Heater, fixing device, and image forming apparatus

Abstract

A heater includes a heat generating element and a protective layer. The protective layer covers the heat generating element, and at least part of a surface thereof has a convex surface that is convex toward the heat generating element.

What is claimed is: 
     
         1 . A heater comprising:
 a heat generating element; and   a protective layer configured to cover the heat generating element, at least part of a surface of the protective layer having a convex surface that is convex toward the heat generating element.   
     
     
         2 . The heater according to  claim 1 , wherein one of ends of the protective layer in a shorter-side direction of the heat generating element protrudes in a stacking direction of the heat generating element and the protective layer and has a curved top surface. 
     
     
         3 . The heater according to  claim 2 , wherein the other one of the ends of the protective layer in the shorter-side direction protrudes in the stacking direction and has a curved top surface. 
     
     
         4 . The heater according to  claim 3 , wherein a curvature of the one end and a curvature of the other end differ from each other. 
     
     
         5 . A fixing device comprising:
 an endless belt;   a heater; and   a pressure element placed at a position to face the heater via the endless belt and configured to form, together with the endless belt, a nip to interpose a sheet being conveyed,   the heater comprising:
 a heat generating element; and 
 a protective layer configured to cover the heat generating element and to be in contact with the endless belt, a surface of the protective layer that faces the pressure element having a concave surface that is concave with respect to the pressure element. 
   
     
     
         6 . The fixing device according to  claim 5 , wherein a curvature of the concave surface is smaller than a curvature of a surface of the pressure element. 
     
     
         7 . The fixing device according to  claim 5 , wherein an upstream end of the protective layer in a conveyance direction of the sheet protrudes in a stacking direction of the heat generating element and the protective layer and has a curved top surface. 
     
     
         8 . The fixing device according to  claim 7 , wherein a downstream end of the protective layer in the conveyance direction protrudes in the stacking direction and has a curved top surface. 
     
     
         9 . The fixing device according to  claim 8 , wherein a curvature of the curved surface of the upstream end is smaller than a curvature of the curved surface of the downstream end. 
     
     
         10 . An image forming apparatus comprising:
 an image forming unit configured to form a toner image on a sheet; and   a fixing device configured to heat the sheet and thereby fix the toner image onto the sheet, the fixing device comprising:
 an endless belt; 
 a heater; and 
 a pressure element placed at a position to face the heater via the endless belt and configured to form, together with the endless belt, a nip to interpose a sheet being conveyed, 
 the heater comprising:
 a heat generating element; and 
 a protective layer configured to cover the heat generating element and to be in contact with the endless belt, a surface of the protective layer that faces the pressure element having a concave surface that is concave with respect to the pressure element.