JP2010176009A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus including a fixing device capable of controlling heater temperature to be low, and also, capable of preventing offset even at the low controlled temperature. <P>SOLUTION: The image forming apparatus includes the fixing device wherein a recording material P carrying an unfixed toner image is guided into between the outer surface of a fixing film 22 and a pressure member 11 at a fixation nip portion N, and the recording material P is moved to pass through the fixation nip portion N together with the fixing film 22, then, the heat of a heating body 100 is applied to the recording material P through the fixing film 22. The circumferential length of the fixing film 22 is set longer than the length of the longest recording material P usable in the image forming apparatus, and also, at a point of time when almost the downmost stream end of the recording material P reaches the fixation nip portion N, the recording material P is switched back, then, discharged outside the apparatus, the downmost stream side of the recording material P being discharged first. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile machine including a fixing device that heats and fixes an unfixed toner image on a recording material formed by using an electrophotographic technique or an electrostatic recording technique.

  Conventionally, a laser beam printer is widely known as an example of an electrophotographic image forming apparatus using an electrophotographic technique.

  For example, as shown in FIG. 7 attached to the present application, the laser beam printer described in Patent Document 1 includes a sheet feeding unit 1 and a sheet feeding roller 2 on which a recording material is placed as a sheet feeding unit below the apparatus main body 10A. Is arranged. A transfer roller 9 as a transfer unit is disposed at the center of the apparatus main body 10A, and a fixing device F as a fixing unit is disposed at the left end side.

  As described above, the image forming means such as the process cartridge 7 or the like above the recording material conveyance surface formed in the recording material conveyance path leading to the paper feeding unit 1, the paper feeding roller 2, the transfer roller 9, and the fixing device F; Exposure means such as a laser scanner 5 is disposed.

  With the above configuration, the feeding of the recording material P, the transfer of the visible image (toner image) to the recording material P, and the heat fixing of the toner image on the recording material P are sequentially performed.

  A plurality of recording materials P are stacked in the paper feeding unit 1. The recording material P is separated and fed one by one by a sheet feeding roller 2 disposed in the sheet feeding unit 1, and conveyed to a transfer unit in which a transfer roller 9 is disposed by conveying rollers 3a and 3b.

  Further, the registration sensor 4 draws an image from a predetermined position on the recording material P by synchronizing the tip position of the recording material P with the light emission timing of the laser scanner 5.

  Further, the process cartridge 7 is constituted by integrating process means such as a drum-shaped photosensitive member (photosensitive drum) 8 which is an image carrier, a developing device 17 including a developer carrier, a charging roller 18 and a cleaner 19. It is made detachable with respect to.

  The transfer roller 9 transfers the toner image on the photosensitive drum 8 onto the recording material P, and the fixing device F heat-fixes the visible image on the recording material P.

  The recording material P after passing through the transfer roller 9 is conveyed substantially horizontally as described above and enters the fixing device F.

  The fixing device F includes a pressure roller 11 that is rotatably supported and a heater unit H that includes a heating element. In the fixing device F, the heater unit H is in contact with the pressure roller 11 with a predetermined pressure.

  The heater unit H is configured such that a low-heat-capacity planar heating element 100 is fitted into the lower surface of the heating element holder 21 and a cylindrical heat-resistant fixing film 22 is circumscribed.

  The heater unit H is pressed against the elastic pressure roller 11 with a predetermined pressing force, and forms a heating nip portion (hereinafter referred to as “fixing nip portion”) N having a predetermined width.

  When power is supplied to the heating body 100 from a power supply circuit (not shown), the temperature rapidly rises. The temperature rise of the heating body 100 is detected by a thermistor (not shown) disposed on the back side of the heating body. The temperature control circuit controls the power supply from the power supply circuit so that the heating body temperature detected by the thermistor is maintained at a predetermined substantially constant temperature (fixing temperature). That is, the heating body 100 is heated and adjusted to a predetermined fixing temperature.

  Further, when the recording material P, which is a material to be heated, is continuously fed by the heater unit H, the fixing film 22 reaches a temperature of about 150 ° C., for example.

  The fixing film 22 is conveyed and moved, and the heating body 100 is heated to a predetermined temperature and the temperature is adjusted. In this state, the recording material P on which an unfixed toner image Ta as a heated material is formed and supported between the fixing film 22 and the elastic pressure roller 11 in the fixing nip N is arranged on the fixing film 22 side. To introduce. As a result, the recording material P is brought into close contact with the outer surface of the fixing film 22 at the fixing nip portion N and is nipped and conveyed together with the fixing film 22. When the recording material P passes between the pressure roller 11 and the heater unit H, the unfixed toner image Ta is fixed by heat and pressure, and a fixed image Td is obtained.

Then, the recording material P on which the visible image is fixed is conveyed between the discharge guide pairs 29a and 29b, and is discharged onto the discharge tray 14 by the discharge roller 12 with the printing surface facing up.
JP-A-4-44075

  However, in the fixing device F as in the conventional example, in order to sufficiently fix the toner image on the recording material P, it is necessary to control the temperature of the heater unit H to a high temperature of about 150 ° C., for example. Therefore, the material constituting the fixing device F has to use an expensive material having high heat resistance. If the control temperature is controlled to be low, the fixability becomes insufficient, and the toner that could not be fixed remains on the fixing film and becomes a so-called offset image that is retransferred to the recording material after one rotation of the film. It was.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus including a fixing device that can control the temperature of a heating body to be low and can prevent the occurrence of offset even at a low control temperature.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention
An endless belt-like heat-resistant fixing film;
A heating element disposed inside the fixing film;
A fixing nip is formed by sandwiching the fixing film with the heating body, and the fixing film is moved in the recording material conveying direction at a predetermined speed while sliding the inner surface of the fixing film against the heating body. A pressure member to be
A recording material carrying an unfixed toner image is introduced between the outer surface of the fixing film at the fixing nip portion and the pressure member, and the fixing film is moved and passed through the fixing nip portion together with the fixing film. In an image forming apparatus provided with a fixing device that applies heat of the heating body to the recording material via
When the peripheral length of the fixing film is longer than the length of the longest recording material that can be used in the image forming apparatus and the vicinity of the most downstream end of the recording material reaches the fixing nip portion, the recording material is switched. Back and discharged from the most downstream end of the recording material to the outside of the apparatus,
An image forming apparatus characterized by the above.

  According to the present invention, it is possible to fix an unfixed toner image on a recording material at a lower temperature than in a conventional image forming apparatus. For this reason, it is possible to use a material having lower heat resistance for parts around the fixing device such as a heating body holding member and a fixing film.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
(1) Image Forming Apparatus FIG. 1 shows a schematic configuration of an embodiment of an image forming apparatus according to the present invention.

  In this embodiment, the image forming apparatus of the present invention is a laser beam printer using a transfer type electrophotographic process.

  In the present embodiment, the image forming apparatus (printer) 10 includes a sheet feeding unit (sheet feeding tray) 1 on which a recording material is placed as a sheet feeding unit below the apparatus body 10A. Is provided with a fixing device F as a fixing means. Further, an image forming means such as a process cartridge 7 and an exposure means such as a laser scanner 5 are arranged in the central portion of the apparatus main body between the paper feed tray 1 and the fixing device F.

  More specifically, in the image forming apparatus of the present embodiment, the drum-shaped electrophotographic photosensitive member, ie, the photosensitive drum 8, which is an image carrier, is rotationally driven in the clockwise direction indicated by an arrow in response to an image formation start signal. The rotating photosensitive drum 8 is uniformly charged to a predetermined polarity and potential by a charger 18 which is a charging means.

  A laser beam L modulated in accordance with a time-series electric digital pixel signal of target image information is output from the laser scanner 5 to the uniformly charged surface of the photosensitive drum 8, and the target surface is exposed to the target drum 8. The electrostatic latent images corresponding to the image information are sequentially formed. The latent image is then visualized as a toner image by the developing device 17 as developing means.

  In this embodiment, the process cartridge 7 is formed by integrating process means such as the photosensitive drum 8, which is an image carrier, the developing device 17, the charging roller 18, and the cleaner 19, and is detachable from the apparatus main body 10A. ing.

  On the other hand, the recording material P in the sheet feeding tray 1 is fed by the sheet feeding roller 2 and is conveyed to the pair of conveying rollers 3a and 3b through a sheet conveying path formed by the sheet passing guide 40. Thereafter, the recording material P is fed by the registration sensor 4 to a transfer portion Tn that is synchronized with the rotation of the photosensitive drum 8 and includes the photosensitive drum 8 and the transfer roller 9 that is in pressure contact with the photosensitive drum 8. Therefore, the toner image Ta on the photosensitive drum side is sequentially transferred onto the recording material.

  The recording material P that has passed through the transfer portion is separated from the surface of the photosensitive drum 8 and is introduced along a guide 41 into a fixing device F described later.

(2) Fixing device F
a) Overall Schematic Configuration of Fixing Device F FIG. 2 is a cross-sectional view showing a schematic configuration of the fixing device F of this embodiment.

  The heater 100 which is a fixed heating body generates heat by energizing a heating element pattern formed on a ceramic substrate. A thermistor 50 as a temperature control element is disposed on the surface of the heater 100 opposite to the fixing film 22. The temperature detected by the thermistor 50 is fed back to be controlled to a predetermined temperature by an electric circuit (not shown).

  The heater (heater) holder 21 is a member made of a heat-resistant resin. As shown in FIG. 2, the heater 100 is fitted into a groove 21a provided on the upper surface of the heater holder 21 along the length of the holder. It is supported. Further, the heater holder 21 functions as a support member for the heater 100 and also has a function to pressurize and guide the fixing film 22 to the fixing nip portion N and to guide rotational conveyance stability as will be described later. .

  The fixing film 22 is an endless belt-like film material having a longer circumferential length than the longest recording material P that can be used in the image forming apparatus. The fixing film 22 has heat resistance and fluorine on the surface of a material such as polyimide having low shrinkage. It is configured by coating a resin. A heater 100 is disposed inside the fixing film 22.

  The fixing film 22 is stretched between a heater holder 21 that supports the heater 100 and a film driving roller 23 that is disposed so as to be in contact with the inner peripheral surface of the film. Drive is transmitted to the film drive roller 23 from a motor (not shown) that can rotate forward and backward. The film drive roller 23 can switch between forward and reverse rotation in synchronization with a signal from the rear end detection sensor 25 that detects the downstream end of the recording material P.

  A tensioner roller 24 is disposed between the heater holder 21 and the film driving roller 23. When the tensioner roller 24 is pressed with a predetermined pressure by a tensioner spring 27, the fixing film 22 is stretched and arranged with a predetermined tension so that no slack is always generated.

  The elastic pressure roller 11 as a pressure member is pressed against the elasticity of the elastic pressure roller 11 with the fixing film 22 sandwiched therebetween by a pressure spring 26 with a pressing force of, for example, about 80 to 150 [N]. Thus, a fixing nip portion N having a predetermined width as a heating portion is formed.

  In addition, a small amount of lubricant such as heat-resistant grease is interposed on the inner surface of the fixing film 22 so that the fixing film 22, the heater 100, and the heater holder 21 slide and rotate smoothly.

b) Operation of the fixing device F (FIGS. 3 to 5)
Next, the operation of the fixing device F will be described.

  As shown in FIG. 3, the fixing film 22 is rotated by the rotation of the film driving roller 23. The pressure roller 11 is configured to follow the rotation of the fixing film 22. Accordingly, the pressure roller 11 presses the fixing film 22 toward the heater 100 and moves the fixing film 22 in the recording material conveyance direction at a predetermined speed while sliding the inner surface of the fixing film 22 on the heater 100.

  A recording material P carrying an unfixed toner image Ta is introduced between the fixing film 22 of the fixing nip N and the elastic pressure roller 11 in a state where the heater 100 is heated to a predetermined temperature by energizing the heater 100. .

  When the toner image carrying surface of the recording material P is in close contact with the outer surface of the fixing film 22 and moves through the fixing nip N together with the fixing film 22, the heat of the heater 100 is applied to the recording material P via the fixing film 22. The applied unfixed toner image Ta is heated and fixed on the surface of the transfer material P. Here, the temperature of the heater 100 is adjusted to a temperature T2 that is lower by, for example, about 30 ° C. than the temperature T1 at which the toner image is completely fixed. In this state, the toner image Ta cannot be completely fixed on the recording material P, the toner image on the recording material P side becomes a toner image Tb in a semi-fixed state, and cannot be fixed on the fixing film 22 side. Toner Tc remains.

  As shown in FIG. 4, after a predetermined time has elapsed after the most downstream end Pa of the recording material P has passed through the trailing edge detection sensor 25, the vicinity of the most downstream end of the recording material P is positioned at the fixing nip N. At this time, the rotation direction of the film driving roller 23 is switched from normal rotation to reverse rotation.

  That is, the switching time of the film driving roller 23 is a time when the vicinity of the most downstream end of the recording material P reaches the fixing nip portion N, and usually the distance La from the position of the most downstream end Pa of the recording material P to the upstream side. A range of about 4 mm to 12 mm is a position sandwiched by the fixing nip portion N.

  As a result, the fixing film 22 also starts reverse rotation, and the recording material P switches back in synchronism with the movement of the fixing film 22, that is, turns back in the direction opposite to the conveyance movement direction so far and starts moving backward. .

  As shown in FIG. 5, the recording material P that has been switched back is again guided to the fixing nip portion N, where heat and pressure are applied again. As a result, the toner image Tc remaining on the fixing film 22 is also fixed on the recording material P, and the toner image on the recording material P becomes a completely fixed toner image Td.

  Thereafter, as shown in FIG. 1, the recording material P switched back by the fixing device F passes between the most downstream end discharge guide pairs 29a and 29b of the recording material and is discharged by the discharge roller pairs 12a and 12b. The paper is discharged onto the paper tray 14 and conveyed outside the apparatus.

  Here, since the fixing film 22 has a longer circumference than the longest recording material P that can be used in the image forming apparatus, the toner image Tc remaining on the fixing film 22 is equivalent to one recording material P on the fixing film 22. Temporarily retained. Further, since the recording material P and the fixing film 22 are switched back synchronously, the toner image Tc remaining on the fixing film 22 in the outward path reaches the fixing nip portion N, and is in a semi-fixed state on the recording material P. It is re-fixed without shifting from the toner image Tb.

  That is, in this embodiment, as shown in FIG. 4, when the recording material P starts to switch back, the fixing film 22 and the recording material P are the length of the longest recording material that can be used in the image forming apparatus. Is in contact with the fixing film 22 with a length (L) corresponding to approximately half of the length. With this configuration, as described above, the toner image Tc remaining on the fixing film 22 is temporarily held on the fixing film 22 by the amount corresponding to one recording material P.

  As described above, the configuration of the fixing device as shown in the present embodiment makes it possible to perform fixing at a lower fixing temperature than in the past, and expensive parts around the fixing device such as a heating member holding member and a fixing film. There is no need to use heat-resistant materials.

Example 2
Next, another embodiment of the image forming apparatus according to the present invention will be described. FIG. 6 is a schematic configuration diagram of the image forming apparatus of the present embodiment.

  In the first embodiment, the paper feed tray 1 on which a plurality of recording materials P are placed in the image forming apparatus is disposed below the apparatus main body 10A, and the fixing device F and the paper discharge tray 14 are disposed above the apparatus main body 10A. The configuration was arranged.

  On the other hand, in this embodiment, the paper feed tray 1 and the paper discharge tray 14 are stacked and arranged substantially in parallel above the apparatus main body 10A, and the fixing device F is arranged below the apparatus main body 10A.

  In this embodiment, the recording material P fed from the paper feed tray 1 is fed to a fixing device F below the apparatus main body through an image forming unit such as a process cartridge 7. In the fixing device F, as shown in the first embodiment, when the recording material rear end Pa reaches the fixing nip portion N, the fixing film 22 rotates in the reverse direction, and the recording material P is conveyed in a switchback manner.

  The recording material P is fixed with a toner image in the same manner as shown in the first embodiment, and is discharged onto the discharge tray 14 above the apparatus main body through the discharge conveyance path 30.

  As shown in FIG. 6, the paper discharge tray 14 according to the second exemplary embodiment can be rotated upward to improve convenience when the recording material P is set in the paper feed tray 1.

  As described above, with the configuration of the image forming apparatus shown in the present embodiment, for example, it is possible to provide an image forming apparatus that can be installed in a place where the image forming apparatus can be accessed only from above, such as in a drawer. .

1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. 1 is a schematic configuration diagram of an embodiment of a fixing device according to the present invention. FIG. 6 is a transverse cross-sectional view showing the operation (outward path) of the fixing device. FIG. 10 is a cross-sectional view illustrating the operation (switchback) of the fixing device. FIG. 10 is a cross-sectional view illustrating the operation (switchback) of the fixing device. It is a schematic block diagram of the other Example of the image forming apparatus which concerns on this invention. It is a schematic block diagram of an example of the conventional image forming apparatus.

8 Photosensitive drum (image carrier)
11 Pressure roller (Pressure member)
21 Heater holder 22 Fixing film 23 Film driving roller 100 Heater (heating body)
P Recording material N Fixing nip F Fixing device Ta Unfixed toner image Tb Semi-fixed toner image Tc Toner remaining on film Td Fixed toner image

Claims (4)

An endless belt-like heat-resistant fixing film;
A heating element disposed inside the fixing film;
A fixing nip is formed by sandwiching the fixing film with the heating body, and the fixing film is moved in the recording material conveying direction at a predetermined speed while sliding the inner surface of the fixing film against the heating body. A pressure member to be
A recording material carrying an unfixed toner image is introduced between the outer surface of the fixing film at the fixing nip portion and the pressure member, and the fixing film is moved and passed through the fixing nip portion together with the fixing film. In an image forming apparatus provided with a fixing device that applies heat of the heating body to the recording material via
When the peripheral length of the fixing film is longer than the length of the longest recording material that can be used in the image forming apparatus and the vicinity of the most downstream end of the recording material reaches the fixing nip portion, the recording material is switched. Back and discharged from the most downstream end of the recording material to the outside of the apparatus,
An image forming apparatus.   2. The image forming apparatus according to claim 1, wherein the temperature of the fixing nip is controlled to be lower than the temperature at which the unfixed toner image on the recording material is completely fixed.   When the recording material starts to switch back, the fixing film and the recording material have a length corresponding to approximately half of the length of the longest recording material that can be used in the image forming apparatus. The image forming apparatus according to claim 1, wherein the image forming apparatus is in contact with the image forming apparatus. A paper feed tray on which a plurality of recording materials are placed;
A paper discharge tray for discharging and stacking the recording material fixed by the fixing device;
The image forming apparatus according to claim 1, wherein the paper feed tray and the paper discharge tray are stacked in a substantially parallel manner.