JP2008096929A - Fixing device for electrophotographic apparatus, and electrophotographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device 10 used for an electrophotographic apparatus 25, the fixing device being small, capable of high speed processing and preventing paper wrinkles. <P>SOLUTION: The fixing device 10 of the electrophotographic apparatus 25 includes: a heat roller 1 having an elastic layer 1b around a metal core 1a incorporating a heating element 5; a pressure belt 2 disposed in contact with the elastic layer 1b of the heat roller 1; and a pressure member 6 pressing the pressure belt 2 against the heat roller 1. The heat roller 1 has a uniform outside diameter from the middle to each end in the lengthwise direction. The lengthwise shape of the central portion of the pressing face of the pressing part of the pressing member 6 projects toward the heat roller 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device of an electrophotographic apparatus and an electrophotographic apparatus.

  In the fixing device in the electrophotographic apparatus, when the toner image on the printing paper is fixed, the paper is pressed against the heating roller to heat the paper, so that the paper is caused by deformation of the paper or the deflection of the heating roller. Paper wrinkles may occur due to the velocity distribution mismatch in the width direction. In particular, recent electrophotographic apparatuses have been reduced in size and speeded up, and in fixing devices, many belt fixing methods have been proposed in which a sheet is pressed against a heating roller with a small diameter by a pressure belt to fix the heating. Preventing the occurrence of paper wrinkles due to the deformation of the rollers is a major technical issue.

In order to prevent the occurrence of paper wrinkles in such a fixing device, various paper wrinkle generation preventing means are known. For example, as in Patent Document 1 and Patent Document 2, the shape of the heating roller is an inverted crown shape in which the diameter of the end portion is larger than the diameter of the center, so that the sheet to be conveyed is moved from the center to both ends. A method for generating a tensile force has been proposed. Further, in the belt fixing method, as shown in Patent Document 3, a heating roller having an inverted crown shape and a fixing belt having a belt-stretching roller having a normal crown shape in which the diameter of the central portion is larger than the end portion. There has been proposed a method for preventing the generation of paper wrinkles in combination.
Japanese Patent Laid-Open No. 05-40428 JP 2001-215832 A JP 2005-221757 A Journal of Japan Rubber Association Vol.62 No.11 (1989), 683-694

  In the fixing device described above, the outer diameter at the nip portion of the heating roller of the fixing device is made smaller at the central portion in the longitudinal direction, the peripheral speed for the same rotational speed is made smaller at the central portion, and the conveying force at the time of conveying the paper is increased. By making it larger at both ends than at the center, a pulling force is generated from the center to both ends of the paper, thereby preventing the paper from wrinkling.

  However, in the fixing devices described in Patent Document 1 and Patent Document 2, since the heating roller has an inverted crown shape, a precise shape processing by polishing is required in the manufacturing process of the heating roller, which increases the manufacturing cost. there were. In particular, in recent electrophotographic apparatuses that require downsizing of the apparatus and shortening of the warm-up time, it is essential to reduce the diameter of the fixing device, and hence the heating roller, and to reduce the thickness of the core metal. It has become difficult to achieve an accurate inverted crown shape. As a result, completely preventing paper wrinkles presents problems in terms of cost and shape accuracy of the heating roller. In addition, the fixing device disclosed in Patent Document 3 requires another set of pressing belt mechanisms in addition to the fixing belt, which increases the number of parts for the fixing device and has a limit in cost reduction. Further, an increase in the number of parts is not preferable because the cause of failure is likely to increase.

  SUMMARY OF THE INVENTION In view of the above-described problems, an object of the present invention is to provide a fixing device that does not require advanced processing technology for manufacturing a heating roller, has a structure that is inexpensive and suitable for downsizing, and can prevent the generation of paper wrinkles. It is an object to provide an electrophotographic apparatus using this.

  The fixing device of the present invention includes a heating roller having a heating element and provided with an elastic layer around a cored bar, a pressure belt stretched so as to contact the elastic layer of the heating roller, and the pressure A fixing unit of an electrophotographic apparatus including a pressure member that presses a belt against a heating roller, wherein the heating roller is a driving roller, and has the same outer diameter from one end to the other end; The pressing force on the central portion in the longitudinal direction of the heating roller is larger than the pressing force on the end portion. As a structure of the pressure member, for example, there is a fixing device in which the shape in the longitudinal direction of the pressing surface of the pressing portion of the pressure member is convex toward the heating roller.

  As a preferred embodiment of the present invention, there is the above fixing device in which the shape of the pressing surface of the pressing portion of the pressing member along the circumferential direction of the heating roller is concave toward the heating roller. Further, there is the fixing device in which the pressing portion of the pressing member is formed of an elastic layer softer than the elastic layer of the heating roller. In addition, the fixing member includes a first support member that supports the elastic body layer, and a second support member that supports the first support member at a load point at a longitudinal center of the first support member. There is a vessel. Further, there is the fixing device in which the first support member is rotatable with respect to the second support member around a load point. Further, there is the fixing device in which the first support member and / or the second support member includes a load support member that makes the first support member and the second support member abut at a load point. Further, there is the fixing device in which the first support member and the second support member are coupled by a load support pin at a load point. Furthermore, at least one of the first support member and the second support member is the above-described fixing device in which the shape of the vertical cross section with respect to the longitudinal direction is a U-shape.

  The electrophotographic apparatus of the present invention includes any one of the fixing devices described above.

  According to the fixing device of the present invention, generation of paper wrinkles can be prevented, and a fixing device that is easy to manufacture, inexpensive, and suitable for downsizing can be provided. In addition, an electrophotographic apparatus that can prevent the occurrence of paper wrinkles can be provided.

  The fixing device of the present invention includes a heating roller, a pressure belt, and a pressure member. The heating roller is provided with an elastic layer around a core bar having a heating element, and has a columnar shape or a cylindrical shape having the same outer diameter from one end to the other end in the longitudinal direction of the heating roller. The heating roller is provided with a driving device that rotationally drives the heating roller to convey the fixing sheet. The pressure belt is stretched so that the nip portion is in contact with the elastic body layer of the heating roller. The pressure member is disposed so as to press the nip portion of the pressure belt against the heating roller. The pressing member has a structure in which the pressing force on the center portion in the longitudinal direction of the heating roller is larger than the pressing force on the end portion. As a specific structure of the pressing member, for example, the pressing surface of the pressing portion of the pressing member has a so-called regular crown shape in which the central portion is convex toward the heating roller in the longitudinal direction. If the pressing surface of the pressing member has such a regular crown shape, the central portion in the longitudinal direction of the heating roller is pressed more strongly than the end portion.

  Further, as the shape of the pressure member, the shape of the pressing surface in the direction along the circumferential direction of the heating roller (direction perpendicular to the longitudinal direction) is preferably concave toward the heating roller. A concave surface curved with the same curvature as that of the outer peripheral surface of the heating roller is preferable so that the pressure belt can easily adhere to the nip portion of the outer peripheral surface. By doing in this way, the printing paper conveyed while pressing the nip part is pressed uniformly in the circumferential direction of the heating roller of the nip part.

  Moreover, it is preferable that the press part of a pressurization member is an elastic body layer softer (an elastic modulus is smaller) than the elastic body layer of a heating roller. By doing so, the pressing force of the pressure member is larger at the center in the longitudinal direction than at the end, but the soft elastic layer of the pressure member is distorted and the heating roller is almost distorted. Absent. For this reason, the peripheral speed in the middle direction of the heating roller does not change and does not affect the conveyance of the paper by the heating roller. Further, the deformation of the elastic layer of the heating roller pressed by the pressure member can be reduced, and the permanent deformation of the surface of the heating roller can be prevented. When permanent distortion occurs in the heating roller, variations in the conveyance speed of the printing paper at the nip portion tend to cause paper wrinkling of the printing paper.

  The pressure member preferably includes a first support member that supports the elastic layer and a second support member that supports the first support member. If the pressurizing member is composed only of a soft elastic layer, it cannot exert a sufficient pressing force. Therefore, a rigid first support member that supports the elastic layer from behind the pressing surface is provided. Then, by pressing the rigid first support member, the pressure member can press the heating roller with a desired pressing force via the pressing surface of the elastic layer. Further, the first support member is supported by a rigid second support member at the load point at the center in the longitudinal direction. A load point is a location where the second support member presses the first support member, and is also a location where the second support member supports stress from the first support member. When viewed from the direction along the outer periphery of the nip portion of the heating roller, the load point appears as one point in the central portion in the longitudinal direction, but when viewed from the axial direction of the heating roller, the load point is parallel to the direction along the outer periphery of the nip portion of the heating roller. It is a linear part. By supporting the rigid first support member at the load point at the center portion in the longitudinal direction in this way, the pressing force of the pressure member can easily make the center portion of the heating roller larger than the end portion. . Moreover, it is easy to make a pressing structure symmetrical to the longitudinal direction of the heating roller.

  Furthermore, it is preferable that the first support member is rotatable with respect to the second support member about the above-described linear load point as a central axis. In this way, it is possible to more easily achieve a pressing structure that is symmetrical with respect to the longitudinal direction of the heating roller.

  As an aspect for supporting the first support member, at least one of the first support member and the second support member has a structure including a load support member that abuts the first support member and the second support member at a load point. be able to. For example, there is a second support member provided with the contact member 61b in FIG. 7, a first support member provided with the contact member 6d in FIG. The second support member has the same length as the first support member in FIGS. 7 and 8, but may be shorter or longer than the first support member as long as the first support member can be supported. Note that it is preferable that the first support member and the second support member be rotatable about a contact portion that makes the first support member and the second support member contact each other as a central axis.

  As another aspect of supporting the first support member, the first support member and the second support member may be coupled by a load support pin at a load point. In this load support pin, it is preferable that the first support member and the second support member are rotatable about the load support pin as a central axis.

  Furthermore, as a preferable form of the first support member and the second support member, at least one of the first support member and the second support member, preferably both, has a U-shaped vertical cross-sectional shape with respect to the longitudinal direction. There is a fixing device. If it does in this way, manufacture of the 1st support member and the 2nd support member is easy, it is suitable also for size reduction and weight reduction, and it is easy to secure the intensity to pressing force. Other preferable forms of the first support member and the second support member include a rectangular shape, a T shape, an I shape, an M shape, a U shape, and a hollow circle. It may be a mold or the like. The first support member and the second support member are preferably shaped so that they can be fitted to each other. In this way, the first support member and the second support member can be structured to be relatively difficult to move relative to each other in the direction other than the rotation direction. In addition, it is easy to control the maximum moving distance during rotation.

(First embodiment)
An embodiment of the present invention will be described with reference to FIG. 1, FIG. 3 and FIG. First, a schematic section of the fixing device in the electrophotographic apparatus of the present invention is shown in FIG. The fixing device 10 includes a heating roller 1, a pressure belt 2, an inlet guide 3, a peeling guide 4, a pressure pad 6, an outlet guide 7, and a lower case 33. The heating roller 1 is an elastic member having an outer diameter of 26.6 mm covered with a silicone rubber layer 1b having a thickness of 0.8 mm and a JIS hardness of 20 on a pipe-shaped steel core 1a having a thickness of 0.5 mm. The roller is coated with PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer) having a thickness of 30 μm to ensure releasability from the toner. In addition, a heater 5 is provided inside, and the heating roller 1 is heated by the heat of the heater 5 to melt the resin of the toner 9 on the printing paper 32. The heating roller 1 can be rotated in the direction of arrow A by a gear (not shown) and can convey the printing paper in the direction of arrow B.

  The pressure belt 2 is a seamless polyimide belt having a length corresponding to the circumference of 80 μm in thickness and 30 mm in inner diameter, and a PFA having a thickness of 30 μm in the outer peripheral side surface in order to ensure the separation from the toner. Is covered. Further, the pressure belt 2 is brought into contact with the heating roller at a winding angle θ by a pressing pad 6 curved in a concave shape so that the pressing surface thereof is in close contact with the outer periphery of the heating roller, thereby melting the toner 9. A contact portion h (also referred to as a nip portion) is formed. Therefore, the width of the contact portion h necessary for the fixing speed can be ensured even when the heating roller 1 has a small diameter, so that the fixing device can be miniaturized and high-speed fixing can be achieved. In this embodiment, the toner can be fixed at a fixing speed of 200 mm / sec with a contact width h = 11 mm and θ = 47 degrees.

  Around the heating roller 1, a lower case 33 formed of a heat-resistant resin having a guide function for guiding the paper 32 and a sheet passing portion of the heating roller 1 are brought into contact with the surface temperature of the heating roller 1 with high accuracy. The contact type thermistor 31 for controlling the heat generation of the heater 5 by detecting this, and the peeling guide 4 for forming the gap G from the surface of the heating roller 1 and peeling and guiding the paper 32 after fixing from the heating roller 1. Is arranged.

  In the fixing device of this embodiment, the paper 32 onto which the unfixed toner 9 has been transferred is conveyed in the direction of arrow B by the guide of the inlet guide 3 and the lower case 33, contacts the heating roller 1 at the nip portion, and the nip The toner 9 is melted and fixed on the paper. The paper 32 on which the toner 9 is melted and fixed is peeled off from the heating roller 1 by the peeling guide 4 and discharged to a paper discharge section such as a paper tray (not shown). Further, the line connecting the center of the nip portion and the length of the heating roller is inclined by an angle φ with respect to the horizontal line p, so that the paper discharged from the fixing device can be easily conveyed to the paper discharge portion of the main body of the electrophotographic apparatus. Become.

  The fact that this type of fixing device has an excellent effect of preventing the occurrence of paper wrinkles in the process of fixing toner onto paper will be described. The pressure pad 6 is curved in a concave shape so that the cross section thereof is in close contact with the first support member 6b having a U-shape corresponding to the nip portion of the heating roller, and the shape in the longitudinal direction is the central portion. An elastic body layer 6a, which is a silicone rubber having a convex positive crown shape, is bonded. Further, the first support member 6b is supported by a U-shaped second support member 61, a load support pin 62, and a retaining ring 64 so as to be rotatable at the center in the longitudinal direction with respect to the heating roller 1. Yes. The second support member 61 is connected to the main body of the electrophotographic apparatus by a pressure spring 63, and presses the first support member 6b and further the heating roller through the load support pin 62. Note that there are two pressure springs 63 and are arranged near both ends of the second support member 61 (see FIG. 4). By adopting such a configuration, the pressure pad 6 is always supported by the load support pin 62 even if the left and right pressure springs 63 that press the second support member 61 are unbalanced by the rotation operation of the heating roller 1. Since the structure is such that it is pressed at the central portion in the longitudinal direction, the longitudinal pressure distribution in the nip portion of the heating roller can be kept larger than the end portion.

  FIG. 3 shows an exploded perspective view of the pressure member in this embodiment. The elastic body layer 6a bonded to the back surface which is a flat plate surface of the first support member 6b having a U-shaped cross section is made of silicone rubber having a JIS hardness of 30 degrees, and the thickness t2 at the center is changed to the thickness t1 at both ends. The pressing surface of the elastic layer 6a against the heating roller is made to be a regular crown shape with respect to the longitudinal direction by setting it larger than t3. It is economically preferable that the regular crown shape is formed into a desired shape with a rubber mold when the elastic layer 6a is formed on the first support member 6b, instead of machining the rubber surface after molding. . In the present embodiment, the shape is a regular crown shape on an arc in which the rubber thickness t2 at the center is 4 mm and the thicknesses t1 and t3 at both ends are 3.8 mm. Although the details of the crown amount (the difference between the thickness of the center portion and the end portion) and the paper wrinkle will be described later, the pressure pad 6 is attached to the heating roller 1 via the pressure belt 2 by this regular crown shape. The pressure distribution of the abutting portion is convex with respect to the longitudinal direction, that is, the pressing force increases at the central portion in the longitudinal direction and decreases at both ends. In this embodiment, silicone rubber having a rubber hardness of 30 ° and a thickness t2 of 4 mm at the center is used as the elastic body layer 6a of the pressure pad 6. However, the elastic body layer 6a is heat resistant and pressurized. It is sufficient that the elastic deformation due to is larger than that of the elastic layer on the surface of the heating roller. For example, fluororubber may be used.

  The first support member 6b and the second support member 61 of the pressure pad 6 are members having a U-shaped cross section, and are arranged so that the openings face each other. In this embodiment, the first support member 6b has a larger U-shaped cross section than the second support member 61, and a part of the second support member 61 is inside the U-shape of the first support member 6b. The structure fits in. Furthermore, pin holes 6c and 61b serving as load points are provided in the longitudinal center portions of the first support member 6b and the second support member 61. And load support pin 62 is inserted in these pin holes 6c and 61b, and the 1st support member 6b and the 2nd support member 61 are combined. With this configuration, the first support member 6b is rotatably supported by the load support pin 62 with respect to the second support member 61 and receives a load at the central portion in the longitudinal direction. Therefore, the pressure distribution in the longitudinal direction of the pressure pad 6 with respect to the heating roller can be obtained not only by the effect of the positive crown shape of the pressure pad described above but also by a pressure structure in which the load point of the pressure pad is the central portion in the longitudinal direction. In addition, a convex distribution in which the pressure in the central portion is increased can be obtained. Further, the structure in which the pressure pad 6 is rotatably supported at the center portion has an effect of stabilizing the distribution of the pressing force of the pressure pad 6 in the longitudinal direction of the heating roller 1. The heating roller 1 is supported by a support portion of an electrophotographic apparatus main body (not shown). In this case, the support portion of the electrophotographic apparatus main body may be twisted depending on the shake of the heating roller 1 itself or the rotational driving force of the heating roller 1. Then, the second support member 61 that holds the pressure pad 6 and makes contact with the heating roller 1 is relatively inclined to the left and right. However, in this embodiment, even if the second support member 61 is tilted left and right, the load point 6c of the pressure pad is always in the center by the load support pin 62. As a result, the pressure pad 6 to the heating roller 1 is The pressure distribution in the longitudinal direction is kept constant so that the center is large and the end is small. In this way, the pressure distribution in the longitudinal direction of the pressure pad 6 with respect to the heating roller 1 can be a convex distribution that always increases at the center, and a stable fixing device without paper wrinkles can be realized.

  The relationship between the pressure distribution of the pressure pad 6 and the heating roller 1 and the occurrence of paper wrinkles will be described with reference to FIG. FIG. 4 is a perspective view of the fixing device according to the present invention, and the arrows shown in the drawing are as follows. Arrows P 1, P 2, and P 3 are pressing forces in the longitudinal direction of the pressure pad 6 against the heating roller 1. Arrows F1, F2, and F3 are conveying forces in the longitudinal direction of the heating roller 1 at the nip portion with the pressure belt 2 generated by the rotation driving of the heating roller 1 at the rotation speed A. Arrows R1, R2, and R3 are friction load resistance forces on the inner surface of the pressure belt generated by the pressing forces P1, P2, and P3 of the pressure pad 6. An arrow V indicates a velocity distribution in the longitudinal direction of the pressure belt 2. Here, numerals indicate positions in the longitudinal direction, numerals 1 and 3 indicate both end portions, and numeral 2 indicates a central portion.

  In general, when a rotating rubber roller is pressed against a sheet and conveyed, the conveyance speed of the sheet is known to increase depending on the elastic deformation amount of the rubber roller, that is, the pressing load (see Non-Patent Document 1). . Therefore, when the contact width h with the heating roller is formed by elastic deformation of the surface of the heating roller, the pressure belt 2 is conveyed at a speed depending on the amount of elastic deformation of the heating roller. However, in this embodiment, the contact width h of the nip portion is formed by the elastic body layer 6a of the pressure pad 6 that is concavely curved so that the surface closely adheres corresponding to the curvature of the heating roller, Further, since the elastic body layer 6a of the pressure pad 6 is soft and the elastic deformation of the elastic body layer 6a caused by pressing of the pressure pad 6 is larger than the elastic deformation of the heating roller 1, the heating roller 1 of the pressure belt 2 is heated. The movement speed A transmitted from is less influenced by the elastic deformation of the heating roller 1 and substantially corresponds to the peripheral speed of the heating roller 1, that is, the radius of the heating roller 1.

  On the other hand, the contact force Fi is applied to the pressure belt 2 by contacting the heating roller 1 by the rotation speed A of the heating roller 1, while the inner peripheral surface of the pressure belt 2 contacting the pressure pad 6 is pressurized. The friction load resistance Ri is applied by the pressure Pi of the pad. Therefore, the conveying speed V of the pressure belt has an effect proportional to the friction load resistance Ri in addition to the rotational speed A transmitted from the heating roller described above. That is, the conveyance speed V of the pressure belt 2 decreases from the rotation speed A of the heating roller due to the friction load resistance Ri of the pressure pad 6. This friction load resistance force Ri increases in proportion to the pressure Pi of the pressure pad 6 when the friction coefficient between the elastic body layer 6a of the pressure pad and the inner peripheral surface of the pressure belt 2 is constant. Therefore, in this embodiment, the pressure pad 6 has a regular crown shape, and the load point 6c of the pressure pad 6 is in the center, so that the pressing force P2 of the pressure pad 6 is in the center in the longitudinal direction. Is larger than the pressing forces P1 and P3 at both ends, and the friction load resistance R2 also acts greatly. As a result, the pressure belt speed V2 at the center is slower than the speeds V1 and V3 at both ends. In other words, the speeds V1 and V3 at both ends are relatively faster than the central speed V2. Since the conveyance speed distribution of the paper follows the conveyance speed distribution V of the pressure belt 2, the generation of paper wrinkles on the conveyed paper can be prevented.

  Next, the crown amount of the pressure pad and the paper wrinkle will be described. In FIG. 4 described above, both ends of the heating roller 1 are supported on a frame of an electrophotographic apparatus (not shown) by a bearing mechanism or the like, and the center of the surface of the heating roller 1 is recessed by pressing the pressure pad 6. (In FIG. 4, the deflection of the surface of the heating roller 1 is exaggerated). As the deflection amount of the heating roller 1 increases, the pressing force P2 at the central portion decreases, and as a result, the paper conveyance speed at the central portion increases and paper wrinkles are likely to occur. In particular, in a fixing device using a heating roller having a small diameter due to downsizing, the rigidity of the core metal is lowered, and thus the generation of paper wrinkles due to the deflection of the heating roller becomes remarkable. Therefore, in the present invention, by forming the pressure pad into a regular crown shape, the deflection of the heating roller 1 is compensated so that the pressing force P2 at the center portion is increased to prevent the occurrence of paper wrinkles. Specifically, the generation of paper wrinkles can be prevented by making the sum of the positive crown amount of the pressure pad and the deflection amount of the pressure pad itself larger than the deflection amount of the heating roller. However, if the amount of the positive crown of the pressure pad is too large, the pressing force of the pressure pad at both ends of the paper is lowered, and as a result, there is a possibility that the toner cannot be sufficiently fixed. The appropriate range of the sum of the positive crown amount of the pressure pad and the deflection amount of the pressure pad itself is desirably 0.05 to 0.2 mm larger than the deflection amount of the heating roller, more preferably 0. About 0.05 to 1.5 mm is preferable. In this case, it is desirable that the ratio of the pressing force between the central portion and the end portion is 1.2 to 4 times, preferably 2 to 3 times that of the end portion in the central portion.

  In this embodiment, the outer diameter of the core of the heating roller is 0.25 mm, the thickness of the core is 0.5 mm, the core is made of iron, the pressing load of the pressure pad is 392 N, and the deflection of the heating roller is 0.2 mm. In contrast, since the deflection of the first support member 6b of the pressure pad 6 is 0.1 mm, the positive crown amount of the elastic body layer 6a of the pressure pad is 0.2 mm. As a result, in this embodiment, the sum of the positive crown amount of the pressure pad and the deflection amount of the pressure pad itself is 0.3 mm, and the difference from the deflection of the heating roller of 0.2 mm is 0.1 mm, which is appropriate. Is in range.

(Second Embodiment)
2 shows a second embodiment of the fixing device of the present invention. FIG. 6 shows an exploded perspective view of each part of the fixing device of this embodiment. In the above-described embodiment, as a method of making the pressing surface against the pressure pad heating roller into a regular crown shape, the thickness of the elastic body layer in the pressure pad is increased at the center in the longitudinal direction and is decreased at the end. Realized. In this embodiment, the thickness t of the elastic layer 6a is made constant in the longitudinal direction, and the entire pressure pad 6 including the elastic layer 6a and the first support member 6b is bent into a convex shape in the longitudinal direction. As a result, the pressure pad 6 has a regular crown shape. Therefore, the crown amount is the bending amount δ of the first support member 6b. Since this bending amount δ becomes the positive crown amount of the pressure pad, as in the above-described embodiment, as the appropriate range of the total of the positive crown amount of the pressure pad and the deflection amount of the pressure pad itself, It is desirable to increase the deflection amount of the heating roller by 0.05 to 0.2 mm, and more preferably 0.05 to 1.5 mm. In this case, it is desirable that the ratio of the pressing force between the central portion and the end portion is 1.2 to 4 times, preferably 2 to 3 times that of the end portion in the central portion. In this embodiment, δ = 0.2 mm in consideration of the deflection of the heating roller of about 0.1 mm.

  The fixing device of the embodiment already described has a shape with a curved cross section and a regular crown in the longitudinal direction due to the mold of the elastic layer 6a. Is required. On the other hand, in this embodiment, as shown in FIG. 6, since the cross-sectional shape perpendicular to the longitudinal direction of the elastic layer 6a is the same everywhere, extrusion molding or the like can be used, and molding is easy and molding. It is easy to improve accuracy. What is necessary is just to bend the pressure pad 6 before the bending process which joined the elastic body layer 6a to the stage of the 1st support member 6b, or the 1st support member 6b. For this reason, although the number of manufacturing steps is increased, there is an advantage that the mold of the elastic body layer 6a does not become a three-dimensional curved surface, and relatively easy mold processing is sufficient. Further, since the bending process can be realized by pressing the central portion in a state where both ends of the first support member 6b of the pressure pad are supported, it can be handled with relatively easy equipment.

(Third embodiment)
A third embodiment of the fixing device of the present invention is shown in an exploded perspective view of the fixing device in FIG. In the first embodiment, the first support member 6 b and the second support member 61 that are provided with pin holes 6 c and 61 a at the center in the longitudinal direction of the first support member 6 b and the second support member 61 and fitted with the load support pins 62. In this embodiment, the second support member 61 is placed on the side facing the first support member 6b at the center in the longitudinal direction. The shape is provided with a load support member 61b which is a projection on an arc. The load support member 61b is in contact with the first support member 6b of the pressure pad 6, thereby realizing freedom of pressing and rotation with respect to the pressure pad 6. Therefore, the load support pin as in the first embodiment is not necessary, and the number of parts can be reduced and the cost can be reduced.

  In the embodiment shown in FIG. 7, the load support member 61b is provided on the second support member 61. On the contrary, as shown in FIG. 8, the first support member 6b has a first central portion in the longitudinal direction. 2 The load support member 6d may be provided on the side facing the support member 61 in the same manner as shown in FIG.

  Furthermore, a fixing device in which the structure of the pressure pad 6 of the second embodiment is combined with these embodiments can also be used as a preferred embodiment.

  Thus, in the present invention, the shape of the pressing portion of the cross section is in close contact with the heating roller for the purpose of realizing high-speed and high-quality color fixing of small and many types of paper and preventing the occurrence of paper wrinkles. A pressure member having an elastic body layer having a curved shape and having a positive crown shape with a convex shape at the center in the longitudinal direction is heated via a pressure belt with the central portion in the longitudinal direction as a load point. By increasing the pressure distribution in the longitudinal direction of the pressure member with respect to the heating roller in the center portion rather than the end portion by abutting and pressing the roller, the fixing device and the electrophotographic apparatus can be enlarged with the minimum number of parts. Realized without.

(Fourth embodiment)
As an embodiment of the present invention, there is an electrophotographic apparatus provided with the above-described fixing device according to the present invention. An embodiment of the electrophotographic apparatus will be described with reference to FIG. In FIG. 2, an intermediate transfer device 11 is disposed at the center of the electrophotographic apparatus 25, and around the intermediate transfer device 11, a photosensitive device 12, a transfer device 13, a sheet peeling unit 14, and an intermediate transfer device cleaning unit. 15 is arranged. Further, around the photosensitive device 12, a charger 16, a photosensitive member cleaning unit 17, and a residual image removing unit 18 are arranged. In this embodiment, developing devices 19K, 19Y, 19M, and 19C enclosing toners, which are finely colored powders of four different colors, are arranged in an overlapping manner. The paper holding means 21 for storing the paper and the paper supply device 22 are arranged in the paper. Above the electrophotographic apparatus, a fixing device 10 and a paper discharge device 23 are arranged.

  In the electrophotographic apparatus 25 having such a configuration, the charger 16 uniformly charges the surface of the photosensitive device 12. Next, image and character information by a personal computer, an image scanner or the like is transferred by exposing the dot unit by the exposure means 20 to form an electrostatic latent image on the surface of the photosensitive device 12. Thereafter, the electrostatic latent image is visualized as a toner image by being supplied and developed by any of the developing devices 19K, 19Y, 19M, and 19C, and is conveyed to the first transfer position T1. At the first transfer position T1, the toner image is transferred to the surface of the intermediate transfer device 11 due to a potential difference between the photosensitive device 12 and the intermediate transfer device 11 supplied from a power source (not shown). After passing through the first transfer position T1, the surface of the photosensitive device 12 is lowered to a certain potential or less by light irradiation by the afterimage removing means 18, and the electrostatic latent image is erased. Residual toner on the surface remaining without being transferred at the transfer position T1 is cleaned, and the next toner image can be formed. By repeating the above steps by the developing devices 19K to 19C as many times as necessary, a toner image corresponding to image and character information is formed on the surface of the intermediate transfer device 11. Thereafter, the toner image is transferred to the paper supplied from the paper holding means 21 by the paper supply device 22 by the transfer device 13 at the second transfer position T2. The paper on which the toner image has been transferred is peeled off from the intermediate transfer device 11 by the paper peeling means 14, conveyed to the fixing device 10, the toner image is fixed on the paper, and discharged by the paper discharge device 23. Here, the fixing device 10 is the above-described fixing device of the present invention. By using this fixing device 10, the electrophotographic apparatus of the present invention can prevent the generation of paper wrinkles without increasing the size of the apparatus or increasing the number of parts.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the examples. In the present invention, the above-described embodiment of the present invention and this example can be changed or modified without departing from the spirit and scope of the present invention. The parts and% shown below are based on mass unless otherwise specified.

An embodiment relating to the fixing device of the present invention will be described. FIG. 5 shows the results of evaluating the pressure distribution of the pressing force of the pressure pad, the speed distribution of the paper, and the state of occurrence of paper wrinkles for the following three cases of the fixing device configuration.
Case (1): Example (when the shape of the pressure pad in the longitudinal direction is a regular crown (crown amount 0.2 mm) and the load point is the center in the longitudinal direction).
Case (2): In the case of a comparative example (the pressure pad has a flat shape in the longitudinal direction and the load point is in the center in the longitudinal direction).
Case (3): In the case of a comparative example (the shape of the pressure pad in the longitudinal direction is flat and the load points are two places on both ends in the longitudinal direction).

  The pressure distribution of the pressing force is the result of measuring the pressure distribution in the longitudinal direction where the pressure pad contacts the heating roller via the pressure belt using a pressure distribution measurement system (I-SCAN) manufactured by Nitta Corporation. is there. The paper speed distribution is a result of measurement according to the following procedure. First, prepare A4 size paper that is printed only on the leading edge of the paper with special toner that is transferred to the heating roller. From the leading edge of the paper to the trailing edge, slits are made at intervals of 30 mm in the paper width direction for fixing. Pass through the vessel. Then, after the toner is transferred to the heating roller, the toner is transferred again to the paper, and a toner image transferred for each rotation of the heating roller is formed on the paper. The sheet speed is a result obtained by measuring the distance of the toner image.

Evaluation for the occurrence of paper wrinkles was performed under the following conditions.
-Paper: RICOH-6200 (A4 size, vertical mesh, basis weight 69 g / m ² )
・ Printing mode: Blank paper, 50 sheets (4-color mode)
・ Environment (N / N): 22 ° C, 55% RH, (paper is just opened)
・ Environment (H / H), humidity condition: 28 ° C., 80% RH, (250 sheets are stacked and humidity-controlled for 48 hours)
As can be seen from FIG. 5, in the case (1) which is the embodiment, as already described, the distribution of the pressing force of the pressure pad is such that the central pressing force P2 is larger than the pressing forces P1 and P3 at both ends. The distribution became convex in the center. The central pressing force P2 was almost twice the pressing forces P1 and P3 at both ends. The paper speed distribution is a concave distribution in which the speeds V1 and V3 at both ends are faster than the central speed V2. The speeds V1 and V3 at both ends were about 0.2% faster than the central speed V2. As a result, paper wrinkles did not occur in both environments (N / N), environments (H / H), and humidity control conditions.

  On the other hand, in the case (2) as a comparative example, the pressure distribution and the paper speed distribution are almost flat because the shape of the pressure pad is flat. Therefore, there was no paper wrinkle in the state immediately after opening the environment (N / N), but paper wrinkle was generated on 18/50 sheets (36%) in the state of humidity adjustment in the environment (H / H). . This is due to the following reason. Paper that has been conditioned in the environment (H / H) has a high moisture content of 12 to 16%, and when heated by a fixing device, the moisture content of the paper is reduced to about 4%. This is because out-of-plane deformation occurs. For this reason, in the flat paper speed distribution, both ends of the paper cannot be pulled, and the generation of paper wrinkles due to the shrinkage of the paper cannot be sufficiently prevented.

  In the case of the comparative example (3), since the pressure pad is flat and the pressure pad is pressed from both ends, the pressure pad itself is bent and deformed in a concave shape. Is a concave distribution in which the pressing forces P1 and P3 at both ends are larger than the pressing force P2 at the center. The pressing forces P1 and P3 at both ends were approximately 2.2 times the pressing force P2 at the center. Therefore, contrary to the case (1) of the embodiment of the present invention, the paper speed distribution is a convex distribution in the longitudinal direction in which the speeds V1 and V3 at both ends are about 0.1% slower than the central speed V2. Even in the environment (N / N), generation of paper wrinkles is observed in 42 sheets out of 50 sheets or more. When the humidity was adjusted in the environment (H / H), paper wrinkles occurred on all 50 sheets.

  As described above, according to the fixing device of the present invention, it is possible to realize a small, high-speed, high-quality color fixing for various types of paper and to prevent paper wrinkles without increasing the cost of parts with a small number of parts.

Schematic configuration diagram of the fixing device of the present invention Schematic configuration diagram of electrophotographic apparatus of the present invention Example of exploded perspective view of pressure member Explanatory diagram of pressure applied to the fuser Pressure member and its evaluation result Example of exploded perspective view of pressure member Example of exploded perspective view of pressure member Example of exploded perspective view of pressure member

Explanation of symbols

1: heating roller, 1a: cored bar, 1b: elastic layer, 2: pressure belt, 3: entrance guide,
4: peeling guide, 5: heater, 6: pressure pad, 6a: elastic layer, 6b: first support member,
6c: load point (pin hole), 6d: load support member, 7: outlet guide, 9: toner,
10: fixing device, 11: intermediate transfer device, 12: photosensitive device, 13: transfer device,
14: sheet peeling means, 15: intermediate transfer device cleaning means, 16: charger,
17: Photoconductor cleaning means, 18: Afterimage removing means, 19K, 19Y, 19M, 19C: Developer
20; exposure means, 21; paper holding means, 22; paper supply device, 23; paper discharge device,
25: electrophotographic apparatus, 31; thermistor, 32; paper, 33; lower case, 60: pressure member,
61; second support member, 61a; pin hole, 61b: load support member, 62; load support pin,
63; pressure spring, 64; retaining ring

Claims (10)

A heating roller having a heating element and provided with an elastic layer around the core, a pressure belt stretched so as to contact the elastic layer of the heating roller, and pressing the pressure belt against the heating roller A fixing device of an electrophotographic apparatus comprising a pressure member,
The heating roller is a driving roller, and has the same outer diameter from one end to the other end.
The pressure member is a fixing device of an electrophotographic apparatus having a structure in which a pressing force with respect to a central portion in a longitudinal direction of a heating roller is larger than a pressing force with respect to an end portion. A heating roller having a heating element and provided with an elastic layer around the core, a pressure belt stretched so as to contact the elastic layer of the heating roller, and pressing the pressure belt against the heating roller A fixing device of an electrophotographic apparatus comprising a pressure member,
The heating roller is a driving roller, and has the same outer diameter from one end to the other end.
The fixing device of the electrophotographic apparatus, wherein a shape in a longitudinal direction of the pressing surface of the pressing portion of the pressing member is convex toward the heating roller.   The fixing device of the electrophotographic apparatus according to claim 1, wherein a shape of the pressing surface of the pressing portion of the pressing member in a direction along a circumferential direction of the heating roller is concave toward the heating roller.   4. The fixing device for an electrophotographic apparatus according to claim 1, wherein the pressing portion of the pressing member is made of an elastic layer softer than the elastic layer of the heating roller.   The said pressurization member was provided with the 1st support member which supports an elastic body layer, and the 2nd support member which supports a 1st support member in the load point of the longitudinal direction center part of a 1st support member. The fixing device of the electrophotographic apparatus according to any one of 4.   The fixing device for an electrophotographic apparatus according to claim 5, wherein the first support member is rotatable about a load point with respect to the second support member.   The fixing device for an electrophotographic apparatus according to claim 6, wherein the first support member and / or the second support member includes a load support member that causes the first support member and the second support member to abut at a load point.   The fixing device for an electrophotographic apparatus according to claim 6, wherein the first support member and the second support member are coupled by a load support pin at a load point.   The fixing device for an electrophotographic apparatus according to any one of claims 1 to 8, wherein at least one of the first support member and the second support member has a U-shaped vertical cross section with respect to the longitudinal direction.   An electrophotographic apparatus comprising the fixing device according to claim 1.

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