JP3566466B2 - Fixing device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fixing device for a toner image used in an image forming apparatus such as a printer and a facsimile of an electrophotographic copying machine.
[0002]
[Prior art]
As a method of fixing a toner image formed on a recording medium such as paper or a film, a heat fixing method of melting and fixing the toner by heat is generally used. Among the heat fixing systems, the heat roller system is most widely used because of its high thermal efficiency and safety. In this method, for example, two rollers are pressed against each other, at least one of the rollers is heated, and unfixed toner is heated at a nip portion, which is a pressed portion of the fixing roller pair, to fix the toner on a recording medium.
[0003]
When heating one of the two rollers, the roller to be heated is called a heating roller, and the other roller is called a pressure roller. Inside the heating roller, a heat source of the halogen lamp is provided in the axial direction of the heating roller. As another heat source, a heat source using a ceramic heater or the like is known. A temperature sensor is mounted on the outer surface of the heating roller, and power supply to the heat source is controlled so that the temperature of the nip is maintained at a temperature suitable for fixing.
[0004]
Conventionally, in such a heat fixing device, it has been difficult to make the temperature distribution in the axial direction of the fixing roller pair uniform when the size of the recording medium to be fixed differs in size. That is, in an area through which a small-sized recording medium passes (hereinafter, referred to as a “passing portion”), heat is consumed for heating the recording medium and unfixed toner on the recording medium, but an area through which the small-size recording medium does not pass ( Since the heat is not taken away by the recording medium in the non-passing portion, the heat of the heating roller accumulates, and the temperature of the non-passing portion is higher than the temperature of the nip portion of the passing portion which is maintained at a predetermined temperature. That is, a so-called non-passing portion temperature rise occurs.
[0005]
Therefore, when a small-size recording medium is continuously passed and then a large-size recording medium is passed, for example, when a B5-size sheet is continuously passed and then an A4-size sheet is passed, the image is fixed to a large-size recording medium. There have been problems such as unevenness and wrinkles, and toner in a portion corresponding to a non-passing portion of the unfixed toner image is excessively melted and adhered to the heating roller to stain the surface of the recording medium, that is, a problem such as so-called hot offset. Further, if the temperature of the non-passing portion B is too high, a large temperature difference occurs between the non-passing portion and the passing portion in the heating roller, and a difference in thermal expansion between the high temperature portion and the low temperature portion causes distortion in the heating roller, There is also a problem of deterioration.
[0006]
In particular, among the heating rollers, the surface heating roller in which the heating resistor is formed on the surface of the glass or ceramic pipe directly heats the surface of the fixing roller, so that the heat efficiency is good, and the heat capacity of the heating roller can be reduced. This is a fixing method that is excellent in that the heating time can be shortened and the power to the heating roller can be turned off when not in use, and energy saving is achieved. Due to the difference in thermal expansion due to the temperature rise, the diameters of the heating roller and the pressure roller differ from each other between the passing portion and the non-passing portion, and there is also a problem that the heating roller is damaged.
[0007]
Means for making the temperature distribution in the axial direction of the fixing roller pair uniform and solving these problems and disadvantages are described in JP-A-4-51799, JP-A-6-11983, JP-A-5-281877 and JP-A-5-281877. There are JP-A-6-250540, JP-A-3-139682 and JP-A-5-181382, but each has its own problems and disadvantages.
[0008]
[Problems to be solved by the invention]
The above publications, their inconveniences and problems will be outlined below.
[0009]
JP-A-4-51799
A cooling means for selectively cooling the non-passing portion of the fixing device is provided, and the temperature distribution of the fixing device is made uniform by the cooling means. Specifically, the fan and the duct selectively send air to the non-passing portion only during paper passing to prevent an increase in temperature in the non-passing portion. However, since the air is blown to the heating roller on the side where the toner image is formed, there is a possibility that the toner is blown off by the blow and the image quality is often deteriorated. Since the heating roller is directly cooled, even if only the end portion is to be cooled, the temperature tends to be lowered to the temperature at the central portion where fixing is performed. Therefore, there is also a problem that the heated heat is not effectively used, the thermal efficiency is reduced, and the power consumption is increased.
[0010]
JP-A-6-11983
The heat radiating member is brought into contact with the end of the heating roller according to the paper size to prevent a rise in non-passing portion temperature due to heat radiation. Specifically, a roller-shaped heat dissipating member is arranged in a non-passing portion when small-size paper is passed, and when the temperature of the non-passing portion rises, the heat dissipating member abuts on a heating roller to increase the heat generated. By dissipating the heat, the temperature distribution in the axial direction of the heating roller is made uniform. However, there is a need for a movable portion for pressing and releasing the heat radiating member to and from the heating roller, and there is a problem that a failure or breakage is likely to occur when used for a long time. In addition, since the surface is in direct contact with the heating roller surface, the surface is easily scratched. In particular, when a material that is easily broken, such as glass or ceramics, is used for the heating roller in this configuration, there is a problem that the heating roller itself is damaged by the impact at the time of long-term contact.
[0011]
JP-A-5-281877
Two or more heating elements are provided inside the heating roller, and these heating elements are controlled according to the paper width. Specifically, two heating elements having different heating distributions in the axial direction of the heating roller are provided inside the heating roller, and the heating elements are appropriately selected and driven according to the surface temperature of the fixing unit and the width of the recording material. This prevents the non-passing portion temperature from rising. However, when two or more heating elements are placed inside the heating roller, there is a problem that it is difficult to reduce the diameter of the heating roller. In particular, when a variety of paper sizes are used, for example, when an A3 machine is used to fix a toner image on A4, B4, or B5 size recording paper, or even on a postcard or the like, any of the recording papers may have a non-passing portion. In order to solve the temperature rise and accurately uniform the surface temperature of the heating roller, it is necessary to use a heating element having a different heat generation distribution by that amount, and when provided inside the heating roller, the diameter of the heating roller does not increase. However, there is also a problem that the device becomes large, its structure becomes complicated, and the cost increases.
[0012]
JP-A-6-250540
A heat transfer member provided in contact with the pressure roller or a heat transfer means provided in a non-contact manner is provided on a part of the pressure roller which comes into pressure contact with the heating body via the film on the endless belt, In this case, the heat stored in the passage is made uniform, thereby eliminating temperature unevenness and eliminating the temperature difference between the passing portion and the non-passing portion. In general, when the pressure roller is in a warm state, the recording paper is warmer than in a cold state, and the melted toner easily penetrates, and the fixing property is improved. However, if the heat conductive member is simply brought into contact, not only the non-passing portion but also the passing portion is deprived of heat, and the fixing property is reduced. When the temperature of the heating roller is raised, the heated heat is also transmitted to the pressure roller. Therefore, if the heat transfer member of the pressure roller is simply provided, there is a problem that heat is radiated from the pressure roller to the heat transfer member, and the temperature rise of the heating roller is delayed.
[0013]
JP-A-3-139682
Air cooling means for generating an air flow is provided outside the cover that covers the periphery of the heating roller, and the air blowing to the heating roller is made variable. Generally, a recording paper on which an unfixed toner image is formed is conveyed such that the heating roller side is the toner image surface, and is configured to be fixed by heat of the heating roller whose surface temperature is controlled to be constant. . In the technique described in this publication, since air is blown to the heat roller (heating roller) side, an unfixed image is blown off by the air flow, resulting in a problem that image quality is deteriorated.
[0014]
JP-A-5-181382
The amount of air to be blown to the heating roller is made variable by a blowing means and a heat radiating window. However, even though the amount of air can be changed, since the air is blown to the heating roller, it is undeniable that the image is disturbed.
[0015]
The present invention has been made in view of these problems and problems of the related art, and improves a non-passing portion temperature rise caused by passing a large number of small-sized recording media, and generates a hot offset and a heating roller. Provided is a fixing device that does not cause deterioration of the fixing device. Provided is a fixing device in which a heating roller having a heating resistor provided on a surface of glass, ceramics or the like does not cause damage to the heating roller due to a rise in non-passing portion temperature. Due to the rise in the temperature of the non-passing portion, a difference occurs in the diameter of the passing portion and the non-passing portion of the heating roller, and when a recording material having a normal size or a maximum paper passing width that is not a small size passes through the nip portion, Provided is a fixing device capable of obtaining a high-quality recorded image by preventing a recording medium from being wrinkled due to a difference in paper conveyance speed between a passing portion and a non-passing portion, resulting in a poor image. A low-cost fixing device that has a non-passing portion temperature rise improving unit that does not easily affect the temperature rise time, does not have an operating unit for improving the non-passing portion temperature rise, and does not require a special device. I will provide a.
[0016]
The invention according to claim 1 includes a heating roller, The A pressure roller that presses against the heating roller, Between the heating roller and the pressure roller By passing the recording medium in between, Said On the recording body Unfixed In a fixing device that heats and fixes a toner image, Said Pressurizing roller cooling means for cooling the non-passing part of the pressure roller where the small-sized recording material does not pass The pressure roller cooling means has heat absorbing means which is closer to the pressure roller in the non-passing portion than in the passing portion through which the small-sized recording paper of the pressure roller passes, facing the pressure roller. It is characterized by having.
[0017]
The invention according to claim 2 is 2. The fixing device according to claim 1, wherein a thickness of a portion of the heat absorbing unit facing the non-passing portion is set to be thicker than other portions. 3. .
[0018]
The invention according to claim 3 is 3. The fixing device according to claim 1, wherein the heat absorbing unit is a cover installed to cover the heating roller and the pressure roller. .
[0019]
The invention according to claim 4 is 4. The fixing device according to claim 1, wherein the pressure roller cooling unit increases the amount of air blown to the heat absorbing unit and the non-passing part than the amount of air blown to the passing part. 5. Characterized by comprising a blower .
[0020]
The invention according to claim 5 is 5. The fixing device according to claim 4, further comprising control means for controlling an operation timing of the pressure roller cooling means. .
[0021]
The invention according to claim 6 is 6. The fixing device according to claim 5, wherein the control unit includes a recording body detection unit that detects a size of the recording body. .
[0022]
The invention according to claim 7 is 7. The fixing device according to claim 5, wherein the control unit includes a temperature detecting unit that detects a temperature of the non-passing portion. .
[0023]
The invention according to claim 8 is The fixing device according to claim 1, wherein the heating roller has a heat source in a surface layer or an inner layer near a surface. .
[0024]
The invention according to claim 9 is An image forming apparatus for recording an image formed by a series of image forming processes on a recording medium, comprising the fixing device according to any one of claims 1 to 7. .
[0025]
[Action]
According to the present invention, since the cooling means for cooling the pressure roller is provided, the temperature of the non-passing portion of the pressure roller is suppressed from rising significantly, and the non-passing portion of the heating roller which comes into contact with the pressure roller is suppressed. Reduce temperature rise. By cooling around the non-passing portion of the pressure roller, the temperature of the central portion of the pressure roller does not decrease, and the temperature of the central portion of the heating roller does not greatly decrease during paper passing. By changing the distance between the pressure roller and the cover as a heat absorbing means that covers the pressure roller between the passing portion and the non-passing portion of the pressure roller, the heat release amount of the pressure roller from the pressure roller changes, and the heating roller The rise in the temperature of the non-passing portion of the pressure roller caused by the rise in the temperature of the non-passing portion is suppressed.
[0026]
【Example】
As shown in FIGS. 1 and 2, a first embodiment of the present invention employs a heating roller 2 having a heat source 1 therein, and a pressure contact between the heating roller 2 and the heating roller 2. A pressure roller 4 forming a certain nip portion 3 and a guide member 5 for guiding a transfer sheet P as a recording material onto which the toner image T has been transferred to the nip portion 3 are supported and cover both rollers 2, 4. And a cover 6 having an inlet for taking in air for cooling the pressure roller and an outlet for discharging the taken-in air, and a heating roller for keeping the surface temperature of the heating roller 2 at a set temperature. A first sensor 7 provided in contact with the heating roller 2 for detecting the temperature of the surface 2; a second sensor 8 provided as a temperature detecting means provided in contact with the pressure roller 4; Provided at the entrance to cool the pressure roller 4 And a blower 9 as the pressure roller cooling means for.
[0027]
The rollers 2 and 4 forming a pair of fixing rollers pass through a passage portion A, which is an area through which a recording medium having a relatively small size (hereinafter, referred to as a small-size sheet) passes the length of the pair of fixing rollers. , A non-passing portion B which is a region that does not pass through. The non-passing portion B is located at both ends of the roller when the transfer paper P passes through the nip portion 3 with reference to the center (FIG. 2A), and when the transfer paper P passes through the nip portion 3 with reference to the end ( FIG. 2B) is located at the end opposite to the reference end. The first sensor 7 is in contact with the upper portion of the passing portion A of the heating roller 2, and the second sensor 8 as a temperature detecting means for detecting the temperature of the non-passing portion B is provided at the non-passing portion B of the pressure roller 4. Each is provided so as to be in contact with the lower portion, and detects the temperature of the contacted portion. The number of the first sensors 7 is not limited to one, and a plurality of the first sensors 7 may be provided in order to reliably detect the temperature of the passage portion A made of transfer paper of various sizes. Similarly, the number of the second sensors 8 is not limited to one, and a plurality of the second sensors 8 may be provided in order to surely detect the temperature of the non-passing portion B of the transfer paper of various sizes.
[0028]
The heat source 1 is composed of a halogen lamp, and is disposed in the axial direction of the heating roller 2 so as to have a length substantially equal to the entire length of the heating roller 2. Heat to The pressure roller 4 is configured to be able to freely contact and separate from the heating roller 2 by a pressing mechanism (not shown).
[0029]
In the present embodiment, the heating roller 2 employs Al as a base material, but may use a metal such as SUS as a base material. A release layer is provided on the surface of the substrate for the purpose of preventing the toner from adhering thereto. As the material of the release layer, Teflon is used, but a PFA tube or the like can also be used.
[0030]
As a method for forming the release layer, there are a method of directly coating a heating roller, a method of heating a tube-shaped material at a high temperature, and shrinking and adhering to the heating roller. As for the thickness of the heating roller, the thinner the heat capacity, the smaller the heat capacity, and the faster the temperature rise time, which is preferable. However, if the thickness is too small, bending occurs due to the pressure contact force with the pressure roller, and the generation and fixing of transfer paper wrinkles Since an inconvenience such as variation in properties occurs, it is necessary to select an optimal thickness.
[0031]
In the present embodiment, the pressure roller 4 employs SUS as a core rod, but other metals such as iron, Al, and brass may be used as the core rod. An elastic layer of silicon rubber is formed on the core rod. As the elastic layer, a relatively soft material such as foamed silicone rubber may be used in order to reduce a pressing force for securing a nip width necessary for fixing. On the surface of the elastic layer, a release layer for imparting releasability, or silicone rubber, which is an insulating material, is charged by friction and the like, and an unfixed toner image is formed due to the electrostatic force and generation of discharge. As a conductive layer for preventing disturbance, a Teflon layer containing a conductive material such as carbon may be provided.
[0032]
The pressing force of the pressing roller 4 against the heating roller 2 only needs to have a pressing force capable of securing a necessary nip width. In the case of a monochrome PPC, a laser printer, or a PPF, it is generally about 1 kgf to 20 kgf.
[0033]
An air passage for cooling the pressure roller 4 is formed between the pressure roller 4 and the bottom of the cover 6. The blower 9 as a cooling means for sending air to the ventilation passage has a plurality of blades rotating about an axis provided in parallel with the pressure roller 4 and having a length substantially equal to the length of the pressure roller 4 in the axial direction. Consists of fans. The blowing device 9 varies the blowing amount in the axial direction of the pressure roller 4 so that the flow rate of air to the non-passing portion B, which becomes high when small-size paper is continuously passed, becomes larger than that of the passing portion A. Therefore, the size of the blade changes in the axial direction. As a configuration for changing the air flow rate in the axial direction, in addition to the above, an air flow control plate for shielding or changing the direction of the air flow was provided, and the size of the air inlet and outlet was changed. A configuration, a configuration in which a plurality of blowers are provided in the axial direction, and the like are given. In a configuration in which a plurality of air blowers are provided, only the non-passing portion B can be selectively cooled.
[0034]
The operation timing of the blower 9 is determined by a control unit including a recording body detection unit that detects the number and size of the transfer paper P to be sent to the fixing device and a second sensor 8. The recording medium detecting means detects a command from the operator or the size of the transfer paper when the toner image is transferred to the transfer paper, and a control unit (not shown) for selecting the size also serves as this. To detect the size of the paper, a sensor or the like may be provided in the fixing device. The control means may include one of the recording body detection means and the second sensor 8. With such a configuration, it is possible to reduce a decrease in the temperature of the pressure roller in the passing portion and effectively reduce a rise in the temperature in the non-passing portion.
[0035]
It is preferable to generate an air flow in the transfer paper transport direction of the pressure roller 4 from the viewpoint that the passage portion A of the pressure roller 4 can be selectively cooled. You can also shed. In this embodiment, the air blowing device 9 is used as the cooling means, but a Peltier element or the like may be used as long as the pressure roller 4 is actively cooled. In terms of cost, cooling by a blower is preferable. The blower 9 is not limited to the air intake side, and may be provided on the discharge side. In cooling by blowing air, the size and shape of the air intake and exhaust ports are appropriately set and the smooth flow of air can reduce the generation of abnormal noise due to the air flow.
[0036]
In an image forming apparatus used for a PPC, a laser printer, a PPF, or the like, a toner image T is formed on the surface of the transfer paper P by a well-known electrophotographic process of charging, exposure, development, and transfer. The transfer paper P on which the toner image T is formed is conveyed in the direction of arrow C in FIG. 1 and guided to the fixing unit, that is, the nip unit 3 by the guide member 5, where the toner image T is heated and fixed by the heat of the heating roller 2. You. Thereafter, the transfer paper P on which the toner image T has been heated and fixed is discharged from the fixing device. In the fixing step, the thermal energy of the heating roller 2 is deprived by the transfer paper P, thereby lowering the temperature of the heating roller 2. Therefore, the first sensor 7 detects this, and the heat source 1 is driven to drive the heating roller 2. Is heated to the set temperature.
[0037]
When small-size paper is continuously printed, heat energy of the heating roller 2 is deprived only of the passing portion B. Since the temperature detection of the heating roller 2 is performed in the passage portion A of the heating roller, when the temperature decreases, the heat source 1 is driven to increase the temperature of the heating roller 2 to a set temperature. Since the non-passing portion B is similarly heated, the temperature of the non-passing portion B rises above the set temperature by heating even though the temperature does not decrease in the non-passing portion B. At this time, from the experiment of the present inventors, it was found that the temperature of the non-passing portion B becomes higher than that of the passing portion A even in the pressure roller 4.
[0038]
Since the heat capacity of the heating roller 2 is small, the temperature rise in the non-passing portion is relatively quickly eliminated after a while, but the heat capacity of the pressure roller 4 is large and the heat conductivity of the silicone rubber, which is a material of the elastic layer, is large. Therefore, the temperature of the non-passing portion B on the pressure roller 4 side does not readily decrease. Therefore, when the heating roller 2 is rotated again thereafter, the non-passing portion B of the heating roller 2 comes into contact with the high-temperature pressing roller 4 and becomes hot again immediately.
[0039]
In the present embodiment, the blowing device 9 is driven at the time when it is determined that the small size paper is continuously passed and when the temperature of the non-passing portion B is detected to be equal to or higher than the predetermined temperature. At least the non-passing portion B of the pressure roller 4 is cooled. Therefore, the phenomenon that the non-passing portion B of the pressure roller 4 becomes much hotter than the passing portion A does not occur, and the temperature rise of the non-passing portion of the heating roller 2 in contact with the pressure roller 4 is suppressed.
[0040]
Experimental example 1
With the configuration of the present embodiment, a fixing device for A3 recording paper as shown below was prepared, and the temperature rise of the non-passing portion B when the transfer paper of B5 width was continuously passed through the fixing device was measured.
As Comparative Example 1, measurement was also made without the blower 9.
[0041]
Heating roller size: width 335mm, diameter 30mm, heat 0.6mm
Heating roller material: Aluminum
Heat source: Halogen lamp
Heat source supply power: 1000W
Pressure roller: diameter 30mm, core material = iron, elastic layer = silicon rubber
Cooling means: Suction by fan
Recording paper: Ricoh type 6200 paper
Recording paper feed speed: 90 mm / s
Heating roller set temperature: 180 ° C
The non-passing portion temperature rise in the present embodiment on the side of the heating roller 2 is compared with the non-passing portion temperature rise in Comparative Example 1 in the case where the blower is not provided. In FIG. 3, a indicates the temperature of the passage section A measured by the first sensor 7. b and c show the temperature rise characteristics of the non-passing portion B of the pressure roller 4 measured by the second sensor 8, where b is a case where a blower is provided and c is a case where a blower is not provided. It is a characteristic. As shown in FIG. 3, according to the present embodiment, it is found that the temperature rise in the non-passing portion when small-size paper is continuously passed is reduced, and the difference between the temperature of the passing portion A and the temperature is reduced.
[0042]
Immediately after 50 sheets of B5 size paper were continuously passed using the fixing device of the present embodiment, A4 size paper on which a toner image was formed was passed, and the fixed image was evaluated. In the case of the example, a good fixed image was obtained, whereas in Comparative Example 1, an offset occurred in the non-passing portion B, and the occurrence of wrinkles on the transfer paper P was confirmed, resulting in a poor image. Was. Further, when the temperature rise time from room temperature to the set temperature of the heating roller was compared, it was possible to raise the temperature in the same time as Comparative Example 1 by operating the blower 9 only during continuous paper passing.
[0043]
Further, the air flow rate is small in the passage portion A and large in the non-passage portion B, that is, the cooling capacity is large in the non-passage portion B and small in the passage portion A, or only the non-passage portion B is selectively cooled. As a result, the temperature of the passage A is not greatly reduced, so that the temperature is detected by the first sensor 7 and the temperature of the passage A that controls the temperature is the same as that when the blower 9 is not used. And there is no effect on power consumption during continuous paper passing.
[0044]
FIG. 4 shows three examples of the heating roller 10 in which the heating roller itself has a heat storage layer.
The heating roller 10 shown in FIG. 4A has a heating resistor 10b formed on the surface of a base material 10a, on which a releasability from a toner is improved, and a contact between another member and the heating element. The heating roller 10 shown in FIG. 4 (b) is provided with a heat-resistant resin layer 10c of Teflon for the purpose of preventing the heating element from being damaged and electrically insulating the heating resistor. A heat-generating resistor 10b is formed on the inner surface of a base material 10a, and the heat-resistant resin layer 10c is formed on the surface of the base material 10a. The heating roller 10 shown in FIG. 4C has a configuration in which a heat-resistant resin layer 10c is formed on the surface of a roller 10d made of a material that generates heat.
[0045]
The roller 21d is formed of conductive fibers, but may be formed of carbon-dispersed ceramics, so-called self-heating ceramics. Glass is used as the material of the base material 10a, but the material is not limited to this, and ceramics or a metal such as Al or SUS may be used. However, when metal is used, SiO 2 is used for electrical insulation from the heating resistor. ₂ It is necessary to provide an insulating layer of a resin material such as polyimide on the surface layer.
[0046]
As the heating roller 10, although not shown, there is another heating roller in which the base material 10a itself is a heating element. Examples of the heating element include a material in which a conductive material is dispersed in ceramics, a material in which conductive fibers are formed in a cylindrical shape, and the like. The heat roller 10 has a heat source and the heat roller 10 integrated with each other as compared with the heat roller 2 using a halogen lamp or the like. Direct heating of the vicinity of the surface 10 results in good heating efficiency and reduction in power consumption. By thinning the base material 10a, the heat capacity is reduced and the temperature rise time is shortened, and PPC, laser printer, PPF, etc. This is an extremely excellent fixing method in that the so-called wait time until printing is shortened.
[0047]
When glass is used for the base material 10a, there is also an advantage that the cost of the glass itself is low. During standby, the power supply to the heating roller 10 can be stopped or supplied slightly to maintain a low temperature. The waiting time of the user at the time of reprinting is desirably to shorten the heating rise time up to the fixing temperature within usually 30 seconds, preferably within 15 seconds. For this purpose, it is necessary to reduce the heat of the heating roller to 1 mm or less when using Al, SUS, or glass as a base material, and to reduce the thickness of the ceramic to the limit of processing (usually 1 to 2 mm) for ceramics.
[0048]
However, on the other hand, in the case of a heating roller having a small heat capacity, when used in a high-speed machine, the thickness of the heating roller is thin, so that heat in the horizontal direction hardly occurs, and a non-passing portion temperature rise is likely to occur. There is also a problem that. Above all, when glass or ceramics is used as the base material, there is a disadvantage that the temperature rise in the non-passing portion tends to be large because of poor thermal conductivity. In the case where a heating roller having a heat source on or near the surface is used as the heating roller 10, the above-described problem can be solved particularly effectively.
[0049]
Experimental example 2
A fixing device for A3 as shown below was prepared with the configuration using the heating roller 10, and the temperature rise in the non-passing portion when the transfer paper P having the A4 width was continuously passed through the fixing device was measured.
As Comparative Example 2, measurement was performed using the heating roller 10 and without the blower 9.
[0050]
Heating roller configuration: FIG. 4 (a)
Heat source supply power: 700W
Heating roller size: width 335mm, diameter 30mm, thickness 0.6mm, length of heating section 305mm
Heating roller material: Glass
Pressure roller: diameter 30mm, core material = iron, elastic layer = silicon rubber
Cooling means: Suction by fan
Recording paper: Ricoh type 6200 paper
Recording paper feed speed: 90 mm / s
Heating roller set temperature: 180 ° C
The temperature rise of the non-passing portion in the present embodiment on the side of the heating roller 10 is compared with the temperature rise of the non-passing portion of the comparative example 2 without the blower. In FIG. 5, a indicates the temperature of the passage section A measured by the first sensor 7. b and c show the temperature rise characteristics of the non-passing portion B of the pressure roller 4 measured by the second sensor 8, where b is a case where a blower is provided and c is a case where a blower is not provided. It is a characteristic. As shown in FIG. 5, the temperature rise in the non-passing portion when the small-size paper is continuously passed according to the present invention is reduced, and the difference between the temperature of the passing portion A and the temperature is greatly reduced. I understand.
[0051]
Immediately after 50 sheets of B5 size paper were continuously passed using the fixing device of the present embodiment, A4 size paper on which a toner image was formed was passed, and the fixed image was evaluated. In the case of the example, a good fixed image was obtained, whereas in Comparative Example 2, an offset occurred in the non-passing portion, and the occurrence of wrinkles on the recording paper was confirmed, resulting in a poor image.
[0052]
Comparing the temperature rise time from room temperature to the set temperature of the heating roller, the temperature could be raised in the same time as Comparative Example 2 by operating the blower 9 only during continuous paper feeding. Further, the amount of air flow is small in the passing portion A and large in the non-passing portion B, that is, the cooling capacity is large in the non-passing portion B and small in the passing portion A, or selectively only the non-passing portion B. By cooling, the temperature of the passage section A does not drop significantly. Therefore, the temperature is detected by the first sensor 7 and the passage section A controlling the temperature is the same as the case where the blower 9 is not used. And there is no effect on power consumption during continuous paper passing.
[0053]
6A and 6B show a second embodiment of the present invention. In this embodiment, the cover 11 also serves as a heat absorbing means. The first embodiment does not have the air inlet and outlet of the cover 6 and the blower, and the pressure roller cooling means is opposed to the pressure roller 4 and is provided to the pressure roller 4 at the non-passing portion B. This is different from the first embodiment in that the heat absorbing means is close to the apparatus, that is, the cover 11 also serves as a heat absorbing means as a cooling means. FIGS. 6A and 6B show a case where the sheet feeding device is based on the center and a case where the sheet feeding device is based on the end. The heating roller shown in FIG. 4A is employed. The other configuration is the same as that of the first embodiment, and therefore, the description is omitted by attaching the reference numeral.
[0054]
The distance between the pressure roller 4 and the cover 11 is different at portions corresponding to the passing portion A and the non-passing portion B of the pressure roller 4. In the non-passing portion B, the distance is close, and in the passing portion A, the distance is larger. In the non-passing portion B, the heat of the pressure roller 4 is easily radiated to the cover 11, and in the passing portion A, heat is hardly radiated.
[0055]
In general, fixing in a warm state is better than fixing in a cold state of a pressure roller in terms of fixability and power consumption during fixing of a heating roller. This is because the recording paper is heated not only by the heating roller but also by the pressure roller because the pressure roller is warmed, and the recording paper itself is easily heated. To improve the fixability, reduce the decrease in the temperature of the heating roller, and reduce the electric power for reheating.
[0056]
In the present embodiment, the temperature drop of the pressure roller 4 in the passing section A is reduced, the fixing of the toner image is secured, and the power consumption of the heating roller 10 is reduced. Since the excess heat is taken away and the temperature rise in the non-passing portion of the pressure roller 4 is reduced, the temperature rise in the non-passing portion of the heating roller 10 in contact therewith can be reduced.
[0057]
The distance between the pressure roller 4 and the cover 11 in the passing portion A and the non-passing portion B is set to 10 mm and 5 mm, respectively, but can be set to 10 mm or more and 1 mm or more and less than 10 mm, respectively. If the non-passage portion B is too close, the pressure roller 4 may be damaged due to contact with the pressure roller 4.
[0058]
In order to make the temperature inside the cover 11 uniform, a high heat conductive layer such as an Al film may be provided on the inner surface of the cover 11. This can prevent the cover at the position corresponding to the non-passage portion B from becoming hot and reducing the heat absorption effect, and can also prevent the temperature from being abnormally high and the user's safety from being impaired.
If the temperature of the pressure roller 4 is particularly high, the distance may be changed in accordance with a delicate tendency of the temperature of the pressure roller 4 such that the pressure roller 4 is closer to the temperature, and is relatively far away at a slightly lower temperature. Conceivable.
[0059]
Experimental example 3
A fixing device for A3 as shown below was formed with the configuration of the present embodiment using the cover 11, and the temperature rise of the non-passing portion B when the recording paper of A4 width was continuously passed through the fixing device was measured.
As Comparative Example 3, measurement was also performed when the distance was constant at 12 mm, that is, when there was no heat absorbing means.
[0060]
Heating roller configuration: FIG. 4 (a)
Heat source supply power: 700W
Heating roller size: width 335 mm, diameter 30 mm, thickness 0.6 mm, length of heating section 305 mm
Heating roller material: Glass
Pressure roller: diameter 30mm, core material = iron, elastic layer = silicon rubber
Distance between pressure roller and cover: center = 12 mm, end (between both ends of pressure roller 30 mm) = 2 mm
Recording paper: Ricoh type 6200 paper
Recording paper feed speed: 90 mm / s
Heating roller set temperature: 180 ° C
The non-passing portion temperature rise in the present embodiment on the heating roller 10 side is compared with the non-passing portion temperature rise in Comparative Example 3 when the distance between the pressure roller 4 and the cover 6 is fixed at 12 mm. In FIG. 7, a indicates the temperature of the passage section A measured by the first sensor 7. b and c show the temperature rise characteristics of the non-passing portion B of the pressure roller 4 measured by the second sensor 8, and b shows the case where the cover has a heat absorbing means, and c shows the cover as the heat absorbing means. This is the characteristic when not having one. As shown in FIG. 7, according to this embodiment, the rise in the temperature of the non-passing portion when small-size paper is continuously passed is reduced, the difference between the temperature of the passing portion A is significantly reduced, and the temperature is greatly improved. You can see that there is. Also, when compared with the case where the distance between the pressure roller 4 and the cover 6 is fixed at 2 mm, almost the same effect can be obtained with respect to the rise in the temperature at the non-passing portion. But it turned out to be fast. In this embodiment, the power consumption during continuous feeding of small-size paper was also smaller.
[0061]
Immediately after 50 sheets of A4 size paper were continuously passed using the fixing device of the present embodiment, A3 size paper on which a toner image was formed was passed and the fixed image was evaluated. In the case of the example, a good fixed image was obtained, whereas in Comparative Example 3, an offset occurred in the non-passing portion B, and the occurrence of wrinkles on the recording paper was confirmed, resulting in a poor image. .
[0062]
The cover 12 as the heat absorbing means shown in FIGS. 8A and 8B has a different thickness in the axial direction of the pressure roller. FIGS. 8A and 8B show a case where the sheet feeding position is based on the center and a case where the sheet feeding position is based on the end. By increasing the thickness of the portion facing the non-passing portion B of the cover 12 and reducing the thickness of the other portions, the heat capacity of the cover 12 at each portion facing the passing portion A and the non-passing portion B is reduced. Are different. This is suitable in that the non-passing portion B requires a larger amount of heat to keep the temperature in the axial direction of the pressure roller 4 constant.
[0063]
By using the cover 12, even if the heat of the pressure roller 4 is radiated to the cover in the non-passing portion B more than the passing portion A, the heat capacity of the non-passing portion B is large, so that The portion of the cover 12 is not easily heated, and the state in which the temperature difference between the cover 12 and the pressure roller 4 is large can be maintained for a long time, so that the heat radiation effect of the non-passing portion B of the pressure roller 4 can be maintained for a long time. Thereby, the rise in the temperature of the non-passing portion of the heating roller 2 can be reduced for a long time.
[0064]
Therefore, even when a large number of small-size papers are printed, a decrease in the temperature of the pressure roller 4 in the non-passing portion B is reduced, the fixing property is secured, and the power consumption of the heating roller 2 is reduced. By removing excess heat generated by the rise in the temperature of the non-passing portion and reducing the rise in the temperature of the non-passing portion of the pressure roller 4, the rise in the temperature of the non-passing portion of the heating roller 2 in contact therewith can be reduced.
[0065]
The thickness of the portion of the cover 12 facing the non-passing portion B is set to 10 mm. It is preferable that the thickness is as thick as possible, because it is more difficult to warm up. However, if the thickness is too large, the entire fixing device becomes large, so that the thickness is formed in the range of 7 to 20 mm.
[0066]
Experimental example 4
A fixing device for A3 as shown below was prepared with the configuration using the cover 12, and the temperature rise of the non-passing portion when recording paper of A4 width was continuously passed through the fixing device was measured.
[0067]
Heating roller configuration: FIG. 4 (a)
Heat source supply power: 700W
Heating roller size: width 335 mm, diameter 30 mm, thickness 0.6 mm, length of heating section 305 mm
Heating roller material: Glass
Pressure roller: diameter 30mm, core material = iron, elastic layer = silicon rubber
Distance between pressure roller and cover: center = 12 mm, end (between both ends of pressure roller 30 mm) = 2 mm
Recording paper: Ricoh type 6200 paper
Recording paper feed speed: 90 mm / s
Heating roller set temperature: 180 ° C
With this configuration, even when 100 sheets of A4 size paper are continuously passed, the temperature rise in the non-passing portion of the heating roller 2 can be maintained at 20 ° C. or less, and immediately after this, a toner image is formed. As a result of passing the A3 size paper and evaluating the fixed image, a good fixed image was obtained without offset or wrinkling of the recording paper.
[0068]
For convenience of explanation, the pressure roller cooling means is only an air blower in the first embodiment and only a heat absorbing means in the second embodiment. It is possible to use both at the same time, and the combination of these, including the specific arrangement positions of the recording body detecting means and the temperature detecting means, can be appropriately selected.
[0069]
【The invention's effect】
According to the present invention, since the cooling means for cooling the pressure roller is provided, the temperature of the non-passing portion of the pressure roller is suppressed from greatly increasing, and the non-passing portion of the heating roller in contact with the pressure roller is suppressed. The temperature rise in the part was reduced. As a result, even if a large recording medium is passed after the small-size paper is continuously passed, a hot offset does not occur and the recording medium does not wrinkle, and a high-quality recorded image is obtained. I was able to.
[0070]
By cooling around the non-passing portion of the pressure roller, the temperature of the central portion of the pressure roller does not drop, and the temperature of the central portion of the heating roller does not drop significantly during paper passing, and the set temperature is maintained. Power consumption was reduced. Further, since the cooling means can be operated only when the non-passage portion temperature rises, the temperature rise time is not affected and the time required for the temperature rise is shortened.
[0071]
By changing the distance between the pressure roller and the cover as a heat absorbing means that covers the pressure roller between the passing portion and the non-passing portion of the pressure roller, the heat release amount of the pressure roller from the pressure roller changes, and the heating roller The rise in the temperature of the non-passing portion of the pressure roller caused by the rise in the temperature of the non-passing portion is suppressed. In addition to being able to obtain, the passing portion is not cooled and is appropriately warmed, and the temperature of the heating roller is detected near the central portion, which is the passing portion of the heating roller. The power supply to the rollers can be reduced.
[0072]
Since the amount of heat transferred from the heating roller to the pressure roller is smaller than when the distance between the pressure roller and the cover is fixed, the non-passing portion temperature rise can be solved without increasing the temperature rise time, and Both shortening of the warming time can be achieved. Since the thickness of the heat absorbing means in the portion facing the non-passing portion is increased, the ability of the pressure roller to deprive the temperature of the non-passing portion increases, and even if the number of small-size paper sheets continuously passed is increased. , The rise in the temperature of the non-passing portion can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic side view of a fixing device according to a first embodiment of the present invention in which a blower is used as a pressure roller cooling unit.
FIG. 2 is a schematic diagram showing a passing portion and a non-passing portion in the first embodiment of the present invention.
FIG. 3 is a diagram for comparing the temperature rise of each part of a heating roller between a transfer device using the first embodiment having a blower and a transfer device not having a blower according to the present invention. It is.
FIG. 4 is a sectional view showing a structure of a heating roller having a configuration different from that of the heating roller shown in FIG. 1 in the first embodiment of the present invention.
FIG. 5 shows how the temperature of each part of the heating roller of the transfer device in the first embodiment of the present invention in which the heating roller is the one shown in FIG. 4 and that of the transfer device without a blower are increased. It is a figure for comparing.
FIG. 6 is a schematic view of a fixing device according to a second embodiment of the present invention in which a heat absorbing unit is used as a pressing roller cooling unit.
FIG. 7 is a diagram for comparing the temperature rise of each part of the heating roller between the fixing device having the pressure roller cooling unit shown in FIG. 6 and the fixing device not having the pressure roller cooling unit. It is.
FIG. 8 shows a second embodiment of the present invention in the case where the thickness of the heat absorbing means at the portion facing the non-passing portion of the pressure roller is thicker than other portions as the pressure roller cooling means. FIG. 2 is a schematic diagram of the fixing device shown.
[Explanation of symbols]
1 heat source
2, 10 heating roller
4 Pressure roller
8 Temperature detection means
9 Blower
11,12 Heat absorber
A Passing part
B Non-passing part
P record
T toner image

Claims (9)

A heating roller, and a pressure roller pressed against the said heat roller, by passing the recording material between the pressure roller and the heating roller, heat fixing an unfixed toner image on the recording medium in the fixing apparatus, said has a pressure roller cooling means for cooling the non-passage portion where the recording material does not pass through the small size of the pressure roller, wherein the pressure roller cooling means, facing the pressure on the pressure roller A fixing device comprising: a heat absorbing unit that is closer to the pressure roller in the non-passing portion than in a passing portion through which a small-sized recording paper of the pressure roller passes . 2. The fixing device according to claim 1, wherein a thickness of a portion of the heat absorbing unit facing the non-passing portion is set to be thicker than thicknesses of other portions. 3. The fixing device according to claim 1, wherein the heat absorbing unit is a cover installed to cover the heating roller and the pressure roller. 4. The fixing device according to claim 1, wherein the pressure roller cooling unit increases the amount of air blown to the heat absorbing unit and the non-passing portion than the amount of air blown to the passing portion. 5. A fixing device, comprising: a blowing device. 5. The fixing device according to claim 4, further comprising control means for controlling an operation timing of said pressure roller cooling means. The fixing device according to claim 5, wherein the control unit includes a recording body detection unit that detects a size of the recording body. 7. The fixing device according to claim 5, wherein the control unit includes a temperature detection unit that detects a temperature of the non-passing portion. The fixing device according to claim 1, wherein the heating roller has a heat source in a surface layer or an inner layer near a surface of the heating roller. An image forming apparatus for recording an image formed by a series of image forming processes on a recording medium, comprising the fixing device according to claim 1.

Images