JP2006065230A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device, which includes two web pressing rollers and employs a detachable-web cleaning system, with a technique of reducing a decrease in the temperature of the contact face of the web with the heat fixing roller during the separation of the web and of preventing scratches on the surface of the heat fixing roller. <P>SOLUTION: A separation distance at the closest contact where a distance between the web separated and the surface of the fixing roller is the shortest on the web is not shorter than the minimum distance required to prevent contact of the web with the surface of the fixing roller even taking account of fluctuations of a separating operation and slack of the web. Further, the separation distance in which a distance between the web separated and the surface of the fixing roller is the longest is expressed by a formula representing relations between the radius R of the fixing roller, the radius r of each of the web pressing rollers, and a distance d between the centers of the two web pressing rollers. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus having a function of forming an image on a recording medium such as a sheet, for example, a copying machine, a printer, or a facsimile machine, and more particularly, to an unfixed apparatus provided in these apparatuses. The present invention relates to a fixing device for fixing a developer image by heating and pressure.

  The transferred sheet is guided to a fixing device including a fixing roller having a built-in heating source such as a halogen lamp, and a pressure roller that rotates while being pressed against the fixing roller. An image forming apparatus such as a copying machine configured to fix a toner image on a sheet to the sheet is well known.

  Further, in the conventional fixing device, a so-called offset phenomenon occurs in which a part of the toner forming the toner image adheres to the fixing roller. In particular, when the recording paper is jammed, the recording paper stays in the fixing nip or the recording paper is wound around the fixing roller, so that a large amount of offset toner adheres to the fixing roller.

  As a means for removing the toner adhering to the fixing roller, a cleaning means is brought into contact with the surface of the fixing roller. As the cleaning means, a cleaning sheet is usually brought into contact with the surface of the fixing roller. A web cleaning system is in place.

  However, in such a web cleaning system, since the cleaning sheet is always brought into contact with the surface of the fixing roller, there is a problem that the surface of the fixing roller is rubbed by the web, the surface is worn and the life is shortened.

  In addition, the web is usually impregnated with a release oil such as silicone oil in order to enhance the releasability between the fixing roller and the toner, and has an oil application function. Since the web is in contact with the roller surface, the oil application to the surface of the fixing roller becomes excessive, and oil marks (so-called oil streaks) may occur in the image after fixing.

  For such a web cleaning system, a means for contacting and separating the cleaning web from the surface of the fixing roller is provided, and the web is placed on the surface of the fixing roller only when cleaning is necessary (when fixing an unfixed image or jamming). A so-called web attaching / detaching method is adopted in which the contact is made and the contact is made at other times.

Further, in recent years, in the web cleaning system, two web pressing rollers that press the web against the surface of the fixing roller at the time of cleaning are arranged in order to improve the cleaning performance of the toner adhering to the fixing roller. Is used which has a longer circumferential distance in contact with the surface of the fixing roller (see Patent Document 1).
JP-A-06-301251

However, in the fixing device using the web detaching method in which the roller scratches and the oil streaks are combined in this way, the temperature of the web is lowered when the web is separated from the fixing roller. The toner collected on the web from the surface of the fixing roller is solidified, and there is a problem that the surface of the fixing roller is damaged when the solidified toner web is brought into contact with the surface of the fixing roller again.

  For such a decrease in the temperature of the web contact surface when the web is separated, the fixing in which only one web pressing roller is arranged by reducing the separation distance between the web and the fixing roller surface when separating the web as much as possible. In the device, it was possible to take measures.

  However, in the fixing device in which two web pressing rollers are arranged in order to improve the cleaning property as described above, since the circumferential distance in which the web is in contact with the surface of the fixing roller is increased, the contact portion Even if the web separation distance is reduced at the center portion in the circumferential direction, the web separation distance is increased at the most upstream portion and the most downstream portion in the circumferential direction of the contact portion. Sometimes the temperature dropped, and the countermeasures were not enough.

  The present invention has been made to solve the above-described problems of the prior art, and the object of the present invention is to fix a web cleaning system in which two web pressing rollers are arranged and a web detaching system is adopted. It is an object of the present invention to provide a technique capable of preventing the occurrence of scratches on the surface of the heat-fixing roller with little decrease in the temperature of the contact surface when the web is separated.

In order to achieve the above object, the present invention provides:
A heat-fixing roller having a heating means;
A pressure member provided to form a nip portion with the heat fixing roller by rotating in contact with the heat fixing roller and pressing an outer peripheral surface of the heat fixing roller;
Have
A fixing device for fixing a developer image on the sheet to the sheet by passing a sheet carrying an unfixed developer image through the nip portion;
Cleaning means for cleaning the surface of the heat fixing roller;
The cleaning means is a web-type cleaning means that uses a web as a cleaning member, and has two web pressing rollers that press the web against the surface of the heat-fixing roller during cleaning. In the fixing device that can come in contact with and separate from the heat fixing roller,
The radii of the two web pressing rollers are equal, and when the cleaning unit is separated, the separation distance L _S (mm) at the closest point on the web where the distance from the surface of the heat fixing roller is the shortest. )But,
L _MIN ≦ L _S
(However, L _MIN is the minimum separation distance (mm) for preventing the web from coming into contact with the surface of the heat-fixing roller in consideration of variation in the separation operation of the cleaning means and sagging of the web during web separation.)
Meet, and
The radius R (mm) of the heat fixing roller, the radius r (mm) of the web pressing roller, and the distance d (mm) between the centers of the two web pressing rollers are expressed by the relational expression ((R + 2) ^{2 + (r + (d-} 2r) / 2) 2) 1/2 -R <L g
(However, L _g (mm) is the glass transition temperature at the distance from the surface of the heat-fixing roller when the surface temperature of the heat-fixing roller is maintained at the above-mentioned predetermined fixing processing conditions. T _g (° C) distance)
It is characterized by satisfying.

In the image forming apparatus, image forming means for transferring a developer image obtained by developing the electrostatic latent image formed on the image carrier to a sheet;
The fixing device as described above for fixing an unfixed developer image on the sheet;
It is characterized by providing.

  According to the present invention, in a fixing device that employs a web cleaning method in which two web pressing rollers are arranged and adopts a web detaching method, the temperature of the contact surface during the web separation is small, and the surface of the heat fixing roller It is possible to prevent the occurrence of scratches.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

(Embodiment 1)
Hereinafter, a heat fixing apparatus according to Embodiment 1 of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic view showing a heat fixing device (hereinafter referred to as a fixing device) 1 according to Embodiment 1 of the present invention. FIG. 4 is a schematic configuration diagram of the image forming apparatus 10 according to the first embodiment of the present invention.

  First, a schematic configuration of the image forming apparatus will be described.

  In FIG. 4, the sheets P fed one by one from the paper feed cassette 2 by the paper feed roller 3 pass through the transport path A and are transported to the transport roller 4. When the leading end position of the toner image (developer image) formed on the photosensitive drum 5 as the image carrier reaches the position of the transfer nip where the photosensitive drum 5 and the transfer roller 6 are in contact with each other, the sheet P Timing is taken so that the leading edge of the toner is conveyed to the transfer nip. The photosensitive drum 5 and the transfer roller 6 constitute an image forming unit (image forming unit).

  In this way, after the toner image on the photosensitive drum 5 is transferred to the sheet P at the transfer nip portion, the sheet P is separated from the photosensitive drum 5 and conveyed to the fixing device 1. In this fixing device 1, after fixing the unfixed toner image transferred to the sheet P, the sheet P on which the toner image has been fixed passes through the conveyance path B and is discharged by the paper discharge roller pair 8. The paper is discharged to the paper discharge unit 9 of the main body.

  Next, the fixing device 1 according to the present embodiment will be described.

  As shown in FIG. 1, the fixing unit 1 includes a pair of rollers including a heat fixing roller (hereinafter referred to as a fixing roller) 21 and a pressure roller 30. The fixing roller 21 has an internal heater 26 serving as a heating source (heating means) inside, and a heat-resistant elastic release layer 23 is provided on the surface of a thin cored metal roller 22 made of aluminum or iron. is there. The pressure roller 30 is provided with a heat-resistant elastic release layer 32 on the surface of the thin cored bar roller 31 like the fixing roller 21 so that a nip region (nip portion) N is formed at the contact portion of both rollers. Are pressed against the fixing roller 21 by a spring (not shown). Here, the pressure roller 30 constitutes a pressure member.

  25 is a separation claw for efficiently separating the sheet P carrying the toner image T from the surface of the fixing roller 21, and S1 is a thermistor for performing temperature control and temperature detection.

  The control unit 40 sends output data for setting the surface temperature of the fixing roller 21 to a predetermined temperature based on the detection data corresponding to the measured temperature input from the thermistor S1, to a voltage supply power source (not shown). The necessary voltage is supplied to the internal heater 26 constituted by a halogen lamp or the like.

  In the apparatus configured as described above, the surface of the unfixed toner image T formed on the surface of the sheet P through a predetermined image forming process is set to a predetermined temperature (TR = 165 ° C.) by the internal heater 26. After passing through the nip portion N which is a fixing region formed by the fixing roller (driving roller) 21 and the pressure roller (driven roller) 30, the sheet P is removed from the surface of the fixing roller 21 as needed. In this configuration, a fixed image can be obtained by being separated.

  Next, the cleaning means that constitutes the main part of the present embodiment will be described.

  The cleaning unit is a web-type cleaning unit that uses a cleaning web W as a cleaning member. The cleaning web W contacts the fixing roller 21 on the downstream side of the nip region N in the rotation direction of the fixing roller 21. The toner offset to the fixing roller 21 is removed. The cleaning means engages the cleaning web former winding 710 formed by winding one end of the cleaning web W on the roll shaft 705 and winding it on the roll shaft, and the other end of the roll-shaped cleaning web W. The main elements are a winding roll shaft 720 and two pressing rollers 730 and 731 that press the cleaning web W against the surface of the fixing roller 21.

  The two pressing rollers 730 and 731 press the cleaning web W against the surface of the fixing roller 21.

  As described above, the cleaning web W is pressed against the two pressing rollers 730 and 731, so that the cleaning web W extends between the two positions where the two pressing rollers 730 and 731 come into contact with the fixing roller 21. Is brought into contact with the surface of the fixing roller 21, and the contact distance in the circumferential direction of the cleaning web W is longer than in the case where there is one pressing roller, and the cleaning property of the cleaning web W is improved. .

  Further, the take-up roll shaft 720 receives a driving force from a motor provided on the frame of the fixing device, and at the point of contact with the fixing roller 21, the cleaning web W in a direction opposite to the rotation direction of the fixing roller 21. Is configured to be transported and wound up.

  The cleaning web W in the present embodiment has a thickness of about 40 μm and uses a non-woven fabric obtained by mixing aramid fibers and polyester fibers. Further, the cleaning web W is impregnated with a silicone oil for releasing the toner.

  Further, in the present embodiment, in order to prevent the surface of the fixing roller 21 from being worn due to the contact of the cleaning web W and the oil streaks of the image after fixing due to excessive oil application, the surface of the cleaning web W is fixed to the surface of the fixing roller 21. Is provided (web detachment method). That is, as shown in FIG. 1, the supporting members of the two pressing rollers 730 and 731 are moved by moving means (not shown), and the surface of the fixing roller 21 is moved with respect to the surface of the fixing roller 21 as indicated by dotted and solid lines in the figure. The cleaning web W is configured to contact and separate at a predetermined timing. When the sheet P passes through the fixing device, the sheet P contacts the surface of the fixing roller 21 and is otherwise separated.

In such a cleaning method using the web attaching / detaching method, when the cleaning web W is separated from the surface of the fixing roller 21, the temperature decrease of the contact surface of the cleaning web W with the fixing roller 21 becomes a problem. If it is large, the toner collected during cleaning solidifies on the cleaning web W, and the solidified toner is rubbed during cleaning, so that the surface of the fixing roller 21 is scratched.

  FIG. 2 is a diagram showing the relationship between the distance from the surface of the fixing roller and the ambient temperature in a state where the surface temperature of the fixing roller 21 is maintained at TR = 165 ° C. FIG. 3 shows the separation distance at the time of attachment / detachment between the radius of the fixing roller 21 (mm), the radius of the two web pressing rollers 730 and 731 (mm), and the center of the two web pressing rollers 730 and 731. It is a figure for calculating | requiring from distance (mm). FIG. 5 is a diagram showing a contact portion in a single web roller system.

  As a result of studies by the present inventor, in order to prevent solidification of the toner on the cleaning web W, the ambient temperature of the toner collected on the cleaning web W may be set higher than the glass transition temperature Tg. I understood it.

  Further, in a state where the surface temperature TR of the fixing roller 21 is maintained at TR = 165 ° C., the relationship between the distance from the surface of the fixing roller and the ambient temperature is as shown in FIG. At a distance of 5.0 mm, the ambient temperature is 80 ° C. Since the glass transition temperature Tg of the toner is about 60 ° C., if the distance from the fixing roller surface is smaller than 5.0 mm while the surface temperature TR of the fixing roller 21 is maintained at TR = 165 ° C., the solid state of the toner Can be sufficiently prevented.

  From this result, in the configuration with one pressing roller, as shown in FIG. 5, the separation distance of the contact portion (M in the drawing) of the cleaning web W by one pressing roller is smaller than 5.0 mm. You can set this.

  However, in order to improve the cleaning property of the cleaning web W as in the present embodiment, the following considerations are necessary in the configuration in which there are two pressing rollers.

  That is, in the configuration having two pressing rollers, as shown in FIG. 3, the cleaning web W extends between two portions (A and B in the figure) pressed by the two pressing rollers. Is in contact with the fixing roller 21, C corresponding to the midpoint between A and B in the figure has the shortest separation distance when separated, and A and B in the figure have the longest separation distance when separated. It becomes.

  The first requirement is that the separation distance at A and B, which is the longest separation distance, is smaller than 5.0 mm as in the case of a single pressing roller system.

Further, the separation distance L _S of the point C at which the separation distance at the time of separation is the shortest is a distance L _MIN at which the cleaning web W does not contact the surface of the fixing roller 21 at the time of separation in consideration of variation.
It is necessary to set it above. In consideration of variations in the separation operation and sagging of the cleaning web W, L _MIN = 2.0 mm, and in this embodiment, L _S = L _MIN = 2.0 mm.

Therefore, in this embodiment, the configuration is set under the condition that the separation distance between points A and B is smaller than 5.0 mm when the separation distance at point C during separation is 2.0 mm. The separation distance L _A = L _B between the points A and B when the separation distance at the point C at the time of separation is 2.0 mm is approximately obtained as shown in FIG. In the figure, R is the radius (mm) of the fixing roller 21, r is the radius (mm) of the two web pressing rollers, and d is the distance (mm) between the centers of the two web pressing rollers. Further, the separation distance of the point C at which the separation distance at the time of separation is the shortest is 2.0 mm.

From this, the separation distance L _A = L _B between the points A and B is obtained by the relationship of the right triangle OAC, where O is the center of the fixing roller 21,
L _A = L _B = ((R + 2) ² + (r + (d−2r) / 2) ² ) ^1/2 −R
It becomes.

In addition, L _A = L _B <5.0 because the longest separation distance is smaller than 5.0 mm.
So,
((R + 2) ² + (r + (d−2r) / 2) ² ) ^1/2 −R <5.0 Formula (1)
Is obtained.

  In this embodiment, the radius (mm) of the fixing roller 21, the radius (mm) of the two web pressing rollers, and the distance (mm) between the centers of the two web pressing rollers so as to satisfy the formula (1). Is set. In the present embodiment, R = 40 mm, r = 11 mm, and d = 24 mm.

  As described above, in the present embodiment, in the two web pressing rollers, the separation distance is set to 5 at the portion where the cleaning web W comes into contact with the fixing roller 21 at the time of separation and which is the longest separation distance. The ambient temperature at the separation distance at the portion that is the longest separation distance on the contact surface (the most upstream portion or the most downstream portion in the circumferential direction of the web contact portion when the web is separated). Since the temperature of the toner exceeds the glass transition temperature Tg (° C.) of the toner, the temperature can be prevented from decreasing over the entire contact surface of the cleaning web W, and the fixing roller can be prevented from being damaged by the solidified toner. Become.

  In this embodiment, since the web pressing roller has two systems and a web detaching configuration, the cleaning property of the cleaning web W is good and the fixing device with a large amount of offset toner can be used. Since the cleaning web W is brought into contact with the fixing roller only during cleaning, the fixing roller is less worn and the oil streaks of the image after fixing can be eliminated.

(Embodiment 2)
In the first embodiment described above, the cleaning web W is in contact with the surface of the fixing roller 21 only when the sheet P passes through the fixing device 1. However, the cleaning web W is also in contact in the return sequence after the jam processing. May be.

  In the return sequence after the jam processing, when the surface temperature TR of the fixing roller becomes TR = 165 ° C., the cleaning web W is brought into contact, and then the fixing roller 21 is idled for a predetermined time, The surface of the fixing roller 21 is cleaned.

  In this case, in addition to the effect described in the first embodiment, the cleaning web W can be brought into contact with the return sequence after the jam processing to clean the toner attached to the fixing roller during the jam. It is possible to prevent toner contamination of the sheet P to be passed.

(Embodiment 3)
Further, in addition to the return sequence after the jam processing, the cleaning web W is also brought into contact with the start-up sequence after power-on of the image forming apparatus main body including the fixing device as described in the first embodiment. May be.

In the start-up sequence after turning on the power, the cleaning web W is brought into contact when the surface temperature TR of the fixing roller reaches TR = 165 ° C., and thereafter for a predetermined time, as in the second embodiment. Only the fixing roller 21 is idled and the surface of the fixing roller 21 is cleaned.

  In this case, in addition to the effects described in the second embodiment, it is not necessary to divide the sequence after power-on of the main body of the image forming apparatus into two types, normal use and post jamming, and the sequence is This can be simplified and has an effect of reducing the load of sequence control of the main body.

1 is a schematic configuration diagram illustrating a fixing device according to an embodiment of the present invention. FIG. 6 is a diagram illustrating a relationship between a distance from the surface of the fixing roller and an ambient temperature in a state where the surface temperature of the fixing roller is maintained at TR = 165 ° C. In the fixing device according to the embodiment of the present invention, the separation distance at the time of attachment / detachment is the radius of the fixing roller (mm), the radius of the two web pressing rollers (mm), and the center of the two web pressing rollers. It is a figure for calculating | requiring from distance (mm). 1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the contact part in a web roller single system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat fixing apparatus 10 Image forming apparatus 21 Heat fixing roller 30 Pressure roller 25 Separation claw 26 Internal heater 705 Roll axis 710 Cleaning web former winding 720 Take-up roll axis 730, 731 Pressing roller P Sheet S1 Thermistor W Cleaning web

Claims (2)

A heat-fixing roller having a heating means;
A pressure member provided to form a nip portion with the heat fixing roller by rotating in contact with the heat fixing roller and pressing an outer peripheral surface of the heat fixing roller;
Have
By passing a sheet carrying an unfixed developer image through the nip portion, the developer image on the sheet is heated and pressed under predetermined fixing processing conditions, and the developer image is applied to the sheet. A fixing device for fixing,
Cleaning means for cleaning the surface of the heat fixing roller;
The cleaning means is a web-type cleaning means that uses a web as a cleaning member, and has two web pressing rollers that press the web against the surface of the heat-fixing roller during cleaning. In the fixing device that can come in contact with and separate from the heat fixing roller,
The radii of the two web pressing rollers are equal, and when the cleaning unit is separated, the separation distance L _S (mm) at the closest point on the web where the distance from the surface of the heat fixing roller is the shortest. )But,
L _MIN ≦ L _S
(However, L _MIN is the minimum separation distance (mm) for preventing the web from coming into contact with the surface of the heat-fixing roller in consideration of variation in the separation operation of the cleaning means and sagging of the web during web separation.)
Meet, and
The radius R (mm) of the heat fixing roller, the radius r (mm) of the web pressing roller, and the distance d (mm) between the centers of the two web pressing rollers are expressed by the relational expression ((R + 2) ^{2 + (r + (d-} 2r) / 2) 2) 1/2 -R <L g
(However, L _g (mm) is the glass transition temperature at the distance from the surface of the heat-fixing roller when the surface temperature of the heat-fixing roller is maintained at the above-mentioned predetermined fixing processing conditions. T _g (° C) distance)
A fixing device characterized by satisfying the above. Image forming means for transferring a developer image obtained by developing the electrostatic latent image formed on the image carrier to a sheet;
The fixing device according to claim 1, wherein an unfixed developer image is fixed on the sheet;
An image forming apparatus comprising:

Images