Image forming apparatus

Abstract

To reduce leakage of lubricant from an end of a fixing film while ensuring the slidability of the fixing film, with an inexpensive and simple configuration.SOLUTION: In a fixing device 100, of fixing-film guide surfaces of a heater holder 130, only the fixing-film guide surface located upstream of a heater 113 in a rotational direction of a fixing film 112 is provided with recessed portions 132a which extend in the rotational direction, are arranged along a longitudinal direction and are filled with lubricant and whose extension direction is inclined relative to the longitudinal direction and a recording material conveyance direction when viewed in a direction perpendicular to the longitudinal direction and the recording material conveyance direction at a nip. All recessed portions 132a are inclined so as to approach the center of the heater holder 130 in the longitudinal direction toward the downstream side in the rotational direction, and the inclination angle of the recessed portion 132a becomes larger for the recessed portions located closer to the ends in the longitudinal direction. The fixing device is installed such that the upstream side of the fixing-film guide surface is lower, in a vertical direction, than 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 a laser printer.

Background Art

[0002] As a fixing device used in the electrophotographic method, a film heating method has been conventionally known. A fixing device of the film heating method includes a heater having a resistance heating element on a ceramic substrate, a fixing film that is heated and rotated while being in contact with the heater, and a pressure roller that forms a nip portion together with the heater via the fixing film. A recording material carrying an unfixed toner image is heated while being nipped and conveyed at this nip portion, whereby the unfixed toner image on the recording material is fixed to the recording material.

[0003] In a fixing device of the film heating method, a lubricant is interposed between the heater and the inner surface of the fixing film to reduce the sliding frictional resistance between the heater and the inner surface of the fixing film. This lubricant is applied to the heater, for example, at the beginning of assembly and is interposed between the inner surface of the fixing film. Then, by pressing the pressure roller against the heater via the fixing film and rotationally driving the fixing film, the lubricant spreads over the entire inner surface of the fixing film. However, if the fixing film continues to be rotationally driven, the excess lubricant may leak from the end of the fixing film and enter the outer surface of the fixing film, and may enter the nip portion. In such a 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 a lubricant are provided on the downstream side of the heater in the conveyance direction of the recording material with respect to the heater support member that supports the heater, at positions corresponding to both end portions in the longitudinal direction orthogonal to the conveyance direction, or over the entire longitudinal direction including both end portions.

Prior Art Documents

Patent Documents

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

[0006] However, in the conventional example, when the fixing film rotates, the fixing film slides while constantly contacting the portion of the fixing film near the groove portion. As the lubricant applied to the heater, grease mainly composed of base oil and thickener is often used, but especially at high temperatures, the base oil is likely to separate from the thickener. In such a case, the base oil separated from the grease accumulated in the groove portion near the fixing film leaks out of the groove one after another by capillary action through the minute gap between the inner surface of the fixing film and the heater support member. When the base oil is supplied between the fixing film and the heater more than necessary, the base oil is pressurized at the nip portion and spread in the longitudinal direction. Also, the base oil moves in the longitudinal direction toward the end portion of the fixing film by capillary action through the minute gap between the inner surface of the fixing film and the heater, etc., increasing the risk of the base oil, that is, the lubricant, leaking out of the fixing film.

[0007] The present invention has been made under such circumstances, and an object thereof is 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. Means for Solving the Problems

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

[0009] (1) 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 includes a cylindrical fixing film, a heater disposed in the internal space of the fixing film with its longitudinal direction along the longitudinal direction of the fixing film, a heater holder disposed in the internal space of the fixing film with its longitudinal direction along the longitudinal direction of the fixing film, the heater holder having a function of guiding the rotating fixing film, a pressure roller that contacts the outer peripheral surface of the fixing film and sandwiches the fixing film together with the heater to form a nip portion therebetween. In an image forming apparatus that forms a toner image on a recording material by heating the recording material with the heat of the heater while conveying the recording material with the toner image formed thereon through the nip portion, among the fixing film guide surfaces of the heater holder, only on the fixing film guide surface on the upstream side of the heater with respect to the rotation direction of the fixing film, there are a plurality of recesses into which a lubricant has entered, extending in the rotation direction, and when viewed in a direction orthogonal to the longitudinal direction and the recording material conveyance direction in the nip portion, the extending direction is inclined with respect to the longitudinal direction and the recording material conveyance direction. The recesses are arranged in the longitudinal direction, and all of the recesses are inclined so as to approach the center of the heater holder in the longitudinal direction as they go downstream in the rotation direction. The inclination angle of the recesses is larger at the recesses at the longitudinal ends. The fixing unit is arranged such that the upstream side of the fixing film guide surface is below the downstream side in the vertical direction. An image forming apparatus characterized by this.

Effect of the Invention

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

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0012] Hereinafter, modes for carrying out the present invention will be described in detail with reference to the drawings by way of examples.

Examples

[0013] Example 1 will be described below. First, the main body configuration of the image forming apparatus of Example 1 will be described, and then the fixing device according to the present invention will be described in detail.

[0014] (Image Forming Apparatus) An example of the 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 the toner image on the photosensitive drum 1 onto the recording material P. On the circumferential surface of the photosensitive drum 1, which is a photoreceptor, in order along the rotation direction (arrow R1 direction), a charger 2, an exposure device 3 that irradiates the photosensitive drum 1 with laser light L, a developing device 5 which is a developing means, a transfer roller 10 which is a transfer means, and a photosensitive drum cleaner 16 are arranged. First, the surface of the photosensitive drum 1 is charged to a negative polarity by the charger 2. Next, the charged photosensitive drum 1 has an electrostatic latent image formed on its surface by the laser light L of the exposure device 3. Note that the surface potential of the exposed portion of the photosensitive drum 1 increases. The toner of Example 1 is charged to a negative polarity, and the negative toner adheres only to the electrostatic latent image portion on the photosensitive drum 1 by the developing device 5 containing black toner, and a toner image is formed on the photosensitive drum 1.

[0015] When the recording material P is fed by the paper feed roller 4, the recording material P is conveyed to the transfer nip portion Ntr by the conveying roller 6. A transfer voltage of a positive polarity, which is the opposite polarity of the toner, is applied to the transfer roller 10 from a power source (not shown), and the toner image on the photosensitive drum 1 is transferred onto the recording material P at the transfer nip portion Ntr. After the transfer, the photosensitive drum 1 has the toner remaining on its surface removed by the photosensitive drum cleaner 16 having an elastic blade. The recording material P carrying the toner image is conveyed to the fixing device 100, and heat fixing of the toner image on the surface is performed. 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 Example 1 will be described below. The fixing device 100 of Example 1 is a film heating type fixing device aimed at shortening the start-up time and reducing power consumption. FIG. 2 is a cross-sectional view of the fixing device 100 of Example 1. In the following description, the conveyance direction of the recording material P that is orthogonal to each other is A, the longitudinal direction of the heater holder 130 described later is B, and the vertical direction orthogonal to the sliding surface described later is C.

[0017] The heater 113 is held by the heater holder 130, and a fixing film 112, which is a cylindrical belt, is provided around it. The heater holder 130 has a heater holding portion 135 that holds the heater 113. The heater 113 slides on the inner surface of the fixing film 112 and heats the fixing film 112 from the inside. The pressure roller 110 presses the heater 113 from the outside of the fixing film 112. The region where the pressure roller 110 and the fixing film 112 are in contact due to pressure is defined as 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 rotates followingly in the direction of arrow R2. The recording material P with the unfixed toner image T transferred is conveyed in the conveyance direction A of the recording material P in the figure, and when it reaches the fixing nip portion N, the toner image T is fixed on the recording material P.

[0018] The fixing film 112 of Example 1 has an outer diameter of Φ18 mm in a cylindrical state without deformation and has a multilayer structure in the thickness direction. The layers of the fixing film 112 are composed of a base layer for maintaining the strength of the film and a release layer for reducing the adhesion of dirt to the surface. The base layer needs to have heat resistance to receive the heat of the heater 113 and also needs strength to slide with the heater 113. Therefore, it is advisable to use a metal such as stainless steel or nickel or a heat-resistant resin such as polyimide as the material of the base layer. In Example 1, a polyimide resin was used as the material of the base layer of the fixing film 112, and a carbon-based filler was added and used to improve the thermal conductivity and strength. The thinner the thickness of the base layer, the easier it is to transfer the heat of the heater 113 to the surface of the pressure roller 110. However, if it is too thin, the strength will decrease. Therefore, about 15 μm to 100 μm is preferable, and in Example 1, it was set to 60 μm.

[0019] As the material of the release layer of the fixing film 112, it is preferable to use a fluororesin such as perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), or tetrafluoroethylene-hexafluoropropylene resin (FEP). In Example 1, PFA, which is excellent in release property and heat resistance among fluororesins, was used. The release layer may be a coated tube or a surface-coated paint. In Example 1, the release layer was formed by a coat excellent in thin-wall molding. The thinner the release layer, the easier it is to transfer the heat of the heater 113 to the surface of the fixing film 112. However, if it is too thin, the durability will decrease. Therefore, about 5 μm to 30 μm is preferable, and in Example 1, it was set to 10 μm. Also, although not used in Example 1, an elastic layer may be provided between the base layer and the release layer. In that case, silicone rubber, fluororubber, etc. are used as the material of the elastic layer.

[0020] On the inner circumferential side of the fixing film 112, a heater holder 130 is provided. The heater holder 130 is formed of a liquid crystal polymer resin with high heat resistance in order to satisfy heat resistance and rigidity. In Example 1, Sumika Super (registered trademark) manufactured by Sumitomo Chemical Co., Ltd. is used as the liquid crystal polymer resin. Further, the heater holder 130 has a concave shape (heater holding portion 135) in which the heater 113 is held in the cross section, and holds the heater 113. By loosely fitting the fixing film 112 onto the heater holder 130, it also serves to guide the rotation of the fixing film 112. Since the heater holder 130 relates to the features of Example 1, it will be described in detail later.

[0021] The pressing stay 119 is disposed along the longitudinal direction B of the heater holder 130. The pressing stay 119 is formed by bending a highly rigid sheet metal such as stainless steel in order to uniformly press the heater holder 130 in the longitudinal direction B. The pressing roller 110 of Example 1 has an outer diameter of Φ20 mm, and an iron core metal 117 with a diameter of Φ13 mm and an elastic layer 116 with a thickness of 3.5 mm are formed. As the material of the elastic layer 116, solid rubber or foamed rubber is used. Foamed rubber has a low heat capacity and a low thermal conductivity, and since the heat on the surface of the pressing roller 110 is difficult to be absorbed inside, the surface temperature tends to rise, and there is an advantage that the fixing start-up time can be shortened. In Example 1, foamed rubber obtained by foaming silicone rubber was used.

[0022] The smaller the outer diameter of the pressure roller 110, the more the heat capacity can be suppressed. However, if it is too small, the width of the fixing nip portion N will become narrow, so an appropriate diameter is required. 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 required. Therefore, in Example 1, the thickness of the elastic layer 116 was set to 3.5 mm. On the elastic layer 116, a release layer 118 made of perfluoroalkoxy resin (PFA) is formed as a toner release layer. The release layer 118 may be formed by coating the surface with paint or covering a tube, similar to the release layer of the fixing film 112. In Example 1, a tube with excellent durability was used. As the material of the release layer 118, in addition to PFA, fluororesins such as PTFE and FEP, fluororubbers or silicone rubbers with good releasability may be used. The lower the surface hardness of the pressure roller 110, the easier it is to obtain the width of the fixing nip portion N with a light pressure. In Example 1, one with an Asker-C hardness (4.9 N load) of 50° was used. The pressure roller 110 is pressed against the heater by a pressing means (not shown). The pressing force was set to a total pressure of 14 kgf. In Example 1, the width of the fixing nip portion N in the conveyance direction A is about 6.0 mm over the longitudinal direction B. The pressure roller 110 is rotated by a rotating means (not shown) in the direction of arrow R1 in the figure at a surface moving speed of 200 mm / sec.

[0023] The heater 113 of Example 1 is a general heater used in a film heating type fixing device, and uses a heater in which a resistance heating element is provided on a ceramic substrate. The heater 113 is formed by screen printing a Ag / Pd (silver palladium) resistance heating element on the surface of an alumina substrate having a width of 6 mm and a thickness of 1 mm in the conveyance direction A with a thickness of about 10 μm, and covering it with glass having a thickness of 50 μm to protect the heating element and ensure slidability. Further, the temperature of the heater 113 is adjusted by appropriately controlling the current flowing through the resistance heating element according to the signal of a temperature detection element (not shown) that detects the temperature of the ceramic substrate or the fixing film 112. The heater 113 is fitted and fixedly supported in a heater holding portion 135 which is a groove portion provided in the heater holder 130. In Example 1, in order to efficiently transfer heat to the recording material P, the center of the heater 113 and the center of the pressure roller 110 are aligned in the conveyance direction A.

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

[0025] The effect of Example 1 is particularly effective when the ratio of the base oil to the total amount of the grease used is relatively high, and is particularly effective when a grease having a base oil ratio of 80 Wt% or more is used. Greases with a high proportion of base oil have relatively less thickener and lower viscosity, so they have good slidability, but the function of the thickener to hold the base oil is weak. Therefore, it is necessary to supplement the function of holding the grease and the base oil by the configuration of Example 1. In Example 1, a grease having a base oil ratio of 85 Wt% was used. The grease was spray-coated with 200 mg over a length of 210 mm, which is slightly shorter than the width 220 mm of the pressure application region in the longitudinal direction B of the pressure roller 110 of the sliding surface S, which is the contact surface between the fixing film 112 and the heater 113. The protruding portion 131 and the lubricant holding portion 132 will be described later.

[0026] (Features of Example 1) The shape of the heater holder 130, particularly the lubricant holding portion 132 provided in the heater holder 130, which is a feature of Example 1, will be described with reference to FIG. 3. FIG. 3(a) is a schematic view of a main part showing the positional relationship between the heater 113, the fixing film 112, the protruding portion 131, and the lubricant holding portion 132 in an enlarged manner. FIG. 3(b) is a schematic view of a main part as seen from the pressure roller 110 side (pressure roller side) in the vicinity of the lubricant holding portion 132. The heater holder 130 of Example 1 has a lubricant holding portion 132 and a protruding portion 131. The lubricant holding portion 132 is provided on the upstream side in the conveyance direction A of the heater holding portion 135. The protruding portion 131 is provided on the upstream side in the conveyance direction A of the lubricant holding portion 132 and protrudes toward the pressure roller 110 as compared with the opposing surface described later. The opposing surface protrudes toward the pressure roller 110 more than the sliding surface S (in other words, the fixing nip portion N), and the protruding portion 131 protrudes toward the pressure roller 110 more than the lubricant holding portion 132.

[0027] The heater holder 130 has a protruding portion 131 that protrudes toward the pressure roller 110 side more than the sliding surface S of the heater 113 on the upstream side in the conveyance direction A of the fixing nip portion N. The degree of protrusion of the protruding portion 131 from the sliding surface S (hereinafter referred to as the protrusion height) H1 requires a certain height in order to regulate the trajectory of the fixing film 112. However, if the protrusion height H1 is too high, it will become a factor that hinders the entry of the recording material P into the fixing nip portion N, so a height of about 0.1 mm to 1.0 mm is desirable. In Example 1, the protrusion 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 from the sliding surface S of the lubricant holding portion 132 needs to be set lower than the protruding height H1 of the protruding portion 131 (H2 < H1). Also, the lubricant holding portion 132 is higher than the sliding surface S. This is to protect the edge portion (hereinafter referred to as the upstream edge portion) 113e of the heater 113 on the upstream side in the conveyance direction A and on the side of the pressure roller 110 from rubbing against the inner surface of the fixing film 112 when the fixing film 112 rotates in the R2 direction. In Example 1, the height H2 from the sliding surface S of the lubricant holding portion 132 was 0.2 mm. Therefore, the height of the protruding portion 131 from the lubricant holding portion 132 is H1 - H2 = 0.2 mm. Also, the width W1 of the protruding portion 131 in the conveyance direction A is 0.5 mm. Further, the width W2 of the lubricant holding portion 132 in the conveyance direction A is larger than the width W1 of the protruding portion 131 in the conveyance direction A (W2 > W1). In Example 1, the protruding portion 131 was provided by changing the shape of the heater holder 130, but the protruding portion 131 may be provided separately or made of a different material.

[0029] (Lubricant holding portion) The lubricant holding portion 132 of the heater holder 130 has a flat portion 132b which is a facing surface facing the pressure roller 110, and the flat portion 132b has a recess 132a recessed in a direction away from the pressure roller 110. In addition, although it is the flat portion 132b in the first embodiment, the facing surface is not limited to a flat surface. The lubricant holding portion 132 has a plurality of recesses 132a for holding grease over the longitudinal direction B. From the viewpoint of not wanting to spread the held grease as much as possible in the longitudinal direction B, it is desirable that the plurality of provided recesses 132a are arranged isolatedly in the longitudinal direction B. Further, from the viewpoint of holding the grease and preventing it from flowing out excessively onto the sliding surface S, it is desirable that it does not penetrate the heater holding portion 135 (groove portion) holding the heater 113 in the conveying direction A. More desirably, from the viewpoint of directing the movement of the grease in the direction of the fixing nip portion N, that is, the conveying direction A, it is desirable that the length of the recess 132a in the conveying direction A is longer than the length in the longitudinal direction B. That is, assuming the length of the lubricant holding portion 132 in the conveying 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 shape in the cross-section of the flat portion 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 conveying 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 such that the area of the cross-section parallel to the flat portion 132b of the recess 132a becomes smaller as it moves away from the pressure roller 110. In other words, the lubricant holding portion 132 may be a rectangular groove in addition to an arc groove having a shape (bow shape) indicated by the broken line in Fig. 3(a) in the cross-sectional shape perpendicular to the longitudinal direction B of the recess 132a. When the recess 132a of the lubricant holding portion 132 is a rectangular groove, in addition to the configuration where the area of the cross-section parallel to the flat portion 132b is the same regardless of the distance from the pressure roller 110, a configuration where the area becomes smaller as it moves away from the pressure roller 110 may also be acceptable.

[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 spreading 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 spreading 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 according to the study results of the inventor. Therefore, in Example 1, the interval of the recesses 132a was set to 1.0 mm. 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 in Example 1, it is about 20° to 40°. 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 pressure 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 protruding portion 131. Since the fixing film 112 is originally cylindrical, in the vicinity of the protruding portion 131 located upstream of the fixing nip portion N, it rotates while contacting the protruding portion 131 due to the restoring force by which the fixing film 112 tries to return to the cylindrical shape. Since the protruding portion 131 protrudes toward the pressure roller 110 from the sliding surface S of the heater 113, the trajectory of the fixing film 112 is restricted by the protruding portion 131. Therefore, as shown in FIG. 3(a), the lubricant holding portion 132 is arranged near the inner surface of the fixing film 112 upstream of the fixing nip portion N without constantly contacting the fixing film 112 with strong pressure.

[0034] Immediately after assembling the fixing device 100, the grease is applied on the sliding surface S, but by performing the fixing operation, the fixing film 112 rotates and adheres to and rotates on the inner surface of the fixing film 112. A part of the grease reaches the lubricant holding portion 132 along with the rotation of the fixing film 112 and is held in the recess 132a of the lubricant holding portion 132. The grease once held in the recess 132a is not likely to come into direct contact with the inner surface of the fixing film 112 under normal conditions because the fixing film 112 is restricted by the protruding portion 131.

[0035] (Comparison with the comparative example) Next, the action on the grease G according to the configuration of Example 1 will be described while comparing with the comparative example with reference to FIGS. 4 and 5. FIG. 4 is a schematic diagram for explaining the action of supplying the grease G in Example 1. FIG. 5 is a schematic diagram for explaining the action of supplying the grease G in the comparative example without the protruding portion 131. Note that the same components as those described above are denoted by the same reference numerals and the description thereof is omitted.

[0036] In the comparative example shown in Fig. 5, since the protruding portion 131 is absent, the inner surface of the fixing film 112 constantly contacts the concave portion 132a of the lubricant holding portion 132 and the grease G accumulated therein. When the fixing film 112 constantly contacts the concave portion 132a, the grease G constantly moves in the direction of the sliding portion S and becomes over-supplied. In particular, when the grease G constantly contacts the fixing film 112, the grease G tends to become hot and the base oil easily separates from the thickener. The base oil of the separated grease G moves in the direction of the sliding portion S as shown by the arrow in the figure by capillary action through the minute gap Gp (broken line frame portion) between the inner surface of the fixing film 112 and the heater holder 130. When the amount of grease G supplied to the sliding portion S becomes excessive, the grease G pressurized at the fixing nip portion N is crushed and spreads in the longitudinal direction B, and thus is gradually pushed out toward the end in the longitudinal direction B, and may eventually leak from the end in the longitudinal direction B of the fixing film 112.

[0037] In contrast, in the first embodiment with respect to this comparative example, as shown in Fig. 4(a), since the orbit of the fixing film 112 is restricted by the protruding portion 131, the fixing film 112 does not constantly contact the concave portion 132a, so that excessive supply of the grease G to the sliding portion S is suppressed. On the other hand, when the fixing film 112 is heated and then cooled according to the ambient temperature and left for a long time, it has the property of plastically deforming to some extent following the shape of the fixing nip portion N. When the next fixing operation is performed after being left for a long time, when the fixing film 112 starts to rotate, the orbit of the fixing film 112 is different from the normal orbit and shows a behavior of wobbling to some extent between the fixing nip portion N and the protruding portion 131.

[0038] At that time, as shown in FIG. 4(b), the fixing film 112 temporarily comes into contact with the concave portion 132a, and a small amount of grease G is supplied to the sliding portion S by capillary action from the gap Gp 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. For this reason, as shown in FIG. 4(a), the orbit of the fixing film 112 becomes stable again, and the fixing film 112 does not normally come into contact with the concave portion 132a, suppressing an excessive supply amount of the grease G to the sliding portion S. As a result, the amount of the grease G intervening in the sliding portion S becomes an appropriate amount, so that the grease G pressurized in the fixing nip portion N is pushed out in the longitudinal direction B, and the phenomenon of leaking from the end portion of the fixing film 112 in the longitudinal direction B can be reduced.

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

[0040] In the first embodiment, the concave portion 132a has an elliptical shape, but the effects of the first embodiment can also be obtained with other shapes. FIG. 6 is a diagram showing concave portions 132a of other shapes, and the same components as those described above are denoted by the same reference numerals, and the description thereof is omitted. For example, other shapes such as a rectangle as shown in FIG. 6(a) or a rhombus as shown in FIG. 6(b) are also applicable. Thus, in the direction orthogonal to the conveyance direction and the longitudinal direction of the heater holder 130 orthogonal to the conveyance direction, when viewing the flat portion 132b from the pressure roller 110 side, the lubricant holding portion 132 (specifically, the opening shape) may be elliptical, rectangular, or rhombic. In FIGS. 6(a) and 6(b), the shape of the cross section orthogonal to the longitudinal direction B of the concave portion 132a may be various shapes such as a curved shape, a tapered shape, or a rectangular shape. Further, in the first embodiment, the shape of the heater holder 130 is changed to provide the concave portion 132a, but for example, a separate member may be disposed in the concave portion 132a by disposing a non-woven fabric or a pad impregnated with grease in the concave portion 132a.

[0041] According to the above Embodiment 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 an inexpensive and simple configuration.

Embodiment

[0042] Embodiment 2 will be described below. In Embodiment 2, only the portion regarding the shape of the concave portion 132a is different from that of Embodiment 1. Since the other configurations are the same as those of Embodiment 1, the detailed configurations of the image forming apparatus 50 and the fixing apparatus 100 will be omitted. In the concave portion 132a of Embodiment 2, regarding the shape of the cross section in the planar portion 132b, that is, the length in the longitudinal direction B of the portion close 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 far from the sliding surface S.

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

[0044] (Effects of Embodiment 2) The further effects in Example 2 will be described with reference to FIGS. 7(b) and 7(c). For example, consider the case where grease G adheres to a portion far from the sliding portion S of the concave portion 132a as shown in FIG. 7(b), and the case where grease G adheres to a portion close to the sliding portion S of the concave portion 132a as shown in FIG. 7(c). When the base oil separates from the grease G in the state of FIG. 7(b), the width of the concave portion 132a in the longitudinal direction B becomes narrower as it approaches the sliding surface S. Therefore, the base oil easily moves in the direction of the sliding surface S of the concave portion 132a due to capillary action. On the contrary, when the base oil separates from the grease G in the state of FIG. 7(c), the base oil of the grease G hardly moves to a portion far from the sliding surface S. That is, by making the shape of the concave portion 132a the shape of Example 2, it is possible to make the base oil of the grease G unevenly distributed in a portion closer to the sliding surface S within the concave portion 132a. The base oil supplied to the sliding portion S is mainly sequentially supplied and used from a portion close to the sliding surface S among the base oil held in the concave portion 132a. At that time, among the base oil held in the concave portion 132a, the base oil held in a portion far from the sliding surface S is replenished to the position of the concave portion 132a close to the sliding surface S. By this action, since the base oil held in the concave portion 132a is sequentially supplied and used, it is possible to reduce the amount of grease G that remains without contributing to lubrication among the grease G held in the concave portion 132a.

[0045] As described above, according to Example 2, it is possible to reduce the leakage of the lubricant from the end of the fixing film while ensuring the slidability of the fixing film with an inexpensive and simple configuration.

Example

[0046] Example 3 will be described below. In Example 3, only the portion regarding the arrangement of the concave portion 132a is different from that of Example 2. Since the other configurations are the same as those of Example 2, the detailed descriptions of the configurations of the image forming apparatus 50 and the fixing apparatus 100 are omitted.

[0047] (Features of Example 3) The arrangement of the recess 132a, which is a feature of Example 3, will be described with reference to Fig. 8(a). Since the shape is the same as that of Example 2, it will be omitted. In Example 3, as shown in Figs. 8(a) and 8(b), a virtual line M through which the center of the recording material P passing through the conveyance path passes is defined, and with respect to this virtual line M extending in the conveyance direction, the recess 132a is arranged such that the longitudinal direction of the recess 132a is inclined. In other words, the recess 132a is configured to have a shape such that the portion closer to the sliding surface S faces the virtual line M. Specifically, in the conveyance direction A of the recording material P, for the recess 132a, an angle θ is defined as the angle at which a virtual line Cl connecting the center of the width Wn of one end (the downstream side) and the center of the width Wd of the other end (the upstream side) of the recess 132a is inclined with respect to the virtual line M. In Example 3, the recess 132a is inclined at θ = 10° with respect to the center M. Regarding the arrangement of the plurality of recesses 132a, the angle θ may be changed according to the longitudinal position. For example, regarding the arrangement of the plurality of recesses 132a, the angle θ may be changed so that it becomes larger for those located at the longitudinal ends.

[0048] (Effect of Example 3) A further effect in Example 3 will be described with reference to Fig. 8(b). As described in Example 2, the base oil separated from the grease G moves to the portion closer to the sliding part S by capillary action. At this time, as described above, since the recess 132a is arranged to be inclined toward the virtual line M through which the center of the recording material P passing through the conveyance path passes, the moving direction of the base oil is also inclined toward the virtual line M.

[0049] By this action, an effect is produced of collecting the base oil that has been crushed in the fixing nip portion N and spread in the longitudinal direction B toward the virtual line M through which the center of the recording material P passing through the conveyance path passes. Therefore, in Example 3, leakage of the grease G from the longitudinal ends of the fixing film 112 can be further reduced. Note that the configuration of inclining the recess 132a in the shape shown in Figs. 3(b), 6(a), and 6(b) of Example 1 toward the virtual line M of Example 3 may be applied.

[0050] As described above, according to the third embodiment, 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 an inexpensive and simple configuration.

Embodiment

[0051] Example 4 will be described below. In Example 4, only the portion where the shape and arrangement of the concave portions 132a are varied according to the position in the longitudinal direction B is different from Example 3. Since the other configurations are the same as those in Example 2, the detailed configurations of the image forming apparatus 50 and the fixing apparatus 100 will be omitted. In Example 4, in the vertical direction C orthogonal to the conveyance direction A and the longitudinal direction of the heater holder 130 orthogonal to the conveyance direction, when the flat portion 132b is viewed from the pressure roller 110 side, the areas of the plurality of concave portions 132a vary according to the position in the longitudinal direction. Also, the intervals between the concave portions 132a vary according to the position in the longitudinal direction. Specifically, the areas of the plurality of concave portions 132a are larger for those located at the longitudinal ends than for those located at the longitudinal center. Also, the intervals between the concave portions 132a at the longitudinal ends are narrower than the intervals between the concave portions 132a at the longitudinal center. This will be described below with reference to the drawings.

[0052] (Features of Example 4) The arrangement of the recess 132a, which is a feature of Example 4, will be described with reference to FIG. 9. In Example 4, the area (the cross-sectional area in the flat portion 132b) and the pitch of the recess 132a are made different between the central portion (near the virtual line M) and the end portion in the longitudinal direction B. In the central portion of the longitudinal direction B, both the shape and the pitch of the recess 132a are the same as those in Example 3. On the other hand, at the end portion in the longitudinal direction B, the widths (Wn and Wd) are made 1.17 times that of the central portion, and the pitch Pt is set to 18 mm. That is, for the recess 132a of Example 4, the width in the longitudinal direction B becomes larger as it is located closer to the end portion in the longitudinal direction B. In other words, the area of the recess 132a becomes larger as it is located closer to the end portion in the longitudinal direction B. Also, for the recess 132a of Example 4, the pitch Pt (or the interval Sp) becomes narrower as it is located closer to the end portion in the longitudinal direction B. In Example 4, both the width and the pitch (interval) are changed according to the position in the longitudinal direction B, but either one of the width and the pitch may be changed according to the position in the longitudinal direction B. Also, regarding the arrangement of the plurality of recesses 132a, the angle θ formed by the longitudinal direction of the recess 132a and the virtual line M may be changed so as to become larger as the recess 132a is located closer to the end portion in the longitudinal direction.

[0053] (Effect of Example 4) In Example 4, since the area and the pitch of the recess 132a are made different between the central portion and the end portion in the longitudinal direction B, the holding ability of the grease G by the lubricant holding portion 132 can be made different in the longitudinal direction B. For the fixing device 100 of the film heating type as in Example 4, when a recording material P with a narrow length in the longitudinal direction B (hereinafter referred to as the paper width) is conveyed, since the heat capacity is small, the temperature of the end portion in the longitudinal direction B of the members constituting the fixing device 100 tends to rise. That is, a phenomenon of end portion temperature rise occurs.

[0054] Under such circumstances, the separation of the grease G at the end of the longitudinal direction B is promoted compared to the central part of the longitudinal direction B, and there is a possibility that the base oil from the grease G at the end of the longitudinal direction B leaks out from the end of the fixing film 112, or the base oil component of the grease G at the end of the longitudinal direction B is depleted. In such a case, by adopting the configuration as in Example 4, the holding ability of the grease G at the end of the longitudinal direction B can be increased, and an appropriate amount of the grease G can be supplied to the sliding surface S while holding the grease G even when transporting the recording material P with a narrow paper width. In addition, a configuration in which the area and / or pitch of Example 4 are changed according to the position in the longitudinal direction B may be applied to the concave portions 132a having the shapes shown in FIGS. 3(b), 6(a), and 6(b) of Example 1.

[0055] As described above, according to Example 4, it is possible to reduce the leakage of the lubricant from the end of the fixing film while ensuring the slidability of the fixing film with an inexpensive and simple configuration.

Explanation of Reference Numerals

[0056] 100 Fixing device 110 Pressing roller 112 Fixing film 113 Heater 130 Heater holder 131 Protrusion 132 Lubricant holding portion

Claims

1. An image forming unit that forms a toner image on a recording material, A fixing unit that fixes the toner image formed on the recording material to the recording material, comprising a cylindrical fixing film, a heater disposed in the internal space of the fixing film with its longitudinal direction along the longitudinal direction of the fixing film, a heater holder disposed in the internal space of the fixing film with its longitudinal direction along the longitudinal direction of the fixing film, the heater holder having a function of guiding the rotating fixing film, and a pressure roller that contacts the outer peripheral surface of the fixing film and sandwiches the fixing film together with the heater to form a nip portion therebetween. In an image forming apparatus that forms a toner image on a recording material by heating the recording material with the heat of the heater while conveying the recording material with the toner image formed thereon through the nip portion, Among the fixing film guide surfaces of the heater holder, only on the fixing film guide surface upstream of the heater with respect to the rotation direction of the fixing film, there are a plurality of recesses filled with a lubricant extending in the rotation direction, and when viewed in a direction orthogonal to the longitudinal direction and the recording material conveyance direction in the nip portion, the extending direction is inclined with respect to the longitudinal direction and the recording material conveyance direction. All of the recesses are inclined so as to approach the center of the heater holder in the longitudinal direction as they go downstream in the rotation direction. The inclination angle of the recesses is larger at the recesses at the longitudinal ends. An image forming apparatus, characterized in that the fixing unit is arranged such that the upstream side of the fixing film guide surface is below the downstream side in the vertical direction.

2. A photoreceptor on which an electrostatic latent image is formed, Developing means for developing the electrostatic latent image with toner to form a toner image, Transfer means for transferring the toner image to a recording material, The fixing device according to claim 1, An image forming apparatus, characterized by comprising the same.

Images