JP2008064834A - Image fixing device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image fixing apparatus that has a small and inexpensive configuration and is capable of reducing envelope wrinkles and image disturbance, and to provide an image forming apparatus using the image fixing device. <P>SOLUTION: The image fixing device has a heat roller (1), a pressure belt (2), and a pressure member (6) the middle part of which has a curved shape for pressing the pressure belt (2) against the surface of the heat roller (1) and the ends of which have chamfers. The device fixes a toner image to a recording medium by passing the recording medium with the transferred toner image thereon through a nip area. The device includes an entrance guide (3) that guides the recording medium to the nip area from the transfer section. In the case where a line extended from each chamfer is represented by L1, a line connecting the entrance point R of the nip area and the transfer point T of the transfer section is represented by L2, and a tangent line of the heat roller (1) at the entrance point R is represented by L3, and an angle between the lines L1 and L2 is represented by β, and an angle between the lines L2 and L3 is represented by α, the leading end P of the entrance guide (3) is disposed within the angle β and the angle α. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, and a facsimile, and in particular, an image fixing apparatus capable of reducing envelope wrinkles and image disturbances generated in the fixing apparatus and The present invention relates to the image forming apparatus used.

  In an image forming apparatus using an electrophotographic system, as a method of fixing a toner image carried on a recording body, a pair of heated rollers are pressed against each other, and the recording body is passed through the pressure contact area to form a toner image. A heat and pressure roll type fixing system that melts and adheres to a recording medium is generally used.

  In recent years, as demands for downsizing and speeding up of image forming apparatuses have increased, a belt nip fixing system in which a pressure belt is pressed against a heating roll has been adopted (see Patent Document 1).

  This fixing method has the advantage of good fixing efficiency, but has a problem that the nip has a small curvature and the recording medium is likely to wrinkle because a pressure belt is wound around a small-diameter heating roller to secure the nip. .

  That is, when a recording body such as an envelope in which a plurality of sheets overlap each other is passed through the nip portion, a difference in curvature of the recording body is generated between the envelope surface in contact with the heating roller and the back surface of the envelope in contact with the pressure roller. Body speed difference occurs and wrinkles are likely to occur. In addition, after the envelope trailing edge has passed the transfer point, the envelope trailing edge vibrates and splashes, and unfixed toner scatters from the paper surface, causing a problem that the image is easily disturbed.

  As described above, various proposals have been made to reduce envelope wrinkles after fixing and image disturbance. For example, Patent Document 2 discloses that the speeds of the surfaces of two fixing rollers in the nip portion are matched by using both rollers of a heating roller and a fixing roller as driving rollers. .

JP-A-8-262903 JP-A-7-261593

  However, the configuration disclosed in Patent Document 2 has a problem that the number of parts is large and the assembly process is large and expensive.

  The present invention has been made to solve the above-described problems. An image fixing apparatus capable of reducing envelope wrinkles and image disturbances with a small and inexpensive configuration without increasing the number of parts, and image formation using the same. An object is to provide an apparatus.

  To achieve the above object, the present invention provides a heating roller, a pressure belt that abuts the heating roller to form a nip portion, and a central portion for pressing the pressure belt against the surface of the heating roller. And a pressure member having a chamfered portion at the end, and the toner image is fixed to the recording member by passing the recording member onto which the toner image has been transferred in the transfer portion through the nip portion. The fixing device includes an entrance guide for guiding the recording medium from the transfer portion to the nip portion, and connects an extension line of the chamfered portion to L1 and an entrance point R of the nip portion and a transfer point T of the transfer portion. When the line is L2, the tangent line of the heating roller at the entrance point R is L3, the angle between the line L1 and the line L2 is β, and the angle between the line L2 and the line L3 is α, the tip of the entrance guide is Is within the angle β and the angle α It has one of the features that has been arranged so as to be positioned.

  Another feature of the present invention is that the angle β is selected in the range of 40 to 60 °, and the angle α is selected to be 30 ° or less.

  Another feature of the present invention resides in that the angle θ is selected in the range of 45 to 50 °, where θ is the angle at which both ends of the pressure member are viewed from the central axis of the heating roller.

  Another feature of the present invention is that when a line connecting the distal end portion P of the inlet guide and the nip portion entrance point R is L4, and an angle between the line L2 and the line L4 is γ, the angle γ is set to 0 to 0. It is in the range of 30 °.

  Another feature of the present invention resides in that the distance between the distal end portion of the inlet guide and the nip portion inlet point R is selected to be 15 to 25 mm.

  Other features and advantages of the present invention will be more clearly understood from the following description.

  According to the present invention, since it is configured to cause local bending deformation at the front end of the inlet guide before the recording body is conveyed to the nip portion, it is caused by the difference in curvature between the front surface and the back surface of the recording body in the nip portion. It becomes possible to absorb the speed difference, and this has the effect of reducing wrinkles of the recording medium.

  In addition, by providing the pressure member on the inlet side of the nip with an inclined portion having a predetermined angle, it is possible to stabilize the posture of the recording body when entering the nip and to prevent the trailing edge from jumping up due to vibration of the recording body. There is an effect that image disturbance can be prevented.

  First, a schematic configuration of an image forming apparatus according to the present invention will be described with reference to FIG. In FIG. 1, reference numeral 12 denotes an endless photosensitive belt, which is rotated counterclockwise by a motor (not shown). A charger 16, an exposure device 20, and black K, yellow Y, magenta M, and cyan C developing machines 19K, 19Y, 19M, and 19C are disposed along the photosensitive belt 12.

  The surface of the photosensitive belt 12 is uniformly charged by the charger 16. An electrostatic latent image is formed on the charged photosensitive belt 12 by a laser irradiated from the exposure device 20. The photosensitive belt 12 on which the electrostatic latent image is formed sequentially passes through developing machines 19C, 19M, 19Y, and 19K having developing rollers. Each of the developing machines 19C, 19M, 19Y, and 19K is prepared with toners of four colors, cyan, magenta, yellow, and black. Each time the exposed photosensitive belt 12 passes, a toner image of each color is generated. It is formed. That is, a one-color toner image is formed on the photosensitive belt 12 per rotation.

  The photosensitive belt 12 on which the toner image is formed contacts the intermediate transfer belt 11 at the first transfer position T1. The intermediate transfer belt 11 is rotated clockwise in the figure following the rotation of the photosensitive belt 12. The reason why the intermediate transfer belt 11 is driven is to make the configuration simple and inexpensive, and to eliminate the speed difference from the photosensitive belt 12 and to eliminate image shift.

  At the first transfer position T1, the toner image formed on the surface of the photosensitive belt 12 due to the potential difference between the photosensitive belt 12 and the intermediate transfer belt 11 is transferred to the surface of the intermediate transfer belt 11.

  The potential of the photosensitive belt 12 that has passed the first transfer position T1 is subsequently reduced to a certain level by light irradiation for removing afterimages, and the electrostatic latent image is erased. Further, the remaining toner on the surface remaining without being transferred at the first transfer position T1 is cleaned by the photosensitive member cleaning means, and the next toner image can be formed.

  By repeating the above steps as many times as necessary by the developing machines 19K, 19Y, 19M, and 19C, a toner image corresponding to an image to be printed and a character is formed on the surface of the intermediate transfer belt 11. The toner image on the intermediate transfer belt 11 is transferred onto the recording sheet by the transfer roller 13 at the second transfer position T2.

  A sheet holding device 21 for storing sheets is disposed below the image forming apparatus. The paper in the paper holding device 21 is guided to the transfer roller 13 by the paper supply device 22. The toner image transferred to the paper at the second transfer position T2 is fixed by the fixing device 10 and then discharged from the paper discharge device 23.

  Next, an embodiment of the image fixing apparatus according to the present invention will be described with reference to FIG.

  The fixing device 10 according to the present invention mainly includes a heating roller 1, a pressure belt 2, an inlet guide 3, a peeling guide 4, an outlet guide 7, and a lower case 33.

  The heating roller 1 is an elastic roller having an outer diameter of 26.6 mm, for example, and a silicone rubber layer 1b having a thickness of 0.8 mm and a JIS hardness of 20 degrees is formed on the surface of a pipe-shaped metal core 1a having a thickness of 0.5 mm. Made up of. A heater 5 is disposed inside the heating roller 1, and the toner is melted by this heat. The heating roller 1 is rotated in the direction of arrow A by a motor (not shown).

  Around the heating roller 1, a lower case 33, a contact thermistor 31, an inlet guide 3 and a peeling guide 4 are arranged. The lower case 33 and the entrance guide 3 guide the paper 32 to which the unfixed toner 9 is attached to the heating roller 1.

  The contact type thermistor 31 is in contact with the sheet passing portion of the heating roller 1 and detects the surface temperature of the heating roller 1 with high accuracy. This detection signal is applied to a control device (not shown), and the heat generation of the heater 5 is controlled. The peeling guide 4 is disposed with a gap G away from the surface of the heating roller 1 and has a function of peeling the fixed paper 32 from the heating roller 1 and guiding it to the outlet side.

  On the other hand, the pressure belt 2 is a seamless polyimide belt having an inner diameter of 30 mm, and the surface thereof is coated with PFA in order to ensure the diameter separation from the toner. Further, the pressure belt 2 is brought into contact with the heating roller 1 at a winding angle θ by a pressure pad 6 having a curved surface corresponding to the curvature of the heating roller 1, and contact for melting the toner 9. A width h is formed. Hereinafter, a portion where the heating roller 1 and the pressure belt 2 are in contact with each other with the contact width h is referred to as a nip portion. The pressure pad 6 on the inlet side of the nip portion is formed with an inclined portion (chamfered portion), whereby the posture of the paper 32 is stabilized when the paper 32 enters the nip portion.

  The sheet 32 on which the unfixed toner 9 is transferred is conveyed in the direction of arrow B by the guide of the inlet guide 3 and the lower case 33 and contacts the heating roller 1 with a contact width h, where the toner 9 is melted and fixed on the sheet 32. Is done. Thereafter, the paper 32 is peeled from the heating roller 1 by the peeling guide 4. Since the heating roller 1 and the pressure pad 6 are arranged so that the line q connecting the center of the pressure pad 6 and the center of the heating roller 1 is inclined by an angle θ with respect to the horizontal line p, the fixing device 10 The discharged paper 32 is peeled off from the heating roller 1 and then conveyed to the paper discharge device 23 (FIG. 1). In the present embodiment, the angle φ is selected to be 17 °.

  In such a configuration, assuming that the angle at which both ends of the pressure pad 6 are viewed from the center of the heating roller 1 is θ, θ = 45 ° to 50 ° is selected in this embodiment, and the heating roller 1 and the pressure belt 2 are The contact width h is 9 to 13 mm, and the fixing speed is 200 mm / s. 2 can form the contact width h necessary for the fixing speed even when the heating roller 1 has a small diameter, and thus a small and high-speed fixing device can be realized.

  In the apparatus configured as shown in FIG. 2, the present invention is characterized by the arrangement and structure of the inlet guide 3. FIG. 3 is an explanatory view showing the inlet guide 3 and its peripheral members in an enlarged manner. Hereinafter, for convenience of explanation, it is assumed that the printing paper is an envelope 34, and the envelope 34 has an envelope front paper 34a having a thickness t and an envelope back paper 34b having the same thickness t.

  The front sheet 34a of the envelope 34 is conveyed with a radius r of the heating roller 1, and the back sheet 34b of the envelope 34 is conveyed with a radius (r + t) that is larger by the paper thickness t. Accordingly, the speed ratio between the front sheet 34a and the back sheet 34b is (1 + t / r). For this reason, the smaller the radius r of the heating roller 1, the greater the influence of the paper thickness, and the envelope wrinkle due to the speed difference between the front paper 34a and the back paper 34b occurs.

  For this reason, the present invention provides an envelope by providing a contact portion P having a curved surface with a curvature r ′ on the inlet guide 3 that contacts the back surface of the envelope, and disposing the contact portion P at a predetermined position as will be described later. 34 was bent in the opposite direction to the bending of the nip at the contact portion P, and then guided to the nip.

  That is, the envelope 34 is transported along the S-shaped transport path, so that the contact portion P cancels out the speed difference between the front surface 34a and the back surface 34b in the nip portion. In this embodiment, the curvature r 'is selected in the range of 0.5-1.

  Hereinafter, the arrangement relationship between the contact portion P and other members will be described in detail with reference to FIG.

  In the following description, the radius of the heating roller 1 is r, the entry point of the nip formed by the heating roller 1 and the pressure belt 2 is R, and the exit point is S. In addition, the distance between the entrance point R and the contact portion P is z. Further, a chamfered portion is provided on the inlet side of the pressure pad 6, and an extension line of the chamfered portion is indicated by L1, a second transfer point T2 where the intermediate transfer belt 11 and the transfer roller 13 in FIG. L2 is a line connecting the heating roller 1 at the nip entrance point R, and L4 is a line connecting the tip portion P of the entrance guide 3 and the nip entrance point R.

  Further, when the angle formed by the lines L2 and L3 is α, the angle formed by the lines L1 and L2 is β, and the angle formed by the lines L3 and L4 is γ, the present invention defines the tip contact portion P of the inlet guide 3 as follows. It is characterized by being arranged within the angle β and within the angle α.

  In FIG. 4, when the tip contact portion P of the inlet guide 3 is closer to the heating roller 1 than the straight line L2 connecting the transfer point T2 and the nip inlet point R, the envelope is less likely to be conveyed to the nip portion. As a result, a paper jam is likely to occur. In addition, when the envelope is conveyed to the nip portion, the tip contact portion P of the inlet guide 3 causes excessive S-shaped bending deformation, and wrinkles are likely to occur at the nip portion.

  On the other hand, when the tip contact portion P of the inlet guide 3 is closer to the pressure belt 2 than the tangent L3 of the heating roller 1 at the nip entrance point R, the envelope is bent by the tip contact portion P of the inlet guide 3. Does not cause deformation. As a result, a speed difference is generated due to a difference in curvature between the front and back surfaces of the envelope generated at the nip portion, and envelope wrinkles are generated.

  Accordingly, the straight line L1 formed by the chamfered portion of the pressure pad 6, the angle L formed by the straight line L2 connecting the transfer point T where the intermediate transfer device and the transfer roller are in contact with the nip entrance point R, and the nip entrance point R By disposing the tip contact portion P of the inlet guide 3 within an angle α formed by the straight line L2 connecting the transfer point T and the tangent L3 of the heating roller 1 at the nip inlet point R, the fixing device 10 can Reduction of envelope wrinkles can be realized.

  Next, selection of each angle will be described.

(Range of angle β)
FIG. 5 is an enlarged view of the vicinity of the nip entrance point R in FIG. 4. The straight line L1 formed by the chamfered portion 6a of the pressure pad 6, the transfer point T2 where the intermediate transfer belt 11 and the transfer roller 13 contact, and the nip entrance point. The relationship between the angle β formed by the straight line L2 connecting R and the shape of the pressure pad 6 is shown. The angle β is an angle determined from the positional relationship between the transfer unit (transfer point T2 in this embodiment) for transferring the toner image to the sheet and the fixing device 10, and in this embodiment, β = 40 ° to 60 °. When β is 40 ° or less, the tip of the envelope 34 which is a printing sheet touches the heating roller 1, and unfixed toner attached to the envelope 34 is transferred to the heating roller 1. As a result, hot offset occurs. When β is 60 ° or more, after the rear end of the envelope 34 passes through the transfer point T2, the vibration of the envelope 34 increases and the rear end of the envelope 34 rises. As a result, unfixed toner is scattered and image distortion occurs. Accordingly, β = 40 ° to 60 ° is set so that the image is not disturbed and the envelope is not wrinkled.

(Range of angle α)
In FIG. 4, the angle α formed between the straight line L2 connecting the nip entrance point R and the transfer point T2 and the tangent L3 of the heating roller 1 at the nip entrance point R is the positional relationship between the transfer point in the intermediate transfer device and the fixing device 10. Determined from. In this embodiment, α ≦ 30 °. When α is 30 ° or more, the conveyance speed of the envelope 34 increases between the transfer device and the fixing device 10, and image wrinkles (color misregistration) in the transfer device due to an impact when the envelope 34 is inserted into the fixing device 10. Will occur. Accordingly, the angle α that plays the role of stabilizing the posture of the envelope 34 from the transfer device to the fixing device 10 is set to α ≦ 30 ° in order to prevent the occurrence of color misregistration in the transfer device.

(Range of angle γ)
In FIG. 4, an angle formed by a straight line L4 connecting the tip position P of the inlet guide 3 and the nip inlet point R and a straight line L2 connecting the transfer point T2 and the nip inlet point R where the transfer roller 13 of the intermediate transfer device contacts. In this embodiment, γ is set to γ = 0 to α, that is, 0 to 30 °. When the angle γ is 0 ° or less, the envelope 34 is easily scratched by the entrance guide 3. This is because the pressure applied from the inlet guide tip P to the envelope 34, which is a sheet, increases. When the angle γ is greater than or equal to α, the S-curve bends gradually with respect to the speed difference due to the difference in curvature between the envelope front side 34a and the envelope back side 34b at the nip portion. Therefore, the speed difference due to the curvature difference at the nip portion cannot be absorbed, and the effect of reducing wrinkles is reduced. Therefore, the wrinkle reduction rate is high, and γ = 0 to α is set so that the guide rubbing scratch due to the distal end portion P of the entrance guide is difficult to be attached.

(Range of distance z)
In FIG. 3, the distance z between the nip entrance point R and the tip position P of the entrance guide 3 is set to z = 15 to 25 mm in this embodiment. When the distance z is 15 mm or less, the envelope 34 has a sharp S-shape, and the pressure applied to the envelope 34 from the inlet guide tip P is increased. Therefore, the envelope 34 is scratched by the inlet guide tip P, and the envelope is wrinkled. On the other hand, when the distance z is 25 mm or more, the inlet guide 3 does not play a role of guidance, and the envelope 34 is difficult to be conveyed to the nip inlet point R. A paper jam is likely to occur due to the difficulty of being conveyed. Therefore, the wrinkle generation rate is low, and z = 15 to 25 mm where paper jam is unlikely to occur.

  According to the present invention, since the wrinkle of the envelope is reduced by adjusting the position of the tip contact portion P of the inlet guide 3 in the fixing device 10, even if the configuration of the photosensitive device, the intermediate transfer device, or the like is changed, Envelope wrinkles can be reduced.

  Although the embodiments of the present invention have been described above, various modifications and changes can be easily made without changing the basic concept of the present invention, and these also belong to the scope of the present invention. For example, the image fixing apparatus according to the present invention can be applied not only to the image forming apparatus of FIG. 1 but also to any electrophotographic image forming apparatus.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. 1 is a schematic configuration diagram illustrating an embodiment of an image fixing device according to the present invention. It is explanatory drawing of the image fixing apparatus which concerns on this invention. It is explanatory drawing of the image fixing apparatus which concerns on this invention. It is explanatory drawing of the image fixing apparatus which concerns on this invention.

Explanation of symbols

1: heating roller, 1a: iron core, 1b: silicone rubber, 2: pressure belt,
3: inlet guide, 4: peeling guide, 5: heater, 6: pressure pad, 7: outlet guide,
8: toner, 10: fixing device, 11: intermediate transfer belt, 12: photosensitive belt,
13: transfer roller, 16: charger, 19K, 19Y, 19M, 19C: developing machine,
20: Exposure device, 21: Paper holding device, 22: Paper supply device, 23: Paper discharge device,
31: thermistor, 32: paper, 33: lower case, 34: envelope, 34a: envelope front paper, 34b: envelope back paper

Claims (8)

  A heating roller, a pressure belt that abuts against the heating roller to form a nip portion, and a central portion is curved to press the pressure belt against the surface of the heating roller, and a chamfered portion is provided at the end. A fixing member that fixes the toner image to the recording body by passing the recording body on which the toner image has been transferred in the transfer section through the nip section, from the transfer section to the nip section. An entrance guide for guiding the recording medium, L1 as an extension line of the chamfered portion, L2 as a line connecting the entrance point R of the nip portion and the transfer point T of the transfer portion, and the heating roller at the entrance point R Is L3, the angle formed by the lines L1 and L2 is β, and the angle formed by the lines L2 and L3 is α, the tip of the inlet guide is located within the angle β and positioned within the angle α. Characterized by the arrangement Image fixing apparatus.   2. An image fixing apparatus according to claim 1, wherein said angle [beta] is selected in a range of 40 to 60 [deg.].   2. The image fixing apparatus according to claim 1, wherein the angle α is selected to be 30 ° or less.   2. The image fixing apparatus according to claim 1, wherein the angle [theta] is selected in a range of 45 to 50 [deg.], Where [theta] is an angle at which both ends of the pressure member are viewed from the central axis of the heating roller.   In Claim 1, when the line which connects the front-end | tip part P of the said entrance guide and the said nip part entrance point R is set to L4, and the angle which the line L2 and the line L4 make is set to (gamma), angle (gamma) is 0-30 degrees. A fixing device characterized by being selected in a range.   The fixing device according to claim 1, wherein a distance between a front end portion of the inlet guide and the nip portion inlet point R is selected to be 15 to 25 mm.   2. The fixing device according to claim 1, wherein the front end portion of the inlet guide has a contact surface that is bent in a direction opposite to the curve of the nip portion and contacts the recording member with a predetermined curvature. A charging unit that uniformly charges the surface of the photoconductor, an exposure unit that irradiates the charged photoconductor surface with a laser beam to form an electrostatic latent image, and a toner image corresponding to the electrostatic latent image on the surface of the photoconductor. In an image forming apparatus comprising a developing unit to be formed, a transfer unit for transferring a toner image to a recording body, and a fixing unit for a toner image carried on the recording body, the fixing unit includes a heating roller, the heating roller, A pressure belt that abuts to form a nip portion; and a pressure member that has a curved central portion and a chamfered portion at the end for pressing the pressure belt against the surface of the heating roller. An entrance for guiding the recording medium from the transfer section to the nip section by passing the recording body onto which the toner image has been transferred in the transfer section through the nip section. A guide is provided to extend the chamfered part. 1. The line connecting the entrance point R of the nip part and the transfer point T of the transfer part is L2, the tangent of the heating roller at the entrance point R is L3, the angle formed by the line L1 and the line L2 is β, An image forming apparatus, wherein the leading end portion of the inlet guide is located within the angle β and located within the angle α, where α is an angle formed by L2 and the line L3.

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