Image forming apparatus

Abstract

To reduce leakage of a lubricant from an end of a fixing film while securing slidability of the fixing film with an inexpensive and simple configuration.SOLUTION: Among the fixing film guide surfaces of the heater holder 130, only on the fixing film guide surface on the upstream side of the heater 113 with respect to the rotation direction of the fixing film 112, a plurality of recessed portion side walls are arranged in the longitudinal direction, each recessed portion side 132a extending in the rotation direction and having an extending direction inclined with respect to the longitudinal direction and the recording material conveyance direction when viewed in a direction orthogonal to the longitudinal direction and the recording material conveyance direction at the nip portion, the recessed portion side walls containing the lubricant. The 132a of the recessed portion is inclined so as to approach the center of the heater holder 130 in the longitudinal direction toward the downstream side in the rotation direction, the inclination angle of the 132a of the recessed portion increases toward the recessed portion at the end portion in the longitudinal direction, and the fixing device 100 is disposed so that the upstream side of the fixing film guide surface is lower in the vertical direction with respect to the downstream side.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, and more particularly to a fixing device used in an image forming apparatus such as an electrophotographic copying machine or laser printer. [Background technology]

[0002] A film heating type fixing device has been known for use in electrophotography. A film heating type fixing device includes a heater having a resistance heating element on a ceramic substrate, a fixing film that rotates while being heated in contact with the heater, and a pressure roller that forms a nip with the heater via the fixing film. A recording material bearing an unfixed toner image is heated while being sandwiched and conveyed through the nip, thereby fixing the unfixed toner image on the recording material.

[0003] In a film-heating fixing device, a lubricant is interposed between the heater and the inner surface of the fixing film to reduce the sliding friction between them. This lubricant is applied to the heater, for example, at the initial assembly stage and interposed between the heater and the inner surface of the fixing film. Then, by pressing a pressure roller against the heater via the fixing film to rotate the fixing film, the lubricant spreads over the entire inner surface of the fixing film. However, as the fixing film continues to rotate, excess lubricant may leak from the edge of the fixing film, spread around the outer surface of the fixing film, and enter the nip. In this state, the lubricant may adhere to the recording material, causing problems such as image defects.

[0004] For example, Patent Document 1 discloses the following configuration: A configuration is proposed in which grooves for storing lubricant are provided downstream of the heater in the conveying direction of the recording material on a heater support member that supports the heater, and at positions corresponding to both ends in the longitudinal direction perpendicular to the conveying direction, or over the entire longitudinal area including both ends. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-076589 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in conventional examples, as the fixing film rotates, it slides while constantly in contact with the portion of the groove closest to the fixing film. Grease, primarily composed of base oil and thickener, is often used as a lubricant applied to the heater. However, the base oil is prone to separating from the thickener, especially at high temperatures. In such cases, the base oil separated from the grease stored in the groove near the fixing film leaks out of the groove due to capillary action through tiny gaps between the inner surface of the fixing film and the heater support member. If more base oil than necessary is supplied between the fixing film and the heater, the base oil is pressurized in the nip and spread out in the longitudinal direction. Furthermore, the base oil may migrate from tiny gaps between the inner surface of the fixing film and the heater due to capillary action toward the end of the fixing film in the longitudinal direction, increasing the risk of the base oil, or lubricant, leaking out of the fixing film.

[0007] The present invention has been made under these circumstances, and has as its object to reduce leakage of lubricant from the end of the fixing film while ensuring the slidability of the fixing film with an inexpensive and simple configuration. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0009] (1) An image forming apparatus including: an image forming unit that forms a toner image on a recording material; and a fixing unit that fixes the toner image formed on the recording material to the recording material, the fixing unit including a cylindrical fixing film, a heater that is disposed in an internal space of the fixing film with its longitudinal direction aligned with the longitudinal direction of the fixing film, a heater holder that is disposed in an internal space of the fixing film with its longitudinal direction aligned with the longitudinal direction of the fixing film and also has a function of guiding the rotating fixing film, and a pressure roller that contacts the outer surface of the fixing film to sandwich the fixing film together with the heater and form a nip portion between the fixing film and the pressure roller, and the toner image is formed on the recording material by heating the recording material with the heat of the heater while transporting the recording material with the toner image formed on it through the nip portion, the heater an image forming apparatus characterized in that, of the fixing film guide surface of the holder, only the fixing film guide surface upstream of the heater with respect to the rotation direction of the fixing film extends in the rotation direction, and the extension direction of the lubricant is inclined with respect to the longitudinal direction and the recording material transport direction when viewed in a direction perpendicular to the longitudinal direction and the recording material transport direction at the nip portion, and a plurality of recesses filled with lubricant are lined up in the longitudinal direction, all of the recesses are inclined so as to approach the center of the heater holder in the longitudinal direction as they move downstream in the rotation direction, and the inclination angle of the recesses is larger for recesses at the ends in the longitudinal direction, and the fixing unit is arranged so that the upstream side of the fixing film guide surface is downward in the vertical direction relative to the downstream side. [Effects of the Invention]

[0010] According to the present invention, it is possible to reduce leakage of lubricant from the end portions of the fixing film while ensuring the slidability of the fixing film with an inexpensive and simple configuration. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment of the present invention; [Figure 2] 1 is a schematic cross-sectional view of a fixing device according to a first embodiment of the present invention; [Figure 3] 1 is a schematic cross-sectional view of the periphery of a lubricant retaining portion of a fixing device according to a first embodiment of the present invention; [Figure 4] FIG. 1 is a diagram illustrating the action on grease in Example 1. [Figure 5] FIG. 1 is a diagram illustrating the effect of a comparative example on grease for comparison with Example 1. [Figure 6] FIG. 10 is a diagram illustrating a modified example of the recessed portion of the first embodiment. [Figure 7] FIG. 10 is a diagram illustrating the lubricant holding portion of the second embodiment and the action on the grease. [Figure 8] FIG. 10 is a diagram illustrating the lubricant retaining portion of the third embodiment and its action on grease. [Figure 9] FIG. 10 is a diagram illustrating a lubricant retaining portion according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail by way of examples with reference to the accompanying drawings. [Example]

[0013] The first embodiment will be described below. First, the main body configuration of the image forming apparatus of the first embodiment will be described, and then the fixing device according to the present invention will be described in detail.

[0014] (Image forming device) An example of an image forming apparatus used in Example 1 will be described with reference to the schematic diagram shown in FIG. 1. The image forming apparatus 50 of Example 1 is an electrophotographic image forming apparatus that directly transfers a toner image on a photosensitive drum 1 onto a recording material P. On the circumferential surface of the photosensitive drum 1, which is a photosensitive member, are arranged, in order along the direction of rotation (the direction of arrow R1), a charger 2, an exposure device 3 that irradiates the photosensitive drum 1 with laser light L, a developing device 5 that serves as developing means, a transfer roller 10 that serves as transfer means, and a photosensitive drum cleaner 16. First, the surface of the photosensitive drum 1 is negatively charged by the charger 2. Next, an electrostatic latent image is formed on the surface of the charged photosensitive drum 1 by the laser light L from the exposure device 3. Note that the surface potential of the exposed portion of the photosensitive drum 1 increases. The toner in Example 1 is negatively charged, and a developer 5 containing black toner adheres the negative toner only to the electrostatic latent image portion on the photosensitive drum 1, forming a toner image on the photosensitive drum 1.

[0015] The recording material P is fed by the paper feed roller 4, and then conveyed to the transfer nip Ntr by the conveying roller 6. A transfer voltage of positive polarity, which is opposite to the polarity of the toner, is applied from a power source (not shown) to the transfer roller 10, and the toner image on the photosensitive drum 1 is transferred to the recording material P at the transfer nip Ntr. After transfer, the toner remaining on the surface of the photosensitive drum 1 is removed by a photosensitive drum cleaner 16 having an elastic blade. The recording material P bearing the toner image is conveyed to the fixing device 100, where the toner image on the surface is heated and fixed. Note that the image forming apparatus to which the fixing device of the present invention can be applied is not limited to the image forming apparatus 50 shown in FIG. 1. For example, it may be a color image forming apparatus.

[0016] (fixing device) The fixing device 100 of the first embodiment will be described below. The fixing device 100 of the first embodiment is a film heating type fixing device intended to shorten the warm-up time and reduce power consumption. Fig. 2 is a cross-sectional view of the fixing device 100 of the first embodiment. In the following description, the conveying direction of the recording material P, which are perpendicular to each other, is designated as A, the longitudinal direction of a heater holder 130 (described later) is designated as B, and the vertical direction perpendicular to a sliding surface (described later) is designated as C.

[0017] The heater 113 is held by a heater holder 130, and the fixing film 112, which is a cylindrical belt, is provided around the heater holder 130. The heater holder 130 has a heater holding portion 135 that holds the heater 113. The heater 113 slides against the inner surface of the fixing film 112, heating it from the inside. The pressure roller 110 presses the heater 113 from the outside of the fixing film 112. The area where the pressure roller 110 and the fixing film 112 come into contact with each other due to the pressure is called the fixing nip portion N (nip portion). When the pressure roller 110 is driven in the direction of arrow R1 in the figure, the fixing film 112 receives power from the pressure roller 110 at the fixing nip portion N and is driven to rotate in the direction of arrow R2. The recording material P, onto which the unfixed toner image T has been transferred, is conveyed in the conveying direction A of the recording material P, indicated by the arrow in the figure, and when it reaches the fixing nip portion N, the toner image T is fixed to the recording material P.

[0018] The fixing film 112 of Example 1 has an outer diameter of 18 mm in an undeformed cylindrical state and a multi-layer structure in the thickness direction. The fixing film 112 is composed of a base layer to maintain the strength of the film and a release layer to reduce the adhesion of dirt to the surface. The base layer must be heat-resistant to receive the heat from the heater 113 and must also be strong to slide against the heater 113. For this reason, the base layer is preferably made of a metal such as stainless steel or nickel, or a heat-resistant resin such as polyimide. In Example 1, a polyimide resin was used as the base layer of the fixing film 112, with a carbon-based filler added to improve thermal conductivity and strength. The thinner the base layer, the easier it is to transfer heat from the heater 113 to the surface of the pressure roller 110. However, if the base layer is too thin, the strength decreases. Therefore, a thickness of approximately 15 μm to 100 μm is preferable, and in Example 1, the thickness was set to 60 μm.

[0019] The material of the release layer of the fixing film 112 is preferably a fluororesin such as perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), or tetrafluoroethylene-hexafluoropropylene resin (FEP). In Example 1, PFA was used, which has excellent releasability and heat resistance among fluororesins. The release layer may be a tube covering or a surface coated with paint. In Example 1, the release layer was formed using a coating that is excellent for thin-wall molding. The thinner the release layer, the easier it is to transfer heat from the heater 113 to the surface of the fixing film 112. However, if the release layer is too thin, durability decreases. Therefore, a thickness of approximately 5 μm to 30 μm is preferable, and in Example 1, a thickness of 10 μm was used. Furthermore, although not used in Example 1, an elastic layer may be provided between the base layer and the release layer. In this case, silicone rubber, fluororubber, or the like is used as the material for the elastic layer.

[0020] A heater holder 130 is provided on the inner circumferential side of the fixing film 112. The heater holder 130 is made of a liquid crystal polymer resin with high heat resistance to satisfy heat resistance and rigidity requirements. In Example 1, Sumikasuper (registered trademark) manufactured by Sumitomo Chemical Co., Ltd. is used as the liquid crystal polymer resin. The heater holder 130 has a concave shape (heater holding portion 135) in cross section that holds the heater 113, and holds the heater 113. The fixing film 112 is loosely fitted around the heater holder 130, which also serves to guide the rotation of the fixing film 112. The heater holder 130 is related to the features of Example 1 and will be described in detail later.

[0021] The pressure stay 119 is disposed along the longitudinal direction B of the heater holder 130. The pressure stay 119 is made of a highly rigid sheet metal such as stainless steel that has been bent to apply uniform pressure to the heater holder 130 in the longitudinal direction B. The pressure roller 110 in Example 1 has an outer diameter of 20 mm and is formed with a 13 mm diameter iron core 117 and a 3.5 mm thick elastic layer 116. The elastic layer 116 is made of solid rubber or foam rubber. Foam rubber has a low heat capacity and low thermal conductivity, and heat from the surface of the pressure roller 110 is not easily absorbed into the interior, which has the advantage of making it easy for the surface temperature to rise and shortening the fixing start-up time. In Example 1, foam rubber made from foamed silicone rubber was used.

[0022] A smaller outer diameter of the pressure roller 110 reduces heat capacity, but if it is too small, the width of the fixing nip N becomes narrow, so an appropriate diameter is necessary. Therefore, in Example 1, the outer diameter of the pressure roller 110 was set to Φ20 mm. Regarding the thickness of the elastic layer 116, if it is too thin, heat will escape to the metal core, so an appropriate thickness is also necessary. Therefore, in Example 1, the thickness of the elastic layer 116 was set to 3.5 mm. A release layer 118 made of perfluoroalkoxy resin (PFA) is formed on the elastic layer 116 as a toner release layer. Like the release layer of the fixing film 112, the release layer 118 may be covered with a tube or coated with paint. However, in Example 1, a tube was used due to its excellent durability. In addition to PFA, the release layer 118 may be made of fluororesins such as PTFE and FEP, or fluororubbers or silicone rubbers with good release properties. The lower the surface hardness of the pressure roller 110, the lighter the pressure required to obtain the desired width of the fixing nip portion N. In Example 1, a pressure roller with an Asker-C hardness (4.9 N load) and an angle of 50° was used. The pressure roller 110 is pressed against the heater by a pressure means (not shown). The total pressure was 14 kgf. In Example 1, the width of the fixing nip portion N in the conveying direction A is approximately 6.0 mm across the longitudinal direction B. The pressure roller 110 is rotated by a rotation means (not shown) in the direction of arrow R1 in the figure at a surface movement speed of 200 mm / sec.

[0023] The heater 113 in Example 1 is a typical heater used in a film-heating fixing device, and is configured with a resistance heating element mounted on a ceramic substrate. The heater 113 is constructed by screen-printing an Ag / Pd (silver-palladium) resistance heating element to a thickness of approximately 10 μm on the surface of an alumina substrate 6 mm wide and 1 mm thick in the conveyance direction A, and then covering it with a 50 μm thick glass to protect the heating element and ensure sliding properties. The temperature of the heater 113 is adjusted by appropriately controlling the current flowing through the resistance heating element in response to a signal from a temperature detection element (not shown) that detects the temperature of the ceramic substrate or the fixing film 112. The heater 113 is fixedly supported by being fitted into a heater holding portion 135, which is a groove portion formed in the heater holder 130. In Example 1, the center of the heater 113 is aligned with the center of the pressure roller 110 in the conveyance direction A to efficiently transfer heat to the recording material P.

[0024] A lubricant is applied to the heater 113 to be interposed between the heater 113 and the fixing film 112. In Example 1, fluorine-based grease was used as the lubricant applied to the heater 113. Specifically, perfluoropolyether (PFPE) oil was used as the base oil, and grease mixed with polytetrafluoroethylene (PTFE) powder was used as the thickener.

[0025] The effect of Example 1 is particularly effective when the ratio of base oil to the total amount of grease used is relatively high, and is particularly effective when grease with a base oil ratio of 80 wt% or more is used. Grease with a high base oil ratio has a relatively small amount of thickener and a low viscosity, which provides good sliding properties, but the thickener's ability to retain the base oil is weak. Therefore, it is necessary to supplement the function of retaining the grease and base oil using the configuration of Example 1. In Example 1, grease with a base oil ratio of 85 wt% was used. 200 mg of grease was spray-applied over a 210 mm area, slightly shorter than the 220 mm pressure region width of the pressure roller 110, on the sliding surface S, which is the contact surface between the fixing film 112 and the heater 113, in the longitudinal direction B. The protrusion 131 and the lubricant retaining portion 132 will be described later.

[0026] (Features of Example 1) The shape of the heater holder 130, which is a feature of the first embodiment, and in particular the lubricant holding portion 132 provided in the heater holder 130, will be described with reference to FIG. 3. FIG. 3(a) is a schematic diagram of the essential parts, showing an enlarged view of the positional relationship between the heater 113, the fixing film 112, the protruding portion 131, and the lubricant holding portion 132. FIG. 3(b) is a schematic diagram of the essential parts, showing the vicinity of the lubricant holding portion 132, as viewed from the pressure roller 110 side (pressure roller side). The heater holder 130 of the first embodiment has the lubricant holding portion 132 and the protruding portion 131. The lubricant holding portion 132 is provided upstream of the heater holding portion 135 in the conveying direction A. The protruding portion 131 is provided upstream of the lubricant holding portion 132 in the conveying direction A, and protrudes toward the pressure roller 110 compared to an opposing surface, which will be described later. The opposing surface protrudes toward the pressure roller 110 beyond the sliding surface S, in other words, the fixing nip portion N, and the protruding portion 131 protrudes toward the pressure roller 110 beyond the lubricant retaining portion 132.

[0027] The heater holder 130 has a protruding portion 131 on the upstream side of the fixing nip N in the conveying direction A that protrudes further toward the pressure roller 110 than the sliding surface S of the heater 113. The degree to which the protruding portion 131 protrudes from the sliding surface S (hereinafter referred to as the protruding height) H1 needs to be a certain height to regulate the trajectory of the fixing film 112. However, if the protruding height H1 is too high, it may hinder the recording material P from entering the fixing nip N, so a height of approximately 0.1 mm to 1.0 mm is desirable. In the first embodiment, the protruding height H1 of the apex V of the protruding portion 131 from the sliding surface S is set to 0.4 mm.

[0028] A lubricant holding portion 132 for holding grease is provided between the fixing nip portion N and the protruding portion 131. The height H2 of the lubricant holding portion 132 from the sliding surface S needs to be set lower than the protruding height H1 of the protruding portion 131 (H2 In the first embodiment, the protrusion 131 is provided by changing the shape of the heater holder 130, but the protrusion 131 may be provided as a separate body or may be made of a different material.<h1>

[0029] (Lubricant holding section) The lubricant retaining portion 132 of the heater holder 130 has a flat portion 132b, which is a surface facing the pressure roller 110, and the flat portion 132b has a recessed portion 132a recessed in a direction away from the pressure roller 110. Note that, although the flat portion 132b is used in the first embodiment, the facing surface is not limited to a flat surface. The lubricant retaining portion 132 has a plurality of recessed portions 132a for retaining grease along the longitudinal direction B. From the viewpoint of minimizing the spread of the retained grease in the longitudinal direction B, it is desirable that the plurality of recessed portions 132a be arranged isolated from each other in the longitudinal direction B. Furthermore, from the viewpoint of retaining the grease and preventing excessive outflow onto the sliding surface S, it is desirable that the recessed portions 132a do not penetrate the heater retaining portion 135 (groove portion) that retains the heater 113 in the conveying direction A. More desirably, the shape of the recessed portions 132a is such that the length in the conveying direction A is longer than the length in the longitudinal direction B from the viewpoint of directing the movement of the grease toward the fixing nip portion N, i.e., in the conveying direction A. That is, when the length of the lubricant holding portion 132 in the transport direction A is La and the length in the longitudinal direction B is Lb, it is desirable that La>Lb.

[0030] In the first embodiment, the recess 132a has an elliptical cross section at the flat surface 132b as shown in FIG. 3(b). The recess 132a has a smooth concave shape with a length La of 2.0 mm in the conveyance direction A, a length Lb of 1.0 mm in the longitudinal direction B, and a depth of 0.5 mm. That is, the lubricant holding portion 132 only needs to have a concave shape in which the area of ​​the cross section parallel to the flat surface 132b of the recess 132a decreases with increasing distance from the pressure roller 110. In other words, the cross section of the lubricant holding portion 132a perpendicular to the longitudinal direction B of the recess 132a may have a rectangular groove in addition to a circular arc groove having a shape (bow-like) as shown by the dashed line in FIG. 3(a). In addition, when the recess 132a of the lubricant holding portion 132 is a rectangular groove, the area of ​​the cross section parallel to the flat portion 132b may be the same regardless of the distance from the pressure roller 110, or may be smaller as the distance from the pressure roller 110 increases.

[0031] The pitch Pt of the recesses 132a (the distance in the longitudinal direction B between the centers of adjacent lubricant holding portions 132) and the interval Sp (a predetermined interval) are determined as follows. When the amount of base oil contained per pitch of the applied grease is dropped onto the flat portion 132b of the heater holder 130, if the spread amount of the base oil is the diameter D (mm), it is desirable to set the interval Sp of the recesses 132a to be D or less (Sp < D). By setting it in this way, even if the base oil separates from the grease adhering between the recesses 132a, the base oil can be captured and held by the recesses 132a. Thus, the interval of the recesses 132a is smaller than the diameter by which the base oil spreads when the amount of base oil held by one recess 132a is dropped onto the flat portion 132b. In Example 1, the pitch Pt and the interval Sp are set to be smaller than the diameter by which the base oil spreads when the amount of base oil per recess 132a is dropped onto the flat portion 132b.

[0032] In Example 1, since the recesses 132a have a constant pitch of 2 mm (Pt = 2 mm), the amount of base oil contained per pitch is 200×0.85 / 210×2 = 1.6 mg. The spread amount of the base oil when this amount of base oil is dropped onto the flat portion 132b of the heater holder 130 was about 2.2 mm in Example 1 based on the study results of the inventor. Therefore, the interval of the recesses 132a was set to 1.0 mm in Example 1. Also, from the viewpoint of the ease of holding the base oil in the recesses 132a, the contact angle of the base oil with respect to the heater holder 130 by the droplet method is desirably 90° or less, and it is about 20° to 40° in Example 1. In Example 1, a large number of recesses 132a are arranged in isolation as described above over the width of the pressurization region in the longitudinal direction B of the pressurization roller 110.

[0033] (Effect of Example 1) The fixing film 112 is backed up by the fixing nip portion N, the heater holder 130, and the protrusion 131. Because the fixing film 112 is originally cylindrical, near the protrusion 131 located upstream of the fixing nip portion N, the fixing film 112 rotates while contacting the protrusion 131 due to a restoring force that causes the fixing film 112 to return to its cylindrical shape. Because the protrusion 131 protrudes further toward the pressure roller 110 than the sliding surface S of the heater 113, the trajectory of the fixing film 112 is regulated by the protrusion 131. Therefore, as shown in FIG. 3( a), the lubricant retaining portion 132 is disposed near the inner surface of the fixing film 112 upstream of the fixing nip portion N without steadily contacting the fixing film 112 with strong pressure.

[0034] Immediately after the fixing device 100 is assembled, grease is applied to the sliding surface S, but as the fixing film 112 rotates when a fixing operation is performed, the grease adheres to the inner surface of the fixing film 112 and rotates. As the fixing film 112 rotates, some of the grease reaches the lubricant holding portion 132 and is held in the recessed portion 132a of the lubricant holding portion 132. The grease once held in the recessed portion 132a is unlikely to come into direct contact with the inner surface of the fixing film 112 in a steady state because the fixing film 112 is restricted by the protruding portion 131.

[0035] (Comparison with comparative examples) Next, the action of the configuration of Example 1 on the grease G will be described in comparison with a comparative example using Figures 4 and 5. Figure 4 is a schematic diagram for explaining the action of supplying grease G in Example 1. Figure 5 is a schematic diagram for explaining the action of supplying grease G in a comparative example without a protruding portion 131. Note that the same components as those described above are assigned the same reference numerals, and their explanation will be omitted.

[0036] In the comparative example shown in FIG. 5 , the protrusion 131 is not present, so the inner surface of the fixing film 112 constantly contacts the recess 132a of the lubricant holding portion 132 and the grease G stored therein. If the fixing film 112 constantly contacts the recess 132a, the grease G constantly moves toward the sliding portion S, resulting in excessive supply. In particular, if the grease G constantly contacts the fixing film 112, the grease G is likely to become hot, and the base oil is likely to separate from the thickener. The separated base oil of the grease G moves toward the sliding portion S due to capillary action from a minute gap Gp (enclosed in a dashed line) between the inner surface of the fixing film 112 and the heater holder 130, as shown by the arrow in the figure. If too much grease G is supplied to the sliding portion S, the grease G pressurized in the fixing nip portion N is crushed and spread in the longitudinal direction B as well, gradually being pushed out toward the end portion in the longitudinal direction B, and eventually may leak from the end portion of the fixing film 112 in the longitudinal direction B.

[0037] In contrast to this comparative example, in Example 1, the trajectory of the fixing film 112 is regulated by the protruding portion 131 as shown in FIG. 4(a), and therefore the fixing film 112 is not in steady state contact with the recessed portion 132a, thereby preventing excessive supply of grease G to the sliding portion S. On the other hand, when the fixing film 112 is heated and then cooled in accordance with the ambient temperature and left for a long time, it has the characteristic of undergoing some degree of plastic deformation following the shape of the fixing nip portion N. If the next fixing operation is performed after being left for a long period of time, the trajectory of the fixing film 112 when it starts to rotate differs from the normal trajectory and exhibits some degree of oscillation between the fixing nip portion N and the protruding portion 131.

[0038] At this time, as shown in FIG. 4(b), the fixing film 112 temporarily comes into contact with the recessed portion 132a, and a small amount of grease G is supplied to the sliding portion S from the gap Gp by capillary action, as indicated by the arrow in the figure. However, when the fixing film 112 is heated to a high temperature, the deformation of the fixing film 112 returns to its original state. Therefore, the trajectory of the fixing film 112 stabilizes again, as shown in FIG. 4(a), and the fixing film 112 no longer steadily comes into contact with the recessed portion 132a, thereby preventing excessive supply of grease G to the sliding portion S. As a result, the amount of grease G present in the sliding portion S becomes appropriate, and the grease G pressurized in the fixing nip portion N is pushed out in the longitudinal direction B, reducing the phenomenon of grease G leaking from the end of the fixing film 112 in the longitudinal direction B.

[0039] As described above, in the configuration of the first embodiment, the grease G is held in the lubricant holding portion 132, and an appropriate amount of grease G is periodically supplied to the sliding portion S. This makes it possible to reduce leakage of the grease G from the end portion of the fixing film 112 in the longitudinal direction B while maintaining slidability.

[0040] Although the recess 132a in Example 1 is elliptical, the effects of Example 1 can be achieved with other shapes. FIG. 6 illustrates recesses 132a of other shapes. The same reference numerals are used to designate the same components as those described above, and their descriptions are omitted. For example, other shapes, such as a rectangle as shown in FIG. 6(a) or a diamond as shown in FIG. 6(b), are also applicable. Thus, when the planar portion 132b is viewed from the pressure roller 110 side in a direction perpendicular to the conveyance direction and the longitudinal direction of the heater holder 130 perpendicular to the conveyance direction, the lubricant holding portion 132 (specifically, the opening shape) may be elliptical, rectangular, or diamond. In FIGS. 6(a) and 6(b), the cross-sectional shape of the recess 132a perpendicular to the longitudinal direction B may be various shapes, such as a curved shape, a tapered shape, or a rectangle. In addition, in the first embodiment, the heater holder 130 is modified in shape to provide the recess 132a, but a separate member may be placed inside the recess 132a, for example, by placing a nonwoven fabric or pad impregnated with grease inside the recess 132a.

[0041] As described above, according to Example 1, it is possible to reduce the leakage of the lubricant from the end portion of the fixing film while ensuring the slidability of the fixing film with a low-cost and simple configuration.

Example

[0042] Example 2 will be described below. In Example 2, only the portion regarding the shape of the recess 132a is different from that in Example 1. Since the other configurations are the same as those in Example 1, the detailed configurations of the image forming apparatus 50 and the fixing apparatus 100 will be omitted. In the recess 132a of Example 2, regarding the shape of the cross section in the flat portion 132b, that is, the length in the longitudinal direction B of the portion closer to the sliding surface S (in other words, the fixing nip portion N) is shorter than the length in the longitudinal direction B of the portion farther from the sliding surface S.

[0043] (Features of Example 2) The shape of the recess 132a, which is a feature of Example 2, will be described using FIG. 7(a). In Example 2, as shown in FIG. 7(a), the width in the longitudinal direction B of the recess 132a is changed between the portion closer to the sliding surface S and the portion farther from it, and it has a wedge-like shape. In Example 2, the width Wn of the portion closer to the sliding portion S is set to be smaller than the width Wd of the portion farther from the sliding portion S. That is, the recess 132a has a shape such that for the width in the longitudinal direction B, the width Wn of the portion closer to the sliding surface S and the width Wd of the portion farther from the sliding surface S satisfy Wn < Wd. Specifically, the width Wn of the portion closer to the sliding portion S is 0.3 mm, and the width Wd of the portion farther from the sliding portion S is 1.2 mm. The length La of the recess 132a in the conveying direction A is 2.0 mm as in Example 1. In FIG. 7(a), the shape of the cross section orthogonal to the longitudinal direction B of the recess 132a may be various shapes such as a curved shape or a tapered shape.

[0044] (Effects of Example 2) Further advantages of the second embodiment will be described with reference to FIGS. 7(b) and 7(c). For example, consider a case in which grease G adheres to a portion of the recess 132a far from the sliding portion S, as shown in FIG. 7(b), and a case in which grease G adheres to a portion of the recess 132a close to the sliding portion S, as shown in FIG. 7(c). When the base oil separates from the grease G in the state shown in FIG. 7(b), the width of the recess 132a in the longitudinal direction B narrows as it approaches the sliding surface S, and the base oil easily moves toward the sliding surface S of the recess 132a due to capillary action. Conversely, when the base oil separates from the grease G in the state shown in FIG. 7(c), the base oil of the grease G does not easily move to a portion far from the sliding surface S. In other words, by adopting the shape of the recess 132a as in the second embodiment, the base oil of the grease G can be unevenly distributed in the portion of the recess 132a closer to the sliding surface S. The base oil supplied to the sliding portion S is sequentially supplied and used from the base oil held in the recess 132a, mainly from the portion closest to the sliding surface S. At that time, the base oil held in the recess 132a farther from the sliding surface S is replenished to the position of the recess 132a closer to the sliding surface S. Because of this action, the base oil held in the recess 132a is sequentially supplied and used, and therefore it is possible to reduce the amount of grease G held in the recess 132a that remains held without contributing to lubrication.

[0045] As described above, according to the second embodiment, it is possible to reduce leakage of the lubricant from the end portion of the fixing film while ensuring the slidability of the fixing film with an inexpensive and simple configuration. [Example]

[0046] The third embodiment will be described below. The third embodiment differs from the second embodiment only in the arrangement of the recesses 132a. Since the other configurations are the same as those of the second embodiment, a detailed description of the configurations of the image forming apparatus 50 and the fixing device 100 will be omitted.

[0047] (Features of Example 3) The arrangement of the recesses 132a, which is a feature of the third embodiment, will be described with reference to FIG. 8A. The shape is the same as in the second embodiment, and therefore will not be described here. In the third embodiment, as shown in FIGS. 8A and 8B, an imaginary line M is defined as a line passing through the center of the recording material P passing through the conveyance path. The recesses 132a are arranged so that the longitudinal direction of the recesses 132a is inclined relative to the imaginary line M extending in the conveyance direction. In other words, the recesses 132a are configured so that the portion close to the sliding surface S faces the imaginary line M. Specifically, the angle of inclination of the imaginary line Cl connecting the center of the width Wn of one end (downstream side) of the recess 132a to the center of the width Wd of the other end (upstream side) of the recess 132a relative to the imaginary line M in the conveyance direction A of the recording material P is defined as θ. In the third embodiment, the recesses 132a are arranged so that they are inclined at θ=10° relative to the center M. The angle θ may be varied depending on the longitudinal position of the recesses 132a. For example, the arrangement of the recesses 132a may be changed so that the angle θ increases as the recesses 132a are positioned closer to the ends in the longitudinal direction.

[0048] (Effects of Example 3) A further effect of the third embodiment will be described with reference to Fig. 8(b). As described in the second embodiment, the base oil separated from the grease G moves by capillary action to a portion close to the sliding portion S. At this time, since the recessed portion 132a is disposed so as to be inclined toward the imaginary line M along which the center of the recording material P passing through the conveying path passes, as described above, the direction of movement of the base oil is also inclined toward the imaginary line M.

[0049] This action has the effect of collecting the base oil, which is crushed in the fixing nip portion N and spread in the longitudinal direction B, toward the imaginary line M along which the center of the recording material P passing through the conveying path passes. Therefore, in the third embodiment, it is possible to further reduce leakage of the grease G from the end portion in the longitudinal direction B of the fixing film 112. Note that the recessed portion 132a having the shape shown in FIGS. 3(b), 6(a), and 6(b) in the first embodiment may be configured to be inclined toward the imaginary line M in the third embodiment.

[0050] As described above, according to the third embodiment, it is possible to reduce leakage of the lubricant from the end portion of the fixing film while ensuring the slidability of the fixing film with an inexpensive and simple configuration. [Example]

[0051] Example 4 will be described below. Example 4 differs from Example 3 only in that the shape and arrangement of the recesses 132a are varied depending on the position in the longitudinal direction B. Other configurations are the same as Example 2, so detailed configurations of the image forming apparatus 50 and the fixing device 100 will not be described. In Example 4, when the flat portion 132b is viewed from the pressure roller 110 side in the conveying direction A, the longitudinal direction of the heater holder 130 perpendicular to the conveying direction, and the vertical direction C perpendicular to the conveying direction, the area of ​​the multiple recesses 132a varies depending on the position in the longitudinal direction. Furthermore, the spacing between the recesses 132a varies depending on the position in the longitudinal direction. Specifically, the areas of the multiple recesses 132a located at the longitudinal ends are larger than those located at the longitudinal center. Furthermore, the spacing between the recesses 132a at the longitudinal ends is narrower than the spacing between the recesses 132a at the longitudinal center. The following description will be made with reference to the drawings.

[0052] (Features of Example 4) The arrangement of the recesses 132a, which is a feature of Example 4, will be described with reference to FIG. 9. In Example 4, the area (cross-sectional area of ​​the flat portion 132b) and pitch of the recesses 132a are different between the center portion (near the virtual line M) and the end portions in the longitudinal direction B. In the center portion in the longitudinal direction B, the shape and pitch of the recesses 132a are the same as in Example 3. On the other hand, in the end portions in the longitudinal direction B, the width (Wn and Wd) is 1.17 times that of the center portion, and the pitch Pt is reduced to 18 mm. That is, the recesses 132a in Example 4 have a larger width in the longitudinal direction B as they are located closer to the end portions in the longitudinal direction B. In other words, the recesses 132a have a larger area as they are located closer to the end portions in the longitudinal direction B. Furthermore, the pitch Pt (or spacing Sp) of the recesses 132a in Example 4 is narrower as they are located closer to the end portions in the longitudinal direction B. In the fourth embodiment, both the width and the pitch (spacing) are changed depending on the position in the longitudinal direction B, but either the width or the pitch may be changed depending on the position in the longitudinal direction B. Furthermore, the arrangement of the multiple recesses 132a may be changed so that the angle θ between the longitudinal direction of the recesses 132a and the virtual line M becomes larger as the recesses 132a are located closer to the ends in the longitudinal direction.

[0053] (Effects of Example 4) In the fourth embodiment, the area and pitch of the recesses 132a are different between the center and the ends in the longitudinal direction B, so that the ability of the lubricant retaining portion 132 to retain the grease G can be made to differ in the longitudinal direction B. In the fixing device 100 of the film heating type as in the fourth embodiment, when a recording material P having a narrow length in the longitudinal direction B (hereinafter referred to as paper width) is conveyed, the temperature of the ends in the longitudinal direction B of the members constituting the fixing device 100 tends to rise due to the small heat capacity. In other words, a phenomenon called end temperature rise occurs.

[0054] Under such circumstances, oil separation from the grease G is accelerated at the ends in the longitudinal direction B compared to the center in the longitudinal direction B, which may cause the base oil from the grease G at the ends in the longitudinal direction B to leak out from the ends of the fixing film 112 or the base oil component of the grease G at the ends in the longitudinal direction B to be depleted. In such a case, by using the configuration of Example 4, the retention capacity of the grease G at the ends in the longitudinal direction B can be increased, and an appropriate amount of grease G can be supplied to the sliding surface S while retaining the grease G even when conveying a recording material P with a narrow paper width. Note that the configuration of Example 4 in which the area and / or pitch are changed depending on the position in the longitudinal direction B may be applied to the recesses 132a having the shapes of FIGS. 3(b), 6(a), and 6(b) in Example 1.

[0055] As described above, according to the fourth embodiment, it is possible to reduce leakage of the lubricant from the end portion of the fixing film while ensuring the slidability of the fixing film with an inexpensive and simple configuration. [Explanation of symbols]

[0056] 100 fixing device 110 pressure roller 112 Fixing film 113 Heater 130 Heater holder 131 Protrusion 132 Lubricant retention section

Claims

1. an image forming unit that forms a toner image on a recording material; a fixing unit that fixes a toner image formed on a recording material to the recording material, the fixing unit including: a cylindrical fixing film; a heater that is disposed in an internal space of the fixing film with its longitudinal direction aligned with the longitudinal direction of the fixing film; a heater holder that is disposed in an internal space of the fixing film with its longitudinal direction aligned with the longitudinal direction of the fixing film, the heater holder also having a function of guiding the rotating fixing film; and a pressure roller that contacts an outer peripheral surface of the fixing film to sandwich the fixing film together with the heater and form a nip portion between the fixing film and the pressure roller; an image forming apparatus for forming a toner image on a recording material by conveying the recording material through the nip portion and heating the recording material with heat from the heater, a fixing film guide surface of the heater holder, which is located upstream of the heater in the rotation direction of the fixing film, has a plurality of recesses, each recessed portion filled with a lubricant, arranged in the longitudinal direction, the recesses extending in the rotation direction of the fixing film and having an extension direction that is inclined with respect to the longitudinal direction and the recording material conveyance direction when viewed in a direction perpendicular to the longitudinal direction and the recording material conveyance direction at the nip portion; all of the recesses are inclined so as to approach the center of the heater holder in the longitudinal direction toward the downstream side in the rotation direction, The inclination angle of the recessed portion is larger toward the end portion in the longitudinal direction, an image forming apparatus, wherein the fixing unit is disposed so that the upstream side of the fixing film guide surface is positioned vertically below the downstream side of the fixing film guide surface;

2. a photoreceptor on which an electrostatic latent image is formed; a developing means for developing the electrostatic latent image with toner to form a toner image; a transfer means for transferring the toner image onto a recording material; The fixing device according to claim 1 ; An image forming apparatus comprising:

Images