Patent Publication Number: US-2016244353-A1

Title: Method for producing glass sheet with bent portion and glass sheet with bent portion

Description:
TECHNICAL FIELD 
     This invention relates to a method for producing a glass sheet with a bent portion and a glass sheet with a bent portion. 
     BACKGROUND ART 
     In recent years, mobile flat panel displays, such as smartphones and tablet personal computers (tablet PCs), are rapidly spreading. Generally, a glass sheet is used as a front surface layer of a mobile flat panel display. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP-A-2010-30859 
     SUMMARY OF INVENTION 
     Technical Problem 
     For purposes of esthetic improvement and the like of the mobile flat panel display, there is, for example, a demand to cover the front and side surfaces of the mobile flat panel display with a single glass sheet. In such a case, a glass sheet having at least one flattened portion and bent portions is necessary. 
     A conceivable method for producing a glass sheet with a bent portion is a method of press-forming a flat glass sheet as described in, for example, Patent Literature 1. However, press forming is performed by heating the entire flat glass sheet to its softening point or above and pressing the entire glass sheet using forming dies, so that the flattened portion of the resultant glass sheet may be likely to have low flatness and low smoothness. 
     A principal object of the present invention is to provide a method capable of producing a glass sheet with a bent portion in which a flattened portion has high flatness and high smoothness. 
     Solution to Problem 
     A method for producing a glass sheet with a bent portion according to the present invention is directed to a method for producing a glass sheet including a flattened portion and a bent portion continued to the flattened portion. In the method for producing a glass sheet with a bent portion according to the present invention, a flat glass sheet is radiationally heated with a first portion of the flat glass sheet held between first and second heat-insulating members. And then, a second portion of the flat glass sheet not held between the first and second heat-insulating members is bent. 
     In the method for producing a glass sheet with a bent portion according to the present invention, the flat glass sheet is preferably heated so that the first portion thereof has a temperature below the softening point of the flat glass sheet. 
     In the method for producing a glass sheet with a bent portion according to the present invention, the flat glass sheet is preferably heated so that the second portion of the flat glass sheet reaches a higher temperature than the first portion thereof. 
     In the method for producing a glass sheet with a bent portion according to the present invention, an entire region of the second portion is preferably heated. 
     In the method for producing a glass sheet with a bent portion according to the present invention, the flat glass sheet used is preferably a flat glass sheet having a linear coefficient of thermal expansion of 120×10 −7 /° C. or less at 30° C. to 380° C. 
     In the method for producing a glass sheet with a bent portion according to the present invention, it is preferred that the heat-insulating member include a through hole and the heating and bending be performed while a coolant is fed through the through hole. 
     In the method for producing a glass sheet with a bent portion according to the present invention, the heat-insulating members preferably have a lower thermal conductivity than the flat glass sheet. 
     In the method for producing a glass sheet with a bent portion according to the present invention, the heat-insulating members are preferably formed of ceramic material. 
     The second portion is preferably bent with the flat glass sheet pressed by the first and second heat-insulating members. 
     A glass sheet with a bent portion according to the present invention includes: a flattened portion substantially in the shape of a flat sheet; and a bent portion continued to an end region of the flattened portion in a transverse direction thereof. When viewed in cross section along a thickness direction of the glass sheet, no gap is created between an imaginary line tangent to a back surface of a middle region of the flattened portion in the transverse direction and the end region of the flattened portion in the transverse direction. 
     Front and back surfaces of the flattened portion are preferably unground surfaces. 
     A front surface of the end region of the flattened portion in the transverse direction is preferably flush with a front surface of the middle region of the flattened portion in the transverse direction. 
     The end region of the flattened portion in the transverse direction may be provided to extend along a direction inclined toward a bent-away side of the bent portion relative to a direction of extension of the middle region of the flattened portion in the transverse direction. 
     The back surface of the flattened portion may be formed of a curved surface having a radius of curvature of 1000 mm or more. 
     The glass sheet with a bent portion according to the present invention may further includes a flange continued to an opposite end of the bent portion to the flattened portion and having a shape of a substantially flat sheet. In this case, the angle formed between a direction of extension of a back surface of the flange and a direction of extension of a back surface of the end region of the flattened portion in the transverse direction may be larger than 90°. 
     Advantageous Effects of Invention 
     The present invention can provide a method capable of producing a glass sheet with a bent portion in which a flattened portion has high flatness and high smoothness. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic perspective view of a glass sheet with a bent portion, which has been produced in an embodiment of the present invention. 
         FIG. 2  is a schematic cross-sectional view for illustrating a production step for the glass sheet with the bent portion in the above embodiment of the present invention. 
         FIG. 3  is a schematic cross-sectional view for illustrating another production step for the glass sheet with the bent portion in the above embodiment of the present invention. 
         FIG. 4  is a schematic cross-sectional view for illustrating a production step for a glass sheet with a bent portion in a reference example. 
         FIG. 5  is a schematic cross-sectional view of a glass sheet with a bent portion, which will be produced in the reference example. 
         FIG. 6  is a schematic cross-sectional view of part of the glass sheet with the bent portion, which has been produced in the above embodiment of the present invention. 
         FIG. 7  is a schematic cross-sectional view of a glass sheet with a bent portion according to a first modification. 
         FIG. 8  is a schematic cross-sectional view of a glass sheet with a bent portion according to a second modification. 
         FIG. 9  is a schematic cross-sectional view of a glass sheet with a bent portion according to a third modification. 
         FIG. 10  is a schematic cross-sectional view for illustrating a production step for a glass sheet with a bent portion in a fourth modification. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a description will be given of an exemplary preferred embodiment for working of the present invention. However, the following embodiment is merely illustrative. The present invention is not at all limited to the following embodiment. 
     Throughout the drawings to which the embodiment and the like refer, elements having substantially the same functions will be referred to by the same reference signs. The drawings to which the embodiment and the like refer are schematically illustrated. The dimensional ratios and the like of objects illustrated in the drawings may be different from those of the actual objects. Different drawings may have different dimensional ratios and the like of the objects. Dimensional ratios and the like of specific objects should be determined in consideration of the following descriptions. 
     This embodiment relates to a method for producing a glass sheet  1  shown in  FIG. 1 . The glass sheet  1  includes first to third flattened portions  11  to  13  and first and second bent portions  14 ,  15 . One edge of the first flattened portion  11  in the transverse direction thereof and the second flattened portion  12  are connected by the first bent portion  14 . The other edge of the first flattened portion  11  in the transverse direction thereof and the third flattened portion  13  are connected by the second bent portion  15 . The first and second bent portions  14 ,  15  may have a cross-sectional shape of, for example, an arc or an elliptic arc. The thickness of the first and second bent portions  14 ,  15  is preferably substantially equal to that of the first to third flattened portions  11  to  13 . 
     No particular limitation is placed on the usage of the glass sheet  1 . For example, the glass sheet  1  can be used as a housing of a mobile flat panel display, such as a smartphone or a tablet personal computer (tablet PC). In using the glass sheet  1  like this, the thickness of the glass sheet  1  can be, for example, about 0.2 mm to about 2 mm and preferably about 0.3 mm to about 1.8 mm. 
     Furthermore, if the glass sheet  1  is a mobile display glass cover for use in a mobile display, the surface roughness (Ra) of the outside surfaces of the bent portions  14 ,  15  and flattened portions  12 ,  13  located laterally of the mobile display body is preferably at least partly larger than the surface roughness (Ra) of the outside surface of the first flattened portion  11  located at the top of the display. In this case, the mobile display can be improved in graspability. From the viewpoint of further improving the graspability of the mobile display, the surface roughness (Ra) of at least part of the outside surfaces of the bent portions  14 ,  15  and the flattened portions  12 ,  13  is preferably equal to or more than 100 times the surface roughness (Ra) of the outside surface of the first flattened portion  11  and more preferably equal to or more than 200 times that surface roughness. Specifically, the surface roughness (Ra) of at least part of the outside surfaces of the bent portions  14 ,  15  and the flattened portions  12 ,  13  is preferably 0.5 μm or more and more preferably 0.8 μm or more. On the other hand, the surface roughness (Ra) of the first flattened portion  11  is preferably 0.01 μm or less and more preferably 0.008 μm or less. The surface roughness (Ra) used herein refers to the arithmetic mean roughness (Ra) defined in JIS B0601-2001. 
     Alternatively, the graspability of the mobile display may be improved by providing irregularities on at least part of the outside surfaces of the bent portions  14 ,  15  and the flattened portions  12 ,  13 . In this case, the distance between the top and foot of the irregularities in the normal direction of the flattened portions  12 ,  13  is preferably 50 μm or more and more preferably 70 μm or more. The distance between the top and foot of the irregularities is preferably not more than ½ of the average thickness of the flattened portions  12 ,  13 . Thus, the flattened portions  12 ,  13  can be improved in graspability while being prevented from decreasing in rigidity. 
     No particular limitation is placed on the shape of the irregularities. The irregularities may be linear or may be formed in the shape of a pyramid, a cone, a truncated pyramid, a prism or a column. 
     Furthermore, if irregularities are provided on at least part of the outside surfaces of the bent portions  14 ,  15  and the flattened portions  12 ,  13 , it is not always necessary that the surface roughness (Ra) of at least part of the outside surfaces of the bent portions  14 ,  15  and the flattened portions  12 ,  13  is larger than the surface roughness (Ra) of the outside surface of the first flattened portion  11  located at the top of the display. 
     No particular limitation is placed on the composition of glass forming the glass sheet  1  and it can be appropriately selected depending upon the properties required for the glass sheet  1 . The glass sheet  1  can be formed of, for example, silicate glass or borosilicate glass. More specifically, a glass sheet  1  can be used which has a composition, in % by mass, of 50 to 80% SiO 2 , 5 to 25% Al 2 O 3 , 0 to 15% B 2 O 3 , 0 to 3.5% Li 2 O, 1 to 20% Na 2 O, 0 to 10% K 2 O, 5 to 25% Li 2 O+Na 2 O+K 2 O, 0 to 12% MgO, 0 to 10% CaO, 0 to 5% SrO, 0 to 5% BaO, 0 to 6% ZnO, 0 to 10% ZrO 2 , 0 to 10% P 2 O 5 , and 0 to 3% As 2 O 3 +Sb 2 O 3 +SnO 2 +F+Cl+SO 3 . 
     Next, a description will be given of a method for producing the glass sheet  1  in this embodiment with reference mainly to  FIGS. 2 and 3 . 
     First, a flat glass sheet  20  shown in  FIG. 2  is prepared. The flat glass sheet  20  is a glass sheet for use in forming a glass sheet  1 . The thickness of the flat glass sheet  20  is substantially equal to the thickness of the glass sheet  1 . 
     In this embodiment, the flat glass sheet  20  is radiationally heated with a first portion  21  thereof held between first and second heat-insulating members  31 ,  32 . And then, second portions  22   a,    22   b  of the flat glass sheet  20  not held between the first and second heat-insulating members  31 ,  32  are bent by pressing them using pressing tools  51 ,  52 . Thus, a glass sheet  1  can be obtained which has bent portions  14 ,  15  formed at least partly of the second portions  22   a,    22   b,  respectively, and a first flattened portion  11  formed of the first portion  21 . 
     The method for producing the glass sheet  1  will be described in further detail below. First, a forming apparatus  30  for use in producing the glass sheet  1  is described. 
     The forming apparatus  30  includes a forming chamber  33 . The forming chamber  33  is internally provided with a heater  41 . The heater  41  radiates heat rays. Therefore, the forming apparatus  30  can radiationally heat an object placed in the forming chamber  33 . 
     The first and second heat-insulating members  31 ,  32  are disposed in the forming chamber  33 . The first and second heat-insulating members  31 ,  32  are members for reducing the transfer of radiation heat to the first portion  21  of the flat glass sheet  20 . In order to reduce the transfer of radiation heat to the first portion  21  of the flat glass sheet  20 , the first and second heat-insulating members  31 ,  32  preferably have a lower thermal conductivity than the flat glass sheet  20 . Furthermore, the first and second heat-insulating members  31 ,  32  preferably block heat rays emitted from the heater  41 . The first and second heat-insulating members  31 ,  32  can be formed of, for example, ceramic material containing as a major ingredient alumina, silicon carbide or diatomite. 
     Each of the heat-insulating members  31 ,  32  includes at least one through hole  31   a,    32   a.  A coolant, such as air, is fed through these through holes  31   a,    32   a  during heating and forming. Thus, the temperature of the heat-insulating members  31 ,  32  can be controlled. For example, an undesirable temperature rise of the heat-insulating members  31 ,  32  can be prevented. 
     In this embodiment, an example is described in which both the two heat-insulating members are provided with their respective through holes through which a coolant is to be fed. However, the present invention is not limited to this configuration. Only one of the two heat-insulating members may be provided with such a through hole or none of the two heat-insulating members may be provided with such a through hole. 
     In forming the flat glass sheet  20 , first, the flat glass sheet  20  is placed between the first heat-insulating member  31  and the second heat-insulating member  32  and the first portion  21  of the flat glass sheet  20  is held between the first and second heat-insulating members  31 ,  32 . Portions of the flat glass sheet  20  other than the first portion  21 , which are not held between the first and second heat-insulating members  31 ,  32 , form the second portions  22   a,    22   b.    
     With the first portion  21  of the flat glass sheet  20  held between the first and second heat-insulating members  31 ,  32 , the heater  41  is actuated to radiationally heat the flat glass sheet  20  (heating step). 
     And then, as shown in  FIG. 3 , the second portions  22   a,    22   b  are bent by pressing them using the pressing tools  51 ,  52  provided on both sides of the first and second heat-insulating members  31 ,  32  (forming step). Thus, the glass sheet  1  shown in  FIG. 1  can be obtained. 
     No particular limitation is placed on the type of the pressing tools  51 ,  52  so long as they can appropriately press the flat glass sheet  20 . Each pressing tool  51 ,  52  may be formed of, for example, a rod. 
     Alternatively, without use of the pressing tools  51 ,  52 , the second portions  22   a,    22   b  may be bent, for example, under their own weights. 
     As thus far described, in this embodiment, the flat glass sheet  20  is radiationally heated with the first portion  21  thereof held between the first and second heat-insulating members  31 ,  32 . Therefore, the temperature rise of the first portion  21  can be reduced. Thus, it can be easily implemented to increase the temperature of the second portions  22   a,    22   b  not held between the first and second heat-insulating members  31 ,  32  while reducing the temperature rise of the first portion  21 . In addition, even if the second portions  22   a,    22   b  reach a deformable temperature, the first portion  21  can be held at a low temperature so as not to change the surface condition. Hence, a glass sheet  1  can be produced in which the first flattened portion  11  has high flatness and high smoothness. Furthermore, since the first flattened portion  11  has high flatness and high smoothness, the front and back surfaces of the first flattened portion  11  can be unground surfaces. Thus, a glass sheet  1  having high mechanical strength can be produced. 
     From the viewpoint of reducing the strain of the flat glass sheet  20 , the flat glass sheet  20  is preferably heated so that the first portion  21  thereof reaches a temperature equal to or higher than the strain point of the flat glass sheet  20 . In addition, from the viewpoint of further increasing the flatness and smoothness of the first flattened portion  11 , the flat glass sheet  20  is preferably heated so that the first portion  21  has a temperature below the softening point of the flat glass sheet  20  and, more preferably, the flat glass sheet  20  is heated so that the first portion  21  has a temperature equal to or lower than the glass transition point of the flat glass sheet  20  plus 100° C. 
     Furthermore, from the viewpoint of facilitating the bending of the second portions  22   a,    22   b,  the flat glass sheet  20  is preferably heated so that the second portions  22   a,    22   b  reach a higher temperature than the first portion  21 . 
     Moreover, the entire regions of the second portions  22   a    22   b  are preferably heated. Thus, the second portions  22   a,    22   b  can be bent, using the pressing tools  51 ,  52 , at a relatively low temperature within a temperature range in which the flat glass sheet  20  can be deformed. Therefore, it can be prevented that indentations are produced on the second portions  22   a,    22   b  by the pressing tools  51 ,  52 . 
     Moreover, the time taken for the second portions  22   a,    22   b  to reach a deformable temperature is shorter than the time for the first portion  21  to reach a temperature equal to or higher than the strain point of the flat glass sheet  20 . Therefore, it is necessary to continue to heat the flat glass sheet  20  until the first portion  21  reaches a temperature equal to or higher than the strain point of the flat glass sheet  20 . 
     Furthermore, it is preferred that a coolant be fed through the through holes  31   a,    32   a  to reduce the temperature rise of the first and second heat-insulating members  31 ,  32 . This makes it easy to heat the flat glass sheet  20  to avoid that the temperature of the first portion  21  is above the softening point of the flat glass sheet  20 , and thus makes it easy to further increase the flatness and smoothness of the first flattened portion  11 . 
     When a temperature difference is produced between the first portion  21  and the second portions  22   a,    22   b  as in this embodiment, the first portion  21  becomes different in amount of thermal expansion from the second portions  22   a,    22   b.    
     Specifically, the amount of thermal expansion of the first portion  21  becomes lower than that of the second portions  22   a,    22   b.  Owing to this difference in amount of thermal expansion, the flat glass sheet  20  may cause distortion, such as warpage or waviness. Therefore, from the viewpoint of reducing the distortion of the flat glass sheet  20  to obtain a glass sheet  1  having a high shape accuracy, the flat glass sheet  20  preferably has a small coefficient of thermal expansion. Specifically, the linear coefficient of thermal expansion of the flat glass sheet  20  at 30° C. to 380° C. is preferably 120×10 −7 /° C. or less, more preferably 105×10 −7 /° C. or less, still more preferably 100×10 −7 /° C. or less, even more preferably 90×10 −7 /° C., particularly preferably 85×10 −7 /° C., and most preferably 80×10 −7 /° C. 
     For example, as shown in  FIG. 4 , it is conceivable that without use of the first heat-insulating member  31 , the flat glass sheet  20  placed on the second heat-insulating member  32  is bent using the pressing tools  51 ,  52 . In this case, however, the flat glass sheet  20  will not be given a shape fully conforming to the second heat-insulating member  32 , because of the rigidity of the flat glass sheet  20 . Specifically, as shown in  FIG. 5 , the flat glass sheet  20  will be given a shape in which the ends of the first flattened portion  111  next to the bent portions  114 ,  115  are raised from the second heat-insulating member  32 . If the flat glass sheet  20  is given a shape in which the ends of the first flattened portion  111  next to the bent portions  114 ,  115  are raised from the second heat-insulating member  32 , and when the resultant glass sheet  100  is used as a display and the ends of the first flattened portion  111  are located in the display region, the display quality of the display will be decreased. On the other hand, when the ends of the first flattened portion  111  are located outside the display region, the area ratio of the display region in the display will be decreased. 
     In contrast, in this embodiment, the second portions  22   a,    22   b  of the flat glass sheet  20  are bent with the first portion  21  thereof held between the first and second heat-insulating members  31 ,  32 . Therefore, the temperature rise of the first portion  21  is reduced. The first portion  21  is less likely to reach a deformable temperature. In addition, the deformation of the first portion  21  is restricted by the first and second heat-insulating members  31 ,  32 . Therefore, the first portion  21  can be held in a shape conforming to the second heat-insulating member  32 . Thus, as shown in  FIG. 6 , when viewed in cross section along the thickness direction, no gap is created between the imaginary line L tangent to the back surface of a middle region of the first flattened portion  11  in the transverse direction and end regions  11   a  of the first flattened portion  11  in the transverse direction. The back surface of the middle region of the first flattened portion  11  in the transverse direction is substantially flush with the back surfaces of the end regions  11   a.  Furthermore, the front surface of the middle region of the first flattened portion  11  in the transverse direction is substantially flush with the front surfaces of the end regions  11   a.  In addition, the first flattened portion  11  has high flatness and high smoothness and, therefore, the front and back surfaces of the first flattened portion  11  can be unground surfaces. Thus, a glass sheet  1  having high mechanical strength can be provided. Hence, in the case of using the glass sheet  1  as a display, a display can be obtained which has high mechanical strength and in which even if the end regions  11   a  of the first flattened portion  11  are located in the display region, the display quality is less likely to be decreased and superior and the area ratio of the display region is high. 
     From the viewpoint of more reliably avoiding the creation of a gap between the imaginary line L and the end regions  11   a  of the first flattened portion  11  in the transverse direction, the shape of the second heat-insulating member  32  is preferably made different from that in the above embodiment and, for example, as shown in  FIG. 7 , each end region  11   a  of the first flattened portion  11  in the transverse direction is preferably provided to extend along a direction inclined toward a bent-away side of the associated bent portion  14 ,  15  (along the direction y inclined downward in  FIG. 7 ) relative to the direction x of extension of the middle region of the first flattened portion  11  in the transverse direction. The angle formed between the directions x and y is preferably 178° to 180° and more preferably 179° to 180°. If the angle formed between the directions x and y is too large, this makes it less likely to achieve the effect of more reliably avoiding the creation of a gap between the imaginary line L and the end regions  11   a  of the first flattened portion  11  in the transverse direction. If the angle formed between the directions x and y is too small, the resultant glass sheet may be inadequate for use as a display. 
     Furthermore, from the viewpoint of more reliably avoiding the creation of a gap between the imaginary line L and the end regions  11   a  of the first flattened portion  11  in the transverse direction, the shape of the second heat-insulating member  32  is preferably made different from that in the above embodiment and, for example, as shown in  FIG. 8 , the back surface of the first flattened portion  11  is preferably formed of a gently curved surface raised opposite to the direction of extension of the second and third flattened portions  12 ,  13  and having a radius of curvature of not less than 1000 mm and more preferably not less than 5000 mm. However, if the radius of curvature of the back surface of the first flattened portion  11  is too large, this may make it less likely to achieve the effect of more reliably avoiding the creation of a gap between the imaginary line L and the end regions  11   a  of the first flattened portion  11  in the transverse direction. Therefore, the radius of curvature of the back surface of the first flattened portion  11  is preferably not more than 10000 mm and more preferably not more than 6000 mm. 
     In the present invention, a surface having a radius of curvature of not less than 800 mm is considered as a flat surface and a sheet portion whose principal surface has a radius of curvature of not less than 800 mm is considered as a flattened portion. 
     Moreover, from the viewpoint of more reliably avoiding the creation of a gap between the imaginary line L and the end regions  11   a  of the first flattened portion  11  in the transverse direction, the shape of the second heat-insulating member  32  is preferably made different from that in the above embodiment and, for example, as shown in  FIG. 9 , the angle θ formed between the direction of extension of each of the back surfaces of the flattened portions  12 ,  13  and the direction of extension of the back surface of the associated end region  11   a  of the first flattened portion  11  in the transverse direction (the angle formed between the tangent line Z of each of the back surfaces of the second and third flattened portion  12 ,  13  and the imaginary line L) is preferably larger than 90° and is more preferably 90.1° or more. However, if the angle formed between the direction of extension of each of the back surfaces of the flattened portions (flanges)  12 ,  13  and the direction of extension of the back surface of the associated end region  11   a  of the first flattened portion  11  in the transverse direction is too large, the resultant glass sheet may be inadequate for use as a display. Therefore, the angle formed between the direction of extension of each of the back surfaces of the flattened portions  12 ,  13  and the direction of extension of the back surface of the associated end region  11   a  of the first flattened portion  11  in the transverse direction is preferably not more than 95° and more preferably not more than 93°. 
     Furthermore, from the viewpoint of more reliably avoiding the creation of a gap between the imaginary line L and the end regions  11   a  of the first flattened portion  11  in the transverse direction, it is preferred that, as shown in  FIG. 10 , a pressing mechanism  60  be provided and the second portions  22   a,    22   b  be deformed with the flat glass sheet  20  pressed by the first and second heat-insulating members  31 ,  32 . 
     From the viewpoint of increasing the flatness and smoothness of the second and third flattened portions  12 ,  13 , the pressing tools  51 ,  52  are preferably made of a heat-insulating material, such as ceramic material. From the viewpoint of preventing breakage due to thermal shock, the pressing tools  51 ,  52  are preferably preheated to a temperature near the temperature of the flat glass sheet  20  prior to the pressing. 
     The shape of the bent portions  14 ,  15  is generally determined depending upon the shape of the corners of the second heat-insulating member  32 . Therefore, the shape of the bent portions  14 ,  15  can be easily changed by appropriately changing the shape of the corners of the second heat-insulating member  32 . 
     Although in the above embodiment an example has been described in which the first flattened portion  11  is provided on both sides with bent portions  14 ,  15 , the present invention is not limited to this configuration. The glass sheet produced by the present invention may have a single bent portion. 
     REFERENCE SIGNS LIST 
     
         
           1  . . . glass sheet 
           11  . . . first flattened portion 
           11   a  . . . end region of first flattened portion 
           12  . . . second flattened portion 
           13  . . . third flattened portion 
           14  . . . first bent portion 
           15  . . . second bent portion 
           20  . . . flat glass sheet 
           21  . . . first portion 
           22   a,    22   b  . . . second portion 
           30  . . . forming apparatus 
           31  . . . first heat-insulating member 
           32  . . . second heat-insulating member 
           31   a,    32   a  . . . through hole 
           33  . . . forming chamber 
           41  . . . heater 
           51 ,  52  . . . pressing tool 
           60  . . . pressing mechanism