JP4298272B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fixing device and an image forming apparatus, and more particularly to a configuration for fixing an unfixed image on a recording medium using a belt.
[0002]
[Prior art]
In an image forming apparatus such as a copying machine, a facsimile, a printer, or a printing machine, an unfixed image transferred and carried on a sheet-like recording medium (hereinafter referred to as a sheet) such as paper is heated and fixed. Copies and records can be obtained.
The fixing device has a configuration in which an unfixed image on a sheet is heated from one roller while the sheet is nipped and conveyed by a pair of rollers.
[0003]
There is a configuration in which a roller and a belt are combined in addition to a configuration in which fixing is performed between rollers (for example, Patent Document 1).
In this configuration, as shown in FIG. 8, instead of the roller located on the side facing the unfixed image, the belt C wound around the pair of rollers A and B is arranged to face the unfixed image. A pressure roller D for pressing the sheet is opposed to one of the rollers A.
Among the rollers around which the belt C is wound, the roller A facing the pressure roller D is a fixing roller facing the surface carrying the toner T of the sheet S, and rollers B and D other than this fixing roller. Is a heating roller incorporating heat sources B1 and D1 for heating the belt.
[0004]
Since the heat capacity can be reduced by reducing the volume of the belt compared to the rollers, the temperature can be increased in a short time, and the temperature rise at the start-up is higher than when only the above-described roller pair is used. There is an advantage of being fast.
[0005]
On the other hand, in the fixing device using the fixing belt, the first nip portion that can convey and clamp the sheet S when the belt C abuts along the circumferential surface of the pressure roller D is the moving direction of the sheet S (in FIG. 8). , A direction indicated by an arrow) is configured on the upstream side, and a second nip portion that can hold and convey the sheet S to and from the fixing roller A facing the pressure roller D continuously to the nip portion is configured. It has become.
The sheet S enters the first nip portion located on the upstream side, moves toward the second nip portion while moving between the belt C and the peripheral surface of the pressure roller D, and moves the second nip portion. After passing, separation is performed using the curvature of the fixing roller A. When the fixing belt is used in this way, there is an advantage that the range in which the sheet receives heat can be lengthened as compared with the configuration using the roller pair.
[0006]
By the way, in the configuration shown in FIG. 8, in order to secure the second nip portion constituted by the belt C and the pressure roller D, the heating roller B moves the sheet S in the moving direction more than the first nip portion. Arranged upstream. For this reason, the sheet S directed toward the first nip portion must enter an extremely narrow angle θ between the belt C and the pressure roller D, and moves in a state of being close to the belt S. . Therefore, if the belt C or the sheet S has poor flatness, that is, if the belt C or the sheet S has a wavy phenomenon or a slack, the unfixed toner T carried on the sheet S easily comes into contact with the belt C. Then, image shift and inadvertent transfer to the belt C occur.
Conventionally, in order to prevent the occurrence of such a problem, a configuration in which an elastic member for pressing the belt C toward the pressure roller D is arranged on the back surface of the belt entering the first nip portion (for example, Patent Document 2). Or a pad-shaped member for pressing the belt C against the pressure roller D in this region with respect to the belt region constituting the second nip portion (for example, Patent Documents 3 to 5) Has been proposed.
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-30796 (Claim 1, FIG. 1)
[Patent Document 2]
JP-A-9-160405 (paragraph numbers “0013” and “0021” columns, FIGS. 1 and 2)
[Patent Document 3]
Japanese Patent Laid-Open No. 11-2979 (paragraph “0007” column, FIG. 1)
[Patent Document 4]
Japanese Patent Laid-Open No. 11-45025 (paragraph number “0036” column, FIG. 1)
[Patent Document 5]
JP-A-10-307493 (paragraph number “0028” column, FIG. 1)
[0008]
[Problems to be solved by the invention]
When an elastic member is used for pressure contact of the belt, problems with respect to slidability and wear resistance between the surface of the elastic member and the belt are likely to occur. The reliability of the durability of the member is low. For this reason, when an elastic member is used, as disclosed in JP-A-9-160405 or as shown in FIG. 9, the elastic member is made into a roller shape so as not to impair the mobility of the belt. As a result, there arises a problem that a roller support structure or the like is required. In addition, in the case of the roller, the pressing area along the circumferential direction of the pressure roller is only a part of the circumferential surface of the pressing roller and is limited to a very narrow range. There is a risk of causing a result that lifting cannot be reliably prevented.
[0009]
In the case of using a belt, as disclosed in Patent Document 3 or 4 and Patent Document 5 mentioned above, the belt is directed toward the heating roller in order to maintain the pressure contact state between the belt and the heating roller that heats the belt. A member for pressurizing is provided. In such a configuration, a nip portion capable of nipping and conveying the sheet is formed at a position where the pressure member and the belt face each other and a position where the heating roller and the belt face each other. As described above, when the nip portion is configured at a plurality of locations, a peripheral speed difference due to slip or roller distortion is likely to occur, and an abnormal image due to the peripheral speed difference between opposing members is likely to occur. There is. An abnormal image is offset on the belt while the toner heated in the nip portion located upstream in the sheet movement direction is melted halfway, and the offset toner is sheeted in the nip portion located downstream in the sheet movement direction. This occurs when the image is transferred again to a position different from the image transfer position. In particular, such a phenomenon becomes more prominent as the length of the nip portion located in the initial stage of melting the powdery toner is shorter. In particular, in the configuration shown in FIG. 9, the first nip portion is constituted by a part of the circumferential surface of the pressing roller, and the length of the nip portion is extremely short, so that an abnormal image is likely to occur.
[0010]
In order to eliminate abnormal images due to toner retransfer, it is necessary to secure the length of the nip portion formed by the pressure contact between the heating roller and the belt, as described in the previous patent document. However, in order to increase the length of the nip portion, the circumferential length of the heating roller must be increased, and as a result, the curvature radius of the heating roller cannot be reduced. For this reason, it takes a long time for the temperature to rise at the roller for heating the belt, and it becomes difficult to obtain a phenomenon that the temperature rise, which is an effect obtained when the belt is used, can be accelerated.
[0011]
In order to secure the contact state between the sheet and the heating roller at the nip portion, it is conceivable to press the sheet toward the heating roller with a high load. A load is increased with respect to the rotation, and it is difficult to maintain the belt mobility, that is, the sheet transportability and the belt durability.
[0012]
On the other hand, as a method of lengthening the nip portion, there is a method of improving the adhesion of the belt to the heating roller by imparting elasticity using a rubber layer or the like to the roller constituting the nip portion by the belt against the heating roller. However, a certain degree of rigidity is required for the member that presses the belt against the heating roller via the rubber layer. As a result, when the pressing member is a roller, the structure is thick. For this reason, an increase in the heat capacity is caused and the temperature rise is worsened.
[0013]
As another method of lengthening the nip portion, there is a method of setting a large curvature radius by increasing the circumference of the heating roller. However, in this method, the curvature separation of the sheet that has passed through the nip portion tends to be insufficient. In particular, when the release agent for preventing toner offset is not used, the above-described inseparability is likely to occur.
[0014]
The object of the present invention is to solve the problems in the above-described conventional fixing device, particularly in the fixing structure using a belt as one of the members constituting the nip portion with respect to the sheet. A fixing device and an image forming apparatus having a configuration that can improve misalignment and prevent inadvertent misalignment and transfer of toner to a belt due to the above, and improve separation characteristics even when no release agent is used. It is to provide.
[0015]
[Means for Solving the Problems]
The invention according to claim 1 is an apparatus for fixing toner in an unfixed image carried on a sheet, the movable endless belt being wound around a plurality of members and contacting the unfixed toner image, A heating member that heats the endless belt as one of the plurality of members, a second member that is another one of the plurality of members, facing the pressure member across the belt, and the plurality of members And a first member that faces the pressure member across the belt, the first member being made of metal or resin. Part of the shape of the pressure member The first nip portion is formed in a pressing region between the pressing member and the first member, and the second nip portion is formed in a pressing region between the second member and the pressing member. The fixing is performed by passing the sheet carrying the unfixed toner image through the second nip portion following the first nip portion.
[0017]
Claim 2 The described invention is claimed. 1 In addition to the invention described above, a friction reducing portion is provided on a surface of the fixing member facing the belt.
[0018]
Claim 3 The invention described in claims 1 to 2 In addition to the invention described in one of the above, the fixing member constitutes a guide portion when the belt enters the first nip portion.
[0019]
Claim 4 The invention described in claims 1 to 3 In addition to the invention described in one of the above, the fixing member is arranged such that an end facing the member facing the pressing member is disposed close to the member.
[0020]
Claim 5 The invention described in claims 1 to 4 In addition to the invention described in one of the above, the length of the first nip portion formed in the pressing region between the fixing member and the pressing member used as the first member is the second member and the additional member. It is characterized by being set longer than the length of the second nip portion formed in the pressing area with the pressure member.
[0021]
Claim 6 The invention described in claims 1 to 5 In addition to the invention described in one of the above, the fixing member and the pressure applied to the pressure per unit area at the second nip formed in the pressing region between the second member and the pressure member. With pressure member Pressing It is characterized in that the pressure per unit area at the first nip portion formed in the region is reduced.
[0022]
Claim 7 The invention described in claims 1 to 6 In addition to the invention described in one of them, the fixing member is characterized in that a plurality of grooves parallel to the moving direction of the belt are provided on the surface facing the belt.
[0023]
Claim 8 The invention described in claims 1 to 7 The fixing device described in any one of the above is used for an image forming apparatus.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a view showing one of image forming apparatuses to which a fixing device according to an embodiment of the present invention is applied. The image forming apparatus shown in FIG. 1 is a copier or printer capable of forming a full-color image. In addition to this, there is a facsimile apparatus capable of performing the same image forming process as the above-described copying machine and printer based on a received image signal. Note that the image forming apparatus includes not only the above-described color image but also an apparatus that targets a single color image.
[0025]
An image forming apparatus 1 shown in FIG. 1 includes a plurality of photosensitive drums 1A, 2A, 3A, and 4A that can form an image corresponding to a color-separated color (yellow, cyan, magenta, and black). The visible image formed on the photosensitive drum is superimposed and transferred onto a transfer sheet S that is a recording medium conveyed by a transfer belt 5 that is movable while facing each photosensitive drum.
[0026]
Now, the configuration relating to the image forming process will be described on behalf of one photosensitive drum 1A as follows. Since the other photosensitive drums 2A to 4A have the same configuration, for convenience, reference numerals assigned to the photosensitive drum 1A are attached to the part numbers of the photosensitive drums.
Around the photosensitive drum 1A, a charging device 1B using a configuration such as a corotron or a scoroton for executing an image forming process along the rotation direction indicated by an arrow (in FIG. 1, a configuration using a roller is shown). A writing device 1C, a developing device 1D, and a cleaning device 1E using laser light are disposed. In the image forming apparatus 1 shown in FIG. 1, a document reading unit 6 is disposed above an image forming unit in which these devices for performing image forming processing are disposed, and a document placed on a document placing table 6A. The image information read by the reading device 7 is output to an image processing control unit (not shown), and the writing information for the writing device 1C described above can be obtained. The charging device 1B is not limited to a contact type using a roller, but can also use a corona discharge type using a discharge wire.
In this embodiment, the developing devices are arranged in the order in which yellow, cyan, magenta and black toners can be supplied from the right side of the extended portion of the transfer belt 5 in FIG.
[0027]
The reading device 7 forms an image on a light source 7A for scanning a document placed on the document placing table 6A and a reflected light from the document on a CCD 7B provided for each color separation. A plurality of reflecting mirrors 7C and an imaging lens 7D are provided, and image information corresponding to the light intensity for each color separation is output from each CCD 7B to the image processing control unit.
[0028]
The transfer belt 5 is a member made of a dielectric material such as a polyester film wound around a plurality of rollers, and one of the extended portions faces each of the photosensitive drums 1A to 4A, and faces the respective photosensitive drums. Inside the position, transfer devices 8A, 8B, 8C and 8D are arranged. The transfer belt 5 is fed with the sheet S fed out from the sheet feeding cassette 9A of the sheet feeding device 10 through the registration roller 9, and the sheet S is corona from the transfer device 8A to the transfer belt 5. It is conveyed by being electrostatically attracted by discharge.
[0029]
At the position where the sheet S on which image transfer from each of the photosensitive drums 1A to 4A has been completed is moved, the sheet S separating device 11 is also a portion on the opposite side of the stretched portion that faces the photosensitive drums 1A to 4A Is disposed with a static eliminating device 12 facing the belt. In FIG. 1, reference numeral 13 denotes a cleaning device that removes the toner remaining on the transfer belt 5.
The transfer devices 8 </ b> A to 8 </ b> D are configured to electrostatically attract the images carried on the photosensitive drums 1 </ b> A to 4 </ b> A toward the sheet S using positive corona discharge.
[0030]
The separation device 11 neutralizes the charge accumulated in the sheet S by performing negative AC corona discharge from the upper surface of the sheet S, and releases the electrostatic adsorption state, thereby reducing the curvature of the transfer belt 5. Separation using the toner is enabled, and toner dust is prevented from being generated due to peeling discharge during separation. Further, the static eliminator 12 neutralizes the accumulated charge of the transfer belt 5 by performing negative AC corona discharge having a polarity opposite to the charging characteristics of the transfer devices 8A to 8D from both the front and back surfaces of the transfer belt 5. Initialization is to be performed.
[0031]
In each of the photosensitive drums 1A to 4A, the surfaces of the photosensitive drums 1A to 4A are uniformly charged by the charging devices 1B to 4B, and based on image information for each color separation color read by the reading device 7 in the document reading unit 6. An electrostatic latent image is formed on the photosensitive drum using the writing devices 1C to 4C, and the electrostatic latent image can be formed by toner of a color having a complementary color relationship corresponding to the color separation color supplied from the developing devices 1D to 4D. After the visual image processing, the sheet S carried on the transfer belt 5 and conveyed is electrostatically transferred via the transfer devices 8A to 8D.
[0032]
The sheet S to which the image for each color separation carried on each of the photosensitive drums 1A to 4A is transferred is discharged by the discharging device 11 and then is separated by using the curvature of the transfer belt 5, and then the fixing device 14 is used. The toner in the unfixed image is fixed and discharged.
[0033]
The configuration of the fixing device 14 is shown in FIG.
In FIG. 2, the fixing device 14 includes a fixing belt 15 that uses an endless belt that is wound around a plurality of members and can convey a sheet.
One of the plurality of members around which the fixing belt 15 is wound is a heating roller 16 including a halogen heater 16A as a heat source as a third member, and the other member includes the fixing belt 15. The fixing roller 18 is used as a second member that is sandwiched and opposed to the pressure roller 17, and yet another member of the plurality of members is located between the heating roller 16 and the fixing roller 18, and The fixing member 19 is used as a first member capable of rotating the fixing belt 15 between both rollers. Details of the fixing member 19 will be described later.
[0034]
For the fixing belt 15, a heat resistant resin is used as a base, and polyimide, polyamideimide, polyetherketone (PEEK), or the like is used as the resin. The thickness of the substrate is set to about 30 to 100 μm in consideration of the balance between heat conduction and strength, and the surface has excellent releasability and heat resistance when pressed against the sheet S and toner T. For example, a surface release layer using a fluorine resin or the like is coated and provided. Further, an elastic layer made of heat-resistant rubber such as silicone rubber or fluorine rubber having a thickness of about 100 to 300 μm is provided below the surface release layer for uniform contact with the image.
[0035]
The heating roller 16 is composed of a thin roller made of aluminum (Al) or iron (Fe) having a thickness of about 0.3 to 1 mm and 20 to 30φ, and a halogen heater 16A serving as a heat source is disposed inside. . In the lighting control of the halogen heater 16A, the surface temperature is kept constant by temperature detection by the temperature control member 20 in contact with the heating roller 16.
The heating roller 16 also has a function as a tension roller of the fixing belt 15, and as shown by a thick arrow in FIG. 2, tension is generated on the fixing belt 15 by an urging means such as a tension spring (not shown). I am letting.
[0036]
The pressure roller 17 is provided with an elastic layer such as fluorine rubber or silicone rubber and a surface release layer made of fluorine resin on the outer periphery of the above-described aluminum (Al) or iron (Fe) cored bar.
In the present embodiment, the thickness of the elastic layer is set to about 0.5 to 5 mm, and the surface hardness is set to Asker C70 to 90Hc. Further, a halogen heater 17A may be disposed as a heat source for accelerating the rise in the roller surface temperature.
[0037]
In order to obtain a nip width on the outer periphery of an iron (Fe) core metal having a diameter of 20 to 30φ, the fixing roller 18 includes a heat resistant elastic body layer made of, for example, foamed silicone rubber or liquid silicone rubber. The layer is set to a thickness of about 3 to 6 mm, and the surface hardness is set to about Asker C30 to 50 Hs.
[0038]
Among the plurality of members around which the fixing belt 15 is wound, the fixing member 19 as the first member in addition to the heating roller 16 and the fixing roller 18, together with the fixing roller 18, attaches the fixing belt 15 to the peripheral surface of the pressure roller 17. In this embodiment, the fixing belt 15 is disposed on the peripheral surface of the pressure roller 17 at a position where pressure contact is started. Thus, the fixing belt 15 is also wound around and the pressing portion for the pressure roller 17.
[0039]
As a material used for the fixing member 19, a metal such as iron, stainless steel, or aluminum, or a heat-resistant resin such as polyphenylene sulfide (PPS) is used, and a surface facing the pressure roller 17 is a pressure roller. The contact surface of the fixing belt 15 with respect to the pressure roller 17 is improved by forming a concave shape such as a planar shape or a downward arc shape in accordance with the curvature of the peripheral surface so as to follow the shape of the surface, that is, the peripheral surface. Yes.
[0040]
A plurality of grooves (not shown) parallel to the moving direction of the sheet S are formed on the surface of the fixing member 19 facing the fixing belt 15 along a direction perpendicular to the moving direction of the sheet. A plurality of grooves set to a width of 0.2 to 0.5 mm and a depth of 0.2 to 0.5 mm are formed along the sheet moving direction. In addition, a friction reducing portion is provided on the surface of the fixing member 19 that faces the fixing belt 15. In the present embodiment, a fluorine resin such as Teflon (registered trademark) or a sheet of glass fiber is laminated. Has been. In this case, the lamination is configured by wearing a sheet or by painting.
[0041]
The fixing member 19 is disposed at a position where the fixing belt 15 is extended along the peripheral surface of the pressure roller 16 together with the fixing roller 18, and the fixing belt 15 is pressed against the pressure roller 16 to the upstream side in the sheet moving direction. An inlet portion of a first nip portion (portion indicated by a symbol L1 in FIG. 2) formed in a pressing area with the pressure roller 16 is provided. For this reason, the fixing member 19 functions as a guide portion into which the fixing belt 15 enters when the fixing belt 15 goes around the surface of the fixing member 19.
The second nip portion (the portion indicated by reference numeral L2 in FIG. 2) with respect to the first nip portion L1 is a portion where the sheet S is nipped and conveyed by the pressure roller 17 and the fixing roller 18 opposite to the pressure roller 17. It corresponds.
[0042]
On the other hand, an end portion of the fixing member 19 provided along the peripheral surface of the pressure roller 17, that is, an end portion facing the fixing roller 18 is a gap between the fixing roller 18 (the first portion in FIG. 2). The distance between the end portions of the nip portion L1 and the second nip portion L2 facing each other) is made close to a position where it can be minimized. As a result, when the fixing belt 15 moves along the peripheral surface of the pressure roller 17, the distance from which the nip portion is removed is minimized so that the sheet is prevented from being lifted.
[0043]
In FIG. 2, the lengths of the first nip portion L1 and the second nip portion L2 are set such that L1> L2. That is, the length of the first nip portion L1 configured by the fixing member 19 and the pressure roller 17 is longer than that of the second nip portion configured by the fixing roller 18 and the pressure roller 17. . This is a phenomenon that occurs when the sheet S that has entered the first nip portion L1 is not rubbery by lengthening the heat receiving time to melt and soften the toner T in an unfixed state to make it rubbery. The reverse transfer of the toner to the belt is prevented to prevent the occurrence of an abnormal image due to the reverse transfer toner adhering to other portions of the sheet.
[0044]
In the present embodiment, the pressure relationship per area between the first nip portion L1 and the second nip portion L2 is P1 (pressure at the first nip portion) <P2 (second nip portion). Pressure). Accordingly, the load acting on the fixing belt 15 in the first nip portion L1 is made smaller than that in the second nip portion L2 so that the mobility of the fixing belt 15 is not hindered. This prevents the peripheral speed difference from occurring.
[0045]
Since the present embodiment is configured as described above, the sheet S after transfer passes through the second nip portion L2 following the first nip portion L1. That is, when the sheet S reaches the fixing device 14, the sheet S is guided by the fixing member 19 and immediately applied to the first nip L 1, that is, the fixing belt 15 pressed against the pressure roller 17 by the fixing member 19. It enters the surface facing the pressure roller 17 and moves through the first nip portion L1.
[0046]
A guide portion L10 for guiding the sheet S is provided in front of the first nip portion L1, that is, a position immediately before the sheet enters the first nip portion L1, and the fixing belt 15 is disposed on the guide portion L10. Since it is hung along, a wide space for entering the first nip portion L1 of the sheet S can be secured. Therefore, unlike the conventional configuration, even if the fixing belt 15 or the sheet S is wavy or wrinkled on the way to the nip portion, the fixing belt 15 can immediately enter the first nip portion L1 and is not fixed by the fixing belt 15. The situation of rubbing the toner T is eliminated, and the transfer of the toner T does not occur.
[0047]
According to the embodiment as described above, the fixing member 19 that forms the winding portion of the fixing belt 15 is used as the guide portion of the sheet S, and the guide portion is located at the initial position of the first nip portion L1 to which the sheet is directed. By being positioned, it is possible to start the fixing operation by pressing the sheet S against the neighboring member without contacting the neighboring member, and members constituting the nip portion other than the member as the winding portion can be started. Unlike the case where it provides, the member which comprises a nip part can be simplified.
[0048]
Next, the modification regarding the said embodiment is demonstrated. In the following drawings, the same members as those shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.
FIG. 3 shows a configuration characterized in that the fixing member 19 is elastic. In FIG. 3, the surface of the fixing member 19 facing the fixing belt 15 is foamed with a thickness of about 1 to 5 mm. An elastic body layer 21 made of silicone rubber or liquid silicone rubber is integrated, and a friction reducing layer made of a fluorine-based material or a glass fiber sheet is formed on the surface of the elastic body layer 21 facing the fixing belt 15. For convenience, a reference numeral 22 in FIG. 3 is provided. In addition, as a material used for the elastic body layer 22, felt made of glass or ceramic can be used in addition to the above-described materials.
[0049]
In the above configuration, by providing the elastic body layer 22 on the fixing member 19, a uniform pressing state at the first nip portion L 1 can be obtained, and an excessive load increase on the fixing belt 15 can be prevented. 22 can be absorbed by elastic deformation. As a result, an increase in the conveyance resistance of the fixing belt 15 can be suppressed and a difference in peripheral speed between the sheet S and the fixing belt 15 can be prevented, thereby preventing an abnormal image.
[0050]
Next, a partial modification of the configuration shown in FIG. 2 will be described.
FIG. 4 is characterized by having a configuration capable of increasing the heating area in place of the heating roller shown in FIG.
In FIG. 4, a planar heater 23 having a semicircular arc shape is provided at a position where the heating roller 16 was located.
The planar heater 23 includes a resistance heating layer made of silver (Ag) or the like on a surface of a base made of iron (Fe) or aluminum (Al) through a thin insulating layer such as ceramic or polyimide. Such a planar heater 23 can heat the fixing belt 15 in a smaller space than a case where a roller is used, and also has a small heat capacity, so that the temperature rise time can be shortened.
The planar heater 23 is supported at both ends of a semicircular arc shape by a member (not shown) and is urged by a biasing means (not shown) in a direction in which a tension is applied to the fixing belt 15.
[0051]
The configuration using the planar heater 23 shown in FIG. 4 can also be applied to the configuration shown in FIG. 3, and FIG. 5 shows a case where the planar heater 23 is provided for the configuration shown in FIG. It is shown.
[0052]
Next, a modified example relating to a pressure member in which the pressure roller 17 shown in FIG. 2 is used will be described. In the following drawings, the same components as those shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.
FIG. 6 is a schematic diagram showing a configuration using the pressure fixing member 24 instead of the pressure roller 17 for the configuration shown in FIG.
In FIG. 6, the pressure fixing member 24 is made of a heat resistant resin or metal, and sandwiches the sheet S by facing the fixing belt 15 over both the first nip portion L1 and the second nip portion L2. A pressure belt 25 constituting the conveyance path is fitted on the outer surface.
The pressure fixing member 24 is disposed on the back side of the surface of the pressure belt 25 facing the fixing belt 15, the friction reducing layer 26 is in contact with the pressure belt 15, and the friction reducing layer 26 is pressed. An elastic layer 27 is laminated between the fixing member 24 and the fixing member 24.
[0053]
The pressure belt 25 has a planar shape so as to move the first and second nip portions L1 and L2 together with the fixing belt 15, and is driven by the fixing belt 16 in contact with the second nip portion L2. It moves in the direction of the arrow shown in the figure.
[0054]
In the above configuration, since the pressure belt 25 has a planar shape unlike the case of the pressure roller 17, the length of the nip portion can be increased, thereby improving the melt softening and penetration of the toner. And fixability can be improved. In addition, since the portion where the temperature rises in contact with the fixing belt 15 is thin unlike the roller, the heat capacity can be reduced, thereby shortening the time required for temperature rise.
[0055]
In the above configuration, the pressure fixing member 24 is located on the back side of the sheet S, that is, on the back side of the toner T carrying surface. Therefore, unlike the fixing belt 15, the pressure fixing member 24 starts from the initial position of the first nip portion L1. Further, it can be extended toward the upstream side in the sheet moving direction. For this reason, the heat transfer region from the fixing belt 15 that can be formed between the extended portion and the position facing the fixing member is made longer than the fixing belt 15 to be a preheating zone of the sheet S, thereby melting the toner T. The softening can be promoted to accelerate the penetration of the toner T into the sheet S.
[0056]
The configuration of the pressure fixing member shown in FIG. 6 can also be applied to the configuration shown in FIG. 5, and FIG. 7 shows the case where the pressure fixing member 24 is provided for the configuration shown in FIG. It is shown.
[0057]
【The invention's effect】
Claim 1 And 5 According to the described invention, the member corresponding to one of the circulating portions of the belt and the member facing the pressure member function as a belt wrapping member to press the belt against the pressure member, and the entrance portion of the nip portion is provided. Since the fixing member that is the first member is used, the belt-wrapped portion can be used as the inlet member of the nip portion as it is. In particular, in the invention according to claim 2, a part of the fixing member is shaped to follow the surface of the pressure member, so that a nip portion can be formed that adheres with a long and uniform pressure even with a small load. The difference in fixing efficiency due to the deterioration of the transportability and the difference in pressure distribution can be eliminated, and in the invention of claim 6, the length of the first nip portion constituted by the fixing member and the pressure member Is set to be longer than the length of the second nip portion constituted by the pressure member and the member facing the pressure member. A molten state is obtained, and in this state, the toner can be in a rubber state, that is, in a state where reverse transfer to the belt does not occur. As a result, when a plurality of nip portions are formed, even if a difference in peripheral speed occurs between the members constituting the nip, it is possible to reliably prevent a part of the toner from reversely transferring to the belt and causing an abnormal image. It becomes possible to do.
[0058]
Claim 2 According to the described invention, since the friction reducing portion is provided on the surface of the fixing member facing the belt, the slidability of the belt is not deteriorated. As a result, it is possible to prevent the occurrence of an abnormal image by suppressing the occurrence of a peripheral speed difference.
[0059]
Claim 3 According to the described invention, since the fixing member constitutes the entry guide portion that can secure a wide space for the belt to enter the nip portion, the belt and the sheet come into contact with each other on the way to the nip portion unlike the conventional configuration. You can avoid it. As a result, even if the belt or sheet is wavy or wrinkled, it can immediately enter the nip, thereby eliminating the situation where the belt rubs unfixed toner and preventing toner transfer. It is possible to prevent the occurrence of an abnormal image.
[0060]
Claim 4 According to the described invention, since the end portion of the fixing member is disposed so as to be close to the member facing the pressure member, the interval between the member facing the pressure member can be reduced. As a result, it is possible to prevent the occurrence of abnormal images by preventing the sheet from being lifted or slackened when the interval is increased.
[0061]
Claim 6 According to the described invention, the pressure per unit area in the nip portion constituted by the pressure member and the member opposed to the pressure member per unit area in the nip portion constituted by the fixed member and the pressure member. Since the pressure is larger than the pressure, the sliding resistance between the belt and the fixing member can be reduced and the moving load of the belt can be minimized. Accordingly, it is possible to prevent an abnormal image caused by the peripheral speed difference by minimizing the peripheral speed difference between the belt and the pressure member.
[0062]
Claim 7 According to the described invention, since a plurality of grooves parallel to the moving direction of the belt are provided on the surface of the fixing member facing the belt, friction between the belt and the fixing member can be reduced. As a result, it is possible to eliminate a condition for generating a difference in peripheral speed by suppressing the moving load of the belt. In addition, it is possible to prevent the belt from shifting in a direction perpendicular to the moving direction, thereby preventing deterioration in mobility.
[0063]
Claim 8 According to the described invention, it is possible to prevent the occurrence of abnormal images by preventing the difference in the peripheral speed of the belt in the fixing device.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an example of an image forming apparatus in which a fixing device according to an embodiment of the present invention is used.
FIG. 2 is a schematic diagram for explaining a configuration of a fixing device according to an embodiment of the present invention.
FIG. 3 is a schematic diagram showing one of the main modifications of the fixing device shown in FIG. 2;
4 is a schematic diagram for explaining a modification of members used in the fixing device shown in FIG. 2; FIG.
FIG. 5 is a schematic diagram for explaining a modified example of a member used in the fixing device shown in FIG. 3;
6 is a schematic diagram for explaining a modified example of members used in the fixing device shown in FIG. 4; FIG.
7 is a schematic diagram for explaining a modification of members used in the fixing device shown in FIG.
FIG. 8 is a schematic diagram for explaining one conventional example of a fixing device.
FIG. 9 is a schematic diagram for explaining one of the conventional examples of the configuration for eliminating the problem in the fixing device shown in FIG. 8;
[Explanation of symbols]
1 Full-color copier, one of image forming devices
14 Fixing device
15 Fixing belt
16 Heating roller as third member
17 Pressure roller as a pressure member
18 Fixing roller as second member
19 Fixing member which is the first member
S sheet
T Toner

Claims (8)

An apparatus for fixing toner in an unfixed image carried on a sheet,
A movable endless belt that is wound around a plurality of members and contacts an unfixed toner image, a heating member that heats the endless belt as one of the plurality of members, and another member of the plurality of members. A second member that faces the pressure member across the belt, and a first member that faces the pressure member across the belt, which is still another one of the plurality of members. With
Said first member is Ri Do of metal or resin, a part is formed by a fixing member that has a shape to follow the shape of the pressure member, the first nip and the pressing member first member And a second nip portion is formed in the pressing region between the second member and the pressure member, and a sheet carrying an unfixed toner image is continued from the first nip portion to the second nip portion. Fixing device characterized in that fixing is carried out by passing through. The fixing device according to claim 1 .
A fixing device, wherein a friction reducing portion is provided on a surface of the fixing member facing the belt . The fixing device according to claim 1 or 2,
The fixing device, wherein the fixing member constitutes a guide portion when the belt enters the first nip portion . The fixing device according to any one of claims 1 to 3,
The fixing device, wherein the fixing member is arranged so that an end portion facing the member facing the pressure member is close to the member . The fixing device according to any one of claims 1 to 4 , wherein:
The length of the first nip portion formed in the pressing region between the fixing member and the pressing member used as the first member is the second nip formed in the pressing region between the second member and the pressing member. The fixing device is set to be longer than the length of the portion . The fixing device according to any one of claims 1 to 5 ,
The first nip formed in the pressing region between the fixed member and the pressing member against the pressure per unit area at the second nip portion formed in the pressing region between the second member and the pressing member. A fixing device characterized in that the pressure per unit area in the section is reduced . The fixing device according to any one of claims 1 to 6, wherein:
The fixing device, wherein the fixing member is provided with a plurality of grooves parallel to a moving direction of the belt on a surface facing the belt . An image forming apparatus characterized by using the fixing device according to one of claims 1 to 7.

Images