JPH0365978A - Image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus having a fixing device that heats and fixes a toner image onto a transfer material.

[Prior Art] Conventionally, a fixing device generally used in an image forming apparatus has a third fixing device.
The configuration is as shown in the figure.

In FIG. 3, 51 is a fixing roller, which is made of silicone rubber, PFA, P
It has a structure in which a mold release resin layer 54 such as TFE is provided, and heating is performed by a heater 50 disposed inside.

On the other hand, 52 is a pressure roller that is in pressure contact with the fixing roller 51 by a spring or the like and rotates as a result of rotation.The pressure roller 52 is made of silicone which has heat resistance and good mold releasability on a fully flexible core metal 56 made of iron or stainless steel. An elastic layer 57 made of rubber, fluororubber, or the like is formed.

The temperature of the fixing roller 51 is detected as the surface temperature of the fixing roller 51 every - second to two seconds, for example, by a temperature detection element 58 that is in contact with the fixing roller, and the temperature of the fixing roller 51 is detected by a temperature control circuit (not shown) as the surface temperature of the fixing roller 51. By systematically operating 50, the surface temperature is controlled to a predetermined temperature.

That is, when it is determined that the temperature of the fixing roller 51 is below a predetermined temperature, the heater 50 is turned on and continues to be lit until the predetermined temperature is reached, and when it is determined that the predetermined temperature has been reached, the heater 50 is turned off. It is a control method. Therefore, the greater the degree of temperature drop from the predetermined temperature, the longer the number of times the heater 50 is lit and the longer it is lit.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional example, the pressure roller 52 allows the heat from the fixing roller 51 to pass through the paper when the roller rotates, or to be directly conducted when the paper is not passing through, such as during pre-rotation or between sheets. is heated by. This resulted in the following drawbacks.

In other words, when passing cardboard, envelopes, etc., the cardboard, envelopes, etc.
Heat is absorbed by the envelope and insufficient heat is transferred to the pressure roller. For example, if the temperature of the fixing roller is adjusted to 150°C in an environment of 22°C, it will weigh 75g.
/m” paper (plain paper) at a process speed of 25-m/s
When printing continuously with EC, the temperature of the pressure roller is 120°
However, when printing 105g/l thick paper continuously under the same conditions (paper distance: approx. 50mm, the length of the circumference of the pressure roller), the pressure roller gradually cools down from about 80℃. . This situation is as shown in FIG. Therefore, the temperature of the pressure roller increases only when the paper is not passing, such as during one paper interval in the previous rotation, and when one sheet of 105 g/m" paper passes, the temperature of the pressure roller increases from 15 to 30. 'C
It can be seen that this decreases.

When the temperature of the pressure roller is low, such as when a 1M cylinder of thick paper is passed, the amount of heat of the fixing roller is not sufficient to fix the toner image after the third sheet, and low-temperature offset occurs. Furthermore, the toner offset to the fixing roller transfers to the pressure roller between sheets of paper and accumulates there. At this point, stop printing and pressurize the roller to a high temperature of 100℃ due to previous rotation, etc.
If plain paper (75 g/l) is passed under such conditions, there is a problem in that the accumulated toner is transferred to the paper at once and appears as stains on the back side. Furthermore, under such conditions, the pressure roller becomes heavily soiled and its lifespan is shortened.

In order to solve the above problem, there is a method of increasing the fixing temperature itself, but if this is done, a high temperature offset will occur, which will stain the pressure roller and shorten its life. In addition, increasing the fixing temperature is not preferable especially in small machines because of the problem of increasing the temperature inside the machine.

The present invention solves the problems of the conventional devices as described above, and improves the image quality by changing the conveyance interval of the transfer paper without raising the temperature control temperature, and which has a fixing device that does not cause toner offset. The purpose is to provide a forming device.

[Means for Solving the Problems] According to the present invention, the above object is as follows: a fixing roller having a heater inside, a pressure roller disposed in pressure contact with the fixing roller, and a surface of the fixing roller. In an image forming apparatus, the image forming apparatus includes a temperature detection means for detecting the temperature of the surface by contacting the temperature detection means, a heater control means for controlling lighting of the heater according to a signal from the temperature detection means, and a number of lighting times or a lighting time of the heater. This is achieved by comprising a transfer material conveyance control means that adjusts the conveyance interval of the transfer material to the pressure contact portion formed by the fixing roller and the pressure roller so as to become longer as the number of transfer materials increases.

[Function] In the present invention, temperature control is performed by continuous IF lighting of the heater. In this case, when a transfer material such as thick paper that absorbs a lot of heat is passed, the number of times the heater is turned on increases and the period of time the heater is turned on becomes longer. Therefore, since there is a specific relationship between the amount of heat absorbed by the cardboard, etc., and the number of times the light is lit and the number of times the light is lit, the time interval for transporting the transfer paper becomes longer as the number of times the light is lit and the number of times the light is lit increases. Set to . Thus, during this transport time interval, the pressure roller receives direct heat transfer from the fixing roller and rises to a predetermined temperature.

[Example] A first example of the present invention will be described with reference to FIGS. 1 and 2 of the accompanying drawings.

In FIG. 1, l is a photosensitive drum whose surface is endlessly movable. The surface of the photosensitive drum l is connected to a charger 2 disposed above.
The surface is uniformly charged and exposed by a laser beam 7 emitted from a laser emitting means 6 including a laser emitting element 3, a polygon mirror 4, a scanner motor 5, etc., and an electrostatic latent image is formed on the surface. The electrostatic latent image is developed by a developing device 8 disposed opposite the photosensitive drum 1, and a toner image is formed on the surface. The toner image is transferred by a transfer charger 12 onto a transfer material conveyed by a transfer material feeding means including a paper feed cassette 9, a paper feed roller 10, and a registration roller 11.

The transferred transfer material is transported to the fixing device 13 after excess charge is removed by the static eliminating needle 18 and is then transferred to the fixing roller 14.
The pressure roller 15 performs fixing, and the paper discharge roller 16 discharges the paper onto a paper discharge tray 17 .

On the other hand, toner and paper dust remaining on the photosensitive drum l are removed by a cleaner 19, and electric charges remaining on the photosensitive drum l are also removed by a pre-exposure lamp 20.

In the apparatus of this embodiment, the fixing roller 14 has a built-in heater (not shown), and a temperature control circuit (not shown) is activated based on the output of a detection means such as a sensor that contacts the fixing roller. The fixing temperature (temperature control temperature) is controlled by The control is based on pulse-like blinking of the heater (O
N-OFF). Therefore, when the paper is passed, the heat is absorbed by the transfer material, so that not much heat is transferred to the pressure roller. Therefore, the heat of the fixing roller is further conducted to the pressure roller, so the heater is turned on to keep the fixing roller itself at the controlled temperature. For example, if the transfer material is 75 g/sz" plain paper, the number of times (frequency) the heater will turn on is 4 times/minute, and if the transfer material is 105 g/m" thick paper or envelope (COM/10), it will be turned on 8 times/minute. there were. In other words, a large number of lighting times indicates that the transfer material absorbs a lot of heat, such as a cardboard envelope. Taking this into consideration, in this example, the distance between the sheets of the transferred transfer material was set to a normal value (normal value). The distance between sheets is set to be longer than the paper distance (1111) in the case of paper, for example, approximately 100 ms+ for one revolution of the pressure roller. FIG. 2 shows the temperature change of the pressure roller at that time. Second
As is clear from the figure, the distance between the sheets becomes longer and the time for the fixing roller and pressure roller to rotate in direct contact with each other is twice as long as for plain paper, so sufficient heat is applied to the pressure roller and the temperature of the pressure roller increases. The temperature is also about 140'C, which sufficiently secures the predetermined value of 120°C to prevent offset. As a result, conventional problems such as low-temperature offset, pressure roller stains, plain paper back stains, and shortened pressure roller life did not occur at all.

In this embodiment, the distance between the sheets is lengthened to increase the contact length between the fixing roller and the pressure roller to ensure sufficient heat transfer. teeth,
This leads to a reduction in the transfer ability (number of sheets). Therefore, in order to deal with this, for example, if the number of times the heater is turned on or the lighting time increases by 1.5 times or more, the paper interval during continuous printing should be extended by at least the circumference of the pressure roller, and only during that paper interval. The fixing speed was set to 50 mm/sec, which is twice the normal speed. As a result, even during continuous printing, the temperature of the pressure roller can be maintained as in the previous embodiment without slowing down the printing speed, resulting in low temperature offset, pressure roller stains, back side stains on the paper, and reduced life of the pressure roller. A similar effect of preventing was obtained.

[Effects of the Invention] As described above, the present invention provides control to change the paper spacing during continuous printing when the number of times the heater is turned on or the lighting time changes during continuous printing compared to when printing on plain paper. Even if the transfer material is cardboard, envelopes, etc., the temperature of the pressure roller is kept at the specified temperature, and low-temperature offset,
It has the effect of preventing pressure roller stains, paper back stains, and shortening of the pressure roller life, and furthermore, since there is no rise in fixing temperature, there is no problem of internal temperature rise.

[Brief explanation of drawings]

Figure N4i is a schematic configuration diagram of an apparatus according to an embodiment of the present invention, Figure 2 is a diagram showing the temperature change of the pressure roller during continuous printing of the apparatus shown in Figure 1, and Figure 3 is a schematic configuration of the fixing device of the conventional apparatus. figure,
FIG. 4 is a diagram showing temperature changes of the pressure roller during continuous printing using the apparatus shown in FIG. 3. 14... Fixing roller 15... Pressure roller

Claims (1)

[Claims] A fixing roller having a heater inside, a pressure roller disposed in pressure contact with the fixing roller, and a temperature sensor that comes into contact with the surface of the fixing roller to detect the temperature of the surface. an image forming apparatus comprising: a heater control means for controlling lighting of the heater according to a signal from the temperature sensing means; An image forming apparatus comprising: a transfer material conveyance control unit that adjusts the interval between conveyance of the transfer material to the forming pressure portion to be longer.