Fixing unit and image forming apparatus

Abstract

A fixing unit includes: a rotating member; a contact portion disposed in the inner space of the rotating member; a pressing member configured to be in contact with an outer surface of the rotating member; and a heating portion configured to heat the rotating member such that the rotating member heats an image on the recording material sandwiched between the rotating member and the pressing member and conveyed through the nip portion. A lubricant is applied between the inner surface of the rotating member and the contact portion. The lubricant contains a base oil in an amount of 80% or more relative to the total mass of the lubricant. The expansion interface area ratio of the inner surface of the rotating member is 0.10 or more and 0.50 or less. The invention also relates to an image forming apparatus.

Description

Technical Field

[0001] The present invention relates to a fixing unit for fixing an image on a recording material and an image forming apparatus for forming an image on a recording material. Background Art

[0002] Japanese Patent Application Laid-Open No. 2008-076589 discloses a fixing unit including a tubular film, a heater in contact with the inner surface of the film, a support frame for supporting the heater, and a pressure roller that clamps the film and forms a fixing nip portion together with the heater, wherein a lubricant is applied between the inner surface of the film and the surface of the heater. Further, Japanese Patent Application Laid-Open No. 2008-076589 aims to prevent the lateral spillage of the lubricant from the end portions of the film by providing recessed portions for concentrating the lubricant at two longitudinal end portions of the support frame.

[0003] The lubricant used in the fixing unit may contain a base oil and a thickener as main components, and reduces friction by forming an oil layer (i.e., a sliding layer) at the interface between objects sliding against each other. When the fixing unit is used for a long time, if the sliding layer cannot be maintained due to reasons such as extrusion or evaporation of the base oil, the sliding property deteriorates, and image defects may occur during fixing, or deformation and damage of the film may occur.

[0004] If the application amount of the lubricant is increased to maintain the sliding layer for a long time, the thickener may prevent heat conduction, and fixing failure may occur, particularly in the initial state immediately after assembling the fixing unit. At the same time, if the ratio of the base oil in the lubricant increases, the viscosity of the lubricant decreases, such that the base oil may tend to flow out of the area to be lubricated, and the sliding layer may not be maintained for a long time. Summary of the Invention

[0005] The present disclosure provides an image forming apparatus that can achieve good fixing performance and long-term stable slidability.

[0006] According to one aspect of the present disclosure, a fixing unit includes: a rotating member formed in a tubular shape and configured to rotate; a contact portion disposed in an inner space of the rotating member and configured to slidably contact an inner surface of the rotating member; a pressing member configured to contact an outer surface of the rotating member and disposed to sandwich the rotating member together with the contact portion; and a heating portion configured to heat the rotating member such that the rotating member heats an image on a recording material that is held in a holding portion between the rotating member and the pressing member and conveyed through the holding portion, and thus the image is fixed to the recording material, wherein a lubricant is applied between the inner surface of the rotating member and the contact portion, wherein the lubricant contains a base oil in a ratio of 80% or more relative to the total mass of the lubricant, and wherein an unfolded interface area ratio of the inner surface of the rotating member is 0.10 or more and 0.50 or less.

[0007] With reference to the accompanying drawings, other features of the present invention will become apparent from the following description of exemplary embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1A is a cross-sectional view of a fixing unit according to a first example.

[0009] Figure 1B is a schematic view of a fixing film.

[0010] Figure 1C is an exploded perspective view of the fixing unit.

[0011] Figure 2A is a schematic view of a heater according to a first example.

[0012] Figure 2B is Figure 2A a cross-sectional view of.

[0013] Figure 3A and Figure 3B are each an explanatory view of a fixing film according to a first example.

[0014] Figure 4 is a schematic view of an image forming apparatus according to a first example. DETAILED DESCRIPTION

[0015] Embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0016] First Embodiment

[0017] The fixing unit 1 according to the first embodiment will be described. First, an example of the fixing unit 1 and an image forming apparatus equipped with the fixing unit 1 will be described.

[0018] Figure 1A is a cross-sectional view of the fixing unit 1 according to the present embodiment. Figure 1B is a schematic diagram showing the layer configuration of the fixing film 13 according to the present embodiment. Figure 1C is an exploded perspective view of the fixing unit 1 according to the present embodiment.

[0019] The fixing unit 1 is a heat fixing type device, i.e., an image heating device, which heats an image formed on a recording material and fixes the image formed on the recording material to the recording material using a developer or toner in an image forming device employing an electrophotographic system or an electrostatic recording system.

[0020] As Figure 1A and Figure 1C shown, the fixing unit 1 is a film heating type device, which is equipped with a film unit 10 including a fixing film 13 and a pressure roller 20. The film unit 10 includes a heater 11, a holding member 12, a fixing film 13, a metal support frame 14, and a pressing spring 15. As will be described later, a lubricant is applied between the inner surface 131 of the fixing film 13 and the contact surface 111 of the heater 11, which is in sliding contact with the inner surface 131 of the fixing film 13.

[0021] The fixing film 13 is an example of a rotating member formed in a tubular shape or a hollow shape and configured to rotate. The heater 11 is an example of a heating portion that heats the fixing film 13. In addition, the heater 11 according to the present embodiment is an example of a heating body including a contact surface 111 (i.e., a contact portion) that is in sliding contact with the inner surface 131 of the fixing film 13, is disposed in the inner space of the fixing film 13, and heats the fixing film 13. That is, the heater 11 according to the present embodiment is a unit in which a heating portion for heating the fixing film 13 and a contact portion disposed in the inner space of the fixing film 13 to contact the inner surface of the fixing film 13 are integrated. The heating portion and the contact portion are not necessarily integrated, and the heating portion may be a separate unit separated from the contact portion.

[0022] The pressure roller 20 is an example of a pressing member that contacts the outer surface 132 of the fixing film 13 and is disposed to sandwich the fixing film 13 together with the heater 11 (i.e., the heating body). By bringing the contact surface 111 (i.e., the contact portion) of the pressure roller 20 and the heater 11 into pressure contact with the fixing film 13 interposed therebetween, a fixing nip portion N, i.e., a nip portion, is formed between the fixing film 13 and the pressure roller 20.

[0023] Fixing film

[0024] The fixing film 13 is a heating member heated by the heater 11, and heats the image by contacting the image on the recording material passing through the fixing nip portion N. The fixing film 13 according to the present embodiment is formed of a film member (i.e., a thin film) having flexibility and heat resistance, and it may be formed of a resin film or a metal thin film. Alternatively, instead of the flexible fixing film 13, a rotating member having a hollow shape or a cylindrical shape with higher stiffness may be employed. The fixing film 13 may be a composite material in which a plurality of material layers are laminated.

[0025] The fixing film 13 according to the present embodiment is composed of a base layer 13a (i.e., an inner layer) constituting the inner surface 131, a conductive primer layer 13b provided on the base layer 13a, and a release layer 13c formed on the conductive primer layer 13b ( Figure 1B ). The base layer 13a is a resin film, and it may be formed of a polyimide resin having a thickness of 20 μm to 100 μm. The release layer 13c is formed of a fluoropolymer, such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), or tetrafluoroethylene-hexafluoropropylene copolymer (FEP).

[0026] According to an example of the present embodiment, the base layer 13a is formed of polyimide and has a thickness of 60 μm, the conductive primer layer 13b has a thickness of 3 μm, and the release layer 13c is formed by coating PFA added with a conductive agent to a thickness of 10 μm. The total thickness of the fixing film 13 is about 73 μm and its diameter is 18 mm. In addition, the heat conduction of the base layer 13a is enhanced by mixing a highly thermally conductive filler. Further details of the fixing film 13 according to the present embodiment will be described below.

[0027] Heater

[0028] The heater 11 used as the heating portion will be described. The heater 11 is a member having a function of supplying heat to the fixing film 13 to heat the fixing film. The contact portion itself in contact with the fixing film 13 may be a part of the heating unit, or may be provided to transfer the heat received from another heat source to the fixing film 13.

[0029] In the present embodiment, a configuration in which the surface of the heater 11 itself is in contact with the inner surface of the fixing film 13 will be described. Figure 2A is a schematic view showing the state of observing the heater 11 from the pressure roller 20 side (i.e., Figure 1A the lower side in ). Figure 2B is in Figure 2A a cross-sectional view of the heater 11 taken at the line B-B'.

[0030] The heater 11 includes a substrate 11a having heat resistance and insulation properties, and a heating resistor 11b formed on the substrate 11a that generates heat when current passes through it. The substrate 11a is a member in the shape of a long rectangular parallelepiped or a plate shape with high thermal conductivity, such as an insulating substrate formed of alumina or aluminum nitride, or a substrate having insulation properties by applying a glass coating on a metal plate. The heating resistor 11b is formed of a resistive material such as silver palladium (Ag / Pd), and is formed on the surface of the substrate 11a to a thickness of about 10 μm using a method such as screen printing. The heating resistor 11b according to the present embodiment is formed of a pattern including two portions extending in the longitudinal direction of the fixing clamping portion N (i.e., the direction orthogonal to the conveyance direction of the recording material).

[0031] In addition, the heater 11 according to the present embodiment includes a protective layer 11c, and two contacts 11e and a wiring 11d formed on the substrate 11a. The two contacts 11e are connected to a power supply terminal for supplying power to the heating resistor 11b. The wiring 11d electrically connects the contacts 11e and the heating resistor 11b, and is arranged from one of the contacts 11e via the heating resistor 11b to the other contact 11e to form a circuit. The protective layer 11c is formed of a material having heat resistance, such as glass or a fluoropolymer, and is provided to cover the heating resistor 11b and the wiring 11d. In the present embodiment, the contact surface 111 (i.e., the contact portion) that slidably contacts the inner surface of the fixing film 13 is the surface of the protective layer 11c. That is, according to the present embodiment, the contact portion is a part of the heater 11 that serves as the heating portion.

[0032] In an example of the present embodiment, a heater 11 is used, an alumina substrate with a thickness of 1 mm is provided in the heater 11 as the substrate 11a, a heating resistor 11b made of silver palladium is formed on the substrate 11a, and a glass coating with a thickness of 60 μm is applied thereon as the protective layer 11c.

[0033] Holding member

[0034] The holding member 12 is a member that holds the heater 11, that is, a heater holder. The holding member 12 is formed of a heat-resistant resin, such as liquid crystal polymer, phenolic resin, polyphenylene sulfide (PPS), or polyether ether ketone (PEEK). When the thermal conductivity of the holding member 12 becomes lower, the thermal efficiency of the fixing unit 1 becomes higher, and thus the heat-resistant resin may include fillers having low thermal conductivity (such as hollow glass particles and hollow silica particles).

[0035] The holding member 12 receives the pushing force of the compression spring 15 through the metal support frame 14, and pushes the heater 11 toward the pressure roller 20. Thereby, a fixing nip portion N is formed between the fixing film 13 externally assembled to the heater 11 and the holding member 12 and the pressure roller 20, and the fixing nip portion has a substantially uniform contact pressure and nip width in the longitudinal direction. In addition, the holding member 12 is also used to guide the rotation of the fixing film 13.

[0036] A groove hole for holding the heater 11, that is, a groove portion, is formed in the holding member 12. The heater 11 is held on the holding member 12 in a state of being assembled into the groove hole.

[0037] Pressure roller

[0038] As Figure 1A shown, the pressure roller 20 includes a core metal 21, an elastic layer 22 formed on the outer circumference of the core metal 21, and a release layer 23 formed on the outer circumference of the elastic layer 22. The core metal 21 is a shaft-shaped member made of a metal such as stainless steel (SUS) or Al. The elastic layer 22 is an elastic solid rubber layer formed of a heat-resistant rubber such as silicone rubber or fluororubber. In order to further improve the heat insulation property, the elastic layer 22 may be an elastic sponge rubber layer formed by foaming silicone rubber, or an elastic foam rubber layer in which hollow fillers (such as micro-hollow particles) are dispersed in the silicone rubber layer so that gas portions are included in the cured material. The release layer 23 is formed of a fluoropolymer such as PFA and PTFE.

[0039] According to an example of the present embodiment, a silicone hollow sphere rubber layer with a thickness of 3.5 mm is formed as the elastic layer 22, and a PFA layer with a thickness of 30 μm is formed as the release layer 23. The diameter of the pressure roller 20 is 18 mm, and the surface hardness of the pressure roller 20 is Asker C hardness 40.

[0040] Metal support frame

[0041] The metal support frame 14 functions as a reinforcing member (i.e., a rigid member) for enhancing the stiffness of the reinforcing film unit 10. As Figure 1A and Figure 1C shown, the metal support frame 14 is formed in a rectangular shape with one side open in a cross section perpendicular to the longitudinal direction and extends along the longitudinal direction.

[0042] Compression spring

[0043] The pressing spring 15 serves as a pressing member that generates a pressing force in the fixing clamping portion N. According to the present embodiment, the pressing spring 15 is disposed on two end portions of the film unit 10 along the longitudinal direction of the fixing clamping portion N. Spring receiving portions that each receive the pressing force of the pressing spring 15 are provided on two end portions of the metal support frame 14. The load applied by the pressing spring 15 is uniformly transmitted over the entire body of the holding member 12 along the longitudinal direction of the fixing clamping portion N via the metal support frame 14 having high rigidity. At the fixing clamping portion N, the fixing film 13 is clamped between the heater 11 and the pressure roller 20 by the pressing force of the pressing spring 15 and is in close contact with the contact surface 111 of the heater 11.

[0044] Fixing operation

[0045] The pressure roller 20 receives an input of a rotational driving force in the arrow direction from a driving source (i.e., a motor disposed on the main body of the image forming apparatus) via a driving gear (not shown) provided at an end portion of the core metal 21. Together with the rotational driving of the pressure roller 20, the fixing film 13 rotates at the fixing clamping portion N by the frictional force received from the pressure roller 20 as the pressure roller 20 rotates. Figure 2A

[0046] A lubricant is applied between the fixing film 13 and the heater 11. Fluorine or silicone heat-resistant grease can be used as the lubricant. When assembling the film unit 10, the lubricant is applied to the contact surface 111 of the heater 11 or the inner surface 131 of the fixing film 13, or is applied to both the contact surface 111 and the inner surface 131. The lubricant can reduce the friction at the interface between the inner surface 131 of the fixing film 13 and the contact surface 111 of the heater 11, whereby the fixing film 13 can rotate smoothly.

[0047] Temperature control of the fixing unit 1 can be performed as follows. A temperature sensing element (such as a thermistor) is disposed on the rear surface of the substrate 11a of the heater 11, that is, on the surface on the rear side of the contact surface 111. The control portion on the main body of the image forming apparatus controls the duty ratio, that is, the time ratio for turning on and off the power supply from the power circuit to the heater 11, in response to the detection signal of the temperature sensing element. Thereby, the temperature inside the fixing clamping portion N is maintained at a predetermined target temperature suitable for fixing an image.

[0048] In a state where a recording material having an unfixed toner image formed thereon is conveyed to the fixing unit 1, the fixing unit 1 clamps and conveys the recording material through the fixing clamping portion N while heating the toner image on the recording material by the fixing film 13.

[0049] The fixing unit 1 according to this embodiment can perform a fixing process on a letter (LTR) size recording material at a processing speed of 170 mm / second and a target temperature of 180°C at a speed of 30 ppm. In addition, the product life of the fixing unit 1 is set to the cumulative number of 50,000 printed sheets.

[0050] Image forming apparatus

[0051] Figure 4 is an example of the image forming apparatus 100 equipped with the fixing unit 1. The image forming apparatus 100 can perform a series of operations (such as an image forming operation and a sheet feeding operation) while conveying the recording material P one by one based on the image information received from the outside to form an image on the recording material P. Various types of sheet materials of different sizes and materials (including papers such as plain paper and thick paper, surface-treated sheet materials such as coated paper, sheet materials of special shapes such as envelopes and index paper, plastic films, and cloth) can be used as the recording material P, that is, the recording medium. The image forming apparatus 100 can be any one of a single-function printer, a copying machine having a copying function, and a multi-function machine having multiple functions.

[0052] The illustrated image forming apparatus 100 is an electrophotographic monochrome printer having a direct transfer type processing unit 200 as an image forming section. The processing unit 200 includes a photosensitive drum 201 serving as an image bearing member, a charging roller 202 serving as a charging unit, a developing roller 203 serving as a developing section, a toner storage section 204 storing toner as a developer, and a transfer roller 205 serving as a transfer member. The transfer roller 205 and the photosensitive drum 201 constitute a transfer nip portion that serves as a transfer section for performing image formation (i.e., transfer of a toner image) on the recording material P. The processing unit 200 can be a cartridge that can be detachably attached to the main body of the image forming apparatus 100.

[0053] In addition, the image forming apparatus 100 includes an exposure unit 112, a fixing unit 1, and a plurality of rollers 114, 115, 116, and 117 for conveying the recording material P.

[0054] In a state where the control section of the image forming apparatus 100 has received image information, an image forming operation is started. The photosensitive drum 201 is driven to rotate in the direction of the arrow in the figure at a predetermined peripheral speed (i.e., processing speed). The charging roller 202 uniformly charges the surface of the photosensitive drum 201. The exposure unit 112 irradiates the photosensitive drum 201 with light based on the image information, and performs an exposure process of forming an electrostatic latent image on the surface of the photosensitive drum 201. The developing roller 203 carries the toner stored in the toner storage section 204 and supplies it to the photosensitive drum 201, and develops the electrostatic latent image into a toner image. The developed toner image is carried on the photosensitive drum 201 and is transferred to the transfer nip portion by the rotation of the photosensitive drum 201.

[0055] While the toner image is being formed, the recording material P is fed by the feed roller 114 from the storage section provided on the lower portion of the image forming apparatus 100. The separation roller pair 115 conveys the recording material P while separating the recording material P sheet by sheet. The registration roller pair 116 conveys the recording material P that has been conveyed to the transfer nip portion at a timing that matches the arrival of the toner image on the photosensitive drum 201 at the transfer nip portion. Then, by applying a transfer voltage to the transfer roller 205 at the transfer nip portion, the toner image is transferred from the photosensitive drum 201 to the recording material P.

[0056] The recording material P that has passed through the transfer nip portion is conveyed to the fixing unit 1, where the recording material P undergoes a heat fixing process of the toner image at the fixing nip portion N. The recording material P that has passed through the fixing unit 1 is discharged to the outside of the image forming apparatus 100 by the discharge roller pair 117.

[0057] The above-described image forming apparatus 100 is an example of an image forming apparatus on which the fixing unit 1 can be mounted, and the fixing unit 1 can be mounted on an image forming apparatus having other configurations. For example, the image forming apparatus may be a color printer having a plurality of processing units 200 and capable of forming a color image using color toner. Further, the processing unit 200 is not limited to a direct transfer system that directly transfers the toner image from the photosensitive drum 201 to the recording material P, and it may be an intermediate transfer system that transfers the toner image from the photosensitive drum 201 via an intermediate transfer body (such as an intermediate transfer belt) to the recording material P.

[0058] Lubricant retention function of the fixing film

[0059] The fixing film 13 and the lubricant according to the present embodiment will be described. Figure 3A FIG. is a cross-sectional view of the fixing film 13 according to the present embodiment cut along a cross-section perpendicular to the longitudinal direction of the fixing nip portion N, and a partial enlarged view of an enlarged part thereof.

[0060] As Figure 3AAs shown, minute uneven portions are formed on the inner surface 131 of the fixing film 13. The fixing film 13 according to the present embodiment can achieve stable slidability over a long period by holding the base oil of the lubricant in the spaces between the minute uneven portions on the inner surface 131.

[0061] In an example according to the present embodiment, fillers are dispersed in the resin material of the base layer 13a forming the fixing film 13, thereby controlling the degree of unevenness of the inner surface 131. Needle-like fillers 13d are used as fillers. A network structure in which the needle-like fillers 13d are arranged in a complex manner is formed within the base layer 13a.

[0062] In the example of the present embodiment, the base layer 13a is formed of a polyimide resin. Either a thermosetting polyimide resin or a thermoplastic polyimide resin can be used as the base layer 13a, and in this example, a thermosetting polyimide resin is used. The polyimide precursor with the needle-like fillers 13d added in a dispersed manner is called polyimide varnish. The base layer 13a can be formed by depositing a polyimide resin layer on the outer surface of a cylindrical core and then drying and heating the polyimide resin layer to cure the resin. The deposition method can be an impregnation method in which the polyimide varnish is filled in a container and the cylindrical core is inserted into and withdrawn from the polyimide varnish container, or a loop coating method in which the polyimide varnish is spirally coated on the outer surface of the cylindrical core using a dispenser, or any other known method.

[0063] The degree of unevenness of the inner surface 131 of the fixing film 13 can be numerically expressed using the developed interfacial area ratio Sdr as an index. The developed interfacial area ratio Sdr is defined in the standard ISO 25178 established by the International Organization for Standardization. The developed interfacial area ratio Sdr represents the ratio at which the extended area (i.e., the surface area) of a defined region increases from the apparent area of the defined region. The developed interfacial area ratio Sdr can be obtained by measuring the surface shape using a laser microscope such as the VK-9500 (product name) manufactured by Keyence Corp. with an objective lens having a magnification of 150 times.

[0064] In the present embodiment, a lubricant that does not contain a thickener and is formed substantially only of a base oil is used. As the base oil, a fluorine oil such as perfluoropolyether (PFPE) or a silicone oil can be used. PFPE is a polymer containing perfluoroalkyl ether as a repeating unit. Practical examples of perfluoroalkyl ether include perfluoromethyl ether, perfluoroethyl ether, perfluoropropyl ether, and perfluoroisopropyl ether.

[0065] The expression "substantially formed only of base oil" means that it does not contain main components other than the base oil, and it may contain trace amounts of additives, such as additives that are 10% or less, preferably 5% or less, or more preferably 1% or less relative to the total mass of the lubricant. An additive is a component that is added to improve the performance of the lubricant according to the purpose of use of the lubricant, other than the base oil and the thickener, such as an antioxidant, an antifoaming agent, or an antiwear additive. According to the examples of this embodiment, that is, Examples 1-1 to 1-4 described later, a lubricant that contains only base oil components and does not contain any thickener or additive is used, that is, a lubricant with a mixing ratio of the base oil of 100%.

[0066] According to this embodiment, a lubricant that does not contain any thickener is used, so that the heat conduction from the heater 11 (that is, the heating part or the heating body) to the fixing film 13 is not hindered by the thickener. Therefore, even if the application amount of the lubricant is increased, good fixing performance can be obtained.

[0067] In a state where the base oil contacts the minute uneven portions on the inner surface 131 of the fixing film 13, as Figure 3B shown, the base oil infiltrates into the recessed portions due to capillary action and is held by the recessed portions. Thereby, the state of forming a sliding layer 25 as a base oil layer between the inner surface 131 of the fixing film 13 and the contact surface 111 of the heater 11 can be maintained for a long time.

[0068] The holding action of the fixing film 13 on the base oil can be achieved by forming uneven portions on the inner surface 131 of the fixing film 13 so that the spreading interface area ratio Sdr falls within an appropriate range. Thereby, even if the lubricant is composed only of the base oil and does not contain a thickener, the sliding layer 25 is formed on the entire inner surface 131 of the fixing film 13 and is held thereon. Therefore, stable slidability can be achieved for a long time, and the running stability of the fixing film 13 can be enhanced.

[0069] A lubricant containing a thickener can separate the thickener from the base oil at high temperatures. The lubricant has viscosity, while the base oil is a fluid with low viscosity. Therefore, the base oil can be dispersed through the gaps between components by capillary action, or the base oil may be extruded to the outside of the fixing nip portion N due to pressure changes accompanying the fixing operation. In addition, the base oil gradually evaporates through the heating performed during the fixing operation. For such reasons, when used for a long time, the amount of base oil in the lubricant gradually decreases. When the sliding layer cannot be maintained due to the reduction of the base oil, the slidability between the fixing film 13 and the heater 11 decreases, and the running stability of the fixing film 13 is lost, so that during the fixing operation, a transfer failure of the recording material or an image defect may occur.

[0070] According to the present embodiment, by using a lubricant composed only of a base oil and using a fixing film 13 having a developed interface area ratio Sdr within a predetermined range, good fixing performance and long-term stable slidability can be achieved.

[0071] Details of the fixing film

[0072] Reference will be made to Figure 3A and Figure 3B describe the details of the fixing film 13 according to the first example (i.e., Examples 1-1 to 1-4) of the present embodiment. The base layer 13a of the fixing film 13 is a polyimide resin composition, in which needle-like fillers 13d are added to the polyimide resin used as a base material. Needle-like carbon nanotubes, needle-like titanium oxides, or a mixture thereof can be used as the needle-like fillers 13d. In the first example, needle-like carbon nanotubes are employed. Carbon nanotubes having a diameter of 3 μm or less and a length of 50 μm or less are preferably used. In the first example, VGCF-H (VGCF is a registered trademark) of Resonac Holdings Corporation was used. Fillers having a shape other than needle-like can be adopted as long as minute irregularities can be formed on the inner surface 131 of the fixing film 13 so that the developed interface area ratio Sdr described later falls within an appropriate range.

[0073] The addition amount of the needle-like fillers 13d can be adjusted so as to form minute irregularities on the inner surface 131 of the fixing film 13. In the present embodiment, the addition amount of the needle-like fillers 13d is set to 20 vol.% in Example 1-1, 30 vol.% in Example 1-2, 40 vol.% in Example 1-3, and 45 vol.% in Example 1-4. The above unit (i.e., vol.%) refers to the ratio of the total volume of the needle-like fillers 13d dispersed in the base layer 13a to the total volume of the base layer 13a.

[0074] In the first example, a PFPE lubricant (Fomblin M30 of Solvay S.A.) without a thickener added was used as the lubricant. 60 mg of the PFPE lubricant was sprayed onto the inner surface 131 of the fixing film 13.

[0075] Comparative Examples 1 to 3 in which the addition amount or type of the fillers is different from that of the first example have been prepared as comparative examples. In Comparative Example 1, no needle-like fillers 13d were added to the base layer 13a, but 30 vol.% of plate-like fillers were added thereto. In Comparative Example 2, 10 vol.% of the needle-like fillers 13d were added to the base layer 13a. In Comparative Example 3, 50 vol.% of the needle-like fillers 13d were added to the base layer 13a. Comparative Example 4 will be described in detail later.

[0076] Table 1

[0077]

[0078] The "expanded interface area ratio Sdr (initial state)" in Table 1 represents the measurement result of the expanded interface area ratio Sdr according to the corresponding example. There is the following trend: when the addition amount of the needle-shaped filler increases, the value of the expanded interface area ratio Sdr increases, that is, the surface area of the inner surface 131 of the fixing film 13 increases. The magnitude of the expanded interface area ratio Sdr also depends on the shape of the filler, and in the state where the plate-shaped filler is added, it can be recognized that the expanded interface area ratio Sdr is lower compared to the case where the needle-shaped filler is added.

[0079] In addition, the relationship between the expanded interface area ratio Sdr and the holding force of the lubricant was studied. The values in the row of "weight increase after cleaning" in Table 1 represent the difference between the weight measurement value of the fixing film 13 measured in the new state according to each example and the weight measurement value after cleaning measured by thoroughly wiping off the lubricant after the lubricant has been sprayed. That is, the greater the weight increase after cleaning, the greater the holding force of the fixing film 13 for the lubricant. Wiping cleaning is performed by wiping with a cleaning tool in which a product Kimwipes S-200 (product name) of Nippon Paper Crecia Co., Ltd. is attached to a cleaning rod. After wiping a fixing film back and forth 10 times, Kimwipes S-200 is replaced, and this wiping operation is repeated 10 times.

[0080] To compare the influence of the surface shape, Comparative Example 4 was prepared, in which the fixing film 13 was formed of the same material as in Comparative Example 1, and then concavo-convex portions were formed on the inner surface 131 of the fixing film 13. Comparative Example 4 was formed to have minute concavo-convex portions by etching the surface of a mold and transferring the surface shape of the mold to the inner surface 131 of the fixing film 13. The state of the concavo-convex portions was adjusted to be the same as in Examples 1-2.

[0081] Based on the "expanded interface area ratio Sdr (initial state)" and "weight increase after cleaning" in Table 1, it can be recognized that the higher the expanded interface area ratio Sdr, the greater the weight of the lubricant retained in the fixing film 13 after performing wiping cleaning. That is, when the expanded interface area ratio Sdr is higher, the holding force of the fixing film 13 for the lubricant is higher. This is considered to be achieved by the capillary effect causing the lubricant to enter the minute spaces formed by the concavo-convex portions on the inner surface 131 of the fixing film 13 and the lubricant remaining in this space even after performing wiping cleaning.

[0082] In addition, Durability Tests were performed using Examples 1-1 to 1-4 and Comparative Examples 1 to 4. The "Number of sheets printed when image defects occur" and "Number of sheets printed when deformation occurs" in Table 1 show the results of the Durability Tests. The Durability Tests evaluated the running stability of the fixing film 13 when printing was repeatedly performed by the image forming apparatus 100, in which the fixing film 13 of the corresponding example was attached to the fixing unit 1. The running stability of the fixing film 13 was evaluated based on the presence of image defects and the presence of deformation or damage of the fixing film 13. When the sliding layer of the lubricant is lost during the Durability Test, the frictional force increases, resulting in slippage between the fixing film 13 and the recording material P or between the fixing film 13 and the image on the recording material P, whereby image defects may occur. In addition, by applying a load to the fixing film 13 during printing, the fixing film 13 may be damaged or deformed. Printing of sheets was continuously performed until image defects or deformation / damage occurred, and the number of sheets printed at that time was recorded. The unit "K sheets" represents 1,000 sheets, and for example, "41" in Comparative Example 1 means that image defects occurred when approximately 41,000 recording materials P had been printed.

[0083] Based on the "Number of sheets printed when image defects occur" and "Number of sheets printed when deformation occurs" in Table 1, it can be recognized that the durability of the fixing film 13 was significantly improved according to Examples 1-1 to 1-4 compared to Comparative Examples 1 to 4. Based on these results, it is considered that if the developed interface area ratio Sdr is 0.1 or more, that is, 0.10 or more when rounded to the third decimal place, the fixing film 13 will have sufficient lubricant and can maintain the sliding layer for a long time.

[0084] According to Example 1-4 and Comparative Example 3, deformation or damage of the fixing film 13 had occurred before image defects, causing the Durability Test to be interrupted, and the number of sheets printed at that time point was recorded. Generally, if a large amount of highly thermally conductive filler is added to the polyimide tube, the material properties tend to become brittle. From the perspective of the mechanical strength of the fixing film 13, there is an upper limit to the amount of highly thermally conductive filler added, and as a result of the tests, it may be preferable that the amount is at most approximately 45 vol.%. That is, the amount of filler to be added to the polyimide resin is preferably 20 vol.% or more and 45 vol.% or less.

[0085] In addition, since the developed interface area ratio Sdr was 0.503 (Example 1-4) when the addition amount of the needle-like filler 13d was 45 vol.%, it can be recognized that the developed interface area ratio Sdr is preferably 0.5 or less, that is, 0.50 or less when rounded to the third decimal place.

[0086] According to Examples 1-3 and 1-4, the durability is further enhanced compared to Examples 1-1 and 1-4. Therefore, from the perspective of durability, even more preferably, the developed interface area ratio Sdr is 0.26 or more and 0.42 or less to the second decimal place.

[0087] Next, a study was conducted to examine whether the uneven portions on the inner surface 131 of the fixing film 13 were worn after long-term use. The inner surface 131 of the fixing film 13 after the durability test was observed, and the developed interface area ratio Sdr was calculated again. "Developed interface area ratio Sdr (after durability test)" in Table 1 shows the value of the developed interface area ratio Sdr after the durability test calculated for each example.

[0088] As shown in "Developed interface area ratio Sdr (after durability test)" in Table 1, according to Comparative Example 4, it was recognized that the developed interface area ratio Sdr after the durability test was significantly reduced compared to the initial state. That is, in Comparative Example 4, minute uneven portions were applied to the inner surface 131 of the fixing film 13 by transferring the uneven portions of the mold to the inner surface 131, but it was considered that these uneven portions were worn due to abrasion caused by sheet printing. During sheet printing, pressure, heat, and shear force were applied to the inner surface 131 of the fixing film 13, causing the inner surface 131 to become smooth by the external force applied during sheet printing and unable to maintain the minute uneven portions.

[0089] In contrast, according to Examples 1-1 to 1-4 and Comparative Examples 2 and 3, the minute uneven portions on the inner surface 131 were formed by the needle-like fillers 13d added to the base layer 13a. In the inner surface 131, a sea-island structure of the needle-like filler portion and the polyimide resin portion was formed in a three-dimensional manner. Thus, it can be considered that even if the outermost layer of the inner surface 131 is damaged by the external force received during sheet printing, the minute uneven portion structure, that is, the sea-island structure, can be maintained, and compared to Comparative Example 4, the lubricant holding force is maintained at a high holding force for a longer time.

[0090] If the abrasion of the base layer 13a is small, a method of forming minute uneven portions on the inner surface 131 of the fixing film 13 without adding fillers can be adopted as Comparative Example 4.

[0091] According to the above Examples 1-1 to 1-4 and Comparative Examples 1 to 4, Fomblin M30 without any thickener was used as the lubricant. To study the influence of the thickener, Comparative Examples using lubricants containing thickeners were prepared.

[0092] According to Comparative Examples 5 and 6, MOLYKOTE (registered trademark) HP-300 manufactured by Dow Corning Toray was used as the lubricant containing a thickener. In Comparative Example 5, 250 mg of MOLYKOTE HP-300 was applied to the heater 11, and in Comparative Example 6, 60 mg of MOLYKOTE HP-300 was applied to the heater 11. The configuration other than the lubricant of the fixing unit 1 was the same as that of Examples 1-1 to 1-4.

[0093] As described above, the thickener can be used as an obstacle to hinder the heat conduction from the heater 11 (i.e., the heating part or heating element) to the fixing film 13. Therefore, if a lubricant containing a thickener is used in the fixing unit 1, since the lubricant is not adapted in the initial state immediately after the fixing unit 1 is assembled, the heat applied to the recording material P by the thickener may be dispersed, and fixing failure may occur. For example, if a black image is printed on the entire surface in the initial state, the heat unevenness caused by the lubricant may cause a part of the image to peel off, or the output image may peel off when rubbed by hand. To prevent such fixing failure, measures can be taken to set the target temperature of the temperature control of the fixing unit 1 to be 10 °C higher than the normal temperature in the initial state.

[0094] In contrast, according to the present embodiment, a base oil without a thickener is used as the lubricant, so that it is expected to improve the fixing failure caused by the thickener during the initial state. Therefore, a comparative experiment was conducted, which evaluated the fixing performance in the initial state of Comparative Examples 5 and 6 and Examples 1-1 to 1-4, that is, the initial fixing performance. The fixing unit 1 in the initial state was used, and the target temperature was set to the same value in all examples. An image forming apparatus 100 equipped with the fixing film 13 according to each example was used to form a black image on the entire surface of an A4-size sheet having a basis weight of 80 g (i.e., Canon Red Label Premium FSC 80 g / m 2 A4 paper), and it was evaluated whether image peeling occurred. The results are shown in Table 2.

[0095] Table 2

[0096]

[0097] As shown in Table 2, in all of Examples 1-1 to 1-4, the initial fixing performance was good. At the same time, according to Comparative Example 5, image peeling occurred, resulting in poor initial fixing performance. According to Comparative Example 6, the application amount was less than that of Comparative Example 5, but the initial fixing performance was poor.

[0098] As described above, according to the present embodiment, minute uneven portions are provided on the inner surface 131 of the fixing film 13, and a base oil without a thickener is used as a lubricant. The minute uneven portions are set such that the developed interface area ratio Sdr is 0.1 or more and 0.5 or less, that is, up to the second decimal place, 0.10 or more and 0.50 or less. Thereby, the lubricant can be held in the space formed on the minute uneven portions by capillary action, and the sliding layer can be maintained for a long time, so that stable slidability can be obtained for a long time. In addition, by using a base oil without a thickener, good fixing performance can be achieved even in the initial state immediately after assembly.

[0099] As described above, according to the present embodiment, a fixing unit capable of achieving good initial fixing performance and long-term stable slidability, and an image forming apparatus equipped with the fixing unit can be provided.

[0100] Second Embodiment

[0101] As a second embodiment, a configuration in which a small amount of thickener is contained in the lubricant is described. In the following description, unless otherwise specified, elements denoted by the same reference numerals as those in the first embodiment are considered to have substantially the same configurations and effects as the elements described in the first embodiment, and thus mainly the parts different from the first embodiment will be described.

[0102] The ratio of the base oil contained in the lubricant is called the base oil ratio, that is, the oil content ratio. The base oil ratio is the mixing ratio of the mass of the base oil to the total mass of the lubricant. The unit (%) of the base oil ratio is mass percentage.

[0103] To determine an appropriate base oil ratio, the durability and initial fixing performance were evaluated by setting the base oil ratio at four levels of 70%, 80%, 90%, and 100% for Examples 2-1 to 2-3 and Comparative Example 7, each of Examples 2-1 to 2-3 and Comparative Example 7 having a different developed interface area ratio Sdr. The fixing film 13 of Example 2-1 is the same as that of Example 1-1, the fixing film 13 of Example 2-2 is the same as that of Example 1-2, and the fixing film 13 of Example 2-3 is the same as that of Example 1-4. 75 mg of the lubricant was sprayed on the surface of the heater 11.

[0104] In the durability test, if the fixing unit has printed 75,000 sheets, which is 1.5 times the number of sheets of its product life, the durability is evaluated as good (G). And if, for example, due to a rotation failure of the fixing film 13, printing cannot continue before 75,000 sheets are printed, the durability is evaluated as poor (P). Regarding the initial fixing performance, the fixing unit 1 in the initial state is used, and the target temperature is the same under each condition. A black image is printed over the entire surface, and the presence of fixing failures (such as image peeling) is evaluated. The results are shown in Table 3. If there is no fixing failure, the initial fixing performance is evaluated as good (G), and if there is a fixing failure, the initial fixing performance is evaluated as poor (P).

[0105] Table 3

[0106]

[0107] As shown in Table 3, the durability of Examples 2-1 to 2-3 is all good. The goal is achieved and the results are good. At the same time, for Comparative Example 7, according to the conditions where the base oil rate is 70% and 80%, the durability is good, but according to the conditions where the base oil ratio is 90% and 100%, the durability is poor. In Comparative Example 7, the inner surface 131 of the fixing film 13 is smooth, so that if the base oil rate of the lubricant is high, due to the low viscosity of the lubricant, the lubricant tends to leak from the end portion of the fixing film 13. Therefore, as the number of sheets printed increases, the base oil decreases and the sliding layer cannot be maintained, resulting in a rotation failure of the fixing film 13.

[0108] Regarding the initial fixing performance, in Examples 2-1 to 2-3, fixing failures were observed under the condition where the base oil rate was 70%, but under the condition where the base oil ratio was 80% or higher, that is, when the mixing ratio of the thickener was 20% or less, no fixing failures were identified. At the same time, in Comparative Example 7, fixing failures were identified under the conditions where the base oil rate was 70% and 80%, and no fixing failures were identified under the conditions where the base oil rate was 90% and 100%.

[0109] In any case, it was confirmed that when the base oil rate was higher, fewer fixing failures occurred in the initial state. This shows that since the thickener hinders the transfer of heat, as the amount of the thickener increases, more fixing failures tend to occur in the initial state.

[0110] In addition, compared with Comparative Example 7, the tendency of fixing failure occurring in Examples 2-1 to 2-3 is less. According to Comparative Example 7, this is considered to be caused by the fact that the inner surface 131 of the fixing film 13 is smooth, making it difficult for the lubricant with viscosity to spread on the inner surface 131 and the lubricant being unevenly applied. Meanwhile, in Examples 2-1 to 2-3, the inner surface 131 of the fixing film 13 has minute uneven portions, such that the lubricant containing a thickener spreads over the entire inner surface 131, and the lubricant tends to be evenly applied, so that the fixing failure in the initial state is considered to be reduced.

[0111] Based on the above results, even when using a lubricant containing a thickener, it has been recognized that if the base oil rate is 80% or more, good initial fixing performance can be obtained.

[0112] As described above, according to the present embodiment, minute uneven portions are formed on the inner surface 131 of the fixing film 13, and a lubricant containing a small amount of thickener is used. The minute uneven portions are formed such that the spreading interface area ratio Sdr falls within the range of 0.1 or more and 0.5 or less, that is, to the second decimal place, 0.10 or more and 0.50 or less. In addition, the base oil rate of the lubricant is set to 80% or more. Thereby, a fixing unit capable of achieving good initial fixing performance and long-term stable slidability, and an image forming apparatus equipped with the fixing unit can be provided.

[0113] Furthermore, according to the present embodiment, the properties such as viscosity and water resistance of the lubricant can be adjusted by combining thickeners. Therefore, the properties of the lubricant can be adjusted according to the actual configuration of the fixing unit 1 while achieving good initial fixing performance and stable slidability.

[0114] Other embodiments

[0115] In the corresponding embodiments described above, the heater 11 that generates heat by itself and has a contact surface 111 in contact with the fixing film 13 has been described as an example of a heating portion that contacts the inner surface of the fixing film 13 and heats the fixing film 13. The member in contact with the inner surface of the fixing film 13 (i.e., the contact portion) may be a heat conduction member that is different from the heating portion and conducts the heat received from the heating portion (i.e., the heat source) to the fixing film 13. The heat source may be a member that is arranged to be in contact with the heat conduction member and conducts heat to the heat conduction member by heat conduction, or may be a member that is arranged not to be in contact with the heat conduction member and transfers heat to the heat conduction member by heat radiation. For example, the heat conduction member may be a sheet-like member applied between the heater 11 and the fixing film 13. The sheet-like member may have a high thermal conductivity and a high slidability with respect to the fixing film 13, and for example, it may be a thin metal plate or a resin sheet. That is, the contact portion may be a heat conduction member that is arranged between the heater 11 (i.e., the heating portion) and the fixing film 13 (i.e., the rotating member) and conducts the heat generated by the heating resistor 11b of the heater 11 to the fixing film 13. In addition, the heat conduction member may be a plate-like member heated by radiant heat from, for example, a halogen lamp used as a heat source.

[0116] Although the present invention has been described with reference to exemplary embodiments, it should be understood that the present invention is not limited to the disclosed exemplary embodiments. The scope of the appended claims will be given the broadest interpretation so as to cover all such modifications as well as equivalent structures and functions.

Claims

1. A fixing unit, comprising: A rotating member, which is formed in a tubular shape and configured to rotate; A contact portion, which is disposed in the inner space of the rotating member and configured to slidably contact the inner surface of the rotating member; A pressing member, which is configured to contact the outer surface of the rotating member and arranged to clamp the rotating member together with the contact portion; And A heating portion, which is configured to heat the rotating member so that the rotating member heats an image on a recording material that is clamped in the clamping portion between the rotating member and the pressing member and conveyed through the clamping portion, and thus the image is fixed to the recording material, Wherein a lubricant is applied between the inner surface of the rotating member and the contact portion, Wherein the lubricant contains a base oil in a ratio of 80% or more relative to the total mass of the lubricant, and Wherein the developed interface area ratio of the inner surface of the rotating member is 0.10 or more and 0.50 or less.

2. The fixing unit according to claim 1, wherein the lubricant does not contain a thickener.

3. The fixing unit according to claim 1, wherein the lubricant contains a thickener in a ratio of 20% or less relative to the total mass of the lubricant.

4. The fixing unit according to any one of claims 1 to 3, wherein the developed interface area ratio of the inner surface of the rotating member is 0.26 or more and 0.42 or less.

5. The fixing unit according to any one of claims 1 to 3, Wherein the rotating member includes an inner layer configured to form the inner surface, and Wherein the inner layer is a resin film, in which fillers are dispersed in a resin material.

6. The fixing unit according to claim 5, wherein the fillers are needle-shaped.

7. The fixing unit according to claim 6, wherein the fillers are carbon nanotubes, needle-shaped titanium oxide, or a mixture of carbon nanotubes and needle-shaped titanium oxide.

8. The fixing unit according to claim 5, wherein the resin film is a polyimide resin composition, in which the fillers are dispersed in the polyimide resin.

9. The fixing unit according to claim 8, wherein the fillers are added in a ratio of 20 vol.% or more and 45 vol.% or less relative to the total volume of the polyimide resin composition.

10. The fixing unit according to any one of claims 1 to 3, wherein the heating portion includes a substrate and a heating resistor, the heating resistor is formed on the substrate and configured to generate heat when an electric current passes through.

11. The fixing unit according to claim 10, Wherein the heating portion includes a protective layer formed to cover the heating resistor, and Wherein the contact portion is the surface of the protective layer.

12. The fixing unit according to claim 11, further comprising: A holding member, which is configured to hold the heating portion; A support frame, which is configured to support the holding member; And A pressing member configured to press the support frame such that the contact portion and the pressing member are in pressure contact with each other while clamping the rotating member. The rotating member is formed of a flexible film member and configured to rotate by receiving frictional force from the pressing member that rotates by receiving a driving force.

13. The fixing unit according to claim 10, wherein the contact portion is a heat conduction member disposed between the heating portion and the rotating member and configured to conduct heat generated by the heating resistor to the rotating member.

14. An image forming apparatus, comprising: An image forming portion configured to form an image on a recording material; And The fixing unit according to any one of claims 1 to 13, Wherein the fixing unit is configured to fix the image formed by the image forming portion to the recording material.

Images