JPH02131268A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a pressure roller from rising in temperature excessively and to separate a fixation film and a transfer material after sufficient cooling by setting the stop point of electric feeding to a heat generation body and the start point of fixation film rewinding differently. CONSTITUTION:This device has a fixation film take-up means 27 which uses the fixation film 23 while taking up the film in order, a fixation film rewinding means 24 which rewinds the fixation film 23 when fixation is not performed, and a means which stops feeding electricity to the heat generation body 21 when the fixation film is rewound. Then the stop point of electric feeding to the heat generation body 21 and the start point of fixation film rewinding are made different. Thus, both the start and stop points are made different, so the pressure roller 22 is prevented from rising in temperature too much and the fixation film 23 and transfer material P are separated after sufficient cooling.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to an image forming apparatus that forms an image on a transfer using heat-melting toner and heat-fixes the image.

(Prior Art) Conventionally, a fixing device used in this type of device consists of a heating roller maintained at a predetermined temperature, and a pressure port having an elastic layer that presses against the heating roller. A roller fixing method is often used in which a transfer material on which an unfixed toner image is formed is heated while being supported and conveyed.

However, in the roller fixing method, firstly, it is necessary to maintain the heating roller at an optimal temperature, and secondly, it is necessary to heat the transfer material as well, so the heat capacity of the heating roller becomes large. Third, as a result, the energy required for fixing increases, and unnecessary heat is generated, resulting in an increase in temperature inside the machine. Recently, in order to solve the above-mentioned drawbacks of the roller fixing method, the transfer material is brought into close contact with a heating element via a fixing film that moves at the same speed as the conveyance speed of the transfer material, and the undefined toner image on the transfer material is fixed. A film fixing method has been proposed in which the fixing film is heated and melted to fix it, and the fixing film is sequentially rolled up and used. (i!Problem to be solved by the invention) However, in the film fixing method described above in which the fixing film is used while being wound up sequentially, if electricity is applied when the paper is not passing through, the temperature of the pressure roller rises, and the There is a problem in that the transfer material and fixing film cannot be separated, resulting in high-temperature offset.

The present invention attempts to solve these problems. That is, an object of the present invention is to provide an image forming apparatus in a film fixing method that can prevent excessive temperature rise of the pressure roller and separate the fixing film and transfer material after sufficient cooling. be. [Means for Solving Problem n] In order to achieve the above object, the present invention uses a pressurized conveying means that rotationally drives an unfixed toner image on a transfer material while pressing it against a heating body. a heating step of heating and melting the toner image by bringing the transfer material into close contact with the heating body via a fixing film that moves at the same speed as the conveyance speed of the fixing film; and a cooling separation step for separating the transfer material from the transfer material, a fixing film winding means for using the fixing film while sequentially winding it, and a fixing device for rewinding the fixing film when the fixing film is not fixed. The image forming apparatus has a film rewinding means and a means for stopping energization to a heating element when rewinding the fixing film, and furthermore, the time point at which energization to the heating element is stopped and the time point at which the fixing film rewinding starts are different. Made it different.

[For production]

According to the present invention, the electricity supply to the heating element is stopped after the transfer material passes through the heating section, and the fixing film is rewound after the transfer material is completely separated from the fixing film, thereby reducing the temperature rise of the pressure roller. It can be reduced. [Example] The drawing shows an example of the present invention. FIG. 1 shows an overview of the entire apparatus. In the figure, reference numeral 1 denotes a document mounting table made of a transparent member such as glass, which scans the document G by reciprocating in the direction of arrow a. A short-focus, small-diameter imaging element array 2 is arranged directly below the document platform 1, and the document G placed on the document platform 1 is illuminated by an illumination lamp 7, and the reflected light image is reflected from the array 2. A slit is exposed onto the photosensitive drum 3 by . Note that this photosensitive drum 3 is indicated by arrow b.
Rotate in the direction of . A charger 4 uniformly charges the photosensitive drum 3 coated with, for example, a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer. On the photosensitive drum 3 uniformly charged by the charger 4, an electrostatic latent image is formed by image exposure by the array 2.

This electrostatic latent image is visualized by a developing device 5 using toner made of a resin or the like that softens and melts when heated. On the other hand, the transfer material P such as transfer paper stored in the cassette S is rotated by a pair of feeding rollers 6 and the photosensitive drum 3, which are pressed against each other in the vertical direction and rotated at a timing synchronized with the image on the photosensitive drum 3. It is fed onto the photosensitive drum 3 by the conveying roller 9.
Then, the unfixed toner image T formed on the drum 3 is transferred onto the transfer material P by the transfer discharger 8.

Thereafter, the transfer material P separated from the drum 3 by a known separation means is transferred to the fixing device 20 by the conveyance guide 10.
After being guided to a heating and fixing process, it is discharged onto a tray 11. The residual toner on the photosensitive drum 3 is removed by a cleaner 12.
removed by

FIG. 2 is an enlarged view of the fixing device 20 of FIG. In the figure, reference numeral 21 denotes a heating element, which is a heat-resistant and electrically insulating base material such as alumina, or a composite material containing the same, and is coated on the lower surface of the base material with, for example, Ta. It has a linear or band-shaped heat generating layer 28 made of N or the like, and further,
As a sliding protection layer on the surface, for example, Ta. O. is formed. The lower surface of the heating element 21 is smooth, and
The front and rear ends are rounded to enable sliding on the fixing film 23. The fixing film 23 is made of PET as a base material, is heat-resistant treated, and is formed to have a thickness of about 6 μm, for example, and is wound around a delivery shaft 24 so as to be delivered in the direction of arrow C. The film 23 is in contact with the surface of the heating element 21,
It is wound onto a winding shaft 27 via a separating roller 26 with a large curvature. The heat generating layer 28 of the heating element 21 has a small heat capacity, and each time it is energized in a pulsed manner, the temperature is instantaneously raised to around 300°C. Transfer paper detection lever 25 detects the leading and trailing edges of transfer material P.
By detecting this with the transfer paper detection sensor 29, the heat generating layer 28 is energized at the appropriate timing when necessary.

At that time, the transfer material P is detected by the paper feed sensor of the image forming device, etc.
The power supply to the heating element 21 may be controlled using position detection or the like.

On the other hand, the pressure roller 22 has an elastic layer made of silicone rubber or the like on a core material made of metal or the like, and is driven by a drive source (not shown) and guided by the conveyance guide 10. The unfixed toner image T is brought into close contact with the heating element 21 via a fixing film 23 that moves at the same speed as the transfer material P. In FIG. 2, 30 is a fixing film sensor, 32
is a guide.

In this embodiment, the temperature of the heat generating layer 28 of the heat generating element 21 rises instantaneously, so there is no need for preheating, and there is very little heat transfer to the pressure roller 22 during non-fixing. Also, during fixing, the fixing film 23 and the toner image T5 transfer material P are interposed between the heat generating layer 28 and the pressure roller 22, and the heat generation time is short, so that a rapid temperature gradient occurs. The temperature of the pressure roller 22 is difficult to rise, and its temperature is maintained below the melting point of the toner even if continuous image formation is performed to the extent required for practical use.

In the apparatus of this embodiment having such a configuration, the toner image T made of heat-fusible toner on the transfer material P is first heated and melted by the heat-generating layer 28 of the heat-generating element 21 via the fixing film 23. In particular, the surface layer reaches a temperature well above the melting point and completely softens and melts. At this time, the heat generating layer 28, the fixing film 23, the toner image T, and the transfer material P are brought into close contact with each other by the pressure roller 22, and heat is efficiently transferred.

Thereafter, the heat generation layer 28 of the heating element 21 stops generating heat, and the transfer material P is conveyed and separated from the heat generation layer 28, so that the toner image T radiates heat and is cooled and solidified again.
After passing through the separation roller 26 having a large curvature, the fixing film 23 is separated from the transfer material P. At this time, in this example,
Since the temperature of the pressure roller 22 is maintained lower than the melting point of the toner, it is possible to promote heat dissipation from the toner image. Therefore, the time required for cooling is shortened.
The device can be made smaller. Furthermore, as described above, the toner T completely softens and melts once and then solidifies again, so the cohesive force of the toner is very large and it behaves as a group. In addition, when heated and softened and melted, the pressure roller 22
Since at least a part of the toner image T penetrates the surface layer of the transfer material P and is cooled and solidified as it is, it is not offset to the fixing film 23.
It is fixed onto the transfer material P.

Here, a note will be made regarding the expression of the state of the toner described above.

The temperature conveniently expressed as the melting point of the toner means the minimum temperature required for the toner to be fixed, and there are cases where the viscosity decreases to the extent that it can be said to be melted at the lower limit fixing temperature.
In some cases, the viscosity decreases to the extent of softening. Therefore, even if it is conveniently expressed as melting when fixing,
In reality, it may indicate a decrease in viscosity to the extent of softening. Similarly, even if it is conveniently expressed that the toner has been cooled and solidified, depending on the toner, it may not be said that it has solidified.
There may be cases where increasing the viscosity is more appropriate. FIG. 3 is an enlarged view of the heating element 21 in FIG. 2. In the figure, 50 is an electrode, 51 is a surface protection layer, 52 is an insulating layer, 53 is a heat insulating layer, 54 is a substrate, and 55 is a temperature sensing element (thermistor).

That is, the heat insulating layer 53 is made of a material with low thermal conductivity, heat resistance, and electrical insulation, such as Bakelite, and prevents the heat generating layer 28 from dissipating heat. The temperature sensing element 55 has a small heat capacity and is placed close to the heat generating layer 28 with a thin insulator interposed therebetween. The auxiliary heating layer 56 is made of a resistance heating element such as a TaJ thin film, and is connected to the temperature sensing element 55 through a thin insulator.
and is arranged close to the heat generating layer 28. The heating element 21 heats the toner in the heating section H via the fixing film 23 (see FIG. 2).

FIG. 4 is a block diagram of control of the fixing device 20 of FIGS. 1 and 2.

The control circuit 60 includes a paper discharge sensor 81, a paper feed sensor 82,
A transfer paper detection sensor 29 (see FIG. 2) is connected to detect the timing of paper feeding, ejection, and entry of the transfer material into the fixing device 20 (see FIGS. 1 and 2). Further, the pressure release solenoid 83 releases the pressure on the pressure roller 22 (see FIG. 2), and the fixing film rewind clutch 85 is operated to rewind the fixing film 23 (see FIG. 2). . Note that the timing of the control will be described later.

The control circuit 60 performs time management according to the timer 80, and performs temperature control according to the temperature detection element 55 (see FIG. 3). Further, the control circuit 60 detects the outputs of the paper discharge sensor 81, the paper feed sensor 82, and the transfer paper detection sensor 29, and at a predetermined timing, energizes the heat generating layer 28 of the heat generating element 21 from the power source 61. The state of the pressure roller 22 and the feeding direction of the fixing film 23 are controlled.

Next, the control timing of the control circuit 60 will be explained according to the timing diagram of FIG. 5 and the flowchart of FIG. 6.

The transfer material is fed 101, the paper feed sensor 82 is turned on 102, and the control circuit 60 is operated for a predetermined time to
(See Fig. 5) After 103, turn off the fixing film rewind clutch 85.
into the winding state and turn off the pressure release solenoid 83.
105, the pressure roller 22 and the heating layer 28 of the heating element 21 come into contact with each other. Thereafter, energization to the heating element 21 is started 106. When the transfer material enters the fixing device 20, the transfer paper detection sensor 29 turns on, and then the paper ejection sensor 8
1 is also turned ON. Then, the transfer material is detected by the transfer paper detection sensor 2.
9 and the sensor 29 is turned OFF 107, the sensor 29 is turned OFF at 108 (after a time determined by the position of the transfer paper detection sensor 29, the position of the heating section, and the speed of the transfer material) after a time tz (see FIG. 5). After the discharge sensor 81 is turned off, the pressure is released by turning on the pressure release solenoid 83 at 110, and the fixing film winding unwinding clutch 85 is turned on. ．． Then, return to the initial state and repeat this action. By doing this, you can reduce power consumption by eliminating unnecessary energization. Next, another example of operation will be explained. At the time when the fixing film 23 is folded back, the transfer paper detection sensor 29 is used to detect that the sensor 29 is OF.
After F L, the power supply to the heating element 21 is stopped after a time ti, and a time tz (time determined by the separation position of the transfer paper detection sensor 29 and the fixing film 23 and the speed of the transfer material)
Afterwards, the fixing film 23 is rewound.

Furthermore, another example of operation will be explained. The power supply to the heating element 21 is stopped and the fixing film is rewound at the time after the paper feed sensor 82 is turned off.

Further, the time t OFF from a predetermined timing until the power supply to the heating element 21 is stopped, and the time t BACκ from the predetermined timing to the start of rewinding of the fixing film 23 have a relationship of t OFF < t BACK Another example is to make sure that

(Effects of the Invention) As described above, according to the present invention, in an image forming apparatus having a fixing means that uses a fixing film by sequentially rewinding the fixing film, the time point at which electricity is stopped to the heating element and the point at which the fixing film is Since the times of winding and unwinding are separated, excessive temperature rise of the pressure roller can be prevented, and the fixing film and transfer material can be separated after sufficient cooling.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; FIG. 1 is a sectional elevational view showing an overview of the entire device, FIG. 2 is an enlarged view of the fixing device shown in FIG. 1, and FIG. 3 is an enlarged view of the fixing device shown in FIG. Enlarged view of the heating element in Figure 4
5 is an explanatory diagram of the control of the fixing device shown in FIGS. 1 and 2, FIG. 5 is an explanatory diagram of the control timing of the control circuit of FIG. 4, and FIG. 6 is an explanatory diagram of the control operation. P... Transfer material T... Toner image 20...
-Fixing device 21...Heating element 22...Pressure roller 23...Fixing film 24...Feeding shaft
26... Separation roller 27... Winding shaft 28
... Heat generating layer 60 ... Control circuit Fig. 2 Fig. 6

Claims (1)

[Scope of Claims] 1. The unfixed toner image on the transfer material is transferred via a fixing film that moves at the same speed as the conveyance speed of the transfer material using a pressurized conveyance means that is rotated while being pressed against a heating body. A heating fixing means comprising a heating step of bringing a transfer material into close contact with the heating body and heating and melting the toner image, and a cooling separation step of separating the fixing film and the transfer material after the toner image is cooled and solidified again. and a fixing film winding means that is used while sequentially winding the fixing film; a fixing film rewinding means that rewinds the fixing film when the fixing film is not fixed; an image forming apparatus having a means for stopping energization, further comprising: a point in time when energization to the heating element is stopped;
An image forming apparatus characterized in that the fixing film rewinding start point is different from the start point. 2. The time tOFF from a predetermined timing until the power supply to the heating element is stopped, and the time tBACK from the predetermined timing to the start of rewinding the fixing film.
The image forming apparatus according to claim 1, wherein: tOFF<tBACK.