JPH04342276A - Fixing device - Google Patents

Abstract

PURPOSE:To perform stable gloss fixing without dependency of thermal fixability of a toner image upon the quality or the thickness of a transfer material and to obtain a color toner image of a high quality free from picture dirt due to offset transfer. CONSTITUTION:An endless belt 25 wound around a heat roll 11, a peeling roll 21, and a tension roll 22 and a pressure roll which is pressed to the heat roll 11 through the belt 25 are provided, and the position to the heat roll 11 of the pressure roll 31 is changed to obtain a complement alpha of the angle formed between the line connecting axes of both rolls 11 and 31 and the straight part of the heated endless belt 25 which is run from both rolls 11 and 31 toward the peeling roll 21, and positions of both rolls are so calculated that 5 deg.<alpha<40 deg. is true. This fixing device 1 is provided with air coolers 40 and 50 on both sides of the endless belt 25 from the entrance to the exit for the transfer material to obtain a glossy color picture impregnated in the transfer material by sufficient fusion.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to means for preventing offset transfer and dirt transfer of a fixing device in electrophotography, and means for imparting gloss to color images.

0002

2. Description of the Related Art Regarding heat fixing of toner images, in particular, a fixing device using a belt is described in Japanese Patent Application Laid-Open No. 49-36342. is provided via a belt, and the transfer material carrying the toner image is fed between the pressure roller and the belt and fixed. However, a sufficient nip area N1 cannot be obtained,
Since the supply of heat from the upper heating roller through the belt was not guaranteed, the toner was not melted to the extent that the toner image became glossy.

Furthermore, Japanese Patent Laid-Open No. 61-122665 also describes a fixing device that performs thermal fixing via a belt, but the nip area N2 due to the independent angle of the belt to the pressure roller is sufficiently long. Therefore, sufficient melting time is not obtained and the transfer material is not heated sufficiently. In the end, the fixing performance depends on the material and thickness of the transfer material, resulting in unstable thermal fixation.

0004

[Problems to be Solved by the Invention] The present invention has a high heat fixing property that enables stable glossy fixing of toner images without depending on the material or thickness of the transfer material, and that does not cause offset transfer. An object of the present invention is to provide a fixing device capable of producing high-quality color toner images.

[0005]

[Means for Solving the Problem] This object is achieved by any one of the following technical means a, b, c, d, and e. (a) It has a heated endless belt containing an internal heating roller and a peeling roller, and a pressure roller that presses against the internal heating roller via the belt, and heats and presses the transfer material carrying the toner image to fix it. The fixing device includes a first nip area N1 formed by the heating and pressing rollers and the heating endless belt, and a second nip area N2 formed by the heating endless belt and the pressing roller, A complementary angle α between a straight line connecting the axes of the two rollers and a linear portion of the heated endless belt running from the rollers toward the peeling roller satisfies 5°<α<40°. fixing device.

(b) A heated endless belt containing an internal heating roller and a peeling roller, and a pressure roller that presses against the internal heating roller via the belt, and heats and presses the transfer material carrying the toner image. The fixing device has a first nip area N1 formed by the heating and pressing rollers and the heating endless belt, and a second nip area N2 formed by the heating endless belt and the pressing roller. and the complementary angle α of the angle formed by the straight line connecting the axes of the two rollers and the linear portion of the heating endless belt running from the rollers toward the peeling roller satisfies 5°<α<40°, and , a fixing device comprising an entry guide for entering a transfer material into a first nip region N1.

(c) The fixing device according to item a or b, wherein the heating roller and the pressure roller are soft rollers having rubber surfaces.

(d) The fixing device according to item a or b, wherein one of the heating roller and the pressure roller is a soft roller whose surface is made of rubber, and the other is a hard roller.

(e) The fixing device according to item a, b, c, or d, wherein the heating roller and the pressure roller have a heat source.

0010

[Example] An embodiment of the present invention is illustrated in a side view showing the nip area in FIG. 1, a partially enlarged view in FIG. 2, a side sectional view in FIG. 3, an exploded perspective view of the cooling section in FIG. This will be explained using a cross-sectional view of the fixing roller (upper and lower), a cross-sectional view of the layer structure of the belt in FIG. 6, and a toner viscosity-temperature characteristic curve in FIG.

An endless belt 25 is wound around a heating roller 11 having a heat source heater 14 of about 300 to 600 W in its core, a peeling roller 21, and a tension roller 22. The tension roller 22 can also be used to control the oblique movement of the belt 25. Further, the outer diameter of the peeling roller 21 and the tension roller 22 is 5 to 20 mm, and is set to 10 mm in this embodiment. and pressure roller 31
is pressed against the heating roller 11 via the belt 25. Further, the downstream peeling roller 21 of the pressure roller 31
Air cooling devices 40 and 50 are disposed above and below the belt 25, respectively.

On the surfaces of the heating roller 11 and the pressure roller 31, a synthetic rubber layer 1 is formed on the core metals 13 and 33 as shown in FIG.
2 and 32 are coated and finished to have an outer diameter of 40 mm, forming soft rollers that are pressed against each other and easily crushed, forming a nip area N1 that sandwiches an angle θ1 as shown in FIGS. 1 and 2. are doing. However, it is preferable that the pressure roller 31 has a higher rubber hardness than the heating roller 11. Further, the heater 34 at the core of the pressure roller 31 may be omitted in some cases.

Furthermore, due to the arrangement of the pressure roller 31 with respect to the heating roller 11, the hugging angle θ2 by the endless belt 25 is
is formed, and a nip region N2 is formed by the endless belt 25. And the length of the nip region N1 is 3~
20mm, more preferably 3-10mm, nip area N
The length of 2 is 5 to 50 mm, more preferably 10 to 35 m.
It is set to m.

[0014] Then, the heating roller 11 and the pressure roller 31
A complementary angle α is defined between a straight line connecting the axes of the belt and a straight line portion of the heated endless belt running from both rollers toward the peeling roller 21. The angle α is greater than 5° and 40
It is desirable that it be smaller than °.

Further, the transfer material 61 carrying the toner 62 is sandwiched between the pressure roller 31 and the belt 25 along the entrance guide 18, and halfway is placed in the upper part of the air cooling box 52 containing the fan 53 of the lower air cooling device 50. It is conveyed in close contact with the belt 25 between a guide plate 51 with an opening louver 57 provided therein and the endless belt 25, and is peeled off from the belt 25 at the peeling roller 21 to form the upper and lower guides 23A. , 23B and is collected by a pair of rollers 24. A duct 4 is connected to the fan 43 above the endless belt 25 above the lower air cooling device 50.
An upper air cooling device 40 is provided for blowing air to 1. In this way, the intermediate transfer material 61 and the toner 62 are cooled from the outside and inside of the endless belt 25, making it easier to separate and collect them from the belt 25.

Furthermore, the upper part of the heating roller 11 has an outer diameter of 2 mm.
0mm cleaning roller 16 and trace oil roller 1
Similarly, a cleaning roller 36 is provided below the pressure roller 31.

Further, static eliminating brushes 26 and 27 are provided at the return belt near the peeling roller and immediately after being discharged from the roller pair 24.

A gap 56 is formed between the air cooling box 52 and the guide plate 51 having an opening hole (louver) 57 in a portion of the lower air cooling device 50 near the pressure roller 31.
Also, since the gap 46 between the duct 41 of the upper air cooling device 40 and the endless belt 25 closer to the heating roller 11 is kept small, the cooling air can flow to the heating roller 11 and the pressure roller 31.
This prevents the heat from ejecting in the direction of the rollers, cooling the surfaces of those rollers and reducing heating efficiency. Furthermore, temperature detection sensors 19 and 39 are provided near the surface of the heating roller 11 and the surface of the pressure roller 31, respectively.

As shown in FIG. 6, the endless belt 25 is constructed by coating a release layer 29 made of silicone rubber on a polyimide base 28, and the thickness of the polyimide layer is 25 to 75 μm, and the total thickness is is set to 25 to 150 μm, and the belt width is set to 310 mm.

Next, the operation of the fixing device 1 constructed as described above will be described.

First, the viscosity-temperature characteristic curves of the linear polyester toner and the general polyester toner shown in FIG. 7 will be explained.

In this graph, the viscosity is scaled by a common logarithmic value in poise units on the vertical axis, and the temperature is scaled on the horizontal axis. Linear polyester toner is shown by a solid line, and general polyester toner is shown by a chain line. Both toners have a high viscosity of about 100,000 poise near 100°C, that is, are in a glass transition state, and when the temperature exceeds 100°C, both toners become molten. The optimum melt state is when the viscosity is about 5000 poise. and,
Although the heating temperature of conventional polyester toner reaches 150°C, linear polyester toner has a much lower temperature of 120°C.
℃ is sufficient.

Furthermore, compared to the conventional fixing device that performs thermal fixing by a nip between only a pair of rollers, the present invention uses an endless belt 25, which reduces the temperature drop until peeling. Since time can be secured, the melting temperature can be increased higher than before, allowing a much wider heating area. In this heating region, the unfixed image is sufficiently melted by toner, such as linear polyester resin, which can be obtained in a molten state at a low temperature. The adhesive force between the toner 62 and the transfer material 61 in the molten state and the cooling fan 53 applied from the back side of the transfer material
The transfer material 61 and toner 62 are conveyed while being attached to the endless belt 25 due to the air flow from the belt 25, and the temperature is lowered by the temperature of the belt itself and the cooling effect of the air flow.

In this region, the toner 62 and transfer material 61 have been sufficiently cooled, their viscosity has increased, and they have entered a glass transition state.
is peeled off from the endless belt 25 at the end of the endless belt 25 supported by the peeling roller 21. At this time, toner 6
Since the belt 2 is almost in a solidified glass transition state, the surface properties of the belt 25 are maintained as they are, and a glossy surface close to a mirror surface can be obtained. In this way, since the toner 62 is solidified after being sufficiently melted, color reproducibility by melting and mixing a plurality of color toners is ensured, and transparency when fixed on an OHP or the like can also be stably ensured. As mentioned above, since the surface material constituting the endless belt 25 is a material such as silicone rubber which is a mold release agent, the mold release layer itself has elasticity as well as mold releasability, so that uniform heating and application of the toner can be achieved. In addition to realizing the pressure, there is also a damper effect between the toner 62 and the base of the endless belt 25, so that no offset occurs even when using toner that easily melts at relatively low temperatures, such as linear polyester toner. It can be kept to a level that can be cleaned, either not at all, or at a very small level if it occurs.

Furthermore, temperature control is performed by contacting a sensor 19 as a temperature detection means provided along the outer peripheral surface of the heating roller 11 on the side on which the endless belt 25 is stretched, which does not correspond to the belt conveyance path. An advantage of not being dropped is that the surface of the endless belt 25 is not damaged by the sensor 19 at all. On the contrary, endless belt 2
Since the belt 25 and the toner 62 are in contact only on the surface of the toner 6 and the toner does not go around to the back surface, the toner 6
2 will not adhere to the sensor 19 and cause detection failure.

In the case of a fixing device using the endless belt 25, the temperature of the fixing section is likely to be affected by the conditions of the upper air cooling device 40 and the lower air cooling device 50, but temperature detection attached to the pressure roller 31 that presses the Sensor as a means 3
By controlling the heating of the heater by combining the reading value of 9 with the reading value of the sensor 19, it becomes possible to maintain the temperature of the fixing part within a stable range.

Now, the reason why the nip length N1 is necessary is to achieve uniform pressing and melting.
Heating from the upper side (inner side) of the toner 5 ensures melting at the interface between the toner 62 and the endless belt 25. However, if excessive heating is applied, the toner 62 will spread and the toner image will be disturbed. And cooling becomes difficult.

Next, the nip length N2 is required as follows:
This seems to be because the transfer material 61 is sufficiently heated to melt the toner 62 and sufficiently soak into the transfer material 61, thereby improving fixing properties.

Heating on the toner side is performed in a relatively minimum short time to prevent deterioration of image quality. Therefore, there is no need to apply large pressure at the nip portion, and it is only necessary to melt the toner 62. It is important to heat the substrate side of 25 slowly to obtain sufficient toner adhesion.

[0030] Also, the lower limit of the complementary angle α is set to 5° because N
1 and N2 are about the same length, and experimental results show that it is not desirable for N2 to be smaller than N1. Further, the reason why the upper limit is set at 40° is that if the angle is set larger than that, N2 becomes too large compared to N1, which again causes the toner image to dissolve too much and cause a decrease in quality. Furthermore, if N2/N1 becomes too large, the angle between the entrance and exit sides of the transfer material 61 becomes too large. Furthermore, in order to provide a sufficient cooling area for the transfer material 61, N2/N1 cannot be set very large. Making it too large will also hinder miniaturization of the device. Depending on the type of recording material, the occurrence of curls and wrinkles becomes more pronounced as N2/N1 increases.

Furthermore, it is desirable to avoid increasing N2 too much since this increases the driving torque.

As described above, by setting 5°<α<40°, it is possible to stably achieve sufficient penetration of the toner 62 into the transfer material and fixing with sufficient gloss.
Despite obtaining sufficient toner melting and gloss,
Offset transfer of toner to the endless belt is eliminated, and it is possible to practically eliminate any surface staining of subsequent transfer paper due to the offset transfer. It has also become possible to stably achieve high-quality image fixing. Further, the pressure roller 31 may be heated by providing a heater 34 in the center thereof, or may be heated without the heater 34. In any case, the amount of heating may be adjusted and controlled based on the information from the surface temperature detection sensor 39.

[0033]

[Effects of the Invention] With the fixing device of the present invention, there is no offset stain transfer, high-quality image transfer with gloss and no bleeding, and especially color image transfer is stable regardless of the material or thickness of the transfer material. This has been achieved, and the fixing device has been made compact and low-cost.

[Brief explanation of drawings]

FIG. 1 is a side view showing the nip area in the present invention. Figure 2 is a partially enlarged view. FIG. 3 is a side sectional view of one embodiment of the present invention. FIG. 4 is an exploded perspective view of the cooling section of this embodiment. FIG. 5 is a sectional view of a heating roller or a pressure roller. FIG. 6 is a sectional view of the layer structure of the endless belt. Figure 7 shows the viscosity/temperature characteristic curve of toner.

[Explanation of symbols]

1... Fixing device
11...Heating roller 14, 34...Heater
16, 36... Cleaning roller 17... Trace amount oil roller
18... Entrance guide 19, 39... Temperature detection sensor
21... Peeling roller 22... Tension roller
23A, 23B...Upper and lower guide 24...Ejection roller pair 25...Endless belt (heated endless belt)
26, 27... Static elimination brush 31... Pressure roller
40, 50... Air cooling device 41... Duct
43...Fan 46, 56.
··gap
51...Guide plate 52...Air cooling box
53...Fan 57...Opening hole (louver) 61...
Transfer material 62...toner

Claims (5)

[Claims] 1. A heated endless belt containing an internal heating roller and a peeling roller, and a pressure roller that presses against the internal heating roller via the belt, and heats and presses a transfer material carrying a toner image. In the fixing device for fixing, the first roller formed by the heating and pressing rollers and the heating endless belt
and a second nip region N2 formed by the heated endless belt and the pressure roller,
A complementary angle α between a straight line connecting the axes of the two rollers and a linear portion of the heated endless belt running from the rollers toward the peeling roller satisfies 5°<α<40°. fixing device. 2. A heated endless belt containing an internal heating roller and a peeling roller, and a pressure roller that presses against the internal heating roller via the belt, and heats and presses a transfer material carrying a toner image. In the fixing device for fixing, the first roller formed by the heating and pressing rollers and the heating endless belt
and a second nip region N2 formed by the heated endless belt and the pressure roller,
a complementary angle α of the angle formed by a straight line connecting the axes of the two rollers and a linear portion of the heating endless belt running from the two rollers toward the peeling roller satisfies 5°<α<40°, and 1. A fixing device comprising an entry guide for allowing a transfer material to enter a nip region N1. 3. The fixing device according to claim 1, wherein the heating roller and the pressure roller are soft rollers having rubber surfaces. 4. The fixing device according to claim 1, wherein one of the heating roller and the pressure roller is a soft roller whose surface is made of rubber, and the other is a hard roller. 5. The fixing device according to claim 1, wherein the heating roller and the pressure roller have a heat source.