JP2008111920A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which restrains excessive temperature rise in a paper non-passing area at a nip part by existent temperature control without requiring complicated temperature control, and maintains the improvement of fixing property and the shortening of warming-up time in spite of inexpensive and simple constitution, and also to provide an image forming apparatus. <P>SOLUTION: The fixing device is equipped with a heating roller 22 and a pressure roller 23 rotating in a press-contacting state each other, and is provided with a heat radiation member 33 constituted of an aggregate of two kinds of thermal deformation members 34 and 35 having a different thermal expansion coefficient so as to come into contact with the outer periphery of the heating roller, and also arranged in the paper non-passing area W in the nip width of the nip part 21 formed by the heating roller 22 and the pressure roller 23. The heat radiation member 33 is deformed so that contact area with the outer periphery of the heating roller 22 may be changed in accordance with the temperature of the paper non-passing area W due to a difference between the thermal expansion coefficients of the two kinds of thermal deformation members 34 and 35. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus that are provided in an image forming apparatus such as a copying machine, a facsimile machine, a printer, or a combination machine, and that fixes a transfer image formed on the surface of a conveyance sheet.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines, facsimile machines, printers, or a combination machine of these have been provided with a fixing device that fixes an unfixed toner image (transfer image) formed on the surface of a conveyance sheet. Yes.

  In this fixing device, a heating roller (or a heating belt) and a pressure roller are in contact with each other, and a conveyance sheet on which an unfixed toner image is formed is passed through a nip portion formed by the contact between them. By using paper, the toner is melted by the heat of the heating roller and the pressure of the pressure roller, and is fixed on the surface of the transport sheet as a toner image.

  The heating roller is formed by providing an elastic layer or a release layer on the surface of a cylindrical metal core having a heat source such as a halogen heater inside, and heats the surface from the inside by heat generated by the heat source. In addition, a thin roller having a cylindrical shape made of an aluminum material or an iron material is often used for the metal core of the heating roller.

  By using such a thin roller made of an aluminum material or an iron material as the metal core of the heating roller, the warm-up time can be shortened, and a favorable effect can be obtained from the viewpoint of energy saving.

  On the other hand, when a conveyance sheet is passed through the nip portion, a non-sheet passing area is formed in the longitudinal direction of the nip portion depending on the size of the conveyance sheet that has passed through.

  In other words, the maximum size of the transport sheet that can be used is set in the nip portion depending on the capability of the image forming apparatus, for example, the maximum size A3 for business or the maximum size A4 for home use.

  For example, an image forming apparatus for the maximum size A3 can use A3, B4, A4, B5, A5, postcards, etc. as standard-size transport sheets.

  Here, a standard-size transport sheet that is relatively frequently used is B5, and when this B5 transport sheet is passed in landscape orientation, the nip portion is set to a nip width that allows A3 portrait orientation. The conveyance sheet is not passed near both ends (or near one end) of the nip portion.

  When a B5 landscape sheet is passed through such a nip portion corresponding to A3, the temperature of the nip portion where the transport sheet passes is lowered due to the heat of the transport sheet.

  If the transport sheet is allowed to pass through while this temperature drop occurs, toner fixing failure may occur, so the temperature near the center of the nip (or heating roller) is generally monitored with a temperature sensor or the like. It is necessary to control the heat source so that the vicinity of the center is maintained at the toner fixing temperature (for example, 180 ° C. or higher).

  However, in such a temperature management control system, since the heating roller uniformly heats the entire nip width by a heat source, a good toner fixing temperature is maintained in the sheet passing area, and in a non-sheet passing area. It becomes higher than the toner fixing temperature.

  When the temperature of the non-sheet passing area is increased in a state where such a non-sheet passing area is formed, there is a problem in that a problem occurs in durability such that the aging deterioration of the pressure roller is promoted. It was happening.

  Also, for example, if a large conveyance sheet for fixing with a wide nip width is passed immediately after passing a large amount of small conveyance sheet for fixing processing with a narrow nip width, it will be excessive in the non-sheet passing area. The paper will pass in a heated state, and the part corresponding to the non-sheet passing area of the unfixed toner image formed on the surface of the transport sheet will be fixed at a high temperature, causing a high temperature offset such as poor fixing. There was a problem of doing so.

  Further, when a thin roller made of an aluminum material or an iron material is used as the metal core of the heating roller in order to shorten the warm-up time described above, such high temperature offset and durability become a greater problem.

Therefore, in order to reduce the temperature difference between the sheet passing area and the non-sheet passing area when a small-sized transport sheet is continuously passed with respect to the set nip width, A fixing device (for example, see Patent Document 1) that strengthens the wind power of the cooling fan provided, or a heat source that divides the heat source along the nip width direction and uses a heat generating area near the center of the nip width according to the conveyance sheet size And a fixing device (for example, see Patent Document 2) that uses a heat source having a heat generation area near both ends of the nip width can be considered.
JP 05-119669 A JP 2004-212550 A

  However, in the above-described fixing device, for example, a fixing device that strengthens the wind force of the cooling fan provided corresponding to the temperature rise region when small-sized continuous paper is passed, temperature control by the cooling fan becomes complicated, and the cooling fan As a result, there has been a problem that the management cost has increased, such as the deterioration of the aging and the increase in power consumption.

  In addition, when the heat source is divided along the nip width direction, when trying to pass a large size transport sheet immediately after passing a small size transport sheet, heating by a heat source having a heat generation area near both ends of the nip width is performed. This causes a problem that it takes a warm-up time.

  Moreover, in order to eliminate such problems, it is necessary to monitor and control two temperatures, the temperature near the center of the nip width and the temperature near both ends. There were problems such as soaring and complicated temperature control of multiple heat sources.

  Therefore, in consideration of the above circumstances, the present invention suppresses an excessive temperature increase in a non-sheet passing region of the nip portion with existing temperature management without requiring complicated temperature control while being an inexpensive and simple configuration. In addition, an object of the present invention is to provide a fixing device and an image forming apparatus capable of maintaining the improvement of the fixing property and the shortening of the warm-up time.

  The fixing device and the image forming apparatus according to the present invention include two types of thermal deformations having different thermal expansion coefficients so as to be in contact with the outer periphery of the heating member in a fixing device including a heating member and a pressure member that rotate in pressure contact with each other. A heat dissipating member composed of a polymer of members is provided, and the heat dissipating member changes in contact area with the outer periphery according to the temperature of the heating member due to a difference in thermal expansion coefficient between the two types of heat deformable members. It is characterized by being deformed as described above.

  At this time, the heat dissipating member substantially coincides with the maximum allowable transport sheet size set in advance as the image forming processing capacity for the transport sheet size of the nip portion formed by the heating member and the pressure member. Is arranged in the non-sheet passing area so as to include a portion obtained by removing the area used at the time of image forming processing for the conveyance sheet that is assumed to be frequently used from the maximum sheet passing area to be used as a preset normal sheet passing area. It is preferable.

  According to such a configuration, the heat radiating member in contact with the outer periphery of the heating member can adjust the change in the surface temperature accompanying the heating of the heating member by the polymer of two types of thermally deformable members having different thermal expansion coefficients, and is inexpensive. With a simple configuration, it is possible to suppress excessive temperature rise in the non-sheet passing area of the nip portion with existing temperature management without requiring complicated temperature control, and to improve fixing performance and warm-up time. Shortening can be maintained.

  In addition, the present invention can be an image forming apparatus employing the fixing device and the image forming apparatus having any one of the above-described configurations.

  The fixing device of the present invention is capable of suppressing an excessive temperature increase in the non-sheet passing region of the nip portion with existing temperature management without requiring complicated temperature control, while having a low-cost and simple configuration, It is possible to maintain improvement in fixing property and shortening of warm-up time.

  Next, a fixing device according to an embodiment of the present invention is applied to a printer as an image forming apparatus and will be described with reference to the drawings.

  FIG. 1 is an explanatory diagram of a printer as an image forming apparatus using a fixing device according to an embodiment of the present invention, and FIG. 2 is a sectional view of the fixing device according to an embodiment of the present invention.

  As shown in FIGS. 1 and 2, a printer 1 as an image forming apparatus according to an embodiment of the present invention includes a paper feed cassette 3 that is slidably stored in a printer main body 2 as an image forming apparatus main body. A paper feed unit 5 for taking out a transport sheet (not shown) stored in the storage space 4 of the paper feed cassette 3, a manual feed tray 6 installed in front of the printer main body 2, and a manual feed tray 6. A manual sheet feeding unit 7 for taking out a set conveyance sheet (not shown), a conveyance path 8 for conveying conveyance sheets supplied from the respective sheet feeding units 5 and 7, and an upstream side in the sheet conveyance direction of the conveyance path 8 The registration roller pair 9 disposed downstream of the merging portion of each of the sheet feeding units 5 and 7 in the sheet conveyance direction, and the conveyance sheet 8 disposed downstream of the registration roller pair 9 in the sheet conveyance direction of the conveyance path 8. On one side An image forming unit 10 that forms an image, and a fixing device 11 that is disposed downstream of the image forming unit 10 in the sheet conveyance direction of the conveyance path 8 and fixes an image (toner image) formed on one surface of the conveyance sheet; When an image is formed on the other surface of the transport sheet that has passed through the fixing device 11, the image is pulled back from the transport path downstream side of the transport path 8 from the transport path 8 to the upstream side of the transport path 8 in the sheet transport direction from the registration roller pair 9. A reversing path 12 and a paper discharge section 13 provided at the end of the transport path 8 are provided.

  The image forming unit 10 includes a photosensitive drum 14 and a charging device 15, an exposure device 16, a developing device 17, a transfer device 18, a cleaning device 19, and the like disposed around the photosensitive drum 14.

  As a result, in the image forming unit 10, the photosensitive drum 14 is rotationally driven at a predetermined process speed (circumferential speed) by a driving unit (not shown), and the surface thereof is uniformly charged to a predetermined polarity and potential by the charging device 15. .

  An electrostatic latent image is formed on the surface of the charged photosensitive drum 14 by the exposure device 16. Here, the exposure device 16 irradiates the surface of the photosensitive drum 14 with laser light (not shown) based on image data output from a personal computer or the like, and a laser light irradiation portion on the surface of the photosensitive drum 14. The electrostatic latent image corresponding to the image information is formed by removing the charges.

  The electrostatic latent image formed on the surface of the photosensitive drum 14 is developed as a toner image by electrostatically adhering toner having a charge supplied from the toner container 20 by the developing device 17. Further, the toner image is transferred to the transport sheet as a transfer image by the transfer device 18.

  At this time, the photosensitive drum 14 having the toner image transferred to the conveying sheet is subjected to a removal process of residual toner and the like and a charge removal process for charging at the next image formation by the cleaning device 19.

(Configuration of Fixing Device 11)
FIG. 2 is a cross-sectional view of the fixing device showing an example of the fixing device according to the embodiment of the present invention.

  In FIG. 2, the fixing device 11 includes a heating roller 22 and a pressure roller 23 as a pair of rotating bodies that form a nip portion 21 by being pressed against each other.

  In this embodiment, the heating roller 22 has a surface release such as a PFA coat having a thickness of 20 μm on the surface of a metal core (core metal) 22a made of iron (STKM) having an outer diameter of 30 mm and a thickness of 0.3 mm. A layer formed with a layer (not shown because it is a thin film layer) is used. In addition, a heat source 24 made of a heating element such as a halogen heater (for example, power consumption 800 W) is provided inside the heating roller 22, whereby the surface of the heating roller 22 is heated (for example, a set temperature: 180 ° C.). The Both ends of the heat source 24 are connected to power supply wiring (not shown). The heating roller 22 is held by the movable frame 25 via a bearing 26, and the heat source 24 is supported by side plate portions 25 a located at both ends of the movable frame 25.

  The movable frame 25 is supported by the other end of an urging member 27 such as a spring whose one end is fixed to a fixed portion 2a (the detailed structure is omitted) provided in the printer main body 2. The heating roller 22 is biased toward the pressure roller 23 by the biasing member 27.

  The pressure roller 23 is made of a core metal 23a made of iron or the like, and an outer layer 23b of an elastic layer (not shown) made of silicone rubber or the like, and a surface release layer (thin layer) made of a PFA tube having a thickness of about 50 μm. Therefore, the outer diameter is about 25 mm. The pressure roller 23 is supported by a fixed frame 29 with a shaft portion 23 c of a core metal 23 a via a bearing 28. A gear 30 is provided on one of the shaft portions 23c. The gear 30 meshes with the output gear 32 of the drive motor 31, and the pressure roller 23 is rotated by the drive of the drive motor 31, and the heating roller 22 that is in pressure contact with the pressure roller 23 is driven to rotate. The pressure roller 23 has a fixing load of 60 N and an outer peripheral speed of 250 mm / sec with respect to the heating roller 22.

  On the other hand, a pair of heat radiating members (bimetals) 33 are in contact with the heating roller 22 near both ends of the nip portion 21.

(Configuration of heat dissipation member 33)
The heat dissipating member 33 is composed of a polymer of two types of heat deformable members 34 and 35, and a nip that substantially matches the maximum allowable transport sheet size set in advance as the image forming processing capacity for the transport sheet size of the fixing device 11. The non-sheet-passing area W so as to include a portion obtained by removing, from the maximum sheet-passing area H of the unit 21, an area used during image forming processing for a transport sheet that is assumed to be frequently used as a preset normal sheet-passing area h. Is arranged as.

  That is, each of the heat radiating members 33 has, for example, a maximum sheet passing area H that is equal to or larger than a small edge width of the conveying sheet size A3 as the maximum allowable conveying sheet size, and a generally used conveying sheet is set to a B5 landscape size with a small size width (= B5 longitudinal width), A3 fore edge width−B5 longitudinal width≈114 mm, and assuming that both ends of the nip portion 21 are evenly spaced, 114 mm ÷ 2 = 57 mm. It arrange | positions as the area | region W, The thickness is comprised by 0.5 mm (each 0.25 mm).

  Note that the small size width h set here is, for example, an industry or the like (for example, in a direct mail company) when presetting on the basis of a conveyance sheet size generally used by, for example, a sales market survey of a conveyance sheet size. Including the case of setting in advance according to the demand of the conveyance sheet size frequently used by the user, etc. When it is determined that a transport sheet having a high possibility of passing a large amount of paper is small with respect to the maximum sheet passing area H that is the capability (for example, A3 correspondence) of the printer 1, the transport sheet size ( Can be arbitrarily set as the set small size width h.

  Then, by setting the set small size width h, the non-sheet passing area W for the maximum sheet passing area H is determined (set).

  The width of the non-sheet-passing area W is set to 55 to 60 mm because the misalignment (error) in the nip width direction and the image forming process margin that occur when the transport sheet is transported due to the capability of the printer 1 and the like are set. And the like, including the set small size width h of the conveyance sheet for determining the non-sheet passing area W is arbitrary. Further, the thickness of the heat radiating member 33 is also determined in consideration of the material of the heat deformation members 34 and 35 to be used, the setting of the excessive temperature (setting of the toner fixing temperature), and the like.

  The heat radiating member 33 is supported by the other end of an urging member 36 such as a spring whose one end is fixed to the movable frame 25, and is normally urged toward the heating roller 22 by the urging of the urging member 36. Has been. In addition, in order to improve the slidability with the outer peripheral surface of the heating roller 22, the PFA resin coating process etc. may be given to the contact surface side of the heat radiating member 33 with the heating roller 22.

  One thermal deformation member 34 and the other thermal deformation member 35 are made of materials having different coefficients of thermal expansion, and one thermal deformation member 34 is made of a material having a low coefficient of thermal expansion. The surface side of the heating roller 22 is in the form of a plate that is in sliding contact with the outer surface. The other thermal deformation member 35 is made of a material having a large coefficient of thermal expansion, and is located on the back side of the one thermal deformation member 34.

  Here, FIG. 3 is a chart showing a list of main metal thermal expansion coefficients, and FIG. 4 is a chart showing an example of a combination of materials of one thermal deformation member 34 and the other thermal deformation member 35.

  In the above configuration, for example, the A3 portrait size transport sheet is stored in the paper feed cassette 3, and the B5 portrait size transport sheet is stored in the manual feed tray 6, and is based on image data output from a personal computer (not shown). When the B5 portrait transport sheet stored in the manual feed tray 6 is taken out by driving the sheet feeding unit 7, an unfixed toner image is formed in the image forming unit 9 while being guided along the transport path 8. After the toner is fixed by the fixing device 11, the toner is discharged from the paper discharge unit 13.

  At this time, the heat source 24 of the fixing device 11 is temperature-controlled by a temperature sensor (not shown) so that the surface temperature thereof becomes the toner fixing temperature (for example, 180 ° C.).

  Accordingly, as shown in FIGS. 5 and 7, when the surface temperature of the maximum sheet passing area H including the non-sheet passing area W of the heating roller 23 is close to the toner fixing temperature, as shown in FIGS. The state where a part is in contact with the heating roller 23 is maintained.

  Then, when a large amount of B5 vertically long conveyance sheets are passed, as shown in FIGS. 6 and 8, the heat radiating member 33 causes the surface temperature of the non-sheet passing area W of the heating roller 23 to reach an excessive temperature. 8 (see the two-dot chain line portion in the graph of FIG. 8), the entire heat radiation member 33 of the heating roller 23 is caused by the difference in thermal expansion coefficient between the two types of thermal deformation members 34 and 35 having different thermal expansion coefficients. Deforms so that it touches the surface widely.

  As a result, the surface temperature of the non-sheet passing area W of the heating roller 23 is absorbed by the heat radiating member 33 to the vicinity of the toner fixing temperature, and the temperature rise of the heat radiating member 33 due to the heat absorption is cooled by its own heat radiating action.

  Accordingly, immediately after performing a large number of image forming processes using the B5 size transport sheet, an A3 portrait-size transport sheet stored in the paper feed cassette 3 based on image data output from a personal computer (not shown) is obtained. The unfixed toner image taken out by driving of the paper feeding unit 5 and formed on the surface of the conveying sheet has a nip portion 21 in which the entire maximum sheet passing region H of the fixing device 11 maintains a substantially uniform fixing temperature. After the toner is stably fixed by passing the paper, the paper is discharged from the paper discharge unit 13.

  As described above, in the fixing device 11 and the printer 1 as the image forming apparatus of the present invention, the heat radiating member 33 including the two types of heat deformable members 34 and 35 having different thermal expansion coefficients is slid on the outer periphery of the heating roller 23. By making contact, it is possible to reduce the temperature difference between the normal sheet passing area h and the non-sheet passing area W of the heating roller 23 during continuous passing of small-size sheets without providing a complicated control method.

  For this reason, even if a large-sized transport sheet is passed after a large amount of small-size transport sheets are passed, the fixing property is good and warm-up can be shortened without causing high-temperature offset. , Energy consumption can be reduced.

  By the way, in the said embodiment, what used the roller-type heating roller 23 as a heating member was disclosed, but as shown in FIG.9 and FIG.10, even if it is a case where a belt-type heating member is used, it is applicable. can do.

  9 and 10, reference numeral 40 denotes a nip roller to be pressed by the pressure roller 23, 41 denotes a heating source roller having a heat source 42 such as a halogen heater therein, and 43 denotes a heating with the nip roller 41. A heating belt stretched between the heat source roller 41 and the heat generated by the heat source roller 41 is transferred to the heat belt 43 to bring the nip portion 21 to a fixing temperature. The same components are denoted by the same reference numerals, and the description thereof is omitted.

  Also, for example, as shown in FIG. 11, the maximum sheet passing area H is set based on the A3 portrait length as the maximum allowable size of the conveyed sheet, and the minimum size of the conveyed sheet is set to the postcard size. For a non-sheet passing area W obtained by subtracting the postcard portrait size (= normal sheet passing area h) from H, when B4 portrait is transported (B5 landscape transport), A4 portrait (A5 landscape transport), and B5 portrait transport , A5 vertical transport (postcard horizontal transport) difference in width (for example, W1 = (A3 vertical−B4 vertical) / 2≈2 cm, W2 = (B4 vertical−A4 vertical) ÷ 2≈2.5 cm, W3 = (A4 vertical−B5 vertical) ÷ 2≈1.5 cm, W4 = (B5 vertical−A5 vertical) ÷ 2≈1.7 cm, W5 = (A5 vertical−postcard vertical) ÷ 2≈2.3 cm) You may comprise from the several heat radiating member 33-1 to 33-5 divided | segmented into.

  Further, the plurality of divided heat radiating members 33-1 to 33-5 may be arranged across the entire maximum sheet passing region H.

  At this time, the plurality of divided heat dissipating members 33-1 to 33-5 may be thicker as they are located closer to both ends of the heating roller 22.

  In the above embodiment, the fixing device 11 of the present invention has been described as being installed in the printer 1 as an image forming apparatus. However, for example, a copying machine or a multifunction machine having a printer function and a copying function can be used. Of course, the present invention can be applied to all image forming apparatuses.

1 is an explanatory diagram of a printer as an image forming apparatus using a fixing device according to an embodiment of the present invention. FIG. 1 is a cross-sectional view of a fixing device according to an embodiment of the present invention. It is a chart showing a list of thermal expansion coefficients of main metals used for a heat radiating member of a fixing device according to an embodiment of the present invention. It is a graph which shows the example of a combination of the material of the heat deformation member used for the heat radiating member of the fixing device which concerns on one Embodiment of this invention. FIG. 3 is a cross-sectional view of a main part at a toner fixing temperature of a fixing device according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a main part of the fixing device according to an embodiment of the present invention at an excessive temperature rise. FIG. 5 is a graph of a temperature distribution portion at a toner fixing temperature of a fixing device according to an embodiment of the present invention. FIG. 6 is a graph of a temperature distribution part at the time of overheating of a fixing device according to an embodiment of the present invention. FIG. 6 is a cross-sectional view of a main part at a toner fixing temperature of another fixing device according to an embodiment of the present invention. FIG. 10 is a cross-sectional view of a main part at the time of overheating of another fixing device according to an embodiment of the present invention. It is explanatory drawing of the other heat radiating member which concerns on one Embodiment of this invention.

Explanation of symbols

1 ... Printer (image forming apparatus)
11: Fixing device 22 ... Heating roller (heating member)
23. Pressure roller (pressure member)
33 ... Heat dissipation member 34 ... Heat deformation member 35 ... Heat deformation member H ... Maximum sheet passing area h ... Normal sheet passing area W ... Non sheet passing area

Claims (3)

In a fixing device including a heating member and a pressure member that rotate in pressure contact with each other,
A heat dissipating member composed of a polymer of two types of thermally deformable members having different thermal expansion coefficients is provided so as to be in contact with the outer periphery of the heating member, and the heat dissipating member is a difference in coefficient of thermal expansion between the two types of heat deformable members. Due to the above, the fixing device is deformed so that the contact area with the outer periphery changes according to the temperature of the heating member.   The heat dissipating member is frequently used from the maximum sheet passing area that substantially matches the maximum allowable transport sheet size set in advance as the image forming processing capacity for the transport sheet size of the nip portion formed by the heating member and the pressure member. 2. The non-sheet-passing area is disposed so as to include a portion excluding an area to be used during image forming processing for a conveyance sheet assumed to be used for a normal sheet passing area set in advance. The fixing device according to 1.   An image forming apparatus comprising the fixing device and the image forming apparatus according to claim 1.

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