Fixing device and image forming device

Abstract

To achieve excellent initial fixability and stable slidability over a long period of time.SOLUTION: A fixing device has: a rotatable cylindrical rotor; a heating element that has a contact surface that is in sliding contact with an inner surface of the rotor, is arranged in an internal space of the rotor, and heats the rotor; and a pressurization member that is in contact with an outer surface of the rotor, and arranged as to sandwich the rotor together with the heating element. Between the inner surface of the rotor and the contact surface of the heating element, lubricant is interposed. The lubricant contains base oil in a proportion of 80% or more with respect to a total mass of the lubricant. A developed surface area ratio Sdr of the inner surface of the rotor is 0.10 or more and 0.50 or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a fixing device that fixes an image on a recording material, and an image forming apparatus that forms an image on a recording material. [Background technology]

[0002] Patent Document 1 describes a fixing device that has a cylindrical film, a heater that contacts the inner surface of the film, a stay that supports the heater, and a pressure roller that sandwiches the film and forms a fixing nip together with the heater, with a lubricant interposed between the inner surface of the film and the surface of the heater. Patent Document 1 also describes a method of preventing the lubricant from spilling over from the film edges by providing recesses in both longitudinal ends of the stay to store the lubricant. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-76589 Summary of the Invention [Problem to be solved by the invention]

[0004] Lubricants used in fixing devices often contain base oil and thickener as their main ingredients, and the base oil forms an oil film (sliding film) at the interface between sliding objects to reduce friction. If the sliding film cannot be maintained for some reason, such as the base oil being extruded or evaporating, when the fixing device is used over a long period of time, the sliding properties will decrease, which can result in poor images during fixing or deformation or damage to the film.

[0005] If the amount of lubricant applied is increased so as to maintain the sliding film for a long period of time, the thickener may hinder heat conduction, which may result in poor fixing, especially in the initial state immediately after assembly of the fixing device. On the other hand, if the ratio of base oil in the lubricant is increased, the viscosity of the lubricant decreases, making it easier for the base oil to flow out of the area to be lubricated, which does not lead to maintaining the sliding film for a long period of time.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fixing device that can achieve good initial fixing performance and stable sliding performance over a long period of time, and an image forming apparatus equipped with the fixing device. [Means for solving the problem]

[0007] One aspect of the present invention is a fixing device comprising: a rotatable cylindrical rotating body; a heating body having a contact surface that is in sliding contact with the inner surface of the rotating body and is disposed in the internal space of the rotating body to heat the rotating body; and a pressure member that abuts against the outer surface of the rotating body and is disposed so as to sandwich the rotating body together with the heating body, wherein the fixing device heats an image on the recording material while sandwiching and transporting the recording material in a nip portion between the rotating body and the pressure member, and wherein a lubricant is interposed between the inner surface of the rotating body and the contact surface of the heating body, the lubricant containing a base oil in a proportion of 80% or more based on the total mass of the lubricant, and the developed area ratio Sdr of the inner surface of the rotating body is 0.10 or more and 0.50 or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a fixing device that can achieve good initial fixability and stable sliding properties over a long period of time, and an image forming apparatus equipped with the fixing device. [Brief explanation of the drawings]

[0009] [Figure 1] 1A is a cross-sectional view of a fixing device according to a first embodiment, FIG. 1B is a schematic diagram of a fixing film, and FIG. 1C is an exploded perspective view of the fixing device. [Figure 2] 1A is a schematic diagram of a heater according to a first embodiment, and FIG. 1B is a cross-sectional view thereof. [Figure 3] 3A and 3B are explanatory views of a fixing film according to Example 1. FIG. [Figure 4] 1 is a schematic diagram of an image forming apparatus according to a first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0011] First Embodiment A description will be given of the fixing device 1 according to the first embodiment. First, an example of the fixing device 1 and an image forming apparatus including the fixing device 1 will be described.

[0012] Fig. 1(a) is a cross-sectional view of the fixing device 1 according to this embodiment. Fig. 1(b) is a schematic diagram showing the layer structure of the fixing film 13 according to this embodiment. Fig. 1(c) is an exploded perspective view of the fixing device 1 according to this embodiment.

[0013] The fixing device 1 is a thermal fixing device (image heating device) that fixes an image formed on a recording material using a developer (toner) to the recording material by heating it in an image forming device such as an electrophotographic or electrostatic recording device.

[0014] 1(a) and 1(c), the fixing device 1 is a film heating type device having 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, the fixing film 13, a metal stay 14, and a pressure spring 15. As will be described later, a lubricant is interposed between an inner surface 131 of the fixing film 13 and a contact surface 111 of the heater 11 that is in sliding contact with the inner surface 131 of the fixing film 13.

[0015] The fixing film 13 is an example of a rotatable cylindrical (hollow) rotating body. The heater 11 has a contact surface 111 that comes into sliding contact with the inner surface 131 of the fixing film 13, is disposed in the internal space of the fixing film 13, and is an example of a heating body that heats the fixing film 13. The pressure roller 20 is an example of a pressure member that comes into contact with the outer surface 132 of the fixing film 13 and is disposed so as to sandwich the fixing film 13 together with the heater 11 (heating body). The pressure roller 20 and the heater 11 (heating body) are pressed together with the fixing film 13 sandwiched therebetween, thereby forming a fixing nip N (nip portion) between the fixing film 13 and the pressure roller 20.

[0016] (fixing film) The fixing film 13 is a heating member that is heated by the heater 11 and heats the image on the recording material passing through the fixing nip N by contacting the image. The fixing film 13 of this embodiment is formed of a flexible (pliable) and heat-resistant film material (thin film), such as a resin film or a metal thin film. Note that instead of the flexible fixing film 13, a hollow (cylindrical) rotating body with higher rigidity may be used. The fixing film 13 may also be a composite material in which multiple material layers are laminated.

[0017] The fixing film 13 according to this embodiment is composed of a base layer 13a (inner layer) forming the inner surface 131, a conductive primer layer 13b provided on the base layer 13a, and a release layer 13c provided on the conductive primer layer 13b (FIG. 1(b)). The base layer 13a is a resin film made of, for example, a polyimide resin having a thickness of 20 to 100 μm. The release layer 13c is made of, for example, a fluororesin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), or FEP (tetrafluoroethylene-hexafluoropropylene copolymer).

[0018] In this embodiment, the base layer 13a is made 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 a 10 μm thick PFA containing a conductive agent. The total thickness of the fixing film 13 is approximately 73 μm, and the diameter is 18 mm. Furthermore, a highly thermally conductive filler is mixed into the base layer 13a to increase thermal conductivity. Further details of the fixing film 13 in this embodiment will be described later.

[0019] (heating body) The heating element is a member that has the function of supplying heat to the fixing film 13. The heating element may be one that generates heat itself, or one that receives heat from another heat source and transfers the heat to the fixing film 13.

[0020] In this embodiment, a heater 11 that generates heat by itself will be described as an example of a heating body. Fig. 2(a) is a schematic diagram of the heater 11 as seen from the pressure roller 20 side (the lower side in Fig. 1(a)). Fig. 2(b) is a cross-sectional view of the heater 11 taken along line BB' in Fig. 2(a).

[0021] The heater 11 includes a heat-resistant and insulating substrate 11a and a heating resistor 11b formed on the substrate 11a that generates heat when energized. The substrate 11a is a highly thermally conductive, elongated rectangular parallelepiped (plate-like) member, such as an insulating substrate made of alumina or aluminum nitride, or a metal plate with an insulating glass coating. The heating resistor 11b is made of an electrically resistive material such as Ag / Pd (silver-palladium), and is formed on the surface of the substrate 11a by screen printing or other methods to a thickness of approximately 10 μm. In this embodiment, the heating resistor 11b is formed in a pattern including two portions that each extend in the longitudinal direction of the fixing nip N (a direction perpendicular to the recording material conveyance direction).

[0022] The heater 11 of this embodiment also includes a protective layer 11c and two contacts 11e and wiring 11d formed on the substrate 11a. The two contacts 11e are connected to power supply terminals for supplying power to the heating resistor 11b. The wiring 11d electrically connects the contacts 11e and the heating resistor 11b and is arranged to form a circuit extending from one contact 11e to the other contact 11e via the heating resistor 11b. The protective layer 11c is made of a heat-resistant material such as glass or fluororesin and is formed to cover the heating resistor 11b and wiring 11d. In this embodiment, the contact surface 111 of the heater that comes into sliding contact with the inner surface of the fixing film 13 is the surface of the protective layer 11c.

[0023] In the example of this embodiment, an alumina substrate having a thickness of 1 mm is used as the substrate 11a, a silver-palladium heating resistor 11b is formed on the substrate 11a, and a heater 11 having a protective layer 11c coated with glass having a thickness of 60 μm is used.

[0024] (holding member) The holding member 12 is a member (heater holder) that holds the heater 11, etc. The holding member 12 is made of heat-resistant resin such as liquid crystal polymer, phenolic resin, PPS (polyphenylene sulfide), PEEK (polyether ether ketone), etc. The lower the thermal conductivity of the holding member 12, the better the thermal efficiency of the fixing device 1. Therefore, the heat-resistant resin may contain low-thermal-conductivity fillers such as glass balloons or silica balloons.

[0025] The holding member 12 receives the biasing force of the pressure spring 15 via the metal stay 14 and biases the heater 11 toward the pressure roller 20. As a result, a fixing nip N with a substantially uniform contact pressure and nip width in the longitudinal direction is formed between the fixing film 13 fitted around the heater 11 and the holding member 12 and the pressure roller 20. The holding member 12 also serves to guide the rotation of the fixing film 13.

[0026] The holding member 12 is provided with a slot (groove) for holding the heater 11. The heater 11 is held by the holding member 12 in a state where it is fitted into the slot.

[0027] (Pressure roller) As shown in FIG. 1( a), the pressure roller 20 has a core 21, an elastic layer 22 formed on the outer periphery of the core 21, and a release layer 23 formed on the outer periphery of the elastic layer 22. The core 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 heat-resistant rubber such as silicone rubber or fluororubber. To further improve heat insulation, the elastic layer 22 may be an elastic sponge rubber layer formed by foaming silicone rubber, or an elastic foam rubber layer formed by dispersing hollow fillers (microballoons, etc.) in a silicone rubber layer and providing a gas portion within the cured product. The release layer 23 is formed of a fluororesin such as PFA or PTFE.

[0028] In this embodiment, a silicone balloon rubber layer having a thickness of 3.5 mm is formed as the elastic layer 22, and a PFA layer having an Atsumi hardness of 30 μm is formed as the release layer 23. The pressure roller 20 has a diameter of 18 mm and a surface hardness of 40 degrees in Asker C hardness.

[0029] (Metal stay) The metal stay 14 serves as a reinforcing member (rigidity member) that increases the rigidity of the film unit 10. As shown in Figures 1(a) and 1(c), the metal stay 14 is formed in a U-shape in a cross section perpendicular to the longitudinal direction, and extends elongatedly in the longitudinal direction.

[0030] (Compression spring) The pressure springs 15 function as biasing members for generating a pressure force in the fixing nip N. In this embodiment, the pressure springs 15 are disposed at both ends of the film unit 10 in the longitudinal direction of the fixing nip N. Spring bearing portions for receiving the biasing force of the pressure springs 15 are provided at both ends of the metal stay 14. The load of the pressure springs 15 is transmitted uniformly throughout the entire holding member 12 in the longitudinal direction of the fixing nip N via the highly rigid metal stays 14. In the fixing nip N, the biasing force of the pressure springs 15 causes the fixing film 13 to be sandwiched between the heater 11 and the pressure roller 20, and the fixing film 13 is brought into close contact with the contact surface 111 of the heater 11.

[0031] (Fixing operation) 2(a) from a drive source (a motor disposed in the image forming apparatus body) via a drive gear (not shown) provided at the end of the core metal 21. As the pressure roller 20 is rotated, the fixing film 13 rotates following the pressure roller 20 due to the frictional force it receives from the pressure roller 20 at the fixing nip N.

[0032] A lubricant is interposed between the fixing film 13 and the heater 11. Fluorine-based or silicone-based heat-resistant grease can be used as the lubricant. The lubricant is applied to the contact surface 111 of the heater 11 or the inner surface 131 of the fixing film 13, or to both the contact surface 111 and the inner surface 131, when assembling the film unit 10. The lubricant reduces friction at the interface between the inner surface 131 of the fixing film 13 and the contact surface 111 of the heater 11, allowing the fixing film 13 to rotate smoothly.

[0033] The temperature of the fixing device 1 is controlled, for example, as follows: A temperature detection element such as a thermistor is disposed on the back surface (the surface behind the contact surface 111) of the substrate 11a of the heater 11. A control unit of the image forming apparatus main body controls the time ratio (power duty) for turning on / off the power supply from the power supply circuit to the heater 11 in response to a detection signal from the temperature detection element. This allows the temperature inside the fixing nip N to be maintained at a predetermined target temperature suitable for fixing an image.

[0034] When a recording material on which an unfixed toner image has been formed is conveyed to the fixing device 1, the fixing device 1 heats the toner image on the recording material with the fixing film 13 while nipping and conveying the recording material in the fixing nip N.

[0035] The fixing device 1 in this embodiment can fix LTR size recording materials at a speed of 30 ppm at a process speed of 170 mm / sec and a target temperature of 180° C. The product life of the fixing device 1 is set to a cumulative number of printed sheets of 50,000.

[0036] (Image forming device) FIG. 4 shows an example of an image forming apparatus 100 equipped with a fixing device 1. The image forming apparatus 100 can execute a series of operations (image forming operations, paper passing operations) for forming an image on a recording material P while conveying the recording material P one sheet at a time, based on image information received from an external source, for example. A variety of sheet materials of different sizes and materials can be used as the recording material P (recording medium), including paper such as plain paper and cardboard, surface-treated sheet materials such as coated paper, specially shaped sheet materials such as envelopes and index paper, plastic film, cloth, etc. The image forming apparatus 100 may be a single-function printer, a copier with a copying function, or a multifunction machine with multiple functions.

[0037] The illustrated image forming apparatus 100 is an electrophotographic monochrome printer equipped with a direct transfer process unit 200 as an image forming section. The process unit 200 includes a photosensitive drum 201 as an image carrier, a charging roller 202 as a charging section, a developing roller 203 as a developing section, a toner storage section 204 that stores toner as a developer, and a transfer roller 205 as a transfer member. The transfer roller 205 and the photosensitive drum 201 form a transfer nip as a transfer section where an image is formed (a toner image is transferred) onto a recording material P. The process unit 200 may be a cartridge that is detachable from the main body of the image forming apparatus 100.

[0038] The image forming apparatus 100 also includes an exposure device 112, a fixing device 1, and a plurality of rollers (114, 115, 116, 117) for conveying the recording material P.

[0039] When the control unit of the image forming apparatus 100 receives image information, the image forming operation is initiated. The photosensitive drum 201 is driven to rotate in the direction of the arrow in the figure at a predetermined peripheral speed (process speed). The charging roller 202 uniformly charges the surface of the photosensitive drum 201. The exposure device 112 performs an exposure process in which light is irradiated onto the photosensitive drum 201 based on the image information to write an electrostatic latent image onto the surface of the photosensitive drum 201. The developing roller 203 carries toner contained in the toner container 204 and supplies it to the photosensitive drum 201, developing the electrostatic latent image into a toner image. The developed toner image is carried by the photosensitive drum 201 and transported to the transfer nip by the rotation of the photosensitive drum 201.

[0040] In parallel with the creation of the toner image, a feeding roller 114 feeds a recording material P from a storage unit provided at the bottom of the image forming apparatus 100. A pair of separation rollers 115 conveys the recording material P in a separated state, one sheet at a time. A pair of registration rollers 116 conveys the conveyed recording material P to the transfer nip in synchronization with the timing at which the toner image on the photosensitive drum 201 reaches the transfer nip. Then, at the transfer nip, a transfer voltage is applied to a transfer roller 205, so that the toner image is transferred from the photosensitive drum 201 to the recording material P.

[0041] The recording material P that has passed through the transfer nip is conveyed to the fixing device 1, where the toner image is thermally fixed at the fixing nip N. The recording material P that has passed through the fixing device 1 is discharged to the outside of the image forming apparatus 100 by a pair of discharge rollers 117.

[0042] The image forming apparatus 100 described above is one example of an image forming apparatus that can include the fixing device 1, and the fixing device 1 may also be included in an image forming apparatus having a different configuration. For example, the image forming apparatus may be a color printer that has multiple process units 200 and forms color images using toner of multiple colors. Furthermore, the process unit 200 is not limited to a direct transfer type in which a toner image is directly transferred from the photosensitive drum 201 to the recording material P, but may also be an intermediate transfer type in which a toner image is transferred from the photosensitive drum 201 to the recording material P via an intermediate transfer body such as an intermediate transfer belt.

[0043] [Lubricant retention function of fixing film] The fixing film 13 and the lubricant in this embodiment will be described. Fig. 3(a) shows a cross section of the fixing film 13 according to this embodiment cut along a cross section perpendicular to the longitudinal direction of the fixing nip N, and a partially enlarged view of the cross section.

[0044] 3(a), fine irregularities are formed on the inner surface 131 of the fixing film 13. The fixing film 13 of this embodiment holds the base oil of the lubricant in the gaps between the fine irregularities on the inner surface 131, thereby realizing stable sliding properties over a long period of time.

[0045] In an example of this embodiment, the degree of unevenness of the inner surface 131 is controlled by dispersing filler in the resin material forming the base layer 13a of the fixing film 13. Needle-shaped filler 13d is used as the filler. In the base layer 13a, a network structure is formed in which the needle-shaped filler 13d are intricately connected to each other.

[0046] In the examples of this embodiment, the base layer 13a is formed of a polyimide resin. While either a thermosetting polyimide resin or a thermoplastic polyimide resin can be used for the base layer 13a, a thermosetting polyimide resin is used in the examples. A polyimide precursor to which needle-shaped filler 13d is added and dispersed is called a polyimide varnish. The base layer 13a can be formed by forming a polyimide resin film on the outer surface of a cylindrical core, drying it, and then heating and curing it. The film formation method may be a dipping method in which a container is filled with polyimide varnish and a cylindrical core is inserted and pulled out, a ring coating method in which a dispenser is used to spirally coat the polyimide varnish on the outer surface of a cylindrical core, or any other known method.

[0047] The degree of unevenness of the inner surface 131 of the fixing film 13 can be quantified using the developed area ratio Sdr as an index. The developed area ratio Sdr is specified in ISO 25178, a standard of the International Organization for Standardization. The developed area ratio Sdr indicates the rate at which the developed area (surface area) of a defined region increases relative to the apparent area of the defined region. The developed area ratio Sdr can be determined by measuring the surface shape using a laser microscope (for example, VK-9500 (product name) manufactured by Keyence Corporation) with an objective lens at 150x magnification.

[0048] In this embodiment, a lubricant consisting essentially of base oil without thickener is used. As the base oil, a fluorine oil such as PFPE or a silicone oil can be used. PFPE is a polymer having perfluoroalkylene ether as a repeating unit. Specific examples of perfluoroalkylene ether include perfluoromethyl ether, perfluoroethyl ether, perfluoropropyl ether, and perfluoroisopropyl ether.

[0049] The phrase "consisting essentially of base oil" means that the lubricant does not contain any other major components than the base oil, and may contain trace amounts of additives (for example, 10% or less, preferably 5% or less, and more preferably 1% or less, based on the total mass of the lubricant). Additives are components other than the base oil and thickener, such as antioxidants, antifoaming agents, and antiwear agents, that are added to improve the performance of the lubricant depending on the application of the lubricant. In the examples of this embodiment (Examples 1-1 to 1-4 described below), lubricants are used that are composed only of base oil components, without thickeners or additives (lubricants with a base oil blend ratio of 100%).

[0050] In this embodiment, a lubricant that does not contain a thickener is used, so the thickener does not interfere with the heat conduction from the heater 11 (heating element) to the fixing film 13. Therefore, even if the amount of lubricant applied is increased, good fixing properties can be obtained.

[0051] When the base oil comes into contact with the minute concaves and convexes on the inner surface 131 of the fixing film 13, the base oil penetrates into the concaves by capillary action and is retained therein, as shown in Fig. 3(b). As a result, the state in which the sliding film 25, which is a film of base oil, is formed between the inner surface 131 of the fixing film 13 and the contact surface 111 of the heater 11 is maintained for a long period of time.

[0052] By forming unevenness on the inner surface 131 of the fixing film 13 so that the developed area ratio Sdr falls within an appropriate range, it is possible to obtain the effect of retaining the base oil by the fixing film 13. As a result, even if the lubricant is made of only the base oil without adding a thickener, the sliding film 25 is formed and retained over the entire inner surface 131 of the fixing film 13. As a result, stable sliding properties can be obtained over a long period of time, and the running stability of the fixing film 13 can be improved.

[0053] When the temperature of a lubricant containing a thickener rises, the base oil tends to separate from the thickener. In contrast to a viscous lubricant, the base oil is a low-viscosity liquid. Therefore, capillary action causes the base oil to diffuse through gaps between components, and pressure changes associated with the fixing operation push the base oil out of the fixing nip N. Furthermore, the heat generated during the fixing operation gradually evaporates the base oil. Due to these factors, the amount of base oil in the lubricant gradually decreases over long-term use. If the sliding film cannot be maintained due to a decrease in base oil, the sliding ability between the fixing film 13 and the heater 11 decreases, impairing the running stability of the fixing film 13. This can result in poor recording material transport and poor image quality during fixing.

[0054] According to this embodiment, by using a lubricant consisting only of base oil and using a fixing film 13 whose development area ratio Sdr is within a predetermined range, it is possible to achieve good fixing properties and stable sliding properties over a long period of time.

[0055] (Fixing film details) The fixing film 13 according to Example 1 (Examples 1-1 to 1-4) of this embodiment will be described in detail with reference to FIGS. 3(a) and 3(b). The base layer 13a of the fixing film 13 is a polyimide resin composition in which needle-shaped fillers 13d are added to a polyimide resin base material. The needle-shaped fillers 13d can be needle-shaped carbon nanotubes, needle-shaped titanium oxide, or a mixture thereof. In Example 1, needle-shaped carbon nanotubes were used. It is desirable to use carbon nanotubes with a diameter of 3 μm or less and a length of 50 μm or less. In Example 1, VGCF-H (VGCF is a registered trademark) from Resonac Holdings, Inc. was used. Note that fillers with shapes other than needle shapes may be used as long as they can form fine irregularities on the inner surface 131 of the fixing film 13 so that the developed area ratio Sdr, described below, is an appropriate value.

[0056] The amount of needle-like filler 13d added is adjusted to create fine irregularities on the inner surface 131 of the fixing film 13. In this embodiment, the amount of needle-like filler 13d added was set to 20% by volume in Example 1-1, 30% by volume in Example 1-2, 40% by volume in Example 1-3, and 45% by volume in Example 1-4. The above unit (volume %) represents the ratio of the total volume of the needle-like filler 13d dispersed in the base layer 13a to the total volume of the base layer 13a.

[0057] In Example 1, a PFPE lubricant (Fomblin M30 manufactured by Solvay) without adding a thickener was used as the lubricant. 60 mg of the PFPE lubricant was sprayed onto the inner surface 131 of the fixing film 13.

[0058] As comparative examples, Comparative Examples 1 to 3 were prepared in which the amount or type of filler added was different from that of Example 1. In Comparative Example 1, no needle-like filler 13d was added to the base layer 13a, and instead 30 volume % of scaly filler was added. In Comparative Example 2, 10 volume % of needle-like filler 13d was added to the base layer 13a. In Comparative Example 2, 50 volume % of needle-like filler 13d was added to the base layer 13a. Comparative Example 4 will be described later.

[0059] [Table 1]

[0060] "Developed area ratio Sdr (initial)" in Table 1 represents the measurement results of the developed area ratio Sdr for each example. It can be seen that the value of the developed area ratio Sdr increases when the amount of needle-like filler added increases (the surface area of the inner surface 131 of the fixing film 13 increases). It can also be seen that the magnitude of the developed area ratio Sdr depends on the shape of the filler, and that when a scaly filler is added, the developed area ratio Sdr is lower than when a needle-like filler is added.

[0061] The relationship between the developed area ratio Sdr and the lubricant retention was also investigated. The values in the "Weight Gain After Cleaning" row in Table 1 represent the difference between the weight of the fixation film 13 in a new state for each example and the weight after cleaning, in which the lubricant was sprayed on and then carefully wiped off. In other words, the greater the weight gain after cleaning, the greater the lubricant retention by the fixation film 13. Wiping cleaning was performed using a cleaning tool consisting of Kimwipe S-200 (product name) manufactured by Nippon Paper Crecia Co., Ltd., which was placed over a cleaning rod. For each fixation film, the Kimwipe S-200 was replaced every 10 reciprocating rubbing movements, a process that was repeated 10 times.

[0062] In order to compare the influence of the surface shape, a fixing film 13 was formed using the same material as in Comparative Example 1, and comparative example 4 was produced by subsequently forming irregularities on the inner surface 131 of the fixing film 13. In comparative example 4, the surface of a mold was etched to form fine irregularities, and the mold surface shape was transferred to the inner surface 131 of the fixing film 13. The irregularity state was adjusted to be equivalent to that of Example 1-2.

[0063] Looking at the "Expanded area ratio Sdr (initial)" and "Weight increase after cleaning" in Table 1, the higher the expanded area ratio Sdr, the greater the weight of lubricant retained on the fixing film 13 even after wiping and cleaning. In other words, the higher the expanded area ratio Sdr, the stronger the retention of the lubricant by the fixing film 13. This is thought to be because the lubricant penetrates into the minute gaps of the unevenness formed on the inner surface 131 of the fixing film 13 due to capillary action, and the lubricant remains in the gaps even after wiping and cleaning.

[0064] Furthermore, a durability test was conducted using Examples 1-1 to 1-4 and Comparative Examples 1 to 4. The "Number of sheets passed until image failure" and "Number of sheets deformed" in Table 1 represent the results of the durability test. The durability test evaluated the running stability of the fixing film 13 by repeatedly passing the fixing film 13 of each example through the image forming apparatus 100 mounted on the fixing device 1. The running stability of the fixing film 13 was evaluated based on the presence or absence of image failure and deformation / breakage of the fixing film 13. If the sliding film of the lubricant disappears during the durability test, the frictional force increases, causing slippage between the fixing film 13 and the recording material P and between the fixing film 13 and the image on the recording material P, which may result in image failure. Furthermore, the fixing film 13 may be deformed or broken due to the load applied to it as the paper is passed. Paper was passed continuously until image failure or deformation / breakage occurred, and the number of sheets passed was recorded. The unit "K sheets" is 1000 sheets, and for example, "41" in Comparative Example 1 indicates that an image defect occurred when approximately 41000 sheets of recording material P had been passed.

[0065] Looking at the "Number of sheets passed until image failure occurs" and "Number of sheets deformed" in Table 1, it can be seen that the durability of the fixing film 13 in Examples 1-1 to 1-4 was significantly improved compared to Comparative Examples 1 to 4. From this result, it is considered that if the developed area ratio Sdr is 0.1 or more (0.10 or more rounded to two decimal places), the fixing film 13 can sufficiently retain the lubricant and maintain its sliding film properties for a long period of time.

[0066] In Examples 1-4 and Comparative Example 3, deformation and damage of the fixing film 13 occurred before image defects occurred, so the durability test was interrupted and the number of sheets passed at that point was recorded. Generally, adding a large amount of highly thermally conductive filler to a polyimide tube tends to embrittle the material. 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 that can be added, and experimental results have shown that it is preferable to limit it to about 45% by volume. In other words, the amount of filler added to the polyimide resin is preferably 20% by volume or more and 45% by volume or less.

[0067] Furthermore, since the developed area ratio Sdr was 0.503 (Example 1-4) when needle-shaped filler 13d was added in an amount of 45% by volume, it can be said that it is preferable for the developed area ratio Sdr to be 0.5 or less (0.50 or less rounded to the third decimal place).

[0068] In Examples 1-3 and 1-4, the durability was further improved compared to Examples 1-1 and 1-4. Therefore, from the viewpoint of durability, it is more preferable that the developed area ratio Sdr is 0.26 or more and 0.42 or less in value up to two decimal places.

[0069] Next, we investigated whether the irregularities on the inner surface 131 of the fixing film 13 would wear away after long-term use. The inner surface 131 of the fixing film 13 was observed after the durability test, and the developed area ratio Sdr was calculated again. "Developed area ratio Sdr (after durability)" in Table 1 represents the developed area ratio Sdr calculated for each example after the durability test.

[0070] As shown in "Expanded area ratio Sdr (after durability)" in Table 1, it can be seen that in Comparative Example 4, the expanded area ratio Sdr after the durability test was significantly lower than in the initial state. In other words, in Comparative Example 4, fine irregularities were imparted to the inner surface 131 of the fixing film 13 by transferring the irregularities of a mold, but it is thought that this irregularity was reduced by wear during paper passage. When paper is passed, pressure, heat, and shear force are applied to the inner surface 131 of the fixing film 13, and therefore the inner surface 131 is worn by the external force received during paper passage, and it is thought that the fine irregularities could not be maintained.

[0071] In contrast, in Examples 1-1 to 1-4 and Comparative Examples 2 and 3, the needle-like fillers 13d added to the base layer 13a form fine irregularities on the inner surface 131. The sea-island structure of the needle-like filler portions and the polyimide resin portion is formed three-dimensionally on the inner surface 131. This suggests that even if the outermost layer of the inner surface 131 is damaged by external forces received during paper feed, the fine irregularity structure (sea-island structure) is maintained, and the lubricant retention ability is maintained at a high level for a longer period of time than in Comparative Example 4.

[0072] If the wear of the base layer 13a is small, a method of forming minute irregularities on the inner surface 131 of the fixing film 13 without using a filler as in Comparative Example 4 may be adopted.

[0073] Fomblin M30 containing no thickener was used as the lubricant in the above Examples 1-1 to 1-4 and Comparative Examples 1 to 4. To examine the influence of the thickener, a comparative example was prepared in which a lubricant containing a thickener was used.

[0074] In Comparative Examples 5 and 6, Molycoat (registered trademark) HP-300 manufactured by Dow Corning Toray Co., Ltd. is used as a lubricant containing a thickener. In Comparative Example 5, 250 mg of Molycoat HP-300 is applied onto heater 11, and in Comparative Example 6, 60 mg of Molycoat HP-300 is applied onto heater 11. The configuration of fixing device 1 other than the lubricant is the same as in Examples 1-1 to 1-4.

[0075] As mentioned above, the thickener can be an obstacle that hinders the conduction of heat from the heater 11 (heating element) to the fixing film 13. For this reason, if a lubricant containing a thickener is used in the fixing device 1, the lubricant may not have been absorbed in the fixing device 1 in the initial state immediately after assembly, causing variations in the amount of heat that the thickener applies to the recording material P, which can result in fixing defects. For example, if an all-black image is printed in the initial state, uneven heat caused by the lubricant may cause the image to peel off in parts, or the output image may peel off when rubbed by hand. To prevent such fixing defects, a countermeasure may be taken by initially setting the target temperature of the temperature control of the fixing device 1 to, for example, 10°C higher than normal.

[0076] In contrast to this, in this embodiment, a base oil containing no thickener is used as the lubricant, and it is expected that poor fixing in the initial state caused by the thickener will be improved. Therefore, a comparative experiment was conducted to evaluate the fixability in the initial state (initial fixability) of the above-mentioned Comparative Examples 5 and 6 and Examples 1-1 to 1-4. The fixing device 1 in the initial state was used, and the target temperature was the same for each example. A sheet of A4 size paper with a basis weight of 80 g (Canon Red Label Superior FSC 80 g / m) was used for the image forming apparatus 100 equipped with the fixing film 13 of each example. 2 A black image was printed on the entire surface of A4 paper, and the presence or absence of image peeling was evaluated. The results are shown in Table 2.

[0077] [Table 2]

[0078] As shown in Table 2, the initial fixability was good (◯) in all of Examples 1-1 to 1-4. On the other hand, image peeling occurred in Comparative Example 5, so the initial fixability was poor (×). Although the amount of lubricant applied in Comparative Example 6 was less than that in Comparative Example 5, the initial fixability was poor (×).

[0079] As described above, in this embodiment, fine irregularities are provided on the inner surface 131 of the fixing film 13, and a base oil containing no thickener is used as the lubricant. The fine irregularities are set to have a developed area ratio Sdr of 0.1 to 0.5 (0.10 to 0.50, rounded to two decimal places). This allows the lubricant to be retained in the gaps between the fine irregularities by capillary action, maintaining the sliding film for a long period of time, thereby achieving stable sliding properties over a long period of time. Furthermore, using a base oil containing no thickener allows for good fixing properties to be achieved even in the initial state immediately after assembly.

[0080] As described above, according to this embodiment, it is possible to provide a fixing device that can achieve good initial fixability and stable sliding properties over a long period of time, and an image forming apparatus equipped with the fixing device.

[0081] Second Embodiment As a second embodiment, a configuration containing a small amount of thickener as a lubricant will be described. Hereinafter, elements with the same reference numerals as those in Example 1 will have basically the same configuration and function as those described in Example 1 unless otherwise specified, and differences from Example 1 will be mainly described.

[0082] The proportion of base oil contained in a lubricant is called the base oil ratio (oil content). The base oil ratio is the blending ratio of the mass of base oil to the total mass of the lubricant. The unit of base oil ratio (%) is percent by mass.

[0083] In order to examine the appropriate base oil ratio, the base oil ratio was set to four levels of 70%, 80%, 90%, and 100% in Examples 2-1 to 2-3 and Comparative Example 7, which have different developed area ratios Sdr, and durability and initial fixability were evaluated for each. The fixing film 13 of Example 2-1 was the same as that of Example 1-1, the fixing film 13 of Example 2-2 was the same as that of Example 1-2, and the fixing film 13 of Example 2-3 was the same as that of Example 1-4. 75 mg of each lubricant was applied to the surface of the heater 11 by spray application.

[0084] In the durability test, if the printer could withstand 75,000 sheets of paper passing, which is 1.5 times the product's lifespan, it was evaluated as having good durability (○). If printing could not continue before 75,000 sheets of paper had been passed due to poor rotation of the fixing film 13 or other reasons, it was evaluated as having poor durability (×). For initial fixability, the fixing device 1 was used in its initial state, and the target temperature was the same for all conditions. A full black image was printed, and the presence or absence of fixing defects such as image peeling was evaluated. The results are shown in Table 3. If there was no fixing defect, the initial fixability was evaluated as good (○), and if there was fixing defect, the initial fixability was evaluated as poor (×).

[0085] [Table 3]

[0086] As shown in Table 3, Examples 2-1 to 2-3 all exhibited good durability. The target was achieved and the result was OK. On the other hand, in Comparative Example 7, durability was good when the base oil ratio was 70% and 80%, but durability was poor when the base oil ratio was 90% and 100%. In Comparative Example 7, since the inner surface 131 of the fixing film 13 was smooth, when the base oil ratio of the lubricant was increased, the viscosity of the lubricant was low and the lubricant was likely to leak out from the edge of the fixing film 13. As a result, the amount of base oil decreased as the number of sheets passed increased, and it was thought that the sliding film could not be maintained, resulting in poor rotation of the fixing film 13.

[0087] Regarding initial fixability, in Examples 2-1 to 2-3, poor fixation was observed when the base oil ratio was 70%, but not when the base oil ratio was 80% or more (thickener blending ratio was 20% or less). On the other hand, in Comparative Example 7, poor fixation was observed when the base oil ratio was 70% and 80%, but not when the base oil ratio was 90% and 100%.

[0088] In both cases, it was confirmed that a higher base oil content made it less likely for poor fixing to occur in the initial stage. This indicates that, because thickeners inhibit heat transfer, the greater the amount of thickener used, the more likely poor fixing to occur in the initial stage.

[0089] Furthermore, fixing failure was less likely to occur in Examples 2-1 to 2-3 than in Comparative Example 7. This is thought to be because in Comparative Example 7, the inner surface 131 of the fixing film 13 is smooth, making it difficult for the viscous lubricant to spread over the inner surface 131 and making it easy for uneven distribution of the lubricant to occur. On the other hand, in Examples 2-1 to 2-3, the inner surface 131 of the fixing film 13 has fine irregularities, so the lubricant containing the thickener is dispersed over the entire inner surface 131 and uneven distribution of the lubricant is less likely to occur, which is thought to have reduced fixing failure in the initial state.

[0090] From the above results, it was found that even when a lubricant containing a thickener is used, good initial fixation can be obtained as long as the base oil ratio is 80% or more.

[0091] As described above, in this embodiment, fine irregularities are provided on the inner surface 131 of the fixing film 13, and a lubricant containing a small amount of thickener is used. The fine irregularities are set so that the developed area ratio Sdr is 0.1 to 0.5 (0.10 to 0.50, rounded to two decimal places). In addition, the base oil ratio of the lubricant is set to 80% or more. This makes it possible to provide a fixing device that can achieve good initial fixability and stable sliding properties over a long period of time, and an image forming apparatus equipped with the same.

[0092] In addition, in this embodiment, the consistency and water resistance of the lubricant can be adjusted by blending a thickener, which allows the performance of the lubricant to be adjusted according to the specific configuration of the fixing device 1 while achieving good initial fixability and stable sliding properties.

[0093] Other Embodiments In the above-described embodiments, the heater 11, which generates heat itself, has been described as an example of a heating element that contacts the inner surface of the fixing film 13 and heats the fixing film 13. When the heating element transfers heat received from another heat source to the fixing film 13, the heat source may be disposed in contact with the heating element and transfer heat to the heating element by thermal conduction, or may be disposed out of contact with the heating element and transfer heat to the heating element by thermal radiation. For example, the heating element may be a sheet-like member interposed between the heater 11 and the fixing film 13. The sheet-like member may be any member that has high thermal conductivity and high sliding properties with respect to the fixing film 13, such as a thin metal plate or a resin sheet. Alternatively, the heating element may be a plate-like member that is heated by radiant heat from a halogen lamp as a heat source.

[0094] Summary of the Disclosure The present disclosure includes at least the following: (Configuration 1) a rotatable cylindrical rotor; a heating body having a contact surface that is in sliding contact with the inner surface of the rotating body, the heating body being disposed in the internal space of the rotating body and heating the rotating body; a pressure member that is in contact with the outer surface of the rotating body and is arranged to sandwich the rotating body together with the heating body; a fixing device that fixes an image on a recording material by heating the image on the recording material while nipping and conveying the recording material at a nip portion between the rotating body and the pressure member, a lubricant is interposed between the inner surface of the rotating body and the contact surface of the heating body; The lubricant contains a base oil in a proportion of 80% or more based on the total mass of the lubricant, The developed area ratio Sdr of the inner surface of the rotating body is 0.10 or more and 0.50 or less. A fixing device characterized by: (Configuration 2) The lubricant does not contain a thickener. 2. The fixing device according to claim 1, (Configuration 3) The lubricant contains a thickener blended in an amount of 20% or less based on the total mass of the lubricant. 2. The fixing device according to claim 1, (Configuration 4) The development area ratio Sdr is 0.26 or more and 0.42 or less. 4. The fixing device according to any one of configurations 1 to 3. (Configuration 5) the rotating body has an inner layer that forms the inner surface, The inner layer is a resin film in which a filler is dispersed in a resin material. 5. The fixing device according to any one of configurations 1 to 4. (Configuration 6) The filler is acicular. 6. The fixing device according to configuration 5. (Configuration 7) The filler is carbon nanotubes, acicular titanium oxide, or a mixture of carbon nanotubes and acicular titanium oxide. 7. The fixing device according to configuration 6. (Configuration 8) The resin film is a polyimide resin composition in which the filler is dispersed in a polyimide resin. 8. The fixing device according to any one of configurations 5 to 7, wherein: (Configuration 9) The filler is added in an amount of 20% by volume or more and 45% by volume or less based on the total volume of the polyimide resin composition. 9. The fixing device according to configuration 8. (Configuration 10) The heater includes a substrate and a heating resistor formed on the substrate and generating heat when energized. 10. The fixing device according to any one of configurations 1 to 9. (Configuration 11) a holding member for holding the heating body; a stay supporting the holding member; a biasing member that biases the stay so that the heating body and the pressure member are in pressure contact with each other across the rotating body; and the rotating body is formed of a flexible film material, and rotates by receiving a frictional force at the nip portion from the pressure member which rotates by receiving a driving force; 11. The fixing device according to configuration 10. (Configuration 12) an image forming section for forming an image on a recording material; A fixing device according to any one of configurations 1 to 11; Equipped with the fixing device fixes the image formed by the image forming unit onto the recording material; An image forming apparatus characterized by: [Explanation of symbols]

[0095] 11...heating body (heater) / 13...rotating body (fixing film) / 20...pressure member (pressure roller) / 111...contact surface / 131...inner surface

Claims

1. a rotatable cylindrical rotor; a heating body having a contact surface that is in sliding contact with the inner surface of the rotating body, the heating body being disposed in the internal space of the rotating body and heating the rotating body; a pressure member that is in contact with the outer surface of the rotating body and is arranged to sandwich the rotating body together with the heating body; a fixing device that fixes an image on a recording material by heating the image on the recording material while nipping and conveying the recording material at a nip portion between the rotating body and the pressure member, a lubricant is interposed between the inner surface of the rotating body and the contact surface of the heating body; The lubricant contains a base oil in a proportion of 80% or more based on the total mass of the lubricant, a developed area ratio Sdr of the inner surface of the rotating body is 0.10 or more and 0.50 or less; A fixing device characterized by:

2. The lubricant does not contain a thickener.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device.

3. The lubricant contains a thickener blended in an amount of 20% or less based on the total mass of the lubricant.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device.

4. The development area ratio Sdr is equal to or greater than 0.26 and equal to or less than 0.

42.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device.

5. the rotating body has an inner layer that forms the inner surface, The inner layer is a resin film in which a filler is dispersed in a resin material.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device.

6. The filler is acicular.

6. The fixing device according to claim 5,

7. The filler is carbon nanotubes, acicular titanium oxide, or a mixture of carbon nanotubes and acicular titanium oxide.

7. The fixing device according to claim 6, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

8. The resin film is a polyimide resin composition in which the filler is dispersed in a polyimide resin.

6. The fixing device according to claim 5,

9. the filler is added in an amount of 20% by volume or more and 45% by volume or less based on the total volume of the polyimide resin composition; 9. The fixing device according to claim 8, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

10. The heater includes a substrate and a heating resistor formed on the substrate and generating heat when energized.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

11. a holding member for holding the heating body; a stay supporting the holding member; a biasing member that biases the stay so that the heating body and the pressure member are in pressure contact with each other across the rotating body; and the rotating body is formed of a flexible film material, and rotates by receiving a frictional force at the nip portion from the pressure member which rotates by receiving a driving force; The fixing device according to claim 10 .

12. an image forming section for forming an image on a recording material; The fixing device according to claim 1 , Equipped with the fixing device fixes the image formed by the image forming unit onto the recording material; An image forming apparatus characterized by:

Images