JP2022133558A - Fixing device and image forming apparatus - Google Patents

Abstract

To prevent a reduction in fixing performance at the ends in a width direction of a sheet, while improving sheet separation performance and ejected sheet loading properties.SOLUTION: A nip forming member 5 has a first convex part 51 located inside a nip area and in the vicinity of an end on the downstream side in a conveyance direction, and a second convex part 52. In a direction orthogonal to a nip tangent W, a first distance Y1 between a leading end of the first convex part 51 and the nip tangent W is smaller than a second distance Y2 between a leading end of the second convex part 52 and the nip tangent W. The second convex part 52 does not go beyond the nip tangent W and extends toward a pressure roller 3 in the orthogonal direction. The radius of curvature of a leading end part of the second convex part 52 is smaller than the radius of an inner peripheral circle of a fixing film 2. When the second distance at a center part in a longitudinal direction is Y2c (Ya) and the second distance at the ends in the longitudinal direction is Y2e (Yb), Y2e (Yb)>Y2c (Ya) is satisfied.SELECTED DRAWING: Figure 3

Description

The present invention relates to a fixing device and an image forming apparatus, and more particularly to a fixing device in an image forming apparatus such as a laser printer, a copying machine, and a facsimile machine that uses an electrophotographic recording method.

As a fixing device in an image forming apparatus, a fixing device in which a heat source is arranged inside a fixing film as a heating member and a fixing nip portion is formed between a pressure roller as a pressure member and the fixing film is disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-200004. disclosed. In this fixing device, since the heat capacity of the fixing film is small, the fixing film can reach a high temperature instantaneously.

Further, for example, Patent Documents 2 and 3 disclose a fixing device having a fixing film and a pressure roller as in Patent Document 1, and having a fixing nip forming member in contact with the inner peripheral surface of the fixing film at the fixing nip portion. An apparatus is disclosed. The fixing nip forming member has projections on the downstream side in the sheet conveying direction and outside the area of the fixing nip portion (hereinafter referred to as the fixing nip area) to improve the sheet separation performance.

JP 2016-114621 A JP 2012-002956 A Japanese Patent No. 6573414

When the paper passes through the fixing nip area, the toner image formed on the paper contacts the fixing film while being heated. The heated toner increases in viscosity and tends to adhere the toner image to the outer surface of the fixing film (hereinafter referred to as the outer surface of the fixing film). If this adhesive strength is too high, the paper may adhere to the outer surface of the fixing film and may not be separated from the outer surface of the fixing film. In the fixing device of Patent Document 1, the fixing film has an elliptical shape that is close to a perfect circle, and the radius of curvature of the outer surface of the fixing film is almost the same at any point.

In addition, the image forming apparatus is required to have a stackability of ejected sheets. In fuser configurations that place the heat source on the front side of the paper, the front side of the paper reaches a higher temperature than the back side. In such a case, the paper tends to curl into a cylindrical shape with the back side of the paper on the inside. If the paper is curled too much, it may not be possible to stack the paper on the discharge section. In the fixing device of Patent Document 2, the nip forming member has a projection on the downstream side in the conveying direction and outside the fixing nip area, and the projection greatly protrudes in the direction of the pressure roller. Since the paper is ejected along the direction of rotation of the pressure roller, the direction in which it curls due to heating is the same as the direction in which it is curled due to the ejection direction, and the paper is cylindrical under high temperature and high humidity conditions. may be rounded to

The fixing device disclosed in Patent Document 3 is the fixing device disclosed in Patent Document 1, and is provided with projections that are characteristic of Patent Document 2. Projections outside the fixing nip portion may reduce the temperature of the fixing film when it contacts the fixing film. In particular, in the width direction of the paper, the amount of decrease in the temperature of the fixing film is remarkable in the area outside the heating element. As the temperature of the fixing film decreases, the temperature of the fixing film corresponding to the vicinity of the end portion of the heating element also decreases. Therefore, when a wide sheet of paper is conveyed to the fixing nip portion, the fixability of the toner image at the edges in the width direction of the sheet may be impaired.

SUMMARY OF THE INVENTION The present invention has been made under such circumstances, and is intended to improve the paper separation performance and the stackability of ejected paper, while preventing the deterioration of the fixing performance at the edges in the width direction of the paper. for the purpose.

In order to solve the above problems, the present invention has the following configurations.
(1) A rotatable tubular first rotating body, a second rotating body that biases the first rotating body, and a rotating body that is positioned inside the first rotating body and that rotates the first rotating body. a nip forming member that supports the rotating body and forms a nip area that is a contact area between the first rotating body and the second rotating body, and a nip forming member that is in contact with the inner peripheral surface of the first rotating body; a heater substrate held by the nip forming member; and a heater having a linear heating element on the surface of the heater substrate and extending in a longitudinal direction perpendicular to the conveying direction of the recording material, the heater being carried by the recording material. In the fixing device for heating the toner image in the nip area, the nip forming member is positioned inside the nip area and near an end on the downstream side in the conveying direction, and the first rotating body and a second protrusion located outside the nip area and downstream in the conveying direction and in contact with the inner peripheral surface of the first rotating body. through the contact surface between the first rotating body and the second rotating body in the nip region where the heater is in contact with the inner peripheral surface of the first rotating body; A first distance Y1 between the tip of the first protrusion and the nip tangent in the direction perpendicular to the nip tangent extending parallel to the contact surface is the tip of the second protrusion and the nip. is smaller than a second distance Y2 between the tangent and the second protrusion extends toward the second rotating body in the orthogonal direction without crossing the nip tangent; 2 is smaller than the radius of the inner peripheral circle of the first rotating body, the second distance at the central portion in the longitudinal direction is Y2c, and the end portion in the longitudinal direction is Assuming that the second distance is Y2e, the fixing device is characterized in that Y2e>Y2c.
(2) An image forming apparatus comprising: image forming means for forming a toner image on a recording material; and the fixing device according to (1).

According to the present invention, it is possible to improve the paper separation performance and the stackability of the discharged paper, while preventing the deterioration of the fixing performance of the edges in the width direction of the paper.

Cross-sectional view of the fixing device of Example 1 The figure which shows the heater of Example 1. FIG. 2 is a view showing the longitudinal direction and a cross-sectional view of the fixing device according to the first embodiment; A perspective view and a perspective enlarged view showing the nip forming member of Example 1. FIG. 4 is a diagram showing the positional relationship between the nip forming member and the heater in Example 1; FIG. 10 is a view showing the longitudinal direction and a cross-sectional view of a fixing device of Comparative Example 1; FIG. 10 is a view showing the longitudinal direction and a sectional view of a fixing device of Comparative Example 2; FIG. 2 is a cross-sectional view showing the image forming apparatus of Embodiment 1; 4A and 4B are diagrams for explaining the sheet stackability of Example 1 and Comparative Example 1; A diagram for explaining the paper stackability of Comparative Example 2 Graph showing evaluation results of separation performance and paper stackability of Example 1 and Comparative Examples 1 and 2

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

[Fixing device]
The present invention relates to a fixing device in image forming apparatuses such as laser printers, copiers, and facsimiles that use an electrophotographic recording method. A cross-sectional view of the fixing device 1 of Example 1 is shown in FIG. The fixing device 1 includes a fixing film 2 as a cylindrical rotatable first rotating body, a pressure roller 3 as a second rotating body forming a fixing nip portion together with the fixing film 2, a heater 4, and a heater 4. and a nip forming member 5 that holds the . The nip forming member 5 is arranged on the inner peripheral side of the fixing film 2 and supports the fixing film 2 at the fixing nip portion. The fixing device 1 further has a stay 6 that maintains strength in the longitudinal direction of the fixing device 1 . The longitudinal direction of the fixing device 1 is also a direction substantially orthogonal to the conveying direction of paper as a recording material. The fixing nip portion is formed in a nip area, which is a contact area between the fixing film 2 and the pressure roller 3 , which is formed by the nip forming member 5 .

The fixing film 2 is composed of a 200 μm-thick silicone rubber layer on a 50 μm-thick polyimide base material, and a 20 μm-thick PFA release layer thereon. The pressure roller 3 is composed of a SUM core metal with an outer diameter of 13 mm, a silicone rubber elastic layer with a thickness of 3.5 mm thereon, and a PFA release layer with a thickness of 40 μm thereon. A drive source (not shown) rotates the pressure roller 3 , and the fixing film 2 urged by the pressure roller 3 is driven by the pressure roller 3 and rotates.

The heater 4 is held by the nip forming member 5, and the inner peripheral surface of the fixing film 2 and the surface of the heater 4 are in contact with each other. Both ends of the stay 6 are pressed by means (not shown), and the pressing force is received by the pressure roller 3 via the nip forming member 5 and the fixing film 2 . As a result, a fixing nip portion is formed in which the fixing film 2 and the pressure roller 3 are in pressure contact. The nip forming member 5 must have rigidity, heat resistance, and heat insulation, and is made of a liquid crystal polymer.

The heater 4 is formed of a heating element mainly composed of silver and palladium on a plate-like ceramic substrate made of alumina or the like. Heater 4 on the ceramic substrate generates heat. A thermistor (not shown), which is a temperature detection means, and a thermoswitch (not shown), which is a safety element, are arranged in contact with each other on the rear surface of the heater 4 . The thermistor is a chip resistor type thermistor. The chip resistance of the thermistor is detected, and the result detected by the thermistor is used for temperature control of the heater 4 . Alumina (Al2O3), aluminum nitride (AlN), zirconia (ZrO2), silicon carbide (SiC) and the like are widely known as ceramic substrates. Among them, alumina (Al2O3) is inexpensive and industrially readily available. Also, a metal having excellent strength may be used for the substrate, and stainless steel (SUS) is preferably used as the metal substrate because it is excellent in both cost and strength. Regardless of whether a ceramic substrate or a metal substrate is used as the substrate, an insulating layer may be provided if the substrate has conductivity.

Thermistors can also detect overheating. The thermoswitch is a bimetallic thermoswitch, and the heater 4 and the thermoswitch are electrically connected. When the thermoswitch detects excessive temperature rise on the back surface of the heater 4 , the bimetal inside the thermoswitch operates to cut off the power supplied to the heater 4 .

[Structure of heater]
FIG. 2(a) is a view showing the longitudinal direction of the heater 4. FIG. The heater substrate 49 is a plate-like ceramic substrate made of alumina or the like, and has a thickness t of 1 mm, a width W of 7.0 mm, and a length L of 277.2 mm. The width W is the length in the paper transport direction, and the length L is the length in the direction perpendicular to the paper transport direction, that is, in the longitudinal direction. Heating elements 41, 42, 43, 44, conductive paths (no reference numerals), and power supply contacts 45, 46, 47, 48 are formed on the heater substrate 49 (heater substrate surface) by a printing process. In FIG. 2, heating elements 41, 42, 43, and 44 (hereinafter also referred to as 41 to 44) are white, conductive paths are shaded, and power supply contacts 45, 46, 47, and 48 (45 to 48) are shown in black, respectively.

The width W direction (short side) of the heating element 41 as the first heating element, the heating element 42 as the fourth heating element, the heating element 43 as the second heating element, and the heating element 44 as the third heating element direction) is as follows: The heating element 41 has the longest longitudinal length (eg, 222 mm), the heating element 43 has the second longest length (eg, 188 mm), the heating element 44 has the third longest length (eg, 154 mm), and the longest. The heating elements 42 are arranged in order at regular intervals. Each interval between the heating elements 41 to 44 is 0.7 mm. All of the heating elements 41 to 44 have a symmetrical shape when the longitudinal direction is taken as the left-right direction.

FIG. 2(b) is an enlarged end view of the heater 4. FIG. The heating elements 41 and 42 are substantially linear heating elements having different shapes only at the left and right ends. The right ends of the heating elements 41 and 42 are denoted by H, and the change points at which the shapes of the heating elements 41 and 42 change are denoted by I, J, and K. The HI interval is, for example, 7.0 mm, the IJ interval is, for example, 3.0 mm, and the JK interval is, for example, 10.0 mm. The width w1 of the heating elements 41 and 42 at the right end H is, for example, 1.0 mm. The width w2 of the heating elements 41 and 42 at the position of the change point I is, for example, 0.7 mm. The width w3 of the heating elements 41 and 42 at the position of the change point J is, for example, 0.7 mm. The width w4 of the heating elements 41 and 42 at the position of the change point K is, for example, 0.805 mm. The central portions of the heating elements 41 and 42 have a uniform width of 0.805 mm everywhere. The wide region (wide region, near the right end H) of the heating elements 41 and 42 has a lower power density than the narrow region (between IJ). For this reason, both end portions of the heating elements 41, 41 in Example 1 have a characteristic that the power density is slightly lower than that of the central portion. The thickness of the heating elements 41 and 42 is, for example, 10 μm, and the length in the longitudinal direction is, for example, 222 mm as described above.

The heat generating elements 43 and 44 having short longitudinal lengths are linear heat generating elements whose width is uniform in the longitudinal direction. The heating element 43 has a width of 0.8 mm, a thickness of 10 μm, and a length of 188 mm, for example. The heating element 44 has a width of 0.7 mm, a thickness of 10 μm, and a length of 154 mm, for example.

[Paper Width and Heating Element Control]
The maximum sheet width (hereinafter referred to as sheet width) that can be handled by the fixing device 1 of the first embodiment having such heating elements 41 to 44 is LTR sheet of 216 mm. Note that the paper width is the length in the direction substantially perpendicular to the transport direction. When a wide sheet such as LTR sheet or A4 sheet is conveyed through the fixing nip (hereinafter referred to as "passing"), an AC voltage is applied between the power supply contact 45 and the power supply contact 46 to generate heat. An electric current is passed through the bodies 41 and 42 substantially at the same time to generate heat.

Further, when B5 paper with a paper width of 182 mm is passed, control 1 for causing heat to be generated by substantially simultaneously applying current to the heating elements 41 and 42, and applying an AC voltage between the power supply contact 46 and the power supply contact 47, Control 2, in which current is applied only to the heating element 43, is alternately used. Furthermore, when A5 paper with a paper width of 148.5 mm is passed, control 1 causes current to flow through the heating elements 41 and 42 substantially simultaneously to generate heat, and AC voltage is applied between the power supply contact 47 and the power supply contact 48. and control 3, in which current is applied only to the heating element 44 to generate heat, are alternately used.

In the case of LTR paper, the areas of the heating elements 41 and 42 protruding outside the paper area in the width direction are narrow. In the case of A4 paper, the area is wider than that of LTR paper. In general, the fixing film 2 and the pressure roller 3 are longer than the heating elements 41 to 44 in the width direction. If the area of the heating element protruding outside the paper area is narrow, a small amount of energy (calorific value) will heat a wide area outside the paper area (the width direction end portions of the fixing film 2 and pressure roller 3). Therefore, the temperature of the width direction end portions of the fixing film 2 and the pressure roller 3 tends to be low. The narrower the region of the heating element that protrudes outside the paper area, the more likely it is that the temperature drop at the edges in the width direction will become a problem. On the other hand, in the case of B5 paper or A5 paper, long heating elements 41 and 42 may be used. The risk of temperature drop at the end portions of the fixing film 2 and the pressure roller 3 is low.

The heating elements 41 to 44 are made of a conductive material mainly composed of silver and palladium, and the conductive paths and power supply contacts 45 to 48 are made of a conductive material mainly composed of silver. For example, the longest heating elements 41 and 42 are both 20 Ω, the second length heating element 43 is 20 Ω, and the third length heating element is 20 Ω. 44 is 25Ω. A common power supply contact 45 is electrically connected to one end of the longest heating elements 41, 42, and a common power supply contact 46 is electrically connected to the other end thereof. Therefore, the combined electrical resistance of the longest heating elements 41, 42 between the power supply contacts 45, 46 is 10Ω.

[Structure of Nip Shaped Member of Fixing Device]
FIG. 3A shows a longitudinal view of the fixing device 1 as seen from the downstream side in the transport direction. Assuming that the position of the central portion in the longitudinal direction of the fixing device 1 is AA' and the position of the end portion of the fixing device 1 (on the right side of the paper surface) is BB', the positions AA' and BB' are assumed. is 111 mm. The BB' position corresponds to the positions of the ends of the heating elements 41 and 42 of the heater 4 (see FIG. 2(b)). A CC' position is defined between the AA' and BB' positions, and the distance from the AA' position to the CC' position is 61 mm. Similarly, the FF' position is also defined between the AA' position and the BB' position, and the distance from the AA' position to the FF' position is 86 mm. Assuming that the position of the edge of the fixing device 1 (on the left side of the paper) is DD', the distance from the AA' position to the DD' position is 111 mm.

Sections of the fixing device 1 at the center A-A' position and the C-C' position of the fixing device 1 will be described with reference to FIG. 3B. The area where the fixing film 2 and the pressure roller 3 are in contact is called a nip area N1, and the area where the fixing film 2 and the heater 4 are in contact is called a nip area N2. A tangent line to the nip area N2 is defined as a nip tangent line W (broken line), and a direction parallel to the nip tangent line W is defined as an X direction (the right direction (direction opposite to the transport direction) on the paper surface of FIG. 3B is positive). Also, the direction orthogonal to the nip tangent line W on the paper surface of FIG. 3B is defined as the Y direction (the upward direction on the paper surface of FIG. 3B is positive). The nip tangent line W is a straight line passing through the contact surface between the fixing film 2 and the pressure roller 3 in the nip region N2 where the heater 4 is in contact with the inner peripheral surface of the fixing film 2 and extending parallel to the contact surface.

The nip forming member 5 at the center in the longitudinal direction of the fixing device 1 includes a first convex portion 51 and a second convex portion 52 . The first convex portion 51 is positioned downstream of the heater 4 in the sheet conveying direction and is in contact with the pressure roller 3 with the fixing film 2 interposed therebetween. The first convex portion 51 is located in the nip region N1 (within the region) and near the end of the nip region N1 on the downstream side in the transport direction. The first convex portion 51 extends (protrudes) toward the pressure roller 3 (minus side in the Y-axis direction) without crossing the nip tangent line W in a direction substantially orthogonal to the nip tangent line W. The first convex portion 51 presses the inner peripheral surface of the fixing film 2 and changes the radius of curvature of the outer surface of the fixing film 2 at the pressed portion. The first convex portion 51 is arranged at a position immediately before the paper is discharged from the fixing nip portion, and has a function of applying a high pressure (peak pressure) to the paper and fixing the toner image to the paper. The first convex portion 51 presses the inner peripheral surface of the fixing film 2 toward the pressure roller 3 in the vicinity of the downstream end portion in the conveying direction of the fixing nip portion. A vertex 511 of the first protrusion 51 is located in the nip region N1 and projects most toward the pressure roller 3 (minus side in the Y-axis direction). The distance between the vertex 511 of the first convex portion 51 and the nip tangent line W is defined as a first distance.

The second convex portion 52 is located downstream of the heater 4 and the first convex portion 51 in the conveying direction, contacts the inner peripheral surface of the fixing film 2, and does not receive pressure from the pressure roller 3. In other words, it is a convex portion that does not come into contact with the pressure roller 3 through the fixing film 2 . The second convex portion 52 is located outside the nip region and downstream in the conveying direction. The second convex portion 52 extends toward the pressure roller 3 (minus side in the Y-axis direction) in a direction substantially perpendicular to the nip tangent line W. As shown in FIG. The second convex portion 52 does not come into contact with the pressure roller 3 with the fixing film 2 interposed therebetween. The second convex portion 52 presses the inner peripheral surface of the fixing film 2 at a position immediately after the paper is discharged from the fixing nip portion to impart an inflection point to the fixing film 2 . The radius of curvature of the outer surface can be reduced. Thereby, the second convex portion 52 has a function of separating the paper from the fixing film 2 . The inner peripheral surface of the fixing film 2 and the nip forming member 5 do not contact between the first convex portion 51 and the second convex portion 52, and the outer surface of the fixing film 2 and the pressure roller 3 do not contact each other. The fixing film 2 is brought into contact with the second convex portion 52 so as to be wrapped around the second convex portion 52 by providing the space R that does not come into contact with the second convex portion 52 . As a result, the fixing film 2 can more reliably come into contact with the second protrusions 52 , so that the paper can be stably separated from the fixing film 2 . Here, the nip region N1 is, for example, about 8 mm, and the nip region N2 is about 6 mm.

A vertex 521 of the second protrusion 52 is defined as the point of the second protrusion 52 that protrudes most toward the pressure roller 3 (minus side in the Y-axis direction). The first convex portion 51 is located on the upstream side in the transport direction (the positive side in the X direction) of the second convex portion 52, and the vertex 511 of the first convex portion 51 and the vertex 521 of the second convex portion 52 The distance Xa in the X direction between is 3 mm, for example. The second protrusion 52 is arranged with a gap from the nip tangent W without reaching the nip tangent W, and the second distance (minimum retraction) from the vertex 521 of the second protrusion 52 to the nip tangent W Amount) Ya is, for example, 0.8 mm. Here, the distance from the vertex 521 of the second convex portion 52 to the nip tangent line W (minimum retraction amount Ya) is the distance from the vertex 521 of the second convex portion 52 in the direction substantially orthogonal to the nip tangent line W is the distance between the nip tangents W. Note that the first distance (distance Y1) between the vertex 511 (tip) of the first protrusion 51 and the nip tangent W is the distance between the vertex 521 (tip) of the second protrusion 52 and the nip tangent W. is smaller than a second distance (distance Y2) between Further, when the second distance at the central portion in the longitudinal direction is Y2c, and the second distance at the end portions in the longitudinal direction is Y2e, the relationship Y2e>Y2c is established.

The tip portion of the second convex portion 52 has a semicircular cross-sectional shape with a radius of 4 mm, for example, in a direction substantially orthogonal to the longitudinal direction, and the curvature radius R52 of the region that contacts the inner peripheral surface of the fixing film 2 is 4 mm. . The fixing film 2 has a substantially cylindrical shape with an inner peripheral circle having a radius of 9 mm and an outer surface having a curvature radius of basically about 9 mm. The second protrusions 52 having a small radius of curvature are pressed into contact with the inner peripheral surface of the fixing film 2 to reduce the radius of curvature of the surface of the fixing film 2 at the pressed portion, thereby improving the separation performance of the sheet from the fixing film 2 . can be enhanced. The radius of curvature of the second protrusions 52 is preferably smaller than the radius of the inner circumference of the fixing film 2 . Here, the radius of the inner peripheral circle of the fixing film 2 is the radius of the maximum circle inscribed in the substantially circular shape formed by the fixing film 2 in a cross section perpendicular to the direction in which the cylindrical fixing film 2 extends. .

A cross section of the fixing device 1 at the position F-F' will be described with reference to FIG. 3(c). The shape of the first projection 51 is similar to that of the A-A' position and the C-C' position. On the other hand, the second convex portion 52 moves away from the nip tangent line W. For example, the minimum retraction amount Yb at the F-F' position is 1.6 mm (Yb>Ya). Thus, the vertex 521 of the second convex portion 52 forms a slope shape such that the value of the minimum retraction amount Yb increases from the position C-C' to the position B-B'.

A cross section of the fixing device 1 at the position B-B' at the end of the fixing device 1 will be described with reference to FIG. 3(d). The nip forming member 5 at the longitudinal end of the fixing device 1 has a first protrusion 51 . Here, unlike the central portion, the nip forming member 5 does not have the second convex portion. A distance Yc between the nip forming member 5 and the nip tangent line W at a position a distance Xa downstream in the transport direction from the vertex 511 of the first convex portion 51 is, for example, 2.8 mm. Since the fixing film 2 that has passed through the nip region N1 does not come into contact with any member, the temperature drop of the fixing film 2 can be suppressed.

The cross-sectional shape of the nip forming member 5 between the positions A-A' and C-C' in FIG. 3(a) is continuous in the width direction with the cross-sectional shape shown in FIG. 3(b). Then, the apex 521 of the second protrusion 52 becomes farther from the nip tangent line W as it goes from the CC' position to the end BB' position, and the second protrusion 52 forms a slope shape in the width direction. . In the width direction, the nip forming member 5 has a symmetrical shape centering on the A-A' position. Therefore, a detailed description will be given of the shape in the longitudinal direction on the right side of the paper, and a part of the description on the left side will be omitted.

[Longitudinal Configuration of Nip Forming Member]
FIG. 4(a) is a perspective view of the nip forming member 5, which is viewed obliquely with the second convex portion 52 on the downstream side in the conveying direction facing the front side of the paper. Moreover, FIG.4(b) is the figure which expanded a part (mainly right edge part) of Fig.4 (a). FIG. 4 also shows the AA' position of FIG. 3 and the like. The characteristics of the second protrusion 52 of the nip forming member 5 in the width direction will be described with reference to these figures. The second protrusion 52 has the same (constant) distance between the nip tangent W and the vertex 521 of the second protrusion 52 from the AA' position to the CC' position. From the CC' position to the EE' position, the slope shape is such that the distance between the nip tangent line W and the vertex 521 gradually increases. The second convex portion does not exist in the outer region from the EE' position to the BB' position. In other words, the nip forming member 5 has the second protrusions 52 in regions other than the regions corresponding to the wide regions of the heating elements 41 and 42 . The distance between the AA' position and the EE' position is 105 mm, and the distance between the AA' position and the CC' position is 61 mm.

The reason for choosing the slope shape will be explained below. If the second protrusion has the same cross-sectional shape from the AA' position to the EE' position, and the second protrusion suddenly disappears outside the EE' position (in other words, it is discontinuous). b) If it is a nip forming member, a sharp displacement is given to the fixing film 2 at the EE' position. A steep displacement may cause the fixing film 2 to wear or break such as cracks. Therefore, in Example 1, the second convex portion 52 adopts a slope shape that does not impart a sharp displacement to the fixing film 2 .

[Relationship Between Nip Forming Member and Heater]
FIG. 5(a) is an enlarged view of the nip forming member 5 and the end (right end) of the heater 4. FIG. The upper side of the paper is the downstream side in the transport direction. The positions of the extreme ends of the heating elements 41 and 42 are defined as H1-H1' positions. The apex 521 of the second protrusion 52 of the nip forming member 5 becomes farther away from the nip tangent line W toward the end, and the second protrusion 52 does not exist in the region outside the EE' position. The distance between the EE' position and the H1-H1' position is, for example, 7 mm. The second convex portion 52 is arranged on the inner side in the width direction (on the left side as viewed in the drawing) of the ends of the heat generating elements 41 and 42, which are the longest heat generating elements.

Furthermore, the heating elements 41 and 42 are wider at both ends (H in FIG. 2(b)) than at the central portion, as described with reference to FIG. In other words, both ends of the heating elements 41 and 42 generate less heat per unit length. Since the present invention aims at lowering the temperature in the width direction, it is better not to install the second protrusions if possible even in areas where the amount of heat generated is small. In Example 1, the second convex portion 52 is not provided in the region where the amount of heat generated per unit length is relatively small in the width direction (from the position H1-H1' to the position E-E'). In other words, in the width direction, the second convex portion 52 is arranged only in a region where the amount of heat generated per unit length is not relatively small (on the left side of the end of the heating element as viewed from the paper surface).

FIG. 5(b) is an enlarged end view of the nip forming member 5 and the heater 4, showing the opposite direction (left end) in the width direction with respect to the above description. The positions of the extreme ends of the heating elements 41 and 42 are defined as H2-H2' positions. Also in this direction, the second convex portion 52 is arranged so as to be limited to the inner side in the width direction (to the right side when facing the paper surface) of the ends of the heat generating elements 41 and 42 which are the longest heat generating elements. Moreover, the second convex portion 52 is not provided in a region where the amount of heat generated per unit length is relatively small.

[effect]
In order to confirm the effects of Example 1, comparisons were made with Comparative Examples 1 and 2, in which the shape of the nip forming member was different. iii) The fixing performance of the edges in the width direction of the paper was confirmed.

(Comparative example 1)
FIG. 6A shows a longitudinal direction view of the fixing device of Comparative Example 1 as viewed from the downstream side in the conveying direction. Let AA' be the position of the central portion of the fixing device, and BB' be the position of the edge of the fixing device (on the right side of the paper). Here, the distance between the AA' position and the BB' position is 111 mm. In addition, the same code|symbol is attached|subjected to the member and name which are common in FIG.

FIG. 6B is a cross-sectional view of the fixing device taken along line AA' at the center of the fixing device, and FIG. 6C is a cross-sectional view of the fixing device taken along line BB' at the end of the fixing device. be. In Comparative Example 1, the nip forming member 60 does not have a second protrusion at any location in the width direction. The first convex portion 61 has the same shape as the first convex portion 51 described in the first embodiment, and is continuous in the width direction with the same shape. By comparing Example 1 and Comparative Example 1, the effect of the second convex portion is confirmed. Descriptions of conditions similar to those of the first embodiment, such as the fixing film 2, the pressure roller 3, and the heater 4, will be omitted.

(Comparative example 2)
FIG. 7A shows a longitudinal view of the fixing device of Comparative Example 2 as viewed from the downstream side in the transport direction. Let AA' be the position of the central portion of the fixing device, and BB' be the position of the edge of the fixing device (on the right side of the paper). Here, the distance between the AA' position and the BB' position is 111 mm. In addition, the same code|symbol is attached|subjected to the member and name which are common in FIG.

7B is a cross-sectional view of the fixing device taken along line AA' at the center of the fixing device, and FIG. 7C is a cross-sectional view of the fixing device taken along line BB' at the end of the fixing device. be. The fixing device of Comparative Example 2 has a nip forming member 70 provided with a first convex portion 71 having an apex 711 and a second convex portion 72 having an apex 721 . Comparative Example 2 is significantly different from Example 1 in two respects. The first point is the point where the second convex portion 72 intersects the nip tangent line W. As shown in FIG. The distance between the vertex 721 of the second protrusion 72 and the nip tangent line W in the direction orthogonal to the nip tangent line W is 0.3 mm. The second point is that the shape of the second convex portion 72 is the same (constant) and continuous in the width direction from the A-A' position to the B-B' position. These two major differences are compared with the configuration of the first embodiment. Descriptions of conditions similar to those of the first embodiment, such as the fixing film 2, the pressure roller 3, and the heater 4, will be omitted.

(i) Paper Separation Performance The configurations of Example 1 and Comparative Examples 1 and 2 were compared in terms of paper separation performance. A sheet of paper was pushed into the fixing nip portion formed by the fixing film 2 and the pressure roller 3 in such a direction that the toner image was in contact with the fixing film 2 . It was confirmed whether or not the sheet discharged from the fixing nip portion was separated from the fixing film 2 .

Test conditions are described below. The temperature in the test room was 30°C and the humidity was 80%. Canon CS-060F A4 paper having a basis weight of 60 g/m ² and a thickness of 81 μm was used. The electric power supplied to the fixing device 1 was controlled so that the thermistor in the fixing device 1 maintained 220.degree. The pressure roller 3 was rotated by a drive source (not shown) to convey the paper at 200 mm/sec. The top and bottom margins were 5 mm, the left and right margins were 5 mm, and the density of magenta toner and cyan toner was 0.5 mg/cm ² and 0.5 mg/cm ² , respectively. Here, the leading and trailing edges refer to the downstream (leading edge) edge and the upstream (trailing edge) edge in the paper transport direction.

Confirmation results of paper separation performance are described below. In Example 1 and Comparative Example 2, the paper could be separated. On the other hand, in Comparative Example 1, the paper could not be separated. Consider the test results of the separation performance. The nip forming member 5 of Example 1 has the second protrusions 52 with a small radius of curvature, and the nip forming member 70 of Comparative Example 2 has the second protrusions 72 with a small radius of curvature. It is in pressure contact with the inner peripheral surface. As a result, the radius of curvature of the surface of the fixing film 2 can be greatly reduced at the pressed portion, and the paper can be separated at that region. On the other hand, Comparative Example 1 did not have the second convex portion, and the radius of curvature of the surface of the fixing film 2 could not be reduced, making it impossible to separate the paper.

(ii) Stackability of paper ejected from fixing device 1 (Regarding image forming apparatus)
Using the image forming apparatus shown in FIG. 8, whether or not discharged paper can be stacked in the configurations of Example 1 and Comparative Examples 1 and 2 was checked. The image forming apparatus is an in-line color laser beam printer. The configuration of the image forming apparatus will be described below. The image forming apparatus has four stations for yellow (Y), magenta (M), cyan (C), and black (Bk). Each station has the same configuration, and in FIG. 8, the station of black (Bk) is denoted by reference numerals, and the reference numerals of other stations are omitted. Each station has a photosensitive drum 20 as an image carrier, a charging roller 21 for charging the photosensitive drum 20, a cleaning unit 22 for collecting toner on the photosensitive drum 20, and a developing unit 23 comprising a developing roller, toner, and a developing blade. It's ready. These are integrated process cartridges that can be detachably attached to the image forming apparatus. The exposure device 24 is a scanner unit that scans laser light with a polygonal mirror, and irradiates the photosensitive drum 20 with a scanning beam modulated based on an image signal. The photosensitive drum 20 and the primary transfer roller 25 are arranged to face each other with the intermediate transfer belt 13 interposed therebetween. The intermediate transfer belt 13 is stretched around a tension roller 14 , a secondary transfer facing roller 12 and an auxiliary roller 15 , and the secondary transfer roller 11 is arranged to face the secondary transfer facing roller 12 . An intermediate transfer belt cleaning unit 16 removes toner on the intermediate transfer belt 13 . The fixing device 1 is arranged downstream of the secondary transfer roller 11 in the transport direction.

Next, the image forming process will be described. An electrostatic latent image is formed on the photosensitive drum 20 by the exposure device 24 . The photosensitive drum 20 is brought into contact with a developing roller having toner on its surface to develop a toner image on the photosensitive drum 20 . A voltage is applied to the primary transfer roller 25 to transfer the toner image on the photosensitive drum 20 to the intermediate transfer belt 13 . A voltage is applied to the secondary transfer roller 11, the paper is fed to the transport path by the paper feed roller 17, and the intermediate transfer is performed on the paper (the uppermost sheet of the paper bundle) transported to the secondary transfer roller 11 by the transport roller. The toner image on the belt 13 is transferred. A member that contributes to forming an unfixed toner image on the paper before reaching the fixing device 1 functions as image forming means. The fixing device 1 heats and fixes the toner image onto the paper. The paper is stacked on the discharge section of the image forming apparatus.

Test conditions are described below. The temperature in the test room was 30°C and the humidity was 80%. Canon CS-060F A4 paper having a basis weight of 60 g/m ² and a thickness of 81 μm was used. The electric power supplied to the fixing device 1 was controlled so that the thermistor in the fixing device 1 maintained 220.degree. The process speed of the image forming apparatus is 200 mm/sec. Ten sheets of paper were continuously fed without forming a toner image on the paper, and it was confirmed how the paper curled and whether or not it could be stacked in the discharge section.

FIG. 9 shows an explanatory diagram of the stackability of sheets in the first embodiment. FIG. 9A shows the state of the paper discharged from the fixing device 1. FIG. In FIG. 9A, the paper is discharged from the fixing device 1 while gently curving such that the front surface of the paper faces inward with respect to the transport direction. In FIG. 9A, the surface indicated by oblique lines is the back surface of the paper. FIG. 9B shows how the first to third sheets are stacked in the discharge section when the sheets are continuously discharged. The sheets were neatly stacked on the discharge section of the image forming apparatus. Not only in Example 1, but also in Comparative Example 1, the sheets were stacked without difficulty in substantially the same manner.

Next, FIG. 10 shows an explanatory diagram of the stackability of sheets in Comparative Example 2. As shown in FIG. FIG. 10A shows the state of the paper discharged from the fixing device 1. FIG. In the longitudinal direction of the paper, the paper was discharged while being rolled into a cylindrical shape so that the back surface of the paper was on the inside. In FIG. 10(a), the surface indicated by oblique lines is the back surface of the paper. FIG. 10B shows how the first to third sheets are discharged to the discharge unit when the sheets are continuously discharged. First, a paper rolled into a cylindrical shape was discharged to the discharge unit as the first sheet. The second sheet of paper was ejected to the ejection section while pushing out the first sheet of paper. Similarly, the third sheet pushed out the second sheet, the second sheet pushed out the first sheet, and the first sheet dropped from the discharge section. In Comparative Example 2, stacking of sheets was impossible.

In FIG. 11, as separation performance, the paper can be separated from the fixing film 2 by each fixing device 1 (o) or not (x), and as the stackability of discharged paper, the paper can be loaded in the discharge section (o) ) No (x). It also shows a partial cross-sectional view of the central portion in the longitudinal direction of the nip forming members 5, 60, and 70 on the downstream side in the transport direction, and the paper discharge direction Nw. The paper ejection direction Nw is a direction obtained from a tangent line of the nip portion where the fixing film 2 and the pressure roller 3 are in contact on the downstream side in the transport direction. That is, the discharge direction Nw is the tangential direction at the downstream end of the fixing nip portion in the paper transport direction. FIG. 11 also shows an X direction parallel to the nip tangent line W and a Y direction substantially orthogonal to the X direction.

In Example 1 and Comparative Example 1, the paper is discharged in a state where the discharge direction Nw is tilted with a directional component on the positive side in the Y-axis direction. Since the paper is ejected with a curl in the direction opposite to the direction in which the paper is curled by heating, it was possible to stack the paper in the ejection section. On the other hand, in Comparative Example 2, the second convex portion 72 protrudes more to the negative side than the first convex portion 71 in the Y-axis direction, and the paper discharge direction Nw has a directional component on the negative side in the Y-axis direction. The paper is ejected in a slanted state. As a result, the paper curled up and could not be stacked. If the paper is ejected so that the ejection direction Nw is inclined to the positive side of the Y-axis direction, the paper can be ejected while being curved so that the surface of the paper faces inward. You can make a habit of paper. When the nip forming member 5 having the first convex portion 51 and the second convex portion 52 is mounted on the fixing device 1, the tip of the second convex portion 52 is positioned at least in the first direction in the Y-axis direction. By arranging it on the positive side from the tip of the convex portion, it was possible to stack paper. From these results, it was confirmed that, with the configuration of the first embodiment, both the separation performance of the paper and the stackability of the ejected paper can be achieved.

(iii) Fixing Performance at Edges in Paper Width Direction Regarding the fixing performance at edges in the width direction, configurations of Example 1 and Comparative Examples 1 and 2 were compared. A sheet of paper was pushed into the fixing nip portion formed by the fixing film 2 and the pressure roller 3 in such a direction that the toner image was in contact with the fixing film 2 . It was confirmed whether the toner image was fixed on the paper ejected from the fixing nip portion.

Test conditions are described below. The temperature in the test room was 15° C. and the humidity was 10%. As the paper, HP LaserJetPaper (LTR paper) with a basis weight of 90 g/m ² was used. The electric power supplied to the fixing device 1 was controlled so that the thermistor in the fixing device 1 maintained 220.degree. The pressure roller 3 was rotated by a drive source (not shown) to convey the paper at 200 mm/sec. The top and bottom margins were 5 mm, the left and right margins were 5 mm, and the density of magenta toner and cyan toner was 0.5 mg/cm ² and 0.5 mg/cm ² , respectively. Here, the leading and trailing edges refer to the downstream (leading edge) edge and the upstream (trailing edge) edge in the paper transport direction. Ten sheets of paper were continuously passed through to confirm whether or not the toner image could be fixed on the paper.

In the case of Example 1 and Comparative Example 1, the toner image on the paper could be fixed over the entire area. On the other hand, in the case of Comparative Example 2, there were a plurality of locations where the toner image could not be fixed on the paper at the end positions in the width direction of the paper. In Example 1, the second protrusion does not exist outside the ends of the heating elements 41 and 42, downstream in the conveying direction, and outside the nip area. Moreover, Comparative Example 1 does not have the second convex portion. On the other hand, in Comparative Example 2, the second convex portion 72 exists over the entire area. In neither Example 1 nor Comparative Example 1, the temperature of the fixing film 2 did not drop at the edges in the width direction, so the toner image could be fixed over the entire area of the paper. On the other hand, in Comparative Example 2, the second convex portion 72 contacts the fixing film 2 at the edge in the width direction of the LTR paper, the downstream side in the transport direction, and outside the nip area. As a result, the temperature of the fixing film 2 is lowered in the vicinity of the fixing film 2, and this causes a portion where the toner image cannot be fixed on the paper. The fixing performance at the edges in the width direction of the paper is also indicated as acceptable (o) or not (x) in FIG.

According to this comparative experiment, the existence of the second convex portion in contact with the fixing film 2 outside the ends of the heating elements 41 to 44, downstream in the conveying direction, and outside the nip area causes a temperature drop of the fixing film. , it was confirmed that poor fixing occurred. In other words, it was confirmed that it is important not to provide the second convex portion in the above-described area in order to satisfy the fixing performance at the edges in the width direction of the paper.

As described above, according to the first embodiment, the radius of curvature of the tip portion of the second convex portion 52 is made smaller than the radius of the inner surface of the fixing film 2, and the tip portion of the second convex portion 52 is set to the first convex portion. Distal from the pressure roller 3 or nip tangent W than 51 . As a result, it is possible to achieve both the separation performance of the paper and the stackability of the discharged paper. Further, by arranging the second convex portion 52 only inside the heating elements 41 and 42 in the width direction of the paper, it is possible to avoid the deterioration of the fixability at the edge of the LTR paper having the maximum paper width.
In the above description, a color laser beam printer is used as an example, but the fixing device of the first embodiment can be used without any particular limitation, regardless of monochrome or color, as long as it is an image forming device that uses an electrophotographic recording method. can be done.

As described above, according to the first embodiment, it is possible to improve the sheet separation performance and the stackability of discharged sheets, while preventing the deterioration of the fixing performance at the edges in the width direction of the sheets.

2 fixing film 3 pressure roller 4 heater 5 nip forming member 51 first protrusion 52 second protrusion

Claims (8)

a rotatable cylindrical first rotating body; a second rotating body that biases the first rotating body; and a nip forming member that forms a nip area that is a contact area between the first rotating body and the second rotating body by supporting the A toner image carried on a recording material, comprising: a heater substrate held by a member; is heated in the nip region,
the nip forming member includes a first convex portion positioned inside the nip region and in the vicinity of a downstream end portion in the conveying direction and in contact with the inner peripheral surface of the first rotating body; a second convex portion located outside the nip region and downstream in the conveying direction and in contact with the inner peripheral surface of the first rotating body;
a nip extending parallel to the contact surface through the contact surface between the first rotating body and the second rotating body in the nip region where the heater is in contact with the inner peripheral surface of the first rotating body; In a direction perpendicular to the tangent, a first distance Y1 between the tip of the first protrusion and the nip tangent is the second distance between the tip of the second protrusion and the nip tangent. , the second protrusion extends toward the second rotating body in the orthogonal direction without crossing the nip tangent, and the tip of the second protrusion is smaller than the radius of the inner circumference circle of the first rotating body, the second distance is Y2c at the central portion in the longitudinal direction, and the second distance is Y2e at the ends in the longitudinal direction Then, a fixing device characterized by satisfying Y2e>Y2c. 2. The fixing device according to claim 1, wherein the second convex portion has a shape such that the second distance gradually increases from the central portion toward the end portions in the longitudinal direction. 3. The fixing device according to claim 1, wherein the nip forming member has the second convex portion in a region inside the first rotating body in the longitudinal direction. 4. The nip forming member according to any one of claims 1 to 3, wherein the nip forming member has the second convex portion in a region inside an end portion of the heating element in the longitudinal direction. A fixing device as described. The heating element has, in the longitudinal direction, wide regions at both ends having a width that is wider than the width of the central portion in the conveying direction,
The fixing device according to any one of claims 1 to 4, wherein the nip forming member has the second convex portion in a region other than a region corresponding to the wide region. The heater includes a first heating element, a second heating element having a length in the longitudinal direction shorter than that of the first heating element, and a length in the longitudinal direction shorter than that of the second heating element. 6. The fixing device according to claim 1, further comprising a third heating element. The first heating element is arranged at one end in the short direction of the heater substrate,
The heater has a fourth heating element disposed at the other end of the heater substrate in the short direction so as to be symmetrical with the first heating element,
The second heating element and the third heating element are arranged between the first heating element and the fourth heating element in the lateral direction of the heater substrate. Item 7. The fixing device according to item 6. an image forming means for forming a toner image on a recording material;
a fixing device according to any one of claims 1 to 7;
An image forming apparatus comprising:

Images