JPH09166931A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device having excellent heat transfer characteristic and maintaining uniform temperature is the axial direction. SOLUTION: In this device, a sealed fixing member containing a pure fluid substance or the mixture of the pure fluid substance is used. In order to keep the fluid in a two-phase (liquid and vapor) state, heat is applied from inside or outside. When paper 48 having an unfixed image passes between the fixing member 72 and a pressure member, the heat is moved to the paper 48 and the image is welded and fixed. Since the fluid inside the fixing member 72 is in the tow-phase state, the heat is very uniformly and efficiently moved to the paper 48. Therefore, very uniform temperature is maintained along an axial line, and a hot spot caused by the change of the heat transfer efficiency of a heating source and the fixing member 72 and the overheat of the specific part of the fixing member 72 are avoided.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates generally to fusing devices, and more particularly to fusing members which provide a very uniform fusing temperature and high heat transfer efficiency along the fusing member axis for fusing an image to a sheet. Regarding

[0002]

BACKGROUND OF THE INVENTION In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential to render its surface photosensitive. The charged portion of the photoconductive member is then exposed to the light image of the original being reproduced. This exposure selectively erases the charge on the photoconductive member in the illuminated area and records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained in the document. . After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by contact with a developer. Generally, the developer comprises toner particles that are triboelectrically attached to carrier particles. Toner particles are attracted from the carrier particles to the photoconductive member to form a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to copy paper. The toner particles are then heated to permanently fix the toner powder image to the copy sheet.

Modern fusers use heat conduction as the primary heat transfer mechanism for fusing toner to paper. This type of fusing device suffers from a non-uniform axial temperature distribution when sheets of varying widths are fed into the fusing nip. Part of these problems is by shaping the axial profile of the heating lamp, or by using multiple heating lamps to allow control of the axial heating profile. Is being processed.

Since heat transfer is controlled by heat conduction,
Most fusing devices have difficulty transferring energy axially. This inevitably leads to overheating of the rubber layer and is a major cause of shortening the life of the fixing device.

[0005]

It is an object of the present invention to achieve a uniform axial temperature distribution on the surface of the fuser roll, no matter how the width and / or speed of the paper or film changes. is there. Therefore, it is desirable to develop a fixing device that has excellent heat transfer characteristics and that can maintain a uniform axial temperature.

One patent document that is believed to be relevant to various features of the present invention is US Pat. No. 5,119,142. The relevant parts can be briefly summarized as follows.

US Pat. No. 5,119,142 is designed to remove heat from the portion of the belt exiting the fusing nip by a heat exchange roller and return the heat to the portion of the belt entering the nip. A fixing device is disclosed.
The heat exchange roller has a thin thermally conductive layer on the insulating core.

[0008]

SUMMARY OF THE INVENTION The present invention, in a first aspect, provides an apparatus for fixing an image to an image support. The apparatus comprises a pressure member and a heated fusing member, the fusing member being heated such that the axial temperature along the fusing member is substantially constant.

As a second aspect, the present invention provides an electrophotographic printing machine of the type that fixes an image to an image support. The printer comprises a pressure member and a heated fusing member, the fusing member being heated such that the axial temperature along the fusing member is substantially constant.

As a third aspect, the present invention provides a method for heating a fixing member in a printing machine. The method comprises maintaining a substantially pure fluid substance or a mixture of substantially pure fluid substances in a hermetically sealed fixing member, heating the fluid to keep the fluid in a two-phase (liquid and vapor phase) state. And contacting an image support having an unfixed image with a fixing member to fix the image to the image support.

Other toners of the present invention will become apparent upon reading the following description with reference to the accompanying drawings.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION To facilitate a general understanding of the features of the present invention, description will be given with reference to the drawings. In the figures, the same components are identified by the same reference numerals throughout. FIG. 1 is a schematic diagram of an electrophotographic printing machine incorporating features of the present invention. It will be apparent from the following discussion that the phase change fixing device of the present invention can be used in a wide variety of devices, and its use is not limited to the particular embodiments described herein. Ah

As shown in FIG. 1, a document is placed in a document handling device 27 above a raster input scanner (RIS) 28. The RIS 28 includes a document illumination lamp, a lens, a mechanical scanning driving device, and a charge coupled device (CC).
D) Having an array. The RIS 28 captures the entire original document and converts it into a series of raster scan lines. This information is used by the raster output scanner (ROS) 30 described below.
Electronic subsystem (ESS: controller 2)
9).

FIG. 1 is a schematic diagram of an electrophotographic printing machine that generally uses a photoconductive belt 10. Photoconductive belt 10
Preferably comprises an anti-curl support layer, a ground layer coated thereon, and a photoconductive material coated thereon. Belt 10 moves in the direction of arrow 13 to advance its successive sections sequentially and pass through various processing stations located around its path of travel. The belt 10 is stretched around the peeling roller 14, the tension roller 16, and the driving roller 20. When the drive roller 20 rotates, the belt 10 advances in the direction of arrow 13.

First, a portion of the photoconductive surface is charged portion A
Pass through. At charging station A, corona generator 22 charges photoconductive belt 10 to a fairly high, uniform potential.

In the exposure section B, the electronic subsystem (ES
S) That is, the controller 29 receives the image signals representing the desired output image and processes those signals for conversion into a continuous tone or gray scale representation. The continuous tone representation is sent to a modulated output generator, such as a raster output scanner (ROS) 30. The ESS 29 is preferably a stand-alone dedicated minicomputer. The image signal sent to the ESS 29 may originate from the RIS or a computer as described above, in which case the electrophotographic printing machine can serve as a remote printer for one or more computers. Alternatively, the printing press can also serve as a dedicated printer for high speed computers. The signal from the ESS 29 corresponding to the continuous tone image desired to be reproduced by the printing machine is:
Sent to ROS 30. The ROS 30 has a rotating polygon mirror block and a laser. The rotating polygon is preferably a nine-sided polygon. The ROS 30 illuminates the charged portion of the photoconductive belt 10 with a resolution of about 300 ppi or higher. ROS30 exposes the photoconductive belt to ESS29
An electrostatic latent image corresponding to the continuous tone image received from is recorded thereon. Alternatively, ROS 30 may use a linear light emitting diode (LED) array arranged to illuminate the charged portion of photoconductive belt 10 one raster at a time.

After the electrostatic latent image is recorded on photoconductive surface 12, belt 10 advances the latent image to developing station C. The development station uses known techniques to electrostatically attract toner in the form of liquid or powder particles to the latent image. The latent image attracts toner particles from carrier particles to form a toner powder image. As the electrostatic latent image is continuously developed, toner particles are consumed from the developer. Then, the toner particle dispensing device 44 dispenses the toner particles into the developer housing of the developing unit 38.

Continuing with the explanation of FIG. 1, after the electrostatic latent image is developed, the toner powder image existing on the belt 10 advances to the transfer portion D. The copy sheet 48 is fed to the transfer section D by the sheet feeding device 50. The sheet feeding device 50 preferably has a feeding roll 52 that is in contact with the uppermost sheet of the stack 54. The feeding roll 52 rotates to feed the uppermost sheet from the stack 54 to the vertical transport device 56. The vertical transport device 56 sends the paper 48 to the alignment transport device 57.
The aligning and conveying device 57 receives the image from the belt 10 by contacting the sheet 48 with the toner powder image formed on the belt 10 at the transfer portion D, and the sheets 4 are arranged in a timed order.
8 through the transfer section D. The transfer section D includes a corona generating device 58 for dispersing ions on the back surface of the sheet 48. This ionization attracts the toner powder image from the photoconductive surface 12 to the paper 48. After the transfer, the sheet 48 is continuously moved in the direction of the arrow 60 by the belt conveying device 62 and is conveyed to the fixing portion F.

The fixing section F is equipped with a fixing device 70 for permanently adhering the transferred toner powder image to a copy sheet.
The fixing device 70 is composed of a heated fixing roll 72 and a pressure roll 74. The powder image on the copy sheet is fixed to the fixing roll 72.
Contact with. The fixing device 70 will be described later in detail with reference to FIGS.

The paper passes through the fusing device 70 where the image is permanently fixed to the paper. After passing through the fusing device 70, the paper 48 is directed by the gate 80 directly through the exit passage 17 to the finishing device or stacker, or to the duplex copy loop passage 100, specifically to the single paper inverter 82 first. Be directed. That is, if the paper is a single-sided copy paper or a completed double-sided copy paper with both side 1 and side 2 imaged, it is directed directly to the exit passage 17 by the gate 80. However, if the paper is to be duplicated and only the image of side 1 is printed at that time, the gate 80 will cause the inverter 8
It is deflected to 2 and fed into the duplex copying loop passage 100. In that case, the sheet is reversed by the reversing device 82, then recirculated by the acceleration nip 102 and the belt conveying device 110, passes through the transfer section D and the fixing device 70, and receives the image of the surface 2 on the back surface of the double-sided copy sheet. After it is permanently fixed, it exits through the exit passage 17.

After the paper leaves the photoconductive surface 12 of belt 10, residual toner / developer and paper fiber particles adhering to photoconductive surface 12 are removed at cleaning station E. The cleaning section E contacts the photoconductive surface 12 and rotates,
It is equipped with a fiber brush attached to agitate and remove the paper fibers and a cleaning blade to remove untransferred toner particles. The cleaning blade can be modified to the wiper position or the doctor position depending on the purpose.
After cleaning, a discharge lamp (not shown) is placed on the photoconductive surface 1 prior to charging for the next successive imaging cycle.
Flood 2 to erase any residual electrostatic charge remaining on the surface.

Various functions of the copying machine are controlled by the controller (ES
S) 29. The controller 29 is preferably a programmable microprocessor that controls all the above-mentioned functions. The controller 29 controls the comparison of copy sheets, the number of originals to be recirculated, the number of copy sheets selected by the operator, time delay, correction of jam,
Etc. Control of all the typical systems described thus far is provided by conventional control switch inputs from the operator's selected press console. Conventional paper path sensors or switches can be used to obtain information on the position of the original and copy paper.

Next, the fixing device according to the present invention will be described in detail with reference to FIGS. The fixing device according to the present invention is
It is a phase change type fixing device. 2 and 3 are cross-sectional views of two embodiments of the fixing device. The fixing roll 72 is a cylindrical member sealed with a pure working fluid.
A chamber is formed inside. The outside of the fuser roll 72 (FIG. 2) or the fuser roll 7 to heat the working fluid.
A heating source 174 inside two (FIG. 3) is used.

First, at ambient temperature, the pressure in the chamber is made equal to the corresponding saturation pressure. The chamber, previously evacuated of air or any other non-condensable material, is partially filled with working fluid and then sealed. Heating, either internally or externally, raises the fluid temperature to the desired level. In the steady state, the amount of heat added is equal to the amount of heat that escapes to the surroundings. Heat transfer mainly occurs by evaporation of liquid and condensation of vapor.

Table 1 below shows the relationship between saturation temperature and pressure for pure water.

[0026]

Table 1 Temperature (° C) Pressure (psia) 20 0.4 100.6 15 108.9 20 115.6 25 121.3 30 130.7 40

Therefore, for devices using water, at ambient temperature (20 ° C), the chamber must be evacuated to a pressure of 0.4 psia. Temperature is 130.7 ° C
The pressure rises to 40 psia. Therefore,
The chamber must be designed to withstand these two extremes in order to prevent leakage into or out of the chamber.

When the cold (cold) image support contacts the surface of the fuser roll, the image support draws heat from the fuser roll. As a result, the temperature is locally reduced and vapor condensation inside the fuser roll is increased in the contact area. The transfer of energy by latent heat can generate a heat flux that greatly exceeds the heat flux by heat conduction for the same temperature difference. Furthermore, since energy flows only to the cold surface of the contact area, it does not create a large axial temperature gradient and is uniformly heated at any paper width. The high heat transfer coefficient also ensures small temperature fluctuations of the fuser roll, even at very high image carrier speeds.

The image support may be copy paper, a photoreceptor or intermediate transfer belt, or a web-fed film.

The fusing device must accommodate the width and thermal properties of various image supports. Using the device described herein, variations in axial temperature would be essentially eliminated. However, in the case of a fuser of an electrophotographic printer, water is not a suitable working fluid for practice because at typical fusing temperatures (190 ° C) the saturation pressure is 150 psia which is difficult to handle. Propylene glycol, which has a boiling point of 187.2 ° C at atmospheric pressure, is a desirable candidate.

Selective transfer of energy has a very thin, high thermal conductivity which is structurally feasible (eg
Achieved by copper) rolls. An example is shown in FIG. 3 and FIG.
Shown in 4 mil thickness, 42.6 width on a phase change fixing roll containing 115.6 ° C, 25 psia boiling water.
cm, contacting mylar film moving at a speed of 1 inch / sec. The roll has a thickness of 0.25 cm, an outer diameter of 8 cm and is made of copper. The wrap angle of the sheet is 36 ° so that it makes contact over a length of 2.51 cm.

The temperature at which the mylar film enters the winding part is 20 ° C. A three-dimensional thermal voltage simulation program was used to determine the surface temperature distribution in the axial direction when leaving the wound portion. The heat transfer due to condensation of steam is represented by the average heat transfer coefficient h _c obtained from the following equation. h _c = 0.725 [d _l (d _l −d _v ) gh _fg ′ k ³ / DV _l
(T _sv -T _s)] ^1/4 where, c _p = specific heat of the liquid, k = the thermal conductivity of the liquid, the density of d _l = liquid, d _v = density of the vapor, g = gravitational acceleration, h _fg = condensation or evaporation latent heat _{addition,, h fg '= h fg} + 3 / 8c p (T sv -T s), D = roll diameter, v _l = viscosity of the liquid, T _sv = temperature of the saturated steam, and T _s = roll surface temperature.

The above relation is valid for pure saturated vapor condensing inside a horizontal tube (Principles of He
at Transfer by Frank Kreith, 3rd edition).

However, there are two subtleties that make this relational expression a conservative estimate. First, this relational expression assumes the formation of an insulating liquid layer. In practice, the spinning roll will wash away any condensing liquid, so little, if any, liquid will condense just behind the contact area. Secondly, the vapor predominantly condenses along the cold surface of the contact area, but the simulation assumes the same heat transfer coefficient across the entire width of the roll.

Despite these simplifications, the results of FIG. 6 show excellent uniformity of the axial surface temperature of the Mylar film and fuser roll. The fluctuation of the surface temperature of the mylar film is 0.4 ° C or less, and the width of the edge portion is 2 because it is close to the bare surface (slightly hotter) of the fixing roll
It occurs in a narrow strip of cm or less.

FIG. 7 shows the result when a normal fixing device having exactly the same geometric shape and the same operating condition are used. The results of FIG. 6 are also shown for comparison.

In the heating by the ordinary fixing device, the output of the heating lamp is not uniform, so that the surface temperature fluctuates significantly. In the case of this example, 2 having the characteristic curve shown in FIG.
A kW lamp is used. Low emissivity (0.
Despite the cavity of 1), the heating distribution on the surface is
As shown in FIG. 8, the fluctuation in the axial direction is remarkable. The significant improvement in the phase change fuser apparent in FIG. 8 is that the vapor distribution and its relatively smooth flow effectively eliminates any fluctuations in the heating source.

When a narrow sheet is used in a conventional two-roll type fixing device, the temperature on the roll outside the paper path is adjusted unless the profile or shape of the lamp is shaped to some extent or a large number of lamps are used. Usually rises to values much higher than desired. The phase change fuser removes heat from the hot areas outside the paper path by evaporation without using shaped heating means or multiple heating devices, and transfers this heat to areas below the width of the paper where condensation occurs. A uniform axial temperature is maintained by carrying.

[Brief description of the drawings]

FIG. 1 is a schematic front view of an electrophotographic printing machine incorporating a fixing device of the present invention.

FIG. 2 is a sectional view of the fixing device of the present invention.

FIG. 3 is a sectional view of a second embodiment of the fixing device of the present invention.

FIG. 4 is a front view showing a part of a heating roll around which a mylar film is partially wrapped.

5 is a plan view showing a heating roll and a mylar film shown in FIG. 4. FIG.

FIG. 6 is a graph of an axial surface temperature of a phase change type fixing device and a Mylar film in contact with the fixing device.

FIG. 7 is a graph showing the difference between the axial surface temperature of the phase change fixing device and the mylar film in contact with it and the axial surface temperature of the normal fixing device and the mylar film in contact with it.

FIG. 8 is a graph showing a heating profile of a lamp and heating of a roll surface in the case of a normal fixing device.

[Explanation of symbols]

 A charging section B exposure section C developing section D transfer section E fixing section F cleaning section 10 photoconductive belt 12 photoconductive surface 13 belt moving direction 14 peeling roller 16 tension roller 17 exit passage 20 drive roller 22 corona generating device 27 original Handling device 28 Raster input scanner (RIS) 29 Controller (ESS) 30 Raster output scanner (ROS) 38 Developing unit 44 Toner particle dispensing device 46 Developer housing 48 Copy paper 50 Paper feeder 52 Feed roll 54 Stack 56 Vertical transport device 57 Aligning Conveying Device 58 Corona Generating Device 60 Paper Moving Direction 62 Belt Conveying Device 70 Fixing Device 72 Heated Fixing Roll 74 Pressure Roll 80 Gate 82 Paper Inverter 100 Double-sided Copy Loop Passage 102 Acceleration Nip 110 Belt Conveying Device 150 Mylar film 172 Phase change type fixing roll 174 Heating source 178 Evaporation 180 Condensation

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Claims (3)

[Claims] 1. An apparatus for fixing an image to an image support, comprising a pressure member and a heating fixing member, wherein the fixing member has a temperature substantially constant along the axial direction of the fixing member. The fixing member is heated so that the fixing member is rotatably supported by the sealed cylindrical member, the fluid contained in the cylindrical member, and the fluid so as to maintain the fluid in a two-phase state. A fixing device having a heating source that operates. 2. A printing machine of the type for fixing an image to an image support, comprising a pressing member and a heating fixing member, wherein the fixing member has a temperature substantially along the axial direction of the fixing member. The fuser member is heated to a constant temperature and the fuser member is rotatably supported in a sealed cylindrical member, a fluid contained in the cylindrical member, and the fluid to maintain the fluid in a steady state. A printing machine having a heating source that acts on a fluid. 3. A method of heating a fuser member in a printing press, comprising retaining a substantially pure fluid substance or a mixture of substantially pure fluid substances in a sealed fuser member and heating the fluid. A method comprising contacting a sheet having an unfixed image in a two-phase state with the fixing member to fix the image to the sheet.