JPH0638177B2 - Image recorder - Google Patents

Description

The present invention relates to an image recording apparatus such as electrophotography and electrostatic recording, and particularly to a recording member such as paper having a so-called toner image formed of resin, carbon, pigment, dye, etc. The present invention relates to an image recording apparatus including a heat fixing device that applies heat to a sheet) to fix the toner image on the sheet.

The conventional heating and fixing device used in this type of image recording apparatus 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,
If 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 a toner image is 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-mentioned 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 to At 6.5%, an attempt has been made to keep the waist strength of the seat appropriate at that time. However, this approach is limited in 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 sheet 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 quantity 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, and the toner image is scraped off by the conveying roller or the like when the second 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 surely reduce the curl of a sheet caused by passing through a heating and fixing device. In particular, in double-sided printing in which images are formed on both sides of a sheet, the present invention improves the transportability of the sheet to reduce the occurrence of jams and makes the sheet specially separated 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 provides a heat fixing device for applying heat to fix a toner image on a recording member, a water vapor collecting means for locally collecting water vapor in the heat fixing device, and An image recording apparatus comprising: a water vapor applying unit provided near the recording member discharge side of the heat fixing device so as to apply the collected water vapor to 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 the cassette feeding roller 12
After being sent from the cassette 13, the registration roller 14 sends the image 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 charging device 8, the toner image is separated from the photoconductor 5 by the separating corona charging device 10, and the conveying belt 15
Is conveyed to the fixing device 16. The surface of the photoconductor 5 is cleaned by 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 and 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 thereafter, as in the case of single-sided printing, separation, conveyance,
After being fixed, the discharge roller 22 is used to attach the tray 23 to the outside of the machine.
Dispatched on.

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

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 heat fixing device 16 is composed of a pair of a fixing roller 162 and a pressure roller 163 which is in pressure contact with the fixing roller 162. The fixing roller 162 is Sus
・ FLC (trade name: Nitto Kogyo) with non-adhesive heat-resistant resin such as ethylene tetrafluoride on the surface of Al or iron, silicon rubber such as HTV or RTV, or fluorine latex coated on the surface of silicon rubber The non-adhesive heat-resistant elastic layer is covered with a heating source such as a halogen heater 169. The pressure roller 163 is Sus.
The core metal such as iron is coated with a non-adhesive heat resistant elastic body such as HTV, LTV, FLC. In this example, the heating means is provided in the fixing roller, not the pressure roller. Therefore, the surface temperature of the fixing roller side is higher than that of the pressure roller.

The surface temperature of the fixing roller 162 is detected by a temperature sensor such as the thermistor 164, and a known control circuit (not shown).
Is controlled to a constant temperature. The toner offset on the fixing roller is cleaned by a silicone oil-impregnated cleaning web 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. 1 in the figure
Numeral 65 is a winding prevention claw of the sheet 9 which is urged by a spring (not shown) so that its tip comes into contact with the surface of the fixing roller, and 166 is urged by a spring (not shown) so that its tip comes into contact with the surface of the pressure roller. The sheet 9 has a winding preventing claw 167 and a fixing device 16
It is a water vapor flow path formed near the sheet discharge side from the bottom of the sheet, preferably toward the outside of the discharge roller 22. The water vapor flow path 167 serves as a water vapor applying means, and is formed by inclining the side wall of the discharge side portion of the bottom plate of the fixing device toward the discharge side.

The sheet 9 to which the toner image is transferred from the photosensitive drum 5 is conveyed to the heating and fixing device 16, and when passing between the fixing roller 162 and the pressure roller 163, heat is supplied from the fixing device 162 to the toner on the sheet 9. Melts and sticks onto the sheet. At this time, part of the water content is evaporated from the sheet 9 by the heat supply, and the inside of the fixing device 16 is in a state of containing more water vapor than in the general air.

At this time, in the fixing device 16, the vicinity of the separation claw 165 is in a state where the water vapor is richest. The water vapor existing in this portion is collected at the bottom of the fixing device by the cross flow fan 180 and flows in the direction of arrow a through the water vapor flow path 167.

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 sheet 9 immediately after exiting the discharge roller 17
When the lower surface is exposed to the water vapor that has passed through 67, the curl is corrected, and when it is sent to the intermediate tray 20, the curl becomes substantially flat, and the stackability on the intermediate tray 20 and the photosensitive drum 5 after the transfer of the second surface are performed. Both are separated in good condition.

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

It will be described in detail with reference to FIGS. 3 and 4 that the curl is corrected by exposing the sheet 9 to water vapor. The leading edge of the sheet 9 that has entered between the fixing roller 162 and the pressure roller 163 is fixed on the fixing roller 16 by the adhesive force of the melted toner.
It wraps around 2, but is peeled off by the wrapping prevention claw 165. Therefore, the tip of the sheet 9 receives the above-mentioned force and is
Curl downward as shown in FIG.

On the other hand, as shown in FIG. 3B, the rear end of the sheet 9 is supported by only 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 down and curls downward. Thus, when the sheet 9 leaves the fixing device 16, the sheet 9
A downward curl 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. Since this bending action occurs when the sheet 9 is warm immediately after leaving the fixing device 16, the curl of the sheet 9 is greatly affected and the downward curl becomes larger.

Therefore, according to the present invention, the sheet is supplied with the water, as shown in FIG.
By utilizing the phenomenon that the sheet is stretched, the curl of the sheet is corrected by an extremely simple means of applying steam to the sheet surface contracted by the curl as described above.
Then, the water vapor existing in the fixing device 16 is collected by the cross flow fan 180 or the like and is blown to the sheet 9 through the water vapor passage 167, so that the curl correcting effect can be obtained without the need for a special water vapor generating means. Is more effective.

FIG. 5 is a partial front view showing a modified example of the fixing device 16 applied to the image recording apparatus of the present invention. In this example, the fixing device 16
The crossflow fans 170 and 171 are arranged above and below so as to sandwich the sheet discharged from the sheet, and the crossflow fans 170 and 171 are rotated in the direction of the arrow to create an air flow in the direction of the arrow a.

In this case, the cross flow fan 170 sucks in the water vapor collected at the bottom of the fixing device, blows the water vapor onto the lower surface of the sheet 9 immediately after being discharged from the fixing device 16, and the other cross flow fan 171 fixes the water vapor in the vicinity of the separation claw. Sheet 9 immediately after being conveyed to the bottom of the container and discharged from the fixing device
It plays a role of returning the water vapor generated from the sheet and the water vapor blown out from the cross-flow fan 170 when the paper is not passed into the fixing device again.

As described above, by more actively collecting the water vapor in the fixing device and spraying it onto the sheet 9, the curl correcting effect of the sheet 9 becomes more remarkable, and the curl can be corrected within a short time. As a result, it is effective as a heat fixing device for a high-speed image recording device.

The heat fixing device is not limited to the heat roll fixing device in the illustrated example, but may be chamber fixing, induction heating fixing, flash fixing,
Various heat application type fixing devices such as a heating plate can be applied.
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.

In FIG. 2, reference numerals 172 and 173 denote partition plates for restricting the flow direction of the cross flow fan, and the air resistance generated by the partition plates controls the fan wind on the suction side and the discharge side. it can. In FIG. 5, 174 and 175
Is a shield plate that covers the upper portion of the fixing roller 162 so that the heated air flow near the fixing roller 162 is efficiently directed downward and is not wasted to the cleaning web 161 side.

As described above in detail, according to the present invention, a water vapor collecting means for locally collecting water vapor in the heat fixing device is provided, and the flow path for supplying the collected water vapor to the sheet is provided on the sheet discharging side of the heat fixing device. Since it is provided in the vicinity, the following various effects can be obtained.

(1) The curl of the sheet after being discharged from the heating and fixing device can be reliably reduced with a simple configuration.

(2) By reducing the curl, 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 for a sheet left in a high humidity environment. is there.

(4) Since the sheet is subjected to the temperature at which steam is blocked, an extreme increase in the surface resistance of the sheet can be prevented even after the first heat fixing, so that the transferability and the separability are improved.
Good image recording can be obtained the second time. 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 heat fixing apparatus applied to the apparatus, and FIGS. Explanatory drawing, FIG. 5 is a partial cross-sectional view showing a modified example of the heat fixing device. Reference numeral 9 is a recording member (sheet), 16 is a heat fixing device, and 167.
Is a steam flow path, and 170 and 171 are cross flow fans.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 54-74444 (JP, A) JP-A 49-2544 (JP, A) JP-A 59-24862 (JP, A) JP-A 50- 143531 (JP, A) JP-A-50-147725 (JP, A) Actually developed 54-62738 (JP, U) JP-B 42-8198 (JP, B1)

Claims (3)

[Claims] 1. A heat fixing device for applying heat to fix a toner image on a recording member, a water vapor collecting means for locally collecting water vapor in the heat fixing device, and the collected water vapor for the recording member. An image recording apparatus comprising: a water vapor applying unit provided near the recording member discharge side of the heating and fixing apparatus so as to provide the heat fixing apparatus. 2. The image recording apparatus according to claim 1, wherein the water vapor applying means is a flow path. 3. The image recording apparatus according to claim 2, wherein the water vapor applying means has a fan in the flow passage.