JP4956074B2 - Fixing device - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus (hereinafter simply referred to as “image forming apparatus”) such as a copying machine, a facsimile machine, a printer, and a multifunction machine using a recording system such as an electrophotographic system or an electrostatic recording system. The present invention relates to a fixing device that permanently fixes the toner and a method of manufacturing a pressure rotator provided in the fixing device.

  In general, in an image forming apparatus such as a copying machine, a toner image is formed with a developer (toner) on the surface of a sheet as a recording material by an image forming process means using an electrophotographic technique and the like, and is sent to a fixing device to be determined. A printed image is obtained by permanently fixing the toner image on the recording material sheet.

  Conventionally, a heat roller system that heats an unfixed toner image and permanently fixes it on a sheet has been widely used. Further, in recent years, a film heating method excellent in speed of start-up during operation and energy saving has been put into practical use, and has been proposed by the present applicant (see, for example, Patent Documents 1, 2, 3, and 4). . In the fixing devices disclosed in these patent documents, a ceramic heater used as a heating element generates heat, and heat is applied to a nip portion formed between an opposing fixing roller and a cylindrical fixing film. The material of the cylindrical fixing film is a heat-resistant and low heat capacity material.

  In addition, in the film heating system, the heat-resistant resin film feeding system has a structure in which a film is fed in conjunction with a pressure roller by being sandwiched between a dedicated film transport roller and a driven roller while applying tension to the film. . Furthermore, there is also a structure in which a film is formed into a cylindrical shape as a rotating body, and the film rotating body is rotated by the rotational frictional force from the pressure roller by bringing the film rotating body into contact with the pressure roller. The former film tension feeding method provides high film transport performance. On the other hand, the latter film rotating body feeding method has an advantage that the structure is simplified and a low-cost fixing device can be realized.

  By the way, the film heating method has the above advantages, but has the following problems. In the above various fixing devices, since the sheet is heated while being pressed at the nip portion which is a fixing portion, the balance of the pressure distribution in the longitudinal direction of the roller, that is, the rotation axis direction is lost in the nip portion, and pressure is applied to the central portion of the roller. When concentrated, the sheet passing through the nip portion increases in conveying force and speed at the central portion, and a force that draws the entire sheet to the central portion of the sheet acts to cause vertical sheeting (hereinafter referred to as “paper wrinkle”) at the central portion of the sheet. In the case of the conventional heat roller system, the outer diameter of the roller ends on the left and right sides of the roller is thicker than the center of the roller (hereinafter referred to as “reverse crown shape”). Although it was relatively easy to suppress the occurrence of the paper wrinkles, the heat resistance resin film used in the film heating method and in order to improve the thermal conductivity with the recent increase in the printing speed of the apparatus For thin metal films that are started using, it is not impossible to shape the film material to the inverted crown shape, it is difficult to sufficiently act the paper wrinkle suppressing effect since the rigidity is insufficient. For this reason, the applicant of the present invention has proposed that the shape of the paired pressure roller is processed into an inverted crown shape to cope with the occurrence of paper wrinkles (see, for example, Patent Document 5).

  On the other hand, there is an adverse effect caused by making the fixing roller, the film, and the pressure roller into an inverted crown shape. The problem will be described with reference to FIG. FIG. 10A shows an example of a pressure roller 14 ′ processed into an inverted crown shape. In this case, the outer diameter dimension of both ends of the roller with respect to the roller rotation axis direction is larger than the outer diameter dimension of the roller center portion, and is formed thicker by, for example, 120 μm. In such a reverse-crown-shaped pressure roller 14 ′, the outer diameter of the central portion is narrowed by being curved concavely toward the central portion of the roller, and the pressure is applied to the member on the heater side. The nip width of the fixing nip portion formed in this region tends to be insufficient. Although this differs depending on the pressure surface shape and rigidity of the heater side member, when an inverted crown pressure roller 14 ′ having a central curved shape is incorporated into a fixing device and rotated using an actual product, FIG. As shown in FIG. 4, the shape of the nip portion is a thin type with maximum nip widths Nvol and Nvol at both ends of the roller and a minimum nip width Nvc at the center of the roller.

  Further, when conditions such as reverse crown amount, pressure, and heating temperature are not appropriate for the fixing speed, the fixing pressure at the center of the nip with respect to the roller rotation axis is locally insufficient as shown in FIG. 10C. At the same time, the contact area for transferring the heat from the heating source to the sheet 7 is insufficient. As a result, both the pressure and the amount of heat supplied decrease at the center of the nip, resulting in insufficient fixing of the toner image on the sheet 7. In addition, a small amount of toner remaining without being fixed adheres to the fixing roller, the fixing film, or the pressure roller, and if the printing is continued as it is, the remaining toner is accumulated. Is discharged to the sheet 7 at a stretch, and a large number of granular toner stains 5a of various sizes as shown in the figure are generated. FIG. 10D is a diagram showing a conventional countermeasure against such toner contamination, and a weak reverse crown rubber layer 14′a having a reduced reverse crown amount on the rubber surface of the pressure roller is formed to form the center of the nip. In order not to greatly reduce the fixing property of the part, and to compensate for the reduction in the paper wrinkle prevention effect, the crown of the pressure roller metal core gradually decreases in size from the center to both ends. This is a crown cored bar reverse crown-shaped roller 14 ′ composed of a cored bar 14′C. With such a combined configuration, when a large amount of fixing is continuously performed, the thick portions of the left and right rubber layers are thermally expanded to promote deformation so that the roller diameter further increases toward the end portion, and the action causes both ends of the sheet to In this case, the central nip width is relatively reduced, but since the entire roller is in a high temperature state, the deterioration of the fixing property is relatively small. On the other hand, when fixing a small amount, the overall temperature does not rise sufficiently, so the fixability tends to decrease, but at this time the thermal expansion also decreases, so the ratio of the nip width at the center portion becoming relatively smaller also decreases. It has an advantageous effect on fixing properties.

  However, this type of product has recently tended to increase in printing speed. As the printing speed increases, it becomes more difficult to suitably adjust the conditions such as the reverse crown amount, pressure, and heating temperature, and the best fixing performance cannot be caught up. That is, it becomes more difficult to satisfy all the problems such as paper wrinkle prevention, improvement of fixing property, and prevention of granular toner contamination at the same time.

  Toward this end, the inventor previously shown in FIGS. 11A to 11D that the cross section of the upper half of the roller when viewed from the front with the shaft end of the roller being left and right has a W-shaped configuration. A pressure roller 17 having a W-shaped reverse crown having a silicon rubber layer 17a processed and formed so as to be visible is proposed (see Reference 6). In this case, the pressure roller 17 is formed such that the outer diameters Dol and Dor at both ends of the roller (more precisely, both ends of the maximum sheet passing area) are thicker than the other portions and have the maximum diameter, and both the left and right ends and the center of the roller The smallest diameter part with the thinnest outer diameter is provided at two points between the two. And it is a taper part where an outer diameter becomes thick gradually from the minimum diameter part toward the maximum diameter part of both ends. The outer diameters Dol and Dor at both ends are thicker than the outer diameter Dc at the center of the roller, but the normal reverse crown amount is smaller than the reverse crown amount of a conventional V-type reverse crown roller. Incidentally, the reverse crown amount is usually calculated from the difference between the average outer diameter of both end portions of the roller and the outer diameter of the central portion of the roller.

  On the other hand, when the difference between the minimum diameter portion and the maximum diameter portion is compared, a difference equal to or greater than the conventional reverse crown amount is formed, and the distance between the minimum diameter portion and the maximum diameter portion is the conventional reverse crown roller. Since the slope of the reverse crown taper portion formed is closer than the conventional one, the gradient of the reverse crown taper portion is larger than that in the prior art.

  Such a W-shaped reverse crown pressure roller 17 has a thicker outer diameter than the conventional simple V-shaped reverse crown, and therefore has a larger nip width at the central portion. (In general, when there is no great difference in the fixing device configuration and toner characteristics, the wider the fixing nip width, the better the fixing property). The pressure roller 17 shown in FIG. 11 (A) is combined with the reverse crown metal film 13′c shown in FIG. 11 (B), and the shape of the fixing nip portion formed when being pressed and heated as shown in FIG. 11 (C). taking measurement. As a result, as shown in FIG. 11 (D), the central portion in the longitudinal direction has a substantially flat area having the nip width Nwc and substantially the same nip width, and the nip widths Nwsl and Nwsr have substantially the same width on the left and right outer sides. The area where the nip width is the narrowest and the nip gradually increases toward the maximum nip widths Nwol and Nwor at the left and right ends toward the outside of the nip widths Nwsl and Nwsr. Since the nip width through which the left and right paper edge portions with no paper width pass is set to be located further outside the nip widths Nwl1 and Nwlr, which are thicker than the central nip width, the paper wrinkle prevention function is sufficiently exerted.

  As an inexpensive method for manufacturing the W-shaped reverse crown pressure roller 17, as shown in FIG. 12A, the mold release property on the roller surface after molding is improved in the outer mold 16 for manufacturing the pressure roller. After inserting a heat-shrinkable fluororesin tube (not shown), a crown core bar 14'c is inserted. The outer die 16 is formed in a cylindrical shape having a hollowed inner portion, and is subjected to taper processing for attaching reverse crowns to the left and right end portions of the inner surface, and the central portion is formed in a flat shape. The crown metal core 14'c is formed flat by a distance C (distance C <distance L) from the central portion, and has a crown shape tapered so as to become narrower from both ends of the flat portion toward the left and right end portions. Is formed. Here, the length of the central flat portion of the crown metal core 14 ′ c is shorter than the length of the central flat portion of the outer mold 16.

  As shown in FIG. 12 (B), in a state where the crown core metal 14'c is put in the outer die 16, the liquid rubber material is erected from both the left and right ends of the outer die 16 or one side, or the die is erected vertically. Injecting from above, the mold is then heated to cure the rubber layer. Finally, when the curing of the rubber layer is completed, the whole is cooled, and is released from the outer mold 16 by utilizing the shrinkage of the rubber layer due to the cooling. At this time, since the central side of the left and right end portions of the central straight portion of the outer mold partly includes a core metal crown taper portion, a gradient is formed in the thickness of the rubber layer along the taper portion. Yes. As a result, the thicker the rubber layer, the greater the shrinkage when the temperature is lowered, and the outer diameter becomes narrower. As a result, a W-shaped inverted crown shape is formed.

  The reason for using such a manufacturing method is that it is difficult to process thicker than the minimum outer diameter part that passes the outer diameter of the central part in the process of cutting out from the left and right ends when manufacturing the outer mold. Yes, it was newly devised from the viewpoint of workability and cost, but since the central part of the inner surface of the outer mold used in this manufacturing method is a straight shape to the end, the pressure roller formed as described above is actually used. When used for fixing operation, when the heat curing temperature approaches the thermosetting temperature during processing, the smallest diameter part expands and its shape approaches the inner shape of the outer mold, reducing the outer diameter difference from the central part. It is possible to do.

  However, from the evaluation results of the fixing nip shape, it can be seen that the characteristics of this roller shape are maintained even when the sheet is actually passed through and fixed. When the shape was measured by heating and expanding, the outer diameter difference decreased from that at room temperature, and it was confirmed that the minimum diameter portion remained although there was variation depending on the measurement angle and individual difference (upper limit saturation during actual fixing) Although the temperature is sufficiently lower than the thermosetting temperature at the time of roller production, these minimum diameter portions remain even if the heating temperature is higher than the thermosetting temperature of the roller. The reasons for this include the fluidity of rubber during processing and heating temperature distribution conditions, as well as the effects of the roller being opened at the end of the roller axis being sealed at the time of manufacture, and the release layer. The permanent deformation of the fluororesin layer provided on the surface can be considered, and there was no problem at least within the range of the manufacturing conditions of this roller and the design values of the reverse crown amount and the core metal taper amount of the outer die.

  FIG. 13 is an example of temperature dependence measurement data regarding the outer diameter of a W-shaped reverse crown roller actually manufactured by the above-described manufacturing method. This roller has a comparatively reverse crown with a difference of about 50 μm between the minimum diameter portion and the maximum diameter portion. The amount is processed to be small, and there is a concern that the difference in outer diameter between the central portion and the minimum diameter portion at the time of thermal expansion is likely to decrease. In addition to the room temperature t0, the fixing initial temperature t1 is large. In this case, the roller alone is heated in an oven to a temperature corresponding to each case of the saturation temperature t2 during printing, and the outer diameter shape change in each case is measured and compared. In this roller, the two minimum diameter portions formed about 65 mm and about 165 mm from the left end as shown by the down arrow in the figure at room temperature t0 are relatively outside the central portion along with the thermal expansion of the entire roller. The difference from the diameter is slightly reduced, and the difference at room temperature is about 25 μm. On the other hand, it is reduced to about 20 μm at the time of normal small-volume printing. Tends to break the symmetry of the shape. (The cause is that the measurement is started from the left end when measuring the outer diameter, so the time until the measurement on the right end is completed. It is also possible that the expansion rate is attenuated and becomes easier to measure as the roller cools down and goes to the right end side, but mainly in the distribution conditions such as the packing density of the rubber material and the heating temperature inside the mold when the rubber material is injected Subtle differences Seems to have affected.) However, even with such a roller, the minimum diameter portion is maintained although the left-right difference is large. In addition, with this roller, the left and right reverse crown taper parts start to become thicker from the center than the center part at approximately room temperature and approximately 203 mm from the left end at room temperature. Judging from the above, the minimum width of paper for which paper wrinkle countermeasures are to be applied is limited to about B5 paper in the range indicated by the double-ended arrows at the top of the graph. The position is located on the left and right outside of the A5 size paper passing width indicated by a double-ended arrow at the top of the graph, and the paper wrinkle suppressing effect is not exerted, but the thermal expansion occurred at the temperature t1 at which actual fixing starts. In the shape, these positions are slightly different on the left and right as shown by the up arrow in the figure, but are shifted slightly to the center side to fit inside the A5 size area. Locally swollen Paper wrinkles inhibiting effect during actual fixing although the right end portion of the upper arrow portion and A5 size rightmost would substantially overlap in large part arises influence of is shaped to be expected with respect to A5 size sheet.

  The degree of the outer diameter difference between the central portion and the minimum diameter portion differs depending on manufacturing variations or intentionally changing design values and manufacturing conditions. In the worst case, this difference almost disappears even in the temperature range around the fixing initial temperature t1. The central part may be almost flat, but even in that case, the center part has sufficient fixing ability and paper wrinkle suppression effect compared to the simple V-shaped reverse crown roller where the central part is the thinnest. Can be maintained. In other words, if it is processed into a W-shape at least at room temperature, it is fundamental to achieve both the improvement of fixing property at the center and the effect of suppressing paper wrinkles, which are necessary for actual fixing even if the shape changes slightly during expansion. The function is maintained.

JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980 JP-A-9-152803 JP 2005-284089 A

  By using the W-type reverse crown pressure roller 17 disclosed in the above-mentioned Patent Document 6 proposed by the present inventor, the occurrence of toner stains after continuous paper passing through a large-scale printing operation is extremely reduced so that it cannot be confirmed with the naked eye. At the same time, the paper wrinkle prevention function is sufficiently effective, so that the intended purpose is achieved in the product equipped with this roller.

  However, as described above, in the above-described inexpensive manufacturing method, a desired outer diameter difference is not positively formed due to manufacturing limitations. Therefore, when the rubber layer is thermally expanded during actual fixing, W It is inevitable that the shape of the mold varies due to changes in manufacturing conditions, that is, the rubber material and prescription and fluidity thereof, curing temperature conditions and temperature distribution, the material and thickness of the fluororesin tube, and the like.

  In the current equipment, even if this variation is allowed, it is within the range where there is no problem, but in order to cope with further speeding up of the equipment in the future, the margin is set so that the outer diameter of the central part becomes thicker to compensate for insufficient fixing. If the design is increased, the left and right reverse crown amounts will be relatively reduced, and depending on the level of variation, there is a concern that paper wrinkles will deteriorate. However, there is a risk that the outer diameter of the central portion is relatively reduced and the fixing property of the central portion is deteriorated depending on the variation level.

  For this reason, in order to cope with further increase in the speed of the apparatus in the future, the fixing property at the center part is less likely to be deteriorated, and paper wrinkles can be sufficiently prevented. It is desirable to be able to stably exhibit the variation of the pressure, and further improvement of the pressure roller is necessary to realize this.

From the above, the object of the present invention is to form an image that is effective in suppressing paper wrinkles that deteriorate due to further increase in the speed of the apparatus, eliminating the lack of fixability in the center of the nip, preventing particulate toner stains, and realizing high image quality. An object of the present invention is to provide a fixing device used in the apparatus .

In order to achieve the above object, a typical fixing device of the present invention includes a cored bar and an elastic layer formed outside the cored bar, and forms a nip portion that transports a recording material. In a fixing device that includes a roller and heats a recording material carrying a toner image while being conveyed at the nip portion to fix the toner image to the recording material, the core metal has a diameter at the center in the longitudinal direction of the core metal. A concave-shaped area that gradually decreases toward the center along the longitudinal direction of the cored bar, and both ends having the largest outer diameter in the concave-shaped area, respectively, toward the longitudinal end of the conveying roller A taper-shaped area that gradually decreases in diameter, and the elastic layer has a convexity whose diameter gradually increases toward the center along the longitudinal direction of the elastic layer at the center in the longitudinal direction of the elastic layer. The shape area and the convex shape It has a tapered area gradually the diameter increases toward the minimum at both ends of the diameter in the longitudinal direction of the end portion of each of the conveying rollers at A, and the transport of the concave area of the metal core The length of the roller in the longitudinal direction is shorter than the length of the convex area of the elastic layer in the longitudinal direction of the transport roller.

According to the fixing device of the present invention, by improving the shape / internal configuration of the pressure rotator paired with the heating rotator, it is possible to prevent paper wrinkles and insufficient fixability and to prevent toner contamination. That is,
・ Regarding fixing performance, the nip shape of the pressure rotator that expands by receiving heat from the heating rotator during fixing is formed by forming a minimum nip width region between the center in the rotation axis direction and both left and right ends. Improved by preventing the center nip width from becoming the minimum nip width of the nip in the direction of the rotation axis, and increasing the heat capacity of the pressure rotating body in the center region to prevent temperature drop. To do.

  -For paper wrinkles, do not make the center nip width thicker than the nip width through which both ends of the paper you want to prevent paper wrinkling, and form the nip shape in the center part into a drum shape, and put the paper in the center part. This is improved by limiting the region where the attracting action occurs only to the center.

  Moreover, according to the manufacturing method of the pressurization rotary body of this invention, a pressurization rotary body cheap in cost can be manufactured and provided.

  Also, according to the image forming apparatus of the present invention, it is possible to form a high-efficiency and high-quality image by providing a fixing device that has high fixing performance and suppresses paper wrinkles and toner contamination.

The best mode for achieving the above-mentioned problem is as the shape of the pressure roller alone after the thermal expansion when the pressure roller constituting the fixing device is heated to a temperature equivalent to the time of fixing.
・ There is a minimum outer diameter between the center and left and right ends.

  ・ The outer diameter of the central part gradually increases from the left and right minimum outer diameter parts toward the center.

  ・ The rubber layer at the center is gradually thicker toward the center.

  -The outer diameter gradually increases from the left and right minimum outer diameter portions toward the left and right end portions.

  ・ The maximum outer diameter at the center is thinner than the outer diameter of the left and right edge passages of the paper to prevent paper wrinkling.

  It is the form comprised with the pressure roller which has the characteristic of.

  Hereinafter, the image forming apparatus of the present invention, its fixing device, and the manufacturing method of the pressure rotating body for the fixing device will be described in detail with reference to the drawings. Note that corresponding members are denoted by the same reference numerals so that the difference between the fixing device and the pressure roller (pressure rotator) shown in FIGS.

(Image forming device)
FIG. 1 shows a printer using electrophotographic technology as a specific example of the image forming apparatus according to this embodiment. In this printer, a charging bias voltage is applied to the surface of a photosensitive drum 2 as an image carrier by a charging roller 1 of a charging device to uniformly charge it to a predetermined polarity. The charged photosensitive drum 2 is exposed by exposure means 3 using laser light or the like, and a latent image is formed on the drum surface. The latent image is developed with the toner 5 by the developing device 4 to be visualized as a toner image. That is, the toner 5 of the developing device 4 is frictionally charged with the same polarity as the charging surface of the photosensitive drum 2 between the developing blade 4a and the developing sleeve 4b. Then, an AC (alternating current) bias voltage is applied and superimposed on a DC (direct current) bias voltage in a developing gap portion where the photosensitive drum 2 and the developing sleeve 4 b face each other, and the toner 5 is caused to float and vibrate by an electric field action. It is selectively attached to the latent image forming part of the photosensitive drum 2. Then, the adhered toner 5 is conveyed to the transfer nip formed by the transfer roller 6 and the photosensitive drum 2 by the rotation of the photosensitive drum 2.

  On the other hand, the sheet 7 serving as a recording medium on which an image is recorded is fed from the storage tray 7a to the vertical conveying roller pair 7d by a feeding roller pair 7c (the lower roller may be a pad). Thereafter, the sheet is conveyed to the pre-transfer conveyance roller 7e by the vertical conveyance roller pair 7d. When transporting from the manual feed tray 7b, it is transported from the manual feed tray 7b to the pre-transfer transport roller 7e by the feed roller pair 7c. The sheet 7 conveyed to the pre-transfer conveyance roller 7e is conveyed to the transfer nip portion by the pre-transfer conveyance roller 7e along the space between the transfer guide upper plate 9a and the transfer guide lower plate 9b at a predetermined entry angle.

  While the sheet 7 is conveyed from the pre-transfer conveyance roller 7e to the transfer nip portion, the sheet 7 comes into contact with various members. For this reason, there is a possibility that the surface of the sheet 7 is charged by sliding with the various members. In view of this, the neutralization brush 8 provided so as to be in contact with the back side of the sheet 7 being conveyed and grounded removes the charge that causes the image to be disturbed when performing electrostatic recording.

  In the transfer unit, a high voltage having a polarity opposite to that of the toner 5 is applied to the transfer roller 6 on the back surface of the sheet 7 in order to electrostatically attract the toner 5 on the photosensitive drum 2 and move it to the sheet 7 side. As a result, the toner 5 is electrostatically attracted to the back surface of the sheet 7 and the toner image is transferred to the sheet 7. Further, the back surface of the sheet 7 is charged with a bias voltage having a polarity opposite to the polarity of the toner 5, and a transfer charge for continuing to hold the transferred toner 5 is applied to the back surface of the sheet 7.

  The sheet 7 on which the toner image has been transferred is sent to a fixing device 12 including a heating rotator 13 and a pressure rotator (pressure roller 14). The sheet 7 sent to the fixing device 12 is nipped by a fixing portion, that is, a nip portion formed between the heating rotator 13 and the pressure roller 14. At this time, the toner image is heated and fixed by a heater provided on the heating rotator 13 so as to maintain a predetermined fixing temperature set in advance, and the toner image is fused and permanently fixed while controlling the temperature.

  After transfer of the toner image, a slight amount of deposits such as toner having different polarities remain on the surface of the photosensitive drum 2. For this reason, the surface of the photosensitive drum 2 after passing through the transfer nip portion is cleaned by scraping off the adhering matter by bringing the cleaning blade 10a into contact with the cleaning container 10 from the direction against the rotation of the photosensitive drum 2. In preparation for the next image formation.

  The image forming process means includes the charging roller 1, the photosensitive drum 2, the developing device 4, and the cleaning container 10 described above. Since these components are consumed and the replacement cycle is relatively short, they are integrated as a process cartridge and can be replaced in units of the cartridge 11.

( Example )
1) Pressure roller As shown in the cross section of FIG. 2A, the pressure roller 14 of the present embodiment is a silicon rubber layer 14 "having a shape having a roller central portion in the roller rotation axis direction and concave portions on both right and left sides thereof. a is formed, and is formed as a pressure roller 14 ″ having an inverted crown shape in which the fixing property at the center of the roller is enhanced. At the center of the pressure roller 14 ″, a core bar 14 ″ b whose upper half is M-shaped is provided. This M-shaped crown-shaped cored bar 14 ″ b has a concave portion (central outer diameter = 23 mm, central portion longitudinal width = 2 mm centrally tapered shape) in the central portion, and both ends thereof are locally having an outer diameter Da. The maximum outer diameter portion (the outer diameter of the maximum outer diameter portion = 23.45 mm, the width in the longitudinal direction = 2 mm) The length portion extending from the end of the maximum outer diameter portion at both ends to both ends of the roller is A tapered portion is formed by tapering the outer diameter gradually.

  Further, both end portions of the pressure roller 14 ″ have the largest outer diameters Dol and Dor, and are formed to be the thickest. Further, the pressure roller 14 ″ is formed at the two left and right portions between the roller central portion and both end portions. A minimum outer diameter portion where the outer diameter is the thinnest is provided, and the outer diameter Dc of the central portion is approximately the same thickness as the minimum diameter at room temperature. And the part from a minimum diameter part to a roller both ends is formed as a taper part which became thick gradually. The outer diameters Dol and Dor at both ends of the roller are thicker than the outer diameter Dc at the center of the roller, but the normal reverse crown amount is equivalent to the reverse crown amount of a conventional V-shaped reverse crown roller. In general, the reverse crown amount is calculated using the difference between the average outer diameter at both ends and the outer diameter at the center. Further, the pressure roller 14 ″ has a portion which is equal to or thinner than the roller central portion between the roller central portion and both ends. However, these outer diameters Dsl, Dsr, Dc. And the outer diameters Dol, Dor at both ends are processed to be equal to the reverse crown amount of the conventional V-shaped reverse crown roller, and the minimum diameter of the pressure roller 14 is the same even with the same reverse crown amount. As the distance between the roller and the maximum diameter of the roller ends becomes closer, the gradient becomes larger, so that the action of pulling the end of the sheet 7 outward at these portions is higher than that of a normal reverse crown roller. Further, when the total length of the pressure roller 14 ″ is R, the positions of the minimum diameters Dsl and Dsr are located at a distance S from the center of the roller to the left and right. Here, L is a distance shorter by 5 mm from the half of the narrowest paper width of the sheet 7 to be subjected to paper wrinkle countermeasures, and L is set to the left and right from the center portion. Assuming that the diameters are Dll and Dlr, the magnitude relationship between the roller outer diameters at each position in the room temperature state is expressed as “Dol> Dll> Dc≈Dsl” when only the left half region is represented. Therefore, the outer diameter outside from the position of the distance L from the center is always processed to be sufficiently thicker than the outer diameter Dc of the center.

  The pressure roller 14 ″ formed in the above shape is in a room temperature state, and when this roller is heated, the rubber layer expands as a whole, and in particular, the portion where the original rubber thickness is thicker tends to expand greatly.

  FIG. 2 (B) shows the magnitude relationship of the outer diameter of the roller after heating. In the figure, the outer diameter part of each part of the roller is thicker than at room temperature, but the rubber thickness is particularly thick at the left and right end parts and the central part. It becomes thicker than the smallest outer diameter part. Further, the thickness of the central portion is adjusted to be sufficiently thicker than the thickness of the central portion when a conventional simple V-shaped reverse crown roller is heated and expanded. The relationship between the outer diameters of the expanded rollers at each position under the same temperature condition as that at the time of fixing is expressed as “Dol ′> Dll ′> Dc ′> Dsl ′” only in the left half region. For this reason, the nip width of the central portion becomes thicker when heated in actual use, the fixing nip width of this portion becomes thicker, and the rubber thickness of this portion is thicker than the conventional V-shaped reverse crown roller and has a larger heat capacity. Therefore, once the heat is stored, it has a characteristic that the temperature is less likely to be lower than that of the conventional roller, and further acts to prevent the deterioration of the fixing performance of this portion.

  Further, the granular toner stains at the time of continuous paper passage are formed by accumulation of minute toner contamination when a large amount of sheets 7 of several hundred sheets or more are continuously passed. Even the slight difference in the fixing property due to the outer diameter difference of several tens of μm near the center greatly affects the amount and frequency of occurrence of the stain, and the larger the outer diameter, the wider the fixing nip width, so that the toner stain can be removed. Can be suppressed. Accordingly, the pressure roller 14 ″ processed so that the central portion becomes thicker at the time of fixing can increase the outer diameter Dc of the central portion, so that an effect of suppressing toner contamination can be expected.

  On the other hand, the pressure roller 14 ″ with enhanced fixability at the central portion as described above is a rubber at the time of roller manufacture, although the outer diameter of the roller at a distance S from the central portion to the left and right is heated and expands somewhat. It does not expand as much as the central part due to differences in the injection speed of the material, differences in the curing speed of the rubber material due to the heating temperature distribution, release of stress after molding, the effect of fixing pressure, the influence of the core metal shape, etc. However, since the pressure spring for forming the fixing nip portion acts at the left and right ends, the pressure distribution in the longitudinal direction of the fixing nip portion increases from the center toward the end portion. Further, during continuous paper feeding, the temperature at the center is easily lost by the sheet 7 being passed, and the temperature distribution in the longitudinal direction of the fixing nip portion becomes higher from the center toward the edge. Because of this, the position that is left and right from the center However, even if the outer diameter of the roller is somewhat thinner, the fixing conditions are better at higher temperatures and pressures than in the central part, and the deterioration of the fixing property in this part is not as great as when the same outer diameter is provided in the central part. In the reverse crown roller, the pressure drop and the temperature drop occur at one central portion. On the other hand, in the pressure roller 14 ″, the pressure drop at the position left and right from the center portion is reduced. It is further reduced by being distributed to the left and right. For this reason, when the continuous paper-passing durability test is performed, it is possible to prevent the fixability from being lowered at the left and right minimum outer diameter portions.

  As an example of the M-type cored bar W-type reverse crown roller processed in this way in FIG. 14, the roller processed at a room temperature t0 having a sufficiently large reverse crown amount at the left and right end portions of 120 μm or more is equivalent to that during continuous printing. The comparison figure which measured the outer-diameter change of the roller single-piece | unit in each temperature to saturation temperature t2 is shown.

  As can be seen from this figure, the shape of the roller machined according to the above configuration at room temperature t0 is influenced by the cored bar shape and has an M-shaped shape at the center, and is reversed toward the outer side of the left and right ends. Although the crown shape continues, in the vicinity of the temperature ts immediately after the start of fixing, the concave portion expands selectively and greatly due to the difference in expansion coefficient of each rubber layer, and the entire central portion becomes almost flat, and at the start of fixing. In the vicinity of t1, the central part starts to rise slightly, and at the same time, the minimum diameter part begins to be formed again at the boundary with the central end of the left and right reverse crown taper parts. Becomes completely exciting. During this time, the positions corresponding to the two smallest diameter portions formed between the center portion and the left and right end portions shift from around 84 mm and 147 mm in the room temperature state to near the center in the saturated state and become around 98 mm and 140 mm. Overall, during the actual fixing operation, the central part becomes thicker and the fixing property is improved, and the left and right reverse crown taper forming areas are extended to the center side, and the paper wrinkle countermeasure effect also acts on narrower paper It can be seen that an ideal W reverse crown shape is formed (this roller has a reverse crown taper portion formed sufficiently outside of A5 size paper even at room temperature, Due to the expansion, the outer diameter difference between the central part and the paper edge passing line area further increases, and the central part has a drum shape and the thick outer part is only locally formed in the central part. The power to draw in the center is also controlled Is, paper wrinkle suppressing effect becomes higher).

In addition, as a shift factor of the two minimum outer diameter portions at this time,
・ Extrusion pressure from the left and right ends to the center due to expansion of the large left and right reverse crowns ・ This is thought to be due to the pulling force toward the center of both sides due to thermal expansion of the center.

    Since the roller of the present invention has such a characteristic that the left and right outer diameter portions shift larger toward the center than the conventional W reverse crown roller at the time of thermal expansion, the width of the paper on which the paper wrinkle suppressing effect acts at the time of fixing is room temperature. This is also effective for paper that is narrower than the assumed paper, and the target paper type may be set to match the narrower paper for this effect. In the following description, the generation position of the minimum outer diameter portion at room temperature and during expansion is described as being substantially the same position.

  In addition, since the change in the outer shape of the pressure roller that becomes a W-shaped reverse crown shape when expanded using the M-type cored bar greatly varies depending on the temperature condition, it will be referred to as a central fixing reinforced reverse crown roller in the following description.

2) Paper Passing Test Next, with reference to FIGS. 3A to 3D, a description will be given of a test for evaluating paper wrinkles and toner stains of the reverse crown roller with enhanced fixability at the center of the roller.

  As an evaluation apparatus, an electrophotographic printer using the same film heating type fixing device 12 was used. For each of the four types of pressure rollers used in the fixing device 12, two types of tests, a paper wrinkle test and a toner stain test, were performed (a total of eight tests). The printer body used for the evaluation is a high-speed machine with 55 or more sheets per minute.

  As shown in FIG. 3A, the film heating type fixing device 12 a is composed of a pressure roller and a heating rotator 13. Tests are conducted on four types of rollers having different surface shapes as pressure rollers. The following dimensions of the pressure roller and the like are examples for the experiment, and are not limited to these values.

  Each pressure roller has a total length of 235 mm (excluding the shaft portion), and the core metal of the roller other than the pressure roller of this embodiment has a flat portion having a width of 50 mm and an outer diameter Da of 23.45 mm at the center. It has an aluminum crown shape that is tapered so that the outer diameter decreases from the left and right end portions of the flat portion to the left and right end portions of a roller having an outer diameter Db = 21.45 mm. On the other hand, the core of the pressure roller of the present embodiment has the same shape as the core and the left and right ends, but the 50 mm wide region of the central portion has a slightly flat portion inside from both ends of the central 50 mm width. Accordingly, the taper is tapered toward the center portion with a taper amount of 0.225 mm so as to become thinner toward the center portion having a slight flat portion. A silicon rubber layer is provided on the outer periphery of the core metal, and a PFA tube layer having a thickness of 50 μm is provided on the surface thereof. The average hardness of the entire roller is adjusted to 59 ° (when ASKER-C is applied with 500 g).

  In the room temperature state, the surface shape of the silicon rubber of the three types of pressure rollers is as follows.

  (1) Straight shape with substantially the same center and left and right ends.

  (2) A conventional V-shaped reverse crown having a reverse crown amount of 120 μm.

  (3) A shape having two concave portions with a reverse crown amount at the center and the end = approximately 120 μm and a reverse crown amount at the minimum outer diameter portion and the end = 120 μm.

  (4) A shape having three concave portions with a reverse crown amount at the center and the end = approximately 120 μm and a reverse crown amount at the minimum outer diameter portion and the end = 120 μm.

  In this embodiment, the pressure roller 14 ″ of the type having enhanced fixing performance at the central portion of the roller has an outer diameter Dol and Dor of 30.40 mm at the left and right ends at room temperature, and a minimum diameter Dsl and Dsr of 30.38 mm. The outer diameter Dc of the portion is substantially the same as the outer diameter of the minimum diameter portion, however, during heating, similar to the temperature dependency of the pressure roller in FIG. The center part almost disappears and the center part is close to a flat shape, but after the start of fixing, only the center part gradually begins to expand with the heat accumulation of the rubber layer. An outer diameter distribution is formed such that a convex outer diameter increasing portion is formed on the portion, a minimum diameter portion is formed on the left and right sides, and a gap crown taper portion is formed on the left and right end portions, Dol ′ = 30.84 mm, Dc ′ = 30.66 mm, The sl '= 30.64mm (i.e. reverse crown amount at the time of thermal expansion is increased to near 200 [mu] m).

Here, the minimum paper width that is desired to prevent the occurrence of paper wrinkles is set as A5 size paper, and the fixing nip width at the center of the roller at the time of fixing at least at room temperature passes through the left and right end portions of the A5 size paper. The shape of the pressure roller is adjusted so as not to be thicker than the nip width of the position. (In view of manufacturing variations, it is better to adjust the margin between the paper edge position and the minimum nip part). On the other hand, paper types with a width of 100 mm or less in which the reverse crown effect does not work at all have only narrow and relatively thick paper types such as envelopes and postcards, and since the paper width itself is narrow, the rigidity in the width direction is relatively increased. Therefore, it is not likely to be wrinkled, and it is not necessary to prevent wrinkling of paper of this size. Also, for paper types with a width of 100 mm or more and narrower than A5 size paper, the reverse crown effect acts on the left and right edges, but it is easily attracted to the center, so paper is larger than A5 size paper or larger. The wrinkle prevention effect should be reduced,
Actually, the left and right reverse crown action areas are widened at the time of thermal expansion as in the example of the roller of FIG. 14 in which the temperature dependence was actually evaluated, so that the effect can be expected even with B6 size paper, and further continuous When the paper is passed, the left and right non-paper passing areas are heated by the heaters, but the paper does not pass through. Since the expansion rate increases and the influence extends to the left and right ends of the sheet passing portion, the reverse crown effect becomes higher, and the paper wrinkle prevention effect during thermal expansion as a whole becomes higher.

  In FIG. 3A, the heating rotator 13 uses an inverted crown metal film 13c as a fixing film. The reverse crown metal film 13c is a cylindrical metal film having high thermal conductivity, and corresponds to a high speed of 45 sheets / minute or more. Further, the reverse crown metal film 13c is subjected to reverse crown processing by plastic working, and the reverse crown effect is enhanced with the reverse crown amount of (Dfl + Dfr) / 2−Dfc = 50 μm. Here, Dfl and Dfr indicate the outer diameters of the left and right end portions, and Dfc indicates the outer diameter of the central portion.

  The reverse crown metal film 13c is formed of a fluororesin layer (not shown) as a release layer on the surface of a base layer obtained by plastic processing of a metal tube made of stainless steel (SUS) and having a thickness of 35 μm. ing. The thickness of the base layer may be 20 to 200 μm, and a SUS film having a thickness of 20 μm or less is preferable from the viewpoint of heat conduction, but the mechanical strength is insufficient. End edge scraping due to rubbing between the film edge part of the part and the flange (regulating member for preventing the film from being biased to the left and right), and the paper when jammed with the paper sandwiched between the fixing nip part It is not preferable in terms of durability against long-term use from the viewpoint of concerns such as insufficient strength against mechanical load on the film during the removal operation. On the other hand, a SUS film of 200 μm or more has too high film rigidity and flexibility. The contact with the heater surface at the fixing nip portion is deteriorated and the heat of the heater cannot be sufficiently transmitted to the paper or the pressure roller side, so that the fixing property is deteriorated.

  First, a metal film formed with a reverse crown is dipped in a fluororesin primer solution tank in which carbon black is dispersed in an appropriate amount as a conductivity-imparting member in a fluororesin primer serving as an adhesive layer, and the film thickness is about 5 μm. Coating. Then, it is dried for 15 to 45 minutes in a thermostat set to 190 to 230 ° C. and cooled at room temperature.

  Next, a mixed fluororesin dispersion of PTFE resin and PFA resin is used as the fluororesin of the release layer. A metal tube coated with a conductive primer in the previous step is dipped in a liquid tank provided with an appropriate amount of carbon black as a conductivity imparting material to this fluororesin dispersion, and a coating with a film thickness of about 10 μm is formed by dipping. Apply. Then, stepwise baking is performed in a baking furnace at about 250 to 280 ° C. for 10 to 15 minutes, about 300 to 330 ° C. for 20 to 30 minutes, and about 370 to 400 ° C. for 10 to 15 minutes. Fluorine resin of the sleeve surface layer is formed.

  Inside the reverse crown metal film 13c, as shown in FIG. 3A, a ceramic heater 13a and a film guide member 13b are provided.

The ceramic heater 13a includes a ceramic substrate made of Al ² O ³ , AlN, SiC, or the like, a heating element in which a heating paste is printed on the ceramic substrate, a glass coating layer for ensuring protection and insulation of the heating element, and the like. It is configured. The film guide member 13b has a substantially semicircular cross section and guides the reverse crown metal film 13c.

  The heating rotator 13 is pressed against each pressure roller with a total pressure of 18 kg to form a fixing nip portion, and the sheet 7 is nipped and conveyed by the fixing nip portion. At this time, an AC current whose power is controlled is supplied to the heating element of the ceramic heater 13a to cause the ceramic heater 13a to generate heat. The toner image on the sheet 7 is melted and permanently fixed on the sheet 7 by heat transmitted from the ceramic heater 13a through the reverse crown metal film 13c and pressure applied by each pressure roller.

  At that time, a temperature detection element (chip thermistor) (not shown) is adhered to the back of the ceramic substrate, and the thermistor detects the temperature change within the time when the power to the heater is turned off or on for a certain period of time when paper is not passed. Detect. And based on this detection result, the target temperature of the ceramic heater 13a is determined, electric power control is performed by controlling a heater driving means (not shown), and the heater temperature is kept at the target temperature (printing temperature).

  Next, test types will be described. As the paper passing test, two types of tests, a paper wrinkle test and a toner stain test, were performed.

A) Paper wrinkle test A lattice pattern image using a relatively thin A4 size paper having a basis weight of 64 g that is allowed to stand for 48 hours or more in a 30 ° C./80% high temperature and high humidity environment test room. Observe the presence or absence of paper wrinkles on the sheet when 10 sheets are printed continuously. Also, in this paper wrinkle test, all the pressure rollers used are rollers whose overall average hardness is approximately 1 ° lower than the original roller, and the conditions are such that paper creases are more likely to occur by widening the nip width as a whole. We are evaluating.

B) Toner smear test 4% printing using letter size paper containing 90 g of calcium carbonate (paper that easily induces toner smear) left in a low temperature and low humidity environment test room at 15 ° C / 10% for 48 hours or more. The paper is repeatedly added while the character pattern image of the rate is continuously printed 400 sheets at a time. Then, the amount and frequency of occurrence of granular toner stains on the paper when finally printing up to 30,000 sheets are observed and evaluated.

  Table 1 is a table showing the results of comparative evaluation of the four types of pressure rollers through the paper wrinkle test and the toner stain test. In Table 1, × indicates a case where paper wrinkles or toner stains occur, ○ indicates that paper wrinkles or toner stains hardly occur, and even if they occur, they are so slight that they do not cause a problem in practice. The case where it does not occur at all is shown.

  As shown in Table 1, with the straight roller, toner contamination hardly occurred, but the occurrence of paper wrinkles is remarkable. In the V-type reverse crown roller, paper wrinkles hardly occur due to the reverse crown effect. However, a large amount of granular toner stains are generated from about the 8000th sheet from the start of continuous paper feeding in the area of the length of one roller at the front end of the paper at the position corresponding to the central part that is the V-shaped valley. I started. After that, when the test for the first day was completed and the test for the next day was started after the entire device was completely cooled, the amount of toner stains increased and the size of the toner stains became larger and the tip became a lump. It began to occur intensively in the center. The W-type reverse crown roller has a high effect of preventing the occurrence of paper wrinkles. Rather, it is as good as or better than the V-type reverse crown roller that has been used in the conventional countermeasures against paper wrinkles. Further, even with respect to granular toner stains, there is no level of toner stains that would cause a problem during the durability of 30,000 sheets, and a result equal to or higher than that of a straight roller can be obtained.

  Finally, the center fixing property-enhanced reverse crown roller of this example has a higher effect of preventing the occurrence of paper wrinkles, and does not occur at all in this evaluation range. In addition, even with 30,000 sheets of toner, the toner does not stain at all, resulting in a result superior to that of a W-type reverse crown roller. However, evaluation was attempted, but even in that case, toner contamination did not occur, and it was found that the roller of this example had a higher margin for preventing toner contamination if the roller hardness was the same.

  In the above test, the center-fixing-enhanced reverse crown roller has three concave portions at room temperature as described above, and the rubber layer in the central portion expands due to overheating during the actual fixing operation, as shown in FIG. Thus, when the fixing nip shape of the fixing device combined with the reverse crown film is measured, the shape when the upper half is viewed as shown in FIG. The drum-shaped W-shaped nip shape is 15 ". The center nip width during heating expansion is Nc (N4), and the narrowest nip widths Nsr and Nsl (N3) are formed on the left and right sides, and the nip width Nor at both ends is Nol (N1) has the thickest configuration.Nll and Nlr (N2) in Fig. 3 (D) are intended to prevent paper wrinkles at the reverse crown taper portions at the left and right end sides from the roller center. Width of paper An appropriate width nip portion is shown that is distributed by a distance L (see FIG. 2) to an appropriate position inside the left and right paper edge passing positions (here, 5 mm inside) of a narrow sheet (here, A5 sheet), that is, N1. > N2≈N4> N3 In this way, the pressure roller 14 is formed to have a central fixing property-enhanced shape, thereby preventing the occurrence of paper wrinkles and toner stains having a trade-off relationship. It has been found that the occurrence of can be prevented.

  As a factor for obtaining the above results, as for the effect of preventing the occurrence of toner smearing, an increase in the center nip width increases the “fixing pressure increase”, “extension of the fixing area (= fixing time) on the paper” and “center rubber”. This is thought to be due to the improvement of the fixability in this area due to the action of “enhancement of heat capacity accompanying the increase in the layer” and the like. Regarding the high effect, the center fixing reinforced reverse crown roller has a region where the nip width locally increases toward the center of the roller, but the nip width near the center including the region of the minimum nip width on the left and right The overall area is rather smaller than the V-type and W-type reverse crown roller rollers, and the area with a large nip width is substantially limited to an extremely narrow area at the center. It is thought that the action of pulling the paper to the center is less than that of the W-type reverse crown roller. On the other hand, including the W-type reverse crown roller, the nip width increases toward the left and right outside of these minimum nip widths. The rate is larger than that of the conventional roller, so it is considered that a force that pulls the paper to the left and right outside with a stronger force was applied.

  In the pressure roller 14 ″, the difference between the outer diameters Dsl and Dsr of the minimum outer diameter part and the outer diameters Dol and Dor of the end part (reverse crown amount) is limited to 120 μm at room temperature. Rather, it is preferable to set the minimum outer diameter portion at the time of fixing to about 50 to 200 μm at room temperature while maintaining the condition that the minimum outer diameter portion at the time of fixing is not thicker than the central portion as a range in which the same effect as above can be obtained. Based on the experimental results and experience up to this point, there is a risk that a slight reverse crown amount of 50 μm or less cannot be expected to provide sufficient paper wrinkle prevention effects, and it may be hidden within the tolerance range of manufacturing variations and actually become a reverse crown shape. On the other hand, if a reverse crown amount of 200 μm or more is provided, the difference in outer diameter between the roller end and the minimum outer diameter portion becomes too large, and sufficient pressure is not applied to the minimum outer diameter portion. That even with the dispersing effect of the right and left two locations selectively increasing effect and minimum outer diameter of the central portion nip width there is a risk of insufficient margin to prevent local insufficient fixing.

3) Method for Manufacturing Pressure Roller Next, a method for manufacturing the pressure roller 14 of the present embodiment will be described with reference to FIGS.

  First, as shown in FIG. 4 (A), an M-type crown core metal 14 ″ b having a concave portion at the center is inserted into the outer die 16 of the pressure roller molding die like a core and set. The outer die 16 is formed in a cylindrical shape having a hollowed inner portion, and is subjected to taper processing for attaching reverse crowns to the left and right end portions of the inner surface, and the central portion is formed in a flat shape. Therefore, it is not necessary to process a complicated shape such as a W-shaped pattern on the inner surface of the outer mold 16 along the longitudinal direction.

  The inverted crown metal core 14 ″ b has a taper and a center that become narrower from the both ends to the left and right ends with the maximum outer diameter portion at a position away from the center portion by a distance C (distance C <distance L). It is formed in a crown shape with a taper that becomes thinner toward the portion, where the distance C from the central portion is shorter than the length of the central flat portion of the outer die 16. Outer die 16 The flat portion is composed of a flat inner surface having a width of 100 mm extending 50 mm from the center to the left and right. Therefore, the inner diameter Dc and Dsl, Dsr of the outer mold 16 shown in the figure have the same diameter.

  On the other hand, the detailed configuration of the inverted crown metal core 14b is linearly processed as shown in FIG. 4B, and the distance C from the center where the maximum outer diameter Da = 23.45 mm is formed. A width g = 2 mm formed at a central portion at a position 25 mm away from the left and right, having a local flat portion with a width g = 2 mm from the center and a horizontal distance G = 22 mm away from the inner end thereof. A taper portion is formed with a taper amount H = 0.225 mm from the left and right end portions of the central minimum outer diameter Dd = 23 mm, and is formed in an area having a width of 8.3 mm from the end portion of the maximum outer diameter portion to the left and right roller ends. Each of the surfaces that are linearly tapered by 2 mm is also formed on the inner end portion of the minimum outer diameter portion of the end portion having the outer diameter Db = 21.45 mm. With the inverted crown metal core 14 ″ b placed in the outer mold 16, a liquid rubber material is injected from the upper and lower ends or one side of the outer mold 16 or from the top with the mold standing vertically. Fill the mold with rubber material.

  After that, the entire mold is heated to cure the rubber layer. At that time, the heating distribution of this mold is not uniform, and the temperatures at the left and right ends and the center are likely to be relatively high. The rubber material in the intermediate region around the left and right corners is relatively slowly cured just at the central flat portion of the outer mold of the core metal. For this reason, there is some unevenness in the density of the rubber layer after curing, and the density of the rubber layer at the center portion and the left and right end portions is high, and the density of the middle region tends to be lower.

  By utilizing such a tendency, the mold temperature, the viscosity of the rubber material and the injection pressure are appropriately controlled, and after the rubber material is thermally cured, the central fixing reinforced type roller 14 ″ is released from the outer mold 16 to room temperature. Then, since the rubber layer was thermally expanded and closely adhered to the inner surface of the outer mold 16, the entire volume shrinks after cooling.At this time, the rubber layers on the left and right outer sides of the outer mold 16 are molds. Since the inner diameter of the outer die 16 is formed thick with a taper, it is easy to maintain a thicker shape than other regions even after shrinking, but the outer die 16 has the same inner diameter in the rubber layer in the central flat region of the outer die 16, Since all the outer diameters during heating are the same, there are a tapered part toward the left and right outer sides of the maximum outer diameter part of the core metal and a tapered part toward the center side. It has a taper, and after cooling, the thicker the rubber layer is, the easier it is to shrink. .

  Here, the maximum thickness of the rubber layer at the center is 3.725 mm, and the rubber layer thickness at the left and right ends of the center flat portion of the outer mold 16 is also approximately 3.8 mm. From this, in the region of the central flat portion of the outer mold 16, the outer diameter distribution in the longitudinal direction of the roller after cooling should be smaller in the central portion and the left and right end portions of the central flat portion of the outer mold 16.

  Actually measuring the shape of the pressure roller manufactured in this way at room temperature, the outer diameter of the roller center part and the left and right minimum outer diameter parts are almost the same, prescription of rubber material, injection pressure distribution, heating temperature distribution Although there may be some individual differences such as slight left-right differences due to variations in processing conditions such as the center part being thicker or thinner, the roller shape at room temperature is in the center part and both sides A total of three recessed rollers having two substantially equal minimum outer diameter portions (see FIG. 4C).

  On the other hand, at the time of actual fixing, the expansion of the rubber layer at the central portion is larger than the expansion of the rubber layers at the left and right minimum diameter portions by heating, resulting in a central drum-enhanced center-shaped reinforcing roller having a W-shaped inverted crown shape. Since the roller surface temperature at the time of fixing is close to the heating temperature at the time of roller molding, it was expected to be close to the mold, but this simply did not happen. In addition to the fact that the temperature at the time of use is not exactly the same as the temperature condition at the time of molding, the left and right ends of the roller are sealed and restrained at the time of molding, but the left and right ends are opened and the rubber material is the surface of the core metal during use The surface of the rubber layer when heated and expanded easily extends in the direction of the left and right ends, especially in the case of a crown shape where the cored bar is narrower than the left and right ends. The expansion direction of the rubber layer is mainly the outer diameter direction, whereas in the region of the left and right end tapered portions, the ratio of expansion to the left and right outer sides is higher, and the rubber layer has the same thickness. However, during heating, it seems that the left and right minimum outer diameter portions have an effect that the outer diameter tends to be narrowed by the amount easily extending to the left and right.

  Furthermore, since the fixing film is pressed against the roller from above during actual use, the rubber layer pressed by this applied pressure is likely to extend toward the left and right open ends. Is confined in the concave portion at the center of the metal core, so that the pressure during heating and expansion acts to push the upper fixing film side as it is, and as a result, such a nip shape is considered to be formed.

  With this manufacturing method that takes into account changes during use, a central fixing reinforced pressure roller can be manufactured at a low cost without using an outer mold whose inner surface is complicatedly processed into a W shape.

  Further, the minimum diameter portion at room temperature is formed at a position that substantially coincides with both end portions of the flat portion of the outer mold 16. Therefore, by changing the length from the center of each end portion while maintaining the positional relationship between the maximum outer diameter portions of the outer die 16 and the M-shaped crown core metal 14 ″ b, the position where the minimum outer diameter portion is formed is changed. Therefore, it is possible to easily adjust the formation position of the minimum outer diameter portion according to the desired minimum paper size on which the effect of countermeasures against paper wrinkles acts by this adjustment method. However, in an actual roller, depending on the combination of rubber hardness and taper amount, the shrinkage amount of the rubber layer of the reverse crown taper portion outside the minimum outer diameter portion becomes too large, and the outer diameter of these regions is unexpected. Designed with sufficient consideration of rubber hardness (shrinkage amount based on it) and taper amount, etc., and sufficient margin in the position of the minimum outer diameter for the desired minimum paper size where the effect of countermeasures against paper wrinkles acts Provided It is necessary to make the total.

( Reference Example 1 )
Next, Reference Example 1 of the fixing device according to the present invention will be described with reference to FIGS.

(Fixing film)
As shown in FIG. 5A, the fixing film of Reference Example 1 as a heating rotator is formed as a straight fixing PI film 13d having a uniform outer diameter in the longitudinal direction. The layer structure of the film is composed of heat-resistant resin PI instead of SUS of the reverse crown metal film 13c used in the examples as the base layer, and the layer structure thereon is basically the same as the reverse crown metal film 13c. The film has a straight shape of φ30.45 mm in which the outer diameters of the left and right end portions in the longitudinal direction and the central portion are substantially the same.

(Pressure roller)
As shown in FIG. 5 (B), the pressure roller 14 of the present embodiment 1 as pressurizing rotator, of the same central fixing enhancement inverted crown shaped upper it施例is used. The pressure roller 14 ', the fixing unit 12b that combine straight fixing PI film 13d is identical to the fixing unit 12a of the actual施例.

  In the above configuration, the resin film 13d is formed of a PI film that is less expensive than a metal film, and does not need to be subjected to reverse crown processing, and can be suppressed in terms of cost.

Next, test types will be described. In Reference Example 1 , two types of tests, a paper wrinkle test and a toner stain test, were conducted as the paper passing test similar to the example .

  Table 2 is a table showing the results of a comparative evaluation of a paper wrinkle test and a toner smear test in the case where two types of fixing films are combined with the same pressure roller 14 ″. Or, a case where toner stains occur, Δ indicates that paper wrinkles or toner stains are slight, but ○ indicates that paper wrinkles or toner stains hardly occur, and even if they occur, there is no practical problem. The case where it is insignificant is shown.

As described above, when the resin film 13d having low rigidity is used as the fixing film, paper wrinkles tend to be slightly generated even with the conventional W-type reverse crown pressure roller, but the pressure roller 14 ″ of the present invention is used. Therefore, the effect of preventing the paper wrinkle by the film is sufficiently compensated, and the effect of preventing the paper wrinkle can be sufficiently obtained. Although it is promoted, it can be seen that although the conventional W-type reverse crown pressure roller is slightly deteriorated, the use of the pressure roller of the present Reference Example 1 is improved so as not to cause a problem in practice.

  Therefore, by using the straight-shaped resin film 13d as the fixing film, it is possible to prevent the occurrence of paper wrinkles and toner stains to such an extent that they do not cause a problem in practice, and the cost can be reduced.

( Reference Example 2 )
Next, Reference Example 2 will be described with reference to FIG.

As shown in FIG. 6 (A) ~ (D) , a heat roller type fixing device 12c according to the present embodiment 2, as a heating rotary member, instead of the heating rotating body 13 of the upper you施例, reverse crown amount A fixing roller 18b having an inverted crown shape of 100 μm is provided. The fixing roller 18b includes a halogen heater 18a inside.

  In the conventional heat roller type fixing device, it is relatively easy to provide a reverse crown on the fixing roller, and there has been no particular problem in providing a sufficient effect on paper wrinkles. However, when continuous paper durability is performed in a low-temperature and low-humidity environment with a paper type containing calcium carbonate, toner stains tend to occur on the paper and on the upper and lower roller surfaces. This tendency becomes more serious as the printing speed increases, and a cleaning roller for scraping off the toner stains on the roller is added or a cleaning sequence is introduced.

Therefore, in the present reference example 2 , the heat roller type fixing device is also configured to use the central fixability-enhanced pressure roller 14 ″ so as to prevent paper wrinkling and toner contamination. Yes.

This was followed by a similar paper wrinkle test and toner stain test and the actual施例with fuser 12c. Such a test was performed on two types of rollers, a straight pressure roller and a central fixability-enhanced pressure roller 14. Table 3 shows the test results. In Table 3, “X” indicates a case where paper wrinkles or toner stains occur, and “◯” indicates a case where paper wrinkles or toner stains do not occur.

  As described above, toner contamination occurs in the straight pressure roller, whereas toner contamination can be prevented in the pressure roller 14 ″. In the heat roller type fixing device, the shape of the fixing roller itself. The center nip is thickened like a drum, and the left and right end portions of the drum shape are set to the minimum outer diameter portion, and the outer diameter increases toward the left and right roller ends from FIG. D) may be processed into a shape as shown in FIG. 4B, and there is a difference between the respective outer diameters in the longitudinal direction due to the difference between the elastic roller and the rigid roller, but as a result, the nip shape at the time of fixing using the fixing roller is different. The same effect can be obtained by adjusting the machining shape so as to have the same shape as in FIG.

( Reference Example 3 )
FIG. 7A is a cross-sectional view showing an outer mold 16 of a molding die for manufacturing the pressure roller 19 (FIG. 7B) as Reference Example 3 . A center local small-diameter straight cored bar 19a that is basically straight and has a recess only in the central part is inserted into the outer mold 16 to set the mold. The outer die 16 is formed in a cylindrical shape having a hollowed inner portion, and is subjected to taper processing for attaching reverse crowns to the left and right end portions of the inner surface, and the central portion is formed in a flat shape. Therefore, it is not necessary to process a complicated shape that repeats unevenness like the W shape along the longitudinal direction on the inner surface of the outer die 16.

  The central local small-diameter straight cored bar 19a has a uniform outer diameter portion from the position away from the roller central portion by a distance C (distance C <distance L) from the left and right outer sides, and from this position to the inner central portion. It is processed into a shape having a taper portion that becomes narrower. Here, the length C from the center is shorter than the length of the center flat portion of the outer mold 16. Further, the flat portion of the outer mold 16 is constituted by a flat inner surface having a width of 100 mm extending 50 mm from the center to the left and right, and the inner diameter Dc, Dsl, and Dsr of the illustrated outer mold 16 have the same diameter. As a detailed configuration of the central local small-diameter straight cored bar 19a, the distance C from the center of the roller is formed with a uniform outer diameter Da = 2.45 mm between the positions 25 mm to the left and right, and the width 2 mm from the center to the center C A taper of 0.25 mm from the inner end portion to the center portion having a local flat portion and having a center minimum outer diameter Dd of 23 mm and a right and left end portion of 23 mm (shown schematically, The cored bar is linearly tapered).

In this case as well be the real施例, in a state in which in the outer mold 16 was placed in the central local small diameter straight core metal 19a, or to fill the rubber material of the liquid in the left and right ends or one side of the outer mold 16, or the mold vertically The mold is filled with a rubber material using several methods such as pouring from above. After that, when the entire mold is heated to cure the rubber layer, the heating distribution of this mold is not uniform and the temperature at the center of the left and right ends tends to be relatively high, so curing of these parts is promoted, The curing of the rubber material in the middle region around the left and right corners of the outer central flat portion of the core metal is relatively slow. For this reason, there is some unevenness in the density of the rubber layer after curing, and the density of the rubber layer at the center portion and the left and right end portions is high, and the density of the middle region tends to be lower. By utilizing such a tendency, the mold temperature, the viscosity of the rubber material, and the injection pressure are appropriately controlled. After the rubber material is thermally cured, the pressure roller is released from the outer mold 16 and cooled to room temperature. Since the layer was thermally expanded and was in close contact with the inner surface of the outer mold 16, the volume shrinks as a whole after cooling. At this time, the rubber layer on the left and right outer sides from the flat portion of the outer mold 16 is formed thick with the inner diameter of the mold itself having a taper, so that it is easy to maintain a thicker shape than other regions even after contraction. However, since the inner diameter of the outer die 16 is the same in the rubber layer in the central flat region of the outer die 16, the outer diameter at the time of heating is the same, but the taper portion and the center toward the left and right outer sides of the maximum outer diameter portion of the metal core There is a tapered portion toward the side. Therefore, in these regions, the thickness of the rubber layer itself is tapered, and after cooling, the thicker the rubber layer is, the easier it is to shrink.

  Here, the maximum thickness of the rubber layer at the center of the roller is 3.725 mm, and the thickness of the rubber layer at the left and right ends of the central flat portion of the outer mold 16 is approximately 3.5 mm. From this, the outer diameter distribution in the longitudinal direction of the roller after cooling in the region of the central flat portion of the outer die 16 is the outermost portion of the central flat portion of the outer die 16 that is most contracted and the outer diameter becomes narrower. The diameter becomes thinner.

  When the shape of the pressure roller 19 manufactured in this way is measured at room temperature, as shown in FIG. 7B, a minimum outer diameter portion at the center and a slightly thicker and almost flat area on both sides thereof. And a deformed reverse crown roller whose outer diameter increases toward the left and right outer sides.

  On the other hand, at the time of actual fixing, the expansion of the rubber layer in the central portion is larger than the expansion of the rubber layers in the left and right flat portions due to heating, resulting in a central drum-enhanced centrally-enhancing roller having a W-shaped reverse crown shape. Since the roller surface temperature at the time of fixing is close to the heating temperature at the time of roller molding, it was expected to be close to the mold, but this simply did not happen. In addition to the fact that the temperature at the time of use is not exactly the same as the temperature condition at the time of molding, the left and right ends of the roller are sealed and restrained at the time of molding, but the left and right ends are opened and the rubber material is the surface of the core metal during use Since the surface of the rubber layer during heat expansion is easy to extend in the direction of the left and right ends, the minimum outer diameter of the left and right tends to extend to the left and right. It seems to be.

Further, since the fixing film is pressed against the roller from above during actual use, the rubber layer pressed by the applied pressure is likely to extend toward the left and right open ends. There, however, since the rubber layer of the roller center part is confined in the recess of the core center, the pressure at the time of thermal expansion acts to push back the fixing film side of the above as it shows the results and to actual施例2 ( The shape shown in FIG. 7C is the same as that in B), and a nip shape similar to that shown in FIG. 3D is obtained.

  With this manufacturing method that takes into account changes during use, a central fixing reinforced pressure roller can be manufactured at a low cost without using an outer mold whose inner surface is complicatedly processed into a W shape.

However, in the configuration of the present reference example 3 , since the crown shape is not given to the cored bar, if the outer diameter of the cored bar straight part is made too thin, the central part is locally narrowed. When the pressure is applied, the entire roller is easily deflected, and the pressurizing force at the central portion is lowered, and conversely, the nip width at the central portion may be reduced. For this reason, when using this pressure roller configuration, it is needless to say that it is necessary to adjust the outer diameter of the core of the straight portion and the pressure intensity to prevent the deflection of the entire roller.

Further, the rubber layer thickness of the inverted crown region of the left and right ends in the roller configuration of the present embodiment is divided core bar is straight, the rubber layer as compared with the pressure roller of the embodiment is thin, the expansion amount at the time of thermal expansion Therefore, the paper wrinkle prevention effect by this region is reduced. Therefore, it is necessary to adjust such to obtain a pressure roller equivalent to paper wrinkle prevention performance examples to increase the amount of taper of the right and left end portions of the outer die, the case of using the same outer mold The pressure roller is preferably used in a lower-speed apparatus.

( Example)
Figure 8 (A) is a sectional view showing the outer mold 20 of the mold for manufacturing the a real施例pressure roller 21 [Fig 8 (B)]. Outer mold 20, in this embodiment with a simple cylindrical straight outer mold of the entire inner diameter is uniform, and the mold set by inserting the same M-type crown core metal 14 "b and a core metal.

The M-shaped cored bar 14 ″ b has a concave portion (central outer diameter = 23 mm, central-direction taper shape having a central longitudinal length = 2 mm) at the central portion, and both ends thereof are locally maximum outer diameter Da. It has a diameter portion (the outer diameter of the maximum outer diameter portion = 23.45 mm, the width in the longitudinal direction = 2 mm), and the outer diameter becomes narrower from the ends of the left and right maximum outer diameter portions to the left and right ends of the roller. The taper portion is a tapered portion . With the M-shaped crown metal core 14 ″ b inserted into the outer mold 20, a liquid rubber material is filled into the left and right ends or one side of the outer mold 20, or the gold The mold material is filled with a rubber material using several methods such as vertically injecting the mold from above.

  Thereafter, when the entire mold is heated to cure the rubber layer, the heating distribution of the mold is not uniform, and the temperature at the center of the left and right ends tends to be relatively high. Therefore, the curing of those portions is promoted, and the curing of the rubber material in the middle region around the left and right corners of the central flat portion of the outer core 20 of the metal core is relatively slow. For this reason, there is some unevenness in the density of the rubber layer after curing, and the density of the rubber layer at the center portion and the left and right end portions is high, and the density of the middle region tends to be lower.

  Using such a tendency, the mold temperature, the viscosity of the rubber material, and the injection pressure are appropriately controlled, and after the rubber material is thermally cured, the pressure roller 21 is released from the outer mold 20 and cooled to room temperature. Then, since the rubber layer was thermally expanded and adhered to the inner surface of the outer mold 20, the volume shrinks as a whole after cooling. At this time, since the inner diameter of the outer mold 20 is uniform and only the cored bar has a taper in the central part and the right and left end regions, the rubber layer shrinks more greatly in the narrowed part of the cored bar, and after cooling As shown in FIG. 8B, the shape of the surface of the rubber roller in the room temperature state is an M-shaped crown pressure roller 21 that is deformed according to the shape of the metal core as a whole.

Therefore, in the actual施例this, not only it is not necessary to machine the complex shape repeating irregularities such as W-type in the longitudinal direction on the inner surface of the outer mold 20, completely because tapered is unnecessary In addition, a simple pipe-shaped mold can be used, and the pressure roller 21 that is inexpensive in cost can be obtained.

Further, during actual fixing, the hot portion of the rubber layer in the central portion and the left and right tapered portions expands due to heating, and as a result, the W-shaped reverse crown in which the central portion of the roller has a drum shape as shown in FIG. It becomes a central fixing strength reinforcing roller of the shape. However, in the pressure roller 21 of the present embodiment, the position of the minimum outer diameter portion at the time of thermal expansion is different from the case where the positions of the left and right ends of the flat portion of the outer mold are defined as in the above embodiments. However, the concave portion is not formed, but is formed as a boundary region between the left and right inflating portions and the central inflating portion. Therefore, it is easy to form a region where the outer diameter is gradually narrowed in a wider range. Resulting in a shape shown in FIG. 2 (B) similar to FIG. 8 (C), the similar nip shape as FIG. 3 (D) is obtained.

In the case of real施例this, since the reverse crown portions of the left and right that are formed by only expansion change during heating, reverse crown effect compared with the case of forming the positively inverted crown region in the above embodiments Is inferior. For this reason, in order to obtain the same effect with such a configuration, it is necessary to select a rubber material having a high thermal expansion coefficient and to increase the amount of the core metal crown. At that time, it is necessary to adjust the taper amount at the central portion of the roller so that the minimum outer diameter portion is formed sufficiently inside a region through which a paper edge portion of a desired size that does not want to cause paper wrinkles passes.

( Reference Example 4 )
FIG. 9A is a cross-sectional view showing an outer mold 22 of a molding die for manufacturing a pressure roller 23 (FIG. 9B) which is a reference example 4. FIG. The outer die 22 is formed in a convex shape with the inner diameter of the outer die 22 corresponding to the left and right positions away from the center where the minimum outer diameter portion of the roller is to be formed after the pressing roller 23 is formed. An outward tapered portion is formed from the position toward the left and right outer sides to form an inverted crown region similar to the conventional one, and a drum-shaped taper process is performed in which the inner diameter of the outer mold 22 gradually increases toward the center. W-shaped inner surface. A simple straight cored bar 14'b is inserted and set in the outer mold 22 as a cored bar.

As with real施例, on a state of inserting the straight metal core 14'b into the outer mold 22, or to fill the rubber material of the liquid in the left and right ends or one side of the outer mold 22, or the mold upright The mold is filled with a rubber material using several methods, such as pouring and filling.

  Thereafter, when the entire mold is heated to cure the rubber layer, the mold temperature, the viscosity of the rubber material, and the injection pressure are appropriately controlled, and the pressure roller 23 is released from the outer mold 22 after the rubber material is thermally cured. Cool to room temperature. Then, since the rubber layer was thermally expanded and was in close contact with the inner surface of the outer mold 22, the volume shrinks as a whole after cooling. At this time, since only the inner surface of the outer die 22 has a taper in the center portion and the left and right end regions, the rubber layer shrinks more greatly in the portion where the inner diameter is thicker, and the surface of the rubber roller in the room temperature state after cooling As shown in FIG. 9 (B), the minimum and maximum inner diameters of the outer mold are such that the difference between the minimum outer diameter and the maximum outer diameter is deformed according to the inner surface shape of the outer mold 22 as a whole. This is a pressure fixing roller having a central fixing property smaller than the difference between the two.

Therefore, since the cored bar in this case does not need to be tapered at all, a simple bar-shaped cored bar can be used and the pressure roller 23 which is inexpensive in cost can be obtained. Further, the pressure roller 23 (see FIG. 9B), which has already obtained a desired shape at room temperature, basically changes only in its unevenness even when heated and expanded during actual fixing. Maintain this shape. As a result, a nip shape as shown in FIG. 3D is obtained, and an effect equivalent to the effect of the embodiment is obtained. Further, in the present Reference Example 4 , a processing method for providing such an uneven structure on the inner surface of the outer mold 22 is the main point, and the roller diameter is relatively thin and the longitudinal direction is relatively long. Processing is limited from the viewpoint of the size and operability of the processing apparatus. However, as a method for manufacturing a roller having a relatively large roller outer diameter and a short longitudinal direction, a straight cored bar can be used once the outer die 22 is manufactured. Can be manufactured.

In the above real施例, during actual fixing, the nip width of the right and left ends of the maximum paper feed size of at most, most nip narrow region between the left right end portion and the central portion is formed, the central portion The nip has a drum shape that gradually increases toward the center, and the thickest nip width at the center of the nip passes through the left and right edges of the smallest paper of the paper that you want to prevent paper wrinkling. As a configuration for obtaining a fixing nip shape smaller than the width, the configuration of the pressure roller is assumed as the center, and the configuration on the heating rotation side is assumed to be a straight or reverse crown shape, but a similar fixing nip shape can be obtained. Needless to say, the shape on the heating rotation side may be devised and combined with the pressure roller.

1 is a diagram illustrating an electrophotographic image forming apparatus according to an embodiment. FIG. Sectional view showing a room temperature state of the pressure roller according to the actual施例. Estimation sectional view of the fixing overheating of the pressure roller according to the actual施例. Side sectional view of a fixing device using the pressure roller of the real施例. Front view of the fixing film by Real施例. A front view of the fixing device according to the real施例. Fixing nip shape view of the solid施例. Manufacturing equipment cross-sectional view of the pressure roller in the real施例. Metal core central enlarged sectional view in the real施例. Rubber material charging illustration in the real施例. The front view of the fixing film in the reference example 1 which concerns on this invention. The side view of the fixing film in the reference example 1. FIG. The front view of the fixing film in the reference example 1. FIG. The front view of the fixing roller in the reference example 2 which concerns on this invention. FIG. 6 is a side view of a fixing roller in Reference Example 2 . FIG. 6 is a front view of an improved fixing roller fixing device in Reference Example 2 . FIG. 6 is a side view of an improved fixing roller in Reference Example 2 . Sectional drawing of the manufacturing apparatus of the pressure roller in the reference example 3 which concerns on this invention. Sectional drawing of the pressure roller in the reference example 3 in the room temperature state. FIG. 11 is an estimated cross-sectional view of a fixing roller in a fixing heating state in Reference Example 3 . Sectional view of an apparatus for manufacturing a pressure roller in engagement Ru real施例the present invention. Sectional view of the room temperature state of the pressure roller in the real施例. Estimation sectional view of the fixing heating state of the pressure roller in the real施例. Sectional drawing of the manufacturing apparatus of the pressure roller in the reference example 4 which concerns on this invention. Sectional drawing of the pressure roller in the reference example 4 in the room temperature state. Sectional drawing of the reverse crown pressure roller of a prior art example. The nip shape figure of the reverse crown pressurization roller of the prior art example. The figure explaining the granular toner stain on paper of the reverse crown pressure roller of the conventional example. Sectional drawing which shows the reverse crown pressurization roller of the prior art example. Sectional drawing of the W type reverse crown pressure roller of a prior art example. The front view of the fixing film of the prior art example. The front view of the fixing device of the conventional example. The fixing nip shape figure of the conventional example. Sectional drawing of the manufacturing apparatus of the conventional W type reverse crown pressure roller. The rubber material injection explanatory drawing of the W type reverse crown pressure roller of the conventional example. Explanatory drawing of the temperature dependence of the outer diameter of the conventional W type reverse crown pressure roller. Explanatory drawing of the temperature dependence of the outer diameter of the M-type cored bar W-type reverse crown pressure roller of the present invention.

DESCRIPTION OF SYMBOLS 1 Charging roller 2 Photosensitive drum 3 Exposure means 4 Developer 5 Toner 5a Toner dirt 6 Transfer roller 7 Sheet (recording material)
DESCRIPTION OF SYMBOLS 10 Cleaning container 11 Cartridge 12 Fixing device 13 Fixing film (heating rotary body)
13a Ceramic heater 13b Film guide member 13c Reverse crown metal film 13d Straight resin film 14 Pressure roller (pressure rotator)
14a Silicon rubber layer (elastic layer)
14'b Straight core (roller core)
14'c Crown core (roller core)
14 ″ b M-type crown core 15 nip shape 16 outer mold 18 fixing roller 18 ′ W-type fixing roller 18a halogen heater 20 straight outer mold

Claims (1)

A core roller and an elastic layer formed on the outer side of the core metal, and includes a transport roller that forms a nip portion for transporting the recording material, and transports the recording material carrying a toner image at the nip portion. In the fixing device for fixing the toner image on the recording material by heating while
The cored bar has a concave area whose diameter gradually decreases toward the center along the longitudinal direction of the cored bar at the center in the longitudinal direction of the cored bar, and a maximum outer diameter in the concaved area. A taper-shaped area in which the diameter gradually decreases from both ends to the end in the longitudinal direction of the transport roller,
The elastic layer has a convex area in which the diameter gradually increases toward the center along the longitudinal direction of the elastic layer and a minimum diameter in the convex area at the center in the longitudinal direction of the elastic layer. A tapered area in which the diameter gradually increases from both ends toward the longitudinal end of the transport roller,
The fixing device according to claim 1, wherein a length of the concave area of the cored bar in the longitudinal direction of the transport roller is shorter than a length of the convex area of the elastic layer in the longitudinal direction of the transport roller.

Images