JPH06222696A - Image forming device - Google Patents

Abstract

PURPOSE:To make surface-chemical adhesive force between the surface of a heat resistant sheet and the surface of toner weak so that a transfer material is separated from the heat resistant sheet and to prevent offset by heating the toner within the temperature of a toner fixing area and transferring it before the heated and melted toner is perfectly cooled and solidified after the unfixed toner is heated and melted. CONSTITUTION:When a transfer material P on which an image by the unfixed toner T is formed is carried toward a fixing unit 17, it is guided by a transfer material guide 26 and held and carried by a fixing belt 22 and a pressure roller 25. At the same time, the heating element 21a of a thermal head 21 is energized and generates heat, so that the unfixed toner T on the transfer material P is heated and melted at 180 deg.C for 8ms through the belt 22 and the toner image is welded on the transfer material P. Before the melted toner Tm is perfectly cooled and solidified, the transfer material P is separated from the belt 22, carried along a transfer material guide 27, and ejected by paper ejecting rollers 18 and 19 within the temperature of the toner fixing area.

Description

Detailed Description of the Invention

[0001]

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 having a fixing device for fixing an unfixed toner image on a transfer material by heating and melting the toner.

[0002]

2. Description of the Related Art Generally, a fixing device in an image forming apparatus of this type comprises an unfixed toner by a heating roller maintained at a predetermined temperature and a pressure roller rotated by pressing an elastic layer against the heating roller. A fixing method is often used in which a transfer material on which an image is formed is held and conveyed, and toner is heated and melted to fix an unfixed toner image on the transfer material.
However, in the fixing device based on this fixing method, a low temperature offset or a high temperature offset of the toner is likely to occur due to a variation in the fixing temperature due to insufficient heat capacity of the heating roller. Therefore, in this type of fixing device, normally, the heat capacity of the heating roller is set large to prevent toner offset, but when the heat capacity is set large in this way, the heating roller rises (warm-up). ) Takes a long time, and there is a problem that the standby time becomes long at the beginning of use of the device.

Therefore, in order to solve such a problem of the fixing device, conventionally, there is provided an image forming means for forming an unfixed image on a transfer material by a toner made of a heat-meltable resin or the like, and the above-mentioned transfer is performed. An image forming apparatus has been proposed in which a non-fixed toner is fixed to the transfer material by a heating element that generates heat in a pulsed manner through a heat-resistant sheet that moves at the same speed as the material (Japanese Patent Application Laid-Open No. Sho 63). -313182). Further, as a related technique, Japanese Patent Laid-Open No. 1-26367
"Image forming apparatus" described in Japanese Patent Laid-Open No. 9-62, JP-A-62-222
No. 281, “Fixing Method”, JP-A-64-387.
A "fixing device" described in Japanese Patent No. 75 is known.

[0004]

By the way, in the fixing method in the above-mentioned conventional image forming apparatus, the unfixed toner is generated by the heating element which is energized and heated in a pulsed manner through the heat resistant sheet which moves at the same speed as the transfer material. Is heat-welded to the transfer material, and the heat-resistant sheet is separated from the transfer material after the heat-welded toner is completely cooled and solidified.

However, in the fixing device of this fixing system, the heat-resistant sheet can be transferred to the transfer material after the heat-welded toner is completely cooled and solidified, although it can contribute to the reduction of the standby time and the saving of power consumption. Since it is separated from the toner, when the toner is cooled and solidified, the interfacial scientific adhesive force between the surface of the heat-resistant sheet and the toner surface is
It exceeds the condensation power of the toner, and offset easily occurs.

The present invention has been made in view of the above points, and an object thereof is to provide an image forming apparatus capable of preventing an offset due to an interfacial scientific adhesive force between a surface of a heat resistant sheet and a toner surface. To do.

[0007]

According to a first aspect of the present invention, there is provided an image forming means for forming an unfixed image on a transfer material with a toner made of a heat-meltable resin or the like, and at the same speed as the transfer material. In an image forming apparatus in which an unfixed toner is fixed to the transfer material by a heating element that is energized and heated in a pulsed manner through a heat-resistant sheet that moves in The image forming apparatus includes a fixing device configured to separate the heat-resistant sheet from the transfer material within a toner fixing region temperature before being completely cooled and solidified.

According to a second aspect of the present invention, there is provided a heat-resistant sheet having an image forming means for forming an unfixed image on the transfer material with a toner made of a heat-fusible resin or the like, and moving at the same speed as the transfer material. Through a heating element that is energized and heated in a pulsed manner to fix the unfixed toner on the transfer material, heat and melt the unfixed toner, and before the heat-melted toner is completely cooled and solidified, An image forming apparatus for separating the transfer material from a heat resistant sheet, wherein the heating body is maintained at a predetermined temperature during fixing.

According to a third aspect of the present invention, there is provided the image forming apparatus according to the first or second aspect, wherein the heating element is provided with a sliding portion on which the transfer material abuts and slides.

[0010]

According to the first aspect of the invention, after the unfixed toner is heated and melted, the heat-resistant sheet is transferred within the fixing region temperature of the toner before the heat-melted toner is completely cooled and solidified. Since it is separated from the material, the interfacial scientific adhesive force between the surface of the heat resistant sheet and the toner surface is weakened to a value lower than the toner condensing force.

According to the second aspect of the invention, the heating element is maintained at a predetermined temperature during fixing.

According to the third aspect of the invention, the transfer material is separated from the heat resistant sheet and conveyed immediately after the heating portion of the heating element.

[0013]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic sectional view of the entire image forming apparatus according to the embodiment of the present invention. In FIG. 1, the transfer material P stored in a cassette 2 below the apparatus main body 1 is separated and fed by a paper feed roller 3 and sent to a registration roller 5 via a conveyance roller 4.

On the other hand, the image of the original document O set on the contact glass 6 of the apparatus main body 1 is read by the scanner 7 and written as an electrostatic latent image on the photosensitive drum 9 by the writing device 8, and thereafter, An unfixed image is formed (transferred) on the transfer material P fed by the registration roller 5 in synchronism with the electrostatic latent image on the photoconductor drum 9 by toner made of heat-meltable resin or the like.

The unfixed toner image is formed on the transfer material P by a cleaning unit 1 arranged around the photosensitive drum 9 for removing residual toner on the photosensitive drum 9.
0, a discharge lamp 11 for removing the residual charge on the photoconductor drum 9, a charger 12 for uniformly charging the surface of the photoconductor drum 9, and an electrostatic latent image written on the photoconductor drum 9 with toner. The developing unit 13 for forming an image, the transfer charger 14 for transferring the unfixed image formed on the photosensitive drum 9 onto the transfer material P, and the separation for separating the transfer material P on which the unfixed image is transferred from the photosensitive drum 9. Charger 1
This is performed by a well-known electrophotographic process by an image forming unit including 5 or the like.

The transfer material P on which the unfixed toner image is formed and separated from the photosensitive drum 9 in this way is sent to the fixing unit 17 by the transport guide unit 16 to fix the unfixed toner, and then a pair of Paper discharge rollers 18 and 1
9, the discharge tray 2 arranged on the side of the apparatus main body 1
Is discharged above zero.

The fixing unit 17 in this embodiment is
As shown in FIG. 2, the thermal head 21 and the fixing belt 2
2, a belt driving roller 23, a belt driven roller 24, a pressure roller 25, and transfer material guides 26 and 27.

Here, the fixing belt 22 is made of a transparent heat-resistant sheet made of a resin material such as Teflon having a high heat resistance against heat generation at the time of fixing and a high releasability for the heat-melted toner, and thus is formed into an endless belt shape. Is formed in. Further, the fixing belt 22 is endlessly rotated clockwise in FIG. 2 by the belt driving roller 23 and the belt driven roller 24 at substantially the same speed as the conveyance speed of the transfer material P. The thermal head 21 is arranged so that the heating element 21 a faces the inside of the fixing belt 22, that is, the conveyance path of the transfer material P across the fixing belt 22. The heating element 21a is maintained at a temperature of 180 ° C., which is higher than the normal toner fixing temperature (120 ° C.),
In the fixing belt 22, the toner is applied to the heating portion of the heating element 21a.
It is defined as the speed to pass in ms. In addition, JP-A-1
When the temperature (150 ° C.) at which the heating element can be fixed is set as described in JP-A-263679, it takes a long time to heat the toner until sufficient fixability is obtained.

Belt drive roller 2 of thermal head 21
A sliding contact portion 21b with which the fixing belt 22 abuts and slides is provided on the third side portion. The pressure roller 25 is rotatably disposed so as to sandwich the transfer path of the transfer material P and the fixing belt 22 and to be in pressure contact with the heating element 21 a of the thermal head 21. Further, the transfer material guide 26 is
It is arranged so as to guide the transfer material P toward the nip portion between the fixing belt 22 and the pressure roller 25. Furthermore, the transfer material guide 27 transfers the transfer material P carried out from the nip portion between the fixing belt 22 and the pressure roller 25 to the pair of paper discharge rollers 1.
8 and 19 are arranged so as to guide toward the nip portion.

When the transfer material P on which an image is formed by the unfixed toner T is conveyed toward the fixing unit 17 thus constructed, the transfer material P is transferred by the transfer material guide 26.
The fixing belt 22 and the pressure roller 25 pinch and convey the sheet. At the same time, the thermal head 2
The heating element 21 a of No. 1 is energized and heated by on-demand, and the unfixed toner T on the transfer material P passes through the fixing belt 22.
It is heated and melted at 180 ° C. for 8 ms. The heat-melted toner image is fused on the transfer material P. At this time, the surface temperature of the heating element 21a of the thermal head 21 is maintained at the toner fixing region temperature in a range where offset does not occur, as shown in FIG.

The transfer material P thus fused with the toner image is separated from the transfer belt 22 within the toner fixing region temperature before the heat-melted molten toner Tm is completely cooled and solidified. The sheet is conveyed along the transfer material guide 27 and discharged onto the sheet discharge tray 20 by the pair of sheet discharge rollers 18 and 19. Here, the belt drive roller 23
2 is arranged at a position where an angle Θ formed by the transfer belt 22 and the transfer material P satisfies an angle condition that improves the releasability of the transfer material P. Further, the melted toner Tm on the transfer material P is formed by the transfer material P having a pair of discharge rollers 1.
The sheets 8 and 19 are cooled and solidified while being discharged and conveyed toward the discharge tray 20.

[0022]

According to the first aspect of the present invention, after the unfixed toner is heated and melted, the toner is heated within the fixing region temperature of the toner before the heat-melted toner is completely cooled and solidified. Since the transfer force is weakened to less than the toner's condensation force, the transfer material is separated from the heat-resistant sheet and the offset does not occur. .

According to the second aspect of the invention, since the heating element is maintained at a predetermined temperature during fixing, it is possible to reduce power consumption.

According to the third and fourth aspects of the invention, since the heat resistant sheet is provided so that the transfer material is separated from the heat resistant sheet immediately after the heating portion of the heating element, the transfer material is separated from the heat resistant sheet. It is not necessary to provide a separating means for

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a fixing unit in the image forming apparatus according to the embodiment of the invention.

FIG. 3 is a diagram showing an offset occurrence state of the fixing unit in the image forming apparatus according to the embodiment of the present invention.

[Explanation of symbols]

 17 Fixing Unit 21 Thermal Head 21a Heating Element 21b Sliding Part 22 Fixing Belt 23 Belt Drive Roller 24 Belt Driven Roller P Transfer Material T Unfixed Toner Ta Fused Toner

Claims (3)

[Claims] 1. A pulse is provided through a heat resistant sheet having an image forming means for forming an unfixed image on a transfer material with a toner made of a heat-fusible resin or the like and moving at the same speed as the transfer material. In an image forming apparatus in which an unfixed toner is fixed to the transfer material by a heating element that heats up by energizing the toner, after the unfixed toner is heated and melted, the toner is melted before it is completely cooled and solidified. An image forming apparatus comprising a fixing device configured to separate the heat resistant sheet from a transfer material within a fixing region temperature. 2. A pulse is provided through a heat resistant sheet which has an image forming means for forming an unfixed image on a transfer material with a toner made of a heat-meltable resin or the like, and which moves at the same speed as the transfer material. The unfixed toner is fixed to the transfer material by a heating element that heats up in an electric current, and the unfixed toner is heated and melted, and before the heat-melted toner is completely cooled and solidified, An image forming apparatus for separating a transfer material, wherein the heating body is maintained at a predetermined temperature during fixing. 3. The image forming apparatus according to claim 1, wherein the heat generating element is provided with a sliding portion on which the heat resistant sheet abuts and slides.