JPH06103415B2 - Image recorder - Google Patents

Description

The present invention relates to an image recording apparatus such as electrophotography and electrostatic recording, and in particular, a so-called toner image formed of resin, carbon, pigment, dye, etc., a recording member such as paper (hereinafter abbreviated as a sheet). The present invention relates to an image recording apparatus having a fixing device for fixing it on the top.

As a conventional fixing device used in this type of image recording device, a heating fixing device for passing a sheet through a chamber having a heating means inside to heat and fuse a toner image on the sheet, and applying pressure to the sheet There are a pressure fixing device for solidifying the toner image on the sheet, a heat fixing device for heating and fusing the toner image on the sheet by passing the sheet between the heating roller and the pressure roller. However, in any of the fixing devices, there is a problem that the sheet passing through the fixing device is deformed and curled by receiving heat or mechanical pressure. This phenomenon is remarkable in the heat fixing device.

In particular, the heat fixing device applies a large amount of heat to the sheet and the toner. Therefore, the moisture contained in the sheet evaporates, and the sheet curls due to an imbalance in the amount of moisture evaporated on the front and back surfaces. Also, when a sufficient amount of heat is applied to both the front and back surfaces of the sheet, the curl shape is determined by the state immediately after the sheet exits the heat fixing device, because the sheet loses its rigidity as the sheet moisture evaporates.

The occurrence of the above curl does not cause a big problem in the normal image recording mode. However, for example, when a sorter is connected to the image recording device to automatically perform sheet alignment, a problem occurs, and toner images are formed on the front and back surfaces of the sheet. When performing automatic double-sided printing for transfer, inconvenience may occur in the sheet transportability and stackability on the intermediate tray.After the toner image is transferred from the image forming body to the sheet, the sheet is electrostatically discharged from the image forming body. When performing separation, there is a problem that inconvenience occurs in separation after transfer to the second side of the sheet.

Conventionally, in order to solve the above problems, for example, a device for improving the sheet itself to reduce the curl amount, as a specific example, as disclosed in JP-A-57-81270, the water content of the sheet is 5.5 ~ At 6.5%, an attempt has been made to keep the waist strength of the seat appropriate at that time. However, this attempt limits the sheets used, the sheets themselves are easily affected by environmental changes, the sheets lose their stiffness by absorbing moisture in a high-humidity environment, and the amount of water evaporation is high. Therefore, the above improvement was not sufficient for the phenomenon such as increasing the curl amount.

Since the curl shape of the sheet is determined immediately after being discharged from the heat fixing device, the sheet discharging portion of the fixing device is devised. As a concrete example,
As disclosed in 4,375,327, in the case of heat roller fixing consisting of a heat fixing roller and a pressure roller, shortening the distance between the separation claw and the nip portion in contact with the pressure roller,
As disclosed in Japanese Unexamined Patent Publication No. 51-113637, attempts have been made to make the sheet conveying speed of the conveying means after the sheet is discharged from the fixing roller higher than the sheet conveying speed of the fixing roller.

However, these attempts cannot control the curl state of a part of the sheet. In particular, in the case of double-sided printing, the trailing edge of the sheet for the first side will come to the leading edge for printing for the second side, so it is necessary to control the curl state of the trailing edge of the sheet for the first side. Is not enough. That is, the preceding example is effective only for the regulation of the wavy curl, and the latter example is capable of regulating the curl amount only when the sheet is between the fixing roller and the conveying means after the sheet is ejected. There is a problem that the curl amount at the rear end cannot be regulated.

In addition to the above example, the curl amount regulation at the discharging portion of the fixing roller has been devised, but none of them is sufficient in the sense that the curl amount at all portions from the leading edge to the trailing edge of the sheet is regulated. It was

Further, since the curl of the sheet is the most problematic in double-sided printing, the print image on the first side is assumed to be printed as disclosed in, for example, JP-A-53-143339.
It has been proposed that the printed image on the first side be permanently fixed. However, since the heat amount is not supplied so much from the fixing roller to the assumed first surface, the curl of the sheet is reduced, but the fixing property is poor, so that the toner image is scraped off by the conveying roller or the like when the second surface sheet is conveyed. It causes drawbacks. In other words, there is a contradictory condition where a fixing property with practically no problem is obtained and a fixing condition with a small curl amount, and the overlapping area is small. The idea of reducing is practically very difficult.

The present invention has been proposed in view of the above, and an object of the present invention is to efficiently and reliably reduce the curl of a sheet caused by passing through a fixing device. Further, although the present invention prevents curling by steam, it is also an object to effectively utilize the steam. Particularly in double-sided printing in which an image is formed on both sides of a sheet, the present invention improves the transportability of the sheet, reduces the occurrence of jams, and improves the separation property of the sheet from the image forming body after the second-side printing. Therefore, it is particularly preferable for this type of application.

In order to achieve the above object, the present invention is a fixing device for fixing a toner image onto a recording member, and a steam applying unit for applying steam to the recording member immediately after being discharged from the fixing device,
In the image recording apparatus having the above, the water vapor applying unit controls the amount of water vapor according to the thickness of the recording member and / or the amount of moisture absorption, which is an image recording apparatus.

FIG. 1 is a diagram showing an overall outline of a double-sided laser beam printing apparatus as an image recording apparatus of the present invention. A laser beam 1 modulated by a signal from the outside or a signal generated inside is scanned by a scanner 2, passes through an imaging lens 3, and has an optical path bent by a folding mirror 4, and a photosensitive drum 5 as an image forming body. Imaged above. The photosensitive drum 5 is subjected to uniform corona charging by the charger 6, and then irradiated with the laser light 1 to form an electrostatic pattern according to a signal, that is, an electrostatic latent image. The electrostatic latent image is converted into a toner image by passing through the position of the developing device 7.

On the other hand, the sheet 9 as the transfer paper is sent from the cassette 13 by the cassette feeding roller 12 and then fed by the registration roller 14 in synchronization with the image on the photosensitive drum 5.
Then, after the toner image is transferred from the photosensitive drum 5 when passing through the position of the transfer corona charger 8, the separation corona charger 10
Then, it is separated from the photoconductor 5 and conveyed to the fixing device 16 by the conveying belt 15. The surface of the photoconductor 5 is cleaned with a cleaner 11 after the sheet is separated, and is repeatedly used.

The fixed sheet discharged from the fixing device 16 is sent onto the tray 23 by the discharge roller 22 in the case of single-sided printing.
Further, in the case of double-sided printing, the conveyance path is bent by the branching claw 18 to be conveyed, and then the conveyance belt 19 conveys the toner image forming surface upward to the intermediate tray 20.

Next, it is fed from the intermediate tray 20 by the intermediate feeding roller 21, synchronized with the image by the registration roller 14, and is fed downward toward the transfer corona charger 8 with the toner image forming surface. Then, the transfer corona charger 8 transfers the toner image for the second time on the side opposite to the surface for forming the toner image for the first time, and after that, the toner image is separated, conveyed, and fixed as in the case of single-sided printing, and then the discharge roller 22. Is delivered to the tray 23 outside the machine.

Although the optical image exposure is modulated laser light in the example of FIG. 1, it may be optical image exposure from an original document irradiated with light as in a copying machine.

FIG. 2 is a cross-sectional view showing an example of a heat fixing device applied to the image recording apparatus of the present invention. The heating and fixing device 16 is composed of a pair of rollers including a fixing roller 162 and a pressure roller 163 that is in pressure contact with the fixing roller 162.

The fixing roller 162 is a FLC (product name: : Manufactured by Nitto Kogyo Co., Ltd.) and has a heat source such as a halogen heater 169 inside.

The pressure roller 163 has HTV, LTV,
It is a structure coated with a non-adhesive heat resistant elastic body such as FLC.

In this embodiment, the heat fixing device is used, but since the temperature of the fixing roller is higher than that of the pressure roller, curling is likely to occur along the circumference of the fixing roller. The curl is also generated by the pressing method of pressure fixing, which will be described in detail later.

The surface temperature of the fixing roller 162 is detected by a temperature sensor such as the thermistor 164, and is controlled to a constant temperature by a known control circuit (not shown). The toner offset on the fixing roller is cleaned with a silicone oil-impregnated cleaning web.
Cleaned by 161. Other materials may be used as the oil applying member and the cleaning member.

The cleaning web 161 is sent from the supply reel 24, and is wound by the take-up reel 26 while being pressed against the fixing roller 162 by the pressing roller 25. In the figure, reference numeral 165 designates a winding prevention claw of the sheet 9 which is biased by a spring (not shown) so that its tip comes into contact with the surface of the fixing roller, and 166 is attached by a spring (not shown) so that its tip comes into contact with the surface of the pressure roller. The urging prevention claw 167 of the biased sheet 9 is a water vapor flow path formed near the sheet discharge side from the bottom of the fixing device 16, preferably toward the outside of the discharge roller 22. In this example, the water vapor flow path 167 is formed by inclining the side wall of the discharge side of the bottom plate of the fixing device toward the discharge side.

The sheet 9 onto which the toner image has been transferred from the photosensitive drum 5 is conveyed to the heating and fixing device 16, and the fixing roller 162 and the pressure roller 163.
Heat is supplied from the fixing device 162 when passing between
The toner on the sheet 9 is melted and fixed on the sheet. At this time, a part of the water content is evaporated from the sheet 9 by the above heat supply, and the inside of the fixing device 16 contains a larger amount of water vapor than the general air.

The water vapor in the fixing device 16 flows upward together with the flow of warm air, but since the air flow is blocked at the upper part of the fixing device by an elastic body 168 such as maltoplane, the inside of the fixing device is increased. Cause convection. As a result, the warm air and the steam inside the fixing device 16 flow through the steam flow path 167 as indicated by the arrow a.

The sheet 9 that has passed between the fixing roller 162 and the pressure roller 163 is discharged by the discharge roller 17 and guided in the direction of arrow b by the branch claw 18 that switches the path. At this time, the curl is corrected by exposing the lower surface of the sheet 9 to the water vapor that has passed through the water vapor flow path 167 immediately after leaving the discharge roller 17, and becomes substantially flat when fed to the intermediate tray 20, The stackability on the tray 20 and the separability from the photosensitive drum 5 after the transfer of the second surface are both excellent.

On the other hand, the louver 171 provided in the steam channel 167 is
When a control signal is input to the driver 173 and the plunger 170 is energized via the driver, the plunger 170 is pulled in the direction of the arrow d against the restoring spring 172 to open the water vapor flow path 167 in the state of the illustrated example. When the power supply to the plunger 170 is cut off, the louver 171 is pulled in the direction of arrow c by the urging force of the restoring spring 172, closing the water vapor flow path 167 in the state shown by the chain line. In this case, the amount of electricity supplied to the plunger 170 is controlled by a control signal according to the type and state of the seat 9, and the opening angle of the louver 171 is made variable to control the amount of water vapor supplied to the seat 9.

FIG. 3 is a front view of a part showing a modified example of the fixing device 16. In this example, a flow path opening / closing member 18 in the shape of a round bar having a through hole 180a on the peripheral surface is formed at the boundary between the bottom of the fixing device 16 and the water vapor flow path 167.
As shown in FIG. 4, the flow path opening / closing member 180 is provided with a urging force in the clockwise direction of arrow c as shown in FIG. 4, and the through hole 180a is in the state shown in FIG. In FIG. 3, a chain line is shown) to close the flow path.

When the plunger 182 is energized by the print start signal and moves in the direction of arrow d, the flow path opening / closing member 180 rotates in the counterclockwise direction opposite to the direction of arrow c, and the through hole 180a is shown by the solid line in FIG. In this state, the flow path is opened. In this case, the amount of water vapor supplied to the seat 9 is adjusted by controlling the energization of the plunger 182 via the driver 183 by the control signal output according to the type and state of the seat 9 to adjust the opening amount of the flow path. Adjust so that it is optimal for curling.

The sheet guide member 179 disposed near the discharge side of the discharge roller 17 may be a mesh-shaped perforated plate through which water vapor can pass or a comb-shaped guide rod.

It will be described in detail based on FIGS. 5 and 6 that the curl is corrected by exposing the sheet 9 to water vapor. The leading end of the sheet 9 that has entered between the fixing roller 162 and the pressure roller 163 is wrapped around the fixing roller 162 by the adhesive force of the melted toner, but is peeled off by the winding prevention claw 165. Therefore, the tip of the sheet 9 receives the above force and curls downward as shown in FIG.

On the other hand, as shown in FIG. 5B, the rear end of the sheet 9 is supported only by the discharge roller 17 when it is no longer subjected to the binding force sandwiched between the fixing roller 162 and the pressure roller 163.
It hangs downward due to gravity and curls downward. Thus, when the sheet 9 leaves the fixing device 16, the sheet 9 curls downward as shown in FIG. 6a.

The above phenomenon becomes more remarkable when the sheet 9 absorbs moisture. It is considered that this is because the waist of the sheet 9 is weakened by moisture absorption, and the movement of water in the sheet is always directed upward, so that the movement of water on the lower surface of the sheet is increased. Furthermore, when printing on both sides,
As shown in FIG. 2, the sheet 9 is conveyed by being bent and guided in the same direction as the curl by the branch claw 18. This bending action occurs when the sheet 9 is warm immediately after leaving the fixing device 16, so that the curl of the sheet 9 is greatly affected and the downward curl becomes larger.

Therefore, the present invention utilizes the phenomenon that a sheet is supplied with water and expands as shown in FIG. 6 (b), and by the extremely simple means of applying steam to the sheet surface curled as described above. The sheet curl is corrected. In this case, the amount of extension of the lower surface of the sheet differs depending on the amount of water vapor given to the lower surface of the sheet.

Therefore, in order to optimally correct the curl of the sheet 9 discharged from the fixing device 16, it is necessary to control the amount of water vapor supplied to the lower surface of the sheet according to the thickness of the sheet 9 and / or the moisture absorption amount. That is, as described above, the sheet 9 that has been left in a high humidity environment and has a large amount of moisture absorption has an extremely large downward curl, and it is necessary to increase the amount of water vapor in order to correct this curl. In addition, a rigid sheet such as thick paper will hardly curl even if it is discharged from the fixing device, or the heat from the fixing roller will not be sufficiently transferred to the lower surface of the sheet. May evaporate and the sheet may curl upward. In such a case, supplying water vapor to the lower surface of the sheet is not preferable because it promotes curling.

FIG. 7 shows an example of a mechanism for detecting the thickness of the sheet and the amount of moisture absorption. The amount of transmitted light that passes through the sheet 9 by a light source 61 and a photodiode 62 that are arranged opposite to each other across the conveyance path of the sheet 9. Is being detected. Since the amount of transmitted light changes according to the thickness of the sheet 9, the output of the photodiode 62 gives information about the thickness of the sheet 9.

Therefore, the output of the photodiode 62 is set to a known amplifier.
A control signal is supplied to the driver 173 in FIG. 2 or the driver 183 in FIG. 4 according to the thickness of the sheet 9 through the comparator 63, the comparator 64, and the control circuit 65, and the sheet 9
Control the amount of water vapor supplied to.

FIG. 8 shows an example of a mechanism for detecting the thickness and the moisture absorption state of the sheet. When the sheet 9 is fed from the cassette 13 by the feeding roller 12, the sheet feeding path 12 sandwiches the sheet conveying path to face the sheet. The sheet thickness detection mechanism shown in FIG. 7 detects the sheet thickness. Further, the sheet 9 is synchronized with the rotation of the photosensitive drum 5 by a pair of registration rollers 74,
It is sent to the transfer portion that faces the transfer charger 8 through the transfer guide 73.

At this time, a bias voltage (preferably the same polarity as the transfer charge) is applied to the registration roller 74 by the bias power source 72. The transfer guide 73 is grounded via the resistor 71. Therefore, from the registration roller 74 to the sheet 9
By detecting the current flowing through the transfer guide 73, the resistance of the sheet 9 can be known, and as a result, the moisture absorption state of the sheet 9 can be known. That is, sheet 9
The moisture absorption state of can be known as the voltage drop value of the resistor 71.

With the above configuration, the output voltage representing the thickness of the sheet output from the photodiode 62 is supplied to the amplifier 63 and the comparator 64.
To the control circuit 65, and the voltage drop value of the resistor 71 indicating the moisture absorption state of the seat 9 is input to the control circuit 65 through the amplifier 66. Therefore, the control circuit 65 outputs a control signal for controlling the amount of water vapor to be supplied to the seat 9 based on the both inputs.

More specifically, the output V ₁ from the photodiode 62 through the amplifier 63 is compared with the reference voltage V ₀ by the comparator 64. At this time, if V ₁ > V ₀ (the sheet 9 is thin and the amount of transmitted light is large), the output of the comparator 64 becomes “1”. If V ₁ <V ₀ (the sheet 9 is thick and the amount of transmitted light is small), the output of the comparator 64 is “0”.

On the other hand, the output signal V ₂ according to the moisture absorption state of the seat 9 is
It can be obtained by amplifying the voltage drop of 71. When the output signal V ₂ is large, it means that the resistance of the sheet 9 is low and the sheet is in a moisture absorbing state. When the output signal V ₂ is small, the sheet 9 It shows high resistance and not much moisture absorption.

Then, as shown in the flowchart of FIG. 9, the final control signal outputs an output signal having a value proportional to V ₂ when V ₁ > V ₀ , that is, when the output of the comparator 64 is “1”. . Further, when V ₁ <V ₀ , the output signal V becomes “0”.

FIG. 10 is a partial front view showing another modification of the fixing device. In this example, the steam in the fixing device 16 is sucked by a cross flow fan 190 whose air flow rate is variable, and is sprayed from the fixing device 16 to the lower surface of the sheet 9 immediately after being discharged. Cross flow fan 19 above
With 0, the air volume is adjusted by the output of the driver 191 controlled by the control signal V described above. At this time, the characteristic of the driver 191 is that when the control signal V is 0 (the sheet is sufficiently thick), the crossflow fan 190 is turned off, and as the V becomes larger (the sheet is thicker, moisture is absorbed and the resistance is lower), the crossflow fan is reduced. Make sure that the output of 190 increases.

As a result, regardless of the thickness of the sheet and / or the amount of moisture absorption, curl correction is always performed reliably. Also, fixer 16
Since the amount of water vapor discharged from the sheet is appropriately controlled, it is always used effectively for straightening the curl of the sheet 9 without being wasted.

In each of the above embodiments, a flow path for providing the sheet with water vapor in the fixing device is provided in the vicinity of the discharge of the fixing device.However, a water vapor generation source is provided in the vicinity of the discharge, and the generated water vapor is supplied to the sheet. It can also be configured to give.

As the water vapor generation source, for example, a water vapor is generated by vibrating water with a vibrating element such as a piezo element.

The fixing device is not limited to the heat roll fixing device in the illustrated example, but a chamber fixing device, an induction heating fixing device, a flash fixing device, various heat application type fixing devices such as a heat plate, and a pressure fixing device for fixing by pressure are applied. It is possible. Further, as a method for printing a toner image on a sheet, there is a method in which a toner image is once formed on another image forming body and then transferred to a sheet as in the illustrated example, or at the same time when an electrostatic image is directly formed on the sheet. Alternatively, a method of developing immediately after that may be used.

As described above in detail, according to the present invention, the sheet immediately after being discharged from the fixing device is provided with a channel for supplying water vapor, and the amount of water vapor supplied to the sheet according to the thickness and / or the amount of moisture absorption of the sheet. As a result, the following various descents are obtained.

(1) The curl of the sheet after being discharged from the fixing device can be reliably reduced with a simple configuration regardless of the sheet thickness and / or the moisture absorption amount.

(2) Since the curl is reduced, it is possible to reduce the occurrence of jam caused by the curl of the sheet during double-sided printing, and to obtain stable double-sided conveyance characteristics.

(3) When the sheet separation from the photosensitive drum is electrostatic separation as in the illustrated embodiment, deterioration of separability due to curling can be prevented, and it is particularly effective when the sheet is left in a high humidity environment. Is.

(4) Since water vapor, that is, humidity is applied to the sheet, an extreme increase in surface resistance of the sheet can be prevented even after the first fixing, so that transferability and separability are improved, and a good image is obtained in the second time. Records are obtained. That is, according to the present invention, not only curl prevention but also a good humidity control effect of the sheet can be obtained.

[Brief description of drawings]

FIG. 1 is an overall schematic view of a laser beam printer device as an image recording device of the present invention, FIG. 2 is an enlarged cross-sectional view of a fixing device applied to the device, and FIG. 3 shows a modification of the fixing device. Partial enlarged cross-sectional view, FIG. 4 is an end view of the flow path opening / closing member, FIGS. 5 and 6 are explanatory views of sheet curl correction, FIG. 7 is a schematic view of a sheet thickness detection mechanism, and FIG. FIG. 9 is a schematic view of a mechanism for detecting the thickness and moisture absorption state of the sheet, FIG. 9 is a flow chart view, and FIG. 10 is a partial enlarged cross-sectional view showing another modification of the fixing device. 9 is a recording member (sheet), 16 is a fixing device, and 167 is a water vapor flow path.

Continuation of the front page (56) Reference JP 54-74444 (JP, A) JP 49-2544 (JP, A) JP 59-24862 (JP, A) JP 50-143531 (JP , A) JP 50-147725 (JP, A) JP 58-35569 (JP, A) JP 58-63970 (JP, A) JP 58-168073 (JP, A) JP 60-182459 (JP, A) JP 60-182460 (JP, A) JP 60-182462 (JP, A) JP 60-182466 (JP, A) JP 60-182469 (JP, A) A) Actual development Sho 54-62738 (JP, U) Japanese Patent Sho 42-8198 (JP, B1)

Claims (2)

[Claims] 1. An image recording apparatus comprising: a fixing device for fixing a toner image onto a recording member; and a water vapor applying unit for applying water vapor to the recording member immediately after being discharged from the fixing device. An image recording apparatus, wherein the amount of water vapor is controlled according to the thickness of the recording member and / or the amount of moisture absorption. 2. The image recording apparatus according to claim 1, wherein water vapor in the heat fixing device is used as water vapor to be applied to the recording member.