JP2005284089A - Pressurization body of rotation, fixing apparatus, image forming apparatus, and manufacturing method of pressurization body of rotation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressurization body of rotation, a fixing apparatus and an image forming apparatus capable of continuously printing a good image on a paper without causing the deformation of the paper by preventing wrinkles on the paper and insufficient fixation on the center part of a nip easily becoming worse in accordance with a high-speed operation, and preventing the occurrence of dot soil by toner, and to provide a manufacturing method of the pressurization body of rotation. <P>SOLUTION: Regarding the pressurization body ofrotation for fixing the image on the recording medium while carrying the recording medium in press contact with a counter member, the pressurization ofbody of rotation is provided with the smallest outside diameter parts having the smallest outside diameters Dsl and Dsr between each of the left and right end parts in a rotating axis direction and the center part in the rotating axis direction and tapered parts where the outside dimension becomes thicker from the smallest outside diameter part to the end part, and the dimensional relation between the outside diameters Dol and Dor at the left and right end parts and the outside diameter Dc at the center part satisfies Dor≈Dol>Dc, and the dimensional relation between outside diameters Dll and Dlr on the left and right sides away from the center part at a prescribed distance L between the smallest outside diameter part and the end part, and the outside diameter Dc at the center part satisfies Dlr≈ Dll>Dc. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a fax machine using a recording system such as an electrophotographic system or an electrostatic recording system, and is particularly suitable for use in a fixing device to improve a good image and a recording medium. The present invention relates to a fixing device that can be prevented, a pressure rotator used in the fixing device, and a method of manufacturing the pressure rotator.

  Conventionally, various image forming apparatuses generally form an image on a sheet-like recording medium such as plain paper, postcard, cardboard, sealed letter, and OHP plastic thin plate. As typical examples of image forming apparatuses, there are apparatuses such as printers, copiers, and facsimile machines using an electrophotographic system. These apparatuses use toner as a developer to form a toner image on a recording medium by an electrostatic image forming unit, and then heat and press the recording medium by a fixing unit to melt and fix the toner image. Form.

  As an image fixing method, a contact heating type fixing device having good thermal efficiency and safety is widely known. Conventionally, a release layer is mainly formed on the surface of a metal cylindrical core metal, a heat fixing roller containing a halogen heater inside the cylinder, and an elastic layer made of heat-resistant rubber is formed on the metal core, There has been used a heat roller fixing device constituted by pressing a pressure roller formed by forming a pressure-side release layer on the surface.

  However, in recent years, as a method with higher heating efficiency, a fixing film in which a release layer is formed on the surface of a low heat capacity heat-resistant resin film made of a material such as PI (polyimide) instead of the heat fixing roller is used. There has been proposed a film heating type fixing device in which a ceramic heater is brought into contact with and heated from the inside of the fixing nip portion of the film (see Patent Documents 1 to 4).

  Further, the film heating type fixing device includes a method of transporting a film between a pressure roller while applying tension using a dedicated transport roller and a driven roller for transporting the film, and a cylindrical film. There is a method of driving with a conveying force from a pressure roller. The former has the advantage that the film conveyance performance can be kept high, and the latter has the advantage that a low-cost fixing device can be realized with the simplification of the configuration.

  In the heating and fixing apparatus as described above, since heating is performed with the paper sandwiched in the fixing nip portion, the balance of the pressure distribution in the longitudinal direction in the fixing nip portion of the rubber roller is lost, and pressure is concentrated on the central portion of the roller. The transported paper and the speed at the central portion of the passed paper increase, and as a result, a force that draws the entire paper toward the central portion acts, and the central portion of the paper is wrinkled vertically (hereinafter referred to as paper wrinkles). There is a risk of occurrence).

  In order to solve this problem, in the heat roller fixing device, the fixing roller is processed into a shape in which the outer diameters of the left and right end portions are larger than the central portion in the longitudinal direction of the roller (hereinafter referred to as an inverted crown shape). Generation of paper wrinkles is prevented by generating a force that pulls the paper toward both ends at the nip portion. On the other hand, in a film heating type fixing device, it is difficult to form a shape like the above-described reverse crown on the fixing film corresponding to the fixing roller. The structure which prevents generation | occurrence | production of is used.

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

  However, when the reverse roller shape is provided on the fixing roller and the pressure roller as a countermeasure against paper wrinkles in this way, the outer diameters of the left and right end portions are 120 μm thicker than the roller center portion as shown in FIG. 6A, for example. Fixing is performed by the pressure roller 114 having a reverse crown shape. Although the pressure roller 114 appears to be curved in a V-shape or U-shape with a slight inclination on the drawing, the influence of the depression of the central portion of the curvature on the actual fixing nip formation cannot be ignored.

  If conditions such as reverse crown amount, pressure, and heating temperature are not appropriate for the fixing speed, the contact pressure at the center of the fixing nip in the longitudinal direction is locally insufficient and the nip width is at the left and right ends. The contact area for transferring the heat from the heat source to the paper side is also locally reduced at the center of the nip.

  For this reason, both the pressure and the amount of heat supplied decrease, and the fixing property of the central toner image to the recording medium 7 is insufficient. In addition, a small amount of toner that has not been sufficiently fixed adheres to the fixing roller, film, or pressure roller side, and the adhered toner accumulates while continuing to print a large amount. Then, when the toner cannot be held, the accumulated toner is discharged to the paper side at once, and a large amount of large and small granular toner stains 5a as shown in FIG. 6B are generated. .

  As a countermeasure, the reverse crown amount of the pressure roller is suppressed to such an extent that the fixability at the center of the nip is not greatly deteriorated. Then, as shown in FIG. 6 (C), the cored bar shape of the pressure roller is changed to a crown cored bar 114c having a shape in which the outer diameter becomes narrower from the center toward the left and right ends (hereinafter referred to as a crown shape). To do. Thus, a method has been considered in which the thickness of the rubber layer at the left and right ends of the pressure roller is increased to increase the thermal expansion force of the rubber, thereby reinforcing the effect of pulling both ends of the paper.

  However, particularly in recent years, the printing speed of these devices has been increasing. As the printing speed increases, it becomes difficult to properly adjust the conditions such as the reverse crown amount, the pressure, and the heating temperature, and the shortage of fixing worsens. For this reason, it has become difficult to satisfy all of paper wrinkles, prevention of deterioration of fixing ability, and granular toner contamination only by the above-described conventional measures.

  The present invention has been made in view of the above problems, and the object of the present invention is both a paper wrinkle that tends to deteriorate as the speed increases, a lack of fixability at the center of the nip, and the occurrence of granular toner stains associated therewith. An object of the present invention is to provide an image forming apparatus capable of preventing and preventing a paper deformation and continuously printing a good image.

In order to solve the above-described problems, a typical configuration of the pressure rotator according to the present invention is a pressure rotator that performs image fixing while conveying a recording medium while being pressed against an opposing member. The body has a minimum outer diameter Dsl, Dsr between the left and right end portions in the rotation axis direction and a central portion in the rotation axis direction, and the outer shape increases from the minimum outer diameter portion to the end portion. A taper part, and the magnitude relationship between the outer diameters Dol and Dor of the left and right end parts and the outer diameter Dc of the central part is Dor≈Dol> Dc,
The magnitude relationship between the outer diameters Dll and Dlr between the minimum outer diameter part and the end part and separated from the central part by a predetermined distance L to the left and right and the outer diameter Dc of the central part is Dlr. ≒ Dll> Dc.

  As described above, according to the present invention, by using a roller (hereinafter referred to as a W-type reverse crown roller) processed so that the surface shape of the upper half of the roller as viewed from the side looks like a W-type. In addition to preventing the occurrence of paper wrinkles, it is possible to prevent the occurrence of toner stains having a trade-off relationship.

  In addition, as a W-type reverse crown roller manufacturing method, a crown-type core metal having a flat portion at the center portion is used in the same manner as the reverse crown-type outer die having a flat portion at the center portion, and the flat portion of the outer die is used as the core metal. The W-shaped reverse crown roller can be manufactured at a low cost by combining it longer than the flat portion.

[First embodiment]
A first embodiment of a pressure rotating body, a fixing device, and an image forming apparatus according to the present invention will be described with reference to the drawings. 1A is a cross-sectional view of the pressure roller of the fixing device according to the present embodiment, FIG. 1B is an external view of the fixing film, FIG. 1C is a side cross-sectional view of the fixing device, and FIG. FIG. 3 is a cross-sectional view of a main part of the printer.

(1) Entire Image Forming Apparatus As shown in FIG. 2, a printer that employs an electrophotographic system first charges the surface of the photosensitive drum 2 uniformly with a predetermined polarity with the charging roller 1. The charged photosensitive drum 2 is exposed by an exposure means 3 such as a laser to form a latent image on the surface. The latent image is developed by the toner 5 of 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, a DC and AC bias are applied in a superimposed manner at the developing gap portion where the photosensitive drum 2 and the developing sleeve 4b face each other, and the toner 5 is floated and vibrated by the action of an electric field, and selectively adheres to the latent image forming portion of the photosensitive drum 2. Let 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 recording medium 7 such as paper on which an image is recorded is fed from the recording medium storage box 7a to the vertical conveying roller pair 7d by a pair of feeding rollers 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 recording medium 7 transported to the pre-transfer transport roller 7e is transported to the transfer nip portion by the pre-transfer transport roller 7e along the space between the upper transfer guide plate 9a and the lower transfer guide plate 9b at a predetermined entry angle. .

  Until the recording medium 7 is conveyed from the pre-transfer conveying roller 7e to the transfer nip portion, the recording medium 7 comes into contact with various members. For this reason, there is a possibility that the surface of the recording medium 7 may be charged by rubbing with the various members. In view of this, the charge, which is a factor that disturbs the image when performing electrostatic recording, is removed by a grounding static elimination brush 8 provided so as to be in contact with the back side of the recording medium 7 being conveyed.

  In the transfer portion, in order to electrostatically attract the toner 5 on the photosensitive drum 2 and move it to the recording medium 7 side, 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 recording medium 7. As a result, the toner 5 is electrostatically attracted to the back surface of the recording medium 7 and the toner image is transferred to the recording medium 7. Further, the back surface of the recording medium 7 is charged with a polarity opposite to that of the toner 5, and a transfer charge for continuously holding the transferred toner 5 is applied to the back surface of the recording medium 7.

  The recording medium 7 onto which the toner image has been transferred is conveyed to a fixing device 12 including a heating rotator 13 and a pressure roller 14 that is a pressure rotator. The recording medium 7 conveyed to the fixing device 12 is nipped and conveyed by a fixing nip formed by the heating rotator 13 and the pressure roller 14, and the heating rotator 13 is maintained so as to maintain a preset fixing temperature. The toner image is fixed by heating and pressurizing while controlling the temperature by a heater provided on the side.

  A slight amount of deposits such as toner having different polarities remain on the surface of the photosensitive drum 2 after the toner image is transferred. For this reason, the surface of the photosensitive drum 2 after passing through the transfer nip portion is cleaned in the cleaning container 10 by scraping off the adhering matter by the cleaning blade 10a counter-contacted with the surface of the photosensitive drum 2. Prepare for formation.

  The above-described components of the charging roller 1, the photosensitive drum 2, the developing device 4, and the cleaning container 10 have a relatively short replacement cycle, and therefore can be replaced in units of the cartridge 11 in which these components are integrated.

(Pressure roller)
As shown in FIG. 1A, the pressure roller 14 is a W-type reverse crown pressure roller provided with a silicon rubber layer 14a having a W-shaped cross section in the longitudinal direction on the outer periphery. As the core of the pressure roller 14, a crown core 14b is used. The crown metal core 14b has a flat portion having an outer diameter Da at the center portion, and is a tapered portion 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 the roller. ing.

  The pressure roller 14 is formed with the thickest outer diameters Dol and Dor at the left and right end portions. Further, the pressure roller 14 is provided with a minimum outer diameter portion where the outer diameter is the smallest at two positions on the left and right sides between the roller central portion and the left and right end portions. And the taper part which an external shape becomes thick is formed from the minimum outer diameter part to the right and left end parts.

  The outer diameters Dol and Dor at the left and right ends are thicker than the outer diameter Dc at the center, but the normal reverse crown amount is smaller than the reverse crown amount of a conventional V-type reverse crown roller. Normally, the reverse crown amount is calculated using the difference between the average outer diameter of the left and right end portions and the outer diameter of the central portion.

  However, the pressure roller 14 has a narrower portion between the center portion and the left and right end portions than the center portion. The difference between the outer diameters Dsl and Dsr and the outer diameters Dol and Dor at the left and right ends is processed to be equal to the reverse crown amount of a conventional V-type reverse crown roller. Even with the same reverse crown amount, the distance between the minimum outer diameter portion of the pressure roller 14 and the maximum outer diameter portion at both ends of the roller becomes closer, and the gradient becomes larger. For this reason, the action of pulling the end of the recording medium 7 outward at these portions is higher than that of a normal reverse crown roller.

  When the total length of the pressure roller 14 is R, the thinnest outer diameters Dsl and Dsr are located at a distance S from the center to the left and right. Here, let L be a distance that is further 5 mm shorter than the half of the narrowest paper width among the recording media 7 that are passed through the apparatus and are wrinkled. The outer diameters at positions separated by this distance L from the center to the left and right are Dll and Dlr.

  The relationship between the roller outer diameters at the respective positions is expressed as “Dol> Dll> Dc> Dsl” when only the left half region is represented. Therefore, the outer diameter on the outside from the position of the distance L from the center is always processed sufficiently thicker than the outer diameter Dc of the center. Thereby, a sufficient reverse crown effect can be expected even for such a small-sized recording medium 7.

  On the other hand, the pressure roller 14 processed into the W shape as described above can make the outer diameter Dc of the central portion larger than that of a conventional simple V-shaped reverse crown. For this reason, the nip width of the central portion is also increased, and the fixing performance of this portion can be improved.

  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 the recording medium 7 is passed. Further, the amount and frequency of the occurrence of the stain are greatly influenced by a slight difference in the fixing property due to the outer diameter difference of several tens of μm near the center, and the toner contamination can be suppressed when the outer shape is larger. Therefore, the pressure roller 14 processed into a W shape can be expected to have an effect of suppressing toner contamination because the outer diameter Dc of the central portion can be made larger.

  On the other hand, the pressure roller 14 processed into a W shape has a small roller outer diameter at a distance S from the center to the left and right. However, since the pressure spring for forming the fixing nip portion acts at the left and right end portions, the pressure distribution in the longitudinal direction of the fixing nip portion becomes higher from the center toward the end portion. Further, during continuous paper feeding, the temperature at the center is easily lost due to the recording medium 7 being passed, and the temperature distribution in the longitudinal direction of the fixing nip portion becomes higher from the center toward the edge.

  For this reason, even if the outer diameter of the roller is slightly smaller at the position left and right from the central part, the fixing conditions are better at higher temperatures and pressures than the central part, and the fixing property at this part is not as great as the central part.

Furthermore, in the conventional reverse crown roller, the pressure drop and the temperature drop occur in one central portion. On the other hand, in the pressure roller 14, the pressure drop at the position separated by the distance S from the center to the left and right is distributed to the left and right and further reduced. 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.

(2) Paper Passing Test Next, a test for evaluating paper wrinkles and toner stains on the W-type reverse crown roller will be described. As an evaluation apparatus, an electrophotographic printer using the same film heating type fixing device 12 was used. Then, for each of the three 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 six tests).

  As shown in FIG. 1C, the film heating type fixing device 12 includes a pressure roller and a heating rotator 13. Tests are performed on three types of rollers having different surface shapes as pressure rollers. The following dimensions of the pressure roller and the like are merely examples in the experiment, and are not limited to such values.

  Each pressure roller has a total roller length of 220 mm (excluding the shaft portion), and the core metal has an aluminum crown shape. Since the core of the core is a high-speed machine having a printer body of 45 sheets / min or more, the core has a flat portion with a width of 50 mm and an outer diameter Da = 23.45 mm at the center. The tapered portion is tapered so that the outer diameter becomes narrower from the left and right end portions of the flat portion to the left and right end portions of the roller having an outer diameter Db = 21.45 mm.

  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, and the roller hardness is adjusted to 59 ° (when ASKER-C 500 g is applied).

  And the surface shape of the silicone rubber of three types of pressure rollers has the following three shapes. (1) Straight shape with substantially the same center and left and right ends, (2) Conventional V-shaped reverse crown with reverse crown amount of 120 μm, (3) Reverse crown amount between center and end portions = 100 μm, and minimum outer diameter W-type reverse crown with reverse crown amount at the end and end = 120 μm

  The pressure roller 14 of the W-type reverse crown of this embodiment has both outer diameters Dol and Dor of 30.55 mm at the left and right ends, an outer diameter Dc of 30.45 mm at the center, and a minimum outer diameter Dsl and Dsr of 30. .43 mm. The values in the longitudinal direction are R = 220 mm, S = 50 mm, and L = 68 mm, respectively. The roller outer diameter Dll = Dlr = 30.47 mm at a position corresponding to 5 mm inside the minimum size paper, which is 20 μm thicker than the outer diameter Dc = 30.45 mm at the center of the roller.

  Note that the minimum paper width subject to paper wrinkling is set as A5 size, and the paper types with a width of 100 mm or less where the reverse crown effect does not work are limited to relatively thick paper types such as envelopes and postcards. There is no need to prevent paper wrinkles with the reverse crown effect.

  As shown in FIG. 1C, the heating rotator 13 uses a reverse crown metal film 13c as a fixing film. The reverse crown metal film 13c is a cylindrical metal film having a high thermal conductivity, and corresponds to a high speed of 45 sheets / minute or more. Further, the reverse crown metal film 13c has been subjected to reverse crown processing by plastic working, and as shown in FIG. 1B, the reverse crown amount is (Dfl + Dfr) / 2−Dfc = 50 μm with the reverse crown effect. Is increasing. 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 has a fluororesin layer (not shown) formed as a release layer on the surface of a base layer obtained by plastic processing of a flexible metal tube made of SUS and having a thickness of 35 μm.
In addition, the thickness of a base layer should just be 20-200 micrometers. Although a SUS film of 20 μm or less is preferable from the viewpoint of heat conduction, the mechanical strength is insufficient. As a result, rubbing between the film inner surface and the heater surface, edge scraping due to rubbing between the film edge portion of the left and right end portions and the flange (a regulating member for preventing the film from being biased to the left and right), and the fixing nip This is because it is not preferable in terms of durability for long-term use from the viewpoint of concerns such as insufficient strength with respect to a mechanical load applied to the film during the paper removal operation when the paper is jammed in the portion. On the other hand, a SUS film of 200 μm or more has too high rigidity and insufficient flexibility, and the contact with the heater surface at the fixing nip portion is deteriorated, so that the heat of the heater is sufficiently transferred to the paper or pressure roller side. This is because the fixing property is deteriorated due to the fact that it cannot be transmitted.

  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. Thereafter, in a baking furnace, stepwise baking is performed 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.

  A ceramic heater 13a and a film guide member 13b are provided inside the reverse crown metal film 13c.

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 and brought into contact with each pressure roller with a total pressure of 18 kg to form a fixing nip portion, and the recording medium 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 recording medium 7 is melted and permanently fixed on the recording medium 7 by the heat transmitted from the ceramic heater 13a through the reverse crown metal film 13c and the 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 supply to the heater is turned off or on for a certain period of time when paper is not passed. Detect. Based on the detection result, the target temperature of the ceramic heater 13a is determined, and the heater driving means (not shown) is controlled to perform power control, thereby maintaining the heater temperature 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 Using a relatively thin A4 size paper (paper that is prone to wrinkles) with a basis weight of 64 g that has been left in a 30 ° C / 80% high-temperature, high-humidity environment test chamber for 48 hours or more, a lattice pattern Observe the presence or absence of wrinkles on the paper when 10 images are printed continuously.

(B) Toner stain test Using letter size paper containing 90 g of calcium carbonate (paper that easily induces toner stain) left in a low-temperature, low-humidity environment test room at 15 ° C./10% for 48 hours or more, 4% The paper is repeatedly added while the character pattern image of the printing 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 three types of pressure rollers through a paper wrinkle test and a toner stain test. In Table 1, “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 shown in Table 1, the toner on the straight roller was hardly stained, but the occurrence of paper wrinkles was remarkable.

  With the V-type reverse crown roller, paper wrinkles are not generated 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.

  In the W-type reverse crown roller, paper wrinkles are not generated as in the V-type reverse crown roller. Also, even with granular toner stains, there is no level of toner stains that would cause problems during the durability of 30,000 sheets, and almost the same results as with straight rollers can be obtained.

  From the above test, it was found that by making the pressure roller a W-shaped reverse crown shape, it is possible to prevent the occurrence of paper wrinkles and to prevent the occurrence of toner stains in the trade-off relationship.

  The pressure roller 14 is not limited to 120 μm in the difference in outer diameter (reverse crown amount) between the outer diameter Dsl, Dsr of the minimum outer diameter portion and the outer diameter Dol, Dor of the end portion, If it is 50-150 micrometers, the effect equivalent to the above can be acquired. This is because a slight reverse crown amount of 50 μm or less cannot be expected to provide a sufficient paper wrinkle prevention effect, and there is a risk that the reverse crown shape will not actually be formed because it is hidden within the tolerance range of manufacturing variations. On the other hand, if a reverse crown amount of 150 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, which is a feature of this configuration. This is because it is difficult to prevent local insufficiency of fixing even if it has a dispersion effect on the left and right portions of the diameter portion.

(3) Manufacturing Method of Pressing Rotating Body Next, a manufacturing method of the pressing rotating body will be described. 5A is a cross-sectional view of the pressure roller manufacturing apparatus of the fixing device according to the present embodiment, FIG. 5B is an explanatory diagram of rubber material injection, and FIG. 5C is a cross-section of the pressure roller after molding. FIG.

  First, as shown in FIG. 5A, a crown core bar 14b is placed in an outer mold 15 for manufacturing a pressure roller. The outer die 15 is formed in a cylindrical shape hollowed out inside, and is tapered to attach 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 concave / convex shape along the longitudinal direction on the inner surface of the outer mold 15.

  The crown metal core 14b is formed flat by a distance C (distance C <distance L) from the central portion, and is formed in a crown shape having a taper so as to become thinner from both ends of the flat portion toward the left and right end portions. ing. The length of the flat portion at the center of the crown metal core 14 b is shorter than the length of the flat portion at the center of the outer die 15.

  The flat portion of the outer mold 15 is formed of a flat inner surface having a width of 100 mm extending 50 mm from the center to the left and right. The flat portions of the crown metal core 14b are each composed of a flat surface with a width of 50 mm extending 25 mm from the center to the left and right.

  As shown in FIG. 5 (B), a liquid rubber material is injected from the left and right ends of the outer mold 15 with the crown core metal 14 b placed in the outer mold 15. Then, the rubber material enters along the tapered portions of the crown core 14b and the outer mold 15, and the flow of the rubber material from below to above and from above to below is formed at the corners of each taper portion.

  At this time, since the flow in both the upper and lower directions merges with the corner portion of the outer tapered portion, the rubber filling density at the corner portion is relatively low. On the other hand, since the rubber material is filled in the flat portion of the outer mold 15 in a direction of spreading outward along the tapered shape of the crown core bar 14b, the density increases.

  By utilizing such a tendency, the viscosity and injection pressure of the rubber material are appropriately controlled, and the flat portion of the outer mold 15 is removed when the crown core metal 14b is removed from the outer mold 15 after the rubber material is thermally cured. And the residual stress in the rubber material confined between the flat portions of the crown metal core 14b.

  As a result, the volume of the rubber material at the flat portion of the crown metal core 14b is expanded, and the volume of the rubber material at the tapered corner portion of the outer mold 15 is relatively reduced, thereby changing the outer shape of the pressure roller 14. As a result, as shown in FIG. 5C, the outer diameter of the central portion of the pressure roller 14 is increased by about 20 μm, and the minimum outer diameter portion (outer diameter) is located at a position substantially coincident with the taper corner of the outer die 15. Dsl, Dsr).

  The pressure roller 14 thus manufactured has a W-shaped reverse crown shape, and the dimensions of each part are determined by the shapes of the outer mold 15 and the crown core bar 14b, the viscosity of the rubber material, and the injection pressure. Thereby, a W-type reverse crown pressure roller can be manufactured at low cost without using an outer mold whose inner surface is complicatedly processed into a W-type.

  Further, the minimum outer diameter portion is formed at a position substantially coincident with the end portion of the flat portion of the outer mold 15. From this, it is possible to arbitrarily move the formation position of the minimum outer diameter portion by changing the length of the flat portion while maintaining the positional relationship between the flat portion of the outer die 15 and the crown core metal 14b. . Therefore, it is possible to easily adjust the formation position of the minimum outer diameter portion in accordance with the desired minimum paper size on which the paper wrinkle countermeasure effect acts by this adjustment method.

[Second Embodiment]
Next, a second embodiment of the pressure rotator, the fixing device, and the image forming apparatus according to the present invention will be described with reference to the drawings. 3A is a cross-sectional view of the pressure roller of the fixing device according to this embodiment, FIG. 3B is an external view of the fixing film, and FIG. 3C is a side cross-sectional view of the fixing device. About the part which overlaps with said 1st embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIG. 3A, the pressure roller 24 according to the present embodiment is configured by a W-shaped reverse crown roller having the same shape as the pressure roller 14 of the first embodiment in appearance. That is, the outer shape of the silicon rubber layer 24a of the pressure roller 24 is formed with the same dimensions as the outer shape of the silicon rubber layer 14a.

  However, the pressure roller 24 uses a straight core roller 24b having an outer diameter of Da = 23.45 mm. The heating rotator 23 facing the pressure roller 24 uses a straight PI resin film 23c as shown in FIG. 3B instead of the reverse crown metal film 13c of the heating rotator 13. is there.

  As shown in FIG. 3C, the fixing device 22 in which the pressure roller 24 and the heating rotator 23 are combined is formed in the same manner as the fixing device 12 of the first embodiment. The speed is suitably used for a relatively slow film heating method fixing device of 35 sheets / min or less.

  This is because when the fixing speed is low, it is not necessary to increase the thermal conductivity of the fixing film so much that the resin film 23c having a lower thermal conductivity than the reverse crown metal film 13c can be sufficiently fixed. .

  In the above-described configuration, the straight cored bar 24b does not need to be crowned unlike the crowned cored bar 14b, and the production cost can be reduced. Further, the resin film 23c is formed of a PI film that is less expensive than a metal film, so that it is not necessary to perform reverse crown processing, and the cost can be reduced.

  Next, using the fixing device 22, the same paper wrinkle test and toner stain test as in the first embodiment were performed. This test was performed on two types of rollers: a W-type reverse crown roller (pressure roller 14) with a core metal in a crown shape and a W-type reverse crown roller (pressure roller 24) with a metal core in a straight shape. It was. Table 2 shows the test results. In Table 2, “X” indicates the case where paper wrinkles or toner stains occur, and “◯” indicates the case where paper wrinkles or toner stains do not occur.

  As described above, when the resin film 23c having a relatively low speed of at least 35 sheets / min and a low-rigidity resin film is used as the fixing film, the effect of preventing paper wrinkles is sufficiently obtained by the rubber shape of the roller surface. It is done.

  Therefore, by using the straight cored bar roller 24b as the straight core and the resin film 23c as the fixing film, it is possible to prevent the occurrence of paper wrinkles and toner stains and to reduce the cost.

[Third embodiment]
Next, a third embodiment of the pressure rotator, the fixing device, and the image forming apparatus according to the present invention will be described with reference to the drawings. 4A is an external view of the fixing roller according to the present embodiment, and FIG. 4B is a side sectional view of the fixing device. About the part which overlaps with said 1st embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIG. 4, the heat roller type fixing device 32 according to this embodiment has a reverse crown shape with a reverse crown amount = 100 μm instead of the heating rotary body 13 of the first embodiment as a heating rotary body. A fixing roller 33 is provided. The fixing roller 33 includes a halogen heater 33a 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 this embodiment, the heat roller type fixing device is also configured to use the W-type reverse crown pressure roller 14 so as to prevent paper wrinkles and toner contamination.

  Next, using the fixing device 32, a paper wrinkle test and a toner stain test similar to those in the first embodiment were performed. This test was performed on two types of rollers, a straight pressure roller and a W-type reverse crown 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 with the straight pressure roller, whereas the pressure roller 14 can prevent toner contamination. In the heat roller type fixing device, the same effect can be expected even if the fixing roller itself is provided with a W-shaped reverse crown shape.
The difference (reverse crown amount) between the outer diameters Dtl and Dtr at the end of the fixing roller 33 and the outer diameter Dtc at the center is not limited to 100 μm, and may be 50 to 150 μm. This is because a slight reverse crown amount of 50 μm or less cannot be expected to provide a sufficient paper wrinkle prevention effect, and there is a risk that the reverse crown shape will not actually be formed because it is hidden within the tolerance range of manufacturing variations. On the other hand, if a reverse crown amount of 150 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, which is a feature of this configuration. This is because it is difficult to prevent local insufficiency of fixing even if it has a dispersion effect on the left and right portions of the diameter portion.

(A) is sectional drawing of the pressure roller which concerns on 1st embodiment. (B) is a sectional view of the fixing film. (C) is a sectional side view of the fixing device. 1 is a configuration diagram of an electrophotographic image forming apparatus. (A) is sectional drawing of the pressure roller which concerns on 2nd embodiment. (B) is a sectional view of the fixing film. (C) is a sectional side view of the fixing device. FIG. 6A is a cross-sectional view of a fixing roller according to a third embodiment. FIG. 2B is a side sectional view of the fixing device. (A) is sectional drawing of the manufacturing apparatus of the pressure roller which concerns on 4th embodiment. (B) is explanatory drawing of rubber material injection | pouring of a pressure roller. (C) is a sectional view of the pressure roller. (A) is sectional drawing of the conventional reverse crown pressure roller. (B) is an explanatory diagram of granular toner stains on paper. (C) is sectional drawing of the conventional crown metal core reverse crown pressure roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Charging roller 2 ... Photosensitive drum 3 ... Exposure means 4 ... Developing device 5 ... Toner 5a ... Toner dirt 6 ... Transfer roller 7 ... Recording medium 7a ... Recording medium storage box 7b ... Manual feed tray 7c ... Feed roller pair 7d ... Vertical Conveying roller pair 7e: Pre-transfer conveying roller 8: Static elimination brush
10… Cleaning container
11… cartridge
12, 22, 32 ... Fixer
13, 23… Rotating heating body
13a ... Ceramic heater
13b ... Film guide member
13c ... Reverse crown metal film
14, 24… Pressure roller (corresponding to pressure rotor)
14a, 24a ... Silicon rubber layer (corresponding to rubber layer)
14b ... Crown core (corresponds to core)
15… Outer mold
23c ... Resin film
24b ... Straight cored bar roller
33… Fixing roller (corresponding to heated rotating body)
33a Halogen heater

Claims (8)

In a pressure rotator that performs image fixing while conveying a recording medium in pressure contact with a facing member,
The pressurizing rotator has a minimum outer diameter portion Dsl, a minimum outer diameter portion between the left and right end portions in the rotation axis direction and a central portion in the rotation axis direction,
A tapered portion whose outer shape becomes thicker from the minimum outer diameter portion to the end portion,
The magnitude relationship between the outer diameters Dol, Dor of the left and right end portions and the outer diameter Dc of the central portion is Dor≈Dol> Dc,
The magnitude relationship between the outer diameters Dll and Dlr between the minimum outer diameter part and the end part and separated from the central part by a predetermined distance L to the left and right and the outer diameter Dc of the central part is Dlr. ≒ Pressure rotating body characterized by Dll> Dc. The pressure rotating body includes a cored bar and a rubber layer formed on the outer periphery of the cored bar,
2. The pressure rotating body according to claim 1, wherein the core metal is formed in a crown shape having a tapered portion whose outer diameter becomes narrower toward an end portion in a rotation axis direction. 3. The pressurization according to claim 1, wherein a difference between the outer diameters Dsl and Dsr of the minimum outer diameter portion and the outer diameters Dol and Dor of the end portions is 50 to 150 μm. Rotating body. A recording medium having a heating rotator containing a heating source and a pressure rotator that presses against and contacts the heating rotator to form a nip portion, and in which an unfixed toner image is formed at the nip portion. In a fixing device for nipping and conveying and fixing the toner image on the recording medium,
The fixing device according to claim 1, wherein the pressure rotator is the pressure rotator according to claim 1. 5. The fixing device according to claim 4, wherein the base layer of the heating rotator is obtained by plastic processing of a flexible metal tube having a thickness of 20 to 200 [mu] m. The heating rotator has an outer diameter that increases from a central portion in the rotation axis direction toward left and right ends in the rotation axis direction,
The fixing device according to claim 5, wherein a difference between the outer diameters Dtl and Dtr of the end portions and the outer diameter Dtc of the central portion is 50 to 150 μm. Image forming means for forming a toner image on a recording material;
An image forming apparatus comprising: the heat-fixing device according to any one of claims 4 to 6, wherein an unfixed toner image formed by the image forming unit is fixed on a recording material. apparatus. A manufacturing method for manufacturing a pressure rotating body having a rubber layer on a surface,
Placing the cored bar in the outer mold formed in a cylindrical shape hollowed out;
Injecting a molten rubber material between the outer mold and the core;
After the rubber material is cured, it comprises a step of taking out a pressure rotating body in which a rubber layer is formed on the surface of the core metal,
The outer mold has a flat portion in the center in the rotation axis direction of the pressure rotator on the inner surface, and an inner diameter extends from both ends of the flat portion to the left and right ends in the rotation axis direction of the pressure rotator. Tapered to be thicker,
The cored bar has a flat portion in the center in the rotation axis direction of the pressure rotator, and the outer diameter decreases from both ends of the flat portion to the left and right ends in the rotation axis direction of the pressure rotator. It is tapered to
The method for manufacturing a pressure rotating body, wherein the flat portion of the outer mold is formed longer than the flat portion of the core metal.

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