FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a fixing device for fixing a toner image on a sheet and an image forming apparatus equipped with the same.

In general, an image forming apparatus is known to be equipped with a fixing device that transfers a toner image onto a sheet and fixes the toner image onto the sheet by applying heat and pressure to the transferred toner image. The image forming apparatus is equipped with a first feeding roller pair downstream of the fixing device to eject the sheet on which the toner image has been fixed.

In the fixing device, the sheet before it is fixed contains some moisture, and when it is heated during the fixing of the toner image, water vapor is released from the sheet. When this water vapor stays between the fixing device and the first feeding roller pair and condenses on the surface of the feeding guide, the sheet being fed absorbs the condensed water and may cause a jam or image defects.

In the image forming apparatus described in Japanese Laid Open Patent Application No. 2011-90170, the first feeding roller pair comprises a roller pair forming two nip portions in the sheet widthwise direction perpendicular to the sheet feeding direction. In other words, in the sheet widthwise direction, the sheet has a region that contacts these two roller pairs and a region that does not contact the two roller pairs. Specifically, in the widthwise direction of the sheet, the center of the sheet does not contact the two roller pairs of the first feeding roller pair. With this configuration, the air containing water vapor generated when the sheet is fixed by the fixing device is exhausted through the first feeding roller pair and the sheet feeding passage.

However, in the image forming apparatus described in Japanese Laid-Open Patent Application No. 2011-90170, when the sheet that has passed through the fixing device is nipped by the first feeding roller pair, unevenness in the gloss of the fixed image may occur. This is because the first feeding roller pair has two areas in the sheet widthwise direction, one that contacts the sheet and one that does not, so the sheet is quenched by the contact. In recent years, there has been a need to reduce image defects and uneven gloss caused by condensation, and to provide high quality results.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide a fixing device and an image forming apparatus equipped with the same, which can provide high quality results.

One embodiment of the present invention is a fixing device comprising: a fixing portion configured to heat a toner image formed on a first side of a sheet and to fix the toner image on the sheet; a first rotatable member pair provided on a downstream side of said fixing device with respect to a sheet feeding direction and configured to feed the sheet; a second rotatable member pair provided adjacent to the downstream of said first rotatable member pair with respect to the sheet feeding direction and configured to feed the sheet; a guide portion configured to contact with a second side of the sheet opposite to the first side of the sheet fed by said first rotatable member pair and guide toward said second rotatable member pair, said guide portion forming a part of a feeding passage between said first rotatable member pair and said second rotatable member pair with respect to the sheet feeding direction; a blowing portion configured to blow air toward said feeding passage; a first duct configured to guide the air from said blowing portion and communicate with said feeding passage at a first position on the downstream side of said first rotatable member pair and on an upstream side of said second rotatable member pair with respect to the sheet feeding direction; and a second duct configured to guide the air from said blowing portion and communicate with said feeding passage at a second position on the upstream side of the first position and on the downstream side of said first rotatable member pair with respect to the sheet feeding direction; wherein said first rotatable member pair and said second rotatable member pair are contactable to the sheet over an entire width of the sheet passing through said feeding passage with respect to a widthwise direction of the sheet perpendicular to the sheet feeding direction; and wherein the air from said blowing portion passes through said first duct, is sent to said feeding passage from the first position, is sent to the second side of the sheet passing through the feeding passage, and then, the air from said blowing portion passes through said second duct from said feeding passage via the second position and is exhausted.

Another embodiment of the present invention is fixing device comprising: a fixing portion provided with a fixing rotatable member pair configured to heat a toner image formed on a first side of a sheet and to fix the toner image on the sheet; a feeding rotatable member pair provided adjacent to a downstream of said fixing rotatable member pair with respect to a sheet feeding direction and configured to feed the sheet; a guide portion configured to contact with a second side of the sheet opposite to the first side of the sheet fed by said fixing rotatable member pair and guide toward said feeding rotatable member pair, said guide portion forming a part of a feeding passage between said fixing rotatable member pair and said feeding rotatable member pair with respect to the sheet feeding direction; a blowing portion configured to blow air toward said feeding passage; a first duct configured to guide the air from said blowing portion and communicate with said feeding passage at a first position on the downstream side of said fixing rotatable member pair and on an upstream side of said feeding rotatable member pair with respect to the sheet feeding direction; and a second duct configured to guide the air from said blowing portion and communicate with said feeding passage at a second position on the upstream side of the first position and on the downstream side of said fixing rotatable member pair with respect to the sheet feeding direction; wherein said fixing rotatable member pair and said feeding rotatable member pair are contactable to the sheet over an entire width of the sheet passing through said feeding passage with respect to a widthwise direction of the sheet perpendicular to the sheet feeding direction; and wherein the air from said blowing portion passes through said first duct, is sent to said feeding passage from the first position, is sent to the second side of the sheet passing through the feeding passage, and then, the air from said blowing portion passes through said second duct from said feeding passage via the second position and is exhausted.

Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).

