1. Field of the Invention
Example embodiments generally relate to a fixing device and an image forming apparatus, for example, for effectively applying pressure to a recording medium and releasing the pressure, and a method of manufacturing toner for the image forming apparatus.
2. Description of the Related Art
A related-art image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction printer having at least one of copying, printing, scanning, and facsimile functions, typically forms a toner image on a recording medium (e.g., a sheet) based on image data using electrophotography. Thus, for example, a charger charges a surface of an image carrier. An optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data. A development device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the image carrier. The toner image is then transferred from the image carrier onto a sheet. Finally, a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image on the sheet, thus forming the toner image on the sheet.
In one example of the fixing device, a fixing roller, inside which a heater is provided, pressingly contacts a pressing roller. A pressing lever presses the pressing roller toward the fixing roller to form a fixing nip between the pressing roller and the fixing roller. While a sheet bearing a toner image passes through the fixing nip, the fixing roller and the pressing roller apply heat and pressure to the sheet to fix the toner image on the sheet.
When the sheet is jammed, the fixing device may stop operation in a state in which the fixing roller and the pressing roller nip the sheet. Accordingly, a user may not remove the sheet easily due to pressure applied to the sheet at the fixing nip. To address this problem, a pressure release lever may be provided in the fixing device. The user manually operates the pressure release lever to release the pressure applied to the sheet.
Currently, there is market demand for a compact-size image forming apparatus capable of forming an image at high speed. To accommodate such demand, the fixing roller and the pressing roller have a small diameter and rotate at high speed, and need to apply a greater pressure to each other in order to provide a longer nip that is, a larger surface area of contact, capable of supplying the heat needed for adequately fixing the toner image on the sheet. Consequently, when the pressure release lever needs to be released, the user needs to apply a stronger force to do so.
To address this problem, another example of the fixing device includes an automatic pressure release device for automatically releasing pressure applied to the fixing nip using a cam. However, a driver, such as a motor, for activating the automatic pressure release device is needed, resulting in an increase in weight and manufacturing costs of the fixing device.
In yet another example of the fixing device, the pressure release lever moves with opening and closing of a cover on the fixing device, for example by being slidably contacted and moved by the cover. However, when the fixing roller and the pressing roller apply a strong pressure to each other, the pressure release lever may slide on the cover with a strong frictional force generated between the pressure release lever and the cover, resulting in wear of the pressure release lever and the cover.