Chair backrest

Abstract

A chair backrest in which a frame-like back frame is covered with a bag-like upholstering material having an open lower end in a state of tension, the back frame being formed by connecting a pair of left and right side portion frames, which extend in an up and down direction, together at upper ends and lower ends thereof by an upper frame and a lower frame which extend in the left and right direction, wherein intermediate portions in the left and right direction of the upper frame and the lower frame are connected to each other by an intermediate frame which is situated behind the both side portion frames and is extended in the up and down direction, thereby causing an intermediate portion of a rear surface portion of the upholstering material to project rearward. According to such a backrest, when a person sitting on the chair leans against the backrest, the reaction force of the upholstering material does not vary to an extreme extent during the leaning action, and a rearward recess amount of the upholstering material of the backrest in response to a load can be sufficiently secured, thereby obtaining a comfortable sitting sensation.

1 . A chair backrest in which a frame-like back frame is covered with a bag-like upholstering material having an open lower end in a state of tension, the back frame being formed by connecting a pair of left and right side portion frames, which extend in an up and down direction, together at upper ends and lower ends thereof by an upper frame and a lower frame which extend in the left and right direction,
 wherein intermediate portions in the left and right direction of the upper frame and the lower frame are connected to each other by an intermediate frame which is situated behind the both side portion frames and is extended in the up and down direction, thereby causing an intermediate portion of a rear surface portion of the upholstering material to project rearward.   
     
     
         2 . The chair backrest according to  claim 1 ,
 wherein the upper and lower frames have a curved shape in which the intermediate portions are situated behind the both side portion frames in a plan view.   
     
     
         3 . The chair backrest according to  claim 1 ,
 wherein the lower portions of both side portion frames and the intermediate frame have an arced curved shape in which a curvature center is situated in the front when viewed from the side.   
     
     
         4 . The chair backrest according to  claim 1 ,
 wherein rearward displacement amounts of the intermediate frame relative to both side portion frames are in parts different from each other in the up and down direction.   
     
     
         5 . The chair backrest according to  claim 3 ,
 wherein rearward displacement amounts of the intermediate frame relative to both side portion frames are in parts different from each other in the up and down direction.   
     
     
         6 . The chair backrest according to  claim 1 ,
 wherein the intermediate frame is formed by an elastic material, such that the intermediate frame can be elastically deformed forward when a load is applied to a front surface portion of the upholstering material.   
     
     
         7 . The chair backrest according to  claim 3 ,
 wherein the intermediate frame is formed by an elastic material, such that the intermediate frame can be elastically deformed forward when a load is applied to a front surface portion of the upholstering material.   
     
     
         8 . The chair backrest according to  claim 4 ,
 wherein the intermediate frame is formed by an elastic material, such that the intermediate frame can be elastically deformed forward when a load is applied to a front surface portion of the upholstering material.   
     
     
         9 . The chair backrest according to  claim 1 ,
 wherein, in the upper ends of both side portion frames in the back frame, upward-facing extension frames, which are curved such that intermediate portions are situated ahead of the upper and lower portions when viewed from the side surface, are consecutively provided, and upper ends of both extension frames are connected to each other by a top portion frame which extends in the left and right direction, whereby a headrest frame is formed by the extension frames and the top portion frame.   
     
     
         10 . The chair backrest according to  claim 3 ,
 wherein, in the upper ends of both side portion frames in the back frame, upward-facing extension frames, which are curved such that intermediate portions are situated ahead of the upper and lower portions when viewed from the side surface, are consecutively provided, and upper ends of both extension frames are connected to each other by a top portion frame which extends in the left and right direction, whereby a headrest frame is formed by the extension frames and the top portion frame.   
     
     
         11 . The chair backrest according to  claim 4 ,
 wherein, in the upper ends of both side portion frames in the back frame, upward-facing extension frames, which are curved such that intermediate portions are situated ahead of the upper and lower portions when viewed from the side surface, are consecutively provided, and upper ends of both extension frames are connected to each other by a top portion frame which extends in the left and right direction, whereby a headrest frame is formed by the extension frames and the top portion frame.   
     
     
         12 . The chair backrest according to  claim 5 ,
 wherein, in the upper ends of both side portion frames in the back frame, upward-facing extension frames, which are curved such that intermediate portions are situated ahead of the upper and lower portions when viewed from the side surface, are consecutively provided, and upper ends of both extension frames are connected to each other by a top portion frame which extends in the left and right direction, whereby a headrest frame is formed by the extension frames and the top portion frame.