JP2015129792A - image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing apparatus configured to prevent reduction in productivity when a small-size sheet passes, and to prevent reduction in energy-saving effect due to the increase in width of heating means, and an image forming apparatus.SOLUTION: An image forming apparatus includes: a fixing belt 21 which is rotated in contact with an unfixed image; a pressure roller 22 which forms a fixing nip with the fixing belt 21; and heating means 23 which comes into contact with the fixing belt 21 to heat it. The heating means 23 includes a glass substrate having low thermal conductivity, and a resistive-heating section 24 having a plurality of heating areas formed in a longitudinal direction on the glass substrate 25. A uniform-heating member 50 formed of a material having high thermal conductivity, is arranged in a position not in contact with the heating means 23. The uniform-heating member 50 is extended in a longitudinal direction of the fixing belt 21, and comes into contact with the fixing belt 21 directly or via a member.

Description

  The present invention relates to a thermal fixing device in an electrophotographic image forming apparatus, and an image forming apparatus such as a copying machine, a printer, and a facsimile equipped with the fixing device.

  In an image forming apparatus such as a copying machine, a printer, or a facsimile, a toner image is formed on an image carrier based on image information, the toner image is transferred onto a recording material such as paper or an OHP sheet, and the toner image is carried. The recorded material is passed through a fixing device, and the toner image is fixed on the recording material by heat and pressure.

  As such a fixing device, a heat roller type is well known. A heat roller type fixing device forms a nip with a fixing roller heated by a heating source such as a halogen heater or an induction heating coil and a pressure roller, and passes a recording material carrying an image through the nip to generate heat and heat. The toner is melted and fixed by pressure. This fixing roller method is widely used from the viewpoints of safety and compatibility with high speed machines, but there is a problem in energy saving.

  Therefore, in recent years, the latter belt and film type devices are often used as fixing devices for realizing energy saving. For this type of fixing device, a method of heating the heat insulating roller from the outside and a technique of selectively heating only the image area based on the image information are proposed.

As a fixing device suitable for energy saving, there is a film system as described in Patent Documents 1 and 2.
The fixing device described in Patent Document 1 includes a plate-like resistance heating body that comes into contact with a thin cylindrical heat-resistant film, and a pressure roller to sandwich the film and the recording material so that the thermal energy is recorded. It is the composition given to. At this time, since the film is as thin as about 100 μm, it is only necessary to raise the temperature of the heating means having a small heat capacity, so that the rise time can be shortened and the preheating power can be reduced.

  Further, in Patent Document 1, the control temperature of the heating body and the heating area are changed in accordance with the image formed on the recording material, and the energy supply to the non-image area (the area where no image exists in the image forming area) is reduced. Thus, a configuration enabling energy saving is disclosed.

  In the case of a fixing device using a thin film of about 100 μm, when a transfer material having a width smaller than the maximum sheet passing width is passed, the heat energy is not consumed in the non-sheet passing area where the transfer material is not passed. Instead, heat is generated with a predetermined amount of heat as in the paper passing area. For this reason, the temperature of the non-sheet-passing area is higher than that of the sheet-passing area. When a thin film is used, the temperature rise becomes remarkable because the heat capacity of the film is small. In patent document 2, it has the heat generating body which can heat a center part and both ends separately. And a temperature sensor that individually detects the surface temperatures of the center and the end with respect to the main scanning direction of the fixing member, the heating element for heating the center and the heating for both ends based on the detected temperature of the temperature sensor An image forming apparatus including a control unit that controls heating of a heating element is disclosed. Accordingly, the temperature control in the non-sheet passing area can be prevented by performing the heating control in accordance with the sheet passing width.

  However, when the heating means is divided into various paper widths, the number of wirings on the base increases, so the width of the heating means (in the direction orthogonal to the paper transport direction) becomes wide and the heat capacity increases, which impairs energy saving. End up. Moreover, since the contact area with the member which supports a heating means will become large when the width | variety of a heating means becomes wide, the heat dissipation to a support member will increase, and also energy-saving property will be impaired.

Patent Documents 3 and 4 describe fixing devices that prevent a temperature increase in a non-sheet passing portion when a small size is passed.
The fixing device described in Patent Document 3 discloses that a heat equalizing member is disposed downstream of the fixing heater, and the temperature rises by moving the non-sheet passing portion temperature rise to the paper portion. Further, it is disclosed that the fixing device described in Patent Document 4 includes a drive mechanism that varies the position of the heat equalizing member so that the heat equalizing member is brought into contact with or separated from the heater. In Patent Documents 3 and 4, the temperature distribution in the rotation axis direction of the heating body and the thermal film is smoothed to prevent the temperature rise at the non-sheet passing portion while shortening the temperature rise time.

  However, in the configuration of Patent Document 3, the heating region of the heater is not divided or only a small number are divided. Therefore, when small-size paper is passed, the width of the non-sheet-passing portion of the heater (difference between the heating area and the paper size) becomes large, and overheating cannot be prevented by using only a soaking member. In particular, in the case of printing or cardboard in a low temperature environment, the heater lighting rate becomes high, and thus excessive temperature rise becomes remarkable when the heater in the non-sheet passing portion cannot be turned off.

Further, the configuration of Patent Document 4 has a problem in that the cost is increased because a drive mechanism for changing the position of the heat equalizing plate is required.
The present invention solves the above-described conventional problems, does not cause a decrease in productivity even when a small-size paper is passed, and can prevent a decrease in energy saving due to an increase in the width of the heating means. An object is to provide an apparatus and an image forming apparatus.

  To achieve this object, the present invention provides a fixing member that rotates in contact with an unfixed image, a pressure member that forms a fixing nip between the fixing member, and heating that contacts and heats the fixing member. The heating unit includes a glass substrate having a low thermal conductivity, and a heating unit divided into a plurality of heating regions in the longitudinal direction on the glass substrate, the heating unit A soaking member made of a good heat conductive material is provided at a position not in contact with the fixing member, and the soaking member extends in the longitudinal direction of the fixing member and contacts the fixing member directly or through the member. A fixing device is proposed.

  According to the present invention, even when the heating means is divided into various paper widths, the heating means is divided into various paper widths while reducing heat dissipation to the surroundings by using the glass substrate heating means having low thermal conductivity. can do. In addition, even if the paper width that does not match the dividing position of the heating means is passed, the temperature of the fixing member can be made uniform by preventing the decrease in productivity by having a temperature-uniforming member against overheating of the non-sheet passing part. can do.

FIG. 2 is a schematic diagram illustrating an example of a printer as an image forming apparatus in which the fixing device of the present invention is used. 1 is a cross-sectional explanatory view of a fixing device showing an embodiment of the present invention. It is a structure circuit diagram which shows the specific example of a heating means. It is explanatory drawing which shows heater temperature distribution at the time of heater energization. It is a schematic diagram which shows a soaking | uniform-heating member. FIG. 6 is a schematic diagram illustrating a temperature distribution of a fixing belt with and without a heat equalizing member. It is explanatory drawing which shows the example which made the shape of the division | segmentation position of a soaking | uniform-heating member diagonal with respect to the conveyance direction of paper. FIG. 4 is an explanatory diagram illustrating an example in which a heating unit is disposed in a fixing nip and a soaking member is disposed in a portion other than the fixing nip. It is explanatory drawing which shows another embodiment of a soaking | uniform-heating member.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic view showing an example of a printer as an image forming apparatus in which the fixing device of the present invention is used. The printer shown here includes a photoconductive drum 1 as an image carrier, and around the photoconductive drum 1 is a charging unit, an optical writing unit, a developing unit, a transfer unit, a cleaning unit in order of rotation in the clockwise direction. Means and the like are arranged. When the photosensitive drum 1 is driven to rotate clockwise by a driving unit (not shown), the surface is uniformly charged by a charging roller 2 as a charging unit. When this charged portion reaches the optical writing unit 3, exposure light (not shown) irradiates exposure light through the mirror 3A, and an electrostatic latent image corresponding to the image to be created is formed. When the formed electrostatic latent image reaches the developing position, it is visualized by the developing means 4 having the developing roller 4A to become a toner image. Then, the toner image arrives at a position where the transfer means 5 provided with the transfer charger faces. The transfer means 5 is not limited to a transfer charger, and a transfer roller, a transfer brush, a transfer belt, or the like can be used.

  In the present embodiment, a sheet feeding means 10 is disposed below the photosensitive drum 1. The sheet feeding means 10 separates the sheet feeding tray 11 in which sheets P as sheet-like recording materials are accommodated in a stacked state and the sheet P accommodated in the sheet feeding tray 11 one by one from the top. It has a paper feed roller 12 to be sent out.

  The paper P delivered by the paper supply roller 12 is conveyed to the photosensitive drum 1 via a pair of timing conveying rollers 13 (hereinafter referred to as timing rollers). At that time, the paper P is abutted against the timing roller 13 and temporarily stopped. After the posture deviation is corrected, the paper P is sent out at a timing synchronized with the rotation of the photosensitive drum 1. That is, the timing roller 13 sends the toner image formed on the photosensitive drum 1 to the transfer unit at a timing when the leading end of the toner image coincides with a predetermined position at the leading end of the sheet P in the transport direction.

  In the transfer portion, the image is transferred onto the paper P entering the same portion by applying a transfer bias by the transfer means 5. The paper P on which the toner image has been transferred is conveyed toward the fixing device 20 and is fixed by the fixing device 20, and then discharged and stacked on a paper discharge tray (not shown). On the other hand, it is inevitable that toner remains on the photosensitive drum 1 after the transfer, and this residual toner is scraped off by the cleaning blade 15 while passing through the cleaning means 14 as the photosensitive drum 1 rotates. To be cleaned. Thereafter, the residual potential on the photosensitive drum 1 is removed by a neutralizing unit (not shown) and prepared for the next image forming process.

FIG. 2 is a cross-sectional explanatory view of a fixing device showing an embodiment of the present invention.
In FIG. 2, a fixing device 20 of the present embodiment includes a fixing belt 21 as a fixing member, and a pressure roller 22 as a pressure member that is disposed so as to face the fixing belt 21 and is pressed to form a fixing nip SN. With. Further, the fixing device 20 includes a heating unit 23 that heats the fixing belt 21 from the inside.

  The heating means 23 is made of a resistance heating part 24 and a glass substrate 25 (see FIG. 3), and is in contact with the fixing belt 21 on a substantially flat surface. The resistance heating part 24 is composed of a planar or plate-like heating element such as a thermal heater or a ceramic heater. A power source 33 is connected to the resistance heating unit 24, and power is supplied from the power source 33 to the resistance heating unit 24. The output of the power source 33 is controlled by the external control means 32. The external control means 32 is composed of a microcomputer including a CPU, ROM, RAM, I / O interface and the like.

  The fixing belt 21 includes a SUS base 21A having an outer diameter of 40 mm and a thickness of 40 μm, and an elastic layer 21B coated on the surface of the base 21A. The elastic layer 21B is made of silicon rubber and has a thickness of 100 μm. On the surface of the fixing belt 21, a release layer 21 </ b> C having a thickness of 5 to 50 μm is formed by a fluorine-based resin such as PFA or PTFE in order to enhance durability and ensure release properties. The base 21A of the fixing belt 21 is not limited to stainless steel but may be a base made of nickel or polyimide.

  In addition, a belt support member 28 is provided inside the fixing belt 21, and a heat equalizing member 50 that also serves as a nip forming member, which will be described in detail later, is provided at a position of the fixing nip SN. The belt support member 28 and the heat equalizing member 50 are connected to a side plate which is an external member (not shown) to support the fixing belt. Further, a sliding sheet (not shown) is wound around the outer periphery of the soaking member 50 to reduce the frictional force with the fixing belt.

  The pressure roller 22 includes an iron cored bar 22A having an outer diameter of 40 mm and a thickness of 2 mm, and an elastic layer 22B covered on the surface of the cored bar 22A. The elastic layer 22B is made of silicon rubber and has a thickness of 5 mm. It is desirable to form a fluororesin layer having a thickness of about 40 μm on the surface of the elastic layer 22B in order to improve the releasability. The pressure roller 22 is pressed against the fixing belt 21 by an urging means (not shown). Further, the heating member 23 has a support member 26 attached to a stay member (not shown) and pressed against the surface of the fixing belt 21.

  In the fixing device 20 of the present embodiment, a pressing roller 30 is provided on the surface of the fixing belt 21 at a position facing the heating unit 23 to ensure contact of the fixing belt 21 with the heating unit 23. Further, the pressing roller 30 includes a cored bar 30A and an elastic layer 30B covered on the surface of the cored bar 30A.

FIG. 3 is a configuration circuit diagram showing a specific example of the heating means 23 described above.
As described above, the heating means 23 of the present embodiment includes the resistance heating part 24 and the glass base 25 having a low thermal conductivity. The resistance heating section 24 is divided into a total of five resistance heating sections in the longitudinal direction, that is, in the direction orthogonal to the paper transport direction, the central section 24A, the left and right intermediate sections 24B, and the outer sections 24C on both sides. Has been. In the five resistance heating portions 24A to 24C, the heating region a of the central portion 24A, the heating regions b and b ′ of the intermediate portion, and the heating regions c and c ′ of the outer portion 24C are formed. In this embodiment, the width W1 of the heating area a is A6 vertical size, the heating area a + heating area b + the width W2 of the heating area b ′ is A4 vertical size, heating area a + heating area b + heating area b ′ + heating area c + heating area. The width W3 of c ′ is set to be substantially equal to the A3 vertical size. Therefore, when all of the heating areas a, b, b ′, c, and c ′ generate heat, an image up to A3 size can be fixed.

  In FIG. 3, reference numerals 40, 41, and 42 are temperature sensors, and the temperature sensors 40 to 42 are disposed in contact with the heating unit 23 at positions on the back side of the resistance heating unit 24. That is, the temperature sensor 40 is in contact with the glass base 25 on the back side of either the central portion 24A of the resistance heating portion 24, the temperature sensor 41 is on the intermediate portion 24B, or the temperature sensor 42 is on either side of the outer portion 24C. Has been placed. Reference numeral 43 denotes a safety device such as a thermostat, for example, and the safety device 43 is disposed on the back side of the central portion 24 </ b> A of the resistance heating portion 24 in the same manner as the temperature sensor 40.

  Furthermore, in the present embodiment, the wirings of the heating regions b and b 'of the intermediate portion 24B and the heating regions c and c' of the outer portion 24C are connected to form a parallel circuit, and these regions are lit in synchronization.

  In this circuit, the first switch 34 is provided between the wirings connecting the heating region a and the power source 33, and the wirings connecting the heating region b, b ′ or c, c ′ other than the heating region a and the power source 33. Between the first switch 34 and the second switch 35 or the third switch 36. Accordingly, the heating regions b, b 'or c, c' other than the heating region a are configured to be energized only when the heating region a is energized.

  The glass substrate 25 of the heating means 23 has a lower thermal conductivity than glass such as alumina, and the thermal conductivity is 0.5 to 1.5 W / m / K. Heat dissipation can be reduced. Further, the support member 26 (shown in FIG. 2) that supports the heating means 23 is also made of a resin such as LCP having low thermal conductivity and high heat resistance, so that the heat of the heating means 23 is not easily escaped to the support member. Yes. The support member 26 is supported on a side plate (not shown) of the fixing device by a metal stay (not shown).

FIG. 4 is an explanatory diagram showing the heater temperature distribution when the heater is energized.
In FIG. 4, when only the central portion 24A of the resistance heating portion 24 is energized, only the heating area a of the central portion 24A becomes high temperature, and the heat conductivity of the glass substrate 25 is low, so that heat is not easily diffused in the longitudinal direction. The temperature suddenly drops when entering the heating regions b and b ′ from the region a. Similarly, when the central portion 24A and the intermediate portion 24B of the resistance heating portion 24 are turned on, even when the heating regions a, b, and b ′ are turned on, only the ranges are heated and the temperature hardly rises in the outer portion.
Regarding the temperature distribution due to the heating of the resistance heating part 24, as shown in FIG. 4, the temperature of only the resistance heating part 24 in the longitudinal direction and the short direction of the resistance heating part 24 peaks, and outside the resistance heating part 24, The temperature drops rapidly. When the heating region of the resistance heating unit 24 is divided into a plurality of parts, the number of wirings from the power source 33 increases, so the width of the heating unit 23 itself increases, and the heat capacity of the heating unit 23 increases. However, since the glass substrate 25 is used, the temperature does not increase so much at the portion where the wiring of the glass substrate 25 is present, and the energy loss accompanying the increase in the heat capacity can be reduced.

  However, in the case of FIG. 4 as well, if paper having a paper size smaller than the paper width W1 or a paper size between the paper width W1 and the paper width W2 is passed, the paper width is reduced with respect to the heating region, and the excessive temperature rise in the non-sheet passing portion is caused. It will occur. It is possible to cope with various paper widths by further increasing the number of divisions of the heating area of the resistance heating unit 24. However, since a temperature sensor and a safety device are required for each heating area and the cost is increased, the number of divisions may be increased. There is a limit. Further, when the glass substrate 25 is used, the heat transfer in the longitudinal direction is small, so that the excessive temperature rise in the non-sheet passing portion becomes remarkable.

Therefore, the heat equalizing member is mounted so as to correspond to the paper smaller than the paper width W1 or the paper size between the paper width W1 and the paper width W2.
FIG. 5 is a schematic view showing the soaking member 50. The heat equalizing member 50 is configured in such a manner that a heat equalizing member made of a highly heat conductive material such as copper or aluminum, for example, is fitted on an elongated rectangular mounting base 54 made of a resin material. The

  The soaking member 50 is divided into three soaking members 51 and soaking members 52, 53. The soaking members 51 and 52, and the gaps between 51 and 53 have an appropriate width (for example, 1 to 2 mm). The whole is lined up in the longitudinal direction. The division position is about 2 mm outside (the heating areas c and c 'side) from the division position of the heating area b and the heating area c and the heating area b' and the heating area c '. This is in consideration of misalignment of the paper, misalignment between the heater and the fixing device, and the like. In addition, the soaking | uniform-heating member attaches | subjects the code | symbol 50 when describing the whole generically, and attaches | subjects the code | symbol 51, 52, 53 when explaining each member.

  FIG. 6 is a schematic diagram showing the temperature distribution of the fixing belt 21 with and without the soaking member 50. When only the heating region a is energized, the heat is transferred to the heating regions b and b ′ by the soaking member 50, so that the temperature distribution as shown by the solid line in FIG. It will decline.

  However, when the heating regions a, b, and b ′ are energized, the heat equalizing member 50 is divided between the heating regions b, c, and b ′ and c ′, so that the heating regions c and c ′ are directed. Does not transfer heat. As a result, the temperature distribution is almost the same as when the temperature equalizing member 50 is not provided, and there is no temperature drop in the heating regions b and b '. Actually, the heating regions b and b ′ are energized slightly so that the temperature at the end of the heating region 1 is high so that the temperature at the end of the heating region 1 does not decrease even when printing with the paper width W1. I have to.

  By the way, when the heat equalizing member 50 is divided between the heating regions a, b and b ', the temperature drop at the end of the heating region a as shown in FIG. 6 does not occur. However, at the time of excessive temperature rise in the non-sheet passing portion when a paper having a width smaller than the paper width W1 is passed, heat cannot be released to the heating regions b and b ', and soaking performance is lowered. For this reason, whether to divide the heat equalizing member 50 is determined in consideration of the required heat equalizing performance and energy saving performance. Here, the energy saving performance means that the heating regions b and b ′ are energized a little to maintain the temperature in order to prevent a temperature drop at the end of the heating region a, so that the heating region is higher than when the heat equalizing member 50 is divided. It is intended that energy for heating b and b ′ is wasted.

FIG. 7 is an explanatory view showing an example in which the shape of the dividing position of the heat equalizing member 50 is inclined with respect to the paper transport direction.
The soaking member 50 also serves as a nip forming member, and is pressed against the pressure roller 22 to form a fixing nip SN, and fixing is performed by applying heat and pressure to the paper at the nip. As shown in FIG. 5, when the soaking member 50 is divided between the heating regions b and b ′ and the heating regions c and c ′, a seam is formed in the soaking member 50. This is because there is a tolerance of the fit between the heat equalizing member 50 and the mounting base 54, so that the mounting base 54 must be made larger and the heat equalizing member 50 must be made smaller. As a result, a portion where there is no heat equalizing member 50 on the line in the same direction as the paper conveyance direction, that is, a gap portion is formed, so that even if the pressure roller 22 is pressed, there is no opposing portion and no pressure is applied.

  Therefore, in the method of dividing the heat equalizing member 50 shown in FIG. 5, there is a possibility that pressure loss occurs in the fixing nip, so it is desirable to make it oblique as shown in FIG. As shown in FIG. 7, when the heat equalizing member 50 is inclined, only a part of the gap is formed in the same direction as the paper conveyance direction, but the gap is dispersed in the longitudinal direction of the heat equalizing member, so that the pressure loss can be reduced. .

FIG. 8 is an explanatory view showing an example in which the heating means 23 is arranged in the fixing nip and the heat equalizing member 50 is arranged in a part other than the fixing nip.
In the example shown in FIG. 8, the heat equalizing member 50 has an arc shape formed with a curvature close to a rotation circle in the rotation direction of the fixing belt 21, and the fixing belt 21 and the heat equalizing member 50 are in light contact with each other while sliding. . At this time, although not shown, it is also effective to provide a facing member that presses against the heat equalizing member 50 via the fixing belt 21 in order to improve the contact property between the fixing belt 21 and the heat equalizing member 50.

FIG. 9 is an explanatory view showing another embodiment of the heat equalizing member 50.
In FIG. 9, the heat equalizing member of this example is only the heat equalizing member 51, and the heat equalizing members 52 and 53 in the region corresponding to the heating regions c and c ′ are eliminated from the form shown in FIG. 54. This is an example in which the width of the heating regions c and c ′ is narrow and the productivity (CPM) is relatively small and the excessive temperature rise in the non-sheet passing portion is small. Cost reduction can be achieved by eliminating the soaking members 52 and 53 in the region corresponding to the heating regions c and c ′.

  In addition, when a metal having good thermal conductivity (such as Cu) is used for the base material of the fixing belt 21, the heat equalization performance of the heat equalization member 50 can be reduced due to the heat equalization performance of the fixing belt 21. . As a result, the width and thickness of the heat equalizing member 50 can be reduced, and energy savings can be improved by reducing costs and reducing heat capacity.

DESCRIPTION OF SYMBOLS 20 Fixing device 21 Fixing belt 22 Pressure roller 23 Heating means 24 Resistance heating part 25 Glass base body 50 51, 52, 53 Soaking member a, b, b'c, c 'Heating area

Japanese Patent Laid-Open No. 06-95540 JP 2012-189719 A JP 2004-235001 A JP 2001-110551 A

Claims (7)

In a fixing device including a fixing member that rotates in contact with an unfixed image, a pressure member that forms a fixing nip with the fixing member, and a heating unit that contacts and heats the fixing member.
The heating means includes a glass substrate having a low thermal conductivity, and a heating unit divided into a plurality of heating regions in the longitudinal direction on the glass substrate,
A heat equalizing member made of a heat conductive material is provided at a position not in contact with the heating means, and the heat equalizing member extends in the longitudinal direction of the fixing member, and the fixing member is directly or via a member. Fixing device characterized by contacting with   2. The heat equalizing member is divided into at least two or more in the longitudinal direction, and the dividing position of the heat equalizing member is substantially the same as the dividing position of the heating region of the heating means. Fixing device.   The fixing device according to claim 1, wherein the heat equalizing member is copper or aluminum having good thermal conductivity.   The fixing device according to claim 1, wherein a fixing nip is formed by contacting the heating unit with the pressure member via the fixing member.   4. The fixing device according to claim 1, wherein a fixing nip is formed by contacting the pressure equalizing member with the pressure member through the fixing member. 5.   6. The fixing device according to claim 5, further comprising an opposing member that is pressed against the heating unit via the fixing member.   An image forming apparatus using the fixing device according to claim 1.

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