JP2003280426A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device by which a fixing roller is efficiently and also quickly heated so as to obtain fixing feasible temperature. <P>SOLUTION: In the fixing device to fix toner by inserting paper carrying unfixed toner through a nip formed by a fixing roller and a pressure roller a lamp heater possessing curved surface reflection film on a back surface to the fixing roller is provided in the vicinity of the outer peripheral surface of the fixing roller. A metallic roller abutting on the fixing roller is provided on the outer peripheral surface of the fixing roller. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a fixing device that inserts a sheet carrying an unfixed toner image through a nip of a pair of heated rollers to heat and melt the unfixed toner on the sheet to fix it on the sheet. Image forming apparatus. In particular,
The present invention relates to an image forming apparatus using an external heating fixing device that heats the surface of a fixing roller from the outside.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, an unfixed toner image is formed between the nip of a roller pair heated by a heat source incorporated in at least one roller of a roller pair forming a nip. A heat roller fixing method is used in which the carried paper is inserted to fix the toner on the paper. In such a heat roller fixing method, the heat capacity of the fixing roller is large, and it takes a long time for the heat to propagate from the heat source such as a halogen lamp built in the fixing roller to the roll surface. As a result, there is a problem that the image output operation cannot be executed promptly because the warm-up time from turning on the power of the image forming apparatus main body to reaching the fixing temperature at which fixing is possible requires several minutes.

In order to shorten the warm-up time and the power consumption in the conventional heat roller fixing method, for example, Japanese Patent Laid-Open No. 1999-2446 has been used in recent years.
An external heating method such as that described in Japanese Patent Laid-Open No. 1-83242 has been proposed. In this publication, a heating roller for heating the fixing roller from the outside is used, which is suitable for causing heat to propagate to the surface of the fixing roller. However, even in this method, heat is propagated to the fixing roller via the heating roller, so that there is a limit in shortening the warm-up time and reducing the power consumption. Further, Japanese Patent Application Laid-Open No. 2001-66928 proposes a system in which a columnar external heater radiates heat directly to a fixing roller and a heating efficiency is improved by using a reflecting member on the side opposite to the fixing roller.
A reflector is required, and the heater itself shields the reflected heat, making it difficult to effectively concentrate and propagate the reflected heat on the surface of the fixing roller. In addition to the configuration in which the heater and the reflection plate are separately provided, the publication discloses an elongated plate-shaped external heater having a heat reflection plate behind, but it is difficult to concentrate heat on the fixing roller. Is.

[0004]

[Problems to be Solved by the Invention]. Therefore, the first aspect of the present invention
In view of the above problems, it is an object of the present invention to provide a fixing device and an image forming apparatus capable of efficiently heating a fixing roller to a fixable temperature in a short time.

[0005]

In order to achieve the above object, the invention of claim 1 fixes a toner by inserting a sheet carrying unfixed toner between a nip formed by a fixing roller and a pressure roller. In the fixing device described above, a lamp heater having a curved reflective film on the back surface of the fixing roller is provided near the outer peripheral surface of the fixing roller. According to the invention of claim 1, when the radiant heat from the lamp heater is propagated to the surface of the fixing roller, the radiant heat is intensively transferred to the fixing roller side by the curved reflective film provided on the back surface of the lamp heater. Can be further shortened.

Further, the invention of claim 2 is characterized in that, in the fixing device of claim 1, a metal roller is provided on the outer peripheral surface of the fixing roller so as to contact the fixing roller.
According to the second aspect of the invention, the heat transfer through the metal roller promotes the uniformization of the temperature of the fixing roller in the axial direction.

According to a third aspect of the invention, in the fixing device according to the second aspect, a plurality of the metal rollers are installed so as to sandwich the lamp heater with a slight gap on the upstream side and the downstream side of the lamp heater. It is a metal roller of. According to the third aspect of the present invention, the metal roller absorbs radiant heat that tends to dissipate from the side surface of the lamp heater without going to the fixing roller and transfers it to the surface of the fixing roller, thus wasting the power consumption of the lamp heater. There is nothing to do.

Further, the invention of claim 4 is characterized in that, in the fixing device according to claim 2, the metal roller is provided on the downstream side of the lamp heater and on the upstream side of the nip. According to the fourth aspect of the present invention, the heat transfer through the metal roller promotes the uniformization of the temperature in the axial direction of the fixing roller, and then the process proceeds to the fixing nip, so that the fixing state of the toner image on the sheet is stabilized. Can be achieved.

Further, the invention of claim 5 provides an image forming apparatus according to any one of claims 1 to 4, characterized in that the fixing means is provided. According to the invention of claim 5, the warm-up time is shortened and an image forming apparatus having high energy efficiency can be obtained.

[0010]

DETAILED DESCRIPTION OF THE INVENTION An image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a front view schematically showing an example of a schematic configuration of an image forming apparatus according to the present invention. Here, in FIG. 1, the cleaning device 2
The housing 0 is not shown. FIG. 2 is a front view schematically showing each color image forming unit. As shown in FIG. 1, a printer 1 (an example of an image forming apparatus) is a tandem type full color image forming apparatus, and a printer body housing 2
Inside the paper, above the paper transport belt 8, from the upstream to the downstream direction (from right to left in FIG. 1) of the transport direction, the image forming units of black, yellow, cyan and magenta are provided. Is provided above. Either full color image output or monochrome image output is selected according to the color information of the output image from the external PC device, and the image output speed is 20 sheets / minute for both full color image output and monochrome image output in A4 size. . An amorphous silicon photosensitive drum 4 is provided in each image forming unit, a main charger 5 is provided around the photosensitive drum 4, and an LED exposing unit 6 is provided around the photosensitive drum 4.
The developing device 3, the transfer roller 9, and the cleaning device 20 are provided.

As shown in FIG. 2, the developing device 3 is provided with a developing sleeve 3a in which a fixed magnet (not shown) is arranged. Each color developer is formed by mixing 5 parts by weight of each color toner of black, yellow, cyan, and magenta having a median diameter (volume basis) of 9 μm by Coulter counter and 95 parts by weight of ferrite carrier having an average particle diameter of 70 μm. 3 and is housed in the developing sleeve 3a.
A magnetic brush of each color developer is formed on the surface. Here, the toner is positively charged by frictional charging with the carrier. The amorphous silicon photosensitive drum 4 and the developing sleeve 3a of each color image forming unit are rotating in the same direction as shown in the developing regions facing each other, the peripheral speed of the photosensitive drum 4 is 100 mm / sec, the developing sleeve 3a. The peripheral speed of is 200 mm / sec. The gap between the photosensitive drum 4 and the developing sleeve 3a and the gap between the spike cutting plate (not shown) and the developing sleeve 3a are both 0.5 mm. A developing bias voltage of +300 V is applied to the developing sleeve 3a.

In FIGS. 1 and 2, firstly, the photosensitive drum 4
Is uniformly charged to +400 V by the charging unit 5, and LED light based on the original image data input from an external PC or the like is emitted from the LED print head unit 6 onto the drum surface. The exposed portion irradiated with light is attenuated to + 25V, and an electrostatic latent image is formed together with the + 400V portion of the non-exposed portion. By the developing bias voltage of +300 V applied to the developing sleeve, the positively charged toner in the developer is reversely developed on the exposed portion on the surface of the photoconductor. In order to maintain the toner density at a constant value even if the toner in the developer is consumed by repeating the image formation, the toner supply containers 7B, 7Y, 7C,
From 7M, toner is replenished to each color developing device 3 by a conveying unit (not shown). Photoconductor drum 4
The paper conveyance belt 8 installed below the rollers is driven in the same direction as the photoconductor 4 in the transfer area, and the rollers 10, 11 are arranged so that the conveyance speed thereof is 100 mm / sec which is the same speed as the photoconductor drum 4. While being transported by
The transfer roller 9 is urged from the back side of the sheet conveying belt 8 so as to come into contact with the photosensitive drum 4. A voltage of −1.5 KV is applied to the transfer roller 9.

Then, the photosensitive drum 4 and the sheet conveying belt 8
Between the sheet feeding mechanism 12 and the sheet conveying path 13, the sheet is conveyed between the photosensitive drums 4 and the sheet conveying belt 8 by −1.5 KV. The toner images of the positively charged colors on the surface of the photoconductor drums 4 are successively transferred to the paper side by the transfer roller 9 to which is applied.
The paper on which the toner images have been transferred by all the photoconductor drums 4 is conveyed to the fixing device 50 and the toner images are fixed, and a color image is formed. The sheet that has passed through the fixing device 50 is sent to the sheet conveying path 15 and is ejected from the ejecting unit 16.
In the image forming apparatus, as the standby mode after the warm-up is finished, there are a standby mode in which an image can be immediately output and an energy saving mode in which the surface temperatures of the fixing roller and the pressure roller are controlled to be low. The control temperature A on the surface of the fixing roller and the control temperature B on the surface of the pressure roller during standby are both 16
It is set to 0 ° C. The control temperature A on the surface of the fixing roller and the control temperature B on the surface of the pressure roller in the energy saving mode are both set to 120 ° C. In this image forming apparatus, a power switch for the entire image forming apparatus is provided on an operation display unit (not shown). Warm-up starts according to the settings stored when the power switch is turned on.

Next, the internal structure of the fixing device 50 will be described in detail with reference to FIG. A halogen lamp is used as a lamp heater for heating the fixing roller. The fixing roller 51 and the pressure roller 52 are in pressure contact with each other to form a fixing nip portion 59. The sheet P having the unfixed toner 60 on its upper surface is conveyed from the right direction in the drawing to the nip portion by a conveying unit (not shown) at the time of image output. A halogen heater 53 is provided with a gap of 2 mm from the fixing roller 51, and heats the fixing roller 51 by irradiation with heat rays. Halogen heater 5
3 is a white reflective film 53 on the back of the fixing roller.
a is coated, and heat energy is radiated intensively in the direction toward the fixing roller 51. Metal rollers 63 and 64 are provided in the vicinity of the upstream and downstream of the halogen heater 53 so as to contact the fixing roller. The function of the metal roller will be described later. The fixing roller 51, the pressure roller 52, and the metal rollers 63 and 64 can be inserted with a margin for the long side 297 mm of the A4 sheet.
All roller portions have a length of 320 mm. The thermistor 54 as a means for detecting the surface temperature of the fixing roller 51.
And a thermistor 55 as a means for detecting the surface temperature of the pressure roller 52. Since each of these thermistors is provided in the vicinity of the center when viewed in the axial direction of each roller, the roller surface temperature in the paper passing area is detected during image output. A halogen heater 58 as a heat source is provided inside the pressure roller 52. A control unit 70 is provided on the main body side of the image forming apparatus to control and supply electric power to the halogen heaters 53 and 58 based on the detected temperatures of the thermistors 54 and 55 to control the rotational driving of the fixing roller 53. Has been.

Simultaneously with the start of heating, the fixing roller 51 starts rotating in the direction of the arrow at the same peripheral speed of 100 mm / sec as when the image is output, and the pressure roller 52 and the metal rollers 63, 6 are rotated.
The fixing roller 51 is driven to rotate.
The halogen heater 53 lights up and heats with a power consumption of 700 W,
The energization is controlled based on the temperature detected by the thermistor 54 on the surface of the fixing roller 51. In other words, the surface temperature of the fixing roller 51 is 16 when warming up after the power of the apparatus main body is turned on.
It is continuously turned on until it reaches 0 ° C, and when the fixing roller surface temperature exceeds 160 ° C, the system shifts from warm-up to standby control to reduce the fixing roller surface temperature to 16 ° C.
The on / off control is performed so as to maintain the range of 0 ± 3 ° C.

Halogen heater 58 inside the pressure roller 52
Is lit and heated with power consumption of 400 W, and energization is controlled based on the temperature detected by the thermistor on the surface of the pressure roller. That is,
At the time of warming up after the power of the apparatus main body is turned on, the halogen heater 58 is continuously turned on until the surface temperature of the pressure roller 52 reaches 160 ° C., and when the pressure roller surface temperature exceeds 160 ° C., the pressure is applied. Roller surface temperature is 160
The on / off control is performed so as to maintain the range of ± 3 ° C. Here, when at least one of the fixing roller 51 and the pressure roller 52 exceeds 160 ° C., the standby control is performed.

At the end of the warm-up, the control is switched to the standby control, the fixing roller is decelerated to a peripheral speed of 1/4 at the time of image output, and the pressure roller 52 and the metal rollers 63 and 64 are also rotated accordingly. The fixing roller 51 and the pressure roller at 160 ° C. ±
It is designed to be kept warm in the range of 3 ° C. During image output, the fixing roller returns to the original peripheral speed of 100 mm / sec, and the halogen heaters 53 and 58 are on / off controlled so as to maintain the fixing roller 51 and the pressure roller within the range of 160 ° C. ± 3 ° C. .

The fixing roller 51 has a roller length of 320
mm, and an iron core bar 51a having an outer diameter of 12 mm,
An elastic layer 51b having a thickness of 6.5 mm coated on the surface of the cored bar 51a and a PFA tube layer 51c having a thickness of 70 μm coated on the surface of the elastic layer 51b to enhance releasability. Has been done. The elastic layer 51b is Asuka C
It is formed of a silicone rubber foam having a hardness of 25 degrees. Further, the fixing roller receives a drive current from the control unit 70 so that the peripheral speed becomes 100 mm / sec, which is the same speed as the photosensitive drum 4, and is rotated by a drive unit (not shown).

The pressure roller 52 has a roller length of 320 m.
m, the outer diameter is 25 mm, and the wall thickness is 0.4 mm, and the roller outer layer 52a is made of aluminum, and the thickness applied to the surface of the roller body 52a is 15 μm in order to enhance the releasability.
And a PTFE layer 52b. A halogen heater 58 having a maximum power consumption of 400 W is built in the roller body 52a. The pressure roller 52 is pressed against the fixing roller 51 by an urging means (not shown) and is driven to rotate according to the rotation of the fixing roller 51.

Next, the non-contact external heating system of the fixing roller by the external halogen heater, which is a feature of the present invention, will be described. Downstream of the thermistor 54, the nip portion 5
A halogen heater 53 is provided with a gap of 2 mm from the surface of the fixing roller 51 on the upstream side of 9. The halogen heater 53 is coated with a reflective film 53a formed of a white silica layer on the back surface toward the fixing roller, and radiates heat energy intensively in the direction toward the fixing roller 51. According to the configuration of the present embodiment, the external reflection mirror conventionally used for reflecting the heat rays radiated from the back surface of the halogen heater to the fixing roller side is not necessary, and the heat rays are prevented from escaping, thus saving Space and energy saving can be achieved. The reflection film of the halogen heater 53 may be any one as long as it can effectively reflect the radiated heat rays to the fixing roller 51 side, and a heat resistant material other than the silica coating layer can be used. Can use a light-colored material or a specular material.

Further, in this embodiment, metal rollers 63 and 64 are provided near the upstream and downstream of the halogen heater 53 so as not to contact with the halogen heater but to contact the fixing roller.
The metal roller is a hollow cylinder made of Al having an outer diameter of 8 mm and a wall thickness of 0.5 mm, and has a gap of 1 mm with the halogen heater 53. The metal rollers 63 and 64 are halogen heaters 5.
The heat rays radiated from No. 3 are effectively blocked in the intermediate region between the surface of the fixing roller 51 and the halogen heater 53, and have an effect of preventing leakage to other places. Further, the metal rollers 63 and 64 also have an effect of promoting heat conduction in the axial direction and preventing nonuniformity of the surface temperature of the fixing roller due to unevenness of heat radiation of the halogen heater 53.

In the present embodiment, the halogen heater 53
The power consumption was 700 W, but the power consumption is not limited to this, and it is possible to appropriately use a power consumption change product. Further, although the gap between the halogen heater 53 and the fixing roller 51 is set to 2 mm, it is not limited to this, and the gap size can be appropriately determined in consideration of the heat conduction efficiency to the fixing roller. Further, in this embodiment, the metal roller 6
Although the thicknesses of 3 and 64 are set to 0.5 mm and the outer diameter is set to 8 mm, the thickness is not limited to this, and the thickness and the outer diameter can be appropriately changed in consideration of heat conduction, heat capacity and the like. .

Further, in the present invention, the use of the halogen heater with the reflection film is an essential requirement, but the metal roller 6 is used.
3, 64 may be omitted in some cases. If only the effect of uniformizing the surface temperature of the fixing roller is aimed at, the installation place can be appropriately set on the surface of the fixing roller.

In the present embodiment, the thickness of the pressure roller 52 is 0.4 mm, but the thickness is not limited to this, and it can be suitably used in the range of 0.2 to 1.5 mm. The release layer on the surface of the roller body was made of PTFE (polytetrafluoroethylene).
It is possible to select from a fluororesin such as a layer (tetrafluoroethylene-per-fluoroalkyl vinyl ether copolymer), PVF (polyvinyl fluoride), ECTFE (ethylene-chlorotrifluoroethylene copolymer). The thickness of this releasable layer was 15 μm, but 1
It is preferably used in the range of 0 to 100 μm. Further, the pressure roller surface may not have a release layer. Power consumption of the halogen lamp inside the pressure roller is 40
Although the power consumption of 0 W is used, the power consumption is not limited to this, and a power consumption change product can be appropriately used as long as the surface temperature of the fixing roller and the pressure roller can be raised and maintained at the same level. Is.

In the fixing roller 51, the thickness of the elastic layer 51b coated on the surface of the cored bar 51a is 6.5 mm, but the thickness is not limited to this and a range of 2 to 15 mm can be preferably used. The silicon rubber forming the elastic layer 51b has an Asuka C hardness of 25 degrees, but the present invention is not limited to this, and the Asuka C hardness is 10 to 90.
The thing of the degree can be used conveniently. The releasable layer coated on the surface of the elastic layer 51b is formed of PFA (tetrafluoroethylene-
Although a per-fluoroalkyl vinyl ether copolymer) tube is used, it is not limited thereto, and PTFE
It is possible to select from fluororesins such as (polytetrafluoroethylene), PVF (polyvinyl fluoride), and ECTFE (ethylene-chlorotrifluoroethylene copolymer). Furthermore, the thickness of this release layer is 70 μm.
However, it is preferably used in the range of 20 to 100 μm.

In this embodiment, a halogen heater 58 is provided as a heating means inside the pressure roller 52. However, in some cases, an internal heating source is not used, and a halogen heater with a reflection film is used as the pressure roller 52. It is also possible to increase the power of the halogen heater 53 for external heating of the fixing roller 51 by that amount without using a heat source for the pressure roller or by using it as an external heat source.

In this embodiment, the fixing roller is formed of an elastic layer around the core metal,
The present invention is not limited to this, and a hollow thin metal roller may be mainly used, or a pressure roller may be formed by an elastic layer around the core metal. Further, both the fixing roller and the pressure roller may be formed by elastic layers around the cored bar.

In the present embodiment, the control temperature A of the fixing roller is set to 160 ° C. However, the control temperature A is not limited to this, and the best toner fixing property can be obtained according to the melting characteristics of the toner and the process conditions of the image forming apparatus. The temperature can be appropriately selected so as to be obtained, and for example, the range of 140 to 210 ° C. is a suitable temperature range.

In the present embodiment, the control temperature B of the pressure roller is set to 160 ° C. However, the control temperature B is not limited to this, and the best toner fixing property can be obtained according to the melting characteristics of the toner and the process conditions of the image forming apparatus. The temperature range can be appropriately selected so that the temperature range of 100 to 210 ° C. is a suitable temperature range.

In the present embodiment, the peripheral speed of the fixing roller in the standby state after the warm-up is completed and in the energy saving mode is set to 1/4 of that at the time of image formation, but the present invention is not limited to this, and 1/6 to constant speed. The range is preferably used, and intermittent rotation is also possible. Further, although only the fixing roller is driven and the external heating roller and the pressure roller are driven to rotate, the present invention is not limited to this, and the driving may be given so as not to cause a difference in peripheral speed. One of the heating roller and the pressure roller may be driven to rotate the remaining rollers. Further, in this embodiment, the control temperature of the surface of the fixing roller in the energy saving mode is set to 120 ° C. However, the control temperature is not limited to this, and a range of 130 ° C. or lower can be suitably used. It is also possible to have not only one step but a plurality of steps, and gradually shift to the control temperature on the low temperature side according to the lapse of unused time from the last image formation.

A thermistor 54 is provided on the surface of the fixing roller 51.
Cleaning roller 6 for maintaining the surface of the fixing roller in a clean state on the upstream side of the fixing nip and on the downstream side of the fixing nip.
1 is in contact with the surface of the pressure roller 52, and the cleaning roller 62 for maintaining the pressure roller surface in a clean state is in contact with the surface of the thermistor 55 on the upstream side of the thermistor 55. There is. As a result, toner components do not remain on the surface of the fixing roller, the pressure roller, and the heating roller that contacts the fixing roller. Therefore, even if the rollers are rotated during warm-up, the toner solids will not damage each roller. To be done. Also, even during standby such as energy saving mode or standby other than image output, each roller surface is continuously or intermittently rotated and the cleaning roller keeps each roller surface clean.
Prevents damage to each roller.

In the present embodiment, the core metal of the fixing roller main body is made of iron, but the core metal is not limited to this, and metals such as aluminum, copper, nickel and stainless can be used.

[0033]

First, the radiant heat from the halogen heater is directly propagated to the surface of the fixing roller, and the radiant heat is intensively transmitted to the fixing roller side by the reflection film provided on the back surface of the halogen heater, so that the warm-up is performed. It is possible to shorten the time. Secondly, the heat transfer through the metal roller promotes uniform temperature distribution in the axial direction of the fixing roller. Thirdly, the structure in which the upstream side and the downstream side of the halogen heater are sandwiched by the metal rollers absorbs radiant heat which tends to dissipate from the side surface of the halogen heater without going to the fixing roller and transmits it to the surface of the fixing roller. The power consumption of the heater is not wasted. Fourthly, the transfer of heat to the fixing roller in the axial direction of the fixing roller is promoted by the transfer of heat through the metal roller, and then the process proceeds to the fixing nip, so that the fixing state of the toner image on the sheet can be stabilized. Fifth, the warm-up time is shortened and an image forming apparatus with high energy efficiency can be obtained.

[Brief description of drawings]

FIG. 1 is a front view schematically showing an example of a schematic configuration of an image forming apparatus according to the present invention.

FIG. 2 is a front view schematically showing each color image forming unit.

FIG. 3 is a schematic view detailing the internal structure of the fixing device 50 in cross section.

[Explanation of symbols]

50 fixing device 51 fixing roller 51 pressure roller 51a core metal 51b elastic layer 51c PFA tube layer 52 Pressure roller 52a roller body 52b PTFE layer 53 Halogen heater 53a Reflective film 54 Thermistor 55 Thermistor 58 Halogen heater 63 Metal roller 64 metal roller 70 Power supply control unit

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H033 AA30 BA25 BA26 BA27 BB18                       BB21 BB23 BB30 BB38 BB39                 3K058 AA02 BA18 CA12 CA22 CA61                       CA92 CB02 DA02 DA26 EA00                       GA03 GA06

Claims (5)

[Claims] 1. A fixing device for fixing a toner by inserting a sheet carrying unfixed toner between a nip formed by a fixing roller and a pressure roller, wherein the fixing device fixes the toner on the outer surface of the fixing roller and on the back surface of the fixing roller. A fixing device provided with a lamp heater having a curved reflecting film. 2. The fixing device according to claim 1, further comprising a metal roller provided on an outer peripheral surface of the fixing roller so as to contact the fixing roller. 3. The metal roller according to claim 2, wherein the metal roller is a plurality of metal rollers installed so as to sandwich the lamp heater with a slight gap on the upstream side and the downstream side of the lamp heater. Fixing device. 4. The fixing device according to claim 2, wherein the metal roller is provided downstream of the lamp heater and upstream of the nip. 5. The image forming apparatus according to claim 1, further comprising the fixing unit.