Fixing device and image forming apparatus

Abstract

To provide a fixing device that can make a guide direction different between an envelope and plain paper with an inexpensive configuration.SOLUTION: An entry guide member 61 guides a recording medium entering a fixing nip, and has a first entry guide part 62a that has a gap at the center in an axial direction of a heating rotating body for passing a recording medium having a length in the axial direction less than a predetermined length, and guides a recording medium having a length equal to or more than the predetermined length to harder one rotating body of the heating rotating body and a nip forming rotating body. The entry guide member further has a second entry guide part 63a that, when the recording medium having the length less than the predetermined length passing through the gap of the first entry guide part 62a is seen from the axial direction, guides the recording medium to enter the fixing nip along a reference line K passing through an entry and an exit of the fixing nip, or guides the recording medium to enter the fixing nip from a side of softer one rotating body of the heating rotating body and the nip forming rotating body with reference to the reference line K.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a fixing device and an image forming apparatus. [Background technology]

[0002] Conventionally, a fixing device is known that includes a heating rotor that is heated by a heat source, a nip forming rotor that contacts the heating rotor to form a fixing nip, and an entry guide member that guides a recording medium entering the fixing nip.

[0003] Patent document 1 describes a fixing device in which an entry guide member is rotatable so that when the recording medium is plain paper, it takes a first position that guides the recording medium toward a fixing roller, and when the recording medium is an envelope, it takes a second position that guides the recording medium toward a fixing nip, switching the guide direction between plain paper and an envelope. Summary of the Invention [Problem to be solved by the invention]

[0004] However, this increases the complexity of the device configuration, which can lead to increased costs for the device. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, the present invention provides a fixing device comprising: a heating rotor that is heated by a heat source; a nip forming rotor that contacts the heating rotor to form a fixing nip; An ejection guide member that guides the recording medium that has passed through the ejection guide member. In a fixing device having The discharge guide member has a gap in the axial center of the heating rotor, through which a recording medium having a length in the axial direction less than a predetermined length passes, and includes a first discharge guide portion that guides a recording medium having a length equal to or greater than the predetermined length, and a second discharge guide portion that guides a recording medium having a length less than the predetermined length that has passed through the gap in the first discharge guide portion, the first discharge guide portion having a discharge opening that forms the gap, and a spur is provided at a portion of the discharge opening that faces a surface of the recording medium on the side of the harder rotor, the heating rotor or the nip forming rotor. It is characterized by the above. Effect of the Invention

[0006] According to the present invention, it is possible to make the guide directions for envelopes and plain paper different with an inexpensive configuration. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic configuration diagram showing a printer according to an embodiment. [Diagram 2] 13 is a diagram showing a state in which a sheet of paper with curled edges enters a fixing nip. [Diagram 3] 6A and 6B are diagrams illustrating a state of a sheet of paper with curled edges when the sheet enters the fixing nip and when the sheet is discharged. [Figure 4] FIG. 4 is a diagram showing a configuration for guiding a sheet toward a fixing roller. [Diagram 5] 4 is a diagram for explaining the definitions of an approach guide angle β and a discharge guide angle γ. [Figure 6] 11 is a graph summarizing the relationship between the average envelope wrinkle length and the entrance guide angle β, and the average envelope wrinkle length and the discharge guide angle γ. [Figure 7] FIG. 4 illustrates an envelope passing through the fusing nip. [Figure 8] 6 is a diagram showing the distribution of the transport amount of an envelope in the fixing nip; [Figure 9] This is a graph showing the relationship between the length of wrinkles on an envelope and the length of wrinkles on plain paper printed on both sides, and the entrance guide angle β and the exit guide angle γ. [Figure 10] FIG. 2 is a schematic configuration diagram of a fixing device according to the embodiment. [Figure 11] 11 is a perspective view of the entry guide member as viewed from a direction A in FIG. 10 . [Figure 12] 13A and 13B are diagrams illustrating a state in which the entrance guide member guides large-sized plain paper. [Figure 13] 13A and 13B are diagrams illustrating a state in which an entrance guide member guides an envelope. [Figure 14] 5A and 5B are diagrams for explaining the positional relationship between a transfer nip and a fixing nip. [Figure 15] A graph showing the length of standard size paper that can be transported by an image forming device on the horizontal axis and the paper width on the vertical axis. [Figure 16] FIG. 13 is a schematic perspective view of an entrance guide member equipped with an opening width adjustment mechanism. [Figure 17] FIG. 13 is a schematic cross-sectional view of an entry guide member equipped with an opening width adjustment mechanism. [Figure 18] 5A and 5B are diagrams for explaining back curl during single-sided printing on plain paper. [Figure 19] 13 is a graph showing the relationship between the discharge guide angle γ and the amount of back curl when printing on A4 size plain paper on one side. [Figure 20] 13 is a graph showing the relationship between the discharge guide angle γ and the wrinkle length of the envelope. [Figure 21] FIG. 4 is a schematic diagram of a fixing device provided with a discharge guide member. [Figure 22] FIG. 13 is a schematic perspective view showing the ejection state of large-sized plain paper. [Diagram 23] FIG. 13 is a schematic perspective view showing an envelope ejection state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] An electrophotographic printer (hereinafter simply referred to as a printer) that forms images by an electrophotographic method will be described below as an image forming apparatus to which the present invention is applied.

[0009] First, the basic configuration of the printer according to the embodiment will be described. FIG. 1 is a schematic diagram showing the configuration of a printer according to an embodiment. In the figure, the printer includes a photoconductor 1 as an image carrier, and a paper feed cassette 100 that is detachably attached to a main body housing 50. The paper feed cassette 100 contains a stack of paper S as a plurality of recording media.

[0010] The paper S in the paper feed cassette 100 is sent out from the cassette by the rotational drive of the feed roller 35, passes through a separation nip described below, and then reaches the paper feed path 42. The paper S is then sandwiched in the transport nip of the first transport roller pair 41 and transported in the paper feed path 42 from the upstream side to the downstream side in the transport direction. A registration roller pair 49 is disposed near the end of the paper feed path 42. Transport of the paper S is temporarily stopped when the leading edge of the paper S abuts against the registration nip of the registration roller pair 49. At the time of the abutment, the skew of the paper S is corrected.

[0011] The registration roller pair 49 starts rotating at a timing when the paper S can be superimposed on the toner image on the surface of the photoreceptor 1 at a transfer nip described later, and sends the paper S toward the transfer nip. At this time, the first transport roller pair 41 starts rotating at the same time, and resumes the transport of the paper S that was temporarily stopped.

[0012] The main body of the printer holds a manual feed section that includes a manual tray 43, a manual feed roller 43a, a separation pad 43b, etc. Paper manually fed into the manual tray 43 of the manual feed section is sent out from inside the manual tray 43 by the rotational drive of the manual feed roller 43a. The paper then passes through a separation nip formed by the contact between the manual feed roller 43a and the separation pad 43b, and then enters an area upstream of the registration roller pair 49 in the paper feed path 42. The paper then passes through the registration roller pair 49 in the same manner as the paper S sent out from the paper feed cassette 100, and is then sent to a transfer nip, which will be described later.

[0013] A cleaning blade 2, a charging roller 4, a latent image writing device 7, a developing device 8, a transfer roller 10, etc. are arranged around the drum-shaped photoreceptor 1, which is driven to rotate in a clockwise direction in the figure. The charging roller 4 rotates while in contact with the photoreceptor 1 to form a charging nip. A charging bias output from a power source is applied to this charging roller 4. As a result, a discharge occurs between the surface of the photoreceptor 1 and the surface of the charging roller 4 in the charging nip, and the surface of the photoreceptor 1 is uniformly charged.

[0014] The latent image writing device 7 is equipped with an LED array and performs optical scanning with LED light on the uniformly charged surface of the photoconductor 1. The area of ​​the uniformly charged background part of the photoconductor 1 that is irradiated with light by this optical scanning attenuates the electric potential. As a result, an electrostatic latent image is formed on the surface of the photoconductor 1.

[0015] As the photoconductor 1 is rotated, the electrostatic latent image passes through a developing area facing the developing device 8. In this developing area, the developing device 8 supplies toner to the electrostatic latent image formed on the photoconductor 1, and the electrostatic latent image is visualized as a toner image.

[0016] A toner cartridge 9 is disposed above the developing device 8. The toner cartridge 9 contains toner therein, and supplies the toner to the developing device 8 in response to a supply operation signal output from the control unit 51.

[0017] The toner image formed on the photoconductor 1 by development enters the transfer nip where the photoconductor 1 and the transfer roller 10, which serves as a transfer means, come into contact with each other as the photoconductor 1 rotates. A charging bias of the opposite polarity to the latent image potential of the photoconductor 1 is applied to the transfer roller 10, which forms a transfer electric field in the transfer nip.

[0018] As described above, the pair of registration rollers 49 sends the paper S toward the transfer nip at a timing that allows the paper S to be superimposed on the toner image on the photoreceptor 1 within the transfer nip. The toner image on the photoreceptor 1 is transferred to the paper S that has been brought into close contact with the toner image in the transfer nip by the action of the transfer electric field and nip pressure.

[0019] After passing through the transfer nip, residual toner that has not been transferred to the paper S adheres to the surface of the photoreceptor 1. This residual toner is scraped off from the surface of the photoreceptor 1 by a cleaning blade 2 that is in contact with the photoreceptor 1, and the surface of the photoreceptor 1 is cleaned. The surface of the photoconductor 1 cleaned by the cleaning blade 2 is neutralized by a neutralizing means and then uniformly charged again by the charging roller 4.

[0020] The paper S that has passed through the transfer nip where the photoconductor 1 and the transfer roller 10 come into contact is sent to the fixing device 44. The fixing device 44 forms a fixing nip by the contact between the fixing roller 44a, which is a heating rotor containing a heat source 44c such as a halogen lamp, and the pressure roller 44b, which is a nip-forming rotor that is pressed against the fixing roller 44a. The fixing roller 44a has a release promoting layer for improving the release property from toner and paper powder on the outer circumferential surface of a hollow core metal made of stainless steel, aluminum, etc. The pressure roller 44b has an elastic layer made of a heat-resistant elastic material such as fluorine-based rubber or silicone rubber on the outer surface of a core metal made of stainless steel, aluminum, etc.

[0021] A toner image is fixed to the surface of the paper S sandwiched in the fixing nip by the action of heat and pressure. After that, the paper S passes through the fixing device 44 and then through a paper discharge path 45, and is sandwiched in the paper discharge nip of a pair of paper discharge rollers 46.

[0022] This printer can be switched between a single-sided mode in which an image is formed on only one side of the paper S, and a double-sided mode in which an image is formed on the good edge of the paper S. In the single-sided mode, or in the double-sided mode in which images have already been formed on both sides of the paper S, the pair of paper discharge rollers 46 continues to rotate in the forward direction, thereby discharging the paper S in the paper discharge path 45 outside the machine. The discharged paper S is stacked in a stack section provided on the top surface of the main body housing 50.

[0023] On the other hand, in the double-sided mode, when an image is formed only on one side of the sheet S, the pair of discharge rollers 46 is driven to rotate in the reverse direction when the end of the sheet S enters the discharge nip of the pair of discharge rollers 46. At this time, a switching claw 47 disposed near the end of the sheet discharge path 45 is actuated to block the sheet discharge path 45 and open the entrance of the reversal re-sending path 48. The sheet S, which starts to return in the reverse direction due to the reverse drive of the pair of discharge rollers 46, is sent into the reversal re-sending path 48. The sheet is then conveyed while being turned upside down in the reversal re-sending path 48, and then re-sent to the registration nip of the pair of registration rollers 49. After that, the toner image is transferred to the other side at the transfer nip, and the sheet is discharged outside the machine via the fixing device 44, the sheet discharge path 45, and the pair of discharge rollers 46.

[0024] When the toner image is fixed by the fixing device 44, the paper S is exposed to high temperatures, which causes the moisture in the paper to evaporate, and depending on the grain direction of the paper, the paper may curl at its widthwise ends, which is called edge curl. Edge curl is particularly likely to occur when the paper is large-sized plain paper.

[0025] FIG. 2 is a diagram showing a state in which a sheet S with an end curl St enters the fixing nip N. As shown in FIG. When forming images on both sides of the paper S, an edge curl St may occur when the toner image formed on one side is fixed by the fixing device 44. If the edge curl St occurs, the paper with the edge curl St will enter the fixing nip N as shown in FIG.

[0026] FIG. 3 is a diagram showing the state of a sheet S with an edge curl St when it enters the fixing nip N and when it is discharged. When a sheet of paper with edge curl St is caused to enter the fixing nip N, it enters the fixing nip N from the center in the width direction, as shown in Fig. 3. In this way, the sheet of paper enters the fixing nip with its widthwise center and edges misaligned in the transport direction, causing the rear edge of the sheet to enter the fixing nip bent in the width direction. As a result, the sheet that enters the fixing nip N in a bent state is crushed, causing vertical wrinkles SW to occur at the rear edge of the sheet in the transport direction.

[0027] 4, the downstream end of the entry guide member 61 in the conveying direction is positioned on the fixing roller side with reference to a reference line K, and the paper is guided toward the fixing roller 44a. Note that the reference line K is a straight line passing through the entrance N1 and exit N2 of the fixing nip N. By guiding the paper toward the fixing roller 44a with the entrance guide member 61, the leading edge of the paper in the transport direction comes into contact with the outer peripheral surface of the fixing roller 44a, and then moves toward the fixing nip N while being pressed against the outer peripheral surface of the fixing roller 44a. By pressing the leading edge of the paper in the transport direction against the fixing roller 44a in this manner, the paper enters the fixing nip with reduced edge curl. This allows the leading edge of the paper to enter the fixing nip at approximately the same timing in the width direction, and prevents vertical wrinkles SW (hereinafter referred to as plain paper double-sided printing wrinkles) from occurring at the trailing edge of the paper in the transport direction during double-sided printing.

[0028] In addition, even if the paper S is guided toward the pressure roller 44b and the leading edge of the paper S is pressed against the pressure roller 44b, the curl at the leading edge can be reduced and the paper can enter the fixing nip. However, if the leading edge of the paper S is pressed against the pressure roller 44b to enter the fixing nip, the following problem may occur. That is, the fixing roller 44a does not have an elastic layer, but the pressure roller 44b has an elastic layer, so the pressure roller 44b is softer than the fixing roller 44a. Therefore, when the pressure roller 44b is brought into contact with the fixing roller 44a to form the fixing nip, the pressure roller 44b is elastically deformed. As a result, the fixing nip N follows the outer peripheral surface of the fixing roller 44a and has a shape recessed toward the pressure roller. Therefore, if the paper S is guided toward the pressure roller 44b and the leading edge of the paper S is pressed against the pressure roller 44b to reduce the curl at the leading edge and enter the fixing nip, the conveying direction of the paper changes suddenly when the paper enters the fixing nip. As a result, the paper may not smoothly enter the fixing nip N, which may cause problems such as paper jams and bent leading ends. Therefore, as shown in Fig. 4, it is preferable to guide the paper toward the fixing roller 44a, which is harder than the pressure roller 44b, by an entrance guide member 61.

[0029] However, in the configuration shown in FIG. 4, when the sheet S is an envelope, there is a risk that vertical wrinkles (hereinafter, referred to as envelope wrinkles) may occur at the trailing end of the envelope in the transport direction.

[0030] Therefore, the applicant has investigated the relationship between the approach guide angle β and the discharge guide angle γ and the wrinkles in the envelope. The test conditions were: fixing nip width: 2.5 mm, fixing temperature: 210°C, printing speed: 180 mm / s. The envelope had a basis weight of 70 g / m 2 ], 80 [g / m 2 ], 90 [g / m 2 ], 100 [g / m 2 Four types of envelopes were used, each with a basis weight of 70 [g / m 2 ], 80 [g / m 2 ], 100 [g / m 2The envelopes with a basis weight of 90 [g / m2] are long type No. 3, and the envelopes with a basis weight of 90 [g / m2] are COM10. Five envelopes of each of these four types were passed through the envelopes to measure the length of the wrinkles on the envelopes, and the average wrinkle length of the four types of envelopes was calculated. The average value of the average wrinkle length of these four types of envelopes was then calculated and evaluated.

[0031] FIG. 5 is a diagram for explaining the definitions of the approach guide angle β and the discharge guide angle γ. 5, the entry guide angle β is the angle between a reference line K passing through the entrance N1 and exit N2 of the fixing nip N and a line segment connecting the center No of the fixing nip N and the downstream end X of the entry guide member 161 in the conveying direction. The center No of the fixing nip N is the central position between the entrance N1 and exit N2 of the fixing nip N on the reference line K. The discharge guide angle γ is the angle between the reference line K and a line segment connecting the position Y closest to the reference line K on the upper discharge guide member 81 and the center No of the fixing nip N. In addition, the angles β and γ are set with the fixing roller side as a plus and the pressure roller side as a minus with respect to the reference line K.

[0032] The following Table 1 shows the basis weight of 70 [g / m 2 ], 80 [g / m 2 ], 90 [g / m 2 ], 100 [g / m 2 ] is a table showing the test results for four types of envelopes. Also, Fig. 6 is a graph summarizing the relationship between the average envelope wrinkle length and the entrance guide angle β, and the average envelope wrinkle length and the discharge guide angle γ, and Table 2 is a summary of the combinations of the entrance guide angle β and the discharge guide angle γ based on Table 1, and the relationship between the average envelope wrinkle length.

[0033] [Table 1]

[0034] [Table 2]

[0035] In FIG. 6, β=20° is the average value of the average wrinkle length of four brands, Nos. 1 to 3 in Table 1, and β=0° is the average value of the average wrinkle length of four brands, Nos. 4 to 6 in Table 1. In addition, β=-20° is the average value of the average wrinkle length of four brands, Nos. 7 to 9 in Table 1. In addition, γ=18° is the average value of the average wrinkle length of four brands, Nos. 1, 4, and 7 in Table 1, and γ=12° is the average value of the average wrinkle length of four brands, Nos. 2, 5, and 8 in Table 1. γ=5° is the average value of the average wrinkle length of four brands, Nos. 3, 6, and 9 in Table 1.

[0036] As shown in Fig. 6, it can be seen that the smaller the entry guide angle β, the shorter the wrinkle length of the envelope, regardless of the value of the exit guide angle γ. It can also be seen that the smaller the exit guide angle γ, the shorter the wrinkle length of the envelope, regardless of the value of the entry guide angle β. As can be seen from Table 2, when the discharge guide angle γ is 12° or less, at least if the entry guide angle β is 0° or less, no envelope wrinkles will occur. For this reason, in order to prevent envelope wrinkles, it is preferable to set the entry guide angle β to 0° or less and the discharge guide angle γ to 12° or less.

[0037] Here, the occurrence of wrinkles in an envelope will be described. Fig. 7 shows the state of an envelope F passing through the fixing nip N, and Fig. 8 is a diagram showing the transport amount distribution of the envelope F in the fixing nip. Fig. 8(a) shows the transport amount distribution in the fixing nip N of the print side paper portion F1 of the envelope abutting against the outer peripheral surface of the fixing roller 44a, and Fig. 8(b) shows the transport amount distribution of the non-print side paper portion F2 of the envelope abutting against the outer peripheral surface of the pressure roller 44b in the fixing nip N.

[0038] As described above, the fixing nip N, which is formed by the elastic deformation of the pressure roller, which is softer than the fixing roller 44a, is curved with the curvature of the fixing roller 44a. As shown in Fig. 7, when the thickness of the envelope is t, the angle range of the fixing nip N centered on the rotation center of the fixing roller 44a is θ, and the radius of the fixing roller is R, the transport amount L1 in the fixing nip at the widthwise center of the print side paper portion F1 of the envelope F is (2πθ / 360)R. The transport amount L2 at the widthwise center of the non-print side paper portion F2 is (2πθ / 360)(R+t), and the transport amount in the fixing nip N differs between the widthwise center of the print side paper portion F1 and the widthwise center of the non-print side paper portion F2.

[0039] Envelope F is formed by folding or gluing both widthwise sides of the paper to form a two-ply paper. Therefore, the widthwise end of the non-printed side paper portion F2 of envelope F moves integrally with the widthwise end of the printed side paper portion F1 in the fixing nip, and no difference occurs in the amount of transport. Meanwhile, the widthwise center of the non-printed side paper portion F2 of envelope F can move in the transport direction relative to the printed side paper portion F1. Therefore, due to the difference in the amount of transport in the fixing nip N, the widthwise center of the non-printed side paper portion F2 shifts in the transport direction relative to the widthwise center of the printed side paper portion F1, and this shift appears as a wrinkle FW at the rear end of the envelope.

[0040] When the approach guide angle β is positive, the envelope is transported along the outer peripheral surface of the fixing roller 44a and enters the fixing nip N. Therefore, even before entering the fixing nip N, the transport amount of the widthwise center of the non-printed side paper portion F2 is greater than that of the widthwise center of the printed side paper portion F1. As a result, the deviation in the transport direction of the widthwise center of the non-printed side paper portion F2 from the widthwise center of the printed side paper portion F1 is greater, which is considered to have lengthened the envelope wrinkles. On the other hand, when the approach guide angle β is negative, the envelope enters the fixing nip N with a curve (convex curve toward the fixing roller) opposite to the curve of the fixing nip N (concave curve toward the pressure roller). As a result, just before entering the fixing nip N, the transport amount of the widthwise center of the non-printed side paper portion F2 is less than that of the widthwise center of the printed side paper portion F1. As a result, the direction in which the widthwise center of the non-printed side paper portion F2 shifts in the transport direction just before entering the fixing nip is opposite to the direction in which the widthwise center of the non-printed side paper portion F2 shifts in the transport direction at the fixing nip, which is thought to suppress envelope wrinkles.

[0041] FIG. 9 is a graph showing the results of investigating the envelope wrinkle length and the plain paper double-sided printing wrinkle length as a function of the entrance guide angle β and the exit guide angle γ. The test conditions for the wrinkle length of double-sided printing on plain paper were: nip width: 7.7 mm, fixing temperature: 170°C, printing speed: 252 mm / s. The basis weight was 69 g / m 2 ] paper was used.

[0042] As can be seen from graphs 3 and 4 in FIG. 9, the larger the approach guide angle β, the more wrinkles on both sides of plain paper are suppressed, and wrinkles during double-sided printing can be suppressed with an approach guide angle β of 15° or more.

[0043] When the entry guide angle β is negative, depending on the inclination of the entry guide member 161, the envelope moves along the outer peripheral surface of the pressure roller 44b and enters the fixing nip. However, as described above, in the case of an envelope, the fixing nip width is set to 2.5 mm, and the amount of elastic deformation of the pressure roller 44b is suppressed. Therefore, when the envelope moves along the outer peripheral surface of the pressure roller 44b and enters the fixing nip, a sudden change in the conveying direction is suppressed. Therefore, the envelope can be conveyed without problems such as paper jams or bent leading ends.

[0044] From the above, in the case of an envelope, it is preferable that the entry guide angle β is 0° or less, and in the case of double-sided printing on plain paper, it is preferable that the entry guide angle β is positive. In this way, the optimal entry guide angle β differs between the case of plain paper and the case of an envelope. Conventionally, the entry guide member 61 is configured to be rotatable, and the guide direction is made different by changing the position of the entry guide member 61 for plain paper and for an envelope. However, conventionally, a mechanism for rotating the entry guide member is required, which increases the number of parts and complicates the device configuration, and there is a risk of increasing the cost of the device.

[0045] Therefore, in this embodiment, the entrance guide member 61 is provided with a first entrance guide portion that guides large plain paper and a second entrance guide portion that guides envelopes, so that the guide directions for envelopes and large plain paper are different even when the entrance guide member 61 is fixed to the device. Below, the features of this embodiment will be described with reference to the drawings.

[0046] [Example 1] FIG. 10 is a schematic diagram of the fixing device of this embodiment, and FIG. 11 is a perspective view of an entrance guide member 61 of this embodiment as viewed from a direction A in FIG. The entry guide member 61 of this embodiment has a first member 62 and a second member 63. The first member 62 has a first attachment portion 62b attached to a case side plate 44d of the fixing device 44 and a first entry guide portion 62a that guides paper S of a predetermined size or more. The first entry guide portion 62a extends obliquely upward from the first attachment portion 62b toward the downstream in the conveying direction. The first member 62 has a central portion in the width direction cut out from the upstream end in the conveying direction, and a gap is formed in the first entry guide portion 62a to allow paper of a width smaller than a predetermined width to pass through. The first attachment portion 62b has through holes 62c on both sides in the width direction, through which the screws 66 pass.

[0047] The second member 63 has a second attachment portion 63b attached to the first member 62 and a second entry guide portion 63a that guides paper sheets with a predetermined width or less. The second attachment portion 63b has a plate shape that is long in the width direction and crosses the first attachment portions 62b on both sides in the width direction. The second entry guide portion 63a extends from the center of the second attachment portion 63b in the width direction toward the downstream side in the conveying direction. Through holes through which screws 66 pass are provided on both sides in the width direction of the second attachment portion 63b.

[0048] The entry guide member 61 is fixed to the case side plate 44d by passing a screw 66 through the through hole of the first attachment portion 62b and the through hole of the second attachment portion 63b and screwing it to the case side plate 44d.

[0049] Combining the first member 62 and the second member 63 forms an opening 65 that is rectangular when viewed from the conveyance direction. The width W of this opening 65 is determined in consideration of the standard sizes of envelopes and plain paper that can be conveyed by this image forming apparatus, as described below, and is at least larger than the width of a standard-sized envelope that can be conveyed by this image forming apparatus. Therefore, the envelope is configured to pass through the opening 65 and enter the fixing nip N while being guided by the second entrance guide portion 63a.

[0050] Additionally, a plurality of spurs 64 are rotatably attached to an opposing surface 65a that faces the printing surface of the paper guided by the second entrance guide section of the opening 65. Providing the spurs 64 prevents the printing surface of the paper S, on which a toner image is formed, from rubbing against the opposing surface 65a of the opening 65, and makes it possible to suppress disturbance of the toner image formed on the printing surface.

[0051] FIG. 12 is a diagram showing how the entrance guide member 61 guides plain paper that is larger than the width of the opening 65. As shown in FIG. Plain paper larger than the width of the opening 65 is guided by the first entrance guide portion 62a and transported without passing through the opening 65. In this embodiment, as described below, the width of the opening 65 is set between 148 mm (A5 size width) and 182 mm (B5 size width). Therefore, in this embodiment, plain paper with a width equal to or larger than the B5 size is large plain paper.

[0052] 10, the downstream end of the first entrance guide portion 62a in the transport direction is located on the fixing roller side with reference to the reference line K. Therefore, the large-sized plain paper is guided by the first entrance guide portion 62a toward the fixing roller 44a. As a result, the leading edge of the large-sized plain paper is pressed against the surface of the fixing roller and moves along the outer circumferential surface of the fixing roller to enter the fixing nip N.

[0053] As described above, large-size plain paper is prone to edge curling, which makes it easy for double-sided printing wrinkles to occur. However, in this embodiment, the leading edge of the large-size plain paper is pressed against the surface of the fixing roller, and the leading edge curl is reduced when the large-size plain paper enters the fixing nip. This makes it possible to prevent double-sided printing wrinkles from occurring on the large-size plain paper.

[0054] FIG. 13 is a diagram showing the state of guiding by the entrance guide member 61 in the case of an envelope. As shown in FIG. 13, the envelope F passes through the opening 65 and is conveyed toward the fixing nip N while being guided by the second entrance guide portion 63a.

[0055] 10, the downstream end of the second entry guide portion 63a in the conveying direction is located on the pressure roller side with reference to the reference line K. In addition, the lower end of the spur 64 is located on the reference line K. Therefore, the envelope F passing through the opening 65 enters the fixing nip parallel to the reference line K or from the pressure roller side with reference to the reference line K by the second entry guide portion 63a.

[0056] In this manner, the envelope F passes through the opening 65 and is guided by the second entrance guide portion 63a at an entrance guide angle β of 0° or less to enter the fixing nip N. This makes it possible to suppress wrinkles in the envelope compared to when the envelope F is guided by the first entrance guide portion 62a to enter the fixing nip N.

[0057] Furthermore, in the fixing device 44, the discharge guide angle γ is set to 12°. This effectively prevents wrinkles in the envelope. Even if the discharge guide angle γ exceeds 12°, as shown in Table 1 and FIG. 6, guiding the envelope at an entry guide angle β of 0° or less can effectively prevent wrinkles in the envelope compared to guiding the envelope at an entry guide angle β of 20°.

[0058] The fixing device 44 is provided with a first entry guide portion 62a and a second entry guide portion 63a, and the guide portion to be guided can be switched depending on the width W of the opening 65. This allows the guide direction to be switched between envelopes and large-sized plain paper with the entry guide member 61 fixed to the fixing device 44. This allows the fixing device 44 to be attached with a simple configuration such as screw fastening. This allows for a cheaper configuration than a configuration in which the entry guide member 61 is rotatably attached to the fixing device and the guide direction is switched between envelopes and large-sized plain paper by switching the position of the entry guide member.

[0059] In this embodiment, plain paper with a width W or less of the opening is guided by the second entrance guide section and enters the fixing nip. Therefore, when printing on both sides of plain paper with a width W or less of the opening, the paper enters the fixing nip without the end curl being reduced by pressing the leading end against the outer peripheral surface of the fixing roller. However, the end curl increases in proportion to the width of the sheet, so the end curl of plain paper with a width W or less of the opening is slight. Therefore, for plain paper with a width W or less of the opening, even if the end curl is not reduced by pressing the outer peripheral surface of the fixing roller, the occurrence of wrinkles during double-sided printing is sufficiently suppressed. In addition, when a certain degree of end curl occurs on plain paper with a width W or less of the opening, the spur 64 presses the center in the width direction toward the second entrance guide section, and the paper enters the fixing nip N with the end curl reduced. Therefore, even if a certain degree of end curl occurs on plain paper with a width W or less of the opening, the occurrence of wrinkles during double-sided printing can be suppressed.

[0060] In addition, the fixing conditions for plain paper with a width equal to or less than the width W of the opening are preferably the same as those for envelopes. That is, the fixing nip width is 2.5 mm, the fixing temperature is 210° C., and the printing speed is 180 mm / s. This reduces the amount of elastic deformation of the pressure roller 44b compared to the fixing conditions for plain paper (nip width: 7.7 mm, fixing temperature: 170° C., printing speed: 252 mm / s). This reduces the sudden change in the conveying direction when plain paper with a width equal to or less than the width W of the opening enters the fixing nip. This allows the paper to be conveyed without problems such as paper jams or bent leading edges.

[0061] FIG. 14 is a diagram for explaining the positional relationship between the transfer nip NT and the fixing nip N. As shown in FIG. In this embodiment, the transfer nip reference line connecting the entrance and exit of the transfer nip NT coincides with the fixing nip reference line K connecting the entrance and exit of the fixing nip N, and the line connecting the transfer nip center NTo and the fixing nip center No coincides with the reference line. Note that the transfer nip center NTo is the central position between the entrance and exit of the transfer nip NT on the transfer nip reference line, and the fixing nip center is the central position between the entrance and exit of the fixing nip on the fixing nip reference line K.

[0062] As described above, the lower end of spur 64, which is the closest part to the second entry guide part among the parts of opening 65 that face the print surface of the recording medium, is located on reference line K of the fixing nip. Therefore, the line segment connecting the lower end of spur 64 and the center of the fixing nip coincides with the line segment connecting the center NTo of the transfer nip and the center No of the fixing nip.

[0063] Since the positional relationship between the fixing nip, the transfer nip, and the lower end of the spur 64 is as described above, the paper that has passed through the transfer nip can enter the fixing nip without changing the conveying direction significantly. This allows the image forming device to be made more compact.

[0064] Next, the width W of the opening 65 will be described. If the width of the paper being passed is close to the width of the opening 65, the paper may get caught on the widthwise end of the opening 65, making it difficult to transport stably and causing a jam. Therefore, the width W of the opening 65 needs to be determined taking into account the width of the paper being transported. Table 3 below shows the main standard sizes of paper that can be transported by this image forming apparatus.

[0065] [Table 3]

[0066] The maximum size width that can be conveyed by this image forming apparatus is letter size (=215.9 mm (8.5 inches)). Fig. 15 is a graph summarizing the paper lengths shown in Table 3 on the horizontal axis and the paper widths on the vertical axis. In Fig. 15, "■" indicates plain paper and "▲" indicates an envelope. As can be seen from Fig. 15, the maximum size width of an envelope transported by this image forming apparatus is 120 [mm], and the width W of opening 65 is set to 120 [mm] or more. This allows the envelope transported by this image forming apparatus to pass through opening 65 and be guided by second entrance guide portion 63a.

[0067] 15, in the standard sizes, there is no paper width between 148 mm (A5 size width) and 182 mm (B5 size width). Therefore, by setting the width W of the opening 65 between 148 mm and 182 mm (for example, 160 mm), it is possible to prevent the paper from getting caught on the widthwise end of the opening 65 and causing a jam.

[0068] As described above, by setting the width W of the opening 65 between 148 and 182 mm, when the paper to be passed is of a standard size, the occurrence of a paper jam can be suppressed by suppressing the end of the width direction of the opening 65 from getting caught. Since the paper to be passed through the image forming apparatus is generally of a standard size, the above configuration can sufficiently suppress the occurrence of a paper jam. However, there are cases where paper of a non-standard size is passed through. When the width of the paper of the non-standard size is between 148 and 182 mm and close to the width W of the opening 65, a paper jam may occur. In addition, there are cases where an envelope of a non-standard size is passed through, and the width of the envelope of the non-standard size may exceed the width W of the opening 65. In this case, the envelope of the non-standard size may not be guided by the second entrance guide portion 63a through the opening 65, and the envelope may be wrinkled. For this reason, it is preferable to make it possible to adjust the width W of the opening 65. Hereinafter, a configuration of an entry guide member capable of adjusting the width W of the opening 65 will be described as a second embodiment.

[0069] [Example 2] FIG. 16 is a schematic perspective view of an entry guide member equipped with an opening width adjustment mechanism 70 that adjusts the width W of opening 65, and FIG. 17 is a schematic cross-sectional view of an entry guide member equipped with opening width adjustment mechanism 70. The opening width adjustment mechanism 70 is composed of a pair of opening width variable members 71 that are attached to the entry guide member 61 so as to be movable in the width direction, and a set screw 72 that fixes the pair of opening width variable members 71 at a predetermined position in the width direction.

[0070] A pair of extended openings 62e extending in the width direction are formed in the first entry guide portion 62a of the first member 62. These extended openings 62e are formed in the entry path (arrow Z in FIG. 17) of the paper entering the entry guide member. In addition, a pair of grooves 62d to which an opening width variable member is attached so as to be slidable in the width direction are formed on the outer side of the extended openings 62e in the width direction. Screw holes are provided in the bottom surfaces of these grooves 62d.

[0071] The pair of opening width variable members 71 have a trapezoidal shape when viewed in the width direction, and the cross-sectional shape of the groove portion 62d and the cross-sectional shape of the extended opening portion 62e are trapezoidal shapes similar to the trapezoidal shape of the opening width variable member 71. Each opening width variable member 71 is provided with a screw through hole 71a that is long in the width direction. The opening width variable member 71 is fixed to the first member 62 by passing a set screw 72 through the screw through hole 71a of the opening width variable member 71 and screwing the set screw 72 into a screw hole provided in the groove portion 62d.

[0072] When adjusting the width of the opening 65, each opening width variable member 71 can be moved in the width direction by loosening each set screw 72. By moving the pair of opening width variable members 71 inward in the width direction, the width of the extended opening 62e of the opening 65 is narrowed, and the opening width of the opening 65 where the paper enters is narrowed. As a result, both sides in the width direction of the non-standard size paper that has passed through the transfer nip and entered the entry guide member hit the opening width variable members 71 and is guided by the first entry guide portion 62a.

[0073] By moving the pair of opening width variable members 71 outward in the width direction, the width of the extended opening 62e of the opening 65 is increased, and the opening width of the opening 65 where the paper enters is increased. As a result, an envelope of a non-standard size that has passed through the transfer nip and entered the entry guide member passes through the opening 65 and is guided to the second entry guide portion 63a.

[0074] In this way, by making it possible to adjust the opening width of the portion of opening 65 where the paper enters, it is possible to prevent non-standard sized plain paper from getting caught on the widthwise end of the opening. Also, non-standard sized envelopes can be guided through opening 65 by second entrance guide portion 63a.

[0075] In this example, only the opening width of the opening 65 where the paper enters is adjusted, but it may be possible to adjust the opening width of the entire opening. By making it possible to adjust the opening width of the entire opening, the allowable range of deviation of the paper entry position into the entry guide member in the direction perpendicular to the transport direction is increased, making it possible to transport non-standard size paper more smoothly.

[0076] Also, in this example, the screw through hole 71a of the opening width variable member 71 is an elongated hole that is long in the width direction, but multiple screw through holes may be provided at predetermined intervals in the width direction. Also, in this example, the user accesses the entry guide member 61 to adjust the width of the opening 65. However, for example, an operation mechanism including a rack and pinion mechanism or the like may be provided so that the pair of opening width variable members 71 can be moved in the width direction by operating the operation mechanism at a position different from the position where the entry guide member 61 is disposed in the device.

[0077] Also, the width of the opening may be automatically adjusted using a drive source such as a drive motor. For example, the paper width size to be passed is input by operating the operation display unit of the image forming device, or the paper width size to be passed is input from an external device such as a personal computer. Based on the input paper width size information, the device controls the drive source to move the pair of opening width variable members 71 to a predetermined position in the width direction.

[0078] Also, the guide direction of the paper discharged from the fixing nip may be different between plain paper and envelopes. As described above, in the case of envelopes, the envelope wrinkles can be effectively suppressed by lowering the value of the discharge guide angle γ. However, if the discharge guide angle γ is lowered, there is a risk that the so-called back curl, which is curling toward the non-printed side when printing on one side of plain paper, may become large. Therefore, it is preferable to make the guide direction of the paper discharged from the fixing nip different between plain paper and envelopes, since it is possible to effectively suppress envelope wrinkles while suppressing back curl when printing on one side of plain paper.

[0079] Fig. 18 is a diagram for explaining back curl during single-sided printing on plain paper. Fig. 18(a) shows how the sheet S is discharged when the discharge guide angle γ is large, and Fig. 18(b) shows how the sheet S is discharged when the discharge guide angle γ is small. In Fig. 18(b), among the portion of the upper discharge guide member 81 closest to the reference line K, position Y closest to the fixing nip side is closer to the reference line K than in Fig. 18(a). Therefore, the discharge guide angle γ, which is the angle between the line connecting position Y and the center No of the fixing nip and the reference line K, is smaller than in Fig. 18(a).

[0080] Since the fixing nip N is concave toward the pressure roller, the paper S discharged from the fixing nip N is discharged toward the fixing roller side (upper discharge guide member 81 side). The paper discharged from the fixing nip N abuts against the upper discharge guide member 81 and the transport direction is changed. When the discharge guide angle γ is small as shown in FIG. 18(b), the paper abuts against the upper discharge guide member 81 before bending under its own weight, and the abutment angle with the upper discharge guide member 81 is larger than when the discharge guide angle γ is large as shown in FIG. 18(a). As a result, when the discharge guide angle γ is small, the paper is forcibly bent by the upper discharge guide member 81, and the amount of back curl increases.

[0081] FIG. 19 is a graph showing the relationship between the discharge guide angle γ and the amount of back curl during single-sided printing on A4 size plain paper. As shown in FIG. 19, the larger the discharge guide angle γ, the more the amount of back curl is suppressed. 2 When the discharge guide angle γ is set to 18°, the amount of back curl decreases rapidly, but above 18° the decrease in the amount of back curl is small. This shows that by setting the discharge guide angle γ to 18° or more, back curl can be effectively suppressed. Also, if the discharge guide angle γ is at least 24° or less, the paper can be discharged without any problems. This shows that for large-sized plain paper, if the discharge guide angle γ is at least 18° or more and at most 24°, back curl can be suppressed and the paper can be transported without any problems.

[0082] FIG. 20 is a graph showing the relationship between the discharge guide angle γ and the wrinkle length of the envelope. Fig. 20 is a graph created based on the results of Table 1 above, and as shown in Fig. 20, if the discharge guide angle γ is 5° or less, the occurrence of envelope wrinkles can be prevented regardless of the entry guide angle β. Also, even if the discharge guide angle γ is -10°, the envelope can be discharged well. Therefore, for envelopes, if the discharge guide angle γ is at least -10° or more and 5° or less, the envelope can be discharged well and envelope wrinkles can be suppressed.

[0083] Note that a negative discharge guide angle γ means that the Y position of the upper discharge guide member 81 is located closer to the pressure roller than the reference line K. When the discharge guide angle γ is negative, the envelope discharged from the fixing nip immediately comes into contact with the upper discharge guide member 81 and is transported closer to the pressure roller than the reference line K while being guided by the upper discharge guide member 81.

[0084] Since the value of the discharge guide angle γ is small, the envelope comes into contact with the upper discharge guide member 81 immediately after being discharged from the fixing nip, and the conveying direction is switched to the pressure roller side. As a result, the envelope is curved (convex toward the fixing roller side) in the opposite direction to the curvature direction in the fixing nip (concave toward the pressure roller side) near the exit of the fixing nip. This makes the conveying amount of the widthwise center of the non-printed side paper portion F2 of the envelope at the exit of the fixing nip smaller than the conveying amount of the widthwise center of the printed side paper portion F1. As a result, the conveying speed of the widthwise center of the non-printed side paper portion F2 at the exit of the fixing nip is slower than the conveying speed of the widthwise center of the printed side paper portion F1, which suppresses the misalignment of the conveying direction between the widthwise center of the non-printed side paper portion F2 and the printed side paper portion F1, which is thought to suppress wrinkles in the envelope.

[0085] In this way, the optimal discharge guide angle γ differs between large plain paper and envelopes. Therefore, it is preferable to provide a discharge guide member that includes a discharge guide portion that guides envelopes that have passed through the fixing nip, and a discharge guide portion that guides large plain paper that has passed through the fixing nip. Below, a configuration that includes a discharge guide member will be described as Example 3.

[0086] [Example 3] FIG. 21 is a schematic diagram of a fixing device provided with a discharge guide member 91. As shown in FIG. The basic configuration of the discharge guide member 91 is the same as that of the entry guide member 61, and has an opening 95 for passing an envelope. The discharge guide member 91 also has a first discharge guide portion 92 that guides paper that does not pass through the opening 95, and a second discharge guide portion 93 that guides paper that has passed through the opening 95. A plurality of spurs 94 are provided on the upstream side in the transport direction of the opposing surface of the opening 95 that faces the print surface of the paper that passes through the opening 95.

[0087] The discharge guide angle γ1 of the first discharge guide portion 92 of the discharge guide member 91 is set to 18° to 24°, and the discharge guide angle γ2 of the second discharge guide portion 93 is set to 5° to -10°. Note that the discharge guide angle γ2 of the second discharge guide portion 93 is the angle between the reference line K and a line connecting the lower end of the spur 94, which is the position closest to the pressure roller among the portions facing the second discharge guide portion 93, and the center No of the fixing nip.

[0088] FIG. 22 is a schematic perspective view showing how large-sized plain paper is discharged. 22, when the large plain paper leaves the fixing nip N, it is guided by the first discharge guide 92 and discharged. Immediately after leaving the fixing nip, the large plain paper hits the guide member and is conveyed without changing the conveying direction to the pressure roller side. This makes it possible to suppress back curl of the large plain paper during single-sided printing.

[0089] FIG. 23 is a schematic perspective view showing the discharge state of an envelope. The width of the opening 95 is set to be the same as that of the entrance guide member, and is between 148 [mm] (A5 size width) and 182 [mm] (B5 size width). As described above, the maximum size of a standard envelope that the image forming apparatus conveys is 120 [mm], so the envelope that has passed through the fixing nip enters the opening 95 and comes into contact with the spur 94, and the conveying direction is changed. The envelope then passes through the opening 95 and is guided to the second discharge guide portion 93.

[0090] In this way, after the envelope leaves the fixing nip, it enters opening 95 and comes into contact with spurs 94, preventing it from floating up toward the fixing roller and being discharged. This prevents the conveying speed of the widthwise center of the non-printed side paper part immediately after leaving the fixing nip from becoming faster than the widthwise center of the printed side paper part, and prevents the conveying direction of the widthwise center of the non-printed side paper part at the fixing nip from shifting from the widthwise center of the printed side paper part, thereby preventing wrinkles in the envelope.

[0091] Note that plain paper that is narrower than the width of the opening 95 passes through the opening 95 and is guided by the second discharge guide portion 93 before being discharged. This plain paper that is narrower than the width of the opening 95 also enters the opening 95 and comes into contact with the spurs 94, changing the conveying direction. However, the spurs 94 rotate to deflect the force at the time of contact, thereby preventing the paper from bending toward the pressure roller, and thus preventing back curl of the small plain paper.

[0092] Also, the discharge guide member 91 may be provided with an opening width adjustment mechanism 70 similar to the configuration shown in Fig. 16 so that the width of the opening 95 can be adjusted. By providing the discharge guide member 91 with the opening width adjustment mechanism 70 shown in Fig. 16, it is possible to prevent non-standard sized plain paper from getting caught on the width direction end of the opening 95 when it is discharged from the fixing nip, and it is possible to transport the paper satisfactorily. Also, non-standard sized envelopes can be discharged through the opening 95, and it is possible to effectively prevent envelope wrinkles.

[0093] In FIG. 21, an entrance guide member 61 is provided to make the guide direction different between the envelope and the large plain paper, but the guide direction of the envelope may not be different from that of the plain paper, and the envelope may be entered into the fixing nip in the same manner as the large plain paper. That is, the envelope is also guided toward the fixing roller and pressed against the outer peripheral surface of the fixing roller to enter the fixing nip. As shown in FIG. 20, even if the entrance guide angle β is 20°, if the discharge guide angle γ is 5° or less, the envelope wrinkles can be effectively suppressed. Therefore, even if the guide direction is made different between the envelope and the large plain paper only on the discharge side, the envelope wrinkles, the wrinkles during double-sided printing of the plain paper, and the back curl during single-sided printing of the plain paper can be effectively suppressed.

[0094] The above description is merely an example, and each of the following aspects provides unique effects. (Aspect 1) In the fixing device 44, which includes a heating rotor such as a fixing roller 44a heated by a heat source such as a heat source 44c, a nip forming rotor such as a pressure roller 44b that contacts the heating rotor to form a fixing nip N, and an entrance guide member 61 that guides a recording medium such as paper S entering the fixing nip, the entrance guide member 61 has a gap (opening 65 in this embodiment) at the center in the axial direction of the heating rotor to allow a recording medium having an axial length of less than a predetermined length to pass through, and a recording medium having a predetermined length or more is guided to the harder of the heating rotor and the nip forming rotor. The recording medium has a first entry guide portion 62a that guides the recording medium toward the fixing nip N (the fixing roller 44a in this embodiment), and a second entry guide portion 63a that guides the recording medium of less than a predetermined length that has passed through the gap of the first entry guide portion 62a so that it enters the fixing nip N along a reference line K that passes through the entrance N1 and exit N2 of the fixing nip when viewed from the axial direction, or guides the recording medium so that it enters the fixing nip from the side of the softer rotating body between the heating rotating body and the nip forming rotating body (the pressure roller 44b in this embodiment) using the reference line K as a reference. According to this, a recording medium such as an envelope whose axial length of the heating rotator is less than a predetermined width passes through the gap of the first entry guide part and is guided by the second guide part, and a recording medium such as plain paper whose axial length of the heating rotator is equal to or greater than a predetermined width is guided by the first entry guide part. This makes it possible to make the guide directions different for envelopes and plain paper while the entry guide member is fixed to the device body, and compared to a case in which the entry guide member is configured to be rotatable and the position of the entry guide member is changed to make the guide directions different for envelopes and plain paper, this allows for a simpler configuration and makes it possible to make the guide directions different for envelopes and plain paper with a cheaper configuration. Furthermore, the first entry guide member guides the recording medium toward the harder of the heating rotator and the nip forming rotator, thereby suppressing the occurrence of wrinkles during double-sided printing on plain paper, as described in the above verification test. The second entry guide member guides the envelope so that it enters the fixing nip along a reference line K passing through the entrance and exit of the fixing nip when viewed from the axial direction, or guides the envelope so that it enters the fixing nip from the side of the softer of the heating rotator and the nip forming rotator, using the reference line K as a reference. This makes it possible to suppress the occurrence of wrinkles on the envelope, as described in the above verification test.

[0095] (Aspect 2) In the first embodiment, the first entrance guide portion 62a has an entrance opening such as the opening 65 that forms a gap, and a spur 64 is provided at a location of the entrance opening facing the print surface of the recording medium. As a result, as described in the embodiment, the printing surface of a recording medium such as paper S on which a toner image is formed is prevented from rubbing against a surface facing the printing surface of an entry opening such as opening 65, thereby preventing the toner image formed on the printing surface from being disturbed.

[0096] (Aspect 3) In the first or second embodiment, the maximum size width of the transportable recording medium is letter size width, and the axial length of the gap is 148 mm or more and 182 mm or less. According to this, as described in the embodiment, when standard size paper is passed through, it is possible to prevent the paper from getting caught on the axial end of the gap, and thus to prevent the occurrence of a jam.

[0097] (Aspect 4) In any of the first to third embodiments, an entrance adjustment mechanism such as an opening width adjustment mechanism 70 that adjusts the axial length of the gap is provided. According to this, as described in the embodiment, when the width size of the recording medium to be passed is near the axial length of the gap such as the opening width, the axial length of the gap can be adjusted by the entry adjustment mechanism to separate the axial length of the recording medium to be passed from the axial length of the gap. This makes it possible to prevent the recording medium from getting caught on the axial end of the gap, and to prevent jams not only of standard sizes but also of non-standard sizes.

[0098] (Aspect 5) In the fourth embodiment, the entry adjustment mechanism such as the opening width adjustment mechanism 70 has a pair of variable members such as the opening width variable members 71 that are provided axially movable. According to this, as described in the embodiment, the axial length of the gap can be adjusted by moving the pair of variable members in the axial direction.

[0099] (Aspect 6) In any of aspects 1 to 5, when viewed from the axial direction of a heating rotor such as the fixing roller 44a, with the harder rotor (in this embodiment, the fixing roller 44a) between the heating rotor and the nip forming rotor such as the pressure roller 44b being taken as positive and the softer rotor (in this embodiment, the pressure roller 44b) being taken as negative, the entry guide angle β of the first entry guide portion 62a is 15° or more and 25° or less, and the entry guide angle β of the second entry guide portion 63a is -20° or more and 0° or less, with the reference line K being taken as positive and the softer rotor (in this embodiment, the pressure roller 44b) being negative. This makes it possible to effectively prevent wrinkles on both sides of large-sized plain paper and wrinkles on envelopes, as described in the embodiment.

[0100] (Aspect 7) In any of aspects 1 to 6, an ejection guide member 91 is provided that guides the recording medium that has passed through the fixing nip, and the ejection guide member 91 has a gap (opening 95 in this embodiment) in the axial center of the heating rotor to allow a recording medium whose axial length is less than a predetermined length to pass through, and is provided with a first ejection guide portion 9a that guides a recording medium of the predetermined length or more, and a second ejection guide portion 93 that guides a recording medium of less than the predetermined length that has passed through the gap in the first ejection guide portion 92. According to this, as described in the embodiment, the discharge guide section that guides the large plain paper and the envelope can be made different, so that the large plain paper can be guided so as not to cause back curl, and the envelope can be guided so as not to cause wrinkles, thereby suppressing back curl of the large plain paper and wrinkles in the envelope.

[0101] (Aspect 8) In a fixing device 44 including a heating rotor such as a fixing roller 44a that is heated by a heat source such as a heat source 44c, a nip forming rotor such as a pressure roller 44b that abuts against the heating rotor to form a fixing nip N, and an ejection guide member 91 that guides a recording medium that has passed through the fixing nip N, the ejection guide member 91 has a gap (opening 95 in this embodiment) in the axial center of the heating rotor to allow a recording medium whose axial length is less than a predetermined length to pass through, and is equipped with a first ejection guide portion 92 that guides a recording medium of the predetermined length or more, and a second ejection guide portion 93 that guides a recording medium of less than the predetermined length that has passed through the gap in the first ejection guide portion 92. According to this, as described in the embodiment, the discharge guide section that guides the large plain paper and the envelope can be made different, so that the large plain paper can be guided so as not to cause back curl, and the envelope can be guided so as not to cause wrinkles, thereby suppressing back curl of the large plain paper and wrinkles in the envelope.

[0102] (Aspect 9) In aspect 7 or 8, when viewed from the axial direction of a heating rotor such as the fixing roller 44a, the first discharge guide portion 92 guides the recording medium to the harder rotor between the heating rotor and the nip forming rotor such as the pressure roller 44b (the fixing roller 44a in this embodiment) based on a reference line K passing through the entrance N1 and exit N2 of the fixing nip, and the second discharge guide portion guides the recording medium at a position closer to the reference line K than the first discharge guide portion 92, or has a second discharge guide portion 93 that guides the recording medium to the softer rotor between the heating rotor and the nip forming rotor (the pressure roller 44b in this embodiment) based on the reference line K. This makes it possible to suppress back curl of large-sized plain paper and wrinkles in envelopes, as described in the embodiment.

[0103] (Aspect 10) In any of the seventh to ninth aspects, an opposing discharge guide member such as the upper discharge guide member 81 that faces the first discharge guide portion 92 is provided. As a result, as described in the embodiment, the recording medium guided by the first discharge guide portion 92 can be prevented from floating up toward the harder of the heating rotor and the nip forming rotor such as the pressure roller 44b (in this embodiment, the fixing roller 44a) by the opposing discharge guide member such as the upper discharge guide member 81, and the recording medium guided by the first discharge guide portion 92 can be transported in a predetermined direction.

[0104] (Aspect 11) In any of aspects 7 to 10, when viewed from the axial direction of a heating rotor such as the fixing roller 44a, with a reference line passing through the entrance N1 and exit N2 of the fixing nip as a reference, the harder rotor side of the heating rotor and the nip forming rotor such as the pressure roller 44b is taken as plus and the softer rotor side is taken as minus, the discharge guide angle γ of the first discharge guide portion is 18° or more and 24° or less, and the discharge guide angle γ of the second discharge guide portion is -10° or more and 5° or less. According to this, as described in the embodiment, by guiding large-sized plain paper with the first discharge guide section, back curl can be effectively suppressed, and by guiding an envelope with the second discharge guide section, envelope wrinkles can be effectively suppressed.

[0105] (Aspect 12) In any of aspects 7 to 11, the first discharge guide portion has a discharge opening such as an opening 95 that forms the gap, and a spur 94 is provided at a location of the discharge opening facing the surface of the harder rotating body of the recording medium, either the heating rotating body such as the fixing roller 44a or the nip-forming rotating body such as the pressure roller 44b. According to this, as described in the embodiment, when small-sized plain paper passing through the discharge opening rises toward the harder rotating body, it comes into contact with the spur 94. This allows the spur 94 to deflect the impact of the small-sized plain paper in the transport direction, and prevents the small-sized plain paper from significantly switching its transport direction toward the softer rotating body (pressure roller 44b in this embodiment). As a result, it is possible to prevent back curling of small-sized plain paper passing through the discharge opening.

[0106] (Aspect 13) In any of aspects 7 to 12, the maximum size width of the transportable recording medium is letter size width, and the axial length of the gap (opening 95 in this embodiment) is 148 mm or more and 182 mm or less. As a result, as described in the embodiment, it is possible to prevent the widthwise end of a standard size recording medium from getting caught on the axial end of the gap, thereby preventing jams from occurring.

[0107] (Aspect 14) In any one of aspects 7 to 13, a discharge adjustment mechanism is provided that adjusts the axial length of the gap of the first discharge guide portion (in this embodiment, the opening 95). According to this, as described in the embodiment, when the axial length of the recording medium being passed is close to the axial length of the gap, the axial length of the gap can be adjusted by the discharge adjustment mechanism to separate the axial length of the recording medium being passed from the axial length of the gap. This makes it possible to prevent the recording medium from getting caught on the axial end of the gap, and to prevent jams not only of standard sizes but also of non-standard sizes.

[0108] (Aspect 15) In a fourteenth aspect, the discharge adjustment mechanism has a pair of variable members that are axially movable. According to this, as described in the embodiment, the axial length of the gap can be adjusted by moving the pair of variable members in the axial direction.

[0109] (Aspect 16) In an image forming apparatus equipped with a fixing device for fixing an image formed on a recording medium to the recording medium, the fixing device according to any one of the embodiments 1 to 15 was used as the fixing device. This makes it possible to suppress wrinkles in envelopes with an inexpensive configuration, and also to suppress wrinkles caused by double-sided printing on large-size plain paper or back curl on large-size plain paper.

[0110] (Aspect 17) In aspect 16, a transfer member such as a transfer roller 10 that abuts against an image carrier such as a photoconductor 1 to form a transfer nip is provided upstream of the fixing device in the recording medium transport direction, and the entry guide member has an entry opening such as opening 65 through which a recording medium of a predetermined width or less passes, and when viewed from the axial direction of a heated rotating body such as the fixing roller 44a, a line segment connecting the point closest to the second entry guide portion (in this embodiment, the lower end of the spur) among the opposing portions that face the printing surface of the recording medium at the entry opening and the center No of the fixing nip is parallel to or coincident with a line segment connecting the center NTo of the transfer nip and the center No of the fixing nip. According to this, as described in the embodiment, the recording medium that has passed through the transfer nip can enter the fixing nip with almost no change in the conveying direction, which makes it possible to reduce the size of the image forming apparatus. [Explanation of symbols]

[0111] 1: Photoreceptor 10: Transfer roller 44: Fixing device 44a: Fuser roller 44b: Pressure roller 44c: Heat source 44d: Case side plate 61: Entry guide member 62: First member 62a: First entrance guide section 62b: First attachment part 62d: Groove 62e: Extension opening 63: Second member 63a:Second approach guide section 63b: Second mounting part 64: Spur 65: Opening 65a: Opposing surface 66: Screw 70: Opening width adjustment mechanism 71: Variable opening width member 71a: Screw through hole 72: Set screw 81: Upper discharge guide member 91: Discharge guide member 92: First discharge guide part 93: Second discharge guide part 94: Spur 95: Opening F: Envelope F1: Print side paper section F2: Non-print side paper section K:Reference line N: Fixing nip N1: Fixing nip entrance N2: Transfer nip exit NT: Transfer nip NTo: Center of transfer nip S: Paper St: End curl β: Approach guide angle γ: Discharge guide angle [Prior art documents] [Patent documents]

[0112] [Patent Document 1] Patent No. 5835646

Claims

1. A heating rotor heated by a heat source; a nip forming rotor that contacts the heating rotor to form a fixing nip; a discharge guide member that guides the recording medium that has passed through the fixing nip; The discharge guide member is a first discharge guide portion having a gap at a center in an axial direction of the heating rotator for passing a recording medium having a length in the axial direction less than a predetermined length, and for guiding a recording medium having a length equal to or greater than the predetermined length; a second ejection guide portion that guides the recording medium having a length less than the predetermined length that has passed through the gap of the first ejection guide portion; The first discharge guide portion has a discharge opening portion that forms the gap, a fixing device comprising: a spur provided at a portion of said discharge opening facing a surface of said recording medium on the side of one of said heating rotor and said nip forming rotor, which is harder;

2. In the fixing device according to claim 1, a discharge adjustment mechanism for adjusting the length of the gap of the first discharge guide portion in the axial direction;

3. A heating rotor heated by a heat source; a nip forming rotor that contacts the heating rotor to form a fixing nip; a discharge guide member that guides the recording medium that has passed through the fixing nip; The discharge guide member is a first discharge guide portion having a gap at a center in an axial direction of the heating rotator for passing a recording medium having a length in the axial direction less than a predetermined length, and for guiding a recording medium having a length equal to or greater than the predetermined length; a second ejection guide portion that guides the recording medium having a length less than the predetermined length that has passed through the gap of the first ejection guide portion; a discharge adjustment mechanism for adjusting the length of the gap of the first discharge guide portion in the axial direction;

4. The fixing device according to claim 2 or 3, The fixing device, wherein the discharge adjustment mechanism has a pair of variable members that are movably provided in the axial direction.

5. 5. The fixing device according to claim 1, the first discharge guide portion guides the recording medium to a harder rotor side of the heating rotor or the nip forming rotor, based on a reference line passing through an entrance and an exit of the fixing nip when viewed from an axial direction of the heating rotor, and A fixing device characterized in that the second discharge guide portion guides the recording medium at a position closer to the reference line than the first discharge guide portion, or guides the recording medium toward the softer rotating body of the heating rotating body and the nip forming rotating body using the reference line as a reference.

6. 6. The fixing device according to claim 1, A fixing device comprising: a counter discharge guide member that faces a first discharge guide portion.

7. 7. The fixing device according to claim 1, When viewed from the axial direction of the heating rotor, a reference line passing through the entrance and exit of the fixing nip is used as a reference, and the harder rotor side of the heating rotor and the nip forming rotor is taken as a plus and the softer rotor side is taken as a minus, The discharge guide angle γ of the first discharge guide portion is 18° or more and 24° or less, The fixing device, wherein the discharge guide angle γ of the second discharge guide portion is equal to or greater than −10° and equal to or less than 5°.

8. The fixing device according to any one of claims 1 to 7, an entrance guide member for guiding the recording medium entering the fixing nip; The entry guide member is a first entry guide portion having a gap in the center of the axial direction of the heating rotor for allowing a recording medium having a length in the axial direction less than a predetermined length to pass therethrough, and guiding a recording medium having a length equal to or greater than the predetermined length toward the harder rotor of the heating rotor and the nip forming rotor; A fixing device characterized by having a second entry guide portion that guides a recording medium of less than the specified length that has passed through the gap of the first entry guide portion so that it enters the fixing nip along a reference line passing through the entrance and exit of the fixing nip when viewed from the axial direction, or that guides the recording medium so that it enters the fixing nip from the side of the softer rotating body between the heating rotating body and the nip forming rotating body, using the reference line as a reference.

9. The fixing device according to claim 8, The fixing device further comprises an entrance adjustment mechanism for adjusting the length of the gap of the first entrance guide portion in the axial direction.

10. A heating rotor heated by a heat source; a nip forming rotor that contacts the heating rotor to form a fixing nip; A fixing device including an entrance guide member for guiding a recording medium entering the fixing nip, The entry guide member is a first entry guide portion having a gap in the center of the axial direction of the heating rotor for allowing a recording medium having a length in the axial direction less than a predetermined length to pass therethrough, and guiding a recording medium having a length equal to or greater than the predetermined length toward the harder rotor of the heating rotor and the nip forming rotor; a second entry guide portion that guides the recording medium having a length less than the predetermined length that has passed through the gap of the first entry guide portion so as to enter the fixing nip along a reference line passing through an entrance and an exit of the fixing nip when viewed from the axial direction, or guides the recording medium so as to enter the fixing nip from the side of the softer rotating body between the heating rotating body and the nip forming rotating body, using the reference line as a reference; The fixing device further comprises an entrance adjustment mechanism for adjusting the length of the gap of the first entrance guide portion in the axial direction.

11. 11. The fixing device according to claim 9, The fixing device, wherein the penetration adjustment mechanism has a pair of variable members that are movably provided in the axial direction.

12. The fixing device according to claim 8 , The first entry guide portion has an entry opening that forms a gap in the first entry guide portion, a spur provided at a position of the entrance opening facing a print surface of the recording medium;

13. 13. The fixing device according to claim 8, The maximum size width of the transportable recording medium is letter size width, The fixing device, wherein the length of the gap of the first entrance guide portion in the axial direction is 148 mm or more and 182 mm or less.

14. The fixing device according to claim 8 , When viewed from the axial direction of the heating rotor, the harder rotor side of the heating rotor and the nip forming rotor is taken as a plus and the softer rotor side is taken as a minus with respect to the reference line, The entry guide angle β of the first entry guide portion is 15° or more and 25° or less, The fixing device, wherein the second entrance guide portion has an entrance guide angle β of −20° or more and 0° or less.

15. An image forming apparatus including a fixing device for fixing an image formed on a recording medium to the recording medium, 15. An image forming apparatus, comprising the fixing device according to claim 1 as the fixing device.

16. An image forming apparatus having a fixing device for fixing an image formed on a recording medium to the recording medium, The fixing device according to claim 8 or 10 is used as the fixing device, a transfer member that contacts an image carrier and forms a transfer nip, the transfer member being disposed upstream of the fixing device in a conveying direction of the recording medium; the entry guide member has an entry opening through which a recording medium having a width smaller than a predetermined width passes; An image forming apparatus characterized in that, when viewed from the axial direction of the heating rotor, a line segment connecting the point of the entry opening that faces the printing surface of the recording medium closest to the second entry guide portion and the center of the fixing nip is parallel to or coincides with a line segment connecting the center of the transfer nip and the center of the fixing nip.

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