JPH0830128A - Thermal fixing device - Google Patents

Abstract

PURPOSE:To obtain a thermal fixing device capable of shortening a warm-up time and preventing paper from being wrinkled at the time of fixing. CONSTITUTION:The core 52 of a pressure roll 34 out of a heat roll and the pressure roll constituting a thermal fixing device is formed as a hollow metallic roll whose outside diameter is maximum at the center part and is reduced toward both ends. The outer periphery of the core 52 is coated with a cylindrical sponge material whose outside diameter is nearly uniform at any spot in the axial direction of the metallic roll, and a surface layer 54 made of fluororesin is formed on the outer surface thereof. The paper is prevented from being wrinkled by the shape of an elastic layer 53. Since the core of the heat roll is formed to be a cylinder having uniform thickness, the warm-up time is shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device used for fixing a sheet on which a toner image has been transferred in an image processing apparatus such as a copying machine, a printer, a facsimile machine, and the like. The present invention relates to a thermal fixing device which is composed of a pressure roll (pressure roll) which is in contact with the pressure roller, and in which the structure of the pressure roll is devised.

[0002]

2. Description of the Related Art In many image processing apparatuses such as copying machines, printers, and facsimile machines, a toner image is transferred from a photoconductor to a sheet and fixed by a fixing device. The fixing device includes a device that fixes only by pressure and a device that fixes only by heating. However, generally, a heat-fixing roll type apparatus that performs fixing by both pressure and heating is widely used. In the following description, this heat fixing roll type fixing device will be simply referred to as a heat fixing device. In such a heat fixing device, a heat roll provided with a heat source and a pressure roll rolling on the heat roll are used to press them against each other so that heat can be efficiently transferred at the nip portion to fix the heat. ing.

In this type of heat fixing device, warm-up time is often a problem. The warm-up time is the time from when the heat fixing device is turned on until the fixing temperature is reached. The size of the paper to be fixed is A3 size or smaller according to Japanese Industrial Standard, and is often used as recording paper or copying paper in the office.
Therefore, various proposals have been made for reducing the warm-up time in the thermal fixing device for fixing paper of these sizes. As a result, various thermal fixing devices having a warm-up time of less than 1 minute have been realized.

However, in a large image processing apparatus for drawing which handles recording paper or copy paper having a large paper size exceeding A3 size, the width of the paper for fixing is considerably wide, and the warm-up time is shortened. Therefore, the conventional technique for applying the above method cannot be applied as it is. Therefore, in a conventional image processing apparatus using such a relatively large-sized heat fixing device, the time from power-on to completion of warm-up is shortened, but it takes about several minutes. Was said.

On the other hand, a relatively large image processing apparatus for drawings or the like is generally extremely infrequently used as compared with an apparatus for handling a normal size sheet, and there may be days when it is not used at all. Therefore, depending on the office, the power is turned on each time the image processing apparatus is used. However, as already explained, such a device takes a considerable amount of warm-up time, so turning the power on each time of use often makes the user feel frustrated,
There was an increasing demand for shorter warm-up times.

As one of the methods for shortening the warm-up time of the heat fixing device, it is conceivable to increase the output of the heat generating lamp used for the heat roll. However, if the output of the heat-generating lamp is increased, the power consumption of the entire device is increased, and it becomes impossible to use it with a normal household power supply (100 V, 15 amps or less). Moreover, in order to fix a relatively wide sheet such as A0 size paper, the power consumption is originally increased to some extent, and it is difficult to further increase the power consumption to shorten the warm-up time.

As another method for reducing the warm-up time, it is conceivable to reduce the thickness of the heat roll or pressure roll in order to reduce the heat capacity of the device.
However, as the wall thickness is reduced, the strength of the roll itself decreases. In a heat fixing device for fixing a relatively wide sheet such as A0 size, since the length of the roll is long, it is necessary to maintain sufficient strength, and it is difficult to reduce the wall thickness.

By the way, in the heat fixing device of the type in which the paper is pressed against each other by the heat roll and the pressure roll, wrinkles (wrinkles) may occur when the paper passes between them. Therefore, various proposals have been made to prevent the generation of wrinkles. For example, in the case of an image processing apparatus in which the center of the roll is positioned in the direction (width direction) orthogonal to the conveyance direction of the paper with respect to the image, the center position of the paper in the width direction passes through the center position of the roll. . Therefore,
In such a heat fixing device, it has been proposed that the outer diameter of the central portion of the heat roll is set to the minimum diameter, and the flare shape is such that the outer diameter increases toward both ends. With such a shape, the paper is pulled toward both ends and wrinkles are less likely to occur.

However, when the heat roll has such a flare shape, the conveyance speed of the paper in the heat fixing device varies depending on the width of the paper. Therefore, when a roll paper is used to copy or record an image having a length of several meters as in an image processing apparatus for a large drawing, the distance from the leading edge to the trailing edge of the image depends on the width of paper. The length changes so much that it cannot be ignored. For this reason, in the case where the heat roll is flared, a mechanism for switching the sheet conveyance speed according to the width of the sheet used is required.

On the other hand, FIG. 3 shows a sectional structure of a heat fixing device disclosed in Japanese Patent Publication No. 55-34430. This heat fixing device is composed of a heat roll 11 and a pressure roll 12, and a sheet 13 is pressed against them in the figure. The pressure roll 12 includes a metal core 14 having a constant outer diameter at any position in the axial direction.
And a coating layer 15 having a constant thickness. On the other hand, the heat roll 11 has a drum-shaped metal core 17 that is hollow and has a maximum diameter in the center and an outer diameter that decreases toward both ends, and a heating member disposed in the hollow portion of the metal core 17. It is composed of a source 18 and a coating layer 19 made of silicon rubber that covers the outer diameter of the metal core 17. Since it is difficult to process silicon rubber as an elastic material into the flare shape described above, the coating layer 19 has a straight shape with an outer diameter that is constant at any position in the axial direction.

In the heat fixing device shown in FIG. 3, the coating layer 1 extends in the direction from the central portion of the heat roll 11 to both ends thereof.
Since the amount of deformation of sheet 9 gradually increases, the sheet 13 receives tension from the central portion toward both end portions thereof, and wrinkles are prevented from occurring.

On the other hand, in Japanese Unexamined Patent Publication No. 1-250979, an annular pressing member that presses the inner surface of the cylinder of the pressure roll via a bearing is arranged on the pressure shaft of the pressure roll that contacts the heat roll. . Two annular pressing members are provided. When the length of the roll is L, the distance S from each end face of the pressure roll of the two pressing members is set to L / 5 or more and 2L / 5 or less.

The technique disclosed in Japanese Unexamined Patent Publication No. 1-250979 mainly relates to a large-sized heat fixing device for drawings such as A1 size and A0 size. Both the heat roll and the pressure roll have an outer diameter of an axial axis. It has a straight shape that is constant at any position in the direction. If the thickness of the heat roll is reduced and the pressure required for fixing to the paper is applied by supporting both ends of the roll, the roll will bend and the nip of the required uniform width cannot be obtained. The above two points are defined by the above-mentioned distance S, and the supporting position for pressurization is set.

FIG. 4 shows the basic configuration of the heat fixing device disclosed in Japanese Patent Laid-Open No. 2-173687. In this device, the heat roll 21 has a straight shape, and the pressure roll 22 has a drum shape with the maximum diameter at the center and the outer diameter decreasing toward both ends.

FIG. 5 shows the fixing operation of the heat fixing device disclosed in Japanese Patent Laid-Open No. 2-173687. When the stress when the heat roll 21 and the pressure roll 22 are in rolling contact is represented by F, the elastic deformation of the pressure roll 22 causes the stress F to move toward the end side from the central part of the roll toward both ends. To do. As a result, both sides of the sheet (not shown) are pulled outward, and wrinkles are prevented.

[0016]

Among these, in the heat fixing device shown in FIG. 3, the heat roll 11 is composed of a plurality of layers, and the thickness of the metal core 17 and the coating layer 19 is different. There is a problem in that it is necessary to make them relatively thick due to the different relations in the axial direction of the rolls, and the warm-up time becomes long in relation to their heat capacity.

Further, in the technique disclosed in Japanese Patent Laid-Open No. 1-250979, the pressure is applied at two points in the vicinity of the center of the roll, so the mechanism for that is complicated,
There is a problem that the cost of the heat fixing device becomes high.

Further, in the proposed heat fixing device shown in FIGS. 4 and 5, the pressure roll 22 has a drum shape, and therefore the material of the roll is limited to one capable of being cut into such a shape. Actually, it is limited to silicone rubber. Further, in order to be able to accurately cut the outer shape of the roll, a material having a rather hard hardness is required. Therefore, in order to form the nip at the time of fixing with a sufficient width, it is necessary to set the strength of the heat roll relatively high, and the wall thickness cannot be made too thin.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal fixing device capable of shortening the warm-up time and preventing wrinkles from being generated during fixing of paper.

[0020]

According to a first aspect of the present invention, (a) a central portion has a maximum diameter, and a hollow metal roll having an outer diameter that decreases toward both ends, and a hollow metal roll that covers the outer periphery of the metal roll. A pressure roll having a cylindrical elastic body whose outer diameter is substantially uniform at any position in the axial direction of this metal roll, and (b) a heat source inside, which rolls with this pressure roll during heat fixing. The heat fixing device is provided with a heat roll in contact therewith.

That is, according to the first aspect of the present invention, the heat roll has a cylindrical core having a uniform thickness, and the thickness can be made relatively thin so that the warm-up time is shortened. . And for the pressure roll, the metal roll has a maximum diameter in the central part, and the outer diameter decreases as it goes to both ends, and it is covered with an elastic body with a straight outer diameter. Wrinkles are prevented by the difference in the thickness of the elastic body in the axial direction.

According to the second aspect of the invention, (a) the central portion has a maximum diameter and the outer diameter decreases toward both ends, and a hollow metal roll that covers the outer circumference of the metal roll and has an outer diameter of this metal. A pressure roll including a tubular elastic body that is substantially uniform at any position in the axial direction of the roll, and a resin material that covers the outer circumference of the elastic body in a tubular shape,
(B) A heat roll that has a heat source inside and rolls into contact with this pressure roll at the time of heat fixing; and (c) a plate-shaped paper guide whose tip is arranged in the vicinity of the portion where the pressure roll and heat roll roll. D) The heat fixing device is provided with a paper holding means for holding the paper guided by the paper guide in a state where it does not float up from the conveying path.

That is, in the second aspect of the present invention, the heat roll has a cylindrical core having a uniform thickness, and the thickness can be made relatively thin to shorten the warm-up time. . And for the pressure roll, the metal roll has a maximum diameter in the central part, and the outer diameter decreases as it goes to both ends, and it is covered with an elastic body with a straight outer diameter. By covering it with a resin material, the difference in the thickness of the elastic body in the axial direction, and by conveying the paper so that it does not float up from the paper guide and entering it into the rolling contact part of the heat roll and pressure roll, To prevent the occurrence of.

According to the third aspect of the invention, (a) the central portion has the maximum diameter and the outer diameter decreases toward both ends, and a hollow metal roll that covers the outer circumference of the metal roll and has the outer diameter of this metal. A pressure roller having a cylindrical sponge material that is substantially uniform at any position in the axial direction of the roll, and a fluororesin material that covers the outer circumference of this sponge material in a cylindrical shape, and (b) a heat source inside A heat roll that rolls into contact with this pressure roll during heat fixing, (c) a plate-shaped paper guide with its tip located near the rolling contact part of the pressure roll and heat roll, and (d) guide to this paper guide. The heat fixing device is provided with a star wheel that is in rolling contact with a sheet that is transported for fixing.

That is, according to the third aspect of the invention, the heat roll has a cylindrical core having a uniform thickness, and the thickness can be made relatively thin to shorten the warm-up time. . Then, for the pressure roll, the metal roll has a maximum diameter in the central part, and the drum-shaped one whose outer diameter is reduced toward both ends is covered with a sponge material having a straight outer diameter,
Furthermore, by covering it with a fluororesin material, the sponge material has a different axial thickness, and the paper is pushed up by the star wheel's own weight so that it does not rise above the paper guide. Wrinkles are prevented by making them enter.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows the structure of a thermal fixing device according to an embodiment of the present invention. The heat fixing device 31 includes a heat roll 33 having a heat generating lamp 32 built therein, a pressure roll 34, and a contact / separation mechanism 35 for bringing the pressure roll 34 into contact with and separating from the heat roll 33. The contact / separation mechanism 35 includes an arm 37 rotatably arranged around a fulcrum 36 on a frame of an image processing apparatus (not shown), and an arm for vertically moving an end portion of the arm 37 opposite to the fulcrum 36 in the drawing. Drive mechanism 38
It is composed by. A bearing (not shown) is arranged at the center of the arm 37, and the pressure roll 34
One end of the rotary shaft 41 is rotatably attached to this. Although only one side of the pressure roll 34 is shown in the figure, an arm is similarly provided on the other side, and the other end of the rotary shaft 41 of the pressure roll 34 is similarly rotatably attached thereto. Has been.

Heat roll 33 and pressure roll 34
A leading end of a sheet guide 43 made of a metal plate is arranged near the point where the sheet is rolled and contacted, and the sheet 44 is conveyed in the direction of an arrow 45 along the sheet. At a predetermined timing when the sheet 44 reaches the vicinity of the heat fixing device 31, the arm drive mechanism 38 using a solenoid or a motor as a drive source operates to move the other end of the arm 37 in the arrow 46 direction by a predetermined amount. Then, as shown in the figure, the pressure roll 34 is pressed against the heat roll 33. The rotation shaft (not shown) of the heat roll 33 is rotated in the direction of arrow 47 at a predetermined rotation speed by a drive mechanism (not shown). Therefore, the paper 44 passes between the heat roll 33 and the pressure roll 34, and the toner image is thermally fixed. When the trailing edge of the paper 44 has finished passing between the heat roll 33 and the pressure roll 34, the drive of the arm drive mechanism 38 is released at a predetermined timing thereafter, and the pressure roll 34 is again heated.
It will be separated from 3.

In this heat fixing device 31, a star wheel 48 is rotatably arranged above the paper guide 43 so that the paper 44 is lightly pressed against the paper guide 43 by its own weight. Due to the action of the star wheel 48, the leading edge of the sheet 44 does not flip up and is reliably fed between the heat roll 33 and the pressure roll 34. The star wheel 48 does not necessarily have to be used to perform such an operation. For example, it is possible to form a plurality of holes in the paper guide 43 and suck air from below so that the paper 44 being conveyed can be reliably conveyed along the paper guide 43.

FIG. 2 shows a sectional structure of a pressure roll in such a heat fixing device. The pressure roll 34 includes a metal core 52 having a pair of metal hubs 51 attached to both ends thereof, an elastic layer 53 that covers the outer periphery of the core 52, and a surface layer 54 that covers the surface of the elastic layer 53. It is configured. Here, the core 52 has a drum shape in which the center has the maximum diameter and the outer diameter decreases toward both ends, and is made of aluminum (A-6063 material) which is easy to process. The core 52 has an inner diameter (diameter) of 28 mm and a length of 640 mm.

The outer diameter of both ends of the core 52 is 36 mm. For comparison, the outer diameter of the central portion, which is the maximum diameter of the core 52, was set in five ways from 36 mm to 38 mm in diameter as shown in Table 1 below. For the elastic layer 53, a silicon sponge is used to secure the nip necessary for fixing the paper even under a low load. The surface layer 54 is formed by coating the outer circumference of the elastic layer 53 with a fluororesin. The outer circumference of the surface layer 54 was manufactured to have a diameter of 50 mm. The product hardness was equivalent to 15 degrees when it corresponded to Japanese Industrial Standard JISA.

The heat roll 33 is a structural steel pipe (STKM13A) having mechanical strength superior to that of aluminum.
It was used. The length of the heat roll 33 is 670 mm,
The outer diameter is 35.52 mm and the thickness of the cylinder is 0.6.
It was 3 mm. A Colts lamp with an output of 950 W (watt) was arranged inside the cylindrical structural steel pipe. The warm-up time of the heat roll 33 is the time required to reach the fixing control temperature after the power is turned on. The heat roll 33 had a warm-up time of 45 seconds at room temperature.

The nip load between the heat roll 33 and the pressure roll 34 was set to 15 Kgf so that the paper could be well fixed at a conveying speed of 50 mm / sec. Further, the transport speeds of the heat roll 33 of the heat fixing device, the paper supply roll (not shown), and the photosensitive drum for transferring the toner image are set as follows with a slight difference of 1% or less.

Transport Speed of Heat Roll> Rotational Speed of Photoreceptor> Transport Speed of Paper Supply Roll (1)

[0035]

[Table 1]

In Table 1, the symbol ◯ indicating the evaluation of the type of wrinkles indicates that the occurrence of wrinkles is less than 1%, and Δ
It indicates that the occurrence of wrinkles is 1 to 5%. ×
It means that the occurrence of wrinkles exceeds 5%.

In this table, "wrinkles" are classified into three types. Of these, "pull wrinkles" means that when the conveyance speed at both ends is too fast with respect to the center of the paper. It usually occurs and is formed as a wrinkle having an inverted V shape with respect to the paper feeding direction. "Insufficient wrinkles" are generated due to a low transport speed at both end portions with respect to the central portion of the sheet, and are mainly formed as wrinkles parallel to the sheet feeding direction. The “leading edge wrinkle” means that the leading edge of the paper is the heat roll 3 when the height of the central portion of the paper guide 43 is too high.
It is generated by hitting 3 and is formed as a wrinkle parallel to the sheet feeding direction and in the central portion of the leading edge of the sheet.

As can be seen from Table 1, in the present embodiment, with the crown amount of the core 52 (FIG. 2) set to 1 to 2 mm, depending on the height of the paper, the width of the paper of each width is 5 m. It was possible to obtain a long image of a suitable length without wrinkles. This means that the core 52 of the pressure roll 34 has a drum-shaped shape, so that it is possible to obtain the same pulling effect as in the conventional flare-shaped heat roll. Presuming the reason, since the core 52 has a drum shape, the thickness of the elastic layer 53 made of fluororesin is thin at the center of the pressure roll 34 and thick at both ends.
It is considered that, as a result, tension is generated in the direction from the center to both ends, and the pulling effect of pulling the paper to both sides is obtained.

The elastic layer 53 is used in the embodiment described above.
Although a silicon sponge was used as the material, other materials can be used as long as they have elasticity and heat resistance. Further, in the embodiment, the surface of the elastic layer 53 is covered with the surface layer 54, but if the surface of the elastic layer 53 is smooth, it is not necessary to cover it with the surface layer. Further, although the fluororesin is used as the surface layer 54 in the embodiment, it is needless to say that another material having excellent heat resistance and peeling property can be used.

Further, the present invention can be applied not only to a large apparatus for drawings or the like, but also to an image processing apparatus such as a copying machine, a facsimile apparatus, a printer or the like for fixing a normal size sheet. Needless to say.

[0041]

As described above, claims 1 to 3 are as described above.
According to the invention described above, as for the pressure roll, the metal roll is a drum-shaped one having a maximum diameter in the central portion and an outer diameter decreasing toward both ends, and an elastic material having a straight outer diameter thereon. The elastic body is covered with a body to prevent wrinkles due to the difference in thickness in the axial direction. As a result, the heat roll can have a tubular shape with a uniform thickness, and the thickness can be made relatively thin, so that the warm-up time can be shortened.

According to the second aspect of the present invention, the paper guide is arranged up to the vicinity of the rolling contact portion of the heat roll and the pressure roll, and the paper is fed to the rolling contact portion without the leading edge of the paper rising from the paper guide. Since it has been made to enter into, it is possible to effectively prevent the generation of wrinkles. Furthermore, since the outer circumference of the elastic body is covered with the resin material, the durability of the pressure roll is increased.

According to the third aspect of the present invention, the core of the pressure roll is covered with the sponge material, and the fluororesin material is further covered on the core. Paper can be stably fixed on both rolls.

[Brief description of drawings]

FIG. 1 is a side view showing a configuration of a heat fixing device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a pressure roll that constitutes the heat fixing device of this embodiment.

FIG. 3 is a sectional view showing a sectional structure of a conventionally proposed thermal fixing device.

FIG. 4 is a front view showing a heat roll and a pressure roll of another conventionally proposed thermal fixing device.

5 is an explanatory diagram showing the principle of preventing wrinkles during fixing of the thermal fixing device shown in FIG.

[Explanation of symbols]

31 ... Thermal fixing device, 32 ... Exothermic lamp, 33 ... Heat roll, 34 ... Pressure roll, 43 ... Paper guide, 4
4 ... paper, 48 ... star wheel, 52 ... core, 53 ...
Elastic layer, 54 ... Surface layer

Claims (3)

[Claims] 1. A hollow metal roll having a maximum diameter at its central portion and an outer diameter decreasing toward both end portions, and a hollow metal roll covering the outer periphery of this metal roll at any location in the axial direction of this metal roll. A thermal fixing device comprising: a pressure roll having a substantially uniform tubular elastic body; and a heat roll having a heat source inside and contacting the pressure roll during thermal fixing. 2. A hollow metal roll having a maximum diameter at its central portion and an outer diameter decreasing toward both ends, and an outer diameter of the hollow metal roll covering the outer periphery of the metal roll at any location in the axial direction of the metal roll. A pressure roll having a substantially uniform cylindrical elastic body and a resin material in which the outer periphery of the elastic body is covered in a cylindrical shape, and a heat roll having a heat source inside and contacting the pressure roll during heat fixing. A plate-shaped paper guide whose tip is arranged in the vicinity of the portion where the pressure roll and the heat roll are in contact with each other, and paper holding means for holding the paper guided by the paper guide in a state where it does not float up from the transport path. A thermal fixing device comprising: 3. A hollow metal roll whose central portion has a maximum diameter and whose outer diameter decreases toward both ends, and a hollow metal roll which covers the outer circumference of this metal roll and whose outer diameter is at any position in the axial direction of this metal roll. A pressure roll having a substantially uniform cylindrical sponge material and a fluororesin material that covers the outer circumference of the sponge material in a cylindrical shape, and a heat source that has a heat source inside and that contacts the pressure roll during heat fixing. A roll, a plate-shaped paper guide whose tip is arranged in the vicinity of the portion where the pressure roll and the heat roll are in rolling contact, and a star wheel that is guided by this paper guide and is in rolling contact with the paper conveyed for fixing. A thermal fixing device comprising: