JPH08106226A - Fixing device - Google Patents

Abstract

PURPOSE: To stably maintain fixing performance and sheet carrying performance with a small size and at low costs for a long time by providing a recording sheet carrying roll in contact with a heating roll at a position nearer the upstream side than the nip part of the heating roll. CONSTITUTION: A sheet carrying roll 8 for feeding a recording sheet 9 to the nip part is provided on an upstream side position more than a nip part in the rotational direction of the heating roll 1 where the heating roll 1 heated to a specified temperature by an infrared ray lamp 5 and a heat proof fixing member 2 comprising a supporting member 12, a release agent impregnated elastic body 6 and a release agent control layer 7 come into contact with each other. A plurality of sheet carrying rolls 8 are provided in parallel with the rotary shaft of the heating roll 1, pressed to the heating roll 1 by a spring 4 and rotated by being driven by the heating roll 1. Thus, a sufficient sheet carrying capacity is obtained and even when silicone oil is excessively applied to the surface of the heating roll 1 and a friction factor with the recording sheet 9 is reduced, the recording sheet 9 is surely fed to the nip part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus utilizing an electrophotographic system such as an electrophotographic copying machine, a facsimile and a printer.

[0002]

2. Description of the Related Art Generally, in an electrophotographic image forming apparatus, it is necessary to fix an unfixed toner image formed on a recording sheet into a permanent image. As a fixing method, a solvent fixing method or a pressure fixing method is used. Method and heat fixing method are known. However, the solvent fixing method has a drawback that odor and hygienic problems are large due to solvent emission, and the pressure fixing method has a lower fixing performance than other fixing methods and has a dedicated pressure-sensitive toner. Has the drawback of being expensive,
Neither has been widely put into practical use.

On the other hand, a heat fixing method in which a toner fused by heating is fused on a recording sheet is widely adopted. FIG. 2 shows an example of the heat fixing device. As shown in FIG. 2, a rotating heating roll 1 having a heater 21 inside a hollow cylindrical cored bar 20 and a heat-resistant resin layer 22 formed on the outer peripheral surface of the cored bar 20, and a cylindrical cored bar. A pressure roll 30 having a heat resistant elastic layer 32 formed on the outer peripheral surface of 31 is arranged in pressure contact with each other. The recording sheet 9 before fixing is inserted between the heating roll 1 and the pressure roll 30, and the toner image 10 on the recording sheet 9 is fixed by being heated under pressure. Other than the above, as the heat fixing device, there are a hot air fixing system and an oven fixing system. However, since these have lower thermal efficiency and fixing speed than the type of FIG. 2 and have a high risk of fire due to paper jam, the type of FIG. 2 is widely used.
However, this type of method also has a problem that the material of the pressure roll is expensive, and it is difficult to reduce the size of the heating roll and the pressure roll, and it is difficult to reduce the cost.

Therefore, in order to solve the above problem, it is conceivable to arrange a heat-resistant fixing member instead of the pressure roll to construct the fixing device. In this proposal, a rotating heating roll equipped with a heater inside and a heat-resistant fixing member pressed against the heating roll are provided. A nip portion for sandwiching the recording sheet is formed between the heating roll and the heat-resistant fixing member, and the recording sheet before fixing is inserted into the nip portion, and the toner on the recording sheet is heated under pressure to be fixed. Is done. In this case, in order to convey the recording sheet by the rotation of the heating roll, the friction coefficient between the heating roll surface and the recording sheet must be larger than the friction coefficient between the fixing member and the recording sheet. Therefore, silicon rubber is used as the surface material of the heating roll, and Teflon-based material is used as the material of the fixing member. However, since silicone rubber has a poor releasability for toner,
The toner melted by heating easily adheres to the heating roll. Further, since silicone rubber is easily worn, it is necessary to apply a release agent such as silicone oil to the heating roll, and a device for supplying the release agent is required. However, if the amount of the release agent supplied exceeds the appropriate amount, the friction coefficient becomes too small to convey the recording sheet, and if the amount of the release agent is less than the appropriate amount, the above-mentioned role as the release agent is exerted. I can't do it. Therefore, a highly accurate release agent quantitative supply device is required, which leads to an increase in cost.

On the other hand, in JP-A-61-11773, the above-mentioned friction is achieved by using both ends of the heating roll as a sheet conveying roll having a large friction coefficient in order to surely convey the recording sheet. It has been proposed to solve the coefficient problem.

[0006]

However, in the above proposal, if a recording sheet having a size narrower than the width of the heating roll is used, one or both of the sheet conveying rolls having the recording sheet at both ends are used. If the recording sheet comes off, the recording sheet may not be conveyed or may not be conveyed at all.

Therefore, in view of the above circumstances, an object of the present invention is to provide a small-sized and inexpensive fixing device which has stable fixing performance and sheet conveying performance for a long period of time.

[0008]

A fixing device of the present invention which achieves the above object comprises a rotating heating roll heated to a predetermined temperature and a fixing member in contact with the heating roll.
In the fixing device for fixing the toner image by inserting the recording sheet carrying the unfixed toner image between the heating roll and the fixing member, the rotation of the heating roll is more than the nip portion where the heating roll and the fixing member are in contact with each other. It is characterized in that at least one sheet-conveying roll for feeding the recording sheet to the nip portion is provided, which is in contact with the heating roll at a position on the upstream side.

Here, in the fixing device of the present invention,
The outer diameter of the sheet transport roll is smaller than the outer diameter of the heating roll, and the surface material of the sheet transport roll has a rubber hardness of 7
It is preferably a rubber of 0 ° or less.

[0010]

As described above, the fixing device of the present invention is provided with the sheet conveying roll which is in contact with the heating roll at a position on the upstream side of the rotation of the heating roll with respect to the nip portion. Sufficient paper conveyance force is obtained by the roll, and the recording sheet is surely sent to the nip portion. For this reason, even if an excessive amount of silicone oil is applied to the surface of the heating roll and the friction coefficient with respect to the recording sheet is reduced, the recording sheet can be reliably conveyed. Also,
Even if the surface material of the heating roll is selected to have a slightly low friction coefficient, it is possible to secure a reliable conveying force.

Further, since the outer diameter of the sheet conveying roll is smaller than the outer diameter of the heating roll, and the surface material of the sheet conveying roll is rubber having a rubber hardness of 70 ° or less, the above-mentioned action is further ensured. Becomes In the present invention, the outer diameter of the sheet conveying roll is preferably smaller than the outer diameter of the heating roll. It is desirable that the sheet conveying roll has an outer diameter as small as possible in order to downsize the entire fixing device and to make the temperature distribution in the axial direction of the heating roll uniform. However, if the diameter is too small, it becomes difficult for the recording sheet to be properly caught between the sheet conveying roll and the heating roll. This is because when the outer diameter of the sheet-conveying roll becomes small, the contact angle of the sheet-conveying roll with respect to the leading end of the recording sheet becomes large, and a large resistance is generated against the recording sheet entering the nip portion. In order to solve this problem of biting, it is effective to reduce the hardness of the surface material of the sheet conveying roll. By doing so, the leading edge of the recording sheet bites into the nip portion formed between the heating roll and the sheet conveying roll, the above resistance to the sheet conveying roll becomes small, and the sheet is smoothly conveyed. Become.

The surface material of the heating roll may be Teflon resin or silicon rubber. Teflon resin is superior to silicone rubber in mold releasability and heat resistance, and has an advantage that a mold release agent such as silicone oil, which is necessary when silicon rubber is used, is unnecessary. Originally, Teflon resin has a lower friction coefficient than silicone rubber, and the sheet conveying force of the heating roll itself is lowered, but since the sheet conveying roll of the present invention ensures sufficient sheet conveying force, There is no problem even if Teflon resin is used.

[0013]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is a sectional view of a fixing device according to an embodiment of the present invention. The heating roll 1 has a diameter of 15 mm, a wall thickness of 0.3 mm, and a length of 22.
Silicon RTV rubber as a release layer 4 is dip-coated with a thickness of 30 μm on the surface of the 5 mm iron heating roll core 3. At the center of the heating roll 1, an infrared lamp of 100v, 300w is provided as a heating source 5, and the surface temperature of the heating roll is always kept at 150 ° C by a temperature sensor and an automatic temperature controller not shown. The heat-resistant fixing member 2 includes a support member 12, a release agent-impregnated elastic body 6, and a release agent control film 7. As the material of the release agent-impregnated elastic body 6, Asker C is used.
The rubber hardness measured with a type of sponge rubber hardness tester (manufactured by Kobunshi Kagaku Co., Ltd.) under a load of 300 g is 35.
A silicone sponge with a ± 3 ° angle was used. The release agent-impregnated elastic body 6 is pressed against the heating roll under a load of about 4 kgf due to its own elasticity, and the nip width 11 between the heating roll 1 and the release agent-impregnated elastic body 6 is about 6 mm. The deformation of the heating roll under this load is almost negligible.
The release agent-impregnated elastic body 6 is impregnated with 10,000 centistokes of dimethyl silicone oil. The surface of the release agent-impregnated elastic body in contact with the heating roll 1 is covered with a release agent control film 7 made of a porous tetrafluoroethylene film. The thickness of this porous film is 20 μm, the pore size is 0.1 to 2.5 μm, and the porosity is 55%. Under this condition, the amount of silicone oil supplied per A4 size recording sheet is 0.5 mg. The bottom surface and the side surface of the release agent-impregnated elastic body 6 are supported by a metal support member 12.

The sheet conveying roll 8 has an outer diameter of 8 mm and a width of 6 mm. A heat resistant silicone rubber layer having a thickness of 0.5 mm and a rubber hardness of 70 ° is formed on the surface of the sheet conveying roll 8. Four sheet conveying rolls 8 are provided in the vicinity of the nip portion between the heating roll 1 and the heat resistant fixing member 2 in parallel with the rotation axis of the heating roll 1. The sheet conveying roll 8 is pressed against the heating roll 1 by the spring 14, and is rotated by being driven by the heating roll 1. The load per sheet conveying roll is about 400 gf.

The number 4 of sheet conveying rolls 8 is determined based on the size of the recording sheet 1 used in this embodiment, and is not limited to the number in this embodiment, and is not limited to that of the fixing device. It is necessary to determine the number of sheet conveying rolls 8 according to the size and the recording sheet size. Under the above-mentioned conditions, a plain paper L4 size A4 paper manufactured by Fuji Xerox Co., Ltd. was used as a recording sheet, and the friction coefficient between the heating roll 1 and the recording sheet 9 was measured and found to be 0.68. The coefficient of friction between the sheet conveying roll 8 and the recording sheet 9 was 0.12. Since the difference between these two friction coefficients is 0.56, the recording sheet 9 is conveyed in the direction of the arrow 13 shown in FIG. 1 as the heating roll 1 rotates. However, if the heating roll 1 is stopped for a long time or the above-mentioned silicone oil is locally collected near the entrance of the nip portion due to the installation condition of the fixing device, the friction coefficient of the heating roll 1 with respect to the recording sheet 9 is greatly reduced. The recording sheet 9 is no longer caught in the nip,
Cannot be transported. Even in such a case, the total load of about 1.6 kgf of the sheet conveying roll 8 can obtain about 1 kgf of frictional force between the heating roll 1 and the recording sheet 9, so that the conveyance of the recording sheet 9 is not hindered. .

Next, an example in which Teflon resin is used instead of silicon RTV rubber as the surface material of the heating roll 1 will be described. In this case, silicone oil is not impregnated in the silicone sponge of the release agent-impregnated elastic body 6. The outer diameter of the sheet conveying roll 8 in this embodiment is 8 mm and the width is 15 mm. A heat-resistant silicone rubber layer having a thickness of 2 mm and a rubber hardness of 20 ° is formed on the surface of the sheet conveying roll 8 and is pressed against the heating roll 1 with a load of 0.9 kgf. At this time, the friction coefficient between the heating roll 1 and the recording sheet 9 is 0.20. Since the coefficient of friction between the heat-resistant fixing member 2 and the recording sheet 9 is 0.12.
Since the difference in the friction coefficient between the heat-resistant fixing member 2 and the recording sheet 9 is 0.08, and the frictional force is about 0.3 kgf, a sufficient sheet conveying force cannot be obtained only by the heating roll 1 and the heat-resistant fixing member 2. I can't expect. However, 3.6 kgf due to the sheet conveying roll 8 which is rotated by the heating roll 1
By the total load of 1, the sheet conveying force by the frictional force of about 0.7 kgf is obtained between the heating roll 1 and the recording sheet 9, so that the sheet conveying is not hindered.

In this case, the biting property of the recording sheet 9 between the heating roll 1 and the sheet conveying roll 8 becomes a problem. Table 1 shows the results of testing the relationship between the biting property and the surface rubber hardness of the sheet conveying roll.

[0018]

[Table 1]

From Table 1, it can be seen that if the surface rubber hardness of the sheet conveying roll is 70 ° or less, there is no problem in the biting property. In Table 1, the outer diameter of the sheet conveying roll is 15 m
Although the results are in the case of m, substantially the same results were obtained when the sheet conveying rolls having the outer diameters of 10 mm and 7 mm were used. In addition, it is an important issue whether the sheet conveying roll does not cause unevenness in image quality after fixing. Table 2 shows the results of testing the unevenness of the image after fixing caused by the sheet conveying rolls by changing the degree of fixing variously. Here, the fixing degree is an index indicating the degree of adhesion of the toner on the recording sheet after fixing, and the rubbing degree of the toner scratched on the recording sheet after fixing under a predetermined load is used as a reference. It is judged by comparing with the limit sample.

[0020]

[Table 2]

As shown in Table 2, when the fixing degree is low, that is, when the fixing degree is 5 or less, the image unevenness exceeds the allowable limit, but the image unevenness can be suppressed to the allowable level as the fixing degree is increased. I understand.

[0022]

As described above, according to the present invention,
It is possible to obtain a compact and inexpensive fixing device that has stable fixing performance and sheet conveying performance for a long period of time.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a conventional fixing device.

FIG. 2 is a sectional view showing a main part of a fixing device according to an embodiment of the present invention.

[Explanation of symbols]

 1 Heating Roll 2 Heat Resistant Fixing Member 3 Heating Roll Core 4 Release Layer 5 Heating Source 6 Release Agent Impregnated Elastic Body 7 Release Agent Control Film 8 Sheet Conveying Roll 9 Recording Sheet 10 Toner Image 11 Nip Width 12 Supporting Member 14 Spring 20 Cylindrical core metal 21 Heater 22 Heat resistant resin 30 Pressure roll 31 Cylindrical core metal 32 Heat resistant elastic layer

Claims (2)

[Claims] 1. A recording sheet comprising a rotating heating roll heated to a predetermined temperature and a fixing member in contact with the heating roll, and carrying an unfixed toner image between the heating roll and the fixing member. A fixing device for fixing the toner image by inserting the recording sheet into contact with the heating roll at a position upstream of rotation of the heating roll with respect to a nip portion where the heating roll and the fixing member are in contact with each other. A fixing device comprising at least one sheet conveying roll that is fed into the nip portion. 2. The sheet conveying roll has an outer diameter smaller than that of the heating roll, and the surface material of the sheet conveying roll is rubber having a rubber hardness of 70 ° or less. The fixing device according to 1.