JP2007248858A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of maintaining the outer shape of a pressurization member over a long term, preventing generation of image gap and wrinkles of a recording material and stably conveying the recording material over the long period in the belt nip system fixing device. <P>SOLUTION: In the fixing device provided with: a heating fixing member having a heating source; an endless belt which forms a nip part whose peripheral surface is pressurized to the heating fixing member and a recording medium which carries a toner image is sandwiched between the heating fixing part and the peripheral surface; the pressurization member which is contacted on the inner surface of the endless belt and pressurizes the endless belt along the surface of the heating fixing member; a sheet-like member which covers the pressurization member for reducing slide resistance between the pressurization member and the endless belt and a lubricant application part which lubricates between the endless belt and the pressurization member in the inner peripheral surface of the endless belt, the pressurization member consists of a support member and an elastic layer and the support member is provided with a lubricant transfer prevention layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device that heats and fixes an unfixed toner image in an image forming apparatus such as a copying machine, a printer, or a facsimile that employs an electrophotographic method, and in particular, pressurizes a fixing belt to a fixing member having a heating source. The present invention relates to a belt nip type fixing device that is pressed by a member.

  Conventionally, various types of fixing devices that heat and fix unfixed toner images in image forming apparatuses such as copiers, printers, and facsimiles that employ the electrophotographic method have been proposed. It has been commercialized. As such a fixing device, for example, there is a belt nip type in which a fixing belt is pressed against a fixing roll having a heating source by a pressure member.

  As this belt nip type fixing device, for example, as disclosed in Patent Document 1, a heat fixing roll having an elastic layer near the surface and supported rotatably, and an outer peripheral surface thereof is the heat fixing device. An endless belt that forms a nip that is pressed against the roll and carries a toner image between the heat fixing roll and an inner surface of the endless belt is in contact with the surface of the heat fixing roll. And a pressure applying member having a pressure contact surface for pressing the endless belt.

  In the case of the belt nip type fixing device as described above, since the pressure applying member formed of an elastic layer such as rubber is in pressure contact with the inner surface of the endless belt, the endless belt and the pressure applying member are in contact with each other. If the sliding resistance increases, the rotational operation becomes unstable, and image misalignment, conveyance failure, etc. are likely to occur.

  Therefore, in the belt nip type fixing device, in order to suppress wear of the inner surface of the endless belt, the surface of the pressure applying member is a sheet-like member obtained by coating a glass fiber sheet with fluororesin (PFA). Or a sliding sheet (see Patent Document 2) that reduces unevenness by forming irregularities on the surface to reduce friction.

  Further, a configuration in which a lubricating oil such as grease or silicone oil is applied to the inner surface of the endless belt has already been proposed and actually used.

  In addition, when a lubricant such as oil is applied to the inner surface of the endless belt, there is also an effect of retaining the lubricant such as oil on the unevenness of the surface of the sliding sheet. From this point also, the sliding sheet and the inner surface of the endless belt The effect of reducing the sliding resistance is obtained.

  Further, as disclosed in Patent Document 3, the pressure applying member of the belt nip type fixing device has a load acting on the central portion in the axial direction of the heat fixing roll in the nip region formed with the heat fixing roll. It is preferable to have a regular crown shape (see FIG. 4 (a)) so as to form a load distribution that is greater than the load acting on both ends in the axial direction of the roll (see FIG. 5 (a)). With this configuration, the conveyance speed at the central portion in the recording material width direction is slow, both ends are fast, rotational moments are generated at both ends around the center, and the wrinkles of the recording material are stretched in the width direction. , Image displacement and wrinkle generation can be prevented.

The pressure applying member preferably has a soft elastic layer in order to achieve the pressure distribution as described above, and silicone rubber having a rubber hardness of 5 to 30 ° (JIS-A) is generally used.
JP 2004-109878 A JP 2002-148970 A Japanese Patent Laid-Open No. 10-228199

  However, the conventional technique has the following problems. That is, in the case of the conventional belt nip type fixing device, the surface of the pressure applying member is configured to be covered with the sliding sheet, and the lubricant is applied to the surface. For this reason, the lubricant and the elastic layer of the pressure applying member are not in direct contact (see FIG. 3A). However, when a lubricant having a small surface energy such as silicone oil is used, the lubricant spreads to various members in the fixing device when the fixing device is used for a long time (see FIG. 3B). ).

  When this lubricant enters the elastic layer of the pressure applying member, the elastic layer is swollen and the outer shape of the elastic layer is expanded. In particular, in the case of silicone rubber having a low hardness of about 5 to 30 ° (JIS-A), the molecular structure is sparse compared to high-hardness rubber, so that silicone oil easily enters and oil swells easily.

  In the conventional belt nip method, the pressure applying member is covered with a sliding sheet, but the portions corresponding to both ends in the axial direction of the heat fixing roller are openings. For this reason, the lubricant enters the elastic layer from the opening along the surface of the support member of the pressure applying member.

  In this way, when the lubricant enters from the openings corresponding to both ends of the heat fixing roller in the axial direction and the elastic layer of the pressure applying member swells, both ends of the originally medium convex pressure applying member become convex. As a result, a three-crested outer shape is obtained (see FIGS. 4B and 5B).

  When the shape of the elastic layer of the pressure applying member becomes a three-sided shape, the force stretched in the width direction with respect to the recording material is lost, and the image displacement of the recording material causes wrinkles. Transportability becomes unstable.

  As described above, in the case of the conventional belt nip type fixing device, the recording material cannot be stably conveyed over a long period of time.

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to maintain the outer shape of the pressure applying member in a belt nip type fixing device over a long period of time. Another object of the present invention is to provide a fixing device that can prevent image displacement and wrinkles of the recording material and stably convey the recording material over a long period of time.

  In other words, the invention described in claim 1 is a heat fixing member having a heat source and a nip in which an outer peripheral surface is pressed against the heat fixing member and a recording medium carrying a toner image is sandwiched between the heat fixing member. An endless belt that forms a portion, a pressure applying member that is in contact with an inner surface of the endless belt and presses the endless belt along the surface of the heat fixing member, and a sliding resistance between the pressure applying member and the endless belt. In the fixing device in which a sheet-like member that covers the pressure applying member and a lubricant application portion that lubricates between the endless belt and the pressure applying member are provided on the inner peripheral surface of the endless belt to reduce the pressure application. The member includes a support member and an elastic layer, and the support member is provided with a lubricant movement preventing layer.

  Thus, by preventing the movement of the lubricant, it is possible to prevent the lubricant from entering the elastic layer and prevent the elastic layer from swelling due to the lubricant.

  The invention according to claim 2 is the fixing device according to claim 1, wherein the lubricant movement preventing layer is a liquid repellent layer that repels the lubricant.

  Further, the invention according to claim 3 is the fixing device according to claim 1 or 2, wherein the lubricant movement preventing layer is made of a fluororesin.

  Still further, the invention according to claim 4 is characterized in that the lubricant is silicone oil, and the lubricant movement preventing layer has a contact angle with respect to the silicone oil of 30 ° or more. The fixing device according to (1).

  In this way, the oil repellent layer that repels the lubricant forms an oil barrier layer that does not get wet with the oil, and can prevent the oil from entering.

  The invention according to claim 5 is the fixing device according to claims 1 to 4, wherein the elastic layer has a JIS-A rubber hardness of 5 to 30 °.

  As described above, the pressure applying member has a rubber hardness of 5 to 30 ° to make the fixing nip center convex in the axial direction of the heat-fixing roller. If it exceeds 30 °, the pressure at both ends is not applied. Therefore, it becomes impossible to form a middle convex shape. In the case of a high hardness rubber, it is possible to select a rubber that does not easily swell against silicone oil, such as fluoro rubber, and a heat fixing roller provided with a fluoro rubber layer as an oil barrier layer is actually used. . However, fluoro rubber is not suitable as the rubber used for the pressure applying member of the above-described belt nip type fixing device because it has only a high hardness.

  As described above, according to the present invention, in the belt nip type fixing device, the silicone oil that is a lubricant in the endless belt is obtained by performing fluorine coating (baking) on the base plate (support member) of the pressure applying member. Can be prevented from entering the rubber part. Therefore, it is possible for the pressure applying member in the fixing nip portion to maintain the pressure distribution applied to the heat fixing roller via the endless belt so that the convex shape is maintained. It became possible to provide.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 2 is a block diagram showing the fixing device according to Embodiment 1 of the present invention.

  The fixing device includes a heat fixing roll 2 having a built-in heating source, an endless belt 3 pressed against the heat fixing roll 2, and an inner surface of the endless belt 3, along the surface of the heat fixing roll 2. The main part is composed of the pressure applying member 4 that presses the endless belt 3.

  In FIG. 2, reference numeral 2 denotes a heat-fixing roll, and this heat-fixing roll 2 is rotationally driven at a predetermined speed, for example, a peripheral speed of 200 mm / sec, along an arrow direction by a drive source (not shown). ing. The heat fixing roll 2 includes a metal core 5 formed in a cylindrical shape having an outer diameter of 60 mm, an inner diameter of 57 mm, and a length of 350 mm, for example, and the metal core 5 is made of, for example, aluminum or stainless steel. Is used. The surface of the metal core 5 is covered with a 2 mm thick HTV silicone rubber (JIS-A rubber hardness 10 °) as an elastic body layer 6. The surface layer 7 is covered with a fluorine tube having a thickness of 50 μm, and the surface of the surface layer 7 is finished in a state close to a mirror surface state.

  The metal core 5 can be made of a metal having high thermal conductivity other than aluminum or stainless steel, and the surface layer 7 can also be coated with a fluororesin. .

  In addition, a halogen lamp 8 with an output of 1000 W is disposed inside the metal core 5 as a heating source, and the heat fixing roll 2 is heated from the inside by the halogen lamp 8 so that the surface temperature becomes a predetermined temperature. It has come to be. The surface temperature of the heat-fixing roll 2 is detected by a contact or non-contact temperature sensor (not shown) provided on the surface of the heat-fixing roll 2 so that the surface temperature of the heat-fixing roll 2 is, for example, 170 ° C. It is configured to be controlled by a temperature controller (not shown).

  A heat-resistant endless belt 3 is disposed on the surface of the heat fixing roll 2 so as to be in pressure contact over a predetermined nip width. The endless belt 3 is formed of, for example, a polyimide film having a thickness of 75 μm, a width of 340 mm, and a circumferential length of 150 mm, and a fluororesin tube such as PFA is provided on the surface layer. The endless belt is pressed against the heat fixing roll 2 from the inside by the pressure applying member 4, and is driven to rotate as the heat fixing roll 2 rotates. A rubber layer of about 200 μm may be provided between the surface tube of the endless belt and the polyimide base layer, which may be more preferable in a color image forming apparatus.

  As shown in FIG. 1, the pad member 4 that is a pressure applying member is configured by disposing a laminated elastic body layer 24 on the surface of a base plate 21 that is a support member made of a metal such as stainless steel. The surface of the pad member 4 is covered with a sliding surface with an endless belt by a pad sheet 25 as a sheet-like member.

  Further, the pad member 4 is pressed against the heat fixing roll 1 with a pressing force of, for example, 50 kgf by a compression coil spring (not shown) disposed on the base plate 21 side. As the base plate 21, for example, a stainless steel plate having a width (belt traveling direction) of 20 mm, a length (perpendicular to the paper surface) of 360 mm, and a thickness of 5 mm is used. The elastic layer 24 is made of silicone rubber having a rubber hardness of 5 ° or 30 °, and has a thickness of 5 mm at the center in the width direction, and the thickness increases along the circumference of the heat fixing roll 2 on the upstream and downstream sides. Of the shape. Here, the rubber hardness is a result obtained by adding a load of 300 gf with an Asker C type rubber hardness meter for sponge manufactured by Kobunshi Kagaku.

  In the present embodiment, a sheet-like member that covers the pressure-applying member is provided to reduce sliding resistance between the pressure-applying member and the endless belt, and the sheet-like member has heat resistance and wear resistance. Consists of materials.

  An oil application member 30 is in contact with the inner peripheral surface of the endless belt. The oil application member 30 is a heat-resistant non-woven fabric (felt) such as aramid used for a cleaning web or the like, and is impregnated with silicone oil as a lubricant. As the silicone oil, dimethyl silicone oil KF96-300CS manufactured by Shin-Etsu Chemical Co., Ltd. was used. When the fixing roller rotates in the arrow direction in FIG. 2, the endless belt 3 pressurized by the pressure applying member 4 rotates in the arrow direction. Accordingly, in FIG. 3A, the silicone oil impregnated in the oil application member 30 (indicated by a dotted line in the figure) is applied to the inner peripheral surface of the endless belt. By forming an oil film on the inner surface of the endless belt, the sliding load at the pressure applying member 4 pressure contact portion is reduced, the rotation of the endless belt is stabilized, and the transportability of the recording material is stabilized.

However, when the above-described fixing device is used for a long period of time, silicone oil as a lubricant travels along the surface layer of the sliding sheet 25 and enters the surface of the pressure applying member 4.
The present invention is an invention relating to the prevention of silicone oil intrusion. In this example, the pressure applying members having a rubber hardness of 5 ° and 30 ° were examined for the examples in Table 1 and Comparative Examples 1 to 3, respectively.

以下に、実施例および比較例1〜３について詳細に説明する。

Hereinafter, Examples and Comparative Examples 1 to 3 will be described in detail.

  The base plate 21 of the pressure applying member 4 of Example 1 shown in FIG. 1 uses a fluororesin as a lubricant movement preventing layer on a SUS base material. Examples of the fluororesin material include tetrafluoroethylene polymer (PTFE), tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Fluorine resin such as polyethylene-tetrafluoroethylene (ETFE) can be mentioned, but PTFE was used in this example.

  The fluororesin coating material is applied on the base plate coated with the primer by, for example, spray coating, and dried at a temperature from room temperature to about 100 ° C. for 30 minutes to 1 hour, thereby forming a dry film of the fluororesin. Since this fluororesin dry film is unfired and the fluororesin particles are simply overlapped, the surface has irregularities along the shape of the particles, and it is easy to fall off when rubbed strongly. is there. The fluororesin dry film is converted into a smooth and scratch-free fluororesin layer by firing at a temperature of 360 to 400 ° C., for example, for about 10 minutes to 1 hour.

  The elastic layer 24 is formed by fitting the base plate into an outer mold (not shown), injecting and baking silicone rubber.

  The pressure applying member 4 according to the embodiment is completed through the steps as described above.

  The pressure applying member 4 of Comparative Example 1 does not have the fluororesin coat, and corresponds to a conventional example in which an elastic layer 24 of silicone rubber is formed on a SUS base plate 21.

  The pressure applying member 4 of Comparative Example 2 is obtained by performing fluorine coating on the base plate 21 after forming the elastic layer as compared with Comparative Example 1. Since the heat resistance of silicone rubber is about 250 ° C., it is only coated with the fluororesin and dried, and cannot be fired at 360 to 400 ° C. Therefore, the fluorine coat layer is simply a layer of fluororesin particles as described above, and is expected to have a low oil barrier effect. However, mass productivity is advantageous because there are few steps.

Regarding Example and Comparative Example 2, the contact angle of the fluorine coat layer with respect to the silicone oil was measured. When measured with an automatic contact angle meter (manufactured by Kyowa Interface Science Co., Ltd.)
Example: 30 °
Comparative Example 2: 25 °
It became. Since the Example has a baking process, the fluororesin layer is formed and it is thought that oil repellency is higher.

  The pressure applying member 4 of Comparative Example 3 is obtained by performing fluorine coating treatment on the elastic layer after forming the elastic layer as compared with Comparative Example 1. Since it cannot bake at 360-400 degreeC like the comparative example 2, only the particle | grains of a fluororesin overlap on the elastic layer surface. However, since the elastic layer is directly coated, the oil barrier effect may be higher than that applied to the base plate.

  The pressure giving members of the rubber hardness of 5 ° and 30 ° produced as described above and the pressure applying members of Comparative Examples 1 to 3 were mounted on the above-described fixing device for comparison. For each pressure application member, the fixing device is in the initial state of the frequency of image misalignment and wrinkles when a solid image is formed in an environment of 100g plain paper and 64g recycled paper each at room temperature of 30 ° and humidity of 80%. Table 2 and Table 3 show the results of a comparison between the endurance state after passing 100,000 sheets and after endurance.

表２及び表３の結果からわかるように、実施例に関しては初期および１0万枚耐久後に画像ズレ、しわの発生はみられなかった。一方、比較例１〜３はどれも画像ズレまたはしわが発生してしまった。画像ズレは、しわの軽微なものと考えられるものである。

As can be seen from the results in Tables 2 and 3, no image displacement or wrinkle was observed in the examples after the initial stage and after the endurance of 100,000 sheets. On the other hand, in all of Comparative Examples 1 to 3, image displacement or wrinkles occurred. Image misalignment is considered to be a slight wrinkle.

  After examining the endurance of 100,000 pieces of pressure applying members with rubber hardness of 5 ° and 30 ° in the example, it was confirmed that the fluorine coat part of the base plate became an oil barrier and prevented silicone oil from entering the elastic layer did it. Further, when the outer shape of the elastic layer was measured, no change from the initial shape was observed. For external measurement, a laser length measuring instrument manufactured by Keyence Corporation was used.

  When the pressure imparting members having a rubber hardness of 5 ° and 30 ° in Comparative Example 1 were examined after enduring 100,000 sheets, silicone oil intruded into the elastic layer and the silicone rubber was swollen. When the outer shape was measured in the same manner as described above, it was measured that the heights at both ends in the axial direction were higher than in the initial stage, and the swelling was slightly larger at 5 ° than the rubber hardness of 30 °. It is considered that due to this swelling, the force acting in the direction of stretching the recording material to both ends in the axial direction decreased, and image displacement and wrinkles were generated.

  When the pressure imparting members having a rubber hardness of 5 ° and 30 ° of Comparative Example 2 were examined after enduring 100,000 sheets, silicone oil intruded into the elastic layer, although not as much as Comparative Example 1, and the silicone rubber swelled. It was. After all, swelling was slightly larger at 5 ° than rubber hardness 30 °. This is because the fluorine coat of the base plate was not fired, so that the oil penetrated between the fluororesin particles, and it was considered that the effect as in the example could not be obtained.

  When the pressure imparting members having a rubber hardness of 5 ° and 30 ° in Comparative Example 3 were examined after enduring 100,000 sheets, silicone oil intruded into the elastic layer, although not as much as Comparative Example 1, and the silicone rubber swelled. It was. As described above, the swelling was slightly larger at 5 ° than the rubber hardness of 30 °. This is because the fluorine coat of the rubber layer was unfired and the oil penetrated between the fluororesin particles as in Comparative Example 2, and it is considered that the effect as in the example was not obtained.

  From the above results, it has been found that the oil barrier effect cannot be obtained unless the fluorine coat is fired on the base plate or the rubber layer. However, since it cannot be fired after rubber molding, it was confirmed that it is effective to coat the base plate with fluorine.

It is explanatory drawing which shows the pressure provision member of the Example of this invention. FIG. 3 is an explanatory diagram illustrating a configuration of a fixing device of the present invention. (a) It is explanatory drawing explaining the movement of the lubricant of the fixing device initial stage of this invention. (b) It is explanatory drawing explaining the movement of the lubricant after durability of the fixing device of this invention. (a) It is explanatory drawing which shows the initial pressure provision member of the Example and comparative example of this invention. (b) It is explanatory drawing which shows the pressure provision member after durability of the comparative example of this invention. (a) It is explanatory drawing which shows the load which the initial pressure provision member of this invention gives to a heat fixing roller. (b) It is explanatory drawing which shows the load which the pressure provision member after durability of the comparative example of this invention gives to a heat fixing roller.

Explanation of symbols

2 Heat fixing roll 3 Endless belt 4 Pressure applying member 21 Support member (base plate)
24 Elastic layer 25 Sheet-like member (sliding sheet)
28 Lubricant migration prevention layer (fluorine coating)
30 Lubricant application member

Claims (5)

A heat fixing member having a heating source;
An endless belt that forms a nip portion in which an outer peripheral surface is pressed against the heat fixing member and a recording medium carrying a toner image is sandwiched between the heat fixing member;
A pressure applying member that is in contact with an inner surface of the endless belt and presses the endless belt along a surface of the heat fixing member;
A sheet-like member covering the pressure applying member in order to reduce sliding resistance between the pressure applying member and the endless belt;
In the fixing device in which a lubricant application portion that lubricates between the endless belt and the pressure applying member is provided on the inner peripheral surface of the endless belt,
The fixing device according to claim 1, wherein the pressure applying member includes a support member and an elastic layer, and a lubricant movement preventing layer is provided on the support member. The lubricant migration preventing layer is
The fixing device according to claim 1, wherein the fixing device is a liquid repellent layer that repels a lubricant. The lubricant migration preventing layer is
The fixing device according to claim 1, wherein the fixing device is made of a fluororesin.   The fixing device according to claim 1, wherein the lubricant is silicone oil, and the lubricant movement preventing layer has a contact angle with respect to the silicone oil of 30 ° or more. The elastic layer is
5. The fixing device according to claim 1, wherein the JIS-A rubber hardness is 5 ° or more and 30 ° or less.

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