JP4176461B2 - Belt fixing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a belt fixing device used in an image forming apparatus of an electrostatic copying process such as a copying machine, a facsimile machine, a printer or the like. More specifically, the present invention relates to an image forming apparatus including an intermediate transfer member having a cleaning device.
[0002]
[Prior art]
Conventionally, the heat capacity of the fixing belt is extremely small as compared with a fixing roller of a common heat roller fixing method, and a rapid cooling action is obtained when passing through the fixing nip portion, and the effect of preventing the offset phenomenon is great. However, the belt fixing method has a disadvantage that a temperature gradient in the axial direction is likely to occur because the heat capacity of the fixing belt is small. At the start-up, the temperature at the end of the fixing belt is lowered, and the glossiness at the end of the transfer paper is lowered. On the other hand, if small-size transfer paper is output continuously, the temperature at the end of the fixing belt rises and the glossiness at the end of the transfer paper rises. It may cause an offset.
Various inventions for eliminating the temperature gradient on the roller and performing uniform fixing are disclosed.
[0003]
For example, in the technique disclosed in Patent Document 1, in the heat roller fixing device, when the difference between the end temperature of the pressure roller and the center temperature becomes large, the cooling mode is set.
In the cooling mode, the energization to the heater is turned off, and the cooling fan is operated with the fixing roller and the pressure roller stopped to cool the pressure roller. This eliminates the temperature gradient in the axial direction of the pressure roller and makes it uniform.
In the technique disclosed in Patent Document 2, in the heat roller fixing, a first heater having a light distribution corresponding to a small size paper and a second heater having a light distribution corresponding to the other end portion are used. A heater and a third heater having a light distribution corresponding to large size paper are provided. When the small-size sheet is passed, the temperature at the end of the fixing roller is prevented by controlling with the first heater.
[0004]
However, the disclosed technology has the following problems. In Patent Document 1, there is a problem in that an image cannot be output until the machine stops in the cooling mode and the end temperature rise decreases. Moreover, in patent document 2, since three heaters are used and temperature control is required in each heater, there exists a problem of leading to a cost increase. Furthermore, in the connection portion between the light distribution distribution of the small size heater and the light distribution distribution corresponding to the other end portions, temperature unevenness occurs on the fixing roller, which causes a fixing defect. is there. In particular, the tendency is remarkable in the thin fixing roller used to shorten the rise time.
[0005]
[Patent Document 1]
JP-A-8-190303 [Patent Document 2]
JP-A-8-220932 [0006]
[Problems to be solved by the invention]
Therefore, the present invention has been made in view of the above problems, and the problem is to provide a belt fixing device and an image forming apparatus in which the temperature gradient is made uniform and the rise time is shortened without increasing the cooling mode and the heater. Is to provide.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the invention described in claim 1 includes a fixing roller, a heating roller having a heat source, and an endless fixing belt wound around the fixing roller and the heating roller. In a belt fixing device in which a roller is pressed against a fixing roller via a fixing belt, a heat diffusing member provided opposite to the heating roller via the fixing belt and in contact with the outer periphery of the fixing belt, The surface of the heat diffusing member is coated with Teflon, and a scraper is disposed in contact with the outer periphery of the heat diffusing member.
According to a second aspect of the present invention, there is provided an image carrier that carries a latent image, charging means for charging the image carrier by bringing a charging member into contact with or close to the surface of the image carrier, and forming a latent image on the image carrier. A latent image forming unit, a developing unit that forms a toner image by attaching toner to the latent image on the image carrier, and a transfer unit that transfers the toner image formed on the image carrier to a recording member. The image forming apparatus includes a fixing roller, a heating roller having a heat source, and an endless fixing belt wound between the fixing roller and the heating roller, and is heated via the fixing belt. A heat diffusing member that is opposed to the roller and is in contact with the outer periphery of the fixing belt, the surface of the heat diffusing member being coated with Teflon, and contacting the outer periphery of the heat diffusing member; Arranged belt fixing device And an image forming apparatus provided with.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an example of an image forming apparatus equipped with the fixing device of the present invention. The image forming apparatus shown in FIG. 1 is used in a copying machine or printer capable of forming a full-color image. In addition to this, the image forming apparatus 20 has an image similar to that of the above-described copying machine and printer based on the received image signal. There is a facsimile apparatus capable of forming processing, and the present invention can be used for any image forming apparatus. Note that the fixing device of the present invention includes not only the color image forming apparatus having the configuration shown in FIG. 1 but also a device for a single color image.
[0009]
In FIG. 1, an image forming apparatus 20 includes the following apparatuses.
Image forming devices 21C, 21Y, 21M, and 21BK that form images of respective colors according to the original image, transfer devices 22 that are disposed to face the image forming devices 21C, 21Y, 21M, and 21BK, and the respective image forming devices The image forming apparatus 21C forms sheet-like media conveyed from a sheet feeding cassette 24 as sheet-like medium supply means for supplying various sheet-like media to a transfer area where the devices 21C, 21Y, 21M, 21BK and the transfer device 22 face each other. , 21Y, 21M, and 21BK, and a fixing roller 1 that fixes the sheet-like medium after transfer in the transfer region. The image forming apparatus 20 has a larger heat capacity than that of paper such as plain paper generally used for copying, 90 kg paper such as OHP sheets, cards and postcards, thick paper equivalent to a basis weight of about 100 g / m ² or more, and envelopes. Any of so-called special sheets can be used as the sheet-like medium.
[0010]
Each of the image forming devices 21C, 21Y, 21M, and 21BK develops each color of cyan, yellow, magenta, and black, and uses different toner colors, but the configuration is the same. The configuration of 21C will be described as a representative example of each of the image forming devices 21C, 21Y, 21M, and 21BK.
The image forming device 21C includes a photosensitive drum as an electrostatic latent image carrier, a charging device, a developing device, and a cleaning device arranged in order along the rotation direction of the photosensitive drum. A well-known configuration for receiving exposure light between the two is used. Further, a belt fixing device 10 is provided on the downstream side of the transfer device. In addition to the drum shape, the electrostatic latent image carrier may have a belt shape. In the image forming apparatus 20 shown in FIG. 1, since the transfer device 22 extends obliquely, the space occupied by the transfer device 22 in the horizontal direction can be reduced.
[0011]
Here, the belt fixing device 10 will be described. FIG. 2 is a schematic diagram showing a configuration of a belt fixing device according to an embodiment of the present invention.
The embodiment of the present invention has a pressure roller 4 for transporting a transfer material, an endless fixing belt 1 whose surface is coated with a release material, and a plurality of belt transports that rotatably support the fixing belt 1 therein. A roller 236 and a halogen heater 5 for applying heat to the transfer material are provided.
Among the belt conveying rollers in the fixing belt 1, the fixing roller 2 is located at a position facing the pressure roller 4 through the fixing belt 1, and the fixing roller 2 holds the fixing belt 1 between the fixing roller 1 and the pressure roller 4. In this configuration, a nip portion is formed, and among the belt conveyance rollers in the fixing belt 1, an auxiliary roller 6 disposed at a position where the fixing belt 1 is wound around the pressure roller 4 is provided. As shown in FIG. 1, a transfer material on which an unfixed toner image is placed is conveyed from below to the nip portion obtained in this configuration, and is heated and pressurized in this nip portion to be fixed. Of the belt conveying rollers in the fixing belt 1, a heating roller 3 that includes a halogen heater 5 and applies tension to the fixing belt 1 is provided. A heat diffusion member (heat pipe) 7 contacts and rotates on the outer periphery of the fixing belt 1.
[0012]
As the base of the fixing belt 1, an endless belt-like base formed of a heat resistant resin or metal is used. Examples of the material of the heat resistant resin include polyimide, polyamideimide, polyether ether ketone, and examples of the material of the metal belt include nickel, aluminum, iron, and the like. The thickness is preferably 100 μm or less. Since the surface layer of the fixing belt 1 is in pressure contact with the transfer paper and the toner, it needs to be releasable and is preferably excellent in heat resistance and durability. Therefore, the surface layer of the fixing belt 1 is covered with a heat-resistant release layer made of fluorine resin, high release silicone rubber or the like. The fluororesin is applied to the surface of the substrate by spraying or the like, and is heat-sealed to form a surface release layer. The high release silicone rubber layer has a rubber hardness (JIS A hardness meter) of 25 to 65 degrees and a thickness of 100 to 300 μm, which is desirable as a condition for obtaining good fixability and thermal responsiveness.
[0013]
The fixing roller 2 has a metal core, and includes a heat-insulating elastic member made of a soft heat-resistant material, for example, foamed silicon rubber, in order to make the nip width sufficiently wide on the outer periphery thereof. In this embodiment, the thickness of the heat insulating elastic member is 6 mm with respect to the fixing roller 2 having a diameter of 30 mm.
The configuration of the heating roller 3 that heats the fixing belt 1 and applies tension is a thin-walled roller of a hollow metal cylinder such as aluminum, carbon steel, and stainless steel. Although not shown in the present embodiment, since the thermistor and the thermostat of the safety device are in contact with the outer periphery of the heating roller 3 inside the fixing belt 1, the outer periphery is coated with Teflon. In addition, the thinner the heating roller 3 is, the shorter the rise time can be. However, the thicker the temperature gradient in the axial direction, the higher the temperature becomes, and the two are in a trade-off relationship. In this embodiment, the material is aluminum and the thickness is 1 mm for the heating roller 3 having a diameter of 30 mm.
The auxiliary roller 6 arranged for winding the fixing belt 1 around the pressure roller 4 is a solid metal roller made of aluminum, carbon steel, stainless steel or the like. Alternatively, this metal roller may be used as a metal core and may have a rubber layer on the outer periphery for heat insulation. In this embodiment, a metal roller having a surface plated with nickel is used to prevent rust on carbon steel having a diameter of 10 mm.
[0014]
The configuration of the pressure roller 4 that forms a nip portion facing the fixing roller 2 via the fixing belt 1 has three rubber layers on the outer periphery of the hollow core metal. The base layer is a silicon rubber layer that is conductive and has good thermal conductivity, and in this embodiment has a thickness of 2 mm. The intermediate layer has a fluororubber layer having a thickness of about 15 μm in order to prevent oil swelling. And the surface layer consists of a high release silicone rubber layer of about 70 μm. Here, the diameter of the pressure roller 4 is 40 mm.
[0015]
A heat diffusion member (heat pipe) 7 contacts and rotates on the outer periphery of the fixing belt 1. FIG. 3 is a schematic view showing the structure of a heat diffusion member (heat pipe). The heat diffusion member (heat pipe) is a spiral or net-like core material made of ultra fine wire that generates capillary pressure on the inner wall of a hollow cylindrical tube 7a made of a hollow metal core such as aluminum, stainless steel, carbon steel or copper. It has the wick layer 7b formed, and both ends are sealed by the journal 7c, and the inside is close to a vacuum. The working liquid 7d as a heat transfer medium is sealed inside. With this configuration, the working liquid 7d inside the heat diffusing member (heat pipe) instantly vaporizes in the high temperature part and moves to the low temperature part, and liquefies in the low temperature part and spreads throughout the wick layer. This circulation provides higher thermal conductivity than ordinary metals.
Even if a temperature gradient occurs on the fixing belt due to the contact of the heat diffusing member (heat pipe), the temperature is instantly uniform on the heat diffusing member (heat pipe). The temperature gradient is also uniform. Accordingly, it is possible to prevent gloss unevenness and fixing failure due to low edge temperature at the time of start-up, and gloss unevenness and hot offset due to edge temperature increase that occurs during small-size continuous sheet passing.
[0016]
Conventionally, in the belt fixing device, the heating roller 3 and the pressure roller 4 provided with the heat source 5 are stopped until reaching a predetermined temperature, and after reaching the predetermined temperature, rotation is started and the entire fixing belt 1 can be heated and fixed. Reach temperature. The time taken for this will be referred to as the rise time. Here, the earlier the start of rotation of the fixing belt device, the shorter the rise time. In general cleaning of the surface layer of the fixing belt 1, a metal roller is brought into contact with the surface layer of the fixing belt 1, and a scraper 8 is applied to the outer periphery thereof to scrape off offset toner and paper dust on the surface of the cleaning roller.
In this conventional configuration, toner sticking occurs at the contact portion between the metallic cleaning roller and the scraper 8, and rotation cannot be started unless the temperature of this portion becomes equal to or higher than the toner softening point temperature when starting up. When rotation is started below the toner softening point temperature, high torque is required to rotate, and a large and costly high-power motor is required. Further, since the toner rotates in a solid state, the scraper 8 is repelled and an abnormal noise is generated. In severe cases, the fixing belt 1 may be damaged by the solid toner.
[0017]
In the present invention, the heat diffusion member (heat pipe) 7 is disposed so as to face the heating roller 3 with the fixing belt 1 interposed therebetween, and the scraper 8 is in contact with the outer periphery of the heat diffusion member (heat pipe) 7. Further, the surface layer of the heat diffusing member (heat pipe) 7 is subjected to Teflon coating. With this configuration, the heat diffusion member (heat pipe) 7 cleans a small amount of offset toner or paper dust on the fixing belt 1, and the scraper 8 scrapes off the accumulated small amount of offset toner or paper dust.
In addition, when the heat diffusion member (heat pipe) 7 is used, the time until the heat diffusion member (heat pipe) reaches the toner softening point temperature is earlier than that of the normal metal roller. The rise time can be shortened.
[0018]
Here, an image forming operation by the image forming apparatus shown in FIG. 1 will be described.
The recording member fed from the sheet feeding cassette 24 is transported by a transport roller while being guided by a transport guide (not shown), and is transported to a temporary stop position where the registration roller pair 30 is provided. The recording member sent by the registration roller pair 30 at a predetermined timing is carried on the transfer belt, conveyed toward the image forming devices 21Y, 21M, 21C, and 21K, and passes through the transfer units. The toner images developed on the photoreceptors of the image forming devices 21Y, 21M, 21C, and 21K are superimposed on a recording member at each transfer portion by the transfer device 22, and are recorded by receiving the transfer electric field and the nip pressure. Transferred onto the member. By this superposition transfer, a full color toner image is formed on the recording member. The recording member on which the full-color toner image is formed is discharged onto a paper discharge tray provided outside the main body of the image forming apparatus after the full-color toner image is fixed by the belt fixing device 10.
Therefore, by providing the belt fixing device 10, after the image forming operation is started, the operation is started earlier and the image without gloss unevenness can be obtained in a short time.
[0019]
【The invention's effect】
As described above, in the present invention, even if a temperature gradient occurs on the fixing belt, the thermal conductivity of the thermal diffusion member (heat pipe) that is in contact with the fixing belt is usually several hundred times that of metal. On the (heat pipe), the temperature becomes instantaneously uniform, and the temperature gradient on the fixing belt becomes uniform due to the effect. Accordingly, it is possible to prevent gloss unevenness and fixing failure due to low edge temperature at the time of start-up, and gloss unevenness and hot offset due to edge temperature increase that occurs during small-size continuous sheet passing.
Furthermore, here, if the cleaning roller is a heat diffusion member (heat pipe), the time until the heat diffusion member (heat pipe) reaches the toner softening point temperature is usually several hundred times faster than the metal roller. Time is also shortened.
In the image forming apparatus of the present invention, an image having no gloss unevenness and a fast rise time can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of an image forming apparatus equipped with a fixing device of the present invention.
FIG. 2 is a schematic diagram illustrating a configuration of a belt fixing device according to an embodiment of the present invention.
FIG. 3 is a schematic view showing a structure of a heat diffusion member (heat pipe).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fixing belt 2 Fixing roller 3 Heating roller 4 Pressure roller 5 Halogen heater 6 Auxiliary roller 7 Heat diffusion member (heat pipe)
7a Hollow cylindrical tube 7b Wick layer 7c Journal 7d Hydraulic fluid 8 Scraper 10 Fixing device 20 Image forming device 21 Image forming device 22 Transfer device 29 Exposure device

Claims (2)

A fixing roller, a heating roller having a heat source, and an endless fixing belt wound between the fixing roller and the heating roller,
In the belt fixing device in which the pressure roller is pressed against the fixing roller via the fixing belt,
A heat diffusing member that faces the heating roller through the fixing belt and is in contact with the outer periphery of the fixing belt, the surface of the heat diffusing member being Teflon-coated,
A belt fixing device , wherein a scraper is disposed in contact with the outer periphery of the heat diffusion member . An image carrier for carrying a latent image;
Charging means for charging the image carrier by bringing the charging member into contact with or close to the surface of the image carrier;
A latent image forming means for forming a latent image on the image carrier;
Developing means for forming a toner image by attaching toner to the latent image of the image carrier and developing;
In an image forming apparatus comprising transfer means for transferring a toner image formed on an image carrier to a recording member,
The image forming apparatus includes a fixing roller, a heating roller having a heat source, and an endless fixing belt wound around the fixing roller and the heating roller,
A heat diffusing member that faces the heating roller through the fixing belt and is in contact with the outer periphery of the fixing belt, the surface of the heat diffusing member being Teflon-coated,
An image forming apparatus comprising: a belt fixing device in contact with an outer periphery of the heat diffusing member and having a scraper disposed thereon .

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