JP2008058833A - Fixing device, and image forming apparatus with the fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which improves the performance of separating a recording medium (form) from a fixing roller, and to provide an image forming apparatus including the ixing device. <P>SOLUTION: The fixing device which includes the rotatable fixing roller 15 having a heating source 14 inside and a pressure roller 16 pressed against the fixing roller 15 to apply pressure, and heats, presses, and fixes an unfixed toner image together with a recording medium S between the fixing roller 16 and a nip part of the pressure roller 16 is characterized in that when fixing roller temperature needed to fix the unfixed image is denoted as T1 and fixing roller temperature at which separation resisting force when the recording medium S is peeled off the fixing roller 15 after passing through the nip part is less than a predetermined value is denoted as T2, fixing roller temperature Tin right before the nip part is above T1 and fixing roller temperature right after the nip part is below T2, T1 and T2 being controlled so that T1>T2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device in an image forming apparatus such as a copying machine or a laser printer, and an image forming apparatus including the fixing device.

In general, in black and white image forming apparatuses, a paper sheet is separated by contacting a claw-like member with a sharp tip at the downstream side of the fixing nip. However, under various conditions, the separation becomes insufficient and a paper jam occurs. It sometimes occurred.
In addition, the color image forming apparatus is more demanding of image quality than the black and white image forming apparatus, and the fixing member which is mainly used in the black and white image forming apparatus is brought into contact with a claw-like member with a sharp tip to forcibly separate the color image forming apparatus. This method causes deterioration in image quality such as uneven image gloss, for example, because the surface property of the fixing member is different from other portions at the portion that directly contacts the fixing member.
Various techniques for controlling the temperature of the fixing unit have been proposed in order to eliminate inconveniences such as the occurrence of paper jam in the image forming apparatus and image quality deterioration such as uneven image gloss (see, for example, Patent Documents 1 to 6). ).

In Patent Document 1, a technique of blowing cooled air from a fixing separation roller, in Patent Document 2, a technique of moving a shielding plate according to the paper size and blocking heat from the heating means, and in Patent Document 3, a shielding plate is used. A technique for reducing irradiation from a heater to a non-sheet passing portion is disclosed.
Patent Documents 4 and 5 describe the temperature and cooling method when the belt and paper are peeled off when a fixing belt is used. Cooling effect is recognized because each has a cooling means, but the use of a special cooling means and the use of a belt fixing system increases the number of parts, which makes it expensive in terms of cost. The point which becomes and the point which requires space is mentioned as a subject.

Further, Patent Document 6 discloses that a fixing unit is also used to have a cooling unit. Although the effect of the cooling means is recognized, the paper from the nip to the cooling separation receives the heat of the heater directly at the part where the sheet is in contact with the roller, so the cooling effect at that part cannot be obtained, and conversely depending on the heater lighting timing In addition, there is a problem that the cost is increased by using a special cooling means.
JP 2004-347825 A JP 2006-098475 A JP 2002-006665 A JP 2005-181474 A Japanese Patent Laid-Open No. 5-273766 JP 2001-235958 A

However, the above-described prior art aims at improving image quality by sufficiently cooling the sheet when it is separated from the fixing member after being heated at the fixing nip. Another effect of cooling is separation of the paper from the fixing member.
Therefore, in a color image forming apparatus, for example, a non-contact type separation method such as a plate-like member (separation plate) over the entire sheet passing width adjacent to the fixing member with a minute gap is used. It cannot be denied that the separation performance is lowered as compared with the contact type. A factor contributing to the separation performance is the fixing member temperature when the paper and the fixing member are separated.

As described in Patent Document 5, the tendency of “cohesive force between toners”> “adhesive force between toner and fixing member” becomes stronger and the separation performance is improved when cooled. Although the cooling means is disclosed in the prior art, there are problems in terms of cost and space because of the belt fixing device and the use of special cooling means.
Accordingly, an object of the present invention is to achieve temperature cooling of the fixing roller at the separation unit in a roller fixing method that is used for general purposes and has a simple configuration in consideration of the above-described situation, with an inexpensive and space-saving configuration. Accordingly, it is an object of the present invention to provide a fixing device that improves the separation performance of the recording medium (paper) from the fixing roller and an image forming apparatus including the fixing device.

  In order to solve the above-mentioned problems, the invention described in claim 1 includes a rotatable fixing roller having a heating source therein, and a pressure roller that presses and presses the fixing roller. In a fixing device for fixing an unfixed toner image by heating and pressing with a recording medium between nip portions of the pressure roller, the fixing roller temperature required for fixing the unfixed image is T1, and the recording medium is the nip portion. When the fixing roller temperature at which the separation resistance when separating from the fixing roller after passing through the fixing roller becomes T2 or less is T2, the fixing roller temperature Tin immediately before the nip portion is T1 or more and the fixing roller immediately after the nip portion The fixing device is characterized in that the temperature Tout is equal to or lower than T2 and T1> T2.

According to a second aspect of the present invention, there is provided the fixing device according to the first aspect, further comprising a shielding member that is disposed inside the fixing roller and selectively shields the inside of the fixing roller.
According to a third aspect of the present invention, in the second aspect, the shielding member shields a portion near the nip formed by the fixing roller and the pressure roller, and avoids direct heating of the nip portion from a heating source. Features a fixing device.
According to a fourth aspect of the present invention, there is provided the fixing device according to the third aspect, wherein the shielding member is configured to be movable in the fixing roller.
According to a fifth aspect of the present invention, there is provided the fixing device according to the third aspect, wherein the shielding range of the shielding member is changeable.

The invention according to claim 6 is characterized in that the shielding member selects a position and a range of the shielding member according to a recording medium conveyance speed.
The invention according to claim 7 is characterized in that the shielding member selects the position and range of the shielding member according to an installation environment.
The invention according to claim 8 is characterized in that the shielding member changes the position and range of the shielding member according to the number of sheets to be passed.
According to a ninth aspect of the present invention, there is provided the fixing device according to the fourth or fifth aspect, wherein the shielding member selects different positions and ranges at the time of warm-up operation, standby, and paper passing. To do.

According to a tenth aspect of the present invention, there is provided the fixing device according to the fifth aspect, wherein the shielding member changes a position and a range of the shielding member according to a size of a recording medium to be passed.
The invention according to claim 11 is characterized in that the fixing device according to any one of claims 1 to 10 has a non-contact separating means as a recording medium separating means from the fixing roller.
According to a twelfth aspect of the present invention, there is provided the fixing device according to the eleventh aspect, further comprising a blowing unit that blows air from a gap between the recording medium separating unit and the fixing roller toward the nip portion.
According to a thirteenth aspect of the present invention, there is provided an image forming apparatus that implements an electrophotographic system, wherein the image forming apparatus includes the fixing device according to any one of the first to twelfth aspects.

  According to the present invention, the fixing roller temperature required for fixing is T1, and the fixing roller temperature at which the separation force when the recording medium (paper) is separated from the fixing roller after passing through the nip portion is equal to or less than a predetermined value is T2. Sometimes, the fixing roller temperature immediately before the nip formed by the fixing roller and the pressure roller is T1 or more, the fixing roller temperature immediately after the nip is T2 or less, and T1> T2 is controlled. The recording medium can be separated with an inexpensive configuration.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. An embodiment in which the present invention is applied to a color laser printer (hereinafter simply referred to as “printer”) as an image forming apparatus will be described.
FIG. 1 is a schematic configuration diagram showing an embodiment of a printer embodying the present invention. The printer A constitutes a tandem image forming unit by arranging four image forming units of yellow, cyan, magenta, and black side by side.

In the tandem image forming unit, image forming units 13Y, 13C, 13M, and 13K, which are 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 13Y, 13C, 13M, and 13K includes a charging device and a developing device around a drum-shaped photoconductor 12Y, 12C, 12M, and 12K as a latent image carrier. 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. Then, each color developing device 10Y, 10C, 10M, and 10K is replenished by a predetermined replenishment amount from the toner bottles 2Y, 2C, 2M, and 2K 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 12Y, 12C, 12M, and 12K while scanning the laser beam based on 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) serving as a drive source is connected to a 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 12Y, 12C, 12M, and 12K onto the intermediate transfer belt 1 are provided.
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.
Further, a paper feed cassette 8, a paper feed roller 7, a registration roller 6 and the like are provided. Further, a fixing device 5 for fixing the toner image on the recording medium S and a paper discharge roller 3 are disposed downstream of the secondary transfer roller 4 with respect to the traveling direction of the recording medium S to which the toner image is transferred by the secondary transfer roller 4. It has.

Next, the operation of the printer A will be described. The photoreceptors 12Y, 12C, 12M, and 12K are rotated by the individual image forming units. Along with the rotation of the photoreceptors 12Y, 12C, 12M, and 12K, first, the charging devices are used to rotate the photoreceptors 12Y, 12C, 12M, and 12K. Charge the surface uniformly.
Next, the image data is irradiated with laser writing light from the optical writing unit 9 to form electrostatic latent images on the photoreceptors 12Y, 12C, 12M, and 12K. Thereafter, the toner is attached by the developing devices 10Y, 10C, 10M, and 10K, and the electrostatic latent images are visualized to form yellow, cyan, magenta, and black on the photoreceptors 12Y, 12C, 12M, and 12K, respectively. A monochromatic image is formed.

Further, the driving roller 1a is rotationally driven by a driving motor (not shown), the other driven roller 1b and the secondary transfer roller 4 are driven to rotate, the intermediate transfer belt 1 is rotated and conveyed, and the visible image is transferred to the primary image. The images are sequentially transferred onto the intermediate transfer belt 1 by the 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 12Y, 12C, 12M, and 12K after image transfer is cleaned by removing residual toner with a photoconductor cleaning device to prepare for 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 sheet 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 counter roller 4 form a so-called secondary transfer nip across the recording medium S, 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 and has a heating source 14 inside, and a fixing roller 15 whose surface is maintained at a predetermined temperature by a temperature control means, and the fixing roller 15 is opposed to the fixing roller 15. A nip portion (fixing nip portion) is formed by the pressure roller 16 pressed against the fixing roller 15, and the nip portion sandwiches and conveys the recording medium S to heat and press the toner image on the recording medium S. To fix it on the recording medium S.
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, the intermediate transfer belt 1 after the image transfer is removed by the intermediate transfer body cleaning device 18 to remove residual toner remaining on the intermediate transfer belt 1 after the image transfer, and is prepared for re-image formation by the tandem image forming unit.

As described above, the fixing device 5 heats and pressurizes the toner image on the recording medium S by sandwiching and transporting the recording medium S to the nip portion formed by the pressure roller 16 pressed against the fixing roller 15. To fix it on the recording medium S. In the fixing device 5 according to the present invention, in order to fix the toner image on the recording medium S, a predetermined fixing temperature at the fixing nip portion, a predetermined pressure, and a predetermined heating and pressing time are required.
This predetermined condition is mainly determined by the characteristics of the toner, the amount of toner adhered per unit area, the installation environment of the apparatus, the type of recording medium (paper), etc., and these are specific to the fixing device. A value with a range.

Here, T1 is the optimum fixing temperature for fixing the toner image determined from the above various conditions on the recording medium. The optimum temperature is a value having a range, but here, the significance of indicating the lower limit in the optimum range is large. Next, separation of the recording medium discharged from the fixing nip portion from the fixing roller 15 will be considered.
As described in connection with the prior art, it is advantageous that the fixing temperature is lower for the separation of the recording medium. The condition for separating the recording medium from the fixing roller 15 is also a value having a specific range depending on the fixing device, but the upper limit temperature at which separation from the fixing roller 15 can be achieved is T2.
Here, as an index for determining whether or not separation can be achieved, the peeling force between the recording medium (paper) that has passed through the fixing nip and the fixing roller 15 is considered. A recording medium unified so that the toner adhesion amount becomes a constant value is passed through the fixing device.

FIG. 2 is a schematic diagram for explaining a measuring apparatus for measuring the pressing force of the recording medium. In FIG. 2, the recording medium S is conveyed while being pressed against the measuring claw 28. The pressing force at this time is read by the load cell 27 provided at the other end of the measuring claw 28. As shown in FIG. 2, the measurement claw 28 is provided on the fixing roller 15 side immediately after the fixing nip portion.
The value read by the load cell 27 is a force necessary to peel the recording medium S from the fixing roller 15, and this is a separation resistance force. It is determined whether or not the recording medium S can be separated from the fixing roller 15 based on the magnitude of the separation resistance measured based on the predetermined condition.

FIG. 3 is a graph showing the relationship between the fixing temperature and the separation resistance of the fixing roller and the recording medium. FIG. 3 shows an example of a graph in which the fixing temperature is plotted on the horizontal axis and the separation resistance between the fixing roller 15 (FIG. 1) and the recording medium S (FIG. 1) is plotted on the vertical axis.
The individual values vary depending on the conditions specific to the apparatus and external conditions such as the installation environment, but the tendency is the same, with the peak around the optimum fixing temperature, and the separation resistance decreases as the distance increases.
In the case of this example, the separation resistance at a fixing temperature of 160 ° C. to 170 ° C. is peaked, and as the fixing temperature decreases, the separation resistance decreases accordingly. In this fixing device, it has been found that separation of the recording medium S from the fixing roller 15 can be achieved if the separation resistance is 30 gf or less.
The level at which the separation can be achieved here is that when the separation claw is used as the separation member, the recording medium S can be passed through without jamming even when the toner image is printed up to the tip of the recording medium S. Say. When a non-contact separating plate is used as the separating member, it means that the recording medium S can be passed through without jamming in a state where the margin of the leading edge of the recording medium S is secured to 2 mm.

FIG. 4 is a graph showing the relationship between the optimum fixing temperature T1 and the fixing temperature T2. In the fixing device of the present embodiment, the optimum fixing temperature is 160 ° C. to 180 ° C. The relationship between T1 and T2 is shown in FIG. In the figure, the curve is the relationship between the separation resistance shown in FIG. 3 and the fixing temperature, and the upper limit of the separation resistance is separable by the line shown by the horizontal broken line.
The fixing temperature indicated by the intersection of this curve and the horizontal broken line is T2 described above. On the other hand, the optimum fixing temperature T1 is indicated by a vertical broken line. As described above, the separation resistance in the vicinity of the optimum fixing temperature shown in FIG. 4 takes its peak value, and it is often impossible to obtain a range in which the optimum fixing region and the separable region are compatible. The separation resistance decreases by half when the fixing temperature decreases by 10 ° C. to 20 ° C. from the optimum fixing temperature T1, and at this time, it is often a separable region.

FIG. 5 is a schematic view showing a fixing roller and a heating roller of the fixing device. Here, as shown in FIG. 5, the fixing temperature T is divided into a nip inlet temperature Tin and a nip outlet temperature Tout. FIG. 5 further shows the heating source 14, the fixing roller 15, the pressure roller 16, the temperature control unit 17, and the recording medium S.
The amount of heat necessary to ensure the fixability is the temperature across the entire region from Tin to Tout, but the temperature is controlled before the nip entrance, and the nip entrance temperature Tin is considered as a representative value.
On the other hand, the temperature affecting the separation is the toner temperature immediately after the nip portion, and the fixing roller temperature immediately after being discharged from the fixing nip portion, that is, the nip portion outlet temperature Tout is considered as a representative value. In general, when considering the optimum fixing temperature T1 and the separable temperature T2, the determination is often made with the nip inlet temperature Tin.
This is because the nip portion outlet temperature Tout is considered to be a temperature obtained by uniformly reducing the amount of heat taken in the nip portion from the nip portion inlet temperature Tin. However, in the present invention, the optimum fixing temperature T1 is considered as the nip inlet temperature Tin, and the separable temperature T2 is considered as the nip outlet temperature Tout. As described above, since the recording medium and the pressure roller 16 are deprived of heat before and after the nip portion, the nip portion inlet temperature Tin> the nip portion outlet temperature Tout.

FIG. 6 is a graph showing an example of the temperature transition of the fixing roller temperature. As shown in FIG. 6, the fixing temperature is normally controlled by the temperature control means 17 (FIG. 5) so that the fixing inlet temperature Tin becomes the optimal fixing temperature T1 (or higher).
The nip portion outlet temperature Tout is not particularly controlled, but heat is deprived at the nip portion as described above. Therefore, as shown by the broken curve in the figure, the temperature transition obtained by subtracting the deprived heat from the Tin temperature. Appears after the rotation time from the nip entrance to the nip exit (delay indicated by a block arrow).
From the relationship between the nip portion inlet temperature Tin and the nip portion outlet temperature Tout due to the heat deprived in the nip described above and the value obtained by subtracting a fixed temperature from the fixable temperature T1 is the separable temperature T2. In a general fixing device, it can be seen that the nip outlet temperature Tout is equal to or lower than the separable temperature T2.

However, it can be said that the fixing temperature control is usually performed while detecting the temperature near the nip inlet temperature, and the nip inlet temperature Tin is controlled. For this reason, the nip portion outlet temperature Tout may become Tout> T2 depending on the lighting timing of the heating source 14.
This is a case surrounded by a circle in FIG. 6, and the heating source 14 is turned on when the detection unit temperature Ts (Tin) in FIG. 5 becomes low. At this time, since the fixing roller 15 (FIG. 5) is heated not only at the temperature detecting portion but also around the entire circumference, the nip portion outlet temperature Tout is uniformly heated regardless of the temperature at that time, and the nip portion outlet temperature Tout increases. End up.
If the nip portion outlet temperature Tout at this time shows a value just below the nip portion possible temperature T2, for example, it results in deviating from the separable range as indicated by Tout 'in the figure.
In this way, in order to prevent the downstream range, mainly the nip portion, of the temperature detection portion on the fixing roller 15 from being heated more than necessary and exceeding the separable temperature T2, the heating source 14 Consider not giving heat directly to the nip.

FIG. 7 is a schematic view showing a shielding plate provided between the inside of the nip portion of the fixing roller and the heat source. As shown in FIG. 7, direct heating of the nip portion is prevented by providing a shielding plate 19 between the inside of the nip portion in the fixing roller 15 and the heating source 14. FIG. 7 further shows the pressure roller 16, the temperature control means 17, the detection unit temperature Ts, the nip inlet temperature Tin, and the nip outlet temperature Tout.
As a result, the fixing roller temperature behavior that has exceeded the separable temperature T2 indicated by Tout ′ in FIG. 6 becomes the temperature behavior indicated by the broken line T obtained by subtracting the amount of heat absorbed by the nip portion from the nip inlet temperature Tin, and the nip portion The outlet temperature Tout is controlled below the separable temperature T2.
As described above, since the shielding member (shielding plate) 19 disposed inside the fixing roller 15 and capable of selectively heating the inside of the fixing roller 15 is provided, the recording medium can be separated from the fixing roller 15 at a low cost. Can be achieved with a simple configuration.
Further, since the shielding member 19 shields the vicinity of the nip formed by the fixing roller 15 and the pressure roller 16 and avoids direct heating of the nip from the heating source 14, the recording medium can be separated from the fixing roller 15 at a low cost. Can be achieved with a configuration.

FIG. 8 is a schematic perspective view showing an embodiment of the shielding plate. In FIG. 8, the shielding plate 19 is disposed inside the fixing roller 15 substantially in parallel with the heating source 14, and regulates the amount of heat transmitted to the nip portion over the entire sheet passing width. As for the method of attaching the shielding plate 19, both ends thereof are fixed to a part of the casing with a stepped screw or the like in consideration of thermal expansion absorption.
Consider a case where conditions such as the thickness of the fixing roller 15 and the rotation speed of the fixing roller 15 are different. The shielding range by the shielding plate 19 and the appropriate range of the shielding position that make the fixing temperature T1 for securing the fixing property compatible with the fixing temperature T2 for securing the separation property differ depending on the conditions.
The shielding position and shielding range are determined by heat transfer from the inner peripheral surface of the fixing roller 15 that receives heat from the heating source 14 determined by the thickness and material of the fixing roller 15 to the outer peripheral surface that directly contacts the toner and applies the heat. It is necessary to determine the time and the distance by which the fixing roller 15 moves by rotation during the transmission time.

For example, as the thickness of the fixing roller 15 increases, the heat transfer time becomes longer, so that the amount of heat received by the fixing roller 15 further upstream is transferred to the toner at the nip portion. That is, it is necessary to shield the upstream side of the nip portion as the wall thickness increases, and it is necessary to widen the shielding range.
However, when the wall thickness is increased and the heat storage amount of the fixing roller 15 is increased, the temperature drop amount of the nip portion outlet temperature Tout is decreased in order to sufficiently supplement the heat amount taken by the nip portion with the heat storage amount of the fixing roller 15, It should be noted that the effect of the present invention is reduced.
Similarly, as the rotation speed of the fixing roller 15 increases, the amount of heat received by the fixing roller 15 further upstream is transmitted to the toner at the nip portion. It is necessary to shield the upstream side of the nip portion as the rotational speed increases, and it is necessary to arrange the shielding range on the upstream side.

Here, in order to increase the pixel density, consider a case where the linear speed is variable, such as halving the linear speed during high-quality printing. In this case, the shielding range or position at which the separable temperature is optimally obtained varies depending on the linear velocity for the reasons described above.
In such a case, it is conceivable to change the range or position of the shielding plate 19 to an optimum range or position depending on the linear velocity. For the above-described reason, it is considered effective to set the shielding plate 19 that directly shields the nip portion as shown in FIG.
As described above, since the position and range of the shielding plate (shielding member) 19 are selected in accordance with the plurality of recording medium (paper) conveyance speeds, the fixing roller 15 corresponding to the optimum separation condition varies depending on the recording medium conveyance speed. By controlling the temperature at the time of recording medium separation with an inexpensive configuration, the separation of the recording medium from the fixing roller 15 can be achieved.

  FIG. 9 is a schematic view showing a shielding plate disposed on the upstream side of rotation of the fixing roller. In high-speed printing, it is considered effective to set the shielding plate 19 as shown in FIG. 9 moved upstream of the fixing roller. FIG. 9 further shows the heating source 14, the fixing roller 15, the pressure roller 16, the temperature control means 17, the detection part temperature Ts, the nip part inlet temperature Tin, and the nip part outlet temperature Tout.

FIG. 10 is a schematic view showing a shield plate having a double structure. Similarly, consider a case where the shielding range is changed. As an example of the means for changing the shielding range, consider that the shielding plate has a double structure as shown in FIG.
Similarly, at the time of low-speed printing for the reasons described above, it is considered that the separable temperature is optimal by setting the shielding range in which two shielding plates 19 and 19a are overlapped as shown in FIG. FIG. 10 further shows the heating source 14, the fixing roller 15, the pressure roller 16, the temperature control means 17, the detection part temperature Ts, the nip part inlet temperature Tin, and the nip part outlet temperature Tout.

FIG. 11 is a schematic view showing a double-structured shielding plate in which one of the two is movable. In high-speed printing, it is considered that the separable temperature is optimal by moving the shielding plate 19a as shown in FIG.
FIG. 11 further shows the heating source 14, the fixing roller 15, the pressure roller 16, the temperature control means 17, the detection part temperature Ts, the nip part inlet temperature Tin, and the nip part outlet temperature Tout.
Thus, since the shielding member (shielding plate) 19a is configured to be movable in the fixing roller 15, the recording medium separation temperature of the fixing roller 15 corresponding to the optimum separation conditions that differ depending on the printing conditions can be reduced. By controlling, separation of the recording medium (paper) from the fixing roller 15 can be achieved.

  FIG. 12 is a schematic perspective view showing an embodiment of the shielding plate position varying mechanism. As shown in FIG. 12, the shielding plate 19 is held by holding members 20 that can swing at both ends. The holding member 20 can rotate around the rotation fulcrum, and can move the movable range of the shielding plate 19 as shown in FIGS. The movement is generally performed by a combination of a solenoid 21 and an elastic member 22 as shown in FIG.

FIG. 13 is a schematic view showing an embodiment in which a stepping motor is used as a driving source for moving the shielding plate. In order to move the shielding plate, a stepping motor 24 can be used as a drive source as shown in FIG. In order to detect the shielding position of the shielding plate 19, a position sensor 23 that detects the position of the holding member 20 is provided.
Based on the position information detected by the position sensor 23, the stepping motor 24 is driven and controlled via the gear train 25 connected to the holding member 20, so that the target shielding range and position can be obtained.
When the stepping motor 24 is used, fine change control of the position of the shielding plate 19 is possible. Further, if the shield plate 19a fixed to the movable shield plate configuration is combined, the shield range change shown in FIGS. 10 and 11 can be dealt with.
Since the shielding member 19 is configured such that the shielding range can be changed, the fixing roller 15 (FIG. 11) can be controlled by controlling the temperature at the time of recording medium separation of the fixing roller 15 (FIG. 11) corresponding to the optimum separation conditions depending on the printing conditions. Separation of the recording medium from 15 can be achieved.

By using the shielding range and position change as described above, it is possible to cope with different situations of optimum separation conditions. As one of them, it is conceivable to change the shielding range depending on the apparatus installation environment. Since the temperature of the fixing roller 15 is detected by the temperature detection means 17, it is maintained at a predetermined temperature. However, the optimum separation temperature changes due to the recording medium being affected by the installation environment.
In particular, it is conceivable that the optimum temperature for separation also changes because the strain of the recording medium changes due to the moisture content of the recording medium. Therefore, it is considered that the temperature / humidity detecting means is provided in the apparatus and the shielding range is switched depending on the detected value. For example, when the installation environment is high humidity, the recording medium is weak, which is disadvantageous for separation.
In such a case, it is conceivable to widen the shielding range as shown in FIG. Conversely, when the installation environment is low humidity, it is effective to narrow the shielding range as shown in FIG. Here, the case of humidity that greatly contributes to separation has been described, but switching according to the environmental temperature is also conceivable.

Since the position and range of the shielding plate (shielding member) 19 are selected according to the installation environment of the apparatus, the temperature at the time of recording medium separation of the fixing roller 15 corresponding to the optimum separation condition depending on the installation environment is controlled with an inexpensive configuration. Separation of the recording medium from the fixing roller 15 can be achieved.
Similarly, it is conceivable to change the shielding range depending on the number of sheets to be passed. That is, the temperature of the pressure roller 16 rises by repeating the paper passing. As a result, the fixing temperature range in which the fixing property and the separation property are compatible changes. Therefore, by correcting the position of the shielding plate 19 based on the number of sheets to be passed, it becomes possible to achieve both fixing properties and separability regardless of the number of sheets to be passed.
For example, when the number of sheets to be passed is small, the temperature of the pressure roller 16 is low. At this time, the heat from the pressure roller 16 is not obtained, and the heat amount is insufficient from the viewpoint of fixing properties. In general, it is generally compensated for the shortage of heat by increasing the set temperature at the initial stage of paper feeding. It has been broken.
On the other hand, from the viewpoint of separation, when the temperature of the pressure roller 16 is low, it has been confirmed that the pressure roller 16 tends to be separated in the direction of winding around the fixing roller 15. It is advantageous.
In the conflicting state at the initial stage of paper feeding, it is possible to keep the nip outlet temperature Tout low while keeping the nip inlet temperature Tin high by widening the shielding range by the shielding plate 19 as shown in FIG. And separation are possible.

Further, as the number of sheets to be passed increases, there is a margin in fixing performance and separation performance. Therefore, the amount of heat is further increased by lowering the fixing temperature and narrowing the shielding range of the shielding plate 19 as shown in FIG. Can afford. In the case of a fixing device having a heating source in the pressure roller 16 and controlling the temperature of the pressure roller 16, the control position range can be changed by the control temperature of the pressure roller 16.
The optimum position of the shielding plate during paper feeding is as described above. When the state of the apparatus is different, for example, the appropriate range position of the shielding plate during warm-up and standby is also different. At the time of warm-up, it is preferable to apply all of the heat from the heat source 14 to the fixing roller 15.
As described above, since the position and range of the shielding plate (shielding member) 19 are changed according to the number of sheets to be passed, the recording medium separation temperature of the fixing roller 15 corresponding to the optimum separation condition varies depending on the number of sheets to be passed. By controlling with a simple configuration, separation of the recording medium from the fixing roller 15 can be achieved.

However, since the shielding plate itself blocks heat, the shielding range during warm-up is preferably the smallest range that can be set (for example, the state of FIG. 10). Further, the positional relationship between the temperature detecting means 17 and the shielding plate 19 is detected. The temperature detecting means 17 detects the temperature stored in the upstream from the upstream while the fixing roller 15 is rotating. preferable.
However, when the rotation of the fixing roller 15 at the time of warm-up is stopped, if it is in the vicinity of the shielding range of the shielding plate 19, the temperature of the portion where the temperature rise of the fixing roller 15 is slow due to the shielding is detected. The temperature detection means 17 should not be too close to the shielding plate 19. For this reason as well, the shielding range of the shielding plate 19 at the time of warm-up is preferably a minimum range that can be set.
Further, overshoot immediately after the end of warm-up is often a problem, but by increasing the shielding range of the shielding plate 19 immediately before the end of warm-up, the temperature rise rate of the fixing roller 15 is slowed down, and overshoot is reduced. It is also possible to plan.
During standby, it is preferable that the entire fixing roller 15 is accurately detected with a uniform temperature distribution. For this reason, it is preferable that the shielding range is as small as possible in the standby state (for example, the state of FIG. 10), and it is preferable that the shielding range is also away from the temperature detection means 17. This is the same reason as during warm-up.

Generally, the separation of the recording medium is most disadvantageous at the end of the recording medium where the strain of the recording medium becomes weak. That is, when considering the balance between the optimum fixing temperature and the separable temperature, the end of the recording medium may be set with a margin for separation, and the other portions may be set with a margin for fixing. It is done.
As described above, the position and range of the shielding plate (shielding member) 19 that is different during warm-up operation, standby, and paper feeding are selected, so that the recording medium separation, the warm-up time is shortened, and the temperature drop immediately after the paper feeding starts. Request items such as prevention can be established.

FIG. 14 is a schematic perspective view showing a first embodiment of a shielding plate having a different shielding range depending on the recording medium width direction. FIG. 15 is a schematic perspective view showing a second embodiment of a shielding plate having a different shielding range depending on the recording medium width direction. Here, consider shielding plates having different shielding ranges depending on the recording medium width direction as shown in FIGS.
The shielding plate 19b corresponds to the size in the vicinity of the maximum recording medium width through which paper can be passed, and the shielding range in the rotational direction is set wider than the central portion so that the shielding range at both ends is widened. By widening the shielding range at the end of the recording medium in this way, the nip exit temperature Tout at the end of the recording medium becomes lower than the center, and the separation is optimal.

Usually, the maximum width recording medium is used most frequently, so it is effective to increase the shielding range near the maximum width. The shielding plate 19c has a larger shielding range with a width corresponding to a sheet having a smaller size than the shielding plate 19b. Here, the shielding plate 19c is movable in accordance with the size of the recording medium to be passed.
When the recording medium is passed near the maximum width, as shown in FIG. 14, the shielding plate 19c is arranged at a position overlapping the shielding plate 19b, and the shielding range is the same as the shielding range of the shielding plate 19b. The nip outlet temperature Tout at the end of the size recording medium is controlled optimally for separation.

On the other hand, when a small-size recording medium is passed, as shown in FIG. 15, the shielding plate 19c is rotated to a narrow portion of the shielding range of the shielding plate 19c, and the vicinity of the end portion of the small-size recording medium. Install so that the shielding range is wide. By doing so, the nip outlet temperature Tout at the end of the small-sized recording medium is controlled to be optimally separated.
About the movement of the shielding board 19c at this time, it is the same as that of the operation | movement of above-mentioned FIG.12 and FIG.13. Further, as another effect of the shielding plate 19 that can be moved depending on the size of the recording medium, it can be considered that it is used for preventing an end temperature rise at the time of continuous passage of a small size.
At the time of small size continuous paper passing, only the central portion of the fixing roller 15 through which the recording medium passes is deprived of heat, so the temperature of the end portion becomes too high. Since the amount of heat applied to the end portion of the fixing roller 15 can be reduced by setting the shielding area of the image forming portion large, it is possible to prevent an increase in the end portion temperature of the fixing roller.
As described above, since the position and range of the shielding plate (shielding member) 19 are changed depending on the size of the recording medium to be passed, the recording medium separation temperature of the fixing roller 15 corresponding to the optimum separation condition varies depending on the paper size. Separation of the recording medium from the fixing roller 15 can be achieved by controlling with an inexpensive configuration.

As described above, it is possible to achieve separation of the recording medium from the fixing roller 15 by controlling the nip portion outlet temperature Tout using the shielding plate 19. As a result, it has become possible to widen the range of conditions that can be separated using a non-contact separation means in a fixing device that is a combination of the fixing roller 15 and the pressure roller 16 that could not be achieved by a conventional color machine.
As a result, a non-contact separation member can be employed in a low-cost combination of the fixing roller 15 and the pressure roller 16, and high image quality can be achieved. As described above, even in the non-contact separation unit, separation of the sheet from the fixing roller can be achieved with an inexpensive configuration.

FIG. 16 is a schematic diagram illustrating a configuration in which air is allowed to flow through a minute gap between the separation plate and the fixing roller. In FIG. 16, as a means for further increasing the separation margin by combining the fixing roller 15 and the non-contact separation plate 26 disposed in the vicinity thereof by an appropriate method, air is passed through a minute gap between the separation plate 26 and the fixing roller 15. I try to flow.
As shown in FIG. 16, a force for lifting the leading edge of the recording medium is applied by flowing air from the gap between the separation plate 26 and the fixing roller 15 toward the nip portion. Thereby, in addition to the conventional air separation effect that recording medium separation is advantageous, it can be combined with the shielding plate 19 of the present invention.
As a result, in addition to the action of lowering the nip portion outlet temperature Tout by the shielding plate 19, the effect of lowering the nip portion outlet temperature Tout from the outside of the fixing roller 15 by air blowing is added, so that separation can be performed without affecting the nip portion inlet temperature Tin. An advantageous setting of the nip outlet temperature Tout can be achieved.
As described above, since there is a blowing means (details are not shown) for blowing air from the gap between the non-contact separation means (separation plate) 26 and the fixing roller 15 toward the fixing nip portion, the temperature at the time of recording medium separation is further reduced. In addition, by applying a forced separation force, it is possible to reliably achieve non-contact separation of the recording medium from the fixing roller 15.

Although the case of one pressure roller has been described as an embodiment of the present invention, it is not specialized for this configuration. As another configuration, in the case of a plurality of pressure rollers, a case where a pressure belt is used in place of the pressure roller can be considered, but the same effect is considered to be obtained in any case.
As described above, since the fixing device that can reliably achieve the separation of the recording medium from the fixing roller 15 is mounted, an image forming apparatus that reliably achieves the separation of the recording medium can be provided.

1 is a schematic configuration diagram illustrating an embodiment of a printer that implements the present invention. It is the schematic explaining the measuring apparatus which measures the pressing force of a recording medium. FIG. 6 is a graph showing the relationship between the fixing temperature, the separation resistance of the fixing roller and the recording medium. FIG. 7 is a graph showing a relationship between an optimum fixing temperature T1 and a fixing temperature T2. FIG. 3 is a schematic diagram illustrating a fixing roller and a heating roller of the fixing device. FIG. 7 is a graph showing an example of a temperature transition of a fixing roller temperature. FIG. 4 is a schematic diagram illustrating a shielding plate provided between the inside of the nip portion of the fixing roller and a heat source. It is a schematic perspective view which shows embodiment of a shielding board. FIG. 6 is a schematic diagram illustrating a shielding plate disposed on the upstream side of rotation of the fixing roller. It is the schematic which shows the shielding board made into the double structure. It is the schematic which shows the shielding board of the double structure which enabled one side. It is a schematic perspective view which shows embodiment of a shielding board position variable mechanism. It is the schematic which shows embodiment which uses a stepping motor as a drive source of a shielding board movement. FIG. 3 is a schematic perspective view illustrating a first embodiment of a shielding plate having a shielding range different depending on a recording medium width direction. It is a schematic perspective view which shows 2nd Embodiment of the shielding board from which a shielding range differs according to a recording medium width direction. FIG. 3 is a schematic diagram illustrating a configuration in which air is allowed to flow through a minute gap between a separation plate and a fixing roller.

Explanation of symbols

A Image forming device (printer)
S Recording medium (paper)
14 Heat source 15 Fixing roller 16 Pressure roller 17 Temperature control means (temperature detection means)
19 shielding member 19a shielding member 26 non-contact separating means (separating plate)

Claims (13)

  A rotatable fixing roller having a heating source therein and a pressure roller that presses and presses the fixing roller, and an unfixed toner image between the nip portion of the fixing roller and the pressure roller together with a recording medium In a fixing device for fixing by heating and pressing, a fixing roller temperature necessary for fixing an unfixed image is T1, and a separation resistance force when the recording medium is separated from the fixing roller after passing through the nip portion is a predetermined value. When the fixing roller temperature is T2, the fixing roller temperature Tin immediately before the nip portion is T1 or higher, the fixing roller temperature Tout immediately after the nip portion is T2 or lower, and T1> T2. A fixing device characterized.   The fixing device according to claim 1, further comprising a shielding member that is disposed inside the fixing roller and selectively shields the inside of the fixing roller.   The fixing device according to claim 2, wherein the shielding member shields a vicinity of a nip formed by the fixing roller and the pressure roller and avoids direct heating of the nip from a heating source.   The fixing device according to claim 3, wherein the shielding member is configured to be movable in the fixing roller.   The fixing device according to claim 3, wherein the shielding range of the shielding member is changeable.   The fixing device according to claim 4, wherein the shielding member selects a position and a range of the shielding member according to a recording medium conveyance speed.   The fixing device according to claim 4, wherein the shielding member selects a position and a range of the shielding member according to an installation environment.   6. The fixing device according to claim 4, wherein the shielding member changes a position and a range of the shielding member according to the number of sheets to be passed.   6. The fixing device according to claim 4, wherein the shielding member selects different positions and ranges at the time of warm-up operation, standby, and paper passing.   The fixing device according to claim 5, wherein the shielding member changes a position and a range of the shielding member according to a size of a recording medium to be passed.   The fixing device according to claim 1, further comprising a non-contact separating unit as the recording medium separating unit from the fixing roller.   The fixing device according to claim 11, further comprising a blowing unit that blows air from a gap between the recording medium separating unit and the fixing roller toward the nip portion.   An image forming apparatus that performs electrophotography, comprising the fixing device according to claim 1.

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