JP2007212526A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain excellent fixing to an envelope while preventing occurrence of wrinkles and crease during fixing the envelope. <P>SOLUTION: A pressure changing member 18 supported by a shaft 19 is rotated up to only a prescribed amount, and pressure force of a pressure roller 13 to a fixing roller 11 is changeably composed by changing a side facing and contacting a pressure louver 16. When the pressure changing member 18 is rotated up to 90 degrees from a shown normal paper fixture, an envelope turns fixed, and pressure force is decreased. Then, a fixing temperature is increased up to only a prescribed temperature higher than a normal paper fixing time. The occurrence of wrinkles during fixing the envelope due to a decrease in pressure force is prevented, and the fixing temperature is enhanced to secure fixing to the envelope. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

JP 61-294471 A Japanese Patent No. 3219791

  2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, or a facsimile using an electrophotographic system, a thermal fixing device is used as a fixing device that fixes an unfixed image (toner image) transferred onto a recording material such as transfer paper on the recording material. Widely used.

  In some cases, an envelope is used as a recording material in an image forming apparatus including a heat fixing device. Since the envelope has a plurality of overlapping sheets and is thicker than plain paper, wrinkles and creases may occur when fixing the envelope.

  As a technique for improving the fixing property with respect to the envelope, for example, Patent Document 1 discloses that when the recording material is an envelope, the pressure is controlled to a fixing pressure and temperature suitable for fixing the envelope. Patent Document 2 describes that the fixing pressure is released at short intervals during envelope fixing.

  However, in the conventional fixing device and image forming apparatus, there is a problem that the prevention of wrinkles and folds at the time of fixing the envelope and the securing of the fixing property to the envelope are not yet sufficiently compatible.

  The present invention solves the above-described problems in conventional fixing devices and image forming apparatuses, and can provide a fixing device and image forming capable of obtaining good fixability to the envelope while preventing the occurrence of wrinkles and creases during envelope fixing. It is an object to provide an apparatus.

  According to the present invention, there is provided a fixing device that performs fixing by heat and pressure by passing a recording material between nips formed by pressing a pressure member against a fixing member. In the fixing device capable of fixing, the pressing force of the pressure member to the fixing member can be changed, and the pressing force when the envelope is passed is set to 45 to 60% of the time when the plain paper is passed. The problem can be solved by raising the fixing temperature at the time of paper higher than at the time of passing plain paper.

Further, it is preferable that the fixing temperature is set in accordance with the width of the envelope through which the paper is passed.
Further, it is preferable that the wider fixing envelope has a higher fixing temperature than the narrower envelope.

  Further, the decrease in the nip width due to the decrease in the applied pressure during the envelope passing is defined as X mm, and the decrease in the nip width obtained by dividing the nip width by the fixing line speed is defined as Y milliseconds. It is preferable that U = Z · Y when the increase in fixing temperature from the time of passing plain paper is U ° C. and the coefficient is Z.

The coefficient Z when fixing an envelope narrower than a predetermined width is preferably set to 0.6 to 1.3.
Further, it is preferable that the coefficient Z for fixing an envelope having a width greater than or equal to the predetermined width is set to 1.9 to 2.7.

Further, it is preferable that the pressure reduction and the fixing temperature increase are automatically performed during the envelope feeding.
Further, it is preferable that the mechanism for reducing the pressing force when the envelope is fed also serves as a mechanism for reducing the pressing force in order to prevent deformation of the pressure roller.

  In addition, according to the present invention, the above problem is solved by an image forming apparatus comprising the fixing device according to any one of claims 1 to 8.

  According to the fixing device of the first aspect and the image forming apparatus of the ninth aspect, the pressing force of the pressure member to the fixing member can be changed, and the pressing force when passing the envelope is 45 to 45 when passing the plain paper. 60% and the fixing temperature at the time of envelope feeding is higher than that at the time of plain paper feeding, so that the pressure at the time of envelope feeding is lowered to prevent the envelope from wrinkling and the fixing temperature is raised. As a result, fixing failure due to reduced pressure can be prevented and fixing performance can be ensured.

  According to the configuration of the second aspect, the fixing temperature is set according to the width of the envelope through which the paper is passed. Therefore, it is possible to prevent the fixing failure due to the fixing temperature being too low and the generation of wrinkles due to the fixing temperature being too high. In addition, good fixing results can be obtained regardless of the width of the envelope.

  According to the third aspect of the present invention, since the fixing temperature at which the wide envelope is set is higher than that at the narrow envelope, the fixing property can be secured even in the wide envelope in which fixing failure is likely to occur.

According to the configuration of the fourth aspect, it is possible to easily obtain the increase in the fixing temperature when the envelope is fed based on the relational expression U = Z · Y.
According to the configuration of claim 5, the coefficient Z when fixing an envelope narrower than a predetermined width is set to 0.6 to 1.3. Therefore, the optimal fixing conditions for a narrow envelope prevent wrinkles. Both fixing properties can be satisfied.

  According to the configuration of the sixth aspect, since the coefficient Z for fixing an envelope having a width greater than or equal to a predetermined width is set to 1.9 to 2.7, it is possible to prevent wrinkles by fixing conditions optimal for wide envelopes. And fixing ability can be satisfied.

  According to the configuration of the seventh aspect, since the pressure reduction and the fixing temperature rise are automatically performed when the envelope is fed, it is possible to prevent forgetting to set and to cope with network connection.

  According to the configuration of the eighth aspect, the mechanism for reducing the pressing force when the envelope is fed also serves as a mechanism for reducing the pressing force in order to prevent the pressure roller from being deformed. The deformation of the pressure roller at the time can be prevented.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a schematic configuration of a laser printer as an example of an image forming apparatus to which a fixing device according to the present invention can be attached. In the laser printer 100 shown in this figure, a photosensitive drum 1 as an image bearing member is disposed at a substantially central portion of the apparatus main body. Around the photosensitive drum 1, various devices necessary for an electrophotographic process such as a charging roller 2, a developing device 3, a transfer roller 4, and a cleaning unit 5 are arranged. An optical writing device 6 is disposed above each of the above devices constituting the image forming unit. Laser light L that is scanning light from the optical writing device 6 is applied to the photosensitive drum 1 from between the charging roller 2 and the developing device 3.

  A paper feed cassette 7 is set at the lower part of the apparatus main body, and a recording material (not shown) housed in the paper feed cassette 7 is fed toward the registration roller 9 by the paper feed roller 8. A fixing device 10 is disposed on the left side of the image forming unit. A conveyance roller 23 is provided at the exit of the fixing device, and a switching claw 24 for switching the paper conveyance direction is disposed.

An image forming operation in the laser printer 100 configured as described above will be briefly described.
When the image forming operation is started, the photosensitive drum 1 is rotated in the clockwise direction in the drawing by a driving unit (not shown), and the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity by the charging roller 2. . In the optical writing device 6, an LD (laser diode) (not shown) is driven based on image data sent from a host machine such as a personal computer, and irradiates the photosensitive drum 1 with laser light L as writing light. As a result, an electrostatic latent image is formed on the photosensitive drum 71. Toner is applied to the electrostatic latent image from the developing device 3 and visualized as a toner image.

  On the other hand, the recording material is fed from the paper feed cassette 2 by the paper feed roller 8. The recording material is once abutted against the registration roller 9 and then sent out in synchronization with the visible image. The toner image is transferred onto the paper at the transfer nip where the photosensitive drum 1 and the transfer roller 4 face each other. Is transcribed. When the recording material on which the toner image has been transferred passes through the fixing device 10, the toner image is fixed on the recording material by heat and pressure. The recording material after the toner image is fixed is discharged and stacked on a discharge tray 25 formed on the upper surface of the apparatus by the transport roller 23. In the drawing, a duplex unit 26 is mounted on the side of the apparatus on the left side, and the recording material after fixing the toner image on one side is reversed, and the recording material is fed again to the image forming section from the refeed path 27. By doing so, it is possible to form images on both sides of the recording material.

FIG. 2 is a cross-sectional view showing a main configuration of the fixing device 10.
As shown in this figure, the fixing device 10 of this example is a heat roll type heat fixing device including a fixing roller 11 and a pressure roller 13. A heater 12 such as a halogen lamp is disposed in the fixing roller 11. As an example of the fixing roller 11, a thin roller having a diameter of 25 to 45 mm, a metal core material of aluminum alloy, and a thickness of 0.35 to 0.6 mm is preferably used. The pressure roller 13 is configured as a sponge roller having an elastic layer around the core metal, and uses a pressure roller having a small heat capacity. The pressure roller 13 is brought into pressure contact with the fixing roller 11 by a pressure mechanism described later, and a predetermined fixing nip is formed between the two rollers. A separation claw 14 is disposed on the nip exit side of the fixing roller 11. Reference numeral 15 denotes a nip entrance guide plate that guides the recording material onto which the unfixed toner image has been transferred to the fixing nip. In addition, it has a temperature detection means such as a thermistor provided in contact with or close to the fixing roller 11, and the heat generation of the heater 12 is controlled based on the output of the temperature detection means.

The pressure mechanism of the fixing device will be described with reference to FIGS.
As shown in FIG. 3, the pressure roller 13 is pressed against the fixing roller 11 by a pressure lever 16. That is, the pressure lever 16 is supported by a shaft 28 so that the right end portion can be rotated (swinged) in the drawing, and is applied by a spring 17 as an urging member locked to the opposite end portion of the lever. The left end of the pressure lever 16 is pulled up diagonally to the upper right in the figure. The pressure lever 16 is formed with a bearing portion 16a, and the shaft 13a of the pressure roller 13 is fitted into the bearing portion 16a. Accordingly, the pressure roller 13 is pressed against the fixing roller 11 while the shaft 13 a is pressed by the pressure lever 16.

  A pressure switching member 18 is provided on the upper side of the pressure lever 16. The pressure switching member 18 is formed in a rectangular parallelepiped shape, and a shaft 19 is protruded or implanted at a position deviating from the center of the cross-sectional rectangle (intersection of diagonal lines). As shown in FIG. 4, a spur gear 20 is fitted to the shaft end of the shaft 19, and the gear 20 is meshed with a worm gear 22 rotated by a motor 21. Therefore, when the motor 21 rotates, the shaft 19 is rotated via the worm gear 22 and the spur gear 20, and the pressure switching member 18 is rotated. In this example, the motor 21 is rotated by a predetermined amount so that each side surface (four surfaces) of the pressure switching member 18 that is a rectangular parallelepiped can be opposed to the upper side of the pressure lever 16.

  As described above, since the shaft 19 is provided eccentrically in the rectangular cross section of the pressure switching member 18, the pressure switching member 18 has four side surfaces 18a, 18b, 18b, and 18c having three different distances from the shaft 19. Will have. However, since the shaft 19 is provided at a position of a half distance in the short side direction of the rectangular cross section, the two side surfaces 18b and 18b facing each other have the same distance from the shaft 19. The relationship between the distance from the shaft 19 to each side surface is set to 18a <18b <18c. When the upper side (upper surface) of the pressure lever 16 comes into contact with the side surface of the pressure switching member 18, the pressure roller 13 can no longer be pressed. Therefore, the pressure applied to the fixing roller 11 by the pressure roller 13 can be switched by switching the side surface of the pressure switching member 18 opposed to the pressure lever 16. In this example, the pressing force can be switched in three stages.

  FIG. 3 shows a state in which the side surface 18 a of the pressure switching member 18 is opposed to the pressure lever 16. Since the side surface 18a has the shortest distance from the shaft 19, in this state, the applied pressure becomes maximum. In the fixing device of this example, the state in which the side surface 18a is opposed to the pressure lever 16 is the plain paper pressure state.

  Although not shown in the drawing, the state in which the side surface 18b of the pressure switching member 18 is opposed to the pressure lever 16 is smaller than the plain paper pressure state because the distance from the shaft 19 is 18a <18b. Pressure is applied. Further, as the pressure is reduced, the nip width (the length in the sheet passing direction) formed by the pressure contact between the pressure roller 13 and the fixing roller 11 is also reduced. In the fixing device of this example, the state in which the side surface 18b faces the pressure lever 16 is referred to as an envelope pressure state.

  Further, as shown in FIG. 5, when the side surface 18c of the pressure switching member 18 is opposed to the pressure lever 16, the distance from the shaft 19 is 18a <18b <18c. Also, the nip width is minimized. In the fixing device of this example, the state where the side surface 18c is opposed to the pressure lever 16 is referred to as a deformation preventing state. In this deformation prevention state, the pressure applied to the fixing roller 11 by the pressure roller 13 is small. For example, the deformation of the pressure roller 13 can be prevented by switching to the deformation prevention state when not operating. It is also possible to set the distance from the shaft 19 to the side surface 18 c to be a distance at which the pressure roller 13 is separated from the fixing roller 11.

A specific example of fixing conditions in the fixing device 10 of this example will be described.
As an example, the fixing linear velocity is set to 120 mm / s, the pressing force of the plain paper is 79.5 N, the nip width is 4.6 mm of the plain paper and the fixing temperature is 170 ° C. This fixing condition is a favorable condition that can secure the fixing property when plain paper is used and does not cause wrinkles.

  However, when fixing is performed by passing an envelope under fixing conditions suitable for the plain paper, wrinkles occur regardless of the width of the envelope (the length in the direction perpendicular to the paper passing direction). When envelopes are fed, lowering the pressure (lower than the normal paper fixing conditions) is effective in preventing wrinkles.

  Here, a fixing property evaluation experiment performed when the inventor of the present application passes plain paper and envelopes will be described with reference to Table 1. The evaluation was performed using plain paper and two types of envelopes having different sizes. In the following table, “envelope width: small” indicates a width of 118 mm and a length of 235 mm. “Envelope width: large” indicates a width of 240 mm and a length of 330 mm.

  As shown in Table 1, for the plain paper, evaluation was performed under the above-mentioned plain paper fixing conditions, and for the envelope, the fixing property was evaluated by changing the pressure for each of the two types of envelopes. The conditions for each pressing force are as shown in the table, and the evaluation results of wrinkles and fixability are as shown in the table. The fixing temperature was the same at 170 ° C. Table 1 shows typical conditions and evaluation results at that time.

  From this evaluation result, it can be seen that wrinkles are more likely to occur when the envelope is wider. In addition, it can be seen that the fixing property decreases as the envelope width increases. Here, based on the state of wrinkles, it was determined that the pressing force at the time of fixing the envelope had to be 60% or less that at the time of fixing the plain paper.

  Next, the inventor of the present application conducted an evaluation experiment by changing the fixing temperature in addition to the applied pressure. The results are shown in Table 2.

  As shown in Table 2, the nip width decreases as the applied pressure decreases. Accordingly, the time for the recording material to pass through the nip, that is, the nip time is shortened as the pressing force is reduced. When the applied pressure was 40.8 N, the nip width was 3.6 mm, and the nip width was reduced by 1 mm from the above-mentioned plain paper fixing conditions. At this time, the nip time was 30 ms, and the decrease in the nip time from the plain paper fixing condition was 8 ms. The nip width when the pressure was 31.8 N was 3.3 mm, and the decrease in the nip width from the plain paper fixing conditions was 1.3 mm. At this time, the nip time was 27.5 ms, and the decrease in the nip time from the above-mentioned plain paper fixing conditions was 10.58 ms. Then, the fixing temperature was evaluated by making the pressure different for each fixing pressure with respect to the fixing temperature of 170 ° C. under the fixing condition of plain paper. The evaluation of wrinkles and fixability in the two types of envelopes under each condition is as shown in the table. Table 2 shows typical conditions and evaluation results at that time.

  As can be seen from Table 2, when the pressing force was 40% of plain paper, the fixing property was poor even when the fixing temperature was increased to 195 ° C. (envelope width: large). This is because the pressure toner necessary for fixing is not added. Here, it was determined that if the pressing force was 45% or less of that for fixing on plain paper, the fixing force could not be satisfied because the pressing force was insufficient even if the fixing temperature was raised. Therefore, the pressure at the time of fixing the envelope is reduced to 45-60% with respect to the pressure at the time of fixing the plain paper to eliminate the wrinkle of the envelope, and the fixing temperature of the envelope is increased by increasing the fixing temperature as compared with the time of fixing the normal paper. It was supposed to be secured. The necessary fixing temperature was set to an appropriate value based on the envelope width, pressure, and nip time.

  By the way, as can be seen from the section of the applied pressure of 40.8 N in Table 2, the envelope having a narrow width is fixed when the fixing temperature is raised (increased) by 8 ° C. from the above-mentioned fixing condition of 170 ° C. However, the wide envelope width was poor in fixability at the same temperature rise of 8 ° C. This is because the fixing pressure is lower than that of the narrow envelope because the envelope is wider. Therefore, when other conditions were the same and the fixing temperature was increased by 19 ° C. (from 170 ° C. in the above-mentioned plain paper fixing conditions), the fixing property could be satisfied. Therefore, it has been found that the fixing temperature is changed according to the width of the envelope, that is, the fixing temperature is set higher for the wide envelope than the narrow envelope, and the necessary fixing property is ensured.

  However, if the fixing temperature is too low, fixing will be poor, and if the fixing temperature is too high, wrinkles due to excessive heat will occur. Since the effect of preventing wrinkles due to a decrease in pressure is related to the decrease in fixability associated with a decrease in nip time due to a decrease in pressure, it is difficult to set specific conditions that satisfy both the wrinkles and fixability. Accordingly, the inventor of the present application uses the above-mentioned fixing condition of the plain paper as a reference, the reduction of the nip width due to the pressure reduction (decompression) is Xmm, the reduction of the nip time obtained by dividing (X) by the linear velocity is Yms, the fixing temperature When the increment is U ° C., the temperature is determined by U = Z · Y, and the range of the coefficient Z is set so that an appropriate fixing condition can be obtained by increasing the fixing temperature by this temperature (U).

  However, as described above, the wider envelope than the narrow envelope needs to set the fixing temperature higher and ensure the necessary fixability, so the coefficient Z is smaller than that of the narrow envelope. Two wide envelopes were set. Here, the coefficient for a narrow envelope is Zn, and the coefficient for a wide envelope is Zw.

  Now, in the range of the coefficient Z (Zn, Zw), by setting the coefficient Zn in the narrow envelope: 0.6 to 1.3, the fixing condition is optimum for the narrow envelope, and the fixing is performed. It turns out that both sex and wrinkle can be satisfied.

  It was also found that by setting the coefficient Zw for a wide envelope to 1.9 to 2.7, the fixing condition is optimal for a wide envelope, and both fixing properties and wrinkles can be satisfied.

  In the fixing device of the present embodiment described with reference to FIGS. 1 to 5, the side surface 18 b of the pressure switching member 18 is pressed against the pressure lever 16 with respect to the plain paper pressurizing state in which the side surface 18 a of the pressure switching member 18 is opposed to the pressure lever 16. 16 is set so that the pressing force is 45 to 60% of the pressurizing state of the plain paper when the envelope is in a pressing state of the envelope 16. And by switching the fixing temperature in the envelope pressurization state, it is possible to prevent the occurrence of wrinkles in both the narrow envelope and the wide envelope, and to perform good fixing with securing fixability. Become.

  Switching between the fixing pressure and the fixing temperature is performed when a dedicated setting button is provided on the operation panel of the image forming apparatus or when an envelope (narrow and wide) is selected as the recording material. The temperature can be changed to one suitable for the selected recording material.

  However, manual switching of the fixing pressure and switching of the fixing temperature cannot be handled in the case of forgetting to set or a printer connected via a network.

  Therefore, in the case of a printer, the width of the envelope to be used can be known by inputting the paper width in the printer driver or selecting the type of envelope as the recording material. In the case of a copying machine, an envelope is selected as a recording material, and the width of the envelope can be grasped from the position of the side fence on the manual feed tray or the dedicated envelope feeder as well as the paper (recording material) being an envelope. As a result, when the image forming apparatus recognizes that the recording material to be used is an envelope, the pressure switching member 18 of the fixing device 10 is automatically rotated so that the side facing the pressure lever 16 is in a plain paper pressure state. The pressure lever 16 is pushed down by switching from 18a to 18b, and the pressure applied for the envelope can be automatically set. Also, the fixing set temperature is automatically changed according to the envelope width. As a result, fixing conditions suitable for envelopes are automatically set, and it is possible to obtain a good fixed image that does not wrinkle regardless of the envelope width and secures fixing properties, and prevents setting errors. In addition, it can correspond to a network printer.

  Further, in the fixing device 10 of this example, since the sponge roller is used as the pressure roller 13, the pressure roller 13 may be deformed when heated during standby or left for a long period of time. Therefore, by automatically rotating the pressure switching member 18 of the fixing device 10 and switching the side surface facing the pressure lever 16 to 18c to prevent the deformation, the deformation of the pressure roller 13 can be prevented. it can. In this example, since the pressure reducing mechanism for feeding the envelope and the pressure roller deformation preventing mechanism are combined, it is possible to prevent the pressure roller from being deformed without increasing the cost.

  As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this. The fixing device is not limited to the heat roll method, and the present invention can also be applied to a belt fixing device. Further, the arrangement of the heater is arbitrary, and the pressure roller may have a heater. Further, the heating means is not limited to a heater such as a halogen lamp, but may be one using a resistance heating element or an induction heating method. Further, the mechanism for changing the pressing force can adopt an arbitrary configuration, and the number of stages for switching the pressing force is not limited to the three stages in this example, and can be set to any number of stages. Moreover, the structure which can change an applied pressure steplessly (continuously) may be sufficient. The fixing set temperature is also arbitrary, and the amount of temperature rise from the plain paper pressure state can be set as appropriate. The nip width, the fixing line speed, and the like can be set as appropriate. The configuration of each part of the image forming apparatus is also arbitrary, and is not limited to a printer, and may be a copier, a facsimile machine, or a multifunction machine having a plurality of functions.

1 is a cross-sectional view illustrating a schematic configuration of a laser printer which is an example of an image forming apparatus to which a fixing device according to the present invention can be mounted. FIG. 2 is a cross-sectional view illustrating a main configuration of the fixing device. It is a partial side view showing a pressure mechanism of the fixing device. FIG. 3 is a partial perspective view illustrating a pressure switching mechanism of the fixing device. It is a partial side view which shows the pressurization mechanism of a pressurization roller deformation | transformation prevention state.

Explanation of symbols

1 Photosensitive drum 6 Optical writing device 10 Fixing device 11 Fixing roller (fixing member)
12 Heater 13 Pressure roller (Pressure member)
14 Separation claw 16 Pressure lever 17 Spring 18 Pressure switching member 21 Motor 100 Laser printer (image forming apparatus)

Claims (9)

A fixing device for fixing a sheet by passing a recording material between nips formed by press-contacting a pressure member to a fixing member, and fixing by heat and pressure.
The pressing force of the pressure member to the fixing member is configured to be changeable,
The pressure applied during envelope feeding is 45 to 60% of that during plain paper passing,
A fixing device that raises a fixing temperature when an envelope is passed than that when plain paper is passed. The fixing device according to claim 1, wherein the fixing temperature is set according to a width of an envelope through which paper is passed. The fixing device according to claim 2, wherein the set fixing temperature is higher in the wide envelope than in the narrow envelope. The decrease in the nip width due to the decrease in the applied pressure when the envelope is passed is defined as X mm, the nip width decrease: the nip time decrease obtained by dividing X by the fixing line speed is defined as Y milliseconds, When the increase in the fixing temperature from the time of passing plain paper is U ° C and the coefficient is Z,
U = Z ・ Y
The fixing device according to claim 1, wherein the fixing device is a fixing device. The fixing device according to claim 4, wherein the coefficient Z when fixing an envelope narrower than a predetermined width is set to 0.6 to 1.3. 6. The fixing device according to claim 4, wherein the coefficient Z for fixing an envelope having a width greater than or equal to the predetermined width is set to 1.9 to 2.7. The fixing device according to claim 1, wherein a pressure reduction and a fixing temperature increase are automatically performed when the envelope is fed. The fixing device according to claim 1, wherein a mechanism for reducing the pressure when the envelope is fed also serves as a mechanism for reducing the pressure to prevent deformation of the pressure roller. An image forming apparatus comprising the fixing device according to claim 1.

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