Patent Grant
10725407
The present disclosure relates to fixing apparatuses for use in image forming apparatuses, such as electrophotographic copying machines and laser printers. An example of the fixing apparatuses is a fixing apparatus that thermally fixes unfixed toner images formed on a printing material (for example, paper) to the printing material.
Known toner fixing apparatuses for use in an electrophotographic method are of a heat roller type and a film heating type. Fixing apparatuses of the film heating type (for example, Japanese Patent No. 4599189) include a heater having a resistive heating element on a ceramic substrate, a fixing film that rotates while being heated in contact with the heater, and a pressure roller that forms a nip with the heater with the fixing film therebetween. A printing material that bears an unfixed toner image is nipped at the nip and is heated while being conveyed, and thus the toner image on the printing material is fixed to the printing material. Since the fixing apparatuses of the film heating type use a film with a heat capacity smaller than the heat capacity of fixing apparatuses of the heat roller type as a fixing member, the time taken to bring the temperature of the fixing member to a predetermined temperature (start-up time) can be reduced. The short start-up time eliminates the need to heat the fixing member during standby, reducing power consumption as much as possible.
It is known that it is important for the fixing apparatuses of the film heating type to make the gap between the upstream wall surface of the heater and the upstream end face (wall surface) of a groove hole of a holder that holds the heater small. As described in Japanese Patent No. 4599189, if a printing material is inserted into the nip, with small, hard foreign matter, such as a staple, a grain of sand, grit, or dust, attached on the surface, this configuration reduces or eliminates a phenomenon in which the foreign matter enters the gap to damage the film. In other words, decreasing the gap may reduce the force of the foreign matter entering the gap, thereby preventing the film from being punctured.
In the configuration in which the gap between the upstream wall surface of the heater and the upstream end face (wall surface) of the groove hole of the holder that holds the heater is small, the width of the gap is determined only by the width of the groove hole in the printing material conveying direction and the width of the heater. For this reason, there are cases where the gap cannot be made sufficiently small. The heater and the groove hole generally vary in width. Therefore, the width of the heater needs to be sufficiently smaller than the width of the groove hole to avoid cases where assembly is impossible. If the heater width and the groove hole width are normal, or in contrast, the heater width is small and the groove hole width varies widely, the intended small gap cannot be provided, so that sufficient resistance to foreign matter, described above, cannot be achieved.
The present disclosure prevents damage to the film due to foreign matter even if the dimensional accuracy of the components of a fixing apparatus of the film heating type is low.
A fixing apparatus according to an aspect of the present disclosure includes a holding member including a groove-like holding portion, a heater supported by the holding portion, a film rotatable around the heater, the film being configured to be heated by sliding on the heater and to heat a toner image on a conveyed printing material, and a gap filling member including, on an upstream side with respect to the heater in a direction in which the circumferential surface of the film moves, a first portion disposed between the heater and the holding member and a first contact portion connecting to the first portion and being in contact with the film. A second distance between the first portion and the holding member disposed upstream from the first portion and facing the first portion is smaller than a first distance between the heater and the first portion disposed upstream from the heater and facing the holding member.
Further features and aspects of the disclosure will become apparent from the following description of example embodiments with reference to the attached drawings.
First, the configuration of the main body of an image forming apparatus in the present embodiment will be described, and then, a fixing apparatus according to an embodiment of the present disclosure will be described.
Image Forming Apparatus Main Body
In the present embodiment, an example of a method for forming an unfixed toner image on a printing material and an image forming apparatus will be described with reference to the schematic diagram illustrated in
Example Fixing Apparatus
Next, the fixing apparatus 100 of the present embodiment will be described. The fixing apparatus 100 of the present embodiment is of the film heating type aiming at shortening start-up time and reducing power consumption, as described above.
A gap filling member (heat transfer member) 140 is disposed on the back of a heater 113. The heat transfer member 140 and the heater 113 are held by a groove-like holding portion of a heater holder (a holding member) 130, around which a fixing film 112, which is an endless belt, is rotatably disposed. The heater 113 slides on the inner surface of the fixing film 112 to heat the fixing film 112 from the inside. A pressure roller 110 applies pressure to the heater 113 from the outside of the fixing film 112. An area at which the pressure roller 110 and the fixing film 112 are brought into contact by the pressure is a pressure nip N. When the pressure roller 110 is driven in the direction of arrow R1 in
Example Fixing Film
The fixing film 112 of the present embodiment has an outside diameter of 18 mm in an undeformed cylindrical state and has a multilayer structure in the thickness direction. The layer structure of the fixing film 112 includes a base layer for maintaining the strength of the fixing film 112 and a releasing layer for reducing stain adhesion to the surface. The material of the base layer needs thermal resistance because it receives the heat from the heater 113 and also strength because the fixing film 112 slides on the heater 113, so that metal, such as stainless steel or nickel, or a heat-resistant resin, such as polyimide, may be used. In the present embodiment, a polyimide resin is used as the material of the base layer of the fixing film 112, to which a carbon-based filler is added to increase the thermal conductivity and strength. The thinner the base layer, the easier the heat of the heater 113 is transmitted to the surface of the pressure roller 110, which however decreases the strength. For that reason, the base layer preferably has a thickness of about 15 μm to 100 μm, and in the present embodiment, the base layer has a thickness of 50 μm.
The material of the releasing layer of the fixing film 112 may be a fluorocarbon polyester, such as a perfluoroalkoxy polymer (PFA), a polytetrafluoroethylene resin (PTFE), or tetrafluoroethylene-hexafluoropropylene resin (FEP). In the present embodiment, PFA having excellent releasability and heat resistance among fluorocarbon polyesters is used as the material of the releasing layer of the fixing film 112. The releasing layer may be a tube coating or a paint coating on the surface of the base layer. In the present embodiment, the releasing layer is a coating excellent in thin-wall molding. The thinner the releasing layer, the easier the heat of the heater 113 is transmitted to the surface of the fixing film 112. However, an excessively thin releasing layer decreases in durability. For this reason, the releasing layer preferably has a thickness of about 5 μm to 30 μm, and in the present embodiment, the releasing layer has a thickness of 10 μm. Although not used in the present embodiment, an elastic layer may be disposed between the base layer and the releasing layer. In this case, the material of the elastic layer is silicone rubber or fluorine-containing rubber.
Example Pressure Roller
The pressure roller 110 of the present embodiment has an outside diameter of 20 mm. The pressure roller 110 has an elastic layer 116 with a thickness of 4 mm around an iron core 117 with a diameter of 12 mm. The material of the elastic layer 116 is solid rubber or foamed rubber. The foamed rubber has a low heat capacity and low thermal conductivity, so that the heat of the surface of the pressure roller 110 is hardly absorbed inside. This offers the advantage that the surface temperature tends to rise, so that the start-up time can be reduced. In the present embodiment, foamed silicon rubber is used.
The smaller the outside diameter of the pressure roller 110, the smaller the heat capacity is. However, an excessively small outside diameter causes the width of the pressure nip to be small. For this reason, the pressure roller 110 needs a moderate diameter. In the present embodiment, the outside diameter is set to 20 mm. Also for the thickness of the elastic layer 116, an excessively small thickness causes the heat to dissipate to the metal core 117. For this reason, the elastic layer 116 needs an appropriate thickness. In the present embodiment, the thickness of the elastic layer 116 is set to 4 mm. A toner releasing layer 118 made of a perfluoroalkoxy polymer (PFA) is formed on the elastic layer 116. The releasing layer 118 may be a tube coating or a paint coating on the surface of the elastic layer 116, like the releasing layer of the fixing film 112. In the present embodiment, the releasing layer 118 is a tube having high durability. In addition to PFA, the material of the releasing layer 118 may be fluorocarbon polyester such as PTFE or FEP, or fluorine-containing rubber or silicone rubber having high releasability.
The lower the surface hardness of the pressure roller 110, the larger width of the pressure nip N is obtained at low pressure. In the present embodiment, the pressure roller 110 with an Asker-C hardness (a load of 4.9N) of 50 degrees is used. The pressure roller 110 is pressed to the heater 113 by a pressure unit (not illustrated). The total pressing force is set to 15 kg.
The pressure roller 110 is rotated by a rotating unit (not illustrated) in the direction of arrow R1 in
Example Heater
The heater 113 of the present embodiment is a common heater for use in a fixing apparatus of the film heating type and has a resistive heating element 113b on a ceramic substrate 113a. Specifically, the resistive heating element 113b is formed by applying 10-μm silver palladium (Ag/Pd) onto the surface of the alumina substrate 113a with a width of 7 mm and a thickness of 1 mm by screen printing in the conveying direction of the printing material P, that is, a direction in which the circumferential surface of the film 112 moves. A heating-element protective layer 113c is formed from glass with a thickness of 50 μm on the substrate 113a so as to cover the heater 113. The temperature of the heater 113 is regulated by appropriately controlling a current that is to be made flow to the resistive heating element 113b according to the signal of a temperature sensor (not illustrated) for detecting the temperature of the ceramic substrate 113a or the film 112.
Example Gap Filling Member
The gap filling member 140, which is a feature of the present embodiment, will be described with reference to
Example Amount of Protrusion
The sliding portion 140c is disposed so as to protrude on the upstream side of the heater 113 toward the pressure roller 110, that is, toward the film 112, with respect to a plane a of the heater 113 (the heating-element protective layer 113c) extending in a direction perpendicular to the pressing direction a of the pressure roller 110. This allows receiving the friction from the film 112 with the sliding portion 140c. This also prevents a corner 113Eu between the upstream wall surface 113Wu of the heater 113 and a surface (a slide surface) of the heater 113 (the heating-element protective layer 113c) adjacent to the film 112 from coming into contact with the film 112 if foreign matter intrudes between the film 112 and the pressure roller 110. The corner 113Eu of the heater 113 is very sharp. For this reason, when foreign matter intrudes between the film 112 and the pressure roller 110, the inner surface of the film 112 urged by the foreign matter can come into strong-contact with the corner 113Eu of the heater 113 to damage the film 112. In the present embodiment, the amount of protrusion of the sliding portion 140c protruding toward the pressure roller 110 with respect to the plane a of the heater 113 extending in the direction perpendicular to the pressing direction a is set at 0.1 mm or more to prevent the corner 113Eu of the heater 113 from coming into strong-contact with the inner surface of the film 112.
Example Variations in Dimensions of Parts
Variations in dimensions of parts in the present embodiment are the width W1 of the heater 113 in the conveying direction, the width W2 of the groove of the heater holder 130 (the holding portion) in the conveying direction, and the thickness T of the restricting portion 140b. Variations in the width W1 of the heater 113 and the width W2 of the groove of the heater holder 130 are ±0.5 mm. The thickness T of the gap filling member 140 indicated in the drawing, that is, the nominal dimension, is 0.3 mm, and its variations are ±0.1 mm. The heater width W1 and the width W2 of the groove of the heater holder 130 are relatively large in the original dimensions, and the heater 113 and the gap filling member 140 need to be sufficiently long also in the sheet width direction. Therefore, variations in dimensions of the heater 113 and the gap filling member 140 are larger than the variation in the thickness T of the restricting portion 140b in view of variations in dimensions of the parts across the sheet width. Variations in the thickness T of the restricting portion 140b can be reduced by forming the gap filling member 140, for example, by bending a thin plate, although this depends on the manufacturing method. The gap is minimized when the heater 113 can be combined with the heater holder 130 so as to be fitted in the heater holder 130. In this case, to enable the heater 113 to be combined with the heater holder 130, the dimension obtained by adding the thickness T of the restricting portion 140b to the heater width W1 needs to be smaller than the width W2 of the groove of the heater holder 130 by 0.1 mm. In other words, conditions for assembly in the present embodiment include that the heater width W1 is 7.5 mm, which is the largest size that can be taken due to variations, that the thickness T of the restricting portion 140b is 0.4 mm, which is the largest size that can be taken due to variations, and that the width W2 of the groove of the heater holder 130 is 8.0 mm or more. For this reason, the nominal dimension of the width W2 of the groove of the heater holder 130 needs to be 8.5 mm, which is larger than the smallest width W2 of the groove of the heater holder 130 by 0.5 mm, which is the variation of the heater holder 130.
Dimensions of Comparative Example
In the present embodiment, a configuration in which the gap filling member 140 is not disposed is produced as a comparative example for evaluation, as illustrated in the schematic diagram of
Method of Evaluation
A test printing material P to be used in comparative examination will be described with reference to
A group A of staples A-1, A-2, A-3, and A-4 are stapled at the leading end of the printing material P. The staple A-1 is fixed to the printing material P in such a manner that the crown is located in a direction perpendicular to the sheet feeding direction. The crown (the back) of the staple A-1 is placed on the pressure roller 110 side (see
Next, a group B of staples B-1, B-2, B-3, and B-4 are stapled at the trailing end of the printing material P. The staple B-1 is fixed to the printing material P such that the crown is rotated 45 degrees counterclockwise with respect to the sheet feeding direction so that the staple B-1 forms an angle of 45 degrees with the sheet feeding direction. The crown (the back) of the staple B-1 is placed on the film 112 side. The staple B-2 is fixed to the printing material P such that the crown is rotated 45 degrees clockwise with respect to the sheet feeding direction so that the staple B-2 forms an angle of 45 degrees with the sheet feeding direction. The crown of the staple B-2 is placed on the film 112 side. The staple B-3 is fixed to the printing material P such that the crown is parallel to the sheet feeding direction. The crown of the staple B-3 is placed on the film 112 side. The staple B-4 is fixed to the printing material P such that the crown is located in the direction perpendicular to the sheet feeding direction. The crown of the staple B-4 is placed on the film 112 side
Every time 100 printing materials P in this state have been passed, one high-definition print image is printed, and the state of the film 112 is checked. The high-definition print image in this testing is a 1-dot/2-space stripe image output from an image forming apparatus with a resolution of 600 dpi. If an abnormality occurs in the film 112, a poor fixation point occurs at the abnormal film position to cause an image defect. After the testing, the fixing apparatus is disassembled to check the state of the film 112. This evaluation shows that when the gap in the conveying direction upstream from the upstream wall surface 113Wu of the heater 113 is 0.5 mm or more in width, the staple intrudes into the gap to damage the film 112.
Evaluation Results
For comparative examination, the configuration of nominal dimensions, a configuration in which the gap is largest, and a configuration in which the gap is smallest are prepared for each of the present embodiment and the comparative example.
Table 1 illustrates the dimensional relationship among the configurations and the evaluation results in the present embodiment. In the present embodiment, the gap AB was smallest when the heater width W1 and the thickness T of the restricting portion 140b are largest and the groove width W2 of the heater holder 130 is smallest. In this case, the width of the gap ΔB (a second width) between the restricting portion 140b and the upstream wall surface 113Wu of the heater 113 immediately after the heater 113 is embedded in the heater holder 130 and the gap filling member 140 can take 0.1 mm at the maximum. The gap ΔB was largest in the present embodiment when the heater width W1 and the thickness T of the restricting portion 140b are smallest and the groove width W2 of the heater holder 130 is largest. In this case, the width of the gap ΔB immediately after the heater 113 is embedded in the heater holder 130 and the gap filling member 140 can take 2.3 mm at the maximum. Even in such cases, by combining the gap filling member 140 while being slid downstream as in
Next, the dimensional relationship among the configurations and the evaluation results in the comparative example will be described with reference to Table 2. In the comparative example, the gap ΔB was smallest when the heater width W1 is largest and the groove width W2 of the heater holder 130 is smallest. In this case, the width of the gap ΔB between the wall surface 130Wu of the heater holder 130 and the upstream wall surface 113Wu of the heater 113 was 0.1 mm, as described above. The gap ΔB was largest when the heater width W1 is smallest and the groove width W2 of the heater holder 130 is largest. In the configuration of the comparative example, the gap ΔB was 0.1 mm in the configuration of the smallest gap, which falls below 0.5 mm, so that no image defect occurred after the foreign matter testing. However, in the configuration of the nominal dimensions and the configuration of the largest gap, the gap ΔB was respectively 1.1 mm and 2.1 mm, which exceed 0.5 mm, so that an image defect occurred after the foreign matter testing, and the film 112 was punctured.
This shows that setting the gap ΔB (the second width) between the restricting portion 140b and the upstream wall surface 113Wu of the heater 113 smaller than the gap ΔA (the first width) between the restricting portion 140b and the upstream wall surface 130Wu of the heater holder 130 reduces or eliminates an image defect after foreign matter testing. This also shows that it is preferable to set, in particular, the gap ΔB to 0.5 mm or less. This reduces or eliminates an image defect after foreign matter testing, and prevents the film 112 from being punctured.
Example Modification of Gap Filling Member
In the present embodiment, the length of the restricting portion 140b that fills the gap in the pressing direction a of the pressure roller 110 is sufficiently larger than the thickness of the heater 113 so that the sliding portion 140c is disposed adjacent to the pressure roller 110 with respect to the plane α. Alternatively, the sandwiched portion 140a may not be disposed between the heater 113 and the heater holder 130, as in
The sliding portion 140c may not cover the gap between the upstream wall surface 130Wu of the heater holder 130 and the restricting portion 140b, as illustrated in
As illustrated in
As illustrated in
The material of the gap filling member 140 may be a heat resistant resin, metal, or ceramic with sufficient strength not to be broken when foreign matter intrudes. The present embodiment employs aluminum.
A second embodiment of the present disclosure will be described hereinbelow. Since a fixing apparatus according to the second embodiment differs only in the shape of the gap filling member 140 and the shape of the heater holder 130, and the other configurations are the same as those of the first embodiment, the detailed description of the main body will be omitted.
Referring to
Referring again to
Actual dimensional relationship and evaluation results will be described with reference to Table 3. Variations in dimensions of parts were 7±0.5 mm for the heater width W1, 0.3±0.1 mm for the thickness T of the restricting portion 140b, as in the first embodiment, and ±0.5 mm for the positioning distance W3. In the present embodiment, variations in dimensions of parts at which the gap ΔB between the upstream wall surface 113Wu of the heater 113 and the restricting portion 140b was largest when the positioning distance W3 is large, the width W1 of the heater 113 is small, and the thickness T of the gap filling member 140 is small. Also in this case, the positioning distance W3 was set to 7.1 mm at the maximum to make the gap ΔB 0.4 or less. The gap relationship in the configuration of nominal dimensions and the configuration of the smallest gap is illustrated in Table 3. In any configuration, the gap ΔB was 0.4 mm or less, which cleared the foreign matter testing. The deflection amount β of the heater 113 at the longitudinal center of the gap filling member 140 (at a point equally distant from the positioning portions 130a and 130b) was the largest 1.8 mm when the gap ΔB is smallest.
In the present embodiment, the positioning portions 130a and 130b are disposed at both ends, and the supporting portion 130S1 is disposed at the center. Alternatively, the positioning portion 130c for restricting the movement of the heater 113 may be disposed at the center, and the supporting portions 130S2 and 130S3 for restricting the movement of the gap filling member 140 may be disposed at both ends, as illustrated in
In the present embodiment, in the case where the positioning portions 130a and 130b are disposed at both ends, the cross section VIIIB including the positioning portion 130a includes the gap filling member 140. However, the gap filling member 140 may be decreased in longitudinal width so that the cross section VIIIC including the supporting portion 130S1 does not include the gap filling member 140. This configuration reduces the amount of the material of the gap filling member 140.
As described above, the gap relationship between the upstream positioning portion and the downstream positioning portion differs depending on the cross section in the longitudinal position. Thus, even if the component accuracy is low, resistance to foreign matter can be satisfied without decreasing the assembly performance at low cost, without the need for providing an additional component, applying grease between the heater holder 130 and the gap filling member 140, performing a special work, or using a dedicated jig.
The first and second embodiments illustrate a configuration in which the gap filling member 140 has the sliding portion 140c only on the upstream side, but the sliding portion 140c may also be provided on the downstream side.
A groove width W4 between a wall surface 140bW of the restricting portion 140b and a wall surface 140eW of the connecting portion 140e in a cross section of the gap filling member 140 in the present embodiment has a variation of ±0.5 mm, like the heater 113 and the heater holder 130. For that reason, the nominal dimension of the groove width W4 is set to 8.1 mm to enable assembly even when the groove width W4 is smallest and the heater width W1 is largest. The other dimensional relationships are the same as those of the second embodiment.
In the present embodiment, the gap filling member 140 is made of aluminum. In the present embodiment, a temperature sensor (not illustrated) for temperature regulation is disposed on a surface of the gap filling member 140 opposite to a surface in contact with the heater 113. A temperature sensor (not illustrated) in the comparative example is disposed so as to be in contact with a surface of the heater 113 opposite to a surface sliding with respect to the film 112.
Forming the gap filling member 140 from a high thermal conductive member is advantageous in increasing the processing speed. In the configuration of the comparative example illustrated in
Table 4 shows comparisons of the results of foreign matter testing in various gap dimensional relationships and processing speeds at which fixing can be performed at the same controlled temperature between the comparative example and the second and third embodiments. The comparative example does not use the gap filling member 140 in the first embodiment, illustrated in
Also in the present embodiment, the positioning portions 130a and 130b are disposed at both ends, and the supporting portion 130S1 is disposed at the center. Alternatively, the positioning portion 130c may be disposed at the center, and the supporting portions 130S2 and 130S3 may be disposed at both ends as in
In any case, using a jig or the like at assembly allows the gap filling member 140 to be urged downstream against the heater holder 130 for assembly even without the supporting portion 130S1. Without a jig or the like at assembly, adding a spring or the like as in the first embodiment in
As described above, the fixing apparatus 100 has different cross sections depending on the longitudinal position so that the gap relationship differs between the upstream positioning member and the downstream positioning member, the gap filling member is made of a high heat transfer member, and the downstream positioning portion is in contact with the film. This ensures fixing performance even at a high processing speed in case of variations in dimensions of parts while satisfying assembly performance and resistance to foreign matter at low cost without providing an additional member, applying grease, performing a special work, or using a dedicated jig.
While the disclosure has been described with reference to example embodiments, it is to be understood that the invention is not limited to the disclosed example embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2018-068244, filed Mar. 30, 2018, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-068244 | Mar 2018 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20080219723 | Lee | Sep 2008 | A1 |
| 20160274511 | Ogino | Sep 2016 | A1 |
| 20180373186 | Sato | Dec 2018 | A1 |
| Number | Date | Country |
|---|---|---|
| 4599189 | Dec 2010 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20190302664 A1 | Oct 2019 | US |
