JPH06103416B2 - 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 development 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, and as a specific example, as disclosed in JP-A-57-81270, the water content of the sheet is 5.5 to 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 Patent Laid-Open No. 51-113637, attempts have been made to make the sheet conveying speed of the conveying means after discharging the fixing roller of the sheet higher than the feeding speed of the sheet 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. 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-mentioned, the water vapor applying means applies more water vapor to both end portions than the central portion in the width direction of the recording member.

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 water vapor in the fixing device 16 flow through the water vapor passage 167 as indicated by the arrow a.

On the other hand, the sheet 9 passing between the fixing roller 162 and the pressure roller 163 is discharged by the discharging roller 17 and guided in the direction of the arrow b by the branch claw 18 which 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,
When it is fed to the intermediate tray 20, it becomes substantially flat, and both the stackability on the intermediate tray 20 and the separability from the photosensitive drum 5 after the transfer of the second surface are good. Then, in the sheet guide member 179 arranged near the discharge side of the discharge roller 17, as shown in FIG.
By applying more water vapor to both side portions of the sheet 9 passing above the central portion than to the central portion, the curl of the sheet 9 can be corrected not only at the front and rear portions in the traveling direction of the sheet but also at both side portions.

Next, the curl is corrected by exposing the sheet 9 to water vapor, which will be described in detail with reference to FIGS. 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. 4B, 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.

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 the sheet is supplied with water and stretches as shown in FIG. 5 (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 elongation of the sheet 9 increases as the amount of steam supplied increases. Normally, the curl of the sheet 9 is shown in FIG.
It occurs not only in the sheet feeding direction shown in FIG. The curl generated on both sides bends downward on both sides in the same manner as shown in FIG. 4a. Such bending means that the fixing roller 162 and the pressure roller 163 are bent.
That the pressing force on the sheet 9 due to is larger on both sides than the central part of the roller, and that the heat transfer from the sheet 9 is larger on both sides than the central part of the sheet due to this difference in pressing force. Seem. Therefore, as shown in FIG. 3, it is possible to correct curl on both sides of the sheet 9 by applying more steam to both sides than at the center.

FIG. 6 is a front view of a part showing a modified example of the fixing device 16 applied to the image recording apparatus of the present invention. In this embodiment, the steam in the fixing device is sucked by the cross flow fan 170 and the steam is blown to the lower surface of the sheet 9 immediately after being discharged from the fixing device 16, so that the curl correcting effect of the sheet 9 becomes more remarkable. Correct the curl in a short time. In this case, as shown in FIG. 7, the diameter of the cross flow fan 170 driven by the motor 171 is set from the central portion 170a to both end portions 170b.
With a large size, a large amount of water vapor can be applied to both side portions of the sheet 9 and the curls of the both side portions can be corrected at the same time. As a result, it is effective as a heat fixing device for a high-speed image recording device.

The fixing device is not limited to the heat roll fixing device in the illustrated example, but a pressure fixing device including a chamber fixing device, an induction heating fixing device, a flash fixing device, various heat application type fixing devices such as a hot plate, and a steam generator. Etc. are applicable.
Also, as a method for printing a toner image on a sheet,
As shown in the illustrated example, a method of temporarily forming a toner image on another image forming body and then transferring it to a sheet, or a method of developing the electrostatic image directly on the sheet at the same time or immediately after that may be used.

As described above in detail, according to the present invention, since the water vapor is applied to the sheet immediately after being discharged from the fixing device so that both side portions are larger than the central portion, various effects as described below can be obtained. .

(1) Curling of the front and rear portions and both side portions of the sheet in the sheet feeding direction after being discharged from the fixing device can be reliably reduced with a simple configuration.

(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 is prevented, and it is particularly effective for a sheet left in a high humidity environment. is there.

(4) Since water vapor, that is, moisture, is applied to the sheet, an extreme increase in the surface resistance of the sheet can be prevented even after the first fixing, so that the transferability and the 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 as an image recording apparatus of the present invention, FIG. 2 is an enlarged cross-sectional view of a fixing device applied to the apparatus, and FIG. 3 is a plan view of a sheet guide member. Figures 4 and 5 are illustrations of sheet curl correction, No. 6
FIG. 7 is a partial cross-sectional view showing a modified example of the fixing device, and FIG. 7 is a plan view of the cross flow fan. 9 is a recording member (sheet), and 16 is a fixing device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-59-24862 (JP, A) JP-A-60-182459 (JP, A) JP-A-60-182460 (JP, A) JP-A-60- 182461 (JP, A) JP 60-182463 (JP, A) JP 60-182465 (JP, A) JP 60-182467 (JP, A) JP 60-182469 (JP, A)

Claims (1)

[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 characterized in that a large amount of water vapor is applied to both end portions of the recording member in the width direction of the recording member, compared to the central portion.