Image forming apparatus

Abstract

To provide an image forming apparatus that can reduce an adverse effect caused by sand.SOLUTION: An image forming apparatus comprises: an image forming unit that forms a toner image on a recording material by using a photoreceptor; a fixing unit that heats the toner image to fix the toner image to the recording material; and a housing that accommodates the image forming unit and the fixing unit. The housing has an opening that communicates the inside and the outside of the housing, and that is arranged above a nip part in the vertical direction. The image forming apparatus further comprises a filter that covers the opening. The photoreceptor has a conductive substrate, and a surface layer part that is formed on an outer peripheral side of the conductive substrate. When the distance from an outer peripheral surface of the substrate to a surface of the photoreceptor is defined as the thickness of the surface layer part, the maximum particle diameter of particles that can pass through the filter is smaller than the thickness of the surface layer part.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus for forming an image on a recording material. [Background technology]

[0002] Patent Document 1 describes that an opening (discharge hole) is provided in a top cover of an image forming apparatus for discharging steam generated in a fixing unit to the outside of the apparatus. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-281825 Summary of the Invention [Problem to be solved by the invention]

[0004] Sand and dust that enters the inside of the image forming apparatus through an opening provided in the housing may cause problems such as defective images or damage to the film of the fixing unit or the intermediate transfer belt.

[0005] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an image forming apparatus capable of reducing the adverse effects caused by sand and dust. [Means for solving the problem]

[0006] One aspect of the present invention is an image forming apparatus comprising: an image forming unit having a photosensitive member and using the photosensitive member to form a toner image on a recording material; a fixing unit forming a nip portion to hold the recording material and heating the toner image while transporting the recording material through the nip portion to fix the toner image to the recording material; and a housing that accommodates the image forming unit and the fixing unit, wherein the housing has an opening that connects the outside and the inside of the housing and is positioned above the nip portion in the vertical direction, and the image forming apparatus further comprises a filter that covers the opening, the photosensitive member has a conductive substrate and a surface layer formed on the outer periphery of the conductive substrate, the distance from the outer periphery of the substrate to the surface of the photosensitive member is defined as the thickness of the surface layer, and the maximum particle size of particles that can pass through the filter is smaller than the thickness of the surface layer.

[0007] Another aspect of the present invention is an image forming apparatus comprising: an image forming unit that forms a toner image on a recording material; a fixing unit that has a cylindrical film and a heating means for heating the film, forming a nip portion that clamps the recording material, and heats the toner image with the film to fix it to the recording material; and a housing that accommodates the image forming unit and the fixing unit, wherein the housing has an opening that connects the outside and inside of the housing and is positioned above the nip portion in the vertical direction, and the image forming apparatus further comprises a filter that covers the opening, and the maximum particle size of particles that can pass through the filter is smaller than the thickness of the film.

[0008] Another aspect of the present invention is an image forming apparatus including a photosensitive member and an intermediate transfer belt, an image forming unit that performs a primary transfer of a toner image formed on the photosensitive member to the intermediate transfer belt, and then a secondary transfer of the toner image from the intermediate transfer belt to a recording material, a fixing unit that forms a nip portion to hold the recording material and heats the toner image in the nip portion while transporting the recording material, thereby fixing the toner image to the recording material, and a housing that accommodates the image forming unit and the fixing unit, wherein the housing has an opening that connects the outside and the inside of the housing and is positioned above the nip portion in the vertical direction, and the image forming apparatus further includes a filter that covers the opening, and the intermediate transfer belt has a base layer and a surface layer that is provided on the outer periphery of the base layer and supports the toner image, and the maximum particle size of particles that can pass through the filter is smaller than the thickness of the surface layer.

[0009] Another aspect of the present invention is an image forming apparatus including an image forming unit having a photosensitive member and forming a toner image on a recording material using the photosensitive member, a fixing unit forming a nip portion that sandwiches the recording material and heats the toner image while transporting the recording material at the nip portion to fix the toner image to the recording material, and a housing that houses the image forming unit and the fixing unit, the housing having an opening that communicates with the outside and the inside of the housing and is positioned above the nip portion in the vertical direction, the image forming apparatus further including a filter that covers the opening, and the photosensitive member the filter is an open-cell foamed plastic; and, when the average cell diameter of the foamed plastic in a plane perpendicular to the thickness direction of the filter is α (μm), the thickness of the filter is β (μm), the average cell diameter of the foamed plastic in the thickness direction of the filter is γ (μm), and the distance from the outer circumferential surface of the substrate to the surface of the photoreceptor is δ (μm), then α / (β / γ)<δ. Effect of the Invention

[0010] According to the present invention, it is possible to reduce the adverse effects caused by sand and dust. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2A is a schematic diagram of an image forming apparatus according to an embodiment, and FIG. 2B is an explanatory diagram of a photosensitive drum according to the embodiment. [Diagram 2] 1 is a schematic diagram of an image forming apparatus according to an embodiment. [Diagram 3] 1A is a schematic diagram of an image forming apparatus according to an embodiment, and FIG. [Figure 4] 4A and 4B are diagrams showing an outlet according to an embodiment. [Diagram 5] FIG. 4 is a diagram showing an air vent and a filter according to an embodiment. [Figure 6] FIG. [Figure 7] 1A and 1B are diagrams showing examples of image defects caused by dust particles; [Figure 8] 1A and 1B are explanatory diagrams of a filter according to an embodiment. [Figure 9] 4A and 4B are explanatory views of a dustproof performance test of the filter according to the embodiment. [Figure 10] A diagram showing water droplet marks. [Figure 11] FIG. 4 is an explanatory diagram of a sand and dust resistance evaluation test for the image forming apparatus according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0013] Example 1 In this embodiment, an example of the configuration of an image forming apparatus will be described using the image forming apparatus 100 shown in Fig. 1(a) as an example. The image forming apparatus 100 is a monochrome laser printer that forms monochrome images by electrophotography, and forms an image (toner image) using toner as a developer on a recording material P in response to image information transmitted from an external device such as a personal computer. As the recording material P (recording medium), various sheet materials of different materials can be used, including paper such as plain paper and cardboard, sheets of special shapes such as envelopes and index paper, and cloth.

[0014] In the following description, the up-down direction (vertical direction, direction along the direction of gravity) of the image forming apparatus 100 when the image forming apparatus 100 is placed on a horizontal surface is defined as the Z-axis direction. The direction of the rotation axis of the photosensitive drum 1 is defined as the X-axis direction. The direction intersecting both the X-axis direction and the Z-axis direction is defined as the Y-axis direction. The X-axis, Y-axis, and Z-axis directions are preferably perpendicular to each other. In the X-axis direction, the positive side (+X side) is called the right side, and the negative side (-X side) is called the left side. In the Y-axis direction, the positive side (+Y side) is called the front side or front side, and the negative side (-Y side) is called the rear side or back side. In the Z-axis direction, the positive side (+Z side) is called the upper side, and the negative side (-Z side) is called the lower side.

[0015] In this embodiment, the X-axis direction is the width direction of the recording material P that is perpendicular to both the vertical direction and the discharge direction Dc of the recording material P.

[0016] (Image forming device) 1A and 2 are schematic cross-sectional views of an image forming apparatus 100 according to a first embodiment.

[0017] 1(a) and 2, the image forming apparatus 100 includes a feeding section 6, a pair of registration rollers 8, an image forming section 10, a fixing section 9, and a discharge section 16. The image forming apparatus 100 also includes a housing 101 that houses the feeding section 6, the pair of registration rollers 8, the image forming section 10, the fixing section 9, and the discharge section 16.

[0018] The feeding section 6 includes a stacking section (cassette, tray) that is detachable from the housing 101 and on which the recording material P is stacked, and a roller pair 41 that feeds the recording material P one by one from the stacking section. The registration roller pair 8 conveys the recording material P fed by the feeding section 6 to the transfer nip Ntr at a timing synchronized with the creation of a toner image in the image forming section 10. The image forming section 10 executes an electrophotographic process to create a toner image, and transfers the toner image to the recording material P in the transfer nip Ntr to form an image on the recording material P. The fixing section 9 forms a fixing nip Nf as a nip section that sandwiches the recording material P, and heats the toner image in the fixing nip Nf while conveying the recording material P to fix it to the recording material P. The discharge section 16 discharges the recording material P on which the image has been formed to the outside of the image forming apparatus 100 (outside the housing 101, outside the housing) in a discharge direction Dc that intersects with the vertical direction (Z-axis direction).

[0019] Arrow P1 in Fig. 1(a) indicates the transport path of recording material P when image forming apparatus 100 performs single-sided printing (single-sided image formation) in which an image is formed on only one side (first side) of recording material P. When image forming apparatus 100 performs double-sided printing (double-sided image formation) in which an image is formed on both the first side and the opposite second side of recording material P, recording material P is transported along the path of arrow P1 even when image formation on the first side is performed. Arrow P2 in Fig. 2 indicates the transport path when recording material P, after image formation on the first side has been completed, is transported again toward image forming unit 10 when image forming apparatus 100 performs double-sided printing.

[0020] A series of operations in which the image forming apparatus 100 performs single-sided or double-sided printing while transporting one sheet of recording material P and then discharges the sheet outside the image forming apparatus 100 is called an image forming operation or a paper passing operation. Continuous paper passing is when the image forming apparatus 100 performs an image forming operation (paper passing operation) continuously on multiple sheets of recording material P. The cumulative number of sheets passed is the cumulative number of sheets passed, which is the cumulative number of sheets of recording material P on which the image forming apparatus 100 has performed an image forming operation, based on the state at the time of shipment from the factory or the state when initialization processing is performed after shipment.

[0021] Among the recording materials on which the image forming apparatus 100 in this embodiment can form an image, the recording material with the largest width in the X-axis direction (width direction) (maximum size recording material) is an LTR (LETTER) size recording material (width 215.9 mm). Furthermore, the maximum print width, which is the width of the area (effective print area) on which the image forming unit 10 can form an image for an LTR size recording material, is 206 mm. Among the recording materials on which the image forming apparatus 100 in this embodiment can form an image, the recording material with the smallest width in the X-axis direction (width direction) (minimum size recording material) is a recording material with a width of 98.4 mm. In other words, in this embodiment, the maximum paper passing width of the image forming apparatus 100 is 215.9 mm, and the minimum paper passing width is 98.4 mm.

[0022] That is, in this embodiment, in the width direction perpendicular to both the vertical direction and the discharge direction, the passage area of ​​the maximum size recording material, which has the longest length in the X-axis direction (width direction) among the recording materials on which the image forming apparatus can form an image, is an area with a width of 215.9 mm. Also, in this embodiment, the passage area of ​​the minimum size recording material in the width direction is an area with a width of 98.4 mm. In this embodiment, the passage area of ​​the recording material spreads symmetrically with respect to the center of the conveying path CP in the X-axis direction (width direction). The center of the conveying path CP refers to the center of the space through which the recording material P can pass, and may be, for example, the center position in the X-axis direction between the two rubber roller parts 81a located at both ends of the discharge roller 81 shown in FIG. 4(a). Also, when the loading section of the feeding section 6 is provided with positioning sections for positioning both ends of the recording material P in the X-axis direction, it may be the center position of the positioning sections at both ends in the X-axis direction.

[0023] The housing 101 includes a frame of the image forming apparatus 100 and an exterior member (cover member or door member) that becomes the exterior surface of the image forming apparatus 100. A rear door 14 and a discharge tray 17 described later are examples of the exterior member. The space outside the outer surface of the housing 101 is referred to as the outside of the image forming apparatus 100 or the outside of the device, and the space inside the outer surface of the housing 101 is referred to as the inside of the image forming apparatus 100 or the inside of the device. Inside the image forming apparatus 100, a transport path CP is provided as a passage space through which the recording material P passes.

[0024] The housing 101 of this embodiment is provided with an inlet 6s, a discharge port 16s, and an air hole section 51. The inlet 6s, the discharge port 16s, and the air hole section 51 are all openings including an opening that communicates the inside of the image forming apparatus 100 with the outside of the image forming apparatus 100. More specifically, the inlet 6s, the discharge port 16s, and the air hole section 51 are all openings that communicate the conveying path CP with the outside of the image forming apparatus 100. The inlet 6s is an opening (feed port) that receives the recording material P fed by the feeding section 6. The discharge port 16s is an opening through which the recording material P discharged by the discharge section 16 passes. The air hole section 51 will be described later.

[0025] In this embodiment, the inlet 6s and the outlet 16s are each one opening, and the vent portion 51 includes multiple openings (multiple vents 51a described below). Multiple inlets 6s and / or outlets 16s may be provided. The vent portion 51 may have only one opening. Furthermore, the housing 101 may be provided with openings other than those described above.

[0026] The conveying path CP includes a main conveying path CP1 and a double-sided conveying path CP2. The main conveying path CP1 is a conveying path that extends from the receiving entrance 6s to the discharge exit 16s via the transfer nip Ntr and the fixing nip Nf. The double-sided conveying path CP2 is a conveying path that branches off from the main conveying path CP1 between the fixing unit 9 and the discharge unit 16 in the recording material conveying direction of the main conveying path CP1, and joins the main conveying path CP1 between the roller pair 41 and the registration roller pair 8 of the feeding unit 6.

[0027] In other words, the transport path CP includes a main transport path CP1 as a first transport path through which the recording material P passes when an image is formed on the recording material by the image forming unit 10. The transport path CP also includes a double-sided transport path CP2 as a second transport path branched off from the first transport path and through which the recording material, on whose first surface a toner image has been formed by the image forming unit 10, is transported again toward the image forming unit 10 when an image is formed on its second surface opposite to the first surface.

[0028] The image forming unit 10 includes a photosensitive drum 1 as an image carrier, a charging roller 2 as a charging means, a scanner unit 4 as an exposure means, a developing device 3 as a developing means, a transfer roller 5 as a transfer means, and a pre-exposure device 23. The developing device 3 includes a toner container 32 that contains toner T as a developer, and a developing roller 31 that carries the toner in the toner container 32 and supplies it to the photosensitive drum 1. A transfer nip Ntr is formed between the photosensitive drum 1 and the transfer roller 5 as a transfer unit where an image is transferred.

[0029] A part or the whole of the image forming unit 10 may be a cartridge that is detachable from the housing 101. In this case, the housing 101 may have a cover member that is provided on the front or top surface of the housing 101 in an openable and closable manner, and the cartridge may be allowed to be attached and detached by opening the cover member.

[0030] The photosensitive drum 1 is a photosensitive member formed into a cylindrical shape (drum shape). The layer structure of the photosensitive drum 1 in this embodiment will be described later.

[0031] The photosensitive drum 1 is driven to rotate around the rotation axis at a predetermined peripheral speed in the direction of arrow R1 by a driving source (not shown). The peripheral speed of the photosensitive drum 1 determines the speed of image formation by the image forming apparatus 100, and is also called the process speed. The process speed in this embodiment is, for example, 140 mm / sec.

[0032] The charging roller 2 comes into contact with the photosensitive drum 1 with a predetermined contact pressure to form a charging portion. In this embodiment, the width of the contact portion (nip portion) between the charging roller 2 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 is approximately 1 mm. The charging roller 2 has a conductive base. The charging roller 2 applies a predetermined charging voltage to the conductive base by a charging power source, thereby uniformly charging the surface of the photosensitive drum 1 to a predetermined potential. In this embodiment, the photosensitive drum 1 is charged to a negative polarity by the charging roller 2.

[0033] The charging roller 2 used in this embodiment has a core metal with a diameter of 5 mm as a conductive substrate, a base layer of hydrin rubber, and a surface layer of urethane, and is configured to have an outer diameter of 9.7 mm. The resistance of the charging roller 2 is 1×10 6 The hardness is 70 degrees measured by an MD-1 rubber hardness tester. In this embodiment, a DC voltage is used as the charging voltage, but this is not limited to this, and a voltage in which an AC voltage is superimposed on a DC voltage may be used.

[0034] A gear is provided on the core metal, and the gear engages with the gear of the photosensitive drum 1, causing the charging roller 2 to rotate at a constant speed relative to the photosensitive drum 1. In this embodiment, the gear ratio and the like are set so that the peripheral speed ratio between the charging roller 2 and the photosensitive drum 1 during image formation is approximately 107%. The peripheral speed ratio between the charging roller 2 and the photosensitive drum 1 is the ratio of the surface speed of the charging roller 2 to the surface speed of the photosensitive drum 1. Due to the speed difference between the charging roller 2 and the photosensitive drum 1 in the charging section, the toner adhering to the charging roller 2 is more likely to return to the photosensitive drum 1 due to frictional charging.

[0035] In this embodiment, a pressure spring is used to pressurize the charging roller 2 against the photosensitive drum 1. The pressure spring presses the bearings supporting the core metal parts at both ends of the charging roller 2 in a direction perpendicular to the surface of the photosensitive drum 1 at the charging portion. In the direction of the rotation axis of the photosensitive drum 1 (X-axis direction), the pressing force on the side where the gear of the charging roller 2 is arranged, i.e., the driving side, is 7.5 N, and the pressing force on the side opposite the gear, i.e., the non-driving side, is 5.6 N.

[0036] In order to generate a stable discharge in the charging section, the pre-exposure device 23 irradiates light onto an area of ​​the surface of the photosensitive drum 1 after passing through the transfer nip Ntr and before reaching the charging section, thereby removing residual charge.

[0037] The scanner unit 4 uses a polygon mirror to irradiate the photosensitive drum 1 with laser light corresponding to image information input from an external device, thereby scanning and exposing the surface of the photosensitive drum 1. An electrostatic latent image corresponding to the image information is formed on the exposed surface of the photosensitive drum 1.

[0038] The developing device 3 supplies toner T to the photosensitive drum 1 and develops the electrostatic latent image into a toner image. In this embodiment, a contact development method is adopted as the development method, and a toner layer carried by the developing roller 31 comes into contact with the photosensitive drum 1 at a development section where the photosensitive drum 1 and the developing roller 31 face each other. A development voltage is applied to the developing roller 31 by a development power source. Due to an electric field formed in the development section by the development voltage, the toner carried by the developing roller 31 is transferred from the developing roller 31 to the drum surface in accordance with the potential distribution on the surface of the photosensitive drum 1. As a result, the electrostatic latent image on the photosensitive drum 1 is visualized as a toner image.

[0039] The toner T in this embodiment may be a polymerized toner produced by a polymerization method. The normal charge polarity (normal polarity) of the toner T is negative. The toner particle size is 6 μm.

[0040] The transfer roller 5 is brought into contact with the photosensitive drum 1 with a predetermined pressure to form a transfer nip Ntr. The transfer roller 5 is rotated by following the rotating photosensitive drum 1 or by following the recording material P passing through the transfer nip Ntr. A positive voltage is applied to the core of the transfer roller 5 from a transfer power source (not shown). In accordance with an electric field formed by the voltage application, the toner image carried on the photosensitive drum 1 is transferred to the recording material P at the transfer nip Ntr.

[0041] The transfer roller 5 used in this embodiment has a core of a nickel-plated steel bar and a foamed sponge layer mainly composed of NBR and epichlorohydrin rubber formed on the outer periphery of the core. The core has a diameter of 8 mm, and the foamed sponge layer has a thickness of 3 mm. In addition, the bearings that hold both ends of the core are biased by spring members, so that the transfer roller 5 is pressed against the photosensitive drum 1 with a pressure of 1 kgf (9.8 N).

[0042] In this embodiment, a cleaner-less system (drum cleaner-less system, simultaneous development and cleaning system) is adopted in which the developing device 3 collects the toner (transfer residual toner) that remains on the photosensitive drum 1 without being transferred to the recording material P in the transfer nip Ntr. The transfer residual toner is negatively charged by the charging roller 2 in the charging section. The developing voltage is set so that the developing roller 31 has a positive polarity with respect to the surface potential of the non-image portion of the photosensitive drum 1 in the developing section. Therefore, the transfer residual toner adhering to the non-image portion is transferred from the photosensitive drum 1 to the developing roller 31 in the developing section and collected by the developing device 3. The collected transfer residual toner is mixed with the toner T contained in the toner container 32 and is used again for development.

[0043] In a drum cleaner-less system, it is possible to omit a cleaning member that removes the transfer residual toner from the photosensitive drum 1 and a waste toner container that stores the removed transfer residual toner. This makes it possible to reduce the size of the image forming apparatus. However, instead of a drum cleaner-less system, the image forming apparatus 100 may be provided with a cleaning member and a waste toner container in addition to the configuration of this embodiment.

[0044] The fixing unit 9 is a thermal fixing device (image heating device) that heats the toner image to fix it to the recording material P. More specifically, the fixing unit 9 heats and pressurizes the toner image on the recording material P while nipping and conveying the recording material P, onto which the toner image has been transferred in the transfer nip Ntr, in the fixing nip Nf. This causes the toner particles to melt and then solidify, thereby fixing the toner image to the recording material P.

[0045] The fixing unit 9 of this embodiment is a film heating type device that is excellent in terms of shortening the start-up time and reducing power consumption. The fixing unit 9 includes a fixing film 112 as a heating member (fixing member), a heater 113 as a heating means, a heater holder 130 that holds the heater 113, and a pressure roller 110 as a pressure member. The fixing film 112 is a flexible cylindrical (endless) film. The heater 113 is held by the heater holder 130, and is disposed in the internal space of the fixing film 112 together with the heater holder 130. The pressure roller 110 is disposed so as to sandwich the fixing film 112 together with the heater 113. A fixing nip Nf is formed as a contact portion (nip portion) between the fixing film 112 and the pressure roller 110.

[0046] The pressure roller 110 is an elastic roller (rubber roller) including a core metal and an elastic layer. Bearings provided at both ends of the core metal are biased by pressure springs, so that the pressure roller 110 is pressed against the heater 113 via the fixing film 112. Note that the heater holder 130 (or a support member such as a metal stay that supports the heater holder 130) may be configured to be biased toward the pressure roller 110 by a pressure spring.

[0047] The pressure roller 110 rotates by inputting a driving force from a driving source to a driving gear provided at the end of the core metal. The fixing film 112 is rotated by following the rotation of the pressure roller 110 or by following the recording material P passing through the fixing nip Nf.

[0048] A typical heater used in a film heating type heating device can be used as the heater 113. The heater 113 is, for example, a ceramic heater including a ceramic substrate and a resistance heating element arranged in a series circuit on the substrate. Specifically, the heater 113 includes an alumina substrate having a width of 6 mm and a thickness of 1 mm, a 10 μm high Ag / Pd (silver palladium) resistance heating element applied by screen printing to the substrate surface, and a 50 μm thick glass layer as a protective layer formed to cover the resistance heating element.

[0049] The fixing film 112 may have a multi-layer structure in which different material layers are laminated in the thickness direction. The multi-layer structure includes, for example, a base layer that slides against the heater 113, a surface layer that contacts the recording material P, and a conductive primer layer that bonds the base layer and the surface layer. The outermost layer of the surface layer is a release layer for suppressing adhesion of surface dirt. The fixing film 112 of this embodiment has a circumference that results in an outer diameter of 20 mm when formed into a cylindrical shape.

[0050] The base layer is required to be heat resistant since it receives heat from the heater 113, and is also required to be strong since it slides against the heater 113. The material of the base layer may be metal such as SUS (Stainless Used Steel) or nickel, or heat resistant resin such as polyimide. Metal is stronger than resin, so it can be made thinner, and has high thermal conductivity, so it is easy to transfer heat from the heater 113 to the surface layer. On the other hand, resin has a smaller specific gravity than metal, so it has a small heat capacity and is easy to warm up. Furthermore, resin can be molded into a thin film by coating molding, so it can be molded at low cost. In this embodiment, polyimide resin is used as the material of the base layer of the fixing film 112. Also, carbon-based filler is added to the polyimide resin to improve thermal conductivity and strength. The thinner the base layer, the higher the heat transfer efficiency of the fixing film 112, but if it is too thin, sufficient strength may not be obtained. The thickness of the base layer is preferably about 15 μm to about 100 μm, and is 60 μm in this embodiment.

[0051] The conductive primer layer is made of polyimide resin or fluororesin, and carbon or the like is added to reduce resistance. It is preferable to stabilize the potential of the fixing film 112 during image formation by electrically connecting (grounding) the exposed portion of the conductive layer to a ground potential.

[0052] As the material of the outermost layer (release layer), it is preferable to use a fluororesin such as perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), or tetrafluoroethylene-hexafluoropropylene resin (FEP). In this embodiment, PFA, which has excellent release properties and heat resistance among fluororesins, is used, and a conductive agent is dispersed in the matrix of PFA to adjust the resistance value (to a medium resistance). The release layer may be a tube covering the outer periphery of the base layer and the conductive primer layer, or a conductive primer layer coated with paint on the surface. In this embodiment, the release layer is molded by a coating method that is excellent in thin-wall moldability. The thinner the release layer, the higher the heat transfer efficiency of the fixing film 112, but if it is too thin, the durability of the fixing film 112 may decrease. The thickness of the release layer is preferably about 5 μm to about 30 μm, and is 10 μm in this embodiment.

[0053] The pressure roller 110 of this embodiment has, for example, an iron core having an outer diameter of 9 mm, and an elastic layer made of silicone rubber and having a thickness of 2.5 mm on the outer periphery of the core. The elastic layer is made of heat-resistant silicone rubber or fluororubber. The outer diameter of the pressure roller 110 is preferably about 10 mm to about 50 mm. The smaller the outer diameter of the pressure roller 110, the smaller the heat capacity, but if the outer diameter is too small, the width of the fixing nip Nf becomes narrow, and the toner image may not be heated sufficiently, resulting in a decrease in fixability. In this embodiment, the outer diameter of the pressure roller 110 is 14 mm. As for the thickness of the elastic layer, the thinner the elastic layer, the smaller the heat capacity, but if it is too thin, heat is easily lost to the metal core, reducing the thermal efficiency of the entire fixing unit 9, so an appropriate thickness is required.

[0054] A release layer for enhancing the toner releasing property may be provided on the outer periphery of the elastic layer of the pressure roller 110. In this embodiment, a release layer made of perfluoroalkoxy resin (PFA) is formed as the release layer. The release layer may be a tube covering or a surface coated with paint, as in the case of the release layer of the fixing film 112, but in this embodiment, a release layer with a thickness of 20 μm formed of a tube having excellent durability is used. As the material of the release layer, in addition to PFA, fluororesins such as PTFE and FEP, fluororubber and silicone rubber having good releasing property, etc. may be used. The lower the surface hardness of the pressure roller 110, the lighter the pressure is to obtain the width of the fixing nip Nf, but if it is too low, durability is deteriorated. The surface hardness of the pressure roller 110 in this embodiment is 40° in Asker-C hardness (600 g load).

[0055] A temperature detection element 115 such as a thermistor for detecting the temperature of the heater 113 is disposed on the rear surface of the heater 113. The control unit of the image forming apparatus 100 controls the amount of heat generated by the heater 113 so that the heater 113 reaches a predetermined target temperature (controlled temperature) by controlling the power supply to the resistance heating element in response to an output signal from the temperature detection element 115. The control unit controls the amount of heat generated by the heater 113 so that the surface temperature of the fixing film 112 in the fixing nip Nf is maintained at a temperature suitable for fixing a toner image during image formation. The controlled temperature of the fixing unit 9 when plain paper is used as the recording material P is, for example, 180°C.

[0056] The discharge section 16 is a transport unit (discharge means) that discharges the recording material P on which image formation has been completed to the outside of the housing 101. The discharge section 16 includes a pair of discharge rollers formed of a discharge roller 81 and a discharge roller 82. The discharge roller 81 is a drive roller that rotates by receiving a driving force from a drive source, and the discharge roller 82 is a driven roller that forms a nip portion together with the discharge roller 81 and rotates following the discharge roller 81.

[0057] The discharge unit 16 is disposed inside or near a discharge opening 16s of the housing 101. The discharge unit 16 nip the recording material P between a discharge roller 81 and a discharge roller 82 and conveys the recording material P in a discharge direction Dc, thereby discharging the recording material P from the inside to the outside of the housing 101 through the discharge opening 16s. A discharge tray 17 on which the recording material P discharged by the discharge unit 16 is stacked is provided on the upper surface of the housing 101.

[0058] In the case of single-sided printing, as shown in FIG. 1(a), the recording material P that has passed through the fixing nip Nf is discharged by the discharge section 16 through the discharge port 16s. In the case of double-sided printing, as shown in FIG. 2, after the rear end of the recording material P in the discharge direction Dc passes through the fixing nip Nf, the discharge roller 81 is rotated in the opposite direction to the rotation direction along the discharge direction Dc, and the conveying direction of the recording material P is reversed. That is, the recording material P on which an image is formed on the first side while being conveyed along the main conveying path CP1 is switched back in the discharge section 16 and conveyed to the double-sided conveying path CP2. In other words, in this embodiment, the discharge section 16 functions as a reversing means that reverses the recording material P in the case of double-sided printing. Note that a pair of reversing rollers may be provided as a reversing means that reverses the recording material P, separate from the discharge section 16. The recording material P conveyed along the double-sided conveying path CP2 is conveyed to the main conveying path CP1 again with the first side and the second side switched. Then, the recording material P having the image formed on the second surface while being transported again along the main transport path CP1 is discharged by the discharge section 16 through the discharge opening 16s.

[0059] (Double-sided transport path) The double-sided conveying path CP2 will now be described. As shown in Fig. 2, the double-sided conveying path CP2 is formed by the double-sided guide 13, the double-sided rib 42, the U-shaped guide 43, etc. In other words, the housing 101 has the double-sided guide 13, the double-sided rib 42, and the U-shaped guide 43. The double-sided guide 13, the double-sided rib 42, and the U-shaped guide 43 are all examples of guide members that form part of the conveying path CP (part of the double-sided conveying path CP2).

[0060] In this embodiment, the main transport path CP1 extends from the feeding section 6 toward the discharge section 16 in a substantially vertical direction. The double-sided transport path CP2 extends from the branch point with the main transport path CP1 toward the opposite side to the discharge direction Dc in the Y-axis direction (-Y side, the opposite side to the discharge direction Dc), and further extends toward the vertically downward side (-Z side). The double-sided transport path CP2 further merges with the main transport path CP1 via a U-shaped curved portion that curves toward the same side as the discharge direction Dc in the Y-axis direction (+Y side) and then turns back toward the vertically upward side (+Z side).

[0061] The double-sided guide 13 forms a part of the double-sided conveying path CP2 (the upstream part of the double-sided conveying path CP2). The double-sided guide 13 is an example of a guide member (second guide portion) that forms the second conveying path. The double-sided guide 13 guides the first side of the recording material P.

[0062] The double-sided guide 13 has a curved shape that is convex upward when viewed in the direction of the rotation axis of the photosensitive drum 1 (X-axis direction). In other words, the upper surface of the double-sided guide 13 (second guide portion) is curved to have a convex shape that is convex upward when viewed in the width direction (X-axis direction) perpendicular to both the vertical direction and the discharge direction Dc. When viewed in the X-axis direction (width direction), the double-sided guide 13 (second guide portion) is located between the discharge port 16s and the ventilation hole portion 51 (opening) of the housing 101 in the direction (Y-axis direction) perpendicular to the vertical direction.

[0063] The double-sided rib 42 is a part of the rear door 14 (FIG. 6). The double-sided rib 42, together with the guide portion 15a (FIG. 3) of the transfer guide unit 15, forms a part (part extending vertically downward) of the double-sided conveying path CP2. That is, the guide portion 15a of the transfer guide unit 15 is an example of a facing portion that faces the inner surface 14b of the exterior member (rear door 14) with a gap. The guide portion 15a faces the inner surface 14b of the exterior member (rear door 14) and forms a part of the conveying path CP together with the exterior member (rear door 14). In other words, the gap (space) formed between the inner surface 14b and the guide portion 15a is a part of the conveying path CP (a part of the double-sided conveying path CP2) through which the recording material P passes. It can be said that the ventilation hole portion 51 communicates the space connected to the gap formed between the inner surface 14b and the guide portion 15a with the outside of the housing 101. The upper end of the double-sided rib 42 faces the double-sided guide 13 and is curved along the curved shape of the double-sided guide 13 when viewed in the X-axis direction.

[0064] The double-sided rib 42 includes a plurality of rib shapes 42a (FIG. 6) arranged in the width direction. Each rib shape 42a protrudes from the inner surface 14b of the rear door 14 toward the inside (+Y side) of the housing 101 and extends substantially along the Z-axis direction. In other words, the rear door 14 has a rib shape that protrudes from the inner surface 14b in a direction approaching the guide portion 15a of the transfer guide unit 15 and extends along the recording material conveying direction in the conveying path. The double-sided rib 42 comes into contact with the recording material P at the ridge portion (end surface on the +Y side) of the rib shape 42a and guides the second side of the recording material P.

[0065] The U-shaped guide 43 forms a curved portion of the double-sided conveying path CP2. The U-shaped guide 43 guides the first side of the recording material P.

[0066] (Jam Clearance) When a so-called jam occurs in which a recording material P is retained inside the image forming apparatus 100 during printing, a user can remove the retained recording material P from the image forming apparatus 100, thereby performing a so-called jam clearance.

[0067] 3(a) and (b), the housing 101 of the image forming apparatus 100 has a rear door 14 and a transfer guide unit 15. The rear door 14 and the transfer guide unit 15 are each an opening / closing member that is provided so as to be openable and closable relative to other parts of the housing 101. The rear door 14 and the transfer guide unit 15 are opened and closed when a user performs jam clearance.

[0068] The housing 101 of the image forming apparatus 100 has a rear door 14 and a transfer guide unit 15. The rear door 14 is an exterior member (rear cover) having an outer surface 14a as an exterior surface (second exterior surface) on the rear side (-Y side) of the housing 101.

[0069] The rear door 14 can be moved between an open position (FIGS. 3(a) and (b)) where the rear door 14 opens the main body opening 101a provided on the rear side of the housing 101, and a closed position (FIG. 1(a)) where the main body opening 101a is closed. The rear door 14 of this embodiment rotates about an axis extending in the X-axis direction by a hinge portion 141 provided at the lower end of the rear door 14 in the closed position. When the rear door 14 is in the closed position, the recording material P can pass through the double-sided conveying path CP2. In other words, the closed position of the rear door 14 is a position when the image forming apparatus 100 is capable of performing an image forming operation. When the rear door 14 is in the open position, at least a part of the double-sided conveying path CP2 is opened, and the recording material P remaining in the double-sided conveying path CP2 can be accessed from outside the housing 101. In other words, when the rear door 14 as an exterior member is in the open position, the recording material P is allowed to be removed from a part of the conveying path CP (the double-sided conveying path CP2) through the main body opening 101a.

[0070] The transfer guide unit 15 includes a guide portion 15a which forms a part of the double-sided conveying path CP2 together with the double-sided rib 42 of the rear door 14, and the above-mentioned transfer roller 5. The transfer guide unit 15 is disposed between the rear door 14 and the photosensitive drum 1. More specifically, the transfer guide unit 15 is disposed between the photosensitive drum 1 and a gap (space) formed between the inner surface 14b and the guide portion 15a. In the vertical direction, the transfer guide unit 15 is located below the ventilation hole portion 51, and the upper end of the transfer guide unit 15 is located above the photosensitive drum 1.

[0071] The transfer guide unit 15 can be moved between a closed position (shielding position, FIG. 1(a)) in which the photosensitive drum 1 is covered as viewed from the rear side (-Y side) and an open position (exposing position, FIG. 3(a)(b)) in which the photosensitive drum 1 is exposed as viewed from the rear side (-Y side). The transfer guide unit 15 of this embodiment rotates around an axis extending in the X-axis direction by a hinge portion 151 provided at the lower end of the transfer guide unit 15 in the closed position. The position of the hinge portion 151 can be said to be the position of the rotation axis of the transfer guide unit 15. In the vertical direction, the position of the rotation axis of the transfer guide unit 15 is located above the ventilation hole portion 51 and the photosensitive drum 1. When the transfer guide unit 15 is in the closed position, the recording material P can pass through the main transport path CP1. In other words, the closed position of the transfer guide unit 15 is the position when the image forming apparatus 100 is capable of performing an image forming operation. When the rear door 14 is in the open position and the transfer guide unit 15 is in the open position, at least a part of the main transport path CP1 is opened, and the recording material P remaining on the main transport path CP1 becomes accessible from outside the housing 101.

[0072] The transfer guide unit 15 in this embodiment is biased by a spring member in a direction from the open position to the closed position. By biasing the transfer guide unit 15 by the spring member, the contact pressure between the transfer roller 5 and the photosensitive drum 1 can be made more stable.

[0073] When the recording material P is stuck on the main transport path CP1, the user opens both the rear door 14 and the transfer guide unit 15, as shown in Fig. 3(a) and (b). Fig. 3(a) and (b) are a schematic diagram and a detailed diagram showing a jam processing state when the recording material P is stuck on the main transport path CP1 without being able to pass through the fixing unit 9. By opening both the rear door 14 and the transfer guide unit 15, the user can grasp and remove the recording material P stuck on the main transport path CP1. After that, the user closes the rear door 14 and the transfer guide unit 15 again, and the image forming apparatus 100 returns to a state in which it is possible to perform an image forming operation.

[0074] As shown in Fig. 2, during double-sided printing, a jam may occur while the recording material P is passing through the double-sided conveying path CP2. In this case, the user need only open the rear door 14. By opening the rear door 14, the user can grasp and remove the recording material P that is stuck in the double-sided conveying path CP2. After that, the user can close the rear door 14 again, and the image forming apparatus 100 returns to a state in which it is capable of performing an image forming operation.

[0075] (Layer structure of photosensitive drum) The layer structure of the photosensitive drum 1 will be described with reference to Fig. 1(b). Fig. 1(b) shows a schematic diagram of the layer structure of the photosensitive drum 1. The photosensitive drum 1 includes a conductive substrate (hereinafter simply referred to as substrate 1a) and a surface layer 1b formed on the outer periphery of substrate 1a. In this embodiment, surface layer 1b includes an undercoat layer 1b1, a charge generating layer 1b2, and a charge transport layer 1b3.

[0076] The charge generation layer 1b2 and the charge transport layer 1b3 function as a photosensitive layer (photoconductive layer) that attenuates the potential of the surface 1s when irradiated with light. The charge generation layer 1b2 absorbs light irradiated from the scanner unit 4 to generate charges. The charge transport layer 1b3 has a function as an insulating layer that retains the surface charge applied to the surface 1s in the charging process, and a function of transporting the charge generated in the charge generation layer 1b2 to the surface 1s.

[0077] The photosensitive layer in this embodiment is a negatively charged organic photoconductor (OPC). That is, when charge pairs are generated in the charge generating layer 1b2 by light irradiation, the charge transport layer 1b3 transports positive charges toward the surface 1s of the photosensitive drum 1, neutralizing the negative surface charge applied to the surface 1s in the charging process. As a result, the surface potential of the irradiated area irradiated with light from the scanner unit 4 is attenuated, and an electrostatic latent image is formed on the surface 1s of the photosensitive drum 1.

[0078] The photosensitive drum 1 rotates around a rotation axis Ax. In this embodiment, the direction of the rotation axis Ax is parallel to the X-axis direction. A direction perpendicular to the rotation axis Ax of the photosensitive drum 1 is called a radial direction Dr of the photosensitive drum 1. The radial direction Dr is the radial direction of a virtual circle centered on the rotation axis Ax when viewed in the X-axis direction.

[0079] The distance from the outer peripheral surface of the substrate 1a to the surface 1s of the photosensitive drum 1 in the radial direction Dr is defined as the thickness δ (μm) of the surface layer 1b. In this embodiment, the thickness of the undercoat layer 1b1 is 25 μm, the thickness of the charge generation layer 1b2 is 1 μm, and the thickness of the charge transport layer 1b3 is 22 μm. Therefore, the thickness δ of the surface layer 1b of the photosensitive drum 1 is 25+1+22=48 (μm). However, the thickness of each layer constituting the surface layer 1b is not limited to this, and the thickness of the entire surface layer 1b is not limited to this.

[0080] The layer structure of the surface layer 1b is not limited to the above. For example, the surface layer 1b may further include a release layer (protective layer) on the outer periphery of the charge transport layer 1b3 to enhance the releasability of the toner. In this case, the thickness of the release layer (protective layer) is included in the thickness of the surface layer 1b. Also, instead of the structure in which the charge generation layer 1b2 and the charge transport layer 1b3 are laminated, a photosensitive layer having a single layer structure containing a charge generation material and a charge transport material may be used.

[0081] As the cumulative number of sheets of paper passed through the image forming apparatus 100 increases, the surface layer 1b of the photosensitive drum 1 gradually wears away. Unless otherwise specified, the thickness of the surface layer 1b in this embodiment is based on the state immediately after shipment from the factory (the state in which the cumulative number of sheets of paper passed through is substantially zero).

[0082] A more specific example of the configuration of the photosensitive drum 1 will be described below. The base body 1a is a drum-shaped (cylindrical) member (aluminum cylinder) made of aluminum and having a diameter of 24 mm. The surface layer portion 1b is formed by successively applying an undercoat layer 1b1, a charge generating layer 1b2, and a charge transport layer 1b3 to the outer periphery of the base body 1a by a dipping coating method. The photosensitive drum 1 is a cylindrical member having relatively high rigidity as a whole.

[0083] Examples of the undercoat layer 1b1 include those mainly made of resin, those mainly made of white pigment and resin, and metal oxide films obtained by chemically or electrochemically oxidizing the surface of the substrate 1a. Examples of the resin used in the undercoat layer 1b1 include thermoplastic resins such as polyamide, polyvinyl alcohol, casein, and methyl cellulose, and thermosetting resins such as acrylic, phenol, melamine, alkyd, unsaturated polyester, and epoxy. Examples of the white pigment include metal oxides such as titanium oxide, aluminum oxide, zirconium oxide, and zinc oxide. Among them, titanium oxide is a preferred white pigment because it has excellent properties for preventing the injection of electric charges from the substrate 1a. The amount of titanium oxide used among the white pigments in the undercoat layer 1b1 is 60 to 100%, preferably 70 to 100%, and more preferably 80 to 100%, by weight. If the amount of titanium oxide used is less than 60%, the characteristics of the undercoat layer are likely to fluctuate due to environmental changes, and the effect of blocking the injection of electric charges from the conductive support becomes unstable, which may be undesirable.

[0084] The undercoat layer 1b1 is formed between the substrate 1a and the photosensitive layer (the charge generating layer 1b2 and the charge transport layer 1b3), and functions as an intermediate layer that limits the injection of charges from the substrate 1a to the photosensitive layer.

[0085] The photosensitive layer (charge generating layer 1b2 and charge transport layer 1b3) may be made of known organic or inorganic materials, and the photosensitive layer may be formed by known methods.

[0086] Examples of the charge generating material used in the charge generating layer 1b2 include organic pigments or dyes such as monoazo pigments, bisazo pigments, trisazo pigments, tetrakisazo pigments, triarylmethane dyes, thiazine dyes, oxazine dyes, xanthene dyes, cyanine dyes, styryl dyes, pyrylium dyes, quinacridone pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, bisbenzimidazole pigments, indathrone pigments, squarylium pigments, and phthalocyanine pigments, as well as inorganic materials such as selenium, selenium-arsenic, selenium-tellurium, cadmium sulfide, zinc oxide, titanium oxide, and amorphous silicon. These charge generating materials may be used alone or as a mixture.

[0087] Examples of the charge transport material used in the charge transport layer 1b3 include anthracene derivatives, pyrene derivatives, carbazole derivatives, tetrazole derivatives, metallocene derivatives, phenothiazine derivatives, pyrazoline compounds, hydrazone compounds, styryl compounds, styrylhydrazone compounds, enamine compounds, butadiene compounds, distyryl compounds, oxazole compounds, oxadiazole compounds, thiazole compounds, imidazole compounds, triphenylamine derivatives, phenylenediamine derivatives, aminostilbene derivatives, triphenylmethane derivatives, etc. These charge transport materials may be used alone or as a mixture.

[0088] Examples of the binder resin used to form the photosensitive layer include known thermoplastic resins, thermosetting resins, photocurable resins, and photoconductive resins. Suitable binder resins include, for example, thermoplastic resins such as polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-maleic anhydride copolymers, ethylene-vinyl acetate copolymers, polyvinyl butyral, polyvinyl acetal, polyester, phenoxy resins, (meth)acrylic resins, polystyrene, polycarbonate, polyarylate, polysulfone, polyethersulfone, and ABS resins, thermosetting resins such as phenolic resins, epoxy resins, urethane resins, melamine resins, isocyanate resins, alkyd resins, silicone resins, and thermosetting acrylic resins, polyvinyl carbazole, polyvinyl anthracene, and polyvinyl pyrene. These resins may be used alone or as a mixture.

[0089] (Exhaust port) The configuration of the discharge port 16s of this embodiment will be described with reference to Figures 4(a) and 4(b). Figure 4(a) is a schematic diagram of the discharge section 16 of this embodiment as seen from the front side (+Y side) of the image forming apparatus 100, and Figure 4(b) is a detailed diagram thereof.

[0090] In this embodiment, the discharge port 16s is an opening provided in a wall surface 101f (FIG. 1(a)) facing the front side (+Y side) of the housing 101, and is an opening through which the recording material P discharged by the discharge unit 16 passes. In other words, the housing 101 has a wall surface 101f as a first exterior surface facing the discharge direction Dc, in which the discharge port 16s is provided and through which the recording material P discharged by the discharge unit 16 passes. The wall surface 101f extends upward from the upstream end of the discharge tray 17 in the discharge direction Dc, and functions as a reference wall that aligns the recording material P by hitting against the rear end of the recording material P loaded on the discharge tray 17.

[0091] More specifically, in this embodiment, the discharge port 16s is an opening formed in a wall surface 101f of the housing 101 when the image forming apparatus 100 is viewed from the front side (+Y side) and leading to the inside of the image forming apparatus 100. In this embodiment, the conveying path CP, which is the space inside the image forming apparatus 100, communicates with the space outside the image forming apparatus 100 via the discharge port 16s.

[0092] Here, the configuration of the discharge section 16 will be described. As a pair of rollers for nipping and transporting a sheet material such as the recording material P, it is desirable that at least one of the rollers is a split roller including a plurality of rotating bodies (roller portion, roller portion) that contact the recording material P. The split roller is a roller including a plurality of rotating bodies, each of which has a width shorter than the maximum width of the recording material P to be transported in the width direction of the recording material P perpendicular to the discharge direction Dc of the recording material P, and the plurality of rotating bodies are arranged side by side in the width direction. By using a split roller, it becomes difficult for the rollers of the roller pair to not contact each other or to have insufficient contact pressure in some areas in the width direction due to the deflection of the rollers to occur, and the recording material P can be transported more stably.

[0093] In the roller pair for nipping and transporting the sheet material, both rollers may be split rollers. The discharge section 16 of this embodiment is a roller pair including a discharge roller 81 which is a split roller, and a discharge roller 82 which is a split roller.

[0094] The discharge roller 81 includes a shaft 81b extending in the width direction and a plurality of rubber roller portions 81a as a plurality of rotating bodies. In this embodiment, four rubber roller portions 81a are attached to one shaft 81b. A drive gear is provided at the end of the shaft 81b, and a driving force from a driving source is input via the drive gear. When the driving force is input to the shaft 81b, the shaft 81b and the four rubber roller portions 81a rotate integrally.

[0095] The discharge roller 82 includes a plurality of roller parts 82a as a plurality of rotating bodies, a plurality of roller holders 82b that hold the roller parts 82a, and a plurality of springs 82c that bias the roller holders 82b. The discharge roller 82 of this embodiment includes four roller parts 82a, four roller holders 82b, and four springs 82c corresponding to the four rubber roller parts 81a of the discharge roller 81. Each roller part 82a is rotatably supported by the corresponding roller holder 82b. In addition, each roller holder 82b is biased by the corresponding spring 82c, so that the corresponding roller part 82a is pressed against the corresponding rubber roller part 81a. Each roller part 82a rotates following the corresponding rubber roller part 81a.

[0096] In four regions spaced apart from one another in the width direction, nip portions are formed where the rubber roller portion 81a of the discharge roller 81 and the roller portion 82a of the discharge roller 82 come into contact with each other. The discharge portion 16 holds the recording material P at the nip portions, and conveys the recording material P in the discharge direction Dc by rotating the discharge roller 81.

[0097] Since the discharge section 16 has the above-mentioned configuration, a discharge opening 16s is formed as an area (hatched area in FIG. 4A) where the rotating bodies of the divided rollers are not present inside an opening 101h formed in a wall surface 101f of the housing 101. That is, in this embodiment, the "discharge opening 16s" is an area excluding the rubber roller portion 81a of the discharge roller 81 and the roller portion 82a of the discharge roller 82 and the like (i.e., the area where the recording material P cannot pass through) from the area inside the opening 101h provided in the wall surface 101f of the housing 101 when the image forming apparatus 100 is viewed from the front side (+Y side).

[0098] (Ventilation hole near the fixing part) The ventilation hole portion 51 as an opening portion provided near the fixing unit 9 of the image forming apparatus 100 will be described. Fig. 5 is a schematic diagram showing the ventilation hole portion 51, and shows a cross section perpendicular to the X-axis direction of the rear door 14 in which the ventilation hole portion 51 is provided. Fig. 6 is a perspective view of the rear door 14. Note that Fig. 5 shows a cross section at the position of dotted line L in Fig. 6. As will be described later, a filter 50 is provided to cover the ventilation hole portion 51, and therefore the positions of the ventilation holes 51a of the ventilation hole portion 51 are shown by dotted lines in Fig. 6.

[0099] 5, the ventilation hole section 51 includes at least one ventilation hole 51a as an opening that communicates between the outside and the inside of the image forming apparatus 100. More specifically, the ventilation hole 51a communicates between the outside of the image forming apparatus 100 and the transport path CP (particularly, the double-sided transport path CP2 in this embodiment), which is the space inside the image forming apparatus 100. The ventilation hole section 51 in this embodiment includes a plurality of ventilation holes 51a.

[0100] The ventilation hole 51a opens toward the outside of the image forming apparatus 100 on the outer surface 14a, which is the surface facing the opposite side (-Y side) from the discharge direction Dc of the rear door 14. In other words, the housing 101 has the outer surface 14a as a second exterior surface facing the opposite side from the discharge direction Dc of the recording material P, and provided with an opening (ventilation hole portion 51) that communicates between the outside of the housing 101 and a conveying path CP through which the recording material P passes inside the housing 101.

[0101] Inside the image forming apparatus 100, heat is generated in the fixing unit 9 that employs a thermal fixing method. If heat builds up inside the image forming apparatus 100, the temperature of the toner may rise and cause deterioration, and the deterioration of the parts of the image forming apparatus 100 may be accelerated. The ventilation hole 51 reduces these adverse effects by discharging the heat generated in the fixing unit 9 to the outside of the image forming apparatus 100.

[0102] Furthermore, in the fixing unit 9, water vapor is generated from the recording material P which is heated when passing through the fixing nip Nf. If water vapor is trapped inside the image forming apparatus 100, for example, condensation may occur on the conveying path CP, and water droplets may adhere to the recording material P, causing image defects or accelerating deterioration of parts of the image forming apparatus 100 over time (such as rusting of metal members). The ventilation hole portion 51 reduces these adverse effects by releasing the water vapor generated in the fixing unit 9 to the outside of the image forming apparatus 100. The ventilation hole portion 51 is located above the photosensitive drum 1 in the Z-axis direction.

[0103] Heat and water vapor tend to move upward. Therefore, at least a part of the ventilation hole portion 51 is disposed above the upper end position of the fixing nip Nf in the Z-axis direction (FIG. 1(a)). Also, at least a part of the discharge port 16s is disposed above the upper end position of the fixing nip Nf in the Z-axis direction (FIG. 1(a)). In other words, at least a part of the discharge port 16s and at least a part of the opening (ventilation hole portion 51) are located above the upper end position of the nip portion (fixing nip Nf) in the vertical direction.

[0104] The ventilation hole portion 51 in this embodiment is disposed at the upper end of the outer surface 14a of the rear door 14 that forms the exterior surface (second exterior surface) on the rear side of the image forming apparatus 100. In this embodiment, the lower end position of the ventilation hole portion 51 is higher than the upper end position of the fixing nip Nf in the Z axis direction. Also, in this embodiment, the lower end position of the discharge port 16s is higher than the upper end position of the fixing nip Nf in the Z axis direction. It is also possible to provide the ventilation hole portion 51 on the top surface of the housing 101.

[0105] The range in which the ventilation hole portion 51 is provided in the X-axis direction (width direction) is hereinafter referred to as the installation range of the ventilation hole portion 51. When the ventilation hole portion 51 includes a plurality of ventilation holes 51a (a plurality of openings) arranged at different positions in the X-axis direction as in this embodiment, the installation range of the ventilation hole portion 51 can be determined as follows. That is, the installation range of the ventilation hole portion 51 is the range in the X-axis direction from the ventilation hole 51a1 (first opening) on ​​the most one side (+X side) in the X-axis direction among the plurality of ventilation holes 51a to the ventilation hole 51a2 (second opening) on ​​the most other side (-X side) in the X-axis direction. As shown in FIG. 6, the installation range of the ventilation hole portion 51 overlaps with the position of the dotted line L in the X-axis direction. In other words, the dotted line L is located between one end (the position of the ventilation hole 51a1) and the other end (the position of the ventilation hole 51a2) of the installation range of the ventilation hole portion 51 in the X-axis direction. The position of the dotted line L in the X-axis direction coincides with the center position of the conveying path CP in the X-axis direction and the center position of the currency area of ​​the recording material P in the X-axis direction.

[0106] In the fixing unit 9, heat is generated in the area through which the recording material P passes, mainly in the X-axis direction (width direction), to fix the toner image. In addition, since the recording material P is heated in the fixing nip Nf, water vapor is generated from the recording material P, and water vapor is generated in the area through which the recording material P passes in the X-axis direction (width direction). Here, the recording material P having the largest size in the X-axis direction (width direction) among the recording materials P on which the image forming apparatus 100 can perform the image forming operation is called the maximum size recording material P. Therefore, it is preferable that the installation range of the ventilation hole portion 51 is a range that overlaps with the passage area of ​​the maximum size recording material P in the X-axis direction (width direction). In this embodiment, the installation range of the ventilation hole portion 51 overlaps with the passage area of ​​the recording material P of the LTR size, which is the maximum paper passing width of the image forming apparatus 100. This allows the heat and water vapor generated in the fixing unit 9 to be efficiently released to the outside of the image forming apparatus 100.

[0107] In the X-axis direction (width direction), the length of the installation range of the ventilation hole section 51 (the length from one end to the other end of the installation range of the ventilation hole section 51) is preferably 50% or more of the length of the conveying path CP, and more preferably 70% or more. In addition, in the X-axis direction, the length of the installation range of the ventilation hole section 51 is preferably 50% or more of the length of the maximum size recording material P, and more preferably 70% or more. In addition, in the X-axis direction, the installation range of the ventilation hole section 51 preferably includes the maximum width (effective printing area) in which the image forming section 10 can form an image. In this embodiment, in the X-axis direction (width direction), the length of the installation range of the ventilation hole section 51 is 90% or more of the maximum size recording material P. For the reasons described above, in the fixing section 9, heat and water vapor are mainly generated inside the passing area of ​​the maximum size recording material P, particularly inside the effective printing area of ​​the maximum size recording material P. Therefore, by providing the ventilation hole section 51 in an area that encompasses a predetermined percentage or more of the effective printing area for the maximum size recording material P, the heat and water vapor generated in the fixing section 9 can be more efficiently released to the outside of the image forming apparatus 100.

[0108] Here, the recording material P having the smallest size in the X-axis direction (width direction) among the recording materials P on which the image forming apparatus 100 can perform an image forming operation is referred to as the minimum size recording material P. It is preferable that the installation range of the ventilation hole section 51 encompasses at least the passing area of ​​the minimum size recording material P. In other words, the length of the installation range of the ventilation hole section 51 in the X-axis direction (width direction) is longer than the length of the minimum size recording material P. This is because, regardless of the size of the recording material P, at least a part of the recording material P on which an image is formed by the image forming apparatus 100 always passes through the passing area of ​​the minimum size recording material P, and therefore water vapor is likely to be generated in the passing area of ​​the minimum size recording material P.

[0109] The higher the air permeability of the ventilation hole portion 51, the larger the amount of heat and water vapor that can be released from the ventilation hole portion 51, so that the adverse effects of heat and water vapor being trapped can be more reliably reduced. However, if the air permeability of the ventilation hole portion 51 is too high, for example, when wind blows in from the front side (+Y side) of the image forming apparatus 100, the wind speed in the path from the discharge port 16s through the conveying path CP and out of the ventilation hole portion 51 becomes fast, and sand and dust are likely to enter. Therefore, the air permeability of the ventilation hole portion 51 may be set in consideration of the balance between the amount of heat and water vapor that can be released from the ventilation hole portion 51 and the suppression of the intrusion of sand and dust from the discharge port 16s. Specifically, the number of ventilation holes 51a of the ventilation hole portion 51, the opening area of ​​each ventilation hole 51a, the total opening area of ​​all ventilation holes 51a provided in the ventilation hole portion 51a, etc. may be set in consideration of the above balance.

[0110] 6, in this embodiment, each ventilation hole 51a is circular and has a diameter of, for example, 5 mm, although the shape and size of the ventilation hole 51a can be changed.

[0111] In this embodiment, the ventilation hole section 51 is arranged in three rows in the Z axis direction, each row having 19 ventilation holes 51a aligned in the X axis direction (width direction). In other words, the ventilation hole section 51 includes a total of 57 ventilation holes 51a. The width of the range in the X axis direction (width direction) in which the ventilation hole section 51 is provided is 209 mm, which is wider than the width (206 mm) of the effective printing area for the maximum size (LTR size) recording material P.

[0112] The ventilation hole 51a is disposed in an area between multiple rib shapes 42a of the double-sided rib 42 of the rear door 14 in the X-axis direction (width direction). The ventilation hole 51a penetrates from the outer surface 14a to the inner surface 14b of the rear door 14 (FIG. 5).

[0113] (filter) The filter 50 included in the image forming apparatus 100 of this embodiment will be described. As shown in Fig. 5 and Fig. 6, the image forming apparatus 100 includes a filter 50 arranged to cover the ventilation hole portion 51. More specifically, at least one filter 50 is attached to the inner surface 14b of the rear door 14, covering each of the ventilation holes 51a of the ventilation hole portion 51. By providing the filter 50 covering the ventilation hole portion 51, it is possible to suppress the occurrence of image defects caused by sand and dust that has entered the image forming apparatus 100 through the ventilation hole 51a.

[0114] In this disclosure, foreign matter that may enter the inside of image forming apparatus 100 on an air current blown from the outside to the inside of image forming apparatus 100 is collectively referred to as "sand dust." Therefore, "sand dust" may be particles other than sand grains (for example, particles derived from plastic material or wood), or may include multiple types of particles.

[0115] If the filter 50 is not provided in the ventilation hole portion 51, sand dust that has entered the inside of the image forming apparatus 100 through the ventilation hole 51a may move inside the image forming apparatus 100 and adhere to the photosensitive drum 1. In particular, if sand dust larger than the thickness (48 μm in this embodiment) of the surface layer 1b of the photosensitive drum 1 adheres to the photosensitive drum 1, the sand dust may penetrate and scratch the surface layer 1b when passing through the contact portion between the photosensitive drum 1 and another member.

[0116] For example, there is a possibility that the surface layer 1b may be scratched by sand dust being strongly pressed into the surface layer 1b of the photosensitive drum 1 at the contact portion (charging nip) between the charging roller 2 and the photosensitive drum 1. As a result, in the image formed on the recording material P, black dot-like image defects (called black dot images) occur at positions corresponding to the scratches on the surface layer 1b of the photosensitive drum 1.

[0117] More specifically, when scratches penetrating the surface layer 1b are caused by sand dust, the functions of the charge transport layer 1b3, which holds the surface charge applied to the surface 1s in the charging process, and the undercoat layer 1b1 (intermediate layer), which limits the charge injection from the substrate 1a to the photosensitive layer, may be impaired. In this case, the photosensitive drum 1 cannot hold the surface charge applied in the charging process at the scratched area, and the surface potential of the photosensitive drum 1 approaches the potential of the substrate 1a (approaches the ground potential) due to the charge injection from the substrate 1a. Then, regardless of the presence or absence of exposure, a toner image is developed at the scratched area, and it becomes apparent as a black dot image.

[0118] An example of a black dot image is shown in Figure 7. As shown in the figure, black dots appear periodically at intervals corresponding to the outer circumferential length of the photosensitive drum 1, depending on the position of the scratch on the surface layer 1b of the photosensitive drum 1. For one scratch on the photosensitive drum 1, a black dot image repeatedly appears in the transport direction of the recording material P at a period corresponding to the outer circumferential length of the photosensitive drum 1. A row of black dot images that appear periodically in this way is defined as one black dot image. Furthermore, as the number of scratches on the surface layer 1b of the photosensitive drum 1 increases, the number of black dot images also increases.

[0119] The filter 50 is made of a material that has air and moisture permeability and is highly resistant to heat and moisture. In this embodiment, the filter 50 is made of a sheet material of Moltoprene (registered trademark) SM-55, which is a urethane foam manufactured by Inoac Corporation.

[0120] In this embodiment, the urethane foam sheet material (original sheet) is pressed while being heated, and compressed in the thickness direction to be used as the filter 50. The thickness of the original sheet is 2 mm, and the thickness of the filter 50 is 1 mm.

[0121] The thickness of the filter 50 in this embodiment is set so as not to come into contact with the recording material P transported through the double-sided transport path CP2. That is, as shown in Fig. 5, at each position within the range where the filter 50 is provided in the Z-axis direction, the thickness of the filter 50 is smaller than the protrusion amount of the rib shape 42a of the double-sided rib 42 from the inner surface 14b of the rear door 14. In other words, the thickness of the filter 50 is smaller than the minimum value H1 of the protrusion height of the double-sided rib 42 from the inner surface 14b of the rear door 14. The minimum value H1 of the protrusion amount of the rib shape 42a is, for example, 3.5 mm, and the thickness of the filter 50 is 1 mm.

[0122] If the filter 50 comes into contact with the recording material P being transported through the double-sided transport path CP2, the recording material P may become skewed or jam, or the recording material P may become contaminated by water droplets or foreign matter adhering to the filter 50. By making the thickness of the filter 50 smaller than the protruding height of the double-sided ribs 42, the possibility of such problems occurring can be reduced.

[0123] The filter 50 is attached to the inner surface 14b of the rear door 14 with, for example, double-sided tape or adhesive. When the filter 50 is attached to the inner surface 14b with the double-sided tape, it is preferable that the holes formed in the double-sided tape overlap with the ventilation hole portion 51 in order to prevent the double-sided tape from blocking the ventilation hole portion 51. As shown in FIG. 6, in this embodiment, the central filter 50 of the nine filters 50 covers more ventilation holes 51a than the other eight filters 50 and has a wider width in the X-axis direction than the other eight filters 50. Therefore, by making the length of the central filter 50 in the Z-axis direction longer than the other eight filters 50, it is possible to reduce the possibility of the central filter 50 being attached in an incorrect position (misassembly). In other words, when a plurality of filters 50 are arranged and the length of some of the filters 50 in a predetermined direction is different from that of the other filters 50, it is possible to reduce the possibility of misassembly by making the length of the part of the filters 50 in a direction perpendicular to the predetermined direction different from that of the other filters 50. In this manner, the plurality of filters 50 may include a filter 50 having a first shape and a filter 50 having a second shape that is different from the first shape.

[0124] 8(a) and (b) show conceptual diagrams of the filter 50 of this embodiment. FIG. 8(a) shows an original sheet 50S (Moltoprene SM-55) before pressing, and FIG. 8(b) shows the pressed filter 50. In FIG. 8(a) and (b), the shaded areas represent the polyurethane matrix, and the white circles represent the cells CL (air bubbles). Note that in FIG. 8(a) and (b), the cells CL are illustrated as independent circles for the sake of explanation, but the actual filter 50 has a continuous cell structure (open cell structure). The thickness direction TD of the filter 50 is perpendicular to the surface of the filter 50 that is attached to the inner surface 14b of the rear door 14.

[0125] As shown in Fig. 8(a), the raw sheet 50S of the filter 50 has an average cell diameter D of 200 µm. In other words, the diameter of each cell CL in the raw sheet 50S is taken as the cell diameter, and the average cell diameter is 200 µm. The thickness of the raw sheet 50S is taken as 2t.

[0126] As shown in FIG. 8(b), the filter 50 is produced by pressing the original sheet 50S to reduce its thickness to half (2t→t). The pressing process causes the urethane foam structure to shrink almost uniformly in the thickness direction TD. Therefore, the average cell diameter in the thickness direction TD of the filter 50 is 100 μm, half (1 / 2·D) of the original sheet 50S. In this embodiment, the thickness t is 1 mm, so that about 1 mm / 100 μm=10 cells CL are arranged in the thickness direction TD in the filter 50. Hereinafter, the ratio (β / γ) of the thickness (β) of the filter 50 to the average cell diameter (γ) in the thickness direction TD of the filter 50 is referred to as the "cell number in the thickness direction TD of the filter 50."

[0127] Even if the raw sheet 50S is press-processed, there is no expansion or contraction in the direction perpendicular to the thickness direction TD (hereinafter referred to as the horizontal direction), or the expansion or contraction is substantially negligible. Therefore, the average cell diameter D of the filter 50 in the horizontal direction is 200 μm, the same as that of the raw sheet 50S.

[0128] The cell diameter is determined as follows. The filter 50 or the raw sheet 50S is observed using an optical microscope (Keyence VHX-5000). When determining the cell diameter in the horizontal direction, the surface of the filter 50 or the raw sheet 50S is observed from the thickness direction TD as shown in FIG. 8(b). Using image processing software, circles are drawn so as to overlap with each cell, and the diameter of the circle (so-called circle equivalent diameter) is determined as the cell diameter of the cell. Within a 1 mm square field of view (1 mm 2 ) and observe five locations, and the average of the cell diameters of all the cells within the observation area is regarded as the average cell diameter in the horizontal direction of the filter 50 or original sheet 50S.

[0129] The cell diameter in the thickness direction TD of the original sheet 50S is measured by cutting the original sheet 50S with a razor along the thickness direction TD and observing the cross section. Using image processing software, a circle is drawn so that it overlaps with each cell, and the diameter of the circle is taken as the cell diameter of the cell. 2 ) and observe five locations, and the average of the cell diameters of all the cells within the observation area is regarded as the average of the cell diameters in the thickness direction TD of the original sheet 50S.

[0130] In the case of a filter 50 obtained by pressing an original sheet 50S, the cell diameter in the thickness direction TD of the filter 50 is calculated by multiplying the cell diameter in the thickness direction TD of the original sheet 50S by the pressing ratio. Here, the pressing ratio is the ratio (t2 / t1) of the thickness (t2) of the filter 50 after pressing to the thickness (t1) of the original sheet 50S before pressing. In this embodiment, the pressing ratio is 1 / 2.

[0131] The relationship between the cell diameter of the filter 50 and the particle diameter of particles that can pass through the filter 50 will be described. The smaller the cell diameter in the horizontal direction of the filter 50, the more difficult it is for large particles to pass through the filter 50. Also, the greater the number of cells in the thickness direction TD of the filter 50, the greater the number of cells that a particle must pass through to pass through the filter 50, making it more difficult for large particles to pass through.

[0132] Therefore, the maximum particle size of particles that can pass through filter 50 can be considered to be proportional to the average cell diameter (α) in the horizontal direction of filter 50, and inversely proportional to the number of cells (β / γ) in the thickness direction TD of filter 50. In other words, the maximum particle size of particles that can pass through filter 50 can be simply estimated by the following formula (1). Maximum particle size=α / (β / γ)...Equation (1)

[0133] In this embodiment, (average cell diameter in the horizontal direction of the filter 50) / (number of cells in the thickness direction TD of the filter 50)=200 μm / 10 cells=about 20 μm. In other words, it can be estimated that particles larger than about 20 μm cannot pass through the filter 50. In this way, it is preferable that the maximum particle diameter of particles that can pass through the filter 50 estimated by the formula (1) is smaller than the thickness of the surface layer portion 1b of the photosensitive drum 1.

[0134] In other words, when a foamed plastic such as urethane foam is used as the filter 50, the average cell diameter of the foamed plastic in a plane perpendicular to the thickness direction TD of the filter 50 is defined as α (μm), the thickness of the filter 50 is defined as β (μm), the average cell diameter of the foamed plastic in the thickness direction TD of the filter 50 is defined as γ (μm), and the thickness from the outer peripheral surface of the base 1a of the photosensitive drum 1 to the surface 1s of the photosensitive drum 1 is defined as δ (μm), α / (β / γ)<δ It is preferable that:

[0135] In a room in which the image forming apparatus 100 is installed, an air flow may occur through a space communicating with the exhaust port 16s and the ventilation hole portion 51 due to an air conditioning system or a ventilation system. If the image forming apparatus 100 is used in an environment in which there is a large amount of sand and dust in the air and the air flow through the space communicating with the exhaust port 16s and the ventilation hole portion 51 is strong, the sand and dust may enter the image forming apparatus 100 together with the external air. Furthermore, if the photosensitive drum 1 is damaged by the sand and dust that has entered the image forming apparatus 100 and an image defect occurs, these parts will need to be replaced.

[0136] In this embodiment, the filter 50, the maximum particle size of which can pass through the filter 50 is smaller than the thickness δ of the surface layer 1b of the photosensitive drum 1, is provided in the ventilation hole portion 51. This makes it possible to reduce the possibility that large sand particles, which cause black dot images, will enter the image forming apparatus 100 and adhere to the photosensitive drum 1.

[0137] (Dustproof performance of filter) As described above, the possibility of black dot images occurring can be reduced if the maximum particle size that can pass through the filter 50 is smaller than the thickness of the surface layer 1b of the photosensitive drum 1. Therefore, a method for verifying the dustproof performance of the filter 50 according to this embodiment will be described with reference to FIGS.

[0138] As shown in FIG. 9(a), the filter 50 was placed on a black acrylic resin plate 400, and 0.1 g of quartz powder Q was sprinkled on top. The quartz powder Q was a 1:1 mixture of quartz powder No. 7 and No. 8 manufactured by Nakagawa Kofun Co., Ltd. The "No. 7" and "No. 8" are grades that indicate the fineness of the particles, and the larger the number, the finer the particles. The particle size distribution of the quartz powder Q used in the experiment was about several tens of μm to 150 μm. In other words, the quartz powder Q includes both particles with a particle size larger than the thickness of the surface layer 1b of the photosensitive drum 1 and particles with a particle size equal to or smaller than the thickness of the surface layer 1b of the photosensitive drum 1.

[0139] After the quartz powder Q was spread, the acrylic resin plate 400 was tapped with a finger 20 to 30 times to apply vibration, and then the filter 50 was gently removed from the acrylic resin plate 400. As shown in FIG. 9(b), the part of the acrylic resin plate 400 where the filter 50 was placed was observed with an optical microscope to observe the size of the particles that had passed through the filter 50. The optical microscope used was a Keyence VHX-5000, with a magnification of 300 times and a field of view of 1 mm square (1 mm 2 ) in 5 places (i.e., 5 mm in total 2 Observations were conducted on the 100 mm (observation area) of the specimen.

[0140] When the equivalent circle diameter Xq (μm) of the particles was measured, most of them were less than 20 μm, and the maximum was about 20 μm. In other words, the maximum particle size (about 20 μm) of the quartz powder Q that could pass through the filter 50 of this embodiment was sufficiently smaller than the thickness of the surface layer 1b of the photosensitive drum 1. In addition, the result that the maximum particle size was about 20 μm is generally consistent with the estimation result using the above-mentioned formula (1).

[0141] In this disclosure, the "maximum particle size that can pass through the filter" is defined as a particle size that is less than 5 mm in total according to the above verification method. 2 This refers to the maximum value of the equivalent circular diameter Xq of quartz powder Q observed within the observation area.

[0142] It is possible to subject all particles that pass through the filter to a particle size distribution measuring instrument, but during the measurement sample preparation and measurement process, the size of a foreign object different from the intended measurement target (particles that pass through the filter) may be erroneously detected as the maximum particle size. Examples of foreign objects include dust other than quartz powder Q, and air bubbles when using a wet method particle size distribution measuring instrument. Therefore, in this disclosure, the maximum particle size is defined as above.

[0143] The test method for evaluating the water droplet resistance and sand dust resistance performed on the image forming apparatus 100 described above and the results thereof will be described.

[0144] (Water drop resistance test) As an accelerated test to evaluate the water droplet resistance of the image forming apparatus 100, paper that had been left for 48 hours in an environment of room temperature 32.5°C and humidity 80% was set in the feeding section 6, and double-sided printing was performed on 10 sheets of paper to check whether traces of water droplets were visible on the image. This test was started after a sufficient amount of time had passed since the previous image forming operation ended, when the internal temperature of the image forming apparatus 100 had become substantially equal to room temperature. This is because condensation is more likely to occur after the temperature has returned to room temperature than when the inside of the image forming apparatus 100 is warm. The paper used in the test was Canon CS-680. A halftone image with a density of 25% was formed on both sides of the paper over the entire effective printing area.

[0145] During the double-sided printing process, if water droplets accumulate somewhere on the double-sided transport path CP2, the paper passing through the double-sided transport path CP2 comes into contact with the water droplets and becomes wet. Then, when the image is transferred from the photosensitive drum 1 to the second side of the paper, the surface area of ​​the photosensitive drum 1 that comes into contact with the wet part of the paper adsorbs moisture. The surface area of ​​the photosensitive drum 1 that has adsorbed moisture is more strongly charged in the charging section than the surrounding area. In the surface area that is strongly charged in the charging section, the density of the toner image formed through the exposure and development processes becomes lighter than the surrounding area. As a result, in the halftone image transferred to the paper, an image defect (called a water droplet mark or a white spot image) occurs in which the image is white at a position corresponding to the surface area of ​​the photosensitive drum 1 that comes into contact with the wet part of the paper.

[0146] An example of water droplet marks is shown in Figure 10. Water droplet marks are image defects that occur periodically at intervals equivalent to the outer circumferential length of the photosensitive drum 1. If the water vapor generated in the fixing unit 9 can be efficiently released to the outside of the image forming apparatus 100, water droplet marks are less likely to occur.

[0147] (Dust resistance test) The method of the sand and dust resistance test will be described. First, as shown in FIG. 11, the fan 300 blows wind from the rear side (-Y side) of the image forming apparatus 100 while supplying quartz powder Q as sand and dust. The wind speed was set so that the wind was blown at a speed of 1 m / sec against the outer surface 14a of the rear door 14 at the position of the ventilation hole 51. The quartz powder Q was a mixed particle of quartz powder No. 7 and No. 8 manufactured by Nakagawa Kofun Co., Ltd. 1 g of quartz powder Q was placed on a medicine wrapping paper and supplied little by little over 30 seconds. After that, the image forming apparatus 100 was moved to an environment with a room temperature of 32.5° C. and a humidity of 80%, and a durability test was started. In the durability test, 10,000 sheets of A4 paper were passed through. Then, the number of black dot images generated on the output paper was confirmed. The results are shown in Table 1.

[0148] [Table 1]

[0149] In Example 1, slight water droplet marks were observed on the second side of the second sheet of paper out of 10 sheets in the water resistance suitability test, but no water droplet marks were observed on the other sheets. This means that the paper has sufficient water droplet resistance for practical use. In other words, according to this embodiment, even if the filter 50 is provided in the ventilation hole portion 51, the function of the ventilation hole portion 51 to release heat and steam generated in the fixing unit 9 to the outside of the image forming apparatus 100 can be maintained. In other words, by providing the filter 50 in the ventilation hole portion 51, it is possible to suppress the intrusion of sand and dust into the image forming apparatus 100 through the exhaust port 16s and the ventilation hole portion 51 while maintaining the function of the ventilation hole portion 51 to release heat and steam to the outside of the image forming apparatus 100.

[0150] Moreover, in Example 1, no black dot images were observed in the sand and dust resistance test. In this example, the maximum particle size that can pass through the filter 50 is about 20 μm, which is smaller than the thickness of the surface layer 1b of the photosensitive drum 1. Therefore, by providing the filter 50 in the ventilation hole portion 51, it is possible to prevent the quartz powder Q, which has a particle size larger than the thickness of the surface layer 1b of the photosensitive drum 1, from entering the inside of the image forming apparatus 100 through the ventilation hole portion 51. As a result, it is considered that the occurrence of black dot images caused by the large quartz powder Q was prevented.

[0151] Comparative Example 1 As Comparative Example 1, an image forming apparatus was prepared in which the filter 50 was not provided in the ventilation hole portion 51. Except for the absence of the filter 50, the image forming apparatus of Comparative Example 1 has the same configuration as the image forming apparatus 100 of Example 1.

[0152] As shown in Table 1, in Comparative Example 1, the water droplet resistance was comparable to that of Example 1, but eight black dot images were observed in the sand and dust resistance test. In Comparative Example 1, the filter 50 is not provided in the ventilation hole portion 51, so that the quartz powder Q having a particle size larger than the thickness of the surface layer portion 1b of the photosensitive drum 1 can enter the inside of the image forming apparatus 100 through the ventilation hole portion 51. As a result, it is considered that the black dot images were caused by the large quartz powder Q.

[0153] Comparative Example 2 An image forming apparatus in which the ventilation hole portion 51 was blocked with tape was prepared as Comparative Example 2. Except for blocking the ventilation hole portion 51 with tape, the image forming apparatus of Comparative Example 2 has the same configuration as the image forming apparatus 100 of Example 1. The tape used was a heat-resistant polyimide tape manufactured by 3M Company.

[0154] As shown in Table 1, in Comparative Example 2, in the waterproof suitability test, clear water droplet marks were observed on the second side of the sixth sheet out of ten sheets. On the other hand, in the sand and dust resistance test, no black dot images were observed. The reason why the waterproof suitability was inferior to that of Example 1 is considered to be that the water vapor generated in the fixing unit 9 was trapped inside the image forming apparatus due to the ventilation hole portion 51 being blocked with tape, and a lot of condensation occurred on the double-sided conveying path CP2. On the other hand, it is considered that the intrusion of the quartz powder Q through the ventilation hole portion 51 was almost completely prevented by blocking the ventilation hole portion 51 with tape, and therefore no black dot images caused by the quartz powder Q were generated.

[0155] Comparative Example 3 As Comparative Example 3, an image forming apparatus was prepared in which a non-pressed urethane foam (moltoprene) having a thickness of 1 mm was used as the filter 50. Except for the filter 50, the image forming apparatus of Comparative Example 3 has the same configuration as the image forming apparatus 100 of Example 1.

[0156] When the above-mentioned dustproof performance test (FIGS. 9(a) and 9(b)) was performed on the filter 50 used in Comparative Example 3, particles with a maximum diameter of 110 μm passed through the filter 50. In other words, in Comparative Example 3, the maximum diameter of particles that can pass through the filter 50 was larger than the thickness of the surface layer portion 1b of the photosensitive drum 1.

[0157] The cell diameter of the moltoprene used in Comparative Example 3 is 300 μm. Therefore, the number of cells in the thickness direction TD of the filter 50 is 1 mm / 300 μm=3.3. The maximum particle diameter of particles that can pass through the filter 50 is estimated using the above-mentioned formula (1) as follows: (cell diameter in the horizontal direction of the filter 50) / (number of cells in the thickness direction TD of the filter 50)=300 μm / 3.3 ≈100 μm. This estimated value is close to the result of the dustproof performance test (110 μm).

[0158] As shown in Table 1, in Comparative Example 3, the water droplet resistance was comparable to that of Example 1. It is believed that there was no problem with the breathability and moisture permeability of the filter 50 of Comparative Example 3. On the other hand, five black dot images were observed in the sand dust resistance test. Although the filter 50 is provided in the ventilation hole portion 51 in Comparative Example 3, the dustproof performance is lower than that of Example 1, and the large quartz powder Q is more likely to enter the inside of the image forming apparatus 100 than the filter 50 of Example 1. As a result, it is believed that the quartz powder Q having a particle size larger than the thickness of the surface layer portion 1b of the photosensitive drum 1 enters the inside of the image forming apparatus 100 through the ventilation hole portion 51, and black dot images caused by the large quartz powder Q are generated.

[0159] Example 2 As Example 2, an image forming apparatus was prepared in which non-pressed urethane foam (moltoprene) having a thickness of 2 mm was used as the filter 50. Except for the filter 50, the image forming apparatus of Example 2 has the same configuration as the image forming apparatus 100 of Example 1.

[0160] When the above-mentioned dustproof performance test was performed on the filter 50 used in Example 2, particles having a maximum diameter of 20 μm passed through the filter 50. In other words, the dustproof performance of the filter 50 of Example 2 was equivalent to that of the filter 50 of Example 1.

[0161] The cell diameter of the moltoprene used in Example 2 is 200 μm. Therefore, the number of cells in the thickness direction TD of the filter 50 is 2 mm / 200 μm=10. The maximum particle diameter of particles that can pass through the filter 50 is estimated using the above-mentioned formula (1) as follows: (cell diameter in the horizontal direction of the filter 50) / (number of cells in the thickness direction TD of the filter 50)=200 μm / 10 ≈20 μm. This estimated value is close to the result of the dustproof performance test (20 μm).

[0162] As shown in Table 1, in Example 2, the results of both water droplet resistance and dust resistance were equivalent to those of Example 1. In other words, the filter 50 of Example 2 had good air permeability and moisture permeability, and was able to prevent large quartz powder Q from entering the image forming apparatus 100 through the ventilation hole portion 51. In other words, whether the filter 50 was pressed or not had no direct effect on the performance of water droplet resistance and dust resistance.

[0163] Example 3 As Example 3, an image forming apparatus was prepared in which a stainless steel plain weave mesh was used as the filter 50. Except for the filter 50, the image forming apparatus of Example 3 has the same configuration as the image forming apparatus 100 of Example 1.

[0164] The mesh has a fineness of 200 mesh, a wire thickness of 50 μm, and an aperture (the distance between the wires) of 77 μm. When a dustproof performance test was carried out, the maximum particle size that could pass through the filter 50 of Example 3 was about 40 μm. This is smaller than the thickness of the surface layer 1b of the photosensitive drum 1. The reason why the maximum particle size is smaller than the mesh aperture is that when particles try to pass through, they get caught on each other or adhere to the wires, making it difficult for even particles that are slightly smaller than the mesh aperture to pass through the gaps.

[0165] As shown in Table 1, in Example 3, the results of both the water droplet resistance and the sand dust resistance were equivalent to those of Example 1. In other words, the mesh filter 50 of Example 3 had good air permeability and moisture permeability, and was able to prevent large quartz powder Q from entering the image forming apparatus 100 through the ventilation hole portion 51.

[0166] (summary) Thus, in the dustproof performance test, good results were obtained in terms of sand and dust resistance when using a filter 50 in which the maximum particle size that can pass through the filter 50 is smaller than the thickness of the surface layer 1b of the photosensitive drum 1. In other words, it can be seen that a configuration in which the maximum particle size that can pass through the filter 50 is smaller than the thickness of the surface layer of the photosensitive body makes it possible to reduce the adverse effects caused by sand and dust.

[0167] Also, good results were obtained in terms of water droplet resistance except for Comparative Example 2 in which the ventilation hole portion 51 was blocked with tape. Therefore, it is understood that by disposing the filter 50 in the ventilation hole portion 51 and using the filter 50 in which the maximum particle size that can pass through the filter 50 is smaller than the thickness of the surface layer portion 1b of the photosensitive drum 1, it is possible to suppress image defects caused by sand dust while suppressing the occurrence of condensation.

[0168] Note that no difference was observed in water droplet resistance and sand dust resistance between Example 1 and Example 2, but the filter 50 of Example 1 is thinner than the filter 50 of Example 2. Therefore, the filter 50 of Example 1 is less likely to come into contact with the recording material P transported on the transport path CP (double-sided transport path CP2), and has the advantage of realizing more stable transport of the recording material. However, the presence or absence of press processing can be selected taking into consideration the ease of attaching the filter 50, the cost of press processing, and the like.

[0169] <<Variation>> The material of the filter 50 is not limited to the urethane foam or stainless steel plain weave mesh mentioned in the embodiment. The material of the filter 50 may be a foamed sponge material formed from an ester-based or ether-based urethane material other than moltoprene, an olefin-based sponge material, a melamine-based sponge material, or other foamed sponge material. That is, the material of the filter 50 may be an open-cell foamed plastic (synthetic resin foam). The material of the filter 50 may be a nonwoven fabric made of fibers such as cotton, polyethersulfone (PES), PET, or glass. The material of the filter 50 may be filter paper (paper filter) or a metal mesh with a honeycomb structure. Regardless of the material of the filter 50, by using a filter 50 in which the maximum particle size of particles that can pass through the filter 50 is smaller than the thickness of the surface layer portion 1b of the photosensitive drum 1, the same advantages as those of the above-mentioned embodiment can be obtained.

[0170] Moreover, the ventilation hole section 51 in the above-described embodiment is one example of an opening section provided in the housing 101 of the image forming apparatus 100. The position of the opening section (ventilation hole section 51) and the shape, size, number and arrangement of the openings (ventilation holes 51a) provided in the opening section can be changed as appropriate according to the specific configuration of the image forming apparatus 100. For example, the ventilation hole 51a may be a long and narrow hole extending in the X-axis direction (width direction of the recording material P) over a range that includes the effective print area for the maximum size recording material.

[0171] In the above embodiment, the filter 50 is attached to the inner surface 14b of the rear door 14, which is the surface on the inside of the housing 101, but the filter 50 may be attached to the outer surface 14a of the rear door 14. Even in this case, the filter 50 can reduce the intrusion of sand and dust into the image forming apparatus 100 through the ventilation hole portion 51.

[0172] In addition, in the above-described embodiment, an example of an adverse effect caused by sand and dust particles that have entered the image forming apparatus 100 is an image defect (black dot image) caused by scratches on the surface layer 1b of the photosensitive drum 1, but sand and dust particles may cause other adverse effects.

[0173] For example, in the case of the image forming apparatus 100 equipped with the fixing unit 9 of a film heating type that uses a cylindrical film (fixing film 112) as a heating member (fixing member), sand dust may damage the fixing film 112. In other words, when sand dust particles with a large particle size reach the fixing unit 9, the fixing film 112 may be damaged.

[0174] Therefore, it is preferable to use a filter 50 in which the maximum particle size of particles that can pass through the filter 50 is smaller than the thickness of the fixing film 112. In the above-mentioned embodiment 1, the thickness of the fixing film 112 is at least 70 μm (60 μm thickness of the base layer+10 μm thickness of the release layer), so the filter 50 described in embodiments 1 to 3 can be suitably used. This can reduce the possibility that the fixing film 112 will be damaged by sand dust with a large particle size.

[0175] Furthermore, when a foamed plastic such as urethane foam is used as the filter 50, it is preferable that the thickness of the fixing film 112 is δ (μm) and the relationship α / (β / γ)<δ is satisfied under the above-mentioned definitions of α, β, and γ. This can reduce the possibility that large grain size sand dust will accelerate the tearing of the fixing film 112.

[0176] Another problem caused by sand dust particles is that sand dust can cause image defects in an image forming apparatus equipped with an intermediate transfer belt. An image forming apparatus equipped with an intermediate transfer belt is an image forming apparatus that uses a method (intermediate transfer method) in which a toner image is primarily transferred from a photosensitive drum 1 to the intermediate transfer belt, and then secondarily transferred from the intermediate transfer belt to a recording material P at a secondary transfer section, thereby forming an image on the recording material P.

[0177] The intermediate transfer belt has a base layer that provides mechanical strength and a surface layer that serves as a toner image carrying surface, and may have an elastic layer between the base layer and the surface layer.

[0178] When sand and dust particles enter the interior of an image forming apparatus equipped with an intermediate transfer belt, the sand and dust particles are strongly pressed against the intermediate transfer belt at the contact portion between the intermediate transfer belt and other members, and the sand and dust particles may penetrate and scratch the surface layer of the intermediate transfer belt. An example of the "other members" is a cleaning blade that is pressed against the surface (outer peripheral surface) of the intermediate transfer belt to remove residual toner that has not been transferred to the recording material P in the secondary transfer section from the intermediate transfer belt. When the surface layer of the intermediate transfer belt is scratched, unevenness is formed on the surface of the intermediate transfer belt, which may disturb the toner image carried on the surface or reduce the efficiency of the primary transfer and secondary transfer, resulting in a defective image.

[0179] Therefore, it is preferable to use a filter 50 in which the maximum particle size that can pass through the filter 50 is smaller than the thickness of the surface layer of the intermediate transfer belt. This can reduce the occurrence of image defects caused by large particles of sand dust damaging the surface layer of the intermediate transfer belt.

[0180] Furthermore, when using foamed plastic such as urethane foam as the filter 50, it is preferable that the thickness of the surface layer of the intermediate transfer belt is δ (μm) and the relationship α / (β / γ)<δ is satisfied under the above definitions of α, β, and γ. This can reduce the occurrence of image defects caused by large grain size sand dust damaging the surface layer of the intermediate transfer belt.

[0181] In each of the above-described embodiments, the space inside the housing 101 that communicates with the ventilation hole portion 51 functions as a transport path for the recording material P. However, when the present invention is applied to an image forming apparatus, the space inside the housing 101 that communicates with the ventilation hole portion 51 does not need to function as a transport path.

[0182] Summary of the Disclosure The present disclosure includes at least the following configurations.

[0183] (Configuration 1) an image forming section having a photoconductor and forming a toner image on a recording material by using the photoconductor; a fixing section that forms a nip section that holds the recording material and heats the toner image while conveying the recording material through the nip section to fix the toner image onto the recording material; a housing that houses the image forming unit and the fixing unit; An image forming apparatus comprising: the housing has an opening communicating between an outside and an inside of the housing and disposed above the nip portion in a vertical direction; The image forming apparatus further includes a filter that covers the opening. the photoreceptor has a conductive substrate and a surface layer formed on an outer periphery of the conductive substrate; The distance from the outer peripheral surface of the substrate to the surface of the photoreceptor is defined as the thickness of the surface layer portion, The maximum particle size of particles that can pass through the filter is smaller than the thickness of the surface layer. 1. An image forming apparatus comprising:

[0184] (Configuration 2) The filter is an open-cell foamed plastic. 2. The image forming apparatus according to claim 1,

[0185] (Configuration 3) The average cell diameter of the foamed plastic in a plane perpendicular to the thickness direction of the filter is α (μm), the thickness of the filter is β (μm), the average cell diameter of the foamed plastic in the thickness direction of the filter is γ (μm), and the thickness of the surface layer is δ (μm), α / (β / γ)<δ, 3. The image forming apparatus according to claim 2,

[0186] (Configuration 4) The filter is a metal mesh. 2. The image forming apparatus according to claim 1,

[0187] (Configuration 5) the surface layer portion includes a photosensitive layer that generates charges when irradiated with light to attenuate the potential of the surface of the photoreceptor, and an intermediate layer provided between the substrate and the photosensitive layer, the intermediate layer limiting charge injection from the substrate to the photosensitive layer; 5. The image forming apparatus according to any one of configurations 1 to 4.

[0188] (Configuration 6) the housing includes an exterior member having an outer surface forming an exterior surface of the housing and an inner surface opposite to the outer surface, and an opposing portion opposing the inner surface with a gap therebetween; The opening is provided in the exterior member and communicates a space connected to the gap with the outside of the housing. 6. The image forming apparatus according to any one of configurations 1 to 5.

[0189] (Configuration 7) The filter is attached to the inner surface of the exterior member. 7. The image forming apparatus according to configuration 6,

[0190] (Configuration 8) the exterior member has a rib shape protruding from the inner surface in a direction approaching the facing portion, the filter is attached to the inner surface at a position different from the rib shape; At each position within the range in which the filter is provided in the vertical direction, the thickness of the filter is smaller than the protrusion amount of the rib shape relative to the inner surface. 8. The image forming apparatus according to claim 7,

[0191] (Configuration 9) an image forming unit that forms a toner image on a recording material; a fixing section including a cylindrical film and a heating means for heating the film, forming a nip section for holding the recording material therebetween, and heating the toner image with the film to fix the toner image on the recording material; a housing that houses the image forming unit and the fixing unit; An image forming apparatus comprising: the housing has an opening communicating between an outside and an inside of the housing and disposed above the nip portion in a vertical direction; The image forming apparatus further includes a filter that covers the opening. The maximum particle size that can pass through the filter is smaller than the thickness of the film. 1. An image forming apparatus comprising:

[0192] (Configuration 10) an image forming section including a photoconductor and an intermediate transfer belt, which performs primary transfer of a toner image formed on the photoconductor to the intermediate transfer belt, and then performs secondary transfer of the toner image from the intermediate transfer belt to a recording material; a fixing section that forms a nip section that holds the recording material and heats the toner image at the nip section while conveying the recording material, thereby fixing the toner image to the recording material; a housing that houses the image forming unit and the fixing unit; An image forming apparatus comprising: the housing has an opening communicating between an outside and an inside of the housing and disposed above the nip portion in a vertical direction; The image forming apparatus further includes a filter that covers the opening. the intermediate transfer belt has a base layer and a surface layer that is provided on an outer circumferential side of the base layer and that carries the toner image; The maximum particle size of particles that can pass through the filter is smaller than the thickness of the surface layer. 1. An image forming apparatus comprising:

[0193] (Configuration 11) an image forming section having a photoconductor and forming a toner image on a recording material by using the photoconductor; a fixing section that forms a nip section that holds the recording material and heats the toner image while conveying the recording material through the nip section to fix the toner image onto the recording material; a housing that houses the image forming unit and the fixing unit; An image forming apparatus comprising: the housing has an opening communicating between an outside and an inside of the housing and disposed above the nip portion in a vertical direction; The image forming apparatus further includes a filter that covers the opening. the photoreceptor has a conductive substrate and a surface layer formed on an outer periphery of the conductive substrate; The filter is an open-cell foamed plastic. When the average cell diameter of the foamed plastic in a plane perpendicular to the thickness direction of the filter is α (μm), the thickness of the filter is β (μm), the average cell diameter of the foamed plastic in the thickness direction of the filter is γ (μm), and the distance from the outer peripheral surface of the base to the surface of the photoreceptor is δ (μm), α / (β / γ)<δ, 1. An image forming apparatus comprising: [Explanation of symbols]

[0194] 1...photosensitive member (photosensitive drum) / 1a...conductive substrate / 1b...surface layer / 9...fixing section / 10...image forming section / 50...filter / 51...opening (ventilation hole section) / 101...housing

Claims

1. an image forming section having a photoconductor and forming a toner image on a recording material by using the photoconductor; a fixing section that forms a nip section that holds the recording material and heats the toner image while conveying the recording material through the nip section to fix the toner image onto the recording material; a housing that houses the image forming unit and the fixing unit; An image forming apparatus comprising: the housing has an opening communicating between an outside and an inside of the housing and disposed above the nip portion in a vertical direction; The image forming apparatus further includes a filter that covers the opening. the photoreceptor has a conductive substrate and a surface layer formed on an outer periphery of the conductive substrate; The distance from the outer peripheral surface of the substrate to the surface of the photoreceptor is defined as the thickness of the surface layer portion, The maximum particle size of particles that can pass through the filter is smaller than the thickness of the surface layer.

1. An image forming apparatus comprising:

2. The filter is an open-cell foamed plastic.

2. The image forming apparatus according to claim 1,

3. The average cell diameter of the foamed plastic in a plane perpendicular to the thickness direction of the filter is α (μm), the thickness of the filter is β (μm), the average cell diameter of the foamed plastic in the thickness direction of the filter is γ (μm), and the thickness of the surface layer is δ (μm). α / (β / γ)<δ; 3. The image forming apparatus according to claim 2,

4. The filter is a metal mesh.

2. The image forming apparatus according to claim 1,

5. the surface layer portion includes a photosensitive layer that generates charges when irradiated with light to attenuate the potential of the surface of the photoreceptor, and an intermediate layer provided between the substrate and the photosensitive layer, the intermediate layer limiting charge injection from the substrate to the photosensitive layer; 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a multi-color image forming apparatus.

6. the housing includes an exterior member having an outer surface forming an exterior surface of the housing and an inner surface opposite to the outer surface, and an opposing portion opposing the inner surface with a gap therebetween; The opening is provided in the exterior member and communicates a space connected to the gap with the outside of the housing.

5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a multi-color image forming apparatus.

7. The filter is attached to the inner surface of the exterior member.

7. The image forming apparatus according to claim 6,

8. the exterior member has a rib shape protruding from the inner surface in a direction approaching the facing portion, the filter is attached to the inner surface at a position different from the rib shape; At each position within the range in which the filter is provided in the vertical direction, the thickness of the filter is smaller than the protrusion amount of the rib shape relative to the inner surface.

8. The image forming apparatus according to claim 7,

9. an image forming unit that forms a toner image on a recording material; a fixing section including a cylindrical film and a heating means for heating the film, forming a nip section for holding the recording material therebetween, and heating the toner image with the film to fix the toner image on the recording material; a housing that houses the image forming unit and the fixing unit; An image forming apparatus comprising: the housing has an opening communicating between an outside and an inside of the housing and disposed above the nip portion in a vertical direction; The image forming apparatus further includes a filter that covers the opening. The maximum particle size that can pass through the filter is smaller than the thickness of the film.

1. An image forming apparatus comprising:

10. an image forming section including a photoconductor and an intermediate transfer belt, which performs primary transfer of a toner image formed on the photoconductor to the intermediate transfer belt, and then performs secondary transfer of the toner image from the intermediate transfer belt to a recording material; a fixing section that forms a nip section that holds the recording material and heats the toner image at the nip section while conveying the recording material, thereby fixing the toner image to the recording material; a housing that houses the image forming unit and the fixing unit; An image forming apparatus comprising: the housing has an opening communicating between an outside and an inside of the housing and disposed above the nip portion in a vertical direction; The image forming apparatus further includes a filter that covers the opening. the intermediate transfer belt has a base layer and a surface layer that is provided on an outer circumferential side of the base layer and that carries the toner image; The maximum particle size of particles that can pass through the filter is smaller than the thickness of the surface layer.

1. An image forming apparatus comprising:

11. an image forming section having a photoconductor and forming a toner image on a recording material by using the photoconductor; a fixing section that forms a nip section that holds the recording material and heats the toner image while conveying the recording material through the nip section to fix the toner image onto the recording material; a housing that houses the image forming unit and the fixing unit; An image forming apparatus comprising: the housing has an opening communicating between an outside and an inside of the housing and disposed above the nip portion in a vertical direction; The image forming apparatus further includes a filter that covers the opening. the photoreceptor has a conductive substrate and a surface layer formed on an outer periphery of the conductive substrate, The filter is an open-cell foamed plastic. When the average cell diameter of the foamed plastic in a plane perpendicular to the thickness direction of the filter is α (μm), the thickness of the filter is β (μm), the average cell diameter of the foamed plastic in the thickness direction of the filter is γ (μm), and the distance from the outer circumferential surface of the base to the surface of the photoreceptor is δ (μm), α / (β / γ)<δ; 1. An image forming apparatus comprising:

Images