Patent Grant
9377723
1. Field of the Invention
The present invention relates to a stainless-steel seamless belt for use in a base material of a fixing belt for use in a heat fixing apparatus of an electrophotographic image forming apparatus, and a manufacturing method therefor. In addition, the present invention relates to a fixing belt and a heat fixing apparatus for use in the electrophotographic image forming apparatus.
2. Description of the Related Art
The electrophotographic image forming apparatus uses a heat fixing apparatus for fixing an unfixed toner image on a recording material surface.
Recent heat fixing apparatuses use a power-saving ceramic heater as a heat source to heat a resin belt or a metal belt with a small heat capacity.
Examples of materials of the fixing belt for use in such a heat fixing apparatus generally include a heat-resistant resin, and particularly include a polyimide resin excellent in heat-resistance and strength. Unfortunately, with a recent improvement in process speed, the resin fixing belt has insufficient thermal conductivity. In other words, it may be difficult to fix an unfixed toner image to a recording material in a short time and in a sufficient manner. In light of this, there has been proposed that the fixing belt is provided with a base layer containing a metal excellent in thermal conductivity such as stainless steel, nickel, aluminum, and copper (see Japanese Patent No. 3970122).
Japanese Patent No. 3970122 describes a method of manufacturing a stainless base layer. Specifically, the following method is described as a first embodiment.
First, a step is performed of obtaining a cup-shaped stainless cylindrical member (a first-stage metal tube) by subjecting a stainless metal flat plate to a deep-drawing process a plurality of times. Next, a step is performed of obtaining a seamless belt (a second-stage metal tube) by cutting a cup base portion by performing an ironing process using a general spinning drawing process to form a stainless cylindrical member with a predetermined thickness or by performing an ironing process using a continuous die while rotating the first-stage metal tube. Finally, a metal belt of a desired inverted crown shape (a third-stage metal tube) is obtained by subjecting the second-stage metal tube to a hydraulic bulge forming process followed by internal pressure load and plastic forming processes.
Further, as a second embodiment, there is proposed a manufacturing method which includes obtaining a metal belt by performing a complete annealing process at 800° C. to 1,100° C., between the steps of obtaining the second-stage metal tube and the third-stage metal tube according to the first embodiment.
Furthermore, as a third embodiment, there is proposed a method which includes obtaining a metal belt of an inverted crown shape (a third-stage metal tube) by controlling the pressure and the speed at the spinning drawing process in the step of obtaining the second-stage metal tube according to the first embodiment.
According to the study made by the present inventor, the seamless belt obtained by the first and third embodiments according to Japanese Patent No. 3970122 is repeatedly bent in the nip portion, and the stress has caused a metal fatigue to be accumulated, leading to damage such as breaks and cracks. Further, as to the seamless belt obtained by the second embodiment, the metal belt may be softened to reduce the hardness by the complete annealing at 800° C. to 1,100° C. and worn due to sliding with the ceramic heater. Thus, the present inventor has confirmed his recognition that the metal seamless belt according to Japanese Patent No. 3970122 still needs more improvement in the durability.
In view of this, the present invention is directed to providing a stainless-steel seamless belt which is excellent in durability and difficult to crack and break even at the time of repeated bending, and the manufacturing method therefor.
Further, the present invention is directed to providing a fixing belt having high durability.
Furthermore, the present invention is directed to providing a heat fixing apparatus which can fix an unfixed toner image to a recording material in a stable manner.
According to one aspect of the present invention, there is provided a stainless-steel seamless belt which is formed by subjecting a stainless-steel plate to a plastic forming process and having a thickness of 50 μm or less, wherein, in a bending test in which a strip-like stainless-steel test specimen with a width of 20 mm and a length of 45 mm, formed by cutting the seamless belt into a width of 20 mm along a peripheral direction thereof and cutting open in a direction perpendicular to the peripheral direction, is bent by causing a side support plate having a rotating shaft on one side and rotating around the rotating shaft to repeatedly reciprocate from a top dead point having an opening distance of 29 mm to a bottom dead point having an opening distance of 5.5 mm at a speed of 400 rpm, the strip-like stainless-steel test specimen has a bending durability of 100,000 or more times and wherein a Vickers hardness of the seamless belt is 450 (Hv) or more.
Further, according to another aspect of the present invention, there is provided a method of manufacturing a stainless seamless belt, comprising: (1) obtaining a cup-shaped member by subjecting the stainless-steel plate to a drawing process; (2) obtaining a thin-walled sleeve by subjecting the cup-shaped member to a plastic forming process to be thin-walled and cutting a base portion of the thin-walled cup-shaped member; (3) inserting the thin-walled sleeve into a cylindrical outer die having an internal diameter larger than an external diameter of the thin-walled sleeve so as to be coaxial with the cylindrical outer die, pressurizing the thin-walled sleeve from an inside thereof so as to cause the thin-walled sleeve to closely contact an inner wall of the outer die, and thereby expanding a diameter of the thin-walled sleeve; and (4) subjecting the thin-walled sleeve whose diameter is expanded in (3) to low temperature annealing at 200 to 400° C., wherein the step (3) includes expanding the diameter of the thin-walled sleeve without changing the length in a direction perpendicular to the peripheral direction of the thin-walled sleeve.
Furthermore, according to still another aspect of the present invention, there is provided a fixing belt comprising the seamless belt, an elastic layer, and a toner releasing layer in that order.
Still furthermore, according to the present invention, there is provided a heat fixing apparatus comprising the fixing belt, a heater arranged in contact with an inner peripheral surface of the fixing belt, and a pressure roller forming a fixing nip together with the fixing belt.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.
The present inventor has focused attention on the finding that a stainless steel subjected to a cold plastic forming process improves hardness and fatigue strength through low temperature annealing.
In light of this, in order to further improve a dislocation density of the seamless belt in a thickness direction thereof, the thin-walled seamless belt having been subjected to a cold ironing process is further subjected to a plastic forming process of expanding a diameter thereof so as not to change the length in a direction perpendicular to the peripheral direction. Subsequently, the seamless belt is subjected to low temperature annealing in a temperature range of 200 to 400° C. Thus, the stainless-steel seamless belt is obtained which has high hardness and is excellent in bending-resistant fatigue characteristics.
Here, bulge forming is used as the diameter expansion method. When the diameter of a thin-walled sleeve is expanded by the general bulge forming, the diameter of the thin-walled sleeve is expanded while the length in a direction perpendicular to the peripheral direction is reduced. In contrast to this, the present invention expands the diameter of the thin-walled sleeve without changing the length in a direction perpendicular to the peripheral direction. Thus, a large shear stress is applied to the thin-walled sleeve in a direction perpendicular to the ironing direction, namely, in a direction of diameter expansion. As a result, it is considered that the dislocation density effective in increasing the strength of the seamless belt can be increased.
Further, following the diameter expansion by the bulge forming, low temperature annealing is performed. Thus, the dislocation in the thin-walled sleeve is considered to be able to be fixed in a crystal of the stainless steel. More specifically, the seamless belt having a high dislocation density has a high strength by itself, but when the seamless belt is repeatedly bent, the stress due to the bending moves the dislocation from inside to the surface of the seamless belt, which is considered to cause cracks. Meanwhile, the low temperature annealing is considered to be able to prevent a dislocation from easily moving even by the bending in such a manner that a dislocation originally having a high potential energy is fixed to a heterogeneous element or a point fault in the stainless steel to thereby reduce the potential energy.
For the above reason, the stainless-steel seamless belt obtained by the method of the present invention is considered to have both high hardness and excellent bending durability as follows.
Vickers hardness of 450 (Hv) or more;
Bending durability of 100,000 or more times in a bending test in which a strip-like stainless test specimen with a width of 20 mm and a length of 45 mm formed by cutting the seamless belt into a width of 20 mm along a peripheral direction thereof and cutting open the seamless belt in a direction perpendicular to the peripheral direction is bent by causing a side support plate having a rotating shaft on one side and rotating around the rotating shaft to repeatedly reciprocate from a top dead point having an opening distance of 29 mm to a bottom dead point having an opening distance of 5.5 mm at a speed of 400 rpm.
Now, embodiments of the present invention will be described in detail.
The stainless seamless belt according to the present invention is formed by subjecting a stainless-steel plate to a plastic forming process to have a thickness of 50 μm or less. Further, the stainless seamless belt has a bending durability of 100,000 or more times in a bending test in which a strip-like stainless test specimen with a width of 20 mm and a length of 45 mm, formed by cutting the seamless belt along a peripheral direction thereof and further cutting it into a width of 20 mm and cutting open the seamless belt in a direction perpendicular to the peripheral direction, is bent by causing a side support plate having a rotating shaft on one side and rotating around the rotating shaft to repeatedly reciprocate from a top dead point having an opening distance of 29 mm to a bottom dead point having an opening distance of 5.5 mm at a speed of 400 rpm. Furthermore, the stainless seamless belt has a Vickers hardness of 450 (Hv) or more.
The aforementioned stainless seamless belt having high hardness and excellent in bending resistance can be manufactured by a method including the following steps (1) to (4).
(1) A cup-shaped member is obtained by subjecting a stainless-steel plate to a drawing process.
(2) A thin-walled sleeve is obtained by subjecting the cup-shaped member obtained in step (1) to a plastic forming process to be thin-walled and cutting a base portion of the thin-walled cup-shaped member.
(3) The thin-walled sleeve obtained in step (2) is inserted into a cylindrical outer die having an internal diameter larger than an external diameter of the thin-walled sleeve so as to be coaxial with the cylindrical outer die. The thin-walled sleeve is pressurized from inside thereof so as to cause the thin-walled sleeve to closely contact an inner wall of the outer die. At this time, it is necessary to expand a diameter of the thin-walled sleeve without changing the length in a direction perpendicular to the peripheral direction of the thin-walled sleeve.
(4) Then, the thin-walled sleeve obtained in step (3) with expanded diameter is subjected to low temperature annealing at 200 to 400° C.
The step (3) differs from the conventional bulge forming in that when a thin-walled sleeve arranged inside the cylindrical outer die coaxially with the cylindrical outer die is pressurized from inside the thin-walled sleeve to closely contact an inner wall of the cylindrical outer die to expand the diameter, the length in a direction perpendicular to the peripheral direction of the thin-walled sleeve, namely, the length in the axial direction is not changed. In general bulge forming, with the diameter expansion of the thin-walled sleeve, the length along the axial direction of the thin-walled sleeve is reduced.
In contrast to this, the present invention is devised to prevent a change in the length along the axial direction of the thin-walled sleeve even in an advancement of diameter expansion of the thin-walled sleeve. Specifically, for example, both ends of a thin-walled sleeve are clamped by both ends of a cylindrical mold.
Thus, when the change in the length in a direction perpendicular to the peripheral direction of the thin-walled sleeve is suppressed in the diameter expansion step, a larger shear stress is added to the thin-walled sleeve during diameter expansion. As a result, many lattice defects called dislocations can be generated in a crystal of stainless steel constituting the thin-walled sleeve. Thus, the dislocation density in the crystal of stainless steel increases and the strength of a thin-walled sleeve 1 increases. The dislocation at this time, however, is considered to be easily moved when an external force such as bending is added to the thin-walled sleeve. When repeated bending causes a dislocation to move near the surface of a thin-walled sleeve, the dislocation is considered to cause cracks or breaks to be generated in the thin-walled sleeve.
In light of this, the thin-walled sleeve 1 with increased dislocation density in the crystal is subjected to low temperature annealing in step (4). Thus, the dislocation is fixed to a point fault in the stainless steel. The resulting thin-walled sleeve can be used as a seamless belt having high hardness and excellent in bending resistance.
The stainless seamless belt obtained in this manner can be used as a fixing belt for use in a fixing belt for use in a heat fixing apparatus of an electrophotographic image forming apparatus.
The material of the elastic layer 2 is not particularly limited, but any material excellent in heat resistance and thermal conductivity may be selected. Examples of the material of the elastic layer 2 can include at least one material selected from the group consisting of silicone rubber, fluororubber and fluorosilicone rubber, and particularly silicone rubber can be used. Specific examples of the material of the silicone rubber include polydimethylsiloxane, polymethyltrifluoropropylsiloxane, polymethylvinylsiloxane, polytrifluoropropylvinylsiloxane, polymethylphenylsiloxane, polyphenylvinylsiloxane, and polysiloxane copolymer.
In order to obtain excellent fixed image quality, the thickness of the elastic layer 1002 can be 10 μm or more and 1000 μm or less, and further can be 50 μm or more and 500 μm or less.
Examples of the material of the toner releasing layer 1003 include fluororesin, silicone resin, fluorosilicone rubber, fluororubber, and silicone rubber made of PFA (tetrafluoroethylene/perfluoroalkylether copolymer), PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene/hexafluoropropylene copolymer), and the like. In particular, PFA can be used because toner and the like are do not easily adhere to it.
The fixing belt 33 used in the heat fixing apparatus illustrated in
The present invention can provide a stainless-steel seamless belt that is difficult to crack and break due to repeated bending, and excellent in durability. Further, the present invention can provide a fixing belt excellent in durability. Furthermore, the present invention can provide a heat fixing apparatus which can fix an unfixed toner image to a recording material in a stable manner.
Now, a method of manufacturing a stainless-steel seamless belt according to the present invention will be specifically described with reference to the embodiments given below.
In the present embodiment, the stainless-steel seamless belt manufacturing method will be described in regard to separate steps from obtaining a first-stage metal tube to obtaining a fourth-stage metal tube.
(First-Stage Metal Tube)
In
The above steps are repeated, generally about 2 to 6 times so as to gradually reduce the cup diameter using different molds to perform a deep-drawing process to manufacture a cup-shaped member 104 made of metal. Note that the method of obtaining the metal cup-shaped member is not limited to the present embodiment, but a cup-shaped member may be obtained by impact molding, welding, cutting, or the like.
(Second-Stage Metal Tube)
Next, the cup-shaped member 104 is subjected to a plastic forming process to produce a bottomed cylindrical member 2. Then, the base portion of the bottomed cylindrical member 2 is cut away to obtain a thin-walled sleeve 1.
First, the cup-shaped member 104 manufactured in the first stage is placed on an ironing punch 105 in a manner to cover the front end of the ironing punch 105 as illustrated in
Then, the bottomed cylindrical member 2 is demolded from the ironing punch 105. Then, the base portion of the bottomed cylindrical member 2 is cut away by a cutting outer edge 107 and a cutting inner edge 108 to obtain the thin-walled sleeve 1.
(Third-Stage Metal Tube)
Next, the stainless-steel thin-walled sleeve 1 obtained in the second stage is subjected to a plastic forming process to further increase the dislocation density in the thin-walled sleeve 1. In the present stage of the manufacturing method, the thin-walled sleeve 1 obtained in the second stage is inserted into the interior of an outer die, pressurized from inside the thin-walled sleeve so as to cause the thin-walled sleeve to closely contact an inner wall of the outer die to expand the diameter of the thin-walled sleeve, namely, performing diameter expansion.
The present embodiment uses a diameter expansion method using hydraulic bulge forming as means of efficiently increasing the dislocation density of the thin-walled sleeve (stainless-steel seamless belt) subjected to the ironing process. The hydraulic bulge forming refers to a method of molding a metal tube into a desired shape by introducing a pressurized fluid into the metal tube to be processed to apply a pressure (hereinafter referred to as an internal pressure).
Through the above steps, the third-stage metal tube can be thus obtained.
In the diameter expansion step applied to the thin-walled sleeve 1 illustrated in
According to the conventional hydraulic bulge forming method illustrated in
In contrast to this, according to the hydraulic bulge forming method of the present invention illustrated in
Note that the unit for suppressing a change in the length of the thin-walled sleeve 1 in the direction perpendicular to the peripheral direction of the thin-walled sleeve is not limited to the present embodiment. For example, a method may be used such that a force in a direction opposite to that in the present embodiment, namely, a pressure is applied from an outer surface side of the stainless-steel seamless belt toward the axial center to fix the both end portions of the seamless belt and thereby suppress a change in the length of the belt in the direction perpendicular to the peripheral direction.
(Fourth-Stage Metal Tube)
Finally, in order to change movable dislocations grown by the plastic forming to fixed dislocations considered to be effective for bending resistance fatigue, the stainless-steel seamless belt (thin-walled sleeve) whose diameter is expanded in the third stage is subjected to low temperature annealing at 200 to 400° C. to obtain a fourth-stage metal tube. In the present embodiment, the fourth-stage metal tube was subjected to low temperature annealing for about 30 minutes in an electric furnace preliminarily heated to 300° C.
Evaluation Method
(Bending Endurance Test)
In the bending tester, the side support plate 201 repeatedly reciprocated from a top dead point with an opening distance of 29 mm to a bottom dead point with an opening distance of 5.5 mm at a speed of 400 rpm. Then, the test specimen was visually checked for a crack to count the number of reciprocating movements until the crack was found. Note that the test specimen was sufficiently polished with #2000 sandpaper to such a state that the cut end surface did not affect the bending test results.
(Hardness Measurement)
Now, the hardness measurement method will be described. The hardness was measured in accordance with a test method conforming to IS014577-1.
As the measuring instrument, “FISCHERSCOPE HM2000” (product name) manufactured by Fischer Instruments K.K. was used. The load was applied so as to reach a measuring load of 500 mN in 20 sec from the time when an indenter contacted the test specimen and the state was held for 5 sec. At this time, the penetration amount of the indenter was about 2.5 μm.
The bending endurance test results and the hardness measurement results before and after the stainless-steel seamless belt obtained in the first embodiment was subjected to low temperature annealing are listed in Tables 1 and 2, respectively. The low temperature annealing increased the Vickers hardness by about 10%, as shown in Table 2, and the bending durability by about 110%, as shown in Table 1.
Note that in the bending endurance test, for the all the test specimens, a crack occurred in a position of the test specimen whose bending portion had a maximum curvature.
The second embodiment will focus on the manufacturing method after ironing and before cutting the metal cup-shaped member manufactured in the second stage of the first embodiment, namely, the method of subjecting the thin-walled bottomed cylindrical member 2 to a plastic forming process without changing the length in the direction perpendicular to the peripheral direction thereof.
In the same manner as in the first embodiment, a stainless-steel metal flat plate is subjected to a deep-drawing process to obtain a first-stage metal tube. Then, the first-stage metal tube is subjected to an ironing process to obtain a bottomed cylindrical member 2. The manufacturing method up to this has been described in detail in the first embodiment and thus the description is omitted here.
Next, a hydraulic bulge forming process is used as the diameter expansion unit to subject the bottomed cylindrical member 2 to a plastic forming process.
Conventionally, a shrinkage amount H occurs in the seamless belt as described in
Although not illustrated in
Subsequently, in the same manner as in the first embodiment, the base portion of the bottomed cylindrical member 2 subjecting to the diameter expansion is cut and finally is subjected to low temperature annealing.
As described hereinbefore, the bottomed cylindrical member 2 with remaining base portion is used for diameter expansion, which enables the end portion on the base portion side of the cylindrical member 2 to be fixed even in a state in which the binding member 11 is not mounted on the bulge outer die 10 on the base portion side of the bottomed cylindrical member 2.
The first embodiment of mounting the binding members 11 on both sides has a disadvantage in that each time the seamless belt is inserted and discharged, at least one of the binding members needs to be removed from the bulge outer die 10, while the present embodiment has an advantage of eliminating such a cumbersome work.
The evaluation results of the seamless belt obtained in this manner are listed in Tables 1 and 2. The low temperature annealing has a great effect in that Vickers hardness increases by about 10% and the bending durability increased by about 100%.
A stainless-steel seamless belt was obtained in the same manner as in the first embodiment except that after the ironing process, the low temperature annealing was carried out without performing the diameter expansion in the peripheral direction. The evaluation results of the seamless belt obtained in this manner are shown in Tables 1 and 2. The low temperature annealing has no great effect as compared with that in the first and second embodiments because the Vickers hardness increases by about 10% and the bending durability increases by about 10%.
A stainless-steel seamless belt was obtained in the same manner as in the first embodiment except that the conventional hydraulic bulge forming method was used as a means for performing the diameter expansion in the peripheral direction. Note that the shrinkage amount H of the seamless belt occurring in the hydraulic bulge forming in the comparative example 2 was 0.3 mm on both ends.
The evaluation results of the seamless belt obtained in this manner are shown in Table 1. The low temperature annealing does not have so great effect as compared with that in the first and second embodiments because the Vickers hardness increases by about 10% and the bending durability increases by about 50%.
It is understood from the results in Table 1 that the number of times of bending until a crack is found greatly increased in the present embodiments than in the comparative examples in comparison between before and after the low temperature annealing.
Thus, as described hereinbefore, the metal tube subjecting to the ironing process is subjected to the plastic forming process for diameter expansion without changing the length in a direction perpendicular to the peripheral direction, followed by the low temperature annealing process, which can provide a metal seamless belt having highly durable bending fatigue characteristics while maintaining high hardness.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary 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. 2010-161411, filed Jul. 16, 2010, and Japanese Patent Application No. 2011-151979, filed Jul. 8, 2011, which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-161411 | Jul 2010 | JP | national |
| 2011-151979 | Jul 2011 | JP | national |
This is a divisional of U.S. patent application Ser. No. 13/179,932, filed Jul. 11, 2011, pending.
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| Number | Date | Country | |
|---|---|---|---|
| 20140216615 A1 | Aug 2014 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13179932 | Jul 2011 | US |
| Child | 14245104 | US |
