JP2000305407A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize image-defect-free high speed fixing by specifying an angle at which paper is in contact with the periphery of each of heat rollers to a specified angle or less and also setting the temperature of at least a second heat roller above the temperature of the first heat roller. SOLUTION: An arrangement is such that angles (θ1, θ2, and θ3) at which a continuous sheet of paper is in contact with heat rollers 24, 26, and 28, respectively, are 90 deg. or less. The second heat roller 26 is composed as a driving roller and the first heat roller 24 and third heat roller 28 are composed as following rotary rollers. In this case, it is preferable that the heat rollers 26 and 24 be set apart from each other when the first heat roller 24 is independently driven and the temperature of the heat roller 24 be specified below the temperature of the heat roller 26. Further, it is preferable that the temperatures of both the heat rollers 24 and 28 are specified below the temperature of the heat roller 26.

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 fixing a toner image formed on both sides of a continuous paper by heat and pressure.

[0002]

2. Description of the Related Art As a fixing device for fixing a powder toner image formed on continuous paper with heat and pressure, for example, West German Patent No. 271
No. 7260 and JP-T-5-504634 are known. These adopt a configuration in which preheating is performed from the back surface of the sheet before applying heat pressure by a heat roller and the sheet is wound around the heat roller in order to increase fixing efficiency and enable high-speed fixing. This configuration cannot be applied to so-called double-sided simultaneous fixing, in which toner images formed on both sides of a sheet are fixed in one step.

On the other hand, as for the type of fixing device in consideration of simultaneous double-sided fixing, there are two types of fixing devices: atmosphere (oven) fixing as disclosed in JP-A-7-77851, and JP-A-7-120089. As shown, a method using a pair of heat rollers has been proposed.

[0004]

However, in the above-described configuration in which the fixing is carried out by the oven or the pair of heat rollers, 5
It is difficult to apply to a device in which a sheet is conveyed at a high speed such as 0 to 200 cm / s. In the case of a configuration using a pair of heat rollers, a sufficient fixing time cannot be obtained, so that the heat rollers must be heated to a high temperature. However, there is a problem in that sudden thermal stress is applied to the continuous paper, abnormal deformation occurs, and the toner image is transferred to the heat roller due to fluctuations in paper running, causing image defects. Had become.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device capable of realizing high-speed fixing without image defects without excessively increasing the temperature of a heat roller, applying a sudden thermal stress to a sheet. Is to do.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device for fixing a toner image formed on both sides of a continuous paper by heat and pressure, wherein the fixing device is rotatably supported on one surface of the continuous paper. A first heat roller, a second heat roller which is in contact with the other surface of the continuous paper and is pivotally supported so as to be able to press against the first heat roller; and a paper transporting means for the first heat roller. And a third heat roller, which is arranged downstream in the direction and is rotatably supported by the second heat roller, and has a paper contact angle of 90 degrees or less with the outer periphery of each heat roller. And at least the temperature of the second heat roller is set higher than the temperature of the first heat roller.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is applicable to a toner image recording method in which a latent image is developed with colored powder particles in electrophotography, electrostatic recording, magnetic recording, and the like. A description will be given while exemplifying a case where the present invention is applied to an apparatus for forming a toner image by a method.

FIG. 1 shows an embodiment of a laser printer to which the present invention is applied. The continuous paper 1 is fed by a paper feed roller 2 to a laser recording unit 3 at a speed of 50 to 200 cm / s. Continuous paper 1 has a width of 10 to 1000 cm and a thickness of 50 to 200 μm
Plain paper and coated paper are used. In the laser recording unit 3, the photoconductive photosensitive drum 4 is uniformly charged by the corona charger 5, and then a charge latent image is formed on the photoconductor by the laser exposure optical system 6. Next, in the developing device 7, the toner, which is a colored powder particle charged to the charge latent image, is electrostatically attached and developed.

The developed toner image is electrostatically transferred to the surface of the continuous paper 1 by a corona transfer unit 8. Here, continuous paper 1
Is the front surface of the laser recording unit 3 in contact with the photoconductive photosensitive drum 4, and the opposite surface is the back surface. The toner remaining on the drum 4 after the transfer is removed through an AC corona eliminator 9 and a cleaner 10, and the photoconductive photosensitive drum 4 is subjected to the next image forming cycle.

Subsequently, the continuous paper 1 is transferred to the surface of the continuous recording paper 1 via a guide roller 11, a tension roller 12, and a guide roller 13 by a toner charging polarity reversing unit 14 comprising a pair of corona chargers. The charge polarity of the toner is reversed. This is to prevent the toner image transferred on the continuous recording paper surface from being disturbed at the time of the transfer in the next step. For example, when the polarity of the toner in the laser recording unit 3 is positive, the toner charging polarity inverter 14
The polarity of the corona charger (upper side in the figure) facing the toner image is negative and the polarity of the corona charger (lower side in the figure) located on the back side of the continuous recording paper 1 is plus, and the charging polarity of the toner is reversed to minus. Let it.

The laser recording unit 15 includes a photoconductive photosensitive drum 16, a corona charger 17, a laser exposure optical system 18, a developing unit 19, a corona transfer unit 20, an AC corona eliminator 21, and a cleaner 22 similar to the laser recording unit 3. That is, the toner image formed on the photoconductive photosensitive drum 16 is electrostatically transferred to the back surface of the continuous recording paper 1.

In this way, toner images are formed on the front and back of the continuous paper 1. Next, the continuous paper 1 is heated to a temperature close to the glass transition temperature of the toner by a preheating heater 23 as a preheating means, and subsequently, the diameter is approximately 50 mm or more, and the surface temperature is 150 to 25.
The toner image is fixed by being heated and pressed by three heat rollers at 0 ° C., and is transported by a discharge roller 30 to a recording-completed paper storage unit (not shown).

The three heat rollers 24, 26, and 28 are provided with heaters 25, 27, and 29, respectively, and are controlled to a desired temperature. The preheater 23 avoids sudden heating by the heat roller and improves the fixing performance of the toner, and is preferably installed but not essential. Although not shown, each heat roller 24, 2
At 6, 28, a member for coating the surface of the roller with a release agent such as silicone oil and a member for cleaning toner and paper powder attached to the roller are provided as necessary. Further, when the continuous paper 1 is stopped, A retract mechanism is provided so that the sheet is separated from the heat roller.

The toner used in this embodiment has a thermoplastic resin and a coloring pigment as main components, and a fixing aid, a charge controlling agent and the like internally added thereto, and pulverized to an average particle size of 5 to 15 μm. Further, a small amount of a fine particle external additive for stabilizing the fluidity and the amount of charge is added. In the heat-pressure fixing step, the toner is in a melt-softened state and adheres to the paper surface. The definition of the recorded image is 400 to 600 dots / dot.
Inches are common and higher density recording is also desired. Therefore, a decrease in image quality in the fixing step must be suppressed as much as possible.

Hereinafter, the operation of fixing by heat and pressure with three heat rollers will be described in detail with reference to FIG. Heat roller 24,2
The diameter of 6, 28 is about 50 mm or more in order to secure a nip required for fixing at a recording speed of 50 cm / s or more. In addition, from the viewpoint of handling and cost of the heat roller, approximately 15
It is preferably 0 mm or less. Preferably 80 to 1
20 mm. The appropriate surface temperature of the heat roller required for fixing varies from 150 to 250 ° C. depending on the recording speed, the thermal characteristics of the toner, the diameter and the surface material of the heat roller. When the surface material is a silicone rubber or a fluororesin, the temperature is desirably 220 ° C. or lower in order to secure a life due to its heat resistance.

In the present invention, the continuous paper 1 and each heat roller 2
The angles (θ1, θ2, θ3) at which the first and second heat rollers 24, 28 and 28 are in contact with each other are 90 degrees or less. The third heat roller 28 is configured as a driven rotation roller.

A pressure (linear pressure of 1 to 10 k) for fixing with heat and pressure by the second heat roller 26 and the third heat roller 28 is used.
gf / cm), and a lower pressure (a pressure sufficient for the driven rotation) is applied between the second heat roller 26 and the first heat roller 24.

When the first heat roller 24 is driven independently, the heat roller 26 and the heat roller 2 are driven independently.
4 are set to be separated from each other, and it is preferable that the temperature of the heat roller 24 is specified to be lower than the temperature of the heat roller 26. Further, the temperatures of both the heat rollers 24 and 28 are specified to be lower than the temperature of the heat roller 26. It is desirable.

Here, by limiting the paper contact angle to the outer periphery of each heat roller to 90 degrees or less, the deformation stress on the paper can be suppressed, and the moving distance when the rollers are separated can be shortened. , And short-time access is possible.

Further, by increasing the temperature of the second heat roller 26 or sequentially increasing the temperature of each roller, it is possible to alleviate a sudden thermal stress on the sheet. By making the temperature of the third heat roller 28 lower than that of the heat roller 26 within a range where the fixing performance does not decrease, the amount of toner transferred (offset) to the heat roller 28 can be reduced. With this configuration, heat energy can be applied to the paper and toner from the heat roller before applying thermal pressure, so that even at high speeds, a small heat roller can provide both-side fixing performance and damage to the paper. This makes it possible to realize stable paper running.

The three heat rollers include a soft roller in which a silicone rubber layer is formed on a rubber-like member, for example, a base tube to a thickness of 0.1 to 5 mm, preferably 0.2 to 2 mm, and a solid film-like roller. A fluororesin layer is formed on a member, for example, a raw tube, in a thickness of 0.01 to 0.2 mm, preferably 0.02 to 0.05 m.
m and a hard roller formed to have a thickness of m.

First, when the first heat roller 24 and the second heat roller 26 are in contact with each other, and when the second heat roller 26 and the third heat roller 28 are in contact with each other, the heat roller 2
4 is a hard roller, heat roller 26 is a soft roller,
The heat roller 28 is preferably a hard roller or a soft roller.

The heat roller 24 and the heat roller 2
6 are separated, and the heat roller 26 and the heat roller 2
8, the heat roller 24 is a hard roller, the heat roller 26 is a soft roller, and the heat roller 2
Preferably, 8 is a hard roller or a soft roller, or the heat roller 26 is a hard roller and the heat roller 28 is a soft roller. In any case, the reason why the first heat roller 24 is preferably a hard roller is that the heat conduction of this roller is good, so that the preheating efficiency with respect to paper and toner is good, and the surface temperature fluctuation of the roller even at the time of high-speed and continuous fixing is reduced. This is because it can be made smaller.

The heating of the heat roller is performed in the embodiment shown in FIG.
The heating is performed by a heater (for example, a halogen lamp) provided inside the tubular roller. However, in the case of the soft roller, the surface temperature is greatly reduced in high-speed continuous fixing because the surface member is thick. Therefore, a heater (for example, a halogen lamp) is provided from outside the roller.
It is preferable to use a configuration in which heating is performed in combination.

In a more preferable mode at the time of high-speed recording, a non-contact preheating heater 23 is provided before fixing by a heat roller, and the temperature of the toner or the front and back surfaces of the paper in this preheating heater is higher than the glass transition temperature of the toner, preferably. Means heating the glass transition temperature + 10 ° C. to 20 ° C. or more and 100 ° C. or less. The higher the preheating temperature, the lower the fixing ability of the heat roller, so there is an advantage that the temperature and pressure of the heat roller can be lowered,
There is a demerit that the capacity and size of the preheater need to be increased.

Non-contact preheating is not energy efficient,
Further, it is desirable to keep the temperature at 100 ° C. or less in consideration of the damage to the sheet due to the rapid heating in the preheating unit and the adverse effects such as the yellowing of the sheet when the sheet travel stops. Thus, it is preferable to exhibit the preheating effect by combining the preheating by the preheating heater 23 and the preheating by the contact between the heat roll 24 and the continuous paper 1 from the viewpoint of damage to the paper, power consumption, apparatus dimensions, and fixing performance. is there.

The glass transition temperature of a practical toner is 50.
Since the temperature is about 70 to 90 ° C., the sheet temperature is about 70 to 90 ° C. Due to this preheating, the toner starts to become viscous and the adhesion to the paper increases. Of course, when the paper or toner comes into contact with the heat roller 24 in a state other than that the temperature of the heat roller can be lowered by this preheating, the rapid thermal stress is alleviated and the paper deformation is reduced.
4 and 26, the effect of increasing the margin for image quality deterioration due to the speed deviation between the heat roller 24 and the sheet and the sheet flapping at the contact start point can be obtained. In order to suppress the deterioration of the image quality, it is more effective to increase the surface temperature of the sheet on the side in contact with the heat roller 24 when heating with the preheater 23. Such an increase in the margin makes it possible to stop the sheet in a state where the toner image is present on the sheet of the heat roller portion, or to perform a so-called intermittent operation in which the sheet travel repeatedly starts and stops for a short time.

As described above, according to the structure of the embodiment of the present invention, the glass transition point temperature is 50 to 70 ° C. and the softening point temperature is 100 to 130.
It was confirmed that double-sided fixing was possible at a recording speed of 50 to 200 cm / s using a polyester-based or styrene-acryl-based toner at a temperature of 50 ° C.

[0029]

As described above, according to the present invention, it is possible to realize high-speed fixing free from image defects without excessively increasing the temperature of the heat roller, applying a sudden thermal stress to the paper. It is possible to provide a fixing device that can perform the fixing.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a laser printer to which the present invention is applied.

FIG. 2 is a schematic configuration diagram of a fixing device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Continuous paper, 4,16 ... Photoconductive photosensitive drum, 7,19 ... Developer, 23 ... Preheating heater, 24 ... First heat roller,
26 ... second heat roller, 28 ... third heat roller.

Claims (3)

[Claims] 1. A fixing device for fixing a powder toner image formed on both front and back surfaces of a continuous paper by heat and pressure, comprising: a first heat roller rotatably supported so as to contact one surface of the continuous paper;
A second heat roller that is in contact with the other surface of the continuous paper and is supported by the first heat roller so as to be capable of being pressed against the first heat roller; and a second heat roller that is disposed downstream of the first heat roller in the paper transport direction. A third heat roller rotatably supported so as to be able to press against the second heat roller, and having a paper contact angle with respect to the outer periphery of each heat roller of 90 degrees or less; Second
Wherein the temperature of the heat roller is set higher than the temperature of the first heat roller. 2. The fixing device according to claim 1, wherein the first heat roller is a hard roller including a base tube and a fluororesin layer provided on the base tube. 3. A preheating means for preheating a sheet temperature to a temperature equal to or higher than a glass transition point temperature of toner, on the upstream side of the three heat rollers in the sheet conveyance direction.
The fixing device as described in the above.