JP2984352B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a printer using a heat fixing device as a means for fixing a toner image on a transfer material.

2. Description of the Related Art Conventionally, as a heat fixing device used in this type of image forming apparatus, a contact type fixing device such as a roller or a belt type or a non-contact type fixing device such as an oven type is known.

The roller-type fixing device includes a heating roller formed by coating a surface of a metal cylinder having a heat source therein with a release material such as Teflon, and an elastic layer such as silicon rubber provided so as to be pressed against the heating roller. A pressure roller having a pressure roller having a heat-fusible toner image held in a nip between the rollers, so that the transfer surface of the transfer material is in contact with the heating roller, and the toner image is melted by heat and pressure. Fix on transfer material.

Further, the belt-type fixing device uses a pressure belt in place of the above-described pressure roller, and can increase the contact area of the transfer material with the heating roller, that is, the contact time, as compared with the roller type. It is very suitable for an apparatus using a large-size transfer material such as A0 or A1 size which consumes a large amount of heat due to contact.

On the other hand, an oven-type fixing device is arranged such that a heat source such as a halogen lamp is spaced apart from a transfer path of the transfer material, and the toner image carried on the transferred transfer material is melted by radiation heat from the heat source to transfer the transfer material. Settle on top.

[Problems to be Solved by the Invention] By the way, the contact-type fixing device as described above has an advantage that the structure is relatively simple, there is little risk of fire due to paper jam or the like, and the temperature control is easy. On the other hand, if the speed of the apparatus is to be increased, or if a large-sized transfer material is to be used, the set temperature of the heating roller must be somewhat higher than that of a conventional medium-speed machine. . In this case, when tracing paper is used as the transfer material, there is a problem that wrinkles and undulations occur in the tracing paper during fixing. Further, when a synthetic resin film is used as the transfer material, there is a problem that the film is softened due to a high temperature and a practical copy cannot be obtained.

On the other hand, in an oven-type fixing device, wrinkles and waving do not occur, but when tracing paper is used as a transfer material, tracing paper may be foamed due to rapid heat radiation. Further, when a synthetic resin film is used as a transfer material, when the clogging occurs in the fixing unit, there is a problem that the film is melted and the fixing device is damaged.

Furthermore, in the conventional fixing device, when a semi-fixed copy (a toner image is not completely fixed so that a copied drawing or the like can be easily erased with an eraser) is obtained, the fixing temperature of a fixing roller can be adjusted so as to be semi-fixed. At the time of copying, this is performed by setting the temperature to a low temperature. However, a time is required until the fixing temperature changes to a set value, and an immediate response is impossible.

Means for Solving the Problems To solve the above problems, an image forming apparatus according to the present invention includes a pre-heating device that pre-heats a toner image of a conveyed transfer material immediately before a fixing device along a transfer material conveyance path. Is established,
The fixing temperature of the fixing device is set to such a value that the toner image can be sufficiently fixed on the transfer material having an average heat capacity only when the toner image is pre-heated by the pre-heating device. A switch for manually turning on and off the heating device is provided, and a semi-fixed image can be formed by turning off the pre-heating device. The toner image is heated in advance by the preheating device, and is finally fused on the transfer material by continuing to be heated by the fixing device.
On the other hand, when semi-fixed copying is required, it is realized by turning off the pre-heating device.

Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 shows an example of a fixing unit of an image forming apparatus according to the present invention. Reference numeral 1 denotes a transport belt device for transporting a transfer material carrying a toner image to a fixing unit, and has a transport belt 4 stretched by a pair of rotating rollers 2 and 3 and moving in the direction of arrow A. Reference numeral 5 denotes a transfer material position sensor arranged so as to be pivotable about a pivot 5a. When the leading end of the transfer material conveyed on the belt pushes down the sensor 5, the transfer material is conveyed to that position. Detect what has come.

The fixing unit includes a pre-heating device 11 and a fixing device 21. The pre-heating device 11 is provided at a discharge portion of the conveyor belt device 1, and the fixing device 21 is provided immediately after the pre-heating device 11.

As shown particularly in FIG. 2, the pre-heating device 11 has a guide member 12 for receiving the transfer material conveyed by the conveyor belt 4 on its upper surface, and the guide member 12 has a plurality of ventilation holes.
12a and its upper surface is preferably mirrored. The guide member 12 is designed to have a small heat capacity in order to suppress heating of the transfer material. Heating means 13 is provided apart from the upper surface of the guide member. Heating means
13 is a U-shaped lower opening extending in a direction crossing the transfer material.
It has a reflecting mirror 14 having a V-shaped cross section, and the inner surface of the reflecting mirror 14 is formed as a mirror surface. A long-wavelength rod-shaped halogen lamp 16 as a heat source is disposed in the reflector 14 so as to extend in a direction crossing the transfer material. Reference numeral 19 denotes a guide line extending around the lower opening of the reflecting mirror 14 to prevent the transfer material from contacting or approaching the halogen lamp.

On the other hand, the back side of the guide
A heat exhaust fan 17 is provided through a suitable duct (not shown) so as to cool the air. The exhaust heat fan 17 is constantly energized during operation of the machine. Reference numeral 18 denotes a thermoswitch provided on the back side of the guide member 12, which detects the ambient temperature and controls the halogen lamp 16 to turn on and off to control the heating temperature. For example, the saturation surface temperature of the guide member 12 is set so as to be 270 ° C. or less.

As described above, the fixing device 21 is provided immediately after the preheating device 11. The fixing device 21 is a belt-type fixing device in this example, and has a fixing roller 23 in which the surface of an aluminum cylinder having a halogen lamp 22 built therein is coated with Teflon, and a pressure belt 24 pressed against the fixing roller 23. . Around the fixing roller 23, a rubber blade 28 for cleaning the surface of the fixing roller, an application device 29 for applying silicon oil to the surface of the fixing roller, and a thermistor 31 for detecting the temperature of the surface of the fixing roller are arranged. The pressure belt 24 is stretched between the pair of support rollers 26 and 27 and moves in the direction of arrow B, and immediately receives the transfer material discharged from the pre-heating device 11,
The transfer material carrying the preheated toner image is passed between the fixing roller and the pressure belt 24 and is continuously heated to finally fix the toner image.

Next, the transfer material having the toner image fixed thereon is discharged to the outside of the image forming apparatus by the discharge roller pair 32. Note that a transfer material discharge sensor 33 is provided to detect discharge of the transfer material from the fixing device 21.

In such a configuration, when the leading end of the transfer material conveyed by the conveyance belt 4 urges the transfer material detection sensor 5, an appropriate control works based on a signal from the sensor 5, and a predetermined timing, that is, the transfer material is Pre-heating device
The halogen lamp 16 is energized and turned on immediately before reaching the entrance 11 to preheat the toner image on the transfer material by the radiant heat. What is important here is that only the toner image is heated,
The transfer material itself is not heated to a high temperature. If the radiant heat energy from the halogen lamp 16 is too high, the tracing paper may foam when the tracing paper is used as the transfer material. For this reason, it is preferable that the heat generating element 16 has a small heat capacity, and the reflecting mirror 14 has a small heat capacity whose inner surface is polished.
It is preferable to make the surface a mirror surface so as not to be heated and to cool it with a heat exhaust fan. If the heat capacity of the heating element 16 is large and the guide member 12 is heated, there is a possibility that when the transfer material stops at the pre-heating unit, the transfer material may be ignited or blackened.

When the leading edge of the transfer material is detected by the discharge sensor 33,
At a predetermined timing calculated in advance, that is, immediately after the rear end of the transfer material passes through the preheating device 11, the halogen lamp 16 is deenergized and turned off. Thus, the pre-heating device 11 is energized only when the transfer material is passing through the inside of the device, thereby preventing unnecessary heating of the guide member.

In the above configuration, the fixing temperature of the fixing device 21 is set such that the toner image can be sufficiently fixed on the transfer material having the average heat capacity only when the preheating device 11 preheats the toner image. Set to value. In this way, the preheating device 11 is used when a transfer material having a small heat capacity is used, or when a semi-fixed copy (a toner image is not completely fixed so that a copied drawing or the like is easily erased with an eraser). Can be turned off. Such a switch for turning on and off the pre-heating device 11 can be arranged, for example, on the operation panel of the image forming apparatus, and thereby the operator can switch the switch according to the type of the transfer material or the semi-fixed image copy. The on / off of the preheating device is arbitrarily selected, and a copy image of desired properties can be obtained.

EXPERIMENTAL EXAMPLE 1 In the apparatus shown in FIG.
Inches, a plain paper transfer material thickness 80 g / m ² was conveyed by the conveyor belt 4, the transfer material before the heating device by the operation of the sensor 5
Immediately before entering the printer 11, the halogen lamp 16 is turned on, the toner image on the transfer material is pre-heated by the pre-heating device 11, and subsequently the toner image is completely fixed by pressure heating by the fixing roller 23 and the pressure belt 24. In the pre-heating device, the saturation temperature of the guide member 12 is about 85 ° C. where the transfer material is
° C. The fixing roller used was a 3 mm-thick aluminum material whose surface was coated with Teflon, and was heated to 165 ° C. by a halogen lamp 22 and controlled at a constant temperature. The pressure belt had a Teflon coating on the surface of the silicone rubber, and was arranged so as to be lightly pressed against the fixing roller. Exhaust heat fan 17
The guide member 12 was constantly urged to cool the guide member 12 regardless of the presence or absence of the transfer material. Immediately after the rear end of the transfer material passed the preheating device, the halogen lamp 16 was turned off.

The copy obtained in this manner had a toner image completely fixed, had no wrinkles, and had almost no change in magnification.

Example 2 In Example 1, the pre-heating device was turned off and the thickness of the transfer material was reduced.
Copying was performed using a 75 micron tonering paper, and a semi-fixed copy image was obtained without wrinkles and little change in copy magnification.

Experimental Example 3 When the fixing roller temperature was set to 135 ° C. in the configuration of FIG. 1 and tracing paper and film were copied, a completely fixed image was obtained without wrinkles and no change in magnification.

[Effects of the Invention] As described above, according to the present invention, by providing the pre-heating device, it is possible to provide a high-speed image forming apparatus which has conventionally been difficult with large-size transfer materials.

Further, a fully fixed copy / semi-fixed copy can be easily obtained by turning on / off the preheating device.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a fixing unit of the image forming apparatus according to the present invention, and FIG. 2 is a schematic diagram showing a pre-heating device of FIG. DESCRIPTION OF SYMBOLS 1 ... Conveyor belt device, 5 ... Transfer material position sensor, 11 ... Pre-heating device, 12 ... Guide member, 14 ... Reflector mirror, 17 ... Heat exhaust fan 21 ... Fixing device, 33 ... Discharge Sensor.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-77078 (JP, A) JP-A-55-164865 (JP, A) JP-A-60-194481 (JP, A) (58) Investigation Field (Int.Cl. ⁶ , DB name) G03G 15/20 G03G 13/20 G03G 15/00 303 G03G 21/00 370-384

Claims (1)

(57) [Claims] A preheating device for preheating a toner image of a conveyed transfer material is provided immediately before a fixing device along a transfer material conveyance path, and a fixing temperature of the fixing device is adjusted by the preheating device so that the toner image is pre-heated. Only when heated, a value is set so that the toner image can be sufficiently fixed on the transfer material having an average heat capacity, and a switch for manually turning on and off the preheating device is provided. An image forming apparatus wherein a semi-fixed image can be formed by turning off the image forming apparatus.