JP2008242101A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device designed so that satisfactory image quality is ensured, costs are reduced and warmup is more efficient and fast. <P>SOLUTION: The fixing device fixes an unfixed image on a recording medium to this medium by the application of heat and pressure in a nip area. In the fixing device, a fixing roller 22 disposed in contact with the image side of the recording medium S has a releasing layer 22b on the surface of the substrate 22a of a metal pipe, and an elastic layer 22c serving as an intermediate layer. In addition, the pressure roller 23 disposed in contact with the non-image side of the recording medium S has a direct release layer 23b on the surface of the substrate 23a of a metal pipe. Both the rollers 22 and 23 have heating means 24 and 26 respectively in their metal pipes in order to heat the rollers. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device for fixing an unfixed image on a sheet to the sheet by heating and pressing at a nip portion, and an image forming apparatus such as a copying machine and a printer equipped with the fixing device.

As a conventional fixing device, there is an image surface side fixing roller mainly used in a black and white image forming apparatus, which has no elastic layer around a metal tube or has a very thin elastic layer.
In this case, the warm-up time of the fixing device is fast, but when used as a color fixing device, there is a problem in uneven glossiness and image quality due to the use of the contact type separation means. On the other hand, when the image surface side fixing roller configuration mainly used in the color image forming apparatus has an elastic layer around the metal tube, the image quality is good, but the warm-up time is due to the heat capacity of the elastic layer. There is a difficulty of hanging.
On the other hand, the belt fixing system that uses an endless belt on the image surface side and separates the portion that heats the belt and the portion that presses the paper to solve the above problem has a problem of high cost.
A conventional fixing device has been proposed in which the surface of the fixing roller is heated from the outside upstream of the pressure contact portion between the fixing roller and the pressure roller (see, for example, Patent Document 1).
According to the technique disclosed in Patent Document 1, the surface of the fixing roller is deprived of heat by the recording material and the toner, and the temperature is lowered by the self-cooling action. As a result, the temperature of the molten toner does not become higher than necessary, so that the cohesive force is increased and the adhesive force of the molten toner to the fixing roller is reduced.
Japanese Patent No. 3352891

However, according to the technique of Patent Document 1, since the surface of the fixing roller is heated from the outside upstream of the pressure contact portion between the fixing roller and the pressure roller, there is a problem in terms of downsizing and cost reduction of the apparatus. is there.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fixing device with good image quality, low cost, and more efficient warm-up time in consideration of the above situation.

In order to solve the above problems, the invention described in claim 1 is directed to a fixing device that fixes an unfixed image on a recording medium to the recording medium by heating and pressing at a nip portion. The fixing roller in contact with the surface side has a release layer on the surface of the base material of the metal tube and an elastic layer as an intermediate layer, and the pressure roller in contact with the non-image surface side of the recording medium is the surface of the base material of the metal tube And a heating means for heating the fixing roller and the pressure roller is included in each of the metal tubes of the fixing roller and the pressure roller. .
According to a second aspect of the present invention, there is provided the fixing device according to the first aspect, wherein the heating means on the non-image surface side is preferentially used at the time of warm-up to prepare for a fixable state.
According to a third aspect of the present invention, the non-image surface side heating means is preferentially used during warm-up to prepare for a fixable state, and the image surface side heating means is intermittently lit intermittently. A fixing device according to claim 1 is characterized.
According to a fourth aspect of the present invention, the heating means on the non-image surface side is preferentially used during warm-up to prepare for a fixable state, and after the surface temperature of the pressure roller reaches a predetermined temperature. The fixing device according to claim 1, wherein the heating unit on the image surface side is intermittently lit intermittently.

According to a fifth aspect of the invention, there is provided a fixing device according to the first aspect, wherein a plurality of heating means on the image surface side are provided, one of which is a heating means dedicated to warm-up.
According to a sixth aspect of the present invention, there is provided the fixing device according to the first aspect, wherein the rotational speed of the pressure roller during warm-up to prepare for a fixing-ready state is set higher than the speed during normal fixing. It is characterized by.
According to a seventh aspect of the invention, there is provided the fixing device according to the first aspect, wherein the image side heating means is preferentially used during normal fixing.
The invention according to claim 8 is characterized in that the fixing device according to claim 1 uses heating means on the non-image surface side for correcting the temperature distribution in the width direction during normal fixing.
According to a ninth aspect of the present invention, there is provided image forming means for forming a toner image on a photosensitive member, transfer means for transferring the toner image to a recording medium conveyed from a paper feeding device, and on the recording medium. 9. An image forming apparatus including a fixing device for fixing the toner image, wherein the fixing device is the fixing device according to any one of claims 1 to 8.

  According to the present invention, in a fixing device that fixes an unfixed image on a sheet to the sheet by heating and pressing at the nip portion, the fixing roller on the image surface side has the release layer on the surface of the base material of the metal tube. In addition, there is an elastic layer as an intermediate layer, the pressure roller on the non-image surface side has no intermediate layer as an elastic layer, and has a release layer directly on the surface of the base material of the metal tube. Has a heating means for heating the roller, so that a fixing device with high image quality, low cost and quick warm-up time can be provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of a printer embodying the present invention. Hereinafter, an embodiment in which the present invention is applied to a color laser printer (hereinafter simply referred to as “printer”) A which is an image forming apparatus will be described.
This printer A constitutes a tandem image forming unit in which four image forming units of yellow, cyan, magenta, and black are arranged side by side. In the tandem image forming unit, image forming units 20Y, 20C, 20M, and 20K as individual toner image forming units are arranged in order from the left in the drawing.
Here, the suffixes Y, C, M, and K of the respective symbols indicate members for yellow, magenta, cyan, and black, respectively. In the tandem image forming unit, each of the image forming units 20Y, 20C, 20M, and 20K includes a charging device and a developing device around the drum-shaped photoconductors 21Y, 21C, 21M, and 21K as latent image carriers. 10Y, 10C, 10M, 10K, photoconductor cleaning device and the like.

At the top of the printer A, toner bottles 2Y, 2C, 2M, and 2K filled with yellow, cyan, magenta, and black color toners are disposed. Each color toner is supplied from the toner bottles 2Y, 2C, 2M, and 2K to the developing devices 10Y, 10C, 10M, and 10K of each color by a predetermined supply amount through a conveyance path (not shown).
An optical writing unit 9 as a latent image forming unit is provided below the tandem image forming unit. The optical writing unit 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each of the photoreceptors 21Y, 21C, 21M, and 21K while scanning the laser beam based on the image data. It is configured.
Further, an intermediate transfer belt 1 in the form of an endless belt is provided as an intermediate transfer member immediately above the tandem image forming unit. The intermediate transfer belt 1 is wound around support rollers 1a and 1b, and a drive motor (not shown) is connected as a drive source to the rotation shaft of the drive roller 1a among the support rollers.
When this drive motor is driven, the intermediate transfer belt 1 rotates counterclockwise in the figure and the followable support roller 1b rotates. Inside the intermediate transfer belt 1, primary transfer devices 11Y, 11C, 11M, and 11K for transferring the toner images formed on the photoreceptors 21Y, 21C, 21M, and 21K onto the intermediate transfer belt 1 are provided. Yes.
Further, a secondary transfer roller 4 as a secondary transfer device is provided downstream of the primary transfer devices 11Y, 11C, 11M, and 11K in the driving direction of the intermediate transfer belt 1. A support roller 1b is disposed on the opposite side of the secondary transfer roller 4 and the intermediate transfer belt 1, and functions as a pressing member (opposing roller).
In the figure, a paper feed cassette 8, a paper feed roller 7, a registration roller 6 and the like are provided below the optical writing unit 9 described above. Further, fixing for fixing the image on the recording medium S downstream of the secondary transfer roller 4 in the advancing direction of the recording medium S fed from the paper feed cassette 8 and having the toner image transferred by the secondary transfer roller 4. The apparatus 5 and the paper discharge roller 3 are provided.

Next, the operation of the printer A will be described. The individual image forming units rotate the photoconductors 21Y, 21C, 21M, and 21K. Along with these rotations, first, the surface of the photoconductors 21Y, 21C, 21M, and 21K is uniformly charged by the charging device. Next, the image data is irradiated with laser writing light from the optical writing unit 9 to form electrostatic latent images on the photoconductors 21Y, 21C, 21M, and 21B.
Thereafter, toner is attached to the electrostatic latent image by the developing devices 10Y, 10C, 10M, and 10K, and the electrostatic latent image is visualized. As a result, monochrome images of yellow, cyan, magenta, and black are formed on the photoreceptors 21Y, 21C, 21M, and 21K, respectively.
Further, the drive roller 1a is rotationally driven by a drive motor (not shown), the other driven roller 1b and the secondary transfer roller 4 are driven to rotate, and the intermediate transfer belt 1 is rotated and conveyed. The above visible images are sequentially transferred onto the intermediate transfer belt 1 by the primary transfer devices 11Y, 11C, 11M, and 11K.
As a result, a composite color image is formed on the intermediate transfer belt 1. The surface of the photoconductors 21Y, 21C, 21M, and 21K after the image transfer is cleaned by removing residual toner with a photoconductor cleaning device to prepare for the image formation again.

In accordance with the timing of image formation, the leading edge of the recording medium S is fed from the paper feed cassette 8 by the paper feed roller 7 and conveyed to the registration roller 6 and temporarily stops. Then, the recording medium S is conveyed between the secondary transfer roller 4 and the intermediate transfer belt 1 while taking timing with the image forming operation.
Here, the intermediate transfer belt 1 and the secondary transfer roller 4 sandwich the recording medium S to form a so-called secondary transfer nip, and the secondary transfer roller 4 transfers the toner image on the intermediate transfer belt 1 to the recording medium S. Secondary transfer on top.
The recording medium S after the image transfer is sent to the fixing device 5. The fixing device 5 is formed by a fixing roller 22 and a pressure roller 23 that faces the fixing roller 22 and is pressed against the fixing roller 22. The fixing roller 22 has a heating source 24 inside, and is configured to maintain the surface at a predetermined temperature by the temperature control means 25.
The recording medium S is nipped and conveyed to a nip formed by a fixing roller 22 and a pressure roller 23 pressed against the fixing roller 22, whereby the toner image on the recording medium S is heated and pressed to be applied on the recording medium S. Let it settle. In the present invention, the pressure roller 23 also has a heating source 26 inside, and the surface is controlled to a predetermined temperature by the temperature control means 27.
The recording medium S discharged from the nip portion is separated by a separation member (not shown) and then discharged from the paper discharge roller 3 to the outside of the apparatus. On the other hand, after the image transfer, the intermediate transfer belt 1 removes residual toner remaining on the intermediate transfer belt 1 after the image transfer by the intermediate transfer body cleaning device 12, and prepares for the image formation again by the tandem image forming unit.

FIG. 2 is a schematic cross-sectional view illustrating a fixing roller and a pressure roller of the fixing device according to the present invention. In FIG. 2, a recording medium S having toner t on its surface is sent in the direction of the arrow from the secondary transfer roller 4 of FIG. In this case, the configuration of the fixing roller 22 on the image surface (toner t) side is generally made of a metal tube, mainly Al having good thermal conductivity, Fe, or the like in order to maintain rigidity as the base material 22a. Used.
The thickness of the metal tube is about 0.3 to 1 mm. The configuration of the fixing roller 22 has an elastic body such as silicon rubber having a thickness of about 2 to 3 mm as the intermediate layer (elastic layer) 22c. Furthermore, the surface layer 22b is coated or covered with a fluororesin having a film thickness of about 15 to 50 μm and good releasability.
In the configuration of the pressure roller 23 on the non-image surface side, as a base material 23a, in order to maintain rigidity, generally, a metal tube, mainly Al having good thermal conductivity, or Fe is used in order to maintain rigidity. Etc. are used. The thickness of the metal tube is usually about 0.3 to 1 mm.

Further, as the surface layer 23b, a fluororesin having a film thickness of about 15 to 50 [mu] m and good releasability is coated or coated. In the fixing device of the present invention, the fixing roller 22 has an elastic layer, while the pressure roller 23 has no elastic layer, and both the rollers 22 and 23 have a heat source. For example, a halogen lamp may be used as the heating source.
When the fixing roller 22 is provided with the elastic layer 22c, there is an advantage that improvement of the separation property of the recording medium S can be expected by combining with the hardness of the pressure roller 23. By increasing the hardness of the pressure roller 23, the direction of the recording medium S after passing through the nip is directed to the direction of the pressure roller 23, and winding around the fixing roller 22 can be prevented.
There is also an advantage that image quality can be improved. With the improvement of the separation property, it is possible to adopt a non-contact separation method, and as a result, it is possible to eliminate image gloss unevenness due to the separation nail that occurs in the conventional contact method.
Furthermore, the merit of improving durability by non-contact separation can be expected. Further, by using an elastic body on the image surface side, it is possible to expect the merit that the surface property of the image is improved and the texture is improved.
Such an effect can be obtained at low cost by the roller method. On the other hand, there is an inconvenience that the warm-up time increases as the heat capacity of the elastic body increases. The present invention aims to improve the above inconvenience and achieve both of the above merits.
In the present invention, the elastic structure of the pressure roller 23 is eliminated by the above roller configuration, the heat capacity is reduced, the temperature raising speed is increased, and the fixing roller 22 is heated by the pressure roller 23 to shorten the warm-up time. I try to figure it out.
At this time, the fixing roller 22 also has a heating source 24 and is shared with the heating source 26 of the pressure roller 23, thereby further improving efficiency. The heat transfer from the pressure roller 23 to the fixing roller 22 is transmitted from the nip portion by idling during the warm-up.

FIG. 3 is a graph showing the relationship between temperature and time in shortening the warm-up time. Referring to FIG. 3 together with FIGS. 1 and 2, the graph indicated by 23 surface temperature is a transition of the surface temperature of the pressure roller 23 when the heating source 26 generates heat from room temperature.
As described above, when the heating source 26 on the non-image surface side is preferentially used during warm-up when preparing the fixing device in a fixable state, it is possible to provide a fixing device with high image quality, low cost, and fast warm-up time. it can.
The graph shown by 22 surface temperature 1 is a transition of the surface temperature of the pressure roller 23 when only the heating source 24 is heated from room temperature. On the other hand, 22 surface temperature 2 shows the transition of the surface temperature of the fixing roller 22 when only the pressure roller 23 is heated. By receiving heat directly on the surface from the pressure roller 23 that does not have an elastic layer and heats up at a high speed, the heating rate of the fixing roller 22 is faster than when heated from the inside through the elastic layer.
By the way, when the surface temperature of the pressure roller 23 reaches the target value and the temperature control of the heating source 26 is repeatedly turned on / off, the surface temperature rise of the fixing roller 22 becomes dull. In order to eliminate this, the heating source 24 is intermittently lit when the heating source 26 enters the on / off control.
The non-image-side heating source 26 is preferentially used during warm-up when preparing the fixing device in a fixable state, and the image-side heating source 24 is intermittently lit intermittently so that high image quality and low cost are achieved. Thus, a fixing device with a fast warm-up time can be provided.
Both heating sources 24 and 26 cannot be turned on simultaneously from the viewpoint of reducing the maximum power of the apparatus, but can be controlled without exceeding the maximum power by turning on alternately.

FIG. 4 is a waveform diagram showing an outline of the control of alternating lighting of both heating sources. As shown in FIG. 4, during the warm-up, the heating source 26 (FIG. 1) is fully lit while the temperature is being raised (the pressure roller 23 (FIG. 1) is being heated), and the heating source 24 (FIG. 1) is turned on. Is turned off. However, when the pressure roller 23 reaches a predetermined temperature and the heating source 26 is repeatedly turned on / off, the heating source 24 is turned on accordingly.
At the time of warm-up for preparing the fixing device in a fixable state, the non-image surface side heat source 26 is preferentially used, and after the surface temperature of the pressure roller 23 on the non-image surface side reaches a predetermined temperature, the image surface Since the side heating source 24 is intermittently lit intermittently, a fixing device with high image quality, low cost and quick warm-up time can be provided.

FIG. 5 is a graph showing the result of controlling the alternate lighting of both heating sources. In FIG. 5, the surface temperature of the fixing roller 22 (FIG. 1) is heated not only from the outside but also from the inside as shown by 22 surface temperature 3, so that the dull temperature increase rate is compensated. Further, depending on the power distribution of the heating source, the heating source 24 (FIG. 1) can be intermittently lit while the heating source 26 (FIG. 1) is fully lit.
This is because the heating source 24 can be turned on for a lighting time corresponding to the difference when there is a margin even if the heating source 26 is turned on with respect to the maximum power of the apparatus, and the temperature rise of the fixing roller 22 can be accelerated accordingly. It becomes possible.
At the time of warm-up to prepare for the fixing possible state, the non-image surface side heating means (heating source 26) is preferentially used, and the image surface side is heated after the surface temperature of the pressure roller 23 reaches a predetermined temperature. Means (heating source 24) is intermittently lit intermittently. Accordingly, it is possible to provide a fixing device with high image quality, low cost, and quick warm-up time.
Similarly, if there is a margin even when the heating source 26 is fully lit, it is conceivable that the heating source on the fixing roller 22 side has two configurations. One of them has a value corresponding to the difference between the apparatus maximum power and the heating source 26, and is lit during warm-up. By adopting such a configuration, it is possible to avoid the complicated control due to the intermittent lighting as described above and to accelerate the temperature increase of the fixing roller 22 (the apparatus maximum power includes power other than fixing). ).
Although not shown in the drawing, a fixing device with a high image quality, low cost and a fast warm-up time can be obtained by using a plurality of heating sources 24 on the image surface side and using one of them as a dedicated heating source during warm-up. Can be provided.

FIG. 6 is a graph showing the result of controlling the alternate lighting of both heating sources. The heat transfer speed from the pressure roller 23 (FIG. 1) to the fixing roller 22 (FIG. 1) varies depending on the idling speed during the warm-up. FIG. 6 shows 22 surface temperature 4 when idly rotating at the same rotation speed as fixing, 22 surface temperature 5 when the rotation speed is 1.5 times, and 22 surface temperature 6 when the rotation speed is halved. Is shown.
As shown in the figure, the heat transfer speed has a good transfer efficiency at a high idling speed. From this result, it can be seen that setting the idle rotation during warm-up faster than the normal fixing is effective in reducing the warm-up time.
In this way, it is possible to provide a fixing device with a fast warm-up time by setting the rotation speed of the fixing device during warm-up to prepare the fixing device in a fixable state faster than the speed during normal fixing.
During fixing, since the fixing roller 22 cannot be heated from the pressure roller 23 while the recording medium passes, it is effective to control the temperature using the heating source 24 of the fixing roller 22. In the fixing roller 22 once warmed, an elastic layer is interposed to slow down the response, but conversely there is heat storage in the elastic layer, which can be controlled.
Since the heating source 24 of the fixing roller 22 on the image surface side is preferentially used at the time of normal fixing, it is possible to provide a fixing device with high image quality, low cost and quick warm-up time.

FIG. 7 is a graph showing the light emission distribution of the heating source in which the light emission distribution is set high at both ends. FIG. 8 is a graph showing the light emission distribution of a heating source having a flat light emission distribution as a whole.
The heating source 24 of the fixing roller 22 and the heating source 26 of the pressure roller 23 are set with different light emission (heat generation) distributions in the sheet passing width direction. For example, as shown in FIG. 7, the heating source 24, which is a halogen lamp, for example, has a high edge emission in its emission distribution.
On the other hand, as shown in FIG. 8, the heating source 26 of the pressure roller 23 has a flat light emission distribution. If the end of the temperature distribution of the fixing roller 22 becomes higher than that in the center during the sheet passing, the temperature distribution can be made uniform by using the heating source 26 as an auxiliary.
Since the heating source 26 of the pressure roller 23 on the non-image surface side is used for correcting the temperature distribution in the width direction during normal fixing, a fixing device with a fast warm-up time and no waiting time during fixing can be provided.
If the fixing device according to the present invention is installed, an image forming apparatus such as a copying machine or a printer having high image quality, low cost, and quick warm-up time can be provided.

1 is a schematic configuration diagram illustrating an embodiment of a printer that implements the present invention. FIG. 3 is a schematic cross-sectional view illustrating a fixing roller and a pressure roller of the fixing device according to the present invention. It is a figure which shows the relationship between temperature and time in shortening of warm-up time with a graph. It is a wave form diagram showing an outline of control of alternate lighting of both heating sources. It is a figure which shows the result of the control of alternate lighting of both heating sources with a graph. It is a figure which shows the result of the control of alternate lighting of both heating sources with a graph. It is a figure which shows the light emission distribution of the heating source which has set high light emission distribution in both ends. It is a figure which shows the light emission distribution of the heating source which has a flat light emission distribution in the whole in a graph.

Explanation of symbols

A image forming apparatus (printer), S recording medium, 1 transfer means (intermediate transfer belt), 4 transfer means (secondary transfer roller), 5 fixing device, 8 paper feed device (paper feed cassette), 10Y developing device, 20Y Image forming means, 21Y photoreceptor, 22 fixing roller, 22a base material, 22b surface layer, 22c intermediate layer (elastic layer), 23 pressure roller, 23a base material, 23b surface layer, 24 heating means (heating source), 25 temperature control Means, 26 heating means (heating source), 27 temperature control means

Claims (9)

  In a fixing device for fixing an unfixed image on a recording medium to the recording medium by heating and pressurization at a nip portion, a fixing roller contacting an image surface side of the recording medium is a release layer on the surface of a metal tube base material The pressure roller in contact with the non-image surface side of the recording medium has a release layer directly on the base material surface of the metal tube, and the fixing roller and pressure roller Each of the metal tubes includes a heating unit for heating the fixing roller and the pressure roller.   2. The fixing device according to claim 1, wherein the heating means on the non-image surface side is preferentially used during a warm-up to prepare for a fixable state.   2. The fixing according to claim 1, wherein the heating means on the non-image surface side is preferentially used during warm-up to prepare for the fixing possible state, and the heating means on the image surface side is intermittently lit intermittently. apparatus.   At the time of warm-up to prepare for the fixing possible state, the non-image surface side heating means is preferentially used, and after the surface temperature of the pressure roller reaches a predetermined temperature, the image surface side heating means is supplementarily used. The fixing device according to claim 1, wherein the fixing device is intermittently lit.   2. The fixing device according to claim 1, wherein a plurality of heating means on the image surface side are provided, and one of them is a heating means dedicated to warm-up.   2. The fixing device according to claim 1, wherein the rotation speed of the pressure roller at the time of warm-up to prepare for a fixable state is set higher than the speed at the time of normal fixing.   2. The fixing device according to claim 1, wherein the heating means on the image surface side is preferentially used during normal fixing.   2. The fixing device according to claim 1, wherein heating means on the non-image surface side is used for correcting the temperature distribution in the width direction during normal fixing.   Image forming means for forming a toner image on a photoreceptor, transfer means for transferring the toner image to a recording medium conveyed from a paper feeding device, and a fixing device for fixing the toner image on the recording medium 9. The image forming apparatus according to claim 1, wherein the fixing device is the fixing device according to any one of claims 1 to 8.

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