JP2015022274A - Fixing and sheet conveying mechanism in image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing and sheet conveying mechanism that reduces dew condensation on a sheet subjected to thermal fixing and exported to the downstream side with a simple configuration to prevent taint damage to the surface of the sheet.SOLUTION: A sheet conveying mechanism includes a slow cooling roll that is arranged between a fixing unit and a paper ejection roller arranged on the downstream side thereof to decrease the temperature of a sheet to a predetermined temperature, where the slow cooling roll decreases the temperature of the surface of the sheet to the predetermined temperature at which dew condensation does not occur in front of the paper ejecting roller, and subsequently cools the sheet simultaneously with the application of a conveying force to the sheet by a conveying roller. For this purpose, the slow cooling roll has a roll surface formed of a mold release layer having relatively high thermal conductivity, and a heat insulating layer provided between the mold release layer and a rotation shaft member.

Description

  The present invention relates to a fixing sheet conveying mechanism in an image forming apparatus such as a copying machine or a printer, and relates to an improvement of a sheet conveying mechanism in which water droplets due to condensation do not adhere to a heat-fixed sheet.

Generally, a fixing device in an image forming apparatus is widely known as a device for fixing a heat-meltable ink layer by heating a sheet on which an image is formed with a heating roller, a heating belt, or the like.
A heating mechanism that is fixed by a heat roller or a heat belt is known as a relatively simple structure.

  For example, Patent Document 1 proposes a fixing unit that heats at a high temperature as the apparatus becomes smaller and faster. The same document proposes an apparatus for cooling a sheet surface by blowing a sheet heated by a heat roller by a cooling fan disposed in a downstream conveyance path.

  Patent Document 2 discloses an apparatus for cooling a sheet heated by a heat roller by arranging a heat sink on a downstream conveyance guide.

Japanese Patent Laying-Open No. 2010-181667 (FIG. 2) Japanese Patent Laying-Open No. 2007-017616 (FIG. 1)

As described above, a fixing device that heats and fixes a sheet formed with heat-meltable ink in an electrostatic image forming apparatus or the like is widely known. As the speed and resolution become higher, it is required to heat and fix at higher temperatures.
For example, there is a demand for rapid execution from image formation to fixing by shortening warm-up time such as on-demand printing and energy saving, such as a heating method that instantaneously heats a heat roll or a heat belt by a high-frequency heating method.

In this way, by heating the sheet on which the toner image has been transferred in a pressurized state, the melted toner enters the fiber of the paper, and when it is cooled and solidified, it is fixed by the heat applied to the sheet. The problem has been brought.
Insufficient heating temperature and time may cause problems such as poor fixing and damage of part of the image. If the sheet surface is exposed to a high temperature at the required position, the sheet will curl and the sheet surface temperature will be rapidly increased. When it is fixed on the surface, a problem of adhesion of water drops occurs.

Therefore, it is necessary to cool the sheet transported from the fixing unit to a predetermined temperature at the same time as the sheet is heated to a predetermined temperature by the heat fixing unit. If the heating temperature and the fixing temperature are not controlled well, the above-mentioned problem cause.
The optimum values of toner and its additives have evolved and now the problem of incomplete fixing is almost solved. However, higher speed, smaller size, and lower power consumption pose new challenges.

  Conventionally, when an apparatus is activated, the in-machine temperature of the apparatus is kept constant by warming up, and the in-machine temperature of the apparatus is maintained in a standby operation even during an interval during operation of the apparatus. This is a big problem for power saving, and the recent on-demand printing specification requires a reduction in the rise time of the apparatus.

Therefore, an attempt has been made to obtain the fixing temperature instantaneously by employing, for example, an induction heating (IH) device as the fixing unit. However, if the surface temperature of the heated sheet is rapidly cooled, there arises a problem that it is exposed due to a decrease in the saturated water vapor amount.
That is, it is good when the sheet is gradually cooled by a long path from the fixing unit to the paper discharge stacker, but when the sheet is cooled instantaneously by a short path, there is a problem that water droplets adhere to the sheet.

  It is already known that the problem of condensation occurs when the sheet is cooled in such a short time. The reason for this is that the sheet contains moisture in the storage environment, and when heated rapidly after image formation, it gradually evaporates as water vapor (with a delay in time). Condensation occurs due to the drop, and water droplets adhere to the sheet surface.

  Further, water droplets adhering to the sheet surface cause the downstream roller to stain the sheet surface and cause ink rubbing, resulting in poor image quality.

Therefore, conventionally, an attempt has been made to air-cool the sheet surface by disposing a blower fan downstream of the fixing unit.
However, there are problems of power consumption and noise caused by the cooling fan and an increase in the size of the device. Attempts have been made to use a heat sink in place of this cooling fan, but the problems of power consumption and device enlargement cannot be solved.

  The present inventor arranges a roll rotating body that gently reduces the temperature of the sheet surface between the conveying roller body and the heating unit in the sheet unloading mechanism that imparts a conveying force to the sheet downstream of the fixing device (heating unit). This has led to the idea that condensation due to rapid cooling of the sheet surface can be reduced.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing sheet conveying mechanism in an image forming apparatus that can reduce condensation on a sheet conveyed downstream from heat-fixing with a simple structure and can prevent sheet surface contamination.

In order to solve the above problems, the present invention provides a slow cooling roll for reducing the sheet to a predetermined temperature between the fixing unit and a discharge roller disposed downstream thereof, and the surface of the sheet in front of the discharge roller. The temperature is lowered to a predetermined temperature at which no dew is formed, and the sheet is then cooled at the same time as the conveying force is applied to the sheet by the conveying roller.
For this reason, the slow cooling roll is characterized in that the roll surface is formed of a release layer having a relatively high thermal conductivity, and a heat insulating layer is provided between the rotary shaft member and the release layer.

More specifically, the configuration is a sheet transport mechanism in a fixing device that transports a heat-fixed sheet downstream, and includes a fixing unit (14) that heat-presses the sheet and a sheet heated by the fixing unit downstream. A sheet discharge roller (17) conveyed to the side, and a slow cooling roll (20) disposed between the fixing unit and the sheet discharge roller to lower the surface temperature of the sheet to a predetermined temperature.
The slow cooling roll comprises a rotating shaft member (23) that forms a rotation center, a heat insulating layer (25) disposed around the rotating shaft member, a release layer (24) disposed around the heat insulating layer, The release layer is made of a material having a higher thermal conductivity than the heat insulating layer, and the heat insulating layer is made of a material having a lower thermal conductivity than the rotating shaft member and the release layer.

  The present invention provides a slow cooling roll for reducing a sheet to a predetermined temperature between a fixing unit and a paper discharge roller, a rotary shaft member that forms the center of the rotary shaft of the slow cooling roll, and heat insulation disposed on the outer periphery thereof. The layer and the release layer formed on the surface, the release layer has a high thermal conductivity, and the heat insulation layer is formed with a lower thermal conductivity than the release layer and the rotating shaft member. Play.

  Since the sheet heated by the upstream fixing unit is cooled in the order of the slow cooling roll and then the discharge roller, the sheet surface temperature is cooled in at least two stages, and the difference in cooling temperature between the upper and lower rolls is reduced. Is less likely to be exposed.

In particular, since the surface of the slow cooling roll is composed of a release layer having a high thermal conductivity, the rolling sheet rolls while touching the surface to lower the sheet surface. At this time, the water vapor component evaporated from the sheet surface is released so as to diffuse to the periphery.
At the same time, the slow cooling roll is mounted on the apparatus frame from the rotating shaft member through the heat insulating layer, so that heat is not lost rapidly due to heat conduction and is not cooled.

  Furthermore, in the present invention, since the release layer is made of fluororesin and the heat insulating layer is made of melamine foam, the temperature stored in the release layer on the surface is not lost to the outside due to heat conduction from the rotating shaft member, and is stabilized. Thus, the sheet surface temperature can be cooled to a predetermined temperature.

Furthermore, according to the present invention, the apparatus can be reduced in size and cost by setting the outer diameter of the slow cooling roll to be smaller than the outer diameter of the paper discharge roller.
The above-described paper discharge roller can obtain the same effect even if it is a decurling roller that corrects the curling of the sheet.

1 is an explanatory diagram of an overall configuration of an image forming apparatus that employs a fixing sheet conveyance mechanism according to the present invention. FIG. 3 is an explanatory diagram of an overall configuration of a fixing sheet conveyance mechanism according to the present invention. The 1st Embodiment of the cooling roll structure of the conveyance mechanism in the apparatus of FIG. 1 is shown, (a) is sectional drawing, (b) is XX sectional drawing. (A) shows 2nd Embodiment of the cooling roll structure of the conveyance mechanism in the apparatus of FIG. 1, (b) shows 3rd Embodiment of cooling roll structure. The dew condensation generation | occurrence | production experimental data in 3rd Embodiment are shown.

  The present invention will be described in detail below based on the preferred embodiments shown in the drawings. FIG. 1 shows an overall configuration of an image forming apparatus A employing a fixing sheet conveying mechanism B according to the present invention.

In FIG. 1, reference numeral 1 denotes a paper feeding unit, 2 denotes an image forming unit, 3 denotes a paper discharging unit, and the fixing sheet conveying mechanism B is disposed between the image forming unit 2 and the paper discharging unit 3.
The paper feeding unit 1 is arranged in a casing 4 and is composed of a paper feeding cassette 5 that stores sheets for image formation. The illustrated one includes a plurality of cassettes that store sheets of different sizes, and supplies the selected size of sheets to the sheet feeding path 6. A registration roller pair 7 that temporarily waits for a sheet to be sent to the image forming unit 2 is disposed in the sheet feeding path 6.

The image forming unit 2 (shown is an electrostatic image forming mechanism) includes an electrostatic drum 8 (annular roll or belt; photoconductor), a print head 9 (light emitting device), a developing device 10, and a transfer charger 11. It is configured.
Then, a latent image is formed on the photosensitive member 8 by the print head 9, toner (ink) is attached by the developing device 10, and an image is formed on the sheet by the transfer charger 11.

  The paper discharge unit 3 includes a paper discharge path 13 that guides the sheet to the paper discharge port 12, and the fixing sheet conveyance mechanism B is disposed in this path.

In the image forming unit 2, a fixing unit 14 is provided on the downstream side of the transfer charger 11 to fix the toner attached to the sheet surface.
In other words, the toner is fixed by being solidified (cooled) after being melted by heating and pressurizing and penetrating into the fibers of the paper.

For this reason, the fixing unit 14 is formed by a heating roller mechanism that heat-presses the sheet sent from the transfer charger 11 with a heating roller or a fixing belt mechanism that heat-presses the sheet between the fixing belt 15 and the pressure roller 16. The
The illustrated one shows a mechanism for heat-pressing the sheet between the fixing belt 15 and the pressure roller 16, and the fixing belt portion 15 is provided with heating means (not shown) such as an induction heating unit.

The fixing temperature of commonly used toner is 120 ° C. to 180 ° C., and the sheet surface is also close to this. At this time, moisture contained in the sheet evaporates by being heated by the fixing unit 14 and is sent out from the inside of the apparatus by a cooling fan or the like.
Further, the heat-fixed sheet is conveyed to a downstream sheet discharge stacker 21 by a conveyance roller 17 (belt or the like) disposed in the sheet discharge path 13.

  Reference numeral 22 denotes a duplex path, in which the sheet is turned upside down and guided again to the image forming unit 2 to form an image on the back side. The sheet is heated and fixed by the fixing unit 14 in the same manner as the front side, and is then carried out to the paper discharge stacker 21.

[Discharge roller (conveyance roller) structure]
The paper discharge roller 17 is composed of a pair of a driving roller and a driven roller that are in pressure contact with each other. The drive roller 17a is made of a high friction material such as rubber (for example, silicon rubber), and is configured by fitting a rubber roller to a metal shaft member (not shown).
The driven roller 17b is composed of a resin roller (synthetic resin such as Teflon, nylon, or Duracon) and is configured to be in pressure contact with each other by a biasing spring (not shown).
The heat of the sheet conveyed in such a configuration propagates to the roll surface and is propagated from the rotating shaft (metal member) into the apparatus through the apparatus frame.

Therefore, according to the present invention, when a conveying roller (same as the conveying belt) comes into contact with the surface of the sheet heated to a high temperature, the heat is transmitted from the roller surface to the rotating shaft member and is cooled relatively quickly.
As a result, the evaporated water is cooled on the surface of the sheet and is again deposited as water droplets. Therefore, a slow cooling roll (annealing roll) 20 is disposed between the fixing unit 14 and the conveying roller 17 described above.

[Structure of slow cooling roll]
As shown in FIG. 2, a slow cooling roll 20 is disposed between the fixing unit 14 and the paper discharge roller 17. The slow cooling roll 20 is disposed adjacent to the downstream side of the fixing unit 14 and is configured as a single roller or a pair of rollers having a roll surface 20r in contact with the heat-fixed sheet surface.

FIG. 2 shows a case where the first roller body 20a is in contact with the sheet surface (heating surface) and the second roller body 20b is in contact with the sheet back surface. In addition, the slow cooling roll 20 may be composed of only the first roller body 20a (single unit).
In addition, the slow cooling roll 20 is configured to have a roll length L larger than the width size of the maximum size sheet, regardless of the roller pair structure or the roller single structure.
Then, an idling structure that follows the sheet to which the conveying force is applied by the fixing unit 14 and the paper discharge roller 17 is configured. In this case, the roller diameter R20 is configured to be smaller than the paper discharge roller diameter R17 (R20 <R17).

The slow cooling roll 20 (the first and second roller bodies 20a and 20b described above) includes a rotating shaft member 23, a release layer (member) 24 supported by the shaft member and in contact with the sheet surface, and a rotating shaft. It is arrange | positioned between the member 23 and the mold release layer 24, and is comprised by the heat insulation layer (member) 25 which suppresses heat conduction between both. The rotary shaft member 23 is composed of a metal shaft that firmly supports the entire roller structure, and the release layer 24 is composed of a material that is excellent in paper transportability after fixing and easily absorbs heat (good thermal conductivity). .
In an embodiment to be described later, a fluororesin layer (coating film, film layer, sleeve body, etc.) is used. The heat insulating layer 25 is made of a material having a low thermal conductivity (a material having a high heat insulating effect) such as an air layer, a foamed silicon layer, or a melamine foam layer.

With this configuration, the slow cooling roll 20 is rotatably supported in a stable state by an apparatus frame (not shown), and the release layer (layer) on the surface absorbs the surface temperature of the heat-fixed sheet ( The heat insulating layer 24 suppresses (suppresses) the propagation of heat from the rotating shaft member 23 to the apparatus frame or the like due to heat conduction.
Therefore, the slow cooling roll 20 lowers (cools) the heat-fixed sheet to a predetermined temperature, but does not cool it below the predetermined temperature. The predetermined temperature is set according to the outer peripheral diameter and layer thickness of the release layer and the heat conduction characteristics of the heat insulating layer 24.

That is, if the release layer 24 of the slow cooling roll 20 has a large diameter and a large layer thickness, the cooling temperature can be set low, and if the heat conduction characteristic of the heat insulating layer 24 is made of a low material or the layer thickness is set thick, the cooling can be performed. The temperature can be set to a relatively high temperature.
Then, this slow cooling roll 20 is disposed on the downstream side of the fixing unit 14 and on the upstream side of the conveying roller mechanism 17, and the heated and fixed sheet is rapidly cooled by the conveying roller 17, and water droplets adhere to the sheet surface (sheet surface). Reduced amount of saturated water vapor in the atmosphere).
Hereinafter, an embodiment of the slow cooling roll 20 will be described.

[First embodiment of slow cooling roll]
A first embodiment of the slow cooling roll 20 is shown in FIG.
The rotary shaft member 23 is composed of a left rotary shaft member 23R and a right rotary shaft member 23F positioned on the same rotary shaft, and the left and right rotary shaft members 23 are formed symmetrically.
The left and right rotating shaft members 23 are formed with bearing portions 23a having the same left and right diameters, and are supported by bearing members (not shown) of the apparatus frame.
The left and right rotating shaft members 23 are integrally formed with a flange portion 23b. A cylindrical release layer 24 (member) described later is fitted to the flange portion 23.

  The flange portion 23b is formed with a vent hole (not shown) for sending air to the outside. The left and right flange portions 23b are fitted with hollow cylindrical release layers 24 (members). The release layer 24 is formed of a stainless steel (SUS steel) hollow cylindrical body (intermediate cylindrical member) in a sleeve shape, and is integrally formed by fitting rotary shaft members 23R and 23F to the left and right ends of the hollow portion. A cylindrical body is formed.

  The outer surface of the hollow cylindrical body is coated with a fluororesin (tetrafluororesin), and the surface of the release layer 24 has thermal conductivity and toner releasability (easy to peel off toner). It has. Therefore, the release layer 24 configured in this manner lowers the temperature of the sheet surface heated and fixed and sent out to a predetermined temperature. The temperature at this time is set by the peripheral speed of the release layer 24, the film thickness of the fluororesin layer, and the heat conduction characteristics of the sleeve body (SUS).

Air is contained in a hollow portion formed between the release layer 24 and the rotary shaft member 23. The thermal conductivity at this time is zero.
Therefore, the heat propagated from the sheet to the surface of the release layer 24 is not propagated to the rotating shaft member via the air. Even in this case, the heat of the release layer 24 is transmitted to the rotating shaft member 23 through the air convection and the flange portion 23b.

  The slow cooling roll 20 described above is disposed on the downstream side of the fixing unit 14, and on the upstream side of the paper discharge roller 17, the sheet transported by the transport force of the unit (roller or belt) and the paper discharge roller 17 is conveyed. Rotates in sliding contact with the fixing surface. At this time, the surface layer (fluororesin) of the slow cooling roll 20 is rich in thermal conductivity, and the thermal conductivity is set larger than that of the heat insulating layer 25 (air layer) and smaller than that of the rotary shaft member 23 (made of metal). ing.

[Second Embodiment of Slow Cooling Roll]
A second embodiment shown in FIG. 4A will be described. This embodiment employs a roll structure in which the rotary shaft member 23 is constituted by a straight through shaft 23, a heat insulating layer (air layer) 25 is formed on the outer periphery thereof, and a release layer 24 is further formed on the outer periphery thereof.
The release layer 24 is made of stainless steel or other hollow cylindrical body, and is fitted to collar members 26 a and 26 b provided on the rotary shaft member 23. The collar member 26 and the release layer 24 of the hollow cylindrical body are integrated by an adhesive, press-fitting, or the like.

  An air layer 25 is formed between the rotary shaft member 23 and the release layer 24. The air layer 25 may be sealed or an air flow may be formed by forming a vent hole in the collar member 26.

[Third embodiment of slow cooling roll]
In this embodiment, the rotary shaft member 23 is constituted by a metal shaft (rod) having substantially the same diameter, and a bearing portion 23a for bearing support to the apparatus frame is formed at both ends thereof. A heat insulating layer 25 is formed on the rotating shaft member 23 and the outer periphery, and a release layer 24 is formed on the outer periphery thereof. The heat insulating layer 25 is formed of foamed silicon or melamine foam, and the release layer 24 is formed of a fluororesin (FPA) tube.

FIG. 5 is experimental data showing the dew condensation state on the roll surface in the third embodiment.
(I) shows the dew condensation state when the roll surface with a fluorine tube fitted to an iron rotating shaft (without heat insulation layer) is left in contact with the sheet surface heated to 180 ° C. for 5 minutes. Large water droplets were generated on the surface at several locations.

(II) is a state in which a foamed silicon layer (thickness 1 mm) is formed on an iron rotating shaft (same diameter and same material as I), and the roll surface is brought into contact with the sheet surface heated to 180 ° C. as before. Shows the dew condensation state when left for 5 minutes.
Small water droplets were generated on the roll surface at several locations. With visual observation, water droplets smaller than (I) and few occurrences.

  (III) is a state in which a melamine foam layer (thickness 1 mm) is formed on an iron rotating shaft (same diameter and same material as I), and the roll surface is brought into contact with the sheet surface heated to 180 ° C. as before. Shows the dew condensation state when left for 5 minutes. No water droplets are observed on the roll surface.

DESCRIPTION OF SYMBOLS 1 Paper feed part 2 Image formation part 3 Paper discharge part 8 Electrostatic drum 11 Transfer charger 13 Paper discharge path 14 Fixing unit 15 Fixing belt 16 Pressure roller 17 Paper discharge roller 18 Paper discharge roller 19 Paper discharge roller 20 Cooling roller 20a 1 roller body 20b 2nd roller body 23 Rotating shaft member 24 Release layer (member)
25 Thermal insulation layer (member)

Claims (9)

A sheet conveying mechanism in a fixing device that conveys a heat-fixed sheet downstream,
A fixing unit for heat-pressing the sheet;
A paper discharge roller for conveying the sheet heated by the fixing unit to the downstream side;
A slow cooling roll disposed between the fixing unit and the paper discharge roller to lower the surface temperature of the sheet to a predetermined temperature;
With
The slow cooling roll is
A rotating shaft member forming a center of rotation;
A heat insulating layer disposed around the rotary shaft member;
A release layer disposed around the heat insulating layer;
Consists of
The release layer is composed of a material having a higher thermal conductivity than the heat insulating layer,
The sheet insulating mechanism in the fixing device, wherein the heat insulating layer is made of a material having a lower thermal conductivity than the rotating shaft member and the release layer. The slow cooling roll is
2. The sheet conveying mechanism in the fixing device according to claim 1, wherein a temperature difference for reducing the sheet surface temperature is set smaller than a temperature difference for reducing the sheet surface temperature of the paper discharge roller. The slow cooling roll is
The sheet conveying mechanism in the fixing device according to claim 1, wherein the sheet conveying mechanism is a driven roll that comes into line contact with a fixing surface of a sheet fed from the fixing unit and a sheet carried out by the paper discharge roller. The slow cooling roll is
A single roll that contacts the surface of the sheet fed from the fixing unit, or
Alternatively, the sheet conveying mechanism in the fixing device according to any one of claims 1 to 3, wherein the sheet conveying mechanism includes a pair of rolls in contact with the front and back surfaces of the sheet. The sheet conveying mechanism in the fixing device according to claim 1, wherein the heat insulating layer includes at least one of an air layer, a foamed silicon layer, and a melamine foam layer. The rotating shaft member is
It is made of a metal material and consists of a pair of left and right shaft members separated from each other,
The sheet conveying mechanism in the fixing device according to claim 1, wherein the sheet conveying mechanism is made of a metal material. The rotating shaft member is composed of a pair of left and right rotating shaft members that form the same rotating shaft center,
The release layer is a stainless steel or other hollow cylindrical body, and is fitted to a flange member formed integrally with the pair of rotating shaft members,
The sheet conveying mechanism in the fixing device according to claim 1, wherein the heat insulating layer includes an air layer between a release layer of the hollow cylindrical body and the pair of left and right flange members. The rotating shaft member is constituted by a through shaft that forms a rotating shaft center;
The release layer is a stainless steel or other hollow cylindrical body, and is fitted to a flange member formed integrally with a rotary shaft member composed of the through shaft,
The sheet conveying mechanism in the fixing device according to claim 1, wherein the heat insulating layer is configured by an air layer between a release layer of the hollow cylindrical body and the flange member. The rotating shaft member is composed of a metal shaft having substantially the same outer diameter,
The heat insulating layer is composed of a hollow cylindrical body formed of melamine foam fitted to the rotating shaft,
The sheet conveying mechanism in the fixing device according to claim 1, wherein the release layer includes a hollow cylindrical body formed of a fluororesin.

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