JPH0883009A - Fixing unit for electrophotographic printer - Google Patents

Abstract

PURPOSE: To prevent curing and to achieve a stack in satisfactorily neat alignment by absorbing the heat of a medium heated to a fixed temperature by pressing a heater to its toner transfer side by heat conduction using a cooling means provided on the downstream side from the heater. CONSTITUTION: A support 61 is provided with a drive roller 65 and a film-holding roller 67 with a heater part 63 between them, and a belt-like heat-resistant film 69 is stretched between the rollers 65 and 67. Also, the support 61 on the downstream side from the heater 63 in the direction in which the medium is carried, is provided with a cooling rod (cooling means) 85, which is made of aluminum, etc., and has a contact length over the entire width of the medium 87. Because the high temperature medium 87, which has passed the heater 63, is cooled by coming into contact with the cooling rod 85 via the film 69, the temperature decreases to a temperature which is almost the same as outside air temperature. Therefore, fused toner 97 is fixed to the medium 87, in addition, the temperature of the medium 87 itself returns to the temperature that the medium 87 had before heated, and consequently it restores paper elasticity. Because the medium is ejected from a fixing unit 95 in this condition, a curl does not occur in the medium 87, and the media can be accumulated in a stacker while aligning.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an electrophotographic printer, and more particularly to the structure of its heating element.

[0002]

2. Description of the Related Art An electrophotographic printer is equipped with a fixing device for fusing and fixing toner adsorbed on an electrostatic latent image. This type of fixing device, which is a flat type fixing device in a planar state, will be described with reference to FIG. FIG. 4 is a schematic diagram of the configuration of a conventional flat type fixing device. A drive roller 5 and a film holding roller 7 are provided on the support 1 with the heater portion 3 interposed therebetween, and a belt-shaped heat-resistant film 9 is laid over the drive roller 5 and the film holding roller 7. A backup drive roller 13 and a belt holding roller 15 are provided on the backup support 11 provided to face the support 1, and a backup rubber belt 17 is stretched over the backup drive roller 13 and the belt holding roller 15. Further, a backup base 19 is slidably provided on the support 1 via a guide rod 21, and the backup base 19 is biased toward the heater section 3 by a spring 23. The flat type fixing device (fixing device) 25 configured as described above is fed with a medium 27 such as paper sent in the direction of arrow a from an electronic process unit (not shown), and the medium 27 removes unfixed toner 29 from static electricity. Have been adsorbed. The medium 27 inserted into the fixing device 25 is conveyed while being pressed from the front and back by the film 9 and the backup rubber belt 17, and is heated through the film 9 by the heater unit 3 having a constant fixing temperature, so that the toner 29 is fixed. Done.

FIG. 5 is an enlarged view of the heater section. A holder 31 made of heat-resistant resin is provided with a heating element 33 having a predetermined resistance value, and the heating element 33 has electrodes 35a at both ends,
It is heated by applying a voltage to 35b. A thermistor 37 is joined to the heating element 33,
Detects the temperature of the heating element 33. FIG. 6 is an explanatory diagram showing the temperature distribution of the heater section. In the figure, the horizontal axis represents the widthwise position of the heater portion, and the vertical axis represents the surface temperature thereof. Also, T
₀ is the ambient temperature, T ₁ is the temperature of the holder 31, and T _F is the fixing temperature. Therefore, the medium 27 passing through the heater unit 3
The toner adsorption surface is heated by this temperature distribution, and the toner 29 is fused and fixed.

FIG. 7 is a schematic diagram of the configuration of an electrophotographic printer having a conventional fixing device mounted therein. In the electrophotographic printer 39, when printing is started, the medium 27 is fed by the hopping roller 41, the position is adjusted by the registration roller 43, and then the image formed by the toner 29 by the LED head 45 and the electrophotographic process. Is the transfer roller 47
It is transferred onto the medium 27 that passes between them. The medium 27 on which the image is formed is conveyed to the fixing device 25, and the toner 29 is melted and fixed by heating, and then is guided to the first discharge roller 49. And if you want to face up more,
The sheets are stacked below the discharge guide 51 in the direction of arrow b. On the other hand, in the case of face down, the discharge guide 5
1 is rotated and the medium 27 is guided upward, then passes through the second discharge roller 53 in the direction of arrow c, and is stacked on the face-down stacker.

[0005]

However, in the electrophotographic printer 39 having the fixing device 25 described above, the medium 2
When 7 is stacked on the face-down stacker, the medium 27 that remains hot after passing through the first discharge roller 49 is
Since the ejection guide 51 bends the medium 27 at a steep angle, there is a problem in that the medium 27 whose elasticity (waist) is lowered due to high temperature is easily curled and is not properly aligned and stacked. The present invention has been made in view of the above circumstances, and provides a fixing device for an electrophotographic printer that does not curl when a medium discharged at a high temperature is bent at a steep angle. The purpose is to enable stacking always in good alignment.

[0006]

In order to achieve the above object, a fixing device of an electrophotographic printer according to the present invention has a structure in which a heater portion is pressed against a toner transfer surface of a medium in a transport state,
In the flat type fixing device for fixing the toner to the medium, a cooling means for absorbing heat from the medium heated to the fixing temperature by passing through the heater portion by heat conduction is provided on the downstream side of the heater portion in the medium conveying direction. It is characterized by.

[0007]

The high temperature medium that has passed through the heater portion is cooled by contacting the cooling means having a temperature sufficiently lower than that, and the medium itself returns to the temperature state before heating, and the elasticity of the medium (for example, paper) ( Since the waist is restored, curling does not occur in the medium even if the medium is bent at a steep angle immediately after being ejected from the fixing device by an ejection guide or the like.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a fixing device for an electrophotographic printer according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic view of the configuration of a fixing device of the electrophotographic printer of the present invention. The drive roller 6 is sandwiched between the support 61 and the heater 63.
5, the film holding roller 67 is provided, the drive roller 6
5. A belt-shaped heat resistant film 69 is stretched over the film holding roller 67. A backup drive roller 73 and a belt holding roller 75 are provided on a backup support body 71 provided to face the support body 61, and a backup rubber belt 77 is stretched over the backup drive roller 73 and the belt hold roller 75. Further, a backup base 79 is slidably provided on the support body 71 via a guide rod 81, and the backup base 79 is biased toward the heater section 63 by a spring 83.

A cooling rod 85 as a cooling means is provided between the heater portion 63 and the driving roller 65, that is, on the support 61 on the downstream side of the heater portion 63 in the medium conveying direction, and the cooling rod 85 sandwiches the film 69. And is disposed on the opposite side of the medium 87. The cooling rod 85 is a rod-shaped body made of a material having a large heat capacity, for example, a metal such as aluminum or copper, and has a length in contact with the entire width direction of the medium 87 which is a direction orthogonal to the transport direction of the medium 87. There is. The cooling rod 85 transports thermal energy by simply radiating heat from the surface of the rod-shaped body.
That is, in addition to cooling, a cooling fin may be provided on the outer surface other than the contact surface to improve the heat radiation efficiency.

Further, the cooling rod 85 may be of a heat pipe type for transporting heat energy by utilizing the heat transfer coefficient of large boiling and condensation. As a heat pipe type of this kind, for example, a fibrous or porous substance or fin-shaped groove with a small gap is provided on the inner peripheral wall of a sealed tube to transport the working fluid by a capillary tube. A so-called wick, which is performed by a phenomenon, can be used. In this wick, the working fluid in the wick boils and evaporates due to the heat transmitted from the high temperature part, and is transported in the form of vapor at high speed to the low temperature part, where it condenses into a liquid, penetrates into the wick, and becomes a capillary phenomenon. The heat energy is transported by flowing again to the high temperature part.

On the other hand, between the backup table 79 and the backup drive roller 73, that is, on the backup support 71 on the downstream side of the backup table 79 in the medium transport direction, a cooling backup table 89 that operates independently of the backup table 79. Is slidably provided via a guide rod 91, and the cooling backup base 89 is biased toward the cooling rod 85 by a spring 93. That is, the medium 87 is conveyed while being pressed by the cooling rod 85 and the cooling backup base 89 with the front and back sides being sandwiched by the film 69 and the backup rubber belt 77. Support 61, heater 63, drive roller 65, film holding roller 67, film 69, backup support 71,
Backup drive roller 73, belt holding roller 75,
The fixing device 95 is configured with the backup rubber belt 77, the backup table 79, the cooling rod 85, and the cooling backup table 89 as main members.

FIG. 2 is an explanatory view showing a temperature change when the medium passes through the fixing device. In the figure, the horizontal axis represents the position of the fixing device in the medium transport direction, and the vertical axis represents the temperature of the medium. Conventionally,
When the cooling rod 85 is not provided, the medium 8 reaching the heater portion 63
7 is heated from the ambient temperature T ₀ to the fixing temperature T _F all at once, the toner 97 (see FIG. 1) is melted, penetrates into the inside of the medium 87, and so-called fixing starts. After passing through the heater portion 63, the temperature gradually decreases due to natural heat dissipation as shown by the dotted line 99. Therefore, the medium 87 is
(See FIG. 7) Even when the discharge guide 51 (see FIG. 7) is reached, the medium temperature does not drop much.

On the other hand, when the cooling rod 85 is provided as in this embodiment, the high temperature medium 87 passing through the heater portion 63 comes into contact with the cooling rod 85 having a temperature sufficiently lower than that through the film 69, Since it is cooled, the temperature sharply decreases as shown by the solid line 101 and drops to almost the same temperature T _C as the outside air. Therefore, the melted toner 97 is fixed to the medium 87, and the medium 87 itself returns to the temperature state before heating, so that the elasticity (stiffness) of the paper is restored. In this state, the first discharge roller 49 (see FIG. 7) and the discharge guide 51
(See FIG. 7), curling does not occur even when discharged to the face-down stacker.

As described above, according to the fixing device 95 of the electrophotographic printer according to the above-described embodiment, the cooling rod 85 serving as a cooling unit is provided on the downstream side of the heater unit 63 in the medium conveying direction, and the medium temperature is set to the heater unit 63. Temperature T _C sufficiently lower than the temperature T _{F of}
The medium 87 is ejected from the fixing device 95.
The curl does not occur in the stacker, and the stacker can be aligned and accumulated in the stacker.

Next, another embodiment of the fixing device of the electrophotographic printer will be described. FIG. 3 is a schematic configuration diagram of a fixing device according to another embodiment. The same members as those shown in FIG. 1 are designated by the same reference numerals, and a duplicate description will be omitted. In this embodiment, the cooling rod 85 and the cooling backup table 8 described above are used.
9 is not used, the drive roller 103 and the backup drive roller 105 have the same cooling effect, and other configurations are the same as those of the fixing device 95. That is, the drive roller 103 and the backup drive roller 105
Is made of a material having a large heat capacity and good thermal conductivity, such as a metal such as aluminum or copper, and is urged by a spring 107 in a pressure contact state. In other words, the high temperature medium 87 that has passed through the heater portion 63 is pressed by the drive roller 103 and the backup drive roller 105 in a sandwiched state via the film 69 and the backup rubber belt 77, and is cooled and conveyed.

According to the fixing device 109 according to this embodiment,
Since the medium 87 is pressed by the drive roller 103 and the backup drive roller 105 having large heat capacity from the front and back sides, the heat radiation area is increased, and the heat radiation efficiency can be improved.
Further, since the medium 87 can be cooled and conveyed without adding the cooling rod 85 and the cooling backup base 89, the apparatus can be made compact. The drive roller 103 and the backup drive roller 105, like the cooling rod 85, simply radiate heat from the surface, and may be provided with cooling fins on the outer surface other than the contact surface, for example, both side surfaces. It may be of the form.

[0017]

As described above in detail, according to the fixing device of the electrophotographic printer of the present invention, the cooling means for absorbing heat from the medium heated to the fixing temperature by heat conduction is provided in the medium conveying direction of the heater part. Since it is provided on the downstream side, the medium heated to a high temperature by the heater does not reach the discharge guide etc. as it is at a high temperature, and the elasticity (waist) of the medium returns to that before fixing by being cooled, Curling does not occur even if it is bent sharply to be discharged to the face stacker. As a result, stacking can always be performed in a good alignment state.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a fixing device of an electrophotographic printer of the present invention.

FIG. 2 is an explanatory diagram showing a temperature change when a medium passes through a fixing device.

FIG. 3 is a schematic configuration diagram of a fixing device according to another embodiment.

FIG. 4 is a schematic diagram of a configuration of a conventional flat type fixing device.

FIG. 5 is an enlarged view of a heater unit in a conventional flat type fixing device.

FIG. 6 is an explanatory diagram showing a temperature distribution of a heater unit.

FIG. 7 is a schematic diagram of a configuration of an electrophotographic printer in which a conventional fixing device is mounted.

[Explanation of symbols]

 63 heater part 65 drive roller 69 film 73 backup drive roller 77 backup rubber belt 85 cooling rod (cooling means) 87 medium 89 cooling backup stand 95 fixing device 97 toner

Claims (3)

[Claims] 1. A flat-type fixing device that presses a heater portion against a toner transfer surface of a medium in a transport state to fix the toner on the medium, and is heated to a fixing temperature by passing through the heater portion. A fixing device for an electrophotographic printer, characterized in that cooling means for absorbing heat from the medium by heat conduction is provided on the downstream side of the heater portion in the medium conveying direction. 2. A predetermined section in which a medium is conveyed, a belt-like film and a backup rubber belt that are in close contact with the front and back of the medium are moved together with the medium, and a heater unit that presses the toner transfer surface of the medium fixes the film. In a flat-type fixing device that is disposed on the opposite side of the medium with the cooling medium interposed therebetween, a cooling rod that is in contact with the medium via the film is provided on the downstream side of the heater in the medium conveyance direction, and the cooling rubber belt is used to interpose the cooling rod. A fixing device for an electrophotographic printer, wherein a cooling backup stand for pressing a medium toward the cooling rod is provided so as to face the cooling rod. 3. A drive roller for driving a belt-shaped film and a backup drive roller for driving the backup rubber belt are made of a material having good thermal conductivity, and a medium heated to a fixing temperature is used as the film and the backup. A fixing device for an electrophotographic printer, characterized in that the drive roller and the backup drive roller are arranged so as to be pressed against each other via a rubber belt.