JPH077229B2 - Image recorder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image recording apparatus such as electrophotography and electrostatic recording, and a recording member such as paper on the surface of which a so-called toner image composed of resin, carbon, pigment, dye, etc. is formed. 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.

Conventionally, the heat 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. If a sufficient amount of heat is applied to both the front and back of the sheet,
The shape of the curl is determined by the state of the sheet immediately after being discharged from the heat fixing device, because the sheet loses its rigidity as the moisture of the sheet 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 carrying out automatic double-sided printing for transfer, inconvenience arises in sheet conveyance property and stacking control on the intermediate tray. After transferring the toner image 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 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 can regulate the curl amount only when the sheet is between the fixing roller and the conveying means after the sheet is discharged. There is a problem that the curl amount at the edge 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 surely reduce the curl of a sheet caused by passing through a heating and fixing device. Particularly, in double-sided printing in which images are formed on both sides of a sheet, the present invention improves the transportability of the sheet and reduces the occurrence of jams, and also makes the separation of the sheet from the image forming body after the second side printing good. It has a very good heat insulating effect that prevents heat radiation to the outside, and 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, and the above-mentioned recording immediately after discharging water vapor in the heat fixing device from the heat fixing device. An image recording apparatus comprising: a means for giving a member and a means for increasing the water vapor pressure of the heating and fixing device. Further, the image recording apparatus is characterized in that the above-mentioned configuration is provided with a heat insulating means for cutting off heat radiation from the heat fixing device to the outside.

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 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 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 non-adhesive heat-resistant resin such as ethylene tetrafluoride, HTV
Silicone rubber for TV etc. or non-adhesive heat resistant elastic layer such as FLC (trade name: Nitto Kogyo Co., Ltd.) coated with fluorine latex on the surface of silicone rubber is covered, and a heating source such as a halogen heater 169 is provided inside. Is. The pressure roller 163 has a structure in which the surface of a core metal such as Sus or iron is coated with a non-adhesive heat resistant elastic body such as HTV, LTV or 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 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. 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 at the bottom of the fixing device toward the discharge side.

The sheet 9 on which the toner image is transferred from the photosensitive drum 5 is conveyed to the heat fixing device 16, and is fixed to the fixing roller 162 and the pressure roller 1.
Heat is supplied from the fixing device 162 when passing between the sheet 63 and the toner, and the toner on the sheet 9 is melted and fixed on the sheet. At this time, receiving heat from the fixing roller 162 and the pressure roller 163, the water bottle 17 is provided on the inner surface of the fixing device 16.
Water vapor is generated from the water-containing substance 173 (for example, a urethane foam containing water, a porous body having a hydrophilic group, etc.) to which water is supplied from 5 through the passage 176, and the water vapor pressure in the fixing device is increased. Increase.

On the other hand, the sheet 9 generates water content by the heat received when passing through the fixing device. Then, this evaporated water and the water-containing material 173
The water vapor generated by the evaporated water from the above flows upward together with the flow of warm air in the fixing device 16, but the air flow is blocked at the upper part of the fixing device by an elastic body 168 such as maltoprene. Therefore, convection occurs in the fixing device.
As a result, the warm air and the steam in the fixing device 16 will pass through the steam flow path.
Flows through 167 as indicated by 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 stacking property on the intermediate tray 20 and the separation from the photosensitive drum 5 after the transfer of the second surface are in a good state.

The sheet guide member 179 disposed near the discharge side of the discharge roller 17 may be a mesh-shaped perforated plate or a comb-shaped guide rod. In addition, on the inner surface of the fixing device 16, there is an inclusion 173.
Since it is provided, it is desirable to use a heat-resistant resin for the metal of the top plate, bottom plate and side plates of the fixing device 16 plated with SUS or Ni.

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 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, when the trailing edge of the sheet 9 is no longer subjected to the binding force between the fixing roller 162 and the pressure roller 163 as shown in FIG. Droop and curl 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 a phenomenon in which the sheet is supplied with water and expands as shown in FIG. 4 (b), and by the extremely simple means of applying steam to the sheet surface curled as described above. The sheet curl is corrected.

FIG. 5 shows a heat fixing device 16 applied to the image recording apparatus of the present invention.
It is a partial front view which shows the modification. In this practical example, as means for increasing the water vapor pressure in the fixing device, water is sealed in a mold container 171 made of a heat-resistant and easily moldable resin such as melamine and styrene resin, and an opening 172 of the container 171 is filled with a porous material of tetrafluoroethylene. A resin material 173 that allows water vapor to pass through like a resinous film.
The fixing device is provided on the inner surface of the fixing device.
Then, the water vapor in the fixing device is sucked by the cross flow fan 170, and the water vapor is blown onto the lower surface of the sheet 9 discharged from the fixing device 16. Therefore, inside the fixing device, the fixing device becomes hot and the porous resin 17
Water vapor is generated only when 3 is sufficiently warmed, so the water is used effectively and lasts a long time, and the other parts are less likely to be oxidized. Further, by positively collecting the water vapor inside the fixing device and spraying it onto the sheet 9, the curl correction 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.

As described above in detail, according to the present invention, the water vapor pressure in the heat fixing device is increased, so that the amount of water taken from the sheet passing through the heat fixing device is small. Since the amount of water vapor in the heat fixing device is abundant, a large amount of water vapor can be given to the sheet immediately after the fixing device is discharged. By the double effect of, the curl of the seat can be drastically reduced. In addition, water vapor generating means (heat insulating means) is provided on the inner surface of the fixing device.
Since vaporization of the steam from the steam generating means removes the heat of vaporization, the heat radiation to the outside of the fixing device is extremely reduced, and the temperature rise in the vicinity of the fixing device can be effectively prevented. Furthermore, due to curl reduction,
It is possible to reduce the occurrence of jams due to the curl of the sheet during double-sided printing, and to obtain stable double-sided conveyance characteristics.

In the case where the sheet is separated from the photosensitive drum by electrostatic separation as in the illustrated embodiment, reduction in separability due to curling is prevented, and it is particularly effective for a sheet left in a high humidity environment.

Since water vapor, that is, humidity, is applied to the sheet, the extreme increase in the surface resistance of the sheet is prevented even after the first heat fixing, so that the transferability and the separability are improved, and the good image recording is performed the second time. As a result, the present invention not only prevents curling but also obtains good results in the humidity control effect of the sheet.

[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 water vapor flow path.

 ─────────────────────────────────────────────────── ─── 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 (2)

[Claims] 1. A heat fixing device for applying heat to fix a toner image on a recording member; a means for applying water vapor in the heat fixing device to the recording member immediately after being discharged from the heat fixing device; An image recording apparatus comprising: a means for increasing a water vapor pressure of a fixing device. 2. A heat fixing device for applying heat to fix a toner image on a recording member; a means for applying water vapor in the heat fixing device to the recording member immediately after being discharged from the heat fixing device; An image recording apparatus comprising: a means for increasing the water vapor pressure of the fixing device; and a heat insulating means provided on the heating and fixing device to block heat radiation to the outside.