Abstract:
The backrest of a chair comprises an inner low rigidity flexible back-receiving portion and an outer high-rigidity side frame spaced from the back-receiving portion via a slit. The backrest is integrally molded by synthetic resin, thereby shortening manufacturing process and reducing its cost. Comfort of a sitting person is also attained.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to the backrest of a chair in which a back-receiving portion is integrally molded with a frame.  
           [0002]    In a conventional backrest of a chair, to the upper end of a metal back rod which extends from the lower portion of a seat upwards and rearwards, a back plate made of material different from that of the back rod is generally connected directly or indirectly via another material frame.  
           [0003]    However, in the prior art, the back rod is made of material different from those of the frame and the back plate. Therefore, they are connected by screws, and there are disadvantages that it is impossible to shorten manufacturing processes and to decrease cost.  
         SUMMARY OF THE INVENTION  
         [0004]    In view of the disadvantages in the prior art, it is an object of the present invention to provide the backrest of a chair in which a back plate is integrally molded with a frame which comprises at least part of a back rod, thereby shortening manufacturing processes, decreasing cost and providing comfort of a sitting person when one is reclined.  
           [0005]    According to the present invention, there is provided the backrest of a chair, the backrest being an upright plate made of synthetic resin and comprising a low-rigidity flexible back-receiving portion for receiving the back of a sitting person, a pair of back rods, and pair of outer high-rigidity side frames each of which is spaced from said back-receiving portion via a slit, the lower end of each of said frames being connected to each of the back rods.  
           [0006]    The backrest can be integrally formed from synthetic resin, thereby shortening manufacturing process and decreasing cost. The slits between the back-receiving portion and side frames provide sufficient flexibility and a comfortable chair. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The features and advantages of the present invention will become more apparent from the following description with respect to embodiments as shown in appended drawings wherein:  
         [0008]    [0008]FIG. 1 is a side elevational view of a chair which includes one embodiment of the backrest according to the present invention;  
         [0009]    [0009]FIG. 2 is a rear elevational view of the same;  
         [0010]    [0010]FIG. 3 is a front perspective view of a back plate;  
         [0011]    [0011]FIG. 4 is a left-half rear elevational view of the back plate;  
         [0012]    [0012]FIG. 5 is a side elevational view of the back plate;  
         [0013]    [0013]FIG. 6 is an exploded perspective view of a back rod and a cover;  
         [0014]    [0014]FIG. 7 is an exploded sectional plan view taken along the line VII-VII in FIG. 4;  
         [0015]    [0015]FIG. 8 is an exploded sectional plan view taken along the line VIII-VIII in FIG. 4; and  
         [0016]    [0016]FIG. 9 is a side elevational view of a variation of a flexible connector. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0017]    As shown in FIG. 1, a caster  2  is secured at the end of a leg  1  which radially extends from the center. A support  3  is provided on the center of the leg  1 , and is fixed to a base  4  at the upper end. A backrest  5  is supported by a pair of L-shaped back rods  6  which is pivoted on a base  4  by a horizontal shaft  7 . The backrest  5  and back rods  6  can be inclined at a desired angle from a standing position in FIG. 1 rearwards by a spring-reclining mechanism (not shown) in the base  4 .  
         [0018]    Over the base  4 , a seat  8  is supported via a seat support  9  to move down rearwards with inclination of the backrest  5  and the back rod  6 . At each side of the seat support  9 , an armrest  10  is mounted via a support rod  9   a.    
         [0019]    As shown in FIG. 2, the backrest  5  is integrally molded from synthetic resin and has a rectangular shape near which vertical slits  11 , 11   a  are formed. Outside the slits  11 , 11   a , a high-rigidity outer frame  12  is provided, and inside the slits  11 , 11   a , a low-rigidity flexible back-receiving portion  13  is provided. The upper slit  11  is closed at both the upper and lower ends, while the lower slit  11   a  is closed at the upper end and opened at the lower end.  
         [0020]    An upper portion  12   a  of the side frame  12  is formed like V-shape or an arc to increase thickness and rigidity. A lower portion  12   b  of the side frame is a flat front surface and a rear surface which has a plurality of vertical ribs  14  which form a projection  15 . In this embodiment, the number of the rib  14  is three, and the middle rib is the longest.  
         [0021]    Bosses  16  are provided on the rear surface of the lower portion  12   b , and a through-bore  17  is formed at the center of each of the bosses  16 .  
         [0022]    The back rod  6  is made of metal such as Al alloy, and has a concave portion  6   a . The concave portion  6   a  is engaged with a projection  15  of the lower portion  12   b  of the side frame  12 . The upper end of the back rod  6  is engaged with a stepped portion  12   c  between the upper and lower portions  12   a  and  12   b . As shown in FIG. 7, a screw  18  through a bore  17  is engaged in a bore  20  of a boss  19  at a position corresponding to the boss  16 , thereby fastening the lower portion  12   b  of the side frame  12  to the upper portion of the back rod  6 .  
         [0023]    A low-stepped portion  21  is formed at the rear surface of the upper portion of the back rod  6 . An elastic cover  22  made of synthetic resin or rubber is engaged with the low-stepped portion  21 . The elastic cover  22  has the same shape as the upper portion  12   a  of the side frame  12  and substantially the same depth as that of the low-stepped portion  21 . An engagement projection  24  which projects from the front surface of the cover  22  and having an elastically-deformable expanded-diameter portion  23  is engaged in a bore  25  of the back rod  6 , so that the cover  22  is connected to the back rod  6 .  
         [0024]    By connection of the cover  22  to the back rod  6 , the rear end of the bore  20  of the back rod  6  is covered to improve appearance.  
         [0025]    The metal back rod  6  is protected, thereby preventing the back rod  6  from being damaged by a desk, a cabinet etc. The side frame  12  of the backrest  5  forms part or extension of the back rod  6 , thereby acting as frame for supporting the sides of the backrest  5  strongly.  
         [0026]    As shown in FIG. 2, the side frame  12  of the backrest  5 , the back rod  6  and the cover  22  are integrally formed to provide S-shaped good appearance.  
         [0027]    Thickness of the back-receiving portion  13  of the backrest  5  is smaller than that of the side frame  12 , thereby providing flexibility to the back-receiving portion  13 . The intermediate part of the back-receiving portion  13  is cut away to remain three flexible connectors  26  which form a bending portion  27 .  
         [0028]    By the bending portion  27 , the back-receiving portion  13  is divided into upper and lower portions  13   a  and  13   b . Thus, when a sitting person reclines against the back-receiving portion  13  strongly, especially in condition that the backrest  5  is inclined rearwards, the bending portion  27  moves rearwards of the other parts, and the upper and lower portions  13   a  and  13   b  are bent in V-shape. Therefore, even if the backrest  5  is inclined rearwards, the head of the person in a substantially upright position without making the head inclined rearwards, thereby providing comfortable posture to keep his eye to direct forwards.  
         [0029]    Each of the flexible connectors  26  is projected forwards, so that the upper and lower portions  13   a  and  13   b  are easily bendable with respect to a crest of the flexible connector  26 . If the connector  26  is projected rearwards, vertical tensile strength acts at the crest of the connector  26  to make the upper and lower portions difficult in bending. However, in this embodiment, the upper and lower portions  13   a ,  13   b  are likely to open.  
         [0030]    In the upper and lower portions  13   a , 13   b  of the back-receiving portion  13 , a number of hexagonal openings  28  are formed to increase flexibility of the upper and lower portions  13   a , 13   b . Thinner portions may be formed instead of the openings.  
         [0031]    A bending portion  29  projects rearwards at the upper end of the backrest  5  and increases rigidity of the upper end to act as an upper frame. The bending portion  29  holds the upper end of a cushion  30  and acts as a handle when the chair is moved.  
         [0032]    The lower end of the lower portion  13   b  of the back-receiving portion  13  is spaced from the frame  12  by slits  11 , and is connected to the rear end of the seat  8 .  
         [0033]    The cushion  30  covers the whole front surface of the backrest  5 , and the bending portion  29  of the backrest  5  is covered with a winding portion  30   a  of the cushion  30 .  
         [0034]    The connector  26  may be formed like a wave as shown in FIG. 9. One connector  26  may be provided in the middle, and two connectors may be provided on both sides of the middle connector. More than three connectors may be provided at suitable distances.  
         [0035]    The foregoing merely relates to embodiments of the present invention. Various modifications and variations may be made by person skilled in the art without departing from the scope of claims wherein: