Fixing device and image forming apparatus

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

[Technical field]

[0001] 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 that utilizes an electrophotographic recording method, such as a laser printer, a copying machine, or a facsimile. [Background technology]

[0002] As a fixing device for an image forming apparatus, for example, Patent Document 1 discloses a fixing device in which a heat source is disposed inside a fixing film, which is a heating member, and a fixing nip is formed between the fixing film and a pressure roller, which is a pressure member. In this fixing device, the fixing film has a small thermal capacity, so the fixing film can reach a high temperature instantaneously.

[0003] Also, for example, Patent Documents 2 and 3 disclose a fixing device that has a fixing film and a pressure roller, similar to Patent Document 1, and has a fixing nip forming member in the fixing nip that contacts the inner peripheral surface of the fixing film. This fixing nip forming member has a protrusion on the downstream side in the paper transport direction and outside the fixing nip area (hereinafter referred to as the fixing nip area), improving the paper separation performance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-114621 A [Patent Document 2] JP 2012-002956 A [Patent Document 3] Patent No. 6573414 Summary of the Invention [Problem to be solved by the invention]

[0005] When a sheet of paper passes through the fixing nip area, the toner image formed on the sheet of paper comes into contact with the fixing film while being heated. The heated toner becomes more viscous, and the toner image tends to adhere to the outer surface of the fixing film (hereinafter referred to as the outer surface of the fixing film). If the adhesive force is too high, the sheet of paper may remain attached to the outer surface of the fixing film and may not be able to 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 close to a perfect circle, and the radius of curvature of the outer surface of the fixing film is almost the same at every point, so improving the separation performance is an issue.

[0006] In addition, the image forming apparatus is also required to have a stacking ability for the discharged paper. In a fixing configuration in which a heating source is arranged 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 is likely to curl into a cylindrical shape with the back side of the paper facing inward. If the paper curls 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 protrusion on the downstream side of the conveying direction and outside the fixing nip area, and the protrusion protrudes greatly toward the pressure roller. Since the paper is discharged along the rotation direction of the pressure roller, the direction in which the paper curls due to heating and the direction in which the paper is curled due to the discharge direction are the same, and the paper may curl into a cylindrical shape under high temperature and high humidity conditions.

[0007] The fixing device shown in Patent Document 3 is the fixing device shown in Patent Document 1, and is equipped with protrusions that are a feature of Patent Document 2. The protrusions on the outside of the fixing nip portion may lower the temperature of the fixing film when they come into contact with the fixing film. In particular, the temperature of the fixing film is significantly lowered in the region outside the heating element in the width direction of the paper. In conjunction with the temperature drop of the fixing film, the temperature of the fixing film corresponding to the vicinity of the end of the heating element also drops. Therefore, when a wide paper is transported to the fixing nip portion, the fixability of the toner image at the end of the paper in the width direction may be impaired.

[0008] The present invention has been made under these circumstances, and aims to improve paper separation performance and stackability of ejected paper while preventing a decline in fixing performance at the ends of the paper in the width direction. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention has the following configuration. (1) A fixing device comprising: a rotatable cylindrical first rotating body; a second rotating body that biases the first rotating body; a nip forming member that is located on the inner circumferential side of the first rotating body and supports the first rotating body to form a nip region that is a contact region between the first rotating body and the second rotating body; a heater substrate that is held by the nip forming member so as to be in contact with the inner circumferential surface of the first rotating body; and a heater having a heating element that is linear on the heater substrate surface and in a longitudinal direction perpendicular to a conveying direction of a recording material, the fixing device heating a toner image carried on a recording material in the nip region, the nip forming member having a first convex portion that is located inside the nip region and in the vicinity of an end portion on the downstream side in the conveying direction and that abuts against the inner circumferential surface of the first rotating body, and a second convex portion that is located outside the nip region and on the downstream side in the conveying direction and that abuts against the inner circumferential surface of the first rotating body; An extension line of a surface of the heater that is in contact with the first rotating body when viewed in the longitudinal direction In a direction perpendicular to the extension line A first distance Y1 between the tip of the second protrusion and the extension line and the second protrusion is smaller than a second distance Y2 between the extension line a radius of curvature of a tip of the second convex portion is smaller than a radius of an inner circumference of the first rotating body, and the second distance at a center portion in the longitudinal direction is Y2c and the second distance at an end portion in the longitudinal direction is Y2e, where Y2e is greater than Y2c. (2) An image forming apparatus comprising: an image forming means for forming a toner image on a recording material; and the fixing device described in (1) above. Effect of the Invention

[0010] According to the present invention, it is possible to improve the paper separation performance and the stackability of the discharged paper while preventing a decrease in the fixing performance at the end portions in the width direction of the paper. [Brief description of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view of a fixing device according to a first embodiment of the present invention; [Diagram 2] FIG. 1 shows a heater according to a first embodiment. [Diagram 3] 1 is a longitudinal view and a cross-sectional view of a fixing device according to a first embodiment of the present invention; [Figure 4] FIG. 1 is a perspective view and an enlarged perspective view showing a nip forming member according to a first embodiment of the present invention; [Diagram 5] FIG. 1 is a diagram showing the positional relationship between a nip forming member and a heater in the first embodiment; [Figure 6] FIG. 1 is a longitudinal view and a cross-sectional view of a fixing device according to a first comparative example. [Figure 7] FIG. 11 is a longitudinal view and a cross-sectional view of a fixing device according to Comparative Example 2. [Figure 8] FIG. 1 is a cross-sectional view showing an image forming apparatus according to a first embodiment of the present invention. [Figure 9] FIG. 1 is a diagram illustrating the paper loading capacity of Example 1 and Comparative Example 1. [Figure 10] FIG. 10 is a diagram illustrating the paper loading capacity of Comparative Example 2. [Figure 11] FIG. 1 shows the evaluation results of separation performance and paper loading capacity of Example 1 and Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. EXAMPLES

[0013] [Fixing device] The present invention relates to a fixing device in an image forming apparatus using an electrophotographic recording method such as a laser printer, a copier, or a facsimile. A cross-sectional view of a fixing device 1 of a first embodiment is shown in FIG. 1. The fixing device 1 has 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 nip forming member 5 holding the heater 4. The nip forming member 5 is disposed on the inner periphery side of the fixing film 2 and supports the fixing film 2 in the fixing nip portion. The fixing device 1 further has a stay 6 that holds the strength of the fixing device 1 in the longitudinal direction. The longitudinal direction of the fixing device 1 is also a direction substantially perpendicular to the conveying direction of paper as a recording material. The fixing nip portion is formed in a nip region that is a contact region between the fixing film 2 and the pressure roller 3, which is formed by the nip forming member 5.

[0014] The fixing film 2 is composed of a 50μm-thick polyimide base material, a 200μm-thick silicone rubber layer, and a 20μm-thick PFA release layer on top of that. The pressure roller 3 is composed of a SUM core bar with an outer diameter of 13mm, a 3.5mm-thick silicone rubber elastic layer on top of that, and a 40μm-thick PFA release layer on top of that. The pressure roller 3 is rotated by a drive source (not shown), and the fixing film 2, which is biased by the pressure roller 3, is driven to rotate by the pressure roller 3.

[0015] The heater 4 is held by a nip forming member 5, and the inner circumferential surface of the fixing film 2 comes into contact with the surface of the heater 4. Both ends of the stay 6 are pressurized by means not shown, and the pressure roller 3 receives this pressure via the nip forming member 5 and the fixing film 2. This forms a fixing nip where the fixing film 2 and the pressure roller 3 are in pressure contact with each other. The nip forming member 5 must have rigidity, heat resistance, and heat insulation properties, and is made of a liquid crystal polymer.

[0016] The heater 4 is formed of a heating element mainly composed of silver and palladium on a plate-shaped ceramic substrate made of alumina or the like. The heater 4 on the ceramic substrate generates heat. A thermistor (not shown) as a temperature detection means and a thermoswitch (not shown) as a safety element are arranged in contact with each other on the back 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 to control the temperature of the heater 4. Alumina (Al2O3), aluminum nitride (AlN), zirconia (ZrO2), silicon carbide (SiC), etc. are widely known as ceramic substrates. Among them, alumina (Al2O3) is inexpensive and easily available industrially. In addition, metals with excellent strength may be used for the substrate, and stainless steel (SUS) is preferable as a metal substrate because it is inexpensive and has excellent strength. Whether a ceramic substrate or a metal substrate is used as the substrate, an insulating layer may be provided if the substrate is conductive.

[0017] The thermistor can also detect excessive temperature rise. The thermoswitch is a bimetal thermoswitch, and the heater 4 and the thermoswitch are electrically connected. When the thermoswitch detects excessive temperature rise on the back side of the heater 4, the bimetal inside the thermoswitch operates and the power supplied to the heater 4 is cut off.

[0018] [Heater configuration] FIG. 2(a) is a diagram showing the longitudinal direction of the heater 4. The heater substrate 49 is a plate-shaped ceramic substrate made of alumina or the like, and has a thickness t=1 mm, a width W=7.0 mm, and a length L=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, i.e., 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 (on the heater substrate surface) by a printing process. In FIG. 2, the heating elements 41, 42, 43, 44 (hereinafter also referred to as 41 to 44) are represented by white, the conductive paths are represented by diagonal lines, and the power supply contacts 45, 46, 47, 48 (hereinafter also referred to as 45 to 48) are represented by black, respectively.

[0019] The arrangement of the first heating element 41, the fourth heating element 42, the second heating element 43, and the third heating element 44 in the width W direction (short side direction) is as follows: the heating element 41 having the longest length in the longitudinal direction (e.g., 222 mm), the heating element 43 having the second longest length (e.g., 188 mm), the heating element 44 having the third longest length (e.g., 154 mm), and the longest heating element 42 are arranged at equal intervals. The intervals between the heating elements 41 to 44 are 0.7 mm. All of the heating elements 41 to 44 have symmetrical shapes when the longitudinal direction is taken as the left-right direction.

[0020] FIG. 2(b) is an enlarged view of the end of the heater 4. The heating elements 41 and 42 are substantially linear heating elements with 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 position of 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 width of the central part of the heating elements 41 and 42 is a uniform shape of 0.805 mm at any point. The wide region (wide region, near the right end H) of the heating elements 41, 42 has a lower power density than the narrow region (between I and J). Therefore, the heating elements 41, 41 in Example 1 have a characteristic that the power density is slightly lower at both ends than at the center. The heating elements 41, 42 each have a thickness of, for example, 10 μm and a longitudinal length of, for example, 222 mm as described above.

[0021] Heating elements 43 and 44, which are short in the longitudinal direction, are linear heating elements whose width is uniform in the longitudinal direction. Heating element 43 is, for example, 0.8 mm wide, 10 μm thick, and 188 mm long. Heating element 44 is, for example, 0.7 mm wide, 10 μm thick, and 154 mm long.

[0022] [Paper width and heating element control] The maximum paper width (hereinafter referred to as paper width) that can be handled by the fixing device 1 of the first embodiment having such heating elements 41-44 is LTR paper of 216 mm. The paper width is the length in a direction substantially perpendicular to the transport direction. When wide paper such as LTR paper or A4 paper is transported (hereinafter referred to as passing) through the fixing nip, an AC voltage is applied between the power supply contacts 45 and 46, and current is passed through the heating elements 41 and 42 substantially simultaneously to generate heat.

[0023] Furthermore, when B5 paper having a paper width of 182 mm is passed through, control 1 is used alternately to pass current through heating elements 41 and 42 approximately simultaneously to generate heat, and control 2 is used alternately to apply an AC voltage between power supply contacts 46 and 47 to pass current only through heating element 43. Furthermore, when A5 paper having a paper width of 148.5 mm is passed through, control 1 is used alternately to pass current through heating elements 41 and 42 approximately simultaneously to generate heat, and control 3 is used alternately to apply an AC voltage between power supply contacts 47 and 48 to pass current only through heating element 44 to generate heat.

[0024] In the case of LTR paper, the area of ​​the heating elements 41 and 42 that protrude outside the paper area in the width direction is narrow. In the case of A4 paper, the area is wider than that of LTR paper. In the width direction, the fixing film 2 and the pressure roller 3 are generally configured to be longer than the heating elements 41 to 44. If the area of ​​the heating elements that protrude outside the paper area is narrow, a wide area outside the paper area (the ends of the fixing film 2 and the pressure roller 3 in the width direction) is heated with a small amount of energy (heat generation). Therefore, the temperature of the ends of the fixing film 2 and the pressure roller 3 in the width direction is likely to be low. The narrower the area of ​​the heating elements that protrude outside the paper area, the more likely it is that the temperature drop at the ends in the width direction will become an issue. On the other hand, in the case of B5 paper or A5 paper, long heating elements 41 and 42 may be used, and a control (control 1) in which the area of ​​the heating elements 41 to 44 that protrude outside the paper area is wide is used in combination, so the risk of temperature drop at the ends of the fixing film 2 and the pressure roller 3 in the width direction is low.

[0025] The heating elements 41-44 are made of a conductive material mainly composed of silver and palladium, for example, and the conductive paths and power supply contacts 45-48 are made of a conductive material mainly composed of silver, for example. The electrical resistance between both ends of the heating elements 41-44 in the longitudinal direction is, for example, 20Ω for the longest heating elements 41 and 42, 20Ω for the second longest heating element 43, and 25Ω for the third longest heating element 44. A common power supply contact 45 is electrically connected to one end of the longest heating elements 41 and 42, and a common power supply contact 46 is electrically connected to the other end. Therefore, the combined electrical resistance of the longest heating elements 41 and 42 between the power supply contacts 45 and 46 is 10Ω.

[0026] [Configuration of nip-shaped member of fixing device] FIG. 3(a) shows the longitudinal direction of the fixing device 1 as viewed from the downstream side in the transport direction. If the position of the center of the fixing device 1 in the longitudinal direction is A-A' and the position of the end of the fixing device 1 (on the right side of the paper) is B-B', the distance between the A-A' position and the B-B' position is 111 mm. The B-B' position corresponds to the end positions of the heating elements 41 and 42 of the heater 4 (see FIG. 2(b)). The C-C' position is defined between the A-A' position and the B-B' position, and the distance from the A-A' position to the C-C' position is 61 mm. Similarly, the F-F' position is also defined between the A-A' position and the B-B' position, and the distance from the A-A' position to the F-F' position is 86 mm. Furthermore, if the position of the end of the fixing device 1 (on the left side of the paper) is D-D', the distance from the A-A' position to the D-D' position is 111 mm.

[0027] The cross sections of the fixing device 1 at the central portion A-A' and C-C' of the fixing device 1 will be described with reference to FIG. 3(b). The area where the fixing film 2 and the pressure roller 3 contact each other is called the nip area N1, and the area where the fixing film 2 and the heater 4 contact each other is called the nip area N2. The tangent to the nip area N2 is called the nip tangent W (dashed line), and the direction parallel to the nip tangent W is called the X direction (the right direction (opposite the conveying direction) on the paper surface of FIG. 3(b) is positive). The direction perpendicular to the nip tangent W on the paper surface of FIG. 3(b) is called the Y direction (the upward direction on the paper surface of FIG. 3(b) is positive). The nip tangent W is a straight line that passes through the contact surface between the fixing film 2 and the pressure roller 3 in the nip area N2 where the heater 4 contacts the inner circumferential surface of the fixing film 2, and extends parallel to the contact surface.

[0028] The nip forming member 5 at the center of the fixing device 1 in the longitudinal direction includes a first convex portion 51 and a second convex portion 52. The first convex portion 51 is located downstream of the heater 4 in the paper conveying direction and is in contact with the pressure roller 3 with the fixing film 2 sandwiched between them. The first convex portion 51 is located in the nip region N1 (within the region) and in the vicinity of the end of the nip region N1 on the downstream side in the conveying direction. The first convex portion 51 extends (protrudes) toward the pressure roller 3 (Y-axis direction minus side) in a direction substantially perpendicular to the nip tangent line W without crossing the nip tangent line W. The first convex portion 51 presses the inner peripheral surface of the fixing film 2, changing the radius of curvature of the outer surface of the fixing film 2 at the pressed portion. The first convex portion 51 is disposed at a position immediately before the paper is discharged from the fixing nip portion, and has the function of applying 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 of the fixing nip portion in the conveying direction. The point of the first convex portion 51 that is located within the nip region N1 and protrudes most toward the pressure roller 3 side (the negative side in the Y-axis direction) is defined as the apex 511 of the first convex portion 51. The distance between the apex 511 of the first convex portion 51 and the nip tangent line W is defined as the first distance.

[0029] The second convex portion 52 is a convex portion that is located downstream of the heater 4 and the first convex portion 51 in the conveying direction, abuts against the inner circumferential surface of the fixing film 2, and does not receive pressure from the pressure roller 3, in other words, does not contact 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 (negative side in the Y-axis direction) in a direction substantially perpendicular to the nip tangent line W. The second convex portion 52 does not contact the pressure roller 3 across the fixing film 2. The second convex portion 52 can reduce the radius of curvature of the outer surface of the fixing film 2 by pressing the inner circumferential surface of the fixing film 2 at a position immediately after the paper is discharged from the fixing nip portion to give an inflection point to the fixing film 2. As a result, the second convex portion 52 has a function of separating the paper from the fixing film 2. By providing a space R between the first convex portion 51 and the second convex portion 52, where the inner circumferential surface of the fixing film 2 does not come into contact with the nip forming member 5 and the outer surface of the fixing film 2 does not come into contact with the pressure roller 3, the fixing film 2 is brought into contact so as to be wrapped around the second convex portion 52. This allows the fixing film 2 to more reliably come into contact with the second convex portion 52, so that the paper can be stably separated from the fixing film 2. Here, the nip area N1 is, for example, about 8 mm, and the nip area N2 is about 6 mm.

[0030] The point of the second convex portion 52 that protrudes most toward the pressure roller 3 side (negative side in the Y-axis direction) is defined as the apex 521 of the second convex portion 52. The first convex portion 51 is located upstream of the second convex portion 52 in the conveying direction (positive side in the X-direction), and the distance Xa in the X-direction between the apex 511 of the first convex portion 51 and the apex 521 of the second convex portion 52 is, for example, 3 mm. The second convex portion 52 is disposed at a distance from the nip tangent line W without reaching the nip tangent line W, and the second distance (minimum retraction amount) Ya from the apex 521 of the second convex portion 52 to the nip tangent line W is, for example, 0.8 mm. Here, the distance (minimum retraction amount Ya) of the apex 521 of the second convex portion 52 to the nip tangent line W is the distance between the apex 521 of the second convex portion 52 and the nip tangent line W in a direction substantially perpendicular to the nip tangent line W. Note that a first distance (distance Y1) between apex 511 (tip) of first convex portion 51 and nip tangent W is smaller than a second distance (distance Y2) between apex 521 (tip) of second convex portion 52 and nip tangent W. In addition, when the second distance at the center in the longitudinal direction is Y2c and the second distance at the end in the longitudinal direction is Y2e, the relationship Y2e>Y2c holds.

[0031] The tip of the second protrusion 52 has a cross-sectional shape in a direction substantially perpendicular to the longitudinal direction, for example, a semicircular shape with a radius of 4 mm, and the radius of curvature R52 of the region in contact with the inner circumferential surface of the fixing film 2 is 4 mm. The fixing film 2 has a substantially cylindrical shape with an inner circumferential radius of 9 mm, and the radius of curvature of the outer surface is basically about 9 mm. The second protrusion 52 with a small radius of curvature is pressed into contact with the inner circumferential surface of the fixing film 2 to reduce the radius of curvature of the surface of the fixing film 2 at the pressed point, thereby improving the separation performance of the paper from the fixing film 2. The radius of curvature of the second protrusion 52 is preferably smaller than the radius of the inner circumferential circle of the fixing film 2. Here, the radius of the inner circumferential 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.

[0032] A cross section of the fixing device 1 at the F-F' position will be described with reference to FIG. 3(c). The first protrusion 51 has the same shape as the A-A' and C-C' positions. On the other hand, the second protrusion 52 is farther 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 apex 521 of the second protrusion 52 forms a slope shape such that the value of the minimum retraction amount Yb increases from the C-C' position toward the B-B' position.

[0033] A cross section of the fixing device 1 at the B-B' position at the end of the fixing device 1 will be described with reference to FIG. 3(d). The nip forming member 5 at the end of the fixing device 1 in the longitudinal direction has a first convex portion 51. Unlike the central portion, the nip forming member 5 does not have a second convex portion. At a position separated by a distance Xa downstream in the transport direction from the apex 511 of the first convex portion 51, the distance Yc between the nip forming member 5 and the nip tangent line W 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, a decrease in temperature of the fixing film 2 can be suppressed.

[0034] The cross-sectional shape of the nip forming member 5 between the A-A' position and the C-C' position in Fig. 3(a) is the same as the cross-sectional shape shown in Fig. 3(b) in the width direction. From the C-C' position toward the end position B-B', the apex 521 of the second convex portion 52 moves away from the nip tangent line W, and the second convex portion 52 forms a slope shape in the width direction. In the width direction, the nip forming member 5 has a shape symmetrical on the left and right sides with respect to the A-A' position. Therefore, the shape in the longitudinal direction on the right side of the paper will be described in detail, and the description of the left side will be omitted.

[0035] [Longitudinal configuration of nip forming member] FIG. 4(a) is a perspective view of the nip forming member 5, and shows the second convex portion 52 on the downstream side in the conveying direction as seen obliquely from the front of the page. FIG. 4(b) is an enlarged view of a part (mainly the right end) of FIG. 4(a). FIG. 4 also shows the A-A' position in FIG. 3. The characteristics of the second convex portion 52 of the nip forming member 5 in the width direction will be described with reference to these figures. The second convex portion 52 has the same (constant) distance between the nip tangent W and the apex 521 of the second convex portion 52 from the A-A' position to the C-C' position. From the C-C' position to the E-E' position, the second convex portion 52 has a slope shape in which the distance between the nip tangent W and the apex 521 gradually increases. The second convex portion does not exist in the outer region including the E-E' position to the B-B' position. That is, the nip forming member 5 has the second convex portion 52 in the region excluding the region corresponding to the wide region of the heating elements 41 and 42. The distance between the A-A' position and the E-E' position is 105 mm, and the distance between the A-A' position and the C-C' position is 61 mm.

[0036] The reason for selecting the slope shape will be explained below. If the second protrusion has the same cross-sectional shape from the A-A' position to the E-E' position and the second protrusion suddenly disappears outside the E-E' position (in other words, if the nip forming member is discontinuous), a steep displacement will be applied to the fixing film 2 at the E-E' position. The steep displacement may cause wear or damage such as cracks to the fixing film 2. Therefore, in the first embodiment, a slope shape that does not cause a steep displacement is adopted as the second protrusion 52.

[0037] [Relationship between nip forming member and heater] FIG. 5(a) is an enlarged view of the end (right end) of the nip forming member 5 and the heater 4. The upper side in the paper is the downstream side in the transport direction. The positions of the endmost parts of the heating elements 41 and 42 are defined as positions H1-H1'. The apex 521 of the second convex part 52 of the nip forming member 5 becomes farther from the nip tangent line W toward the end, and the second convex part 52 does not exist in the area outside the position E-E'. The distance between the position E-E' and the position H1-H1' is, for example, 7 mm. The second convex part 52 is arranged in a limited area inside (left side in the paper) in the width direction from the end of the heating elements 41 and 42, which are the longest heating elements.

[0038] Furthermore, as explained in FIG. 2, the width of both ends (H in FIG. 2(b)) of the heating elements 41, 42 is wider than that of the center. In other words, the amount of heat generated per unit length is small at both ends of the heating elements 41, 42. Since the present invention aims to reduce the temperature in the width direction, it is better not to provide the second convex portion, 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 area where the amount of heat generated per unit length is relatively small in the width direction (from position H1-H1' to position E-E'). In other words, the second convex portion 52 is arranged only in the area where the amount of heat generated per unit length in the width direction is not relatively small (to the left of the end of the heating element as viewed from the paper surface).

[0039] 5(b) is an enlarged view of the ends of the nip forming member 5 and the heater 4, showing the opposite direction in the width direction (the left end) to the above description. The positions of the extreme ends of the heat generating elements 41 and 42 are taken as positions H2-H2'. In this direction as well, the second protrusions 52 are arranged only on the inner side in the width direction (the right 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 second protrusions 52 are not provided in areas where the amount of heat generated per unit length is relatively small.

[0040] [effect] In order to confirm the effects of Example 1, the following were confirmed by comparing it with Comparative Example 1 and Comparative Example 2, which have different shapes of the nip forming member: (i) paper separation performance, (ii) stackability of the discharged paper, and (iii) fixing performance at the end of the paper in the width direction.

[0041] Comparative Example 1 Fig. 6(a) shows a longitudinal view of the fixing device of Comparative Example 1 as seen from the downstream side in the transport direction. The position of the center of the fixing device is A-A', and the position of the end of the fixing device (on the right side as you face the paper) is B-B'. Here, the distance between the A-A' position and the B-B' position is 111 mm. Note that the same reference numerals are used for members and names that are common to Fig. 3.

[0042] FIG. 6(b) is a cross-sectional view of the fixing device taken at the A-A' position in the center of the fixing device, and FIG. 6(c) is a cross-sectional view of the fixing device taken at the B-B' position in the end of the fixing device. In Comparative Example 1, the nip forming member 60 does not have a second convex portion at any point in the width direction. The first convex portion 61 has the same shape as the first convex portion 51 described in Example 1, and is continuous in the same shape in the width direction. The effect of the second convex portion is confirmed by comparing Example 1 and Comparative Example 1. The description of the same conditions as in Example 1, such as the fixing film 2, pressure roller 3, and heater 4, is omitted.

[0043] Comparative Example 2 Fig. 7(a) shows a longitudinal view of the fixing device of Comparative Example 2 as seen from the downstream side in the transport direction. The position of the center of the fixing device is A-A', and the position of the end of the fixing device (on the right side as you face the paper) is B-B'. Here, the distance between the A-A' position and the B-B' position is 111 mm. Note that the same reference numerals are used for members and names that are common to Fig. 3.

[0044] FIG. 7(b) is a cross-sectional view of the fixing device at the A-A' position in the center of the fixing device, and FIG. 7(c) is a cross-sectional view of the fixing device at the B-B' position at the end of the fixing device. The fixing device of Comparative Example 2 has a nip forming member 70, and the nip forming member 70 is provided with a first convex portion 71 having an apex 711 and a second convex portion 72 having an apex 721. Comparative Example 2 has two major differences from Example 1. The first is the point where the second convex portion 72 intersects with the nip tangent line W. The distance between the apex 721 of the second convex portion 72 and the nip tangent line W in the direction perpendicular to the nip tangent line W is 0.3 mm. The second is that the shape of the second convex portion 72 is the same (constant) and continues in the width direction from the A-A' position to the B-B' position. These two major differences will be compared with the configuration of Example 1. The same conditions as those of Example 1, such as the fixing film 2, the pressure roller 3, and the heater 4, will not be described.

[0045] (i) Paper separation performance The paper separation performance was compared between the configurations of Example 1 and Comparative Examples 1 and 2. A paper was inserted into the fixing nip portion formed by the fixing film 2 and the pressure roller 3 in a direction such that the toner image contacted the fixing film 2. It was confirmed whether the paper discharged from the fixing nip portion was separated from the fixing film 2.

[0046] The test conditions are as follows. The temperature in the test room was 30°C and the humidity was 80%. The paper used had a basis weight of 60 g / m 2 A4 size paper of Canon CS-060F with a thickness of 81 μm was used. The power input to the fixing device 1 was controlled so that the thermistor in the fixing device 1 was maintained at 220° C. The pressure roller 3 was rotated by a drive source (not shown) and the paper was transported at 200 mm / sec. The leading and trailing margins were 5 mm, the left and right margins were 5 mm, and the magenta toner was 0.5 mg / cm 2 , cyan toner 0.5mg / cm 2 Here, the leading and trailing ends refer to the downstream (leading end) end and the upstream (trailing end) end in the conveying direction of the paper.

[0047] The results of the 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. The test results of the separation performance are considered. The nip forming member 5 in Example 1 has a second convex portion 52 with a small radius of curvature, and the nip forming member 70 in Comparative Example 2 has a second convex portion 72 with a small radius of curvature, which is pressed into contact with the inner peripheral surface of the fixing film 2. This makes it possible to significantly reduce the radius of curvature of the surface of the fixing film 2 at the pressed location, making it possible to separate the paper in that area. On the other hand, Comparative Example 1 does not have a second convex portion, and the radius of curvature of the surface of the fixing film 2 cannot be reduced, making it impossible to separate the paper.

[0048] (ii) Loadability of paper discharged from the fixing device 1 (About image forming devices) Using the image forming apparatus shown in FIG. 8, whether or not the discharged paper can be loaded was confirmed in the configurations of Example 1 and Comparative Examples 1 and 2. The image forming apparatus is an in-line type color laser beam printer. The configuration of the image forming apparatus will be described below. The image forming apparatus has four stations, namely, yellow (Y), magenta (M), cyan (C), and black (Bk). Each station has the same configuration, and in FIG. 8, the black (Bk) station is numbered, and the numbers of the other stations are omitted. Each station is equipped with a photosensitive drum 20, which is an image carrier, a charging roller 21 that charges the photosensitive drum 20, a cleaning unit 22 that collects the toner on the photosensitive drum 20, and a developing unit 23 consisting of a developing roller, toner, and a developing blade. These are integrated process cartridges that are detachable from the image forming apparatus. The exposure device 24 is a scanner unit that scans laser light using 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 disposed opposite to each other with the intermediate transfer belt 13 in between. The intermediate transfer belt 13 is stretched around a tension roller 14, a secondary transfer opposing roller 12, and an auxiliary roller 15, and the secondary transfer roller 11 is disposed opposite to the secondary transfer opposing roller 12. An intermediate transfer belt cleaning unit 16 removes toner on the intermediate transfer belt 13. The fixing device 1 is disposed downstream of the secondary transfer roller 11 in the transport direction.

[0049] 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 comes into contact with a developing roller that holds toner on its surface, and a toner image is developed on the photosensitive drum 20. A voltage is applied to the primary transfer roller 25, and the toner image on the photosensitive drum 20 is transferred to the intermediate transfer belt 13. A voltage is applied to the secondary transfer roller 11, and the toner image on the intermediate transfer belt 13 is transferred to a sheet of paper (the uppermost sheet of a stack of paper) that is fed to the conveying path by the paper feed roller 17 and conveyed to the secondary transfer roller 11 by the conveying roller. Members that contribute to forming an unfixed toner image on the paper before it reaches the fixing device 1 function as image forming means. The fixing device 1 heats and fixes the toner image on the paper. The paper is stacked on the discharge section of the image forming device.

[0050] The test conditions are as follows. The temperature in the test room was 30°C and the humidity was 80%. The paper used had a basis weight of 60 g / m 2 A4 size paper of Canon CS-060F with a thickness of 81 μm was used. The power input to the fixing device 1 was controlled so that the thermistor in the fixing device 1 was maintained at 220° C. The process speed of the image forming device was 200 mm / sec. Without forming a toner image on the paper, 10 sheets of paper were fed through in succession to check how the paper curled and whether it could be loaded at the ejection section.

[0051] FIG. 9 shows an explanatory diagram of the paper stacking ability in Example 1. FIG. 9(a) shows the state of the paper discharged from the fixing device 1. In FIG. 9(a), the paper was discharged from the fixing device 1, gently curving so that the front surface (front side) of the paper was on the inside with respect to the conveying direction. In FIG. 9(a), the surface indicated by the diagonal lines is the back surface of the paper. FIG. 9(b) shows how the first to third sheets of paper are stacked in the discharge section when the sheets are continuously discharged. The sheets were neatly stacked and stacked in 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 almost the same manner.

[0052] Next, FIG. 10 shows an explanatory diagram of the stackability of paper in Comparative Example 2. FIG. 10(a) shows the state of paper discharged from the fixing device 1. In the longitudinal direction of the paper, the paper was discharged in a cylindrical shape with the back side of the paper facing inward. In FIG. 10(a), the surface with diagonal lines is the back side of the paper. FIG. 10(b) shows how the first to third sheets of paper are discharged to the discharge section when the paper is continuously discharged. First, the cylindrically curled paper was discharged to the discharge section as the first sheet. The second sheet of paper was discharged to the discharge section while pushing out the first sheet of paper. In the same way, the third sheet of paper pushed out the second sheet of paper, which pushed out the first sheet of paper, and the first sheet of paper fell from the discharge section. In Comparative Example 2, paper stacking was not possible.

[0053] 11 shows the separation performance, i.e., whether or not the paper can be separated from the fixing film 2 by each fixing device 1 (◯) and whether or not the paper can be stacked at the discharge section (◯) as the stackability of the discharged paper. Also shown are partial cross-sectional views of the central portion in the longitudinal direction of the nip forming members 5, 60, 70 on the downstream side of the conveying direction, and the paper discharge direction Nw. The paper discharge direction Nw is the direction determined from the tangent of the nip portion where the fixing film 2 and the pressure roller 3 contact on the downstream side of the conveying direction. In other words, the discharge direction Nw is the tangent direction at the end of the fixing nip portion on the downstream side in the conveying direction of the paper. Also shown in FIG. 11 are the X direction parallel to the nip tangent W and the Y direction approximately perpendicular to the X direction.

[0054] In Example 1 and Comparative Example 1, the paper is discharged in a state in which the discharge direction Nw is inclined with a directional component on the positive side of the Y axis direction. Since the paper is discharged with the paper curled in the opposite direction to the direction in which the paper curls due to heating, it was possible to stack the paper in the discharge section. On the other hand, in Comparative Example 2, the second convex portion 72 protrudes more negatively in the Y axis direction than the first convex portion 71, and the paper is discharged in a state in which the discharge direction Nw of the paper is inclined with a directional component on the negative side of the Y axis direction. Therefore, the paper curls and cannot be stacked. If the paper is discharged with the discharge direction Nw inclined to the positive side of the Y axis direction, the paper can be discharged with a curved shape so that the paper surface faces inward, so that the paper can be curled in the opposite direction to the direction in which the paper curls into a cylindrical shape due to heating. When mounting the nip forming member 5 having the first convex portion 51 and the second convex portion 52 on the fixing device 1, it is possible to stack paper by arranging the tip of the second convex portion 52 at least on the positive side of the tip of the first convex portion in the Y-axis direction. From these findings, it was confirmed that the configuration of Example 1 can achieve both paper separation performance and stackability of discharged paper.

[0055] (iii) Fixing performance at the edge of the paper width direction The fixing performance at the ends in the width direction was compared between the configurations of Example 1 and Comparative Examples 1 and 2. A sheet of paper was inserted into the fixing nip formed by the fixing film 2 and the pressure roller 3 in a direction such that the toner image contacted the fixing film 2. It was confirmed whether the toner image was fixed on the sheet of paper discharged from the fixing nip.

[0056] The test conditions are as follows. The temperature in the test room was 15°C and the humidity was 10%. The paper used had a basis weight of 90 g / m 2 The paper was a LaserJet Paper (LTR paper) manufactured by HP. The power input to the fixing device 1 was controlled so that the thermistor in the fixing device 1 was maintained at 220° C. The pressure roller 3 was rotated by a drive source (not shown) and the paper was transported at 200 mm / sec. The leading and trailing margins were 5 mm, the left and right margins were 5 mm, and the magenta toner was 0.5 mg / cm. 2 , cyan toner 0.5mg / cm 2The toner images were formed on the paper by overlapping them at a density of 1000 x 1000 mm. Here, the leading and trailing ends refer to the downstream (leading end) end and the upstream (trailing end) end in the paper transport direction. Ten sheets were passed through in succession, and it was confirmed whether the toner image was fixed on the paper.

[0057] 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, multiple locations occurred at the end positions in the width direction of the paper where the toner image could not be fixed. In Example 1, the second convex portion does not exist outside the ends of the heating elements 41 and 42, downstream in the conveying direction, and outside the nip area. In Comparative Example 1, the second convex portion does not exist. On the other hand, in Comparative Example 2, the second convex portion 72 exists over the entire area. In both Example 1 and Comparative Example 1, the temperature drop of the fixing film 2 did not occur at the end positions 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 comes into contact with the fixing film 2 at the end positions in the width direction of the LTR paper, downstream in the conveying direction, and outside the nip area. As a result, a temperature drop occurred in the vicinity of the fixing film 2, which caused the toner image on the paper to be unable to be fixed at some locations. The fixing performance at the end positions in the width direction of the paper is also indicated in FIG. 11 as pass (◯) or fail (×).

[0058] This comparative experiment confirmed that the presence of the second protrusions in contact with the fixing film 2 outside the ends of the heat generating elements 41-44, downstream in the transport direction, and outside the nip region causes a drop in the temperature of the fixing film, resulting in poor fixing. In other words, it was confirmed that not providing the second protrusions in the aforementioned region is important in order to satisfy the fixing performance at the ends in the width direction of the paper.

[0059] 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 of the second convex portion 52 is disposed farther from the pressure roller 3 or the nip tangent line W than the first convex portion 51. This makes it possible to achieve both paper separation performance and stackability of the discharged paper. Furthermore, by disposing the second convex portion 52 only inside the heating elements 41, 42 in the width direction of the paper, it is possible to avoid a decrease in fixation at the end of LTR paper of the maximum paper width. In the above explanation, a color laser beam printer has been used as an example, but the fixing device of Example 1 can be used without any particular restrictions in any image forming apparatus that uses an electrophotographic recording method, regardless of whether it is monochrome or color.

[0060] As described above, according to the first embodiment, it is possible to improve the paper separation performance and the stackability of the discharged paper while preventing a decrease in the fixing performance at the end portions in the width direction of the paper. [Explanation of symbols]

[0061] 2 Fixing film 3 Pressure roller 4 Heater 5 Nip forming member 51 First protrusion 52 Second protrusion

Claims

1. a nip forming member located on an inner circumferential side of the first rotor and supporting the first rotor to form a nip region which is a contact region between the first rotor and the second rotor; a heater substrate held by the nip forming member so as to be in contact with an inner circumferential surface of the first rotor; and a heater having a heating element which is linear on the surface of the heater substrate and in a longitudinal direction perpendicular to a conveying direction of a recording material, the fixing device heating a toner image carried on a recording material in the nip region, the nip forming member has a first convex portion located inside the nip region and in the vicinity of an end portion on a downstream side in the transport direction, the first convex portion being in contact with the inner circumferential surface of the first rotating body, and a second convex portion located outside the nip region and on the downstream side in the transport direction, the second convex portion being in contact with the inner circumferential surface of the first rotating body, a fixing device characterized in that, in a direction perpendicular to an extension line of the surface of the heater that contacts the first rotating body when viewed in the longitudinal direction, a first distance Y1 between the tip of the first convex portion and the extension line is smaller than a second distance Y2 between the tip of the second convex portion and the extension line, the second convex portion extends toward the second rotating body in the perpendicular direction without exceeding the extension line, a radius of curvature of the tip of the second convex portion is smaller than a radius of an inner circle of the first rotating body, and the second distance at the center in the longitudinal direction is Y2c and the second distance at an end in the longitudinal direction is Y2e, Y2e > Y2c.

2. 2 . The fixing device according to claim 1 , wherein the second protrusion is shaped such that the second distance gradually increases from a center portion toward an end portion in the longitudinal direction.

3. 3. The fixing device according to claim 1, wherein the nip forming member includes the second protrusion in an inner region of the first rotating body in the longitudinal direction.

4. 4. The fixing device according to claim 1, wherein the nip forming member includes the second protrusion in an area located inside an end of the heat generating element in the longitudinal direction.

5. the heat generating element has wide regions at both ends in the longitudinal direction, the wide regions having a width greater than a width of a central portion in the transport direction; 5. The fixing device according to claim 1, wherein the nip forming member has the second protrusion in an area other than an area corresponding to the wide area.

6. 6. The fixing device according to claim 1, wherein the heater has 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 third heating element having a length in the longitudinal direction shorter than that of the second heating element.

7. the first heating element is disposed at one end in a short side direction of the heater substrate, the heater has a fourth heating element disposed at the other end of the heater substrate in the short side direction so as to be symmetrical to the first heating element, 7. The fixing device according to claim 6, wherein the second heat generating element and the third heat generating element are disposed between the first heat generating element and the fourth heat generating element in the short-side direction of the heater substrate.

8. an image forming means for forming a toner image on a recording material; The fixing device according to claim 1 , An image forming apparatus comprising:

Images