistor 34 is in a common recording material passage area (not shown) through which all the recording materials pass among the recording material passage areas (FIG. 3) through which recording materials of various sizes used in the image forming apparatus pass. Has been placed. Although not described in this embodiment, when small-size paper such as government postcards and COM10 envelopes is used continuously with central paper passing, the temperature may be excessively increased in the non-paper passing region of the fixing device length. In some cases, a thermistor is also arranged at the end, and the fixing temperature is adjusted for each paper size.

  The stay 34 is for supporting the holder 32. The stay 34 is formed in a U-shape with a substantially downward cross section using a predetermined metal material, and is fixed to the holder 32 at the center in the short direction of the holder 32. Both ends of the stay 34 in the longitudinal direction are supported by the apparatus frame.

The sleeve 33 has an endless shape having substantially the same peripheral length as the pressure member 40 and is loosely fitted on the outer periphery of the holder 32 . The sleeve 33 includes an endless base layer 33a, a primer layer 33b provided on the outer periphery of the base layer 33a, an elastic layer 33c provided on the outer periphery of the primer layer 33b, and a release layer provided on the outer periphery of the elastic layer 33c. 33d (refer to the detailed view of part A). The base layer 33a is a base layer made of metal such as SUS excellent in thermal conductivity, and has a thickness of 35 μm in order to have sufficient strength to withstand a heat stress and a mechanical stress and to have a long durability life. It is formed to a thickness of about. The primer layer 33b is formed by applying a conductive primer having an appropriate amount of conductive particles such as carbon (hereinafter referred to as a conductive material) dispersed on the base layer 33a in a thickness of 5 μm. The sleeve 33 has conductivity by the primer layer 33b. The elastic layer 33c is an elastic layer made of silicone rubber or the like and having a thickness of about 50 to 400 μm. The toner image carried on the recording material P can be wrapped by the elasticity of the elastic layer 33c, and uniform heat fixing can be realized. The release layer 33d is a dipping coating method using a PFA resin as a fluororesin having excellent releasability and high heat resistance in order to prevent adhesion of toner and paper powder and to ensure separation of the recording material P from the sleeve 33. It is formed by coating with a thickness of about 10 μm.

  The sleeve 33 is formed in a sleeve (cylindrical shape) having an outer diameter of 30 mm by rolling a laminated sheet of a base layer 33a, a primer layer 33b, an elastic layer 33c, and a release layer 33d. The primer layer 33 b is exposed in the circumferential direction at the longitudinal end portion of the sleeve 33. A conductive brush 35 as a conductive member is in electrical contact with the exposed portion (FIGS. 2 and 4). FIG. 6 is a perspective view showing a state in which the conductive brush 35 is in contact with the primer layer 33 b of the sleeve 33. A first power source 37 is connected to the conductive brush 35 via a protective resistor 36. Accordingly, a negative direct current voltage (−500 V) having the same polarity as the toner is applied from the power source 37 through the protective resistor 36 to the exposed portion of the primer layer 33 b through the conductive brush 35. That is, a DC voltage having the same polarity as the toner is applied to the sleeve 33. Here, although not shown, in the sleeve 33 configuration, the insulating primer is applied with the same longitudinal width as that of the elastic layer 33c, the base layer 33a is exposed at the end, and a negative DC voltage (−500V) is applied to the base layer exposed portion from the conductive brush 35. ) But still shows insulation. For this reason, the surface of the release layer 33d is similarly charged due to the effect of dielectric polarization, which is an insulating charging characteristic, and it goes without saying that the same effect can be obtained regardless of the conductivity of the primer.

The pressing member 40 includes a cored bar 41, an elastic layer 42 provided on the cored bar 41, and an outermost layer (hereinafter referred to as a surface layer) 43 provided on the elastic layer 42. The core metal 41 is made of aluminum having a diameter of 30 mm. The elastic layer 42 is made of heat-resistant conductive silicone solid rubber (volume resistance 2.0 × 10 ⁶ Ω · cm or less), and is formed around the metal core 41 with a thickness of 5 mm. That is, the elastic layer 42 is made of silicone rubber. The elastic layer 42 contains a conductive material such as carbon. The surface layer 43 is made of a fluororesin tube in which a certain amount of carbon is dispersed as a conductive material at a weight ratio, and is fitted on the elastic layer 42. That is, the surface layer 43 is a release layer formed by covering the elastic layer 42 with a conductive fluororesin tube. The release layer 43 is made of, for example, a mixed material of PFA resin and carbon (hereinafter referred to as PFA conductive resin). This fluororesin tube has a surface resistance value (DC 1000 V applied) of 2.0 × 10 ^{13 to} 8.0 × 10 ¹⁵ (Ω / □). The surface resistance was measured by applying a 1000 V for 10 seconds by opening a cylindrical tube created by Dia Instruments Co., Ltd., using a name: Hiresta UP MCP-HT450 type and a probe: UR-100. Details of the surface resistance will be described later.

  In the pressure member 40, the surface layer 43 is made of, for example, a PFA conductive resin having a thickness of 50 μm. The hardness of the surface is about 56.0 (9.8 N weight) in Asker-C. The pressure member 40 is disposed below the sleeve 33 in parallel with the sleeve 33, and both ends in the longitudinal direction of the cored bar 41 are rotatably held by the apparatus frame via bearings 61L and 61R. The pressure member 40 is applied to the heater 31 with a total pressure of 199 N via the sleeve 33 by a pressure spring (not shown) provided between the metal core 41 and the apparatus frame at both longitudinal ends of the metal core 41. It is pressed. In the pressing member 40, the elastic layer 42 is elastically deformed by sandwiching the heater 31 and the sleeve 33 by the pressing force of the pressing spring. As a result, the pressing member 40 forms a nip portion (fixing nip portion) N having a width of about 8 mm with the sleeve 33 interposed between the pressure member 40 and the heater 31. The thickness of the surface layer 43 is not limited to 50 μm, and may be set to an arbitrary thickness in the range of 30 to 60 μm.

  An electrical contact 44 made of a carbon chip or the like is in electrical contact with one end of the cored bar 41 of the pressing member 40. A second power supply 46 is connected to the contact 44 via a protective resistor 45. Accordingly, a positive DC voltage (+700 V) having a polarity opposite to that of the toner is applied to the cored bar 41 through the contact 44 from the power supply 46 through the protective resistor 45. That is, a DC voltage having a polarity opposite to that of the toner is applied to the pressure member 40. The power supply 46 is controlled so that a DC voltage +700 V is applied to the cored bar 41 so that the surface potential of the pressing member 40 is lower than the surface potential of the sleeve 33 and a potential difference is maintained between the sleeve 33 and the pressing member 40. Has been.

(3) Heat Fixing Operation of Fixing Device Fixing motor M (FIG. 4) as a driving source rotates and drives drive gear G provided at the end of cored bar 41 of pressure roller 40 in accordance with the print signal described above. . As a result, the pressure roller 40 is rotated in the direction of the arrow (FIG. 2). The rotational force of the pressure roller 40 is transmitted to the sleeve 33 through the nip portion N. As a result, the sleeve 33 is driven to rotate around the outside of the holder 32 in the direction of the arrow (FIG. 2) in a state where the inner peripheral surface of the sleeve 33 is in contact with the protective layer 31c of the heater 31 and the outer peripheral surface of the holder 32. In order to reduce the frictional resistance between the sleeve 33 and the protective layer 31c of the heater 31, and between the sleeve 33 and the holder 32, a small amount of heat-resistant grease is applied as a lubricant to the surface of the protective layer 31c and the surface of the holder 32. ing.

Further, the energization control unit 62 (FIG. 5) as the energization control unit energizes the resistance layer 31b through the electrode portion 31d of the heater 31 in accordance with the above-described print signal. As a result, the resistance layer 31b generates heat and the heater 31 is rapidly heated . Thermistors 34 outputs to the power supply controller 62 detects the temperature of the heater 31. The energization control unit 62 takes in an output signal (temperature detection signal) from the thermistor 34 and controls energization of the heater 31 so as to maintain a predetermined target temperature (fixing temperature) based on the signal. The energization control to the heater 31 in the energization control unit 62 is performed by a wave number control method for controlling the input power by the wave number of the AC voltage, a phase control method for energizing to the next zero cross after a predetermined delay time from the zero cross of the AC voltage, or the like. Has been made.

  The recording material P carrying the unfixed toner image T is introduced into the nip portion N while the rotation of the sleeve 33 and the pressure roller 40 is stable and the heater 31 is maintained at the target temperature (FIG. 2). The recording material P is nipped and conveyed by the nip portion N, and the unfixed toner image T is heated and fixed on the surface of the recording material P by receiving heat and pressure during the conveyance process.

(4) Description of surface resistance of pressure member The reason why the surface resistance of the pressure member 40 is determined in the range of 2.0 × 10 ^{13 to} 8.0 × 10 ¹⁵ (Ω / □) (DC 1000 v applied) will be described. . The surface resistance measurement relating to this example was performed by applying DC 1000 V for at least 10 seconds in a measurement environment: 23 ± 3 ° C. and 50 ± 5%, and setting the Max value as a measured value.

  First, the fluorine-based tube used in this example was prepared using a melt extrusion molding method after mixing a melt-type fluororesin material in a solid state (hereinafter referred to as pellets). The following three types of fluororesin materials were actually used.

Made by DuPont Brand: Teflon 950HP-J Plus (pellet) to insulating PFA
C-9058 (pellet) to conductive PFA
C-9068 (pellet) to conductive PFA
Teflon is a registered trademark.

The surface resistance was varied by adjusting the stitch amount of each conductive pellet alone to the weight ratio. The surface layer of the pressure member was molded by covering the outer peripheral surface of the elastic layer with the molded tube. The surface resistance was measured by opening a cylindrical tube sample and applying 1000 V for 10 sec in an environment of a temperature of 23.5 ° C. and a humidity of 50% RH. The fixing device having the pressure member prepared as described above was mounted on the image forming apparatus described in the examples. Then, using the image forming apparatus, a one-component insulating toner having a process speed of 400 mm / sec, an A4 vertical feed of 60 ppm, and a volume average particle size of 5.8 μm is disposed at a low temperature and low humidity environment to 15 ° C. and 10% RH. Image confirmation or the like was performed using the cartridge 15. The results are shown in Table 1. 950HP-J Plus + C9058 (LotA)
The test uses charcoal cal paper containing approximately 21% calcium carbonate: A4 Laser80 basis weight 80 g / m ² (manufactured by IPSA) as recording paper P in an environment where the temperature is 15 ° C. and the humidity is 10%. This is performed by continuously feeding up to 10,000 sheets. The following three items were confirmed as confirmation of the fixed image.

  (1) Offset: The offset evaluation is performed by visual inspection of the recording material by the inventor. In Table 1, ○ in the offset evaluation column is a state where no offset is generated, △ is a state where the offset can be confirmed slightly, but × is a state where the offset is clearly confirmed. This is a problem level.

  (2) Stain of pressure member: A case where no toner adheres to the pressure member and no toner adheres to the sheet passing image is confirmed. Next, when the toner is transferred onto the paper while the paper is being passed and the toner is slightly clumped, or when the adhesion of the toner is slightly seen on the surface of the pressure member after passing 10,000 sheets, Δ did. When a large amount of toner was clearly confirmed on the paper, or a large amount of toner adhered to the surface of the pressure member after the paper was passed, it was marked as x.

  (3) Tail & scatter: In the print image, ◯ when there is no tail or scatter caused by the fixing device, △ is a level that can be clearly seen visually, and x when it can be clearly confirmed as a defective image.

  Furthermore, the maximum value of the surface potential of the pressure member during paper feeding was measured with an electrometer. Note that −500 V is applied to the fixing sleeve, and since the insulating rubber and the surface layer are insulating tubes, the surface layer of the fixing sleeve is charged to approximately −500 V.

From Table 1, the surface resistance of the pressure member surface layer is within the range of the surface resistance value (DC 1000 V applied) of about 4.0 × 10 ^{15 to} 2.4 × 10 ¹⁴ Ω / □, offset, pressure member contamination, It was confirmed that fixed images such as tailing and scattering were good. This seems to be because, as can be seen from the pressure member potential, excessive charging of the pressure member surface layer could be prevented by making the pressure member surface layer conductive. However, at a conductivity ratio of 98: 2, which is close to insulation, the potential is equivalent to 100: 0, and an offset is confirmed, and at 70:30 where the surface resistance is low, the toner charge leaks and causes tailing and scattering. And the pressurization member dirt worsened.

  Then, in order to confirm the dispersion | variation in manufacture, the result of having confirmed the material difference (Lot: B) of a conductive tube material is shown in Table 2. 950HPJ Plus + C9068 (LotB)

From Table 2, the surface resistance of the pressure member surface layer is within the range of the surface resistance value (DC 1000 V applied) of about 1.6 × 10 ^{14 to} 7.5 × 10 ¹⁴ (Ω / □), offset, pressure roller It was confirmed that the fixed images such as dirt, tailing & scattering were good. At a conductive ratio of 95: 5, the pressure member potential increases and the potential difference from the fixing sleeve becomes approximately 100 V, so that a slight offset occurs.

  As described above, as a material for forming a conductive PFA tube, a good fixed image can be confirmed by mixing C9508 and C9068, which are conductive PFA, with 950HP-J Plus, which is an insulating PFA, alone. confirmed.

  Here, the transmission densities shown in Tables 1 and 2 will be described. This is a measurement of the created tube using a Macbeth transmission densitometer, model number: TD904. When the conductive ratio is high and the weight of the conductive material is large, a large numerical value is shown, and when the conductive material is low, a small value is shown. In the measured value, when the resistance is high, the fixed image is good at a transmission density of about 3.0 or more, and the correlation is obtained with the surface resistance, but when the resistance is low, the correlation between the fixed image and the surface resistance is I couldn't get it.

  Subsequently, three conductive tubes and pressure members were prepared and measured in order to confirm manufacturing variations at the same compounding ratio with the compounding ratio of conductive tube conductivity ratio 90:10 shown in Tables 1 and 2. The surface resistance was measured in the range of environmental temperature / humidity in the range of 23 ± 3 ° C./50±5% RH. The results are shown in Table 3. LotC (C9058) and LotD (C9068) are used as conductive PFA pellets.

  When the fixed image was confirmed with three pressure members for each lot prepared at the same time as the conductive tube having the surface resistance value shown in Table 3, no offset, tailing & scattering, and pressure roller contamination occurred. A good fixed image was confirmed.

As described above, from the results of Tables 1 to 3, the region where the surface resistance of the pressure member in this example is good is (Table 3 *).
2.0 × 10 ^{13 to} 8.0 × 10 ¹⁵ (Ω / □) (DC 1000 V applied)
It turned out that.

As described above, by defining the surface resistance range of the conductive tube, the charging potential of the pressure member is suppressed and charging due to charge-up is prevented to provide a fixed image free from offset, pressure member contamination, tailing and scattering. I knew it was possible. However, it will be considered below how the charging potential is suppressed by the surface resistance of approximately 1.0 × 10 ¹⁶ (Ω / □) (DC 1000 V applied).

FIG. 7 shows a potential measuring jig 46 for confirming the charging potential of the pressure member 40 used in this embodiment by using an idle rotating machine. In the figure, the pressure member 40 is brought into contact with the metal sleeve 47 and is rotated idly at a speed of 100 cm / sec. At this time, a direct current voltage +600 (V) is applied from the power source 50 to the metal core 41 of the pressurizing member 40 via the contact 51, and is charged to a desired potential by rubbing against the metal sleeve 47. come. Here, the metal sleeve 47 is grounded 49 via a protective resistor 48. At this time, the charged potential of the pressing member 40 is read by the electrometer probe 52, and data is stored by the memory high coder 54 via the electrometer 53. When the idling potential was measured in a normal environment of 23 ° C. and 55% RH, it was found that the idling potential was saturated in about 300 seconds, and the potential was charged to the plus side.

  Here, when a pressurizing member was prepared with a conductive PFA tube using Lot A, and the potential of the pressurizing member was saturated, the idling potential at 270 to 300 sec was analyzed, and as shown in Table 4.

  It can be seen from the conductivity ratios in Table 4 that as the conductive material increases, the difference potential decreases at the saturated potential of the pressure member 40 and the pressure member is uniformly surface charged. That is, according to the DC voltage applied to the core metal 41, the surface of the pressurizing member is made uniform due to the microconductive effect of the conductive tube even when charging due to the pressure sliding with the metal sleeve 47 by idling. It is considered that charging is performed to prevent overcharging of the pressure member 40 due to charge-up. When the surface resistance is high as in the case of the conductivity ratios of 100: 0 and 98: 2, the potential difference is also high, and the difference between the charged portion and the uncharged portion on the tube surface layer becomes large. This is considered that when the potential difference between the fixing sleeve and the pressure member is reduced during normal printing, the surface of the pressure member is partially negatively charged and becomes larger than the fixing sleeve potential, resulting in an offset image.

As described above, by setting the surface resistance of the pressure member surface layer to 2.0 × 10 ^{13 to} 8.0 × 10 ¹⁵ (Ω / □) (DC 1000 V applied), offset, toner contamination of the pressure member , Explained that it can prevent the tailing% and fine scattering. Further, even when the elastic layer of the pressure member is an insulating rubber, a conductive tube is provided on the surface layer (release layer) of about 2.0 × 10 ^{13 to} 8.0 × 10 ¹⁵ (Ω / □) (DC 1000 V applied). Needless to say, a similar effect can be obtained by the effect of uniform charging of the conductive member.

  Further, in the case of using a conductive polyimide film as the surface layer of the fixing sleeve described in the conventional example, the voltage value applied to the fixing sleeve and the pressure member and the surface resistance of the pressure member surface layer are set to desired values. Needless to say, adjustments have similar effects. In this case, when a conductive polyimide film is used as the fixing sleeve, the same result can be obtained by supplying power from the conductive brush at the end of the sleeve as in the present invention.

As described above, according to the present embodiment, the surface layer 43 of the pressure member 40 has a surface resistance value of 2.0 × 10 ¹³ to 8 .8 in a measurement environment of 23 ± 3 ° C. and 50 ± 5% RH. The range was set to 0 × 10 ¹⁵ Ω / □ (DC 1000 V applied). Thereby, it is possible to prevent the pressure member surface layer from being charged up, which occurs when high resistance paper such as charcoal cal is continuously passed as the recording material P. Accordingly, toner offset to the surface layer 43 of the pressure member 40 and toner adhesion can be reduced, and contamination of the pressure member 40 and scattering of a fixed image such as tailing can be reduced.

Configuration model diagram of an example of an image forming apparatus Cross-sectional schematic diagram of an example of a fixing device Longitudinal cross section model of fixing device View of fixing device from recording material introduction side Explanatory drawing showing an example of the heater configuration and temperature control system A perspective view showing a contact state between the fixing sleeve and the conductive brush Schematic configuration diagram of an example of an electric potential measurement jig for a pressure member

Explanation of symbols

22 ... Image heating and fixing device, 31 ... Heater, 33 ... Fixing sleeve, 40 ... Pressure member, 43 ... Outermost layer, N ... Nip part N

Claims (3)

Flexibility and sleeve having a
A heating element for heating the pre-kiss leave,
A metal core, an elastic layer provided on the outside of the metal core, and a release layer formed by coating the outer peripheral surface of the elastic layer with a fluororesin tube or a fluororesin, and in contact with the sleeve A pressure roller that forms a nip,
In the provided image heating apparatus for heating while feeding transportable recording material carrying the toner image by the nip portion,
The surface resistance of the release layer, 23 ± 3 ℃, and have you to 50 ± 5% RH in the measurement environment 2. ^{0 × 10 13 ~8.0 × 10 15} (Ω / □) in the range of (1000V DC applied), a DC voltage having a polarity opposite to that of toner on the pressure roller, before kiss leave the same polarity as the toner of An image heating apparatus that applies a DC voltage to each. An apparatus according to claim 1, thickness before KiHanare type layer is characterized by a 30 to 60 m. The said heating body is a plate-shaped heater which contacts the inner surface of the said sleeve, Comprising: The said heater forms the said nip part through the said sleeve with the said pressure roller. 2. The image heating apparatus according to 2.