Patent Publication Number: US-2023151674-A1

Title: Method for manufacturing multi-layer laminate

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to a method for manufacturing a multi-layer laminate. More particularly, the present disclosure relates to a method for manufacturing a multi-layer laminate including a glass panel unit, a transparent plate, and an intermediate film. 
     BACKGROUND ART 
     A glass panel unit has been known in the art as a structure, in which an evacuated space is provided between a pair of glass panels facing each other. For example, Patent Literature 1 discloses a vacuum-insulated glass window unit, in which a space is provided between two glass substrates. 
     There has been a growing demand for glass panel units with further improved thermal insulation properties and mechanical strength. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP 2015-529623 A 
       
    
     SUMMARY OF INVENTION 
     In view of the foregoing background, it is therefore an object of the present disclosure to manufacture a multi-layer laminate with excellent thermal insulation properties and mechanical strength. 
     A method for manufacturing a multi-layer laminate according to an aspect of the present disclosure has the following feature. The multi-layer laminate includes a glass panel unit, an intermediate film, and a transparent plate assembled to the glass panel unit via the intermediate film. The glass panel unit includes a first glass panel, a second glass panel, and an evacuated space interposed between the first glass panel and the second glass panel. The method for manufacturing the multi-layer laminate includes a step. The step includes exhausting a gas from a bag, loaded with the glass panel unit, the intermediate film, and the transparent plate, to cause the bag to shrink and thereby assembling, using the bag thus shrunk, the glass panel unit and the transparent plate via the intermediate film. The step includes raising a pressure inside the bag from a pressure at an initial stage of heating while increasing a temperature of the intermediate film to a predetermined temperature at which the intermediate film softens. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1 A  is a schematic cross-sectional view illustrating an exemplary multi-layer laminate according to a first embodiment; 
         FIG.  1 B  is a schematic perspective view illustrating a glass panel unit included in the multi-layer laminate shown in  FIG.  1 A ; 
         FIGS.  2 A and  2 B  are schematic cross-sectional views illustrating an exemplary method for manufacturing the multi-layer laminate according to the first embodiment; 
         FIG.  3    is a horizontal cross-sectional view of a furnace for use in the method for manufacturing the multi-layer laminate; 
         FIG.  4    is a perspective view illustrating how to dry a target placed in a flat position according to the method for manufacturing the multi-layer laminate; 
         FIG.  5    is a perspective view illustrating how to heat the target in a different manner from in  FIG.  4    according to the method for manufacturing the multi-layer laminate; 
         FIG.  6    is a perspective view illustrating how to dry the target placed in an upright position according to the method for manufacturing the multi-layer laminate; 
         FIG.  7    is a graph showing how the in-furnace temperature and the pressure inside a bag change with time in the step of assembling a glass panel unit and a transparent plate that are included in the multi-layer laminate; 
         FIG.  8    is a schematic cross-sectional view illustrating an exemplary multi-layer laminate according to a second embodiment; and 
         FIGS.  9 A and  9 B  are schematic cross-sectional views illustrating an exemplary method for manufacturing the multi-layer laminate according to the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     1. First Embodiment 
     1-1. Overview of First Embodiment 
     First, a first embodiment will be described. A method for manufacturing a multi-layer laminate  100  according to this embodiment is designed to manufacture the multi-layer laminate  100  shown in  FIG.  1 A . The multi-layer laminate  100  includes a glass panel unit  10 , an intermediate film  30 , and a transparent plate  20 . The transparent plate  20  is assembled to the glass panel unit  10  via the intermediate film  30 . The glass panel unit  10  includes a first glass panel  1 , a second glass panel  2 , and an evacuated space  3 . The evacuated space  3  is interposed between the first glass panel  1  and the second glass panel  2 . 
     The method for manufacturing the multi-layer laminate  100  according to this embodiment includes a step. The step includes exhausting a gas from a bag  40 , loaded with the glass panel unit  10 , the intermediate film  30 , and the transparent plate  20 , to cause the bag  40  to shrink and thereby assembling, using the bag  40  thus shrunk, the glass panel unit  10  and the transparent plate  20  via the intermediate film  30 . The step includes raising a pressure inside the bag  40  from a pressure at an initial stage of heating while increasing a temperature of the intermediate film  30  to a predetermined temperature at which the intermediate film  30  softens. 
     In the multi-layer laminate  100  obtained by the manufacturing method according to this embodiment, the transparent plate  20  is assembled onto the glass panel unit  10  (see  FIG.  1 B ) via the intermediate film  30 . This enables manufacturing a multi-layer laminate  100  having excellent thermal insulation properties and mechanical strength. 
     In addition, the glass panel unit  10  and the transparent plate  20  are assembled to each other with the bag  40  that has been caused to shrink by exhausting gases therefrom. This enables applying pressure uniformly to the intermediate film  30  and reducing the chances of the intermediate film  30  losing its transparency or producing bubbles therein. 
     Furthermore, the step includes raising the pressure inside the bag  40  from the pressure at the initial stage of heating while increasing the temperature of the intermediate film  30  to a predetermined temperature at which the intermediate film  30  softens. This enables assembling the glass panel unit  10  and the transparent plate  20  together with an appropriate pressure while reducing the chances of the intermediate film  30  sticking out from the gap between the glass panel unit  10  and the transparent plate  20 . 
     1-2. Details of First Embodiment 
     Next, the multi-layer laminate  100  according to the first embodiment and a method for manufacturing the same will be described in detail. 
     1-2-1. Multi-Layer Laminate 
     The multi-layer laminate  100  includes the glass panel unit  10 , the transparent plate  20 , and the intermediate film  30  as shown in  FIG.  1 A . 
     (1) Glass Panel Unit 
     The glass panel unit  10  includes the first glass panel  1  and the second glass panel  2  as shown in  FIG.  1 B . The first glass panel  1  and the second glass panel  2  face each other. 
     The glass panel unit  10  further includes a frame-shaped sealant  5 . The sealant  5  is provided between the first glass panel  1  and the second glass panel  2 . The first glass panel  1 , the sealant  5 , and the second glass panel  2  are stacked in this order one on top of another. The sealant  5  hermetically bonds the first glass panel  1  and the second glass panel  2  together. 
     The glass panel unit  10  also includes the evacuated space  3 . The evacuated space  3  is a hermetically sealed space surrounded with the first glass panel  1 , the second glass panel  2 , and the frame-shaped sealant  5 . 
     The glass panel unit  10  further includes a plurality of pillars  4 . The plurality of pillars  4  are provided in the evacuated space  3  between the first glass panel  1  and the second glass panel  2 . These pillars  4  may maintain an interval (gap distance) between the first glass panel  1  and the second glass panel  2 . 
     The glass panel unit  10  further includes a gas adsorbent  6 . The gas adsorbent  6  is provided in the evacuated space  3 . The gas adsorbent  6  adsorbs a gas in the evacuated space  3 . 
     Next, the first glass panel  1 , the second glass panel  2 , the sealant  5 , the evacuated space  3 , the pillars  4 , and the gas adsorbent  6  that form the glass panel unit  10  will be described in further detail. 
     (1.1) First Glass Panel 
     The first glass panel  1  is a plate member of glass. The first glass panel  1  may have a rectangular shape in plan view. However, the planar shape of the first glass panel  1  does not have to be rectangular but may also be any other polygonal shape, a circular shape, or an elliptical shape. The first glass panel  1  may have a flat plate shape or may also have a curved plate shape. The outer surface  11  of the first glass panel  1  may be either flat or curved, whichever is appropriate. 
     Examples of materials for the first glass panel  1  include soda lime glass, high strain point glass, chemically tempered glass, alkali-free glass, quartz glass, Neoceram, and thermally tempered glass. The thickness of the first glass panel  1  is not limited to any particular value but may fall within the range from 1 mm to 10 mm, for example. 
     The first glass panel  1  has the outer surface  11 , which is a surface exposed to the external environment outside of the glass panel unit  10 , and an inner surface  110  facing the second glass panel  2  (see  FIG.  1 A ). 
     Optionally, a low-emissivity film may be provided on the inner surface  110  of the first glass panel  1 . In that case, the low-emissivity film is located in the evacuated space  3 . The low-emissivity film is a film containing a metal with low emissivity. The low-emissivity film has the capability of reducing the transfer of heat by radiation, and therefore, may reduce the transfer (emission) of the heat, generated by light (radiation) irradiating the outer surface  11  of the first glass panel  1 , to the evacuated space  3 . Examples of metals having low emissivity include silver. 
     (ii) Second Glass Panel 
     The second glass panel  2  is a plate member of glass. The second glass panel  2  has the same planar shape as the first glass panel  1  (see  FIG.  1 A ). The second glass panel  2  may have a flat plate shape or may also have a curved plate shape. The outer surface  12  of the second glass panel  2  may be either flat or curved, whichever is appropriate. In other words, the glass panel unit  10  may have a flat plate shape or a curved plate shape, whichever is appropriate. 
     Examples of materials for the second glass panel  2  include soda lime glass, high strain point glass, chemically tempered glass, alkali-free glass, quartz glass, Neoceram, and thermally tempered glass. The material for the second glass panel  2  may be the same as, or different from, the material for the first glass panel  1 . The thickness of the second glass panel  2  is not limited to any particular value but may fall within the range from 1 mm to 10 mm, for example. The thickness of the second glass panel  2  may be the same as, or different from, the thickness of the first glass panel  1 . 
     The second glass panel  2  has the outer surface  12 , which is a surface exposed to the external environment outside of the glass panel unit  10 , and an inner surface  120  facing the first glass panel  1  (see  FIG.  1 A ). 
     (1.3) Sealant 
     The sealant  5  according to this embodiment is formed in a rectangular frame shape. The sealant  5  is made of a hot glue. As the hot glue, a glass frit such as a low-melting glass frit may be used, for example. Examples of the low-melting glass frit include a bismuth-based glass frit, a lead-based glass frit, and a vanadium-based glass frit. The sealant  5  may contain one or more types of low-melting glass frits selected from this group. 
     (1.4) Evacuated Space 
     The evacuated space  3  is a space surrounded with the first glass panel  1 , the second glass panel  2 , and the sealant  5 . The evacuated space  3  is preferably a vacuum space, for example. Specifically, the evacuated space  3  is preferably a space evacuated to a degree of vacuum of 0.1 Pa or less. This would improve the thermal insulation properties of the glass panel unit  10 . Note that this pressure in the evacuation is only an example and should not be construed as limiting. 
     (1.5) Pillars 
     Each of the pillars  4  is a circular columnar member. The height (i.e., the dimension in the thickness direction) of the pillars  4  may be set appropriately according to the gap distance between the first glass panel  1  and the second glass panel  2 . That is to say, the gap distance between the first glass panel  1  and the second glass panel  2  (i.e., the thickness of the evacuated space  3 ) is defined by the height of the pillars  4 . The height of the pillars  4  may fall, for example, within the range from 10 μm to 1000 μm. The diameter of the pillars  4  may fall, for example, within the range from 0.1 mm to 10 mm. For example, pillars  4  with a diameter of 0.5 mm and a height of 100 μm may be used. The shape of the pillars  4  does not have to be circular columnar but may also be a rectangular columnar shape or a spherical shape. 
     The pillars  4  are preferably transparent. This would make the pillars  4  much less conspicuous in the multi-layer laminate  100  and thereby improve the appearance of the multi-layer laminate  100 . 
     The pillars  4  are made of a resin and are preferably made of a polyimide resin, for example. This would reduce the thermal conductivity of the pillars  4  and thereby reduce the transfer of heat between the first glass panel  1  and the second glass panel  2  that are in contact with the pillars  4 . 
     (1.6) Gas Adsorbent 
     The gas adsorbent  6  is placed in the evacuated space  3 . The gas adsorbent  6  adsorbs gas molecules in the evacuated space  3 . This increases the degree of vacuum in the evacuated space  3  and thereby improves the thermal insulation properties of the glass panel unit  10 . 
     The gas adsorbent  6  may include, for example, a metallic getter material or a non-metallic getter material. The metallic getter material is a getter material of a metal having a metallic surface that may chemically adsorb gas molecules. Examples of the metallic getter materials include zirconium-based (such as Zr—Al and Zr—V—Fe) getter materials and titanium-based getter materials. Each of these metallic getter materials may adsorb molecules of a gas such as H 2 O, N 2 , O 2 , H 2 , or CO 2 . In addition, heating and activating any of these metallic getter materials may also cause the gas molecules, chemically adsorbed into the metallic surface of the metallic getter material, to diffuse inside the metallic getter material. Thus, the gas adsorbent  6  containing the metallic getter material may adsorb molecules of a gas such as H 2 O, N 2 , O 2 , H 2 , or CO 2  in the evacuated space  3 . 
     The non-metallic getter material is a getter material having a porous structure with the ability to adsorb gas molecules. Examples of the non-metallic getter materials include zeolite-based getter materials, activated carbon, and magnesium oxide. The zeolite-based getter material may include an ion-exchanged zeolite. In that case, examples of the ion exchange materials include K, NH 4 , Ba, Sr, Na, Ca, Fe, Al, Mg, Li, H, and Cu. Each of these non-metallic getter materials can adsorb molecules of a gas such as a hydrocarbon-based gas (such as CH 4  and C 2 H 6 ) or ammonia (NH 3 ) gas that a metallic getter material cannot adsorb. In addition, heating and activating any of these non-metallic getter materials may cause the gas molecules, which have been adsorbed into the porous structure of the non-metallic getter material, to be desorbed. 
     (1.7) Method for Manufacturing Glass Panel Unit 
     The glass panel unit  10  may be manufactured by, for example, the following method. First, a hot glue to be the sealant  5  is applied in a frame shape onto the inner surface  120  of the second glass panel  2 . Next, the first glass panel  1  is laid on top of the second glass panel  2  such that the frame-shaped hot glue is sandwiched between the first glass panel  1  and the second glass panel  2 , thereby forming a laminate including the first glass panel  1 , the second glass panel  2 , and the hot glue. Next, the laminate is heated in a heating furnace. In this manner, the sealant  5  is formed out of the frame-shaped hot glue. In addition, a gas is exhausted from the space surrounded with the first glass panel  1 , the second glass panel  2 , and the hot glue. In this manner, the glass panel unit  10  may be manufactured with the evacuated space  3  created therein. 
     (2) Transparent Plate 
     The transparent plate  20  shown in  FIG.  1 A  is a transparent plate member with light-transmitting properties. The transparent plate  20  not only improves the mechanical strength, thermal insulation properties, and sound insulation of the multi-layer laminate  100  but also imparts various functions to the multi-layer laminate  100  according to the shape, capability, or any other parameter of the transparent plate  20 . The transparent plate  20  is provided for the outer surface  11 ,  12  of at least one of the first glass panel  1  or the second glass panel  2 . In the multi-layer laminate  100  according to this embodiment, the transparent plate  20  is provided for the outer surface  11  of the first glass panel  1 . The transparent plate  20  faces the glass panel unit  10 . The transparent plate  20  also faces the first glass panel  1 . 
     The planar shape of the transparent plate  20  may be the same as the planar shape of the glass panel unit  10 , for example. In this embodiment, the transparent plate  20  has the same planar shape as the first glass panel  1 . The glass panel unit  10  may be flat or curved as described above. Accordingly, the transparent plate  20  may also be flat or curved, whichever is appropriate. 
     The thickness of the transparent plate  20  is not limited to any particular value but preferably falls, for example, within the range from 0.5 mm to 12 mm, and more preferably falls within the range from 1 mm to 6 mm. This may reduce the weight of the multi-layer laminate  100  while ensuring sufficient mechanical strength for the multi-layer laminate  100 . 
     The material for the transparent plate  20  is not limited to any particular one as long as the material has light-transmitting properties. For example, the transparent plate  20  is preferably made of polycarbonate. This may reduce the weight of the transparent plate  20  and thereby reduce the overall weight of the multi-layer laminate  100 . 
     The transparent plate  20  is preferably made of glass, for example. This may increase the mechanical strength of the transparent plate  20  and eventually increase the mechanical strength of the multi-layer laminate  100 . If the transparent plate  20  is made of glass, examples of specific glass materials for the transparent plate  20  include annealed glass, chemically tempered glass, and thermally tempered glass. 
     (3) Intermediate Film 
     The intermediate film  30  is interposed between the glass panel unit  10  and the transparent plate  20 . In this embodiment, the intermediate film  30  is interposed between the first glass panel  1  and the transparent plate  20 . The glass panel unit  10  and the transparent plate  20  are bonded together via this intermediate film  30 . In this embodiment, the first glass panel  1  and the transparent plate  20  are bonded together via the intermediate film  30 . 
     The intermediate film  30  is preferably provided over not only the entire outer surface, facing the transparent plate  20 , of the glass panel unit  10  (i.e., the outer surface  11  of the first glass panel  1  in this embodiment) but also the entire surface, facing the glass panel unit  10 , of the transparent plate  20 . The planar shape of the intermediate film  30  is preferably the same as not only that of the (first glass panel  1  of the) glass panel unit  10  but also that of the transparent plate  20  as well. 
     The thickness of the intermediate film  30  is not limited to any particular value as long as the intermediate film  30  may bond the (first glass panel  1  of the) glass panel unit  10  and the transparent plate  20  together but preferably falls, for example, within the range from 0.3 mm to 4 mm and more preferably falls within the range from 0.3 mm to 2 mm This allows the glass panel unit  10  to hold the transparent plate  20  easily and also makes it easier to maintain the light-transmitting properties of the multi-layer laminate  100 . 
     The material for the intermediate film  30  is not limited to any particular one as long as the intermediate film  30  may bond the (first glass panel  1  of the) glass panel unit  10  and the transparent plate  20  together and has light-transmitting properties. For example, the material for the intermediate film  30  is preferably a sheet-shaped resin with light-transmitting properties and is more preferably a sheet of a thermoplastic resin. The intermediate film  30  may be configured as a single sheet of resin or a stack of multiple sheets of resin. If the intermediate film  30  is configured as a stack of multiple sheets of resin, some matter may be interposed between the multiple sheets of resin to improve its design and decorativeness. Examples of such interposed mater include a PET film, a sheet of metal foil, and a plant. 
     The intermediate film  30  is preferably made of a polyvinyl butyral (PVB) resin, for example. The PVB resin is preferred because the PVB resin not only is able to bond the glass panel unit  10  and the transparent plate  20  firmly but also has excellent transparency. In addition, the intermediate film  30  made of the PVB resin may also increase the mechanical strength of the multi-layer laminate  100 . Moreover, the PVB resin increases the anti-penetration ability of the multi-layer laminate  100  as well. 
     The intermediate film  30  is also preferably made of an ethylene vinyl acetate (EVA) copolymer resin, for example. The EVA resin is preferred because of its excellent transparency and flexibility. In addition, the intermediate film  30  made of the EVA resin also increases the anti-scattering ability of the multi-layer laminate  100 . Furthermore, the EVA resin also allows the glass panel unit  10  and the transparent plate  20  to be bonded at a relatively low temperature via the intermediate film  30 . Moreover, the EVA resin increases the transportability of the multi-layer laminate  100  as well. 
     The intermediate film  30  is also preferably made of a cycloolefin resin, for example. The cycloolefin resin is preferred because of its excellent transparency and flexibility. In addition, the intermediate film  30  made of the cycloolefin resin also increases the anti-scattering ability of the multi-layer laminate  100 . Furthermore, the cycloolefin resin also allows the glass panel unit  10  and the transparent plate  20  to be bonded at a relatively low temperature via the intermediate film  30 . Moreover, the cycloolefin resin increases the transportability of the multi-layer laminate  100  as well. 
     The intermediate film  30  is also preferably made of an ionomer resin, for example. The ionomer resin is preferred because of its excellent transparency and flexibility and high mechanical strength. In addition, the intermediate film  30  made of the ionomer resin also increases the anti-scattering ability of the multi-layer laminate  100 . Furthermore, the ionomer resin also allows the glass panel unit  10  and the transparent plate  20  to be bonded at a relatively low temperature via the intermediate film  30 . Moreover, the ionomer resin increases the transportability of the multi-layer laminate  100  as well. As used herein, the “ionomer resin” refers to a resin with a special structure in which the molecules of an ethylene-methacrylic acid copolymer or an ethylene-acrylic acid copolymer are bonded together by intermolecular bonding with ions of a metal such as sodium or zinc. 
     The intermediate film  30  is also preferably made of a polyolefin resin, for example. The polyolefin resin is preferred because of its excellent transparency and flexibility. In addition, the intermediate film  30  made of the polyolefin resin also increases the anti-scattering ability of the multi-layer laminate  100 . Furthermore, the polyolefin resin also allows the glass panel unit  10  and the transparent plate  20  to be bonded at a relatively low assembling temperature falling within the range from 80° C. to 110° C. via the intermediate film  30 . Moreover, the polyolefin resin increases the transportability of the multi-layer laminate  100  as well. 
     Thus, the intermediate film  30  preferably includes at least one resin selected from the group consisting of the PVB resin, the EVA resin, the cycloolefin resin, the ionomer resin, and the polyolefin resin. 
     1-2-2. Method for Manufacturing Multi-Layer Laminate 
     The multi-layer laminate  100  according to this embodiment may be manufactured by performing, for example, the following process steps. Note that the following method for manufacturing the multi-layer laminate  100  is only an example and should not be construed as limiting. 
     First, the glass panel unit  10 , the transparent plate  20 , and the intermediate film  30  are provided. Next, the glass panel unit  10  and the transparent plate  20  are assembled together via the intermediate film  30  (see  FIG.  2 A ). More specifically, the outer surface  11 ,  12  of at least one of the first glass panel  1  or the second glass panel  2  and the transparent plate  20  are assembled together via the intermediate film  30 . In this embodiment, the outer surface  11  of the first glass panel  1  and the transparent plate  20  are assembled together via the intermediate film  30  made of a sheet of resin as shown in  FIG.  2 A . In this manner, the multi-layer laminate  100  shown in  FIG.  1 A  is obtained. 
     The glass panel unit  10  and the transparent plate  20  may be assembled together via the intermediate film  30  by, for example, the following vacuum bagging process. The assembling method by vacuum bagging process includes a preparatory step, an assembling step, and a cooling step. That is to say, the method for manufacturing the multi-layer laminate  100  according to this embodiment includes the preparatory step, the assembling step, and the cooling step. 
     The preparatory step includes forming a laminate  41  including the glass panel unit  10 , the transparent plate  20 , and the intermediate film  30  by sandwiching the intermediate film  30  made of a sheet of resin between the glass panel unit  10  and the transparent plate  20 . Then, the laminate  41  is loaded a bag (vacuum bag)  40  as shown in  FIG.  2 B . Note that the bag  40  may be transparent, semi-transparent, or even opaque. 
     The assembling step is performed after the preparatory step. The assembling step includes exhausting a gas from a bag  40 , loaded with the laminate  41 , to cause the bag  40  to shrink and applying, using the bag  40  thus shrunk, pressure to the laminate  41  in the thickness direction, thereby assembling the glass panel unit  10  and the transparent plate  20  via the intermediate film  30 . This assembling step includes heating the laminate  41  while evacuating the bag  40 . This causes the intermediate film  30  to be heated and soften. The intermediate film  30  in such a state is sandwiched between the glass panel unit  10  and the transparent plate  20  that are being pressed by the bag  40 . In this manner, the glass panel unit  10  and the transparent plate  20  are assembled together via the intermediate film  30 . 
     In the assembling step, the inside of the bag  40  is evacuated by, for example, making a vacuum pump, connected to the bag  40 , exhaust a gas therefrom. In addition, in the assembling step, as the bag  40  enclosing the laminate  41  is heated by a furnace  7  (see  FIG.  3   ), for example, the laminate  41  is heated to a predetermined temperature at which the intermediate film  30  melts and softens. The predetermined temperature may be 140° C., for example. Note that the predetermined temperature varies depending on the softening temperature of the intermediate film  30  to use. Thus, the temperature needs to be adjusted to the properties of the intermediate film  30  to use but normally preferably falls within the range from 135° C. to 140° C. Note that the predetermined temperature is not limited to any particular temperature. For example, if a material that softens at a low temperature is used as a material for the intermediate film  30 , then the predetermined temperature may be set at a temperature falling within the range from 80° C. to 110° C. 
     In the assembling step, while the glass panel unit  10  and the transparent plate  20  are being assembled together, pressing pressure is applied from the bag  40  to the glass panel unit  10  and the transparent plate  20 . That is to say, the “pressing pressure” as used herein refers to the pressure applied to the laminate  41  while the intermediate film  30  is being clamped between the glass panel unit  10  and the transparent plate  20 . If the pressure outside of the bag  40  is the atmospheric pressure, for example, the pressing pressure is a differential pressure between the pressure (degree of vacuum) inside the bag  40  and the atmospheric pressure. That is to say, the lower the pressure inside the bag  40  is, the greater the pressing pressure is. Note that the pressure outside of the bag  40  does not have to be the atmospheric pressure. 
     If the pressing pressure were too high, then the plurality of pillars  4  included in the glass panel unit  10  would collapse under the excessive pressure. In that case, this would cause damage to the glass panel unit  10  or cause a decline in the thermal insulation properties, the mechanical strength, or other properties of the glass panel unit  10 . Thus, in this embodiment, the pressing pressure is preferably approximately as high as the pressure for evacuating the bag  40  with a vacuum pump, e.g., approximately 0.1 MPa or less, which is less than the compressive strength of the plurality of pillars  4 . This may reduce the chances of the plurality of pillars  4  collapsing under the excessive pressure. 
     In this embodiment, the pressing pressure is preferably equal to or lower than 3 atmosphere [atm] (≃0.3 MPa), and more preferably equal to or lower than 1 atm (≃0.1 MPa). 
     Thus, the glass panel unit  10  and the transparent plate  20  are assembled together with a pressure approximately as high as the pressure for evacuating the bag  40  with a vacuum pump without applying further pressure to the bag  40  with a press machine, for example. The lower limit value of the pressing pressure is not limited to any particular value as long as the glass panel unit  10  and the transparent plate  20  may be assembled together, but is preferably equal to or greater than 0.02 atm (≃0.002 MPa) and more preferably equal to or greater than 0.03 atm (≃0.003 MPa). This may further reduce the chances of the plurality of resin pillars  4  collapsing under the excessive pressure, particularly when the pillars  4  are made of a polyimide resin. That is to say, the pressing pressure preferably falls within the range from 0.02 atm to 3 atm and more preferably falls within the range from 0.03 atm to 1 atm. 
     The cooling step is performed after the assembling step. The cooling step includes cooling the laminate  41  inside the bag  40 . This allows the intermediate film  30  that has softened in the assembling step to be cooled and cured, thus integrating the glass panel unit  10  and the transparent plate  20  together via the intermediate film  30 . In the cooling step, the laminate  41  may be cooled by, for example, stopping heating the bag  40  using the furnace  7  described above. 
     In general, to bond the glass panel unit  10  and the transparent plate  20  together with the intermediate film  30  of the PVB resin, heat and pressure need to be applied with an autoclave machine used. In that case, the pressure applied to the intermediate film  30  is usually  13  atm (≃1.3 MPa), for example. Depending on the condition for applying heat and pressure, however, the pillars  4  included in the glass panel unit  10  would be deformed or the first glass panel  1 , the second glass panel  2 , or other members of the glass panel unit  10  would be damaged or deformed, for example In contrast, the PVB resin may bond the glass panel unit  10  and the transparent plate  20  only by heating, without using any autoclave machine, by reducing the moisture content thereof. This allows the glass panel unit  10  and the transparent plate  20  to be bonded together only by heating by drying the intermediate film  30  of the PVB resin and then assembling the glass panel unit  10  and the transparent plate  20  via the intermediate film  30 . 
     According to an exemplary method for drying the intermediate film  30 , only the intermediate film  30  may be loaded, as either a roll or a flat film, into a large chamber in which a desiccant such as a silica gel is put, and then a gas may be exhausted from the large chamber using a vacuum pump to maintain a predetermined degree of vacuum. According to this method, the intermediate film  30  may be dried and may have its moisture content decreased. The dried intermediate film  30  made of the PVB resin is heated while being sandwiched between the glass panel unit  10  and the transparent plate  20  in the bag  40  as described above. In this manner, the glass panel unit  10  and the transparent plate  20  are assembled together via the intermediate film  30 . 
     The condition for drying the intermediate film  30  may be set appropriately according to the size, thickness, or any other parameters of the intermediate film  30 . For example, the intermediate film  30  is preferably dried for at least 12 hours, preferably 48 hours or more, in a state where the pressure in the large chamber lowers to 0.1 atm (≃0.01 MPa) or less, for example. 
     To assemble the glass panel unit  10  and the transparent plate  20  together without using an autoclave machine, the moisture content of the intermediate film  30  before the glass panel unit  10  and the transparent plate  20  are assembled together is preferably set at a value equal to or greater than 0.1% by weight and equal to or less than 0.5% by weight. Also, the moisture content of the intermediate film  30  is more preferably set at a value equal to or greater than 0.15% by weight and equal to or less than 0.3% by weight. This enables assembling the glass panel unit  10  and the transparent plate  20  together via the intermediate film  30  while reducing the deformation of the pillars  4  and the damage and deformation of the first glass panel  1  and the second glass panel  2 . In addition, in this case, if the intermediate film  30  is a PVB resin sheet, this may also reduce the chances of causing a decline in the anti-penetration ability of the intermediate film  30  and/or the loss of transparency of the intermediate film  30  or the production of bubbles therein. 
     In addition, applying non-uniform pressure to the intermediate film  30  while assembling the glass panel unit  10  and the transparent plate  20  together via the intermediate film  30  made of the PVB resin is another cause of the loss of transparency of the intermediate film  30  and/or the production of bubbles therein. According to this embodiment, however, adopting the assembling method by the vacuum bagging process described above allows the glass panel unit  10  and the transparent plate  20  to be assembled together so that pressure is applied uniformly to the intermediate film  30 . Consequently, this may reduce the chances of causing the loss of transparency of the intermediate film  30  and the production of bubbles therein. Note that the intermediate film  30  is preferably dried before being loaded into the bag  40 . However, the intermediate film  30  may also be dried after having been loaded into the bag  40  because the humidity inside the bag  40  may be decreased by evacuation. 
     The bag  40  loaded with the laminate  41  in the assembling step may be heated, for example, by the furnace  7  shown in  FIG.  3   . In the following description, the bag  40  loaded with the laminate  41  will be hereinafter referred to as a “target  400 .” 
     The furnace  7  is a hot air dryer and includes a heating chamber  70 , a door  71 , a hot air circulator  72 , and a base  73 . An opening  700  is provided in front of the heating chamber  70 . 
     Inside the furnace  7 , a heating space  701  is created in the heating chamber  70 . The heating space  701  is opened forward through the opening  700 . The target  400  mounted on the base  73  may be loaded and unloaded, along with the base  73 , for example, into/out of the heating space  701  through the opening  700 . The door  71  is used to expose and shut the opening  700 . 
     The hot air circulator  72  includes a blower  720  and a heater  721 . The blower  720  circulates the air in the heating space  701 . The heater  721  heats the gas circulated by the blower  720 . The heater  721  may be a heat exchanger, for example. The hot air circulator  72  circulates the hot air to cause the hot air to flow, for example, in one direction substantially parallel to the rightward/leftward direction in the heating space  701  as shown in  FIG.  3   . The arrows shown in  FIG.  3    indicate the direction in which the hot air flows inside the furnace  7 . 
     In the furnace  7  (i.e., in the heating space  701 ), the base  73  is installed. The base  73  has a flat upper surface on which the target  400  is mounted. 
       FIG.  4    illustrates an example in which the glass panel unit  10  is heated with the target  400  placed in a flat position on the base  73  installed in the heating space  701  (i.e., in the furnace  7 ). The glass panel unit  10  has excellent thermal insulation properties. Thus, if the target  400 , in which the transparent plate  20  is laid on top of the glass panel unit  10  with the intermediate film  30  interposed between them (see  FIG.  1   ) inside the bag  40 , for example, is mounted on the upper surface of the base  73 , then heat will not be transferred smoothly from the base  73  to the intermediate film  30 . On the other hand, if the target  400 , in which the glass panel unit  10  is laid on top of the transparent plate  20  with the intermediate film  30  interposed between themselves in the bag  40 , is mounted on the upper surface of the base  73 , then heat will not be transferred smoothly from the hot air, passing over the target  400 , to the intermediate film  30 . Unless heat is transferred uniformly to the intermediate film  30 , the glass panel unit  10  and the transparent plate  20  may fail to be bonded together uniformly, or there will be a significant difference in temperature between the first glass panel  1  and the second glass panel  2  of the glass panel unit  10 , thus possibly increasing the warpage of the glass panel unit  10  to the point of breaking either the first glass panel  1  or the second glass panel  2 . For these reasons, heat is preferably transferred uniformly to the intermediate film  30 . 
     Therefore, if the target  400  placed in a flat position on the base  73  as described above is heated inside the furnace  7 , then a gap is preferably left, for example, between the target  400  and the base  73  on which the target  400  is mounted. In that case, the target  400  may be in either a state where the glass panel unit  10  is disposed over the transparent plate  20  with the intermediate film  30  interposed between themselves or in a state where the transparent plate  20  is disposed over the glass panel unit  10  with the intermediate film  30  interposed between themselves, whichever is appropriate. Such a gap may be left by, for example, placing the target  400  on the base  73  with a plurality of spacers interposed between the target  400  and the base  73 . This allows the target  400  to be heated not only from over, but also from under, the bag  40 . This enables heating the bag  40  from both sides more easily, thus making it easier to heat the intermediate film  30  uniformly. 
     In addition, as shown in  FIG.  5   , a ventilation space  730  allowing gases to pass therethrough is preferably provided for the base  73 . In the example shown in  FIG.  5   , the lower surface of the base  73  is provided with a groove that extends along the entire length of the base  73  in the rightward/leftward direction and the space inside this groove serves as the ventilation space  730 . In this case, the target  400  may be in either a state where the glass panel unit  10  is disposed over the transparent plate  20  with the intermediate film  30  interposed between themselves or in a state where the transparent plate  20  is disposed over the glass panel unit  10  with the intermediate film  30  interposed between themselves, whichever is appropriate. Letting the hot air (i.e., the gas in the furnace  7 ) pass through such a ventilation space  730  causes an increase in the temperature of the base  73  and causes the bag  40  placed in a flat position on the base  73  to be heated. This may eliminate, or minimize to say the least, the difference in temperature between the first glass panel  1  and the second glass panel  2  of the glass panel unit  10 . This makes it easier to heat the intermediate film  30  uniformly. Note that although the ventilation space  730  shown in  FIG.  5    is provided between the base  73  and an installation surface  75  on which the base  73  is installed, the ventilation space  730  may also be created inside the base  73 . The ventilation space  730  may also be, for example, a through hole running through the base  73  in the rightward/leftward direction. 
     If the ventilation space  730  is created in the base  73  as shown in  FIG.  5   , the material for the base  73  is preferably a material such as aluminum having better thermal conductivity than the bag  40 . Also, in that case, the thickness of the base  73  (made of aluminum) is preferably equal to or greater than 5 mm. Optionally, a raised portion having such a shape as to collect heat such as a heat sink may be provided for a portion, exposed to the hot air, of the base  73  (which is made of a material with good thermal conductivity). Examples of materials with good thermal conductivity include not only aluminum but also metals such as copper and brass, thermally conductive ceramics such as alumina, graphite, and a laminate including a composite of these materials. 
     On the other hand, if the material for the base  73  does not have good thermal conductivity, then the surface of the base  73  may have through holes as in a punched mesh structure, to allow the heat to be transferred smoothly through the surface. In addition, a flat plate having a larger size than the bag  40  and made of a material having good thermal conductivity such as aluminum may be sandwiched between the base  73  and the bag  40 . In that case, the flat plate made of the material having good thermal conductivity preferably has a thickness equal to or greater than 5 mm. Examples of materials with good thermal conductivity include not only aluminum but also metals such as copper and brass, thermally conductive ceramics such as alumina, graphite, and a laminate including a composite of these materials. 
     Alternatively, the target  400  is also preferably heated, for example, in an upright position as shown in  FIG.  6   . In that case, the target  400  may be mounted, for example, on the base  73  such that the glass panel unit  10 , the intermediate film  30 , and the transparent plate  20  are arranged in this order in the forward/backward direction and the thickness of each of the glass panel unit  10 , the intermediate film  30 , and the transparent plate  20  is substantially parallel to the forward/backward direction. This also allows the target  400  to be heated more easily from both sides thereof (i.e., from both sides of the bag  40 ), thus making it easier to heat the intermediate film  30  uniformly. 
     Optionally, if the target  400  is heated in the upright position, then the target  400  may be supported by, for example, a supporter  74  shown in  FIG.  6   . The supporter  74  includes a plurality of supporting members  740 , supporting only right and left end portions of the target  400 . Using such a supporter  74  allows holding the target  400  in the upright position while reducing the chances of applying force to the glass panel unit  10  and the transparent plate  20  loaded in the bag  40 . 
     In general, when the intermediate film  30  made of an EVA resin is used, the glass panel unit  10  and the transparent plate  20  may be bonded together even at a lower heating temperature than the PVB resin. Thus, bonding the glass panel unit  10  and the transparent plate  20  together via the intermediate film  30  made of the EVA resin may reduce the chances of causing deformation of the pillars  4  included in the glass panel unit  10  and deformation, damage, and other inconveniences of the first glass panel  1  and second glass panel  2  thereof. Furthermore, even when the intermediate film  30  made of the EVA resin is used, the glass panel unit  10 , the intermediate film  30 , and the transparent plate  20  are also preferably arranged in the bag  40  and the glass panel unit  10  and the transparent plate  20  are preferably assembled together via the intermediate film  30  with gases exhausted from the bag  40 . That is to say, the glass panel unit  10  and the transparent plate  20  are preferably bonded together by the vacuum bagging process. This makes it easier to apply pressure uniformly to the intermediate film  30 , thus obtaining a multi-layer laminate  100  with a uniform thickness more easily. 
     In this case, in the method for manufacturing the multi-layer laminate  100  according to this embodiment, the assembling step described above includes raising the pressure inside the bag  40  from a pressure at an initial stage of heating while increasing the temperature of the intermediate film  30  to a predetermined temperature at which the intermediate film  30  melts. Specifically, the assembling step includes starting heating the intermediate film  30  with the pressure reduced inside the bag  40  and then raising the pressure inside the bag  40  from the pressure inside the bag  40  when the intermediate film  30  starts being heated. 
       FIG.  7    is a graph showing how the temperature inside the furnace  7  and the pressure inside the bag  40  change with time in the assembling step in a situation where the intermediate film  30  is made of a PVB resin. In the example illustrated in  FIG.  7   , the assembling step includes raising (increasing) the pressure inside the bag  40  stepwise while continuously increasing the temperature inside the furnace  7  from normal temperature to 140° C. that is the softening temperature (predetermined temperature) of the intermediate film  30 . Raising the pressure inside the bag  40  (lowering the pressing pressure) in this manner according to the temperature inside the furnace  7  which is correlated to the temperature of the intermediate film  30  enables assembling the glass panel unit  10  and the transparent plate  20  with an appropriate pressure while reducing the chances of the intermediate film  30  sticking out from the gap between the glass panel unit  10  and the transparent plate  20 . 
     In the assembling step, the pressing pressure with which the laminate is pressed by the bag  40  is preferably changed within the range from 0.02 atm to 3 atm. This enables assembling the glass panel unit  10  and the transparent plate  20  together with a more appropriate pressure while further reducing the chances of the intermediate film  30  sticking out from the gap between the glass panel unit  10  and the transparent plate  20 . 
     Specifically, in the assembling step, first, the pressure inside the bag  40  is set at 0.01 MPa and the pressing pressure is set at 0.09 MPa. In this state, heating is started inside the furnace  7 . Thereafter, when the temperature inside the furnace  7  reaches 85° C., the pressure inside the bag  40  is raised to 0.05 MPa and the pressing pressure is set at 0.05 MPa. Subsequently, when the temperature inside the furnace  7  reaches  130 ° C., the pressure inside the bag  40  is further raised to 0.07 MPa and the pressing pressure is lowered to 0.03 MPa. After that, the pressure inside the bag  40  is maintained at 0.07 MPa. When a predetermined time passes since the point in time when the temperature inside the furnace  7  reached 140° C., the pressure inside the bag  40  is raised to 0.1 MPa that is the atmospheric pressure, and the pressing pressure is decreased to 0 Pa. After that, a cooling step is performed by stopping heating the target  400  using the furnace  7  with the pressure inside the bag  40  maintained at the atmospheric pressure. Performing this cooling step causes the intermediate film  30  to be cooled to around normal temperature and be cured, thus forming a multi-layer laminate  100  in which the glass panel unit  10  and the transparent plate  20  are assembled together via the intermediate film  30 . 
     In the example illustrated in  FIG.  7   , the assembling step includes raising the pressure inside the bag  40  stepwise as the temperature inside the furnace  7  rises. Alternatively, the pressure inside the bag  40  may be raised continuously. That is to say, the pressure inside the bag  40  after the initial stage of heating in the assembling step may be raised stepwise or continuously, whichever is appropriate, as long as the pressure does not decrease in any period since the initial stage of heating. In addition, the temperature inside the furnace  7  and the pressure inside the bag  40  in the assembling step are not limited to any particular values but may be changed as appropriate according to the material, shape, size, or any other parameter of the intermediate film  30 . 
     1-2-3. Use of Multi-Layer Laminate 
     The multi-layer laminate  100  according to the first embodiment may be used in any field without limitation but is applicable to, for example, a field that requires high mechanical strength and excellent thermal insulation properties. Examples of uses of the multi-layer laminate  100  include various types of moving vehicles such as automobiles, railway trains, watercrafts, spacecrafts, and space stations. For example, when applied to an automobile, the multi-layer laminate  100  may be used in its front windshield, side windows, and rear windshield, for example. 
     2. Second Embodiment 
     2-1 Overview of Second Embodiment 
     Next, a method for manufacturing a multi-layer laminate  100  according to a second embodiment will be described. The method according to this embodiment is designed to manufacture the multi-layer laminate  100  shown in  FIG.  8   . The multi-layer laminate  100  includes the glass panel unit  10 , a first transparent plate  21 , a first intermediate film  31 , a second transparent plate  22 , and a second intermediate film  32 . The first transparent plate  21  is provided for the outer surface  11  of the first glass panel  1  of the glass panel unit  10 . The first intermediate film  31  is interposed between the first glass panel  1  and the first transparent plate  21 . The second transparent plate  22  is provided for the outer surface  12  of the second glass panel  2 . The second intermediate film  32  is interposed between the second glass panel  2  and the second transparent plate  22 . 
     In the multi-layer laminate  100  according to this embodiment, the first transparent plate  21  and the second transparent plate  22  are provided for the outer surface  11  of the first glass panel  1  and the outer surface  12  of the second glass panel  2 , respectively. This allows the multi-layer laminate  100  to have improved mechanical strength, thermal insulation properties, and sound insulation compared to the glass panel unit  10  without any of these transparent plates  21 ,  22 . In addition, this also makes the mechanical strength, thermal insulation properties, and sound insulation of this multi-layer laminate  100  superior to those of the multi-layer laminate  100  in which the transparent plate  20  is provided for only either the outer surface  11  of the first glass panel  1  or the outer surface  12  of the second glass panel  2 . 
     To manufacture the multi-layer laminate  100  according to this embodiment, the outer surface  11  of the first glass panel  1  of the glass panel unit  10  and the first transparent plate  21  are assembled together with the first intermediate film  31  interposed between themselves (see  FIG.  9 A ). In addition, the outer surface  12  of the second glass panel  2  of the glass panel unit  10  and the second transparent plate  22  are assembled together with the second intermediate film  32  interposed between themselves (see  FIG.  9 A ). In this manner, a multi-layer laminate  100  with excellent mechanical strength, thermal insulation properties, and sound insulation may be obtained. 
     2-2. Details of Second Embodiment 
     Next, the multi-layer laminate  100  according to the second embodiment and a method for manufacturing the same will be described in detail. 
     2-2-1. Multi-Layer Laminate 
     In the multi-layer laminate  100  according to this embodiment, the transparent plate  20  includes the first transparent plate  21  and the second transparent plate  22  described above, and the intermediate film  30  includes the first intermediate film  31  and the second intermediate film  32  described above. These constituent elements will be described in detail. In the following description, any constituent element of the multi-layer laminate  100  according to this second embodiment, having the same function as a counterpart of the multi-layer laminate  100  according to the first embodiment described above, will be designated by the same reference numeral as that counterpart&#39;s, and description thereof will be sometimes omitted herein. 
     (1) Glass Panel Unit 
     The glass panel unit  10  according to this embodiment has the same configuration as the glass panel unit  10  according to the first embodiment. Thus, the glass panel unit  10  includes: the first glass panel  1 ; the second glass panel  2 ; and the evacuated space  3  provided between the first glass panel  1  and the second glass panel  2 . In addition, in the evacuated space  3 , the plurality of pillars  4  are provided between the first glass panel  1  and the second glass panel  2 . 
     (2) Transparent Plate 
     The transparent plate  20  according to this embodiment includes the first transparent plate  21  and the second transparent plate  22  as described above. 
     (2.1) First Transparent Plate 
     The first transparent plate  21 , as well as the transparent plate  20  according to the first embodiment, is also a plate member having light-transmitting properties. The material for the first transparent plate  21  may also be the same as the material for the transparent plate  20  according to the first embodiment. 
     In the multi-layer laminate  100  according to this embodiment, the first transparent plate  21  is provided for the outer surface  11  of the first glass panel  1  of the glass panel unit  10 . The first transparent plate  21  faces the glass panel unit  10 . The first transparent plate  21  also faces the first glass panel  1 . 
     (2.2) Second Transparent Plate 
     The second transparent plate  22  is a plate member having the same light-transmitting properties as the transparent plate  20  according to the first embodiment. The material for the second transparent plate  22  may also be the same as the material for the transparent plate  20  according to the first embodiment. In this embodiment, the material for the first transparent plate  21  and the material for the second transparent plate  22  may be either the same as each other or different from each other, whichever is appropriate. 
     For example, the first transparent plate  21  and the second transparent plate  22  may be both made of polycarbonate. Alternatively, the first transparent plate  21  and the second transparent plate  22  may be both made of glass, for example. Still alternatively, one of the first transparent plate  21  or the second transparent plate  22  may be made of polycarbonate and the other may be made of glass. 
     At least one of the first transparent plate  21  or the second transparent plate  22  preferably includes a glass pane. In addition, at least one of the first transparent plate  21  or the second transparent plate  22  preferably includes a polycarbonate plate. 
     In the multi-layer laminate  100  according to this embodiment, the second transparent plate  22  is provided for the outer surface  12  of the second glass panel  2  of the glass panel unit  10 . The second transparent plate  22  faces the glass panel unit  10 . The second transparent plate  22  also faces the second glass panel  2 . 
     (3) Intermediate Film 
     The intermediate film  30  according to this embodiment includes the first intermediate film  31  and the second intermediate film  32  as described above. 
     (3.1) First Intermediate Film 
     The first intermediate film  31  may have the same configuration as the intermediate film  30  according to the first embodiment. In the multi-layer laminate  100  according to this embodiment, the first intermediate film  31  is interposed between the outer surface  11  of the first glass panel  1  of the glass panel unit  10  and the first transparent plate  21 . Thus, the first intermediate film  31  may bond the glass panel unit  10  and the first transparent plate  21  together, and more specifically, bond the first glass panel  1  and the first transparent plate  21  together. 
     (3.2) Second Intermediate Film 
     The second intermediate film  32  may have the same configuration as the intermediate film  30  according to the first embodiment. In the multi-layer laminate  100  according to this embodiment, the second intermediate film  32  is interposed between the outer surface  12  of the second glass panel  2  of the glass panel unit  10  and the second transparent plate  22 . Thus, the second intermediate film  32  may bond the glass panel unit  10  and the second transparent plate  22  together, and more specifically, bond the second glass panel  2  and the second transparent plate  22  together. 
     (3.3) Materials for First Intermediate Film and Second Intermediate Film 
     The first intermediate film  31  may have the same configuration as the intermediate film  30  according to the first embodiment as described above. Thus, the material for the first intermediate film  31  may be the same as the material for the intermediate film  30  according to the first embodiment. Likewise, the second intermediate film  32  may have the same configuration as the intermediate film  30  according to the first embodiment as described above. Thus, the material for the second intermediate film  32  may also be the same as the material for the intermediate film  30  according to the first embodiment. 
     In the multi-layer laminate  100  according to this embodiment, the first intermediate film  31  and the second intermediate film  32  are preferably made of different materials. This would enhance the performance of the multi-layer laminate  100  while facilitating the manufacturing process thereof. 
     For example, at least one of the first intermediate film  31  or the second intermediate film  32  is preferably made of a PVB resin. This would ensure sufficient mechanical strength for the multi-layer laminate  100 , to say the least. In addition, using a PVB resin of a grade that provides sound insulation, heat insulation, and UV cut properties would ensure sufficient mechanical strength and functionalities for the multi-layer laminate  100 . In addition, this would also increase the anti-penetration ability of the multi-layer laminate  100 . 
     In addition, at least one of the first intermediate film  31  or the second intermediate film  32  is preferably made of an EVA resin. This would increase the anti-scattering ability of the multi-layer laminate  100 . In addition, using the EVA resin allows the glass panel unit  10  and the transparent plate(s)  21 ,  22  to be bonded together at a relatively low temperature, thus facilitating the manufacturing process of the multi-layer laminate  100  as well. This would also increase the handleability of the multi-layer laminate  100 . 
     Furthermore, at least one of the first intermediate film  31  or the second intermediate film  32  is preferably made of an ionomer resin. This would increase the anti-scattering ability, anti-penetration ability, and mechanical strength of the multi-layer laminate  100 . In addition, the ionomer resin allows the glass panel unit  10  and the transparent plate(s)  21 ,  22  to be bonded together at the same temperature as the PVB resin, thus facilitating the manufacturing process of the multi-layer laminate  100 . This would also increase the mechanical strength of the overall multi-layer laminate  100 . 
     Furthermore, at least one of the first intermediate film  31  or the second intermediate film  32  is preferably made of a cycloolefin resin. This would increase the transparency, waterproofness, and bond strength of the multi-layer laminate  100 . In addition, the cycloolefin resin allows the glass panel unit  10  and the transparent plate(s)  21 ,  22  to be bonded together at the same temperature as the PVB resin, thus facilitating the manufacturing process of the multi-layer laminate  100 . 
     Furthermore, in this embodiment, the first intermediate film  31  and the second intermediate film  32  are preferably made of different materials. In that case, each of the first intermediate film  31  and the second intermediate film  32  may be made of, for example, a resin selected from the group consisting of the PVB resin, the EVA resin, the ionomer resin, the cycloolefin resin, and the polyolefin resin. Making the first intermediate film  31  and the second intermediate film  32  of two different materials in this manner would allow the multi-layer laminate  100  to achieve both the advantages of the material for the first intermediate film  31  and the advantages of the material for the second intermediate film  32  alike. 
     For example, it is recommended that the first intermediate film  31  be made of the PVB resin and the second intermediate film  32  be made of the EVA resin. Alternatively, it is also recommended that the first intermediate film  31  be made of the EVA resin and the second intermediate film  32  be made of the PVB resin. In each of these cases, the manufacturing process of the multi-layer laminate  100  may be facilitated with sufficient mechanical strength ensured for the multi-layer laminate  100 . That is to say, the mechanical strength enhancement and simplified manufacturing process are achieved at the same time for the multi-layer laminate  100 . In addition, the multi-layer laminate  100  with each of these configurations ensures provide the anti-penetration ability and the anti-scattering ability at a time. For example, one of the first intermediate film  31  or the second intermediate film  32  which is required to have sufficient anti-penetration ability is preferably made of the PVB resin and the other intermediate film  31 ,  32  required to have anti-scattering ability is preferably made of the EVA resin. In addition, using a sound insulating PVB resin as the PVB resin would increase not only the anti-penetration ability and anti-scattering ability of the multi-layer laminate  100  but also the sound insulation thereof as well. The sound insulating PVB resin is suitably used for windows of buildings and railway trains that are required to curtail noise as much as possible for noise-sensitive people and for windows of automobiles and other vehicles in the field of mobility. 
     Alternatively, in this embodiment, the first intermediate film  31  and the second intermediate film  32  may also be made of the same material. In that case, the advantages of the material for the first intermediate film  31  and the second intermediate film  32  would be achieved particularly significantly. 
     For example, the first intermediate film  31  and the second intermediate film  32  are preferably both made of the PVB resin. This would increase the mechanical strength of the multi-layer laminate  100  particularly significantly. In addition, this would also increase the anti-penetration ability of the multi-layer laminate  100  particularly significantly. Alternatively, the first intermediate film  31  and the second intermediate film  32  are also preferably both made of the EVA resin. This would facilitate the manufacturing process of the multi-layer laminate  100  particularly significantly. In addition, this would also increase the anti-scattering ability of the multi-layer laminate  100  particularly significantly. 
     2-2-2. Method for Manufacturing Multi-Layer Laminate 
     The multi-layer laminate  100  according to this embodiment may be manufactured by performing, for example, the following process steps. Note that the following method for manufacturing the multi-layer laminate  100  is only an example and should not be construed as limiting. 
     First, as shown in  FIG.  9 A , the glass panel unit  10 , the transparent plate  20 , and the intermediate film  30  are provided. In the multi-layer laminate  100  according to this embodiment, the transparent plate  20  includes the first transparent plate  21  and the second transparent plate  22 , and the intermediate film  30  includes the first intermediate film  31  and the second intermediate film  32 . Thus, the first transparent plate  21  and the second transparent plate  22  are provided as the transparent plate  20 , and the first intermediate film  31  and the second intermediate film  32  are provided as the intermediate film  30 . 
     Next, the glass panel unit  10  and the transparent plate  20  are assembled together via the intermediate film  30  (see  FIG.  9 A ). In this embodiment, the outer surface  11  of the first glass panel  1  of the glass panel unit  10  and the first transparent plate  21  are assembled together with the first intermediate film  31  interposed between themselves. In addition, the outer surface  12  of the second glass panel  2  of the glass panel unit  10  and the second transparent plate  22  are assembled together with the second intermediate film  32  interposed between themselves. 
     In each of the process step of assembling the glass panel unit  10  and the first transparent plate  21  together and the process step of assembling the glass panel unit  10  and the second transparent plate  22  together, the pressure applied for assembling is less than the compressive strength of the resin pillars  4  included in the glass panel unit  10 . This may reduce the chances of the plurality of resin pillars  4  included in the glass panel unit  10  collapsing under the pressure. 
     Assembling the glass panel unit  10  and the first transparent plate  21  and assembling the glass panel unit  10  and the second transparent plate  22  may be performed either separately from each other or simultaneously, whichever is appropriate. 
     For example, if the first intermediate film  31  and the second intermediate film  32  are made of the same material, then assembling the glass panel unit  10  and the first transparent plate  21  and assembling the glass panel unit  10  and the second transparent plate  22  are preferably performed simultaneously. This allows manufacturing the multi-layer laminate  100  efficiently. For example, the first intermediate film  31  and the second intermediate film  32  are preferably both made of the PVB resin. In that case, the glass panel unit  10 , the first transparent plate  21 , and the second transparent plate  22  are preferably assembled together at a relative humidity of 10% or less. This allows bonding the glass panel unit  10  and the first transparent plate  21  together only by heating and bonding the glass panel unit  10  and the second transparent plate  22  together only by heating. This may also reduce the chances of the first intermediate film  31  and the second intermediate film  32  made of the PVB resin losing their transparency or producing bubbles therein. Alternatively, both the first intermediate film  31  and the second intermediate film  32  are preferably made of, for example, the EVA resin. 
     In this embodiment, the glass panel unit  10 , the first transparent plate  21 , and the second transparent plate  22  are assembled together by the vacuum bagging process. For example, a laminate  41  is loaded into the bag  40  as shown in  FIG.  9 B . The laminate  41  includes the glass panel unit  10 , the first intermediate film  31 , the first transparent plate  21 , the second intermediate film  32 , and the second transparent plate  22 . The laminate  41  is formed by sandwiching the first intermediate film  31  between the glass panel unit  10  and the first transparent plate  21  and sandwiching the second intermediate film  32  between the glass panel unit  10  and the second transparent plate  22 . Then, with gases exhausted from this bag  40 , the glass panel unit  10  and the first transparent plate  21  are assembled together via the first intermediate film  31 , while at the same time, the glass panel unit  10  and the second transparent plate  22  are assembled together via the second intermediate film  32 . In this case, as in the first embodiment, the pressure inside the bag  40  is also raised from the pressure at the initial stage of heating with the temperature of the intermediate films  30  increased to the predetermined temperature at which the intermediate films  30  melt. 
     Assembling the glass panel unit  10 , the first transparent plate  21 , and the second transparent plate  22  together in this manner by the vacuum bagging process makes it easier to apply pressure uniformly to the first intermediate film  31  and the second intermediate film  32  and decrease the humidity inside the bag  40 . This may reduce the chances of the first intermediate film  31  and the second intermediate film  32  losing their transparency or producing bubbles therein. Note that the first intermediate film  31  and the second intermediate film  32  may be dried before being loaded into the bag  40  or after having been loaded into the bag  40 , whichever is appropriate. 
     In this embodiment, the bag  40  may also be heated by the furnace  7  as in the first embodiment described above. Particularly, in this second embodiment, if the bag  40  is placed in a flat position inside the furnace  7 , either the first intermediate film  31  or the second intermediate film  32  may be interposed between the base  73  and the glass panel unit  10 . Since the glass panel unit  10  has excellent thermal insulation properties, heat is transferred less smoothly to the intermediate film, located closer to the base, out of the first intermediate film  31  and the second intermediate film  32 . Thus, in this embodiment, heat is preferably applied uniformly to both the first intermediate film  31  and the second intermediate film  32 . 
     For example, a gap is preferably left between the bag  40  loaded with the laminate  41  and the base on which the bag  40  is mounted. This allows the bag  40  to be heated not only from over, but also from under, the bag  40 . That is to say, this enables heating the bag  40  from both sides more easily, thus making it easier to heat the first intermediate film  31  and the second intermediate film  32  uniformly. For example, as in the example shown in  FIG.  5   , the base  73  may be made of a material having better thermal conductivity than the bag  40  and the ventilation space  730  is created in the base  73 . Alternatively, a raised portion having such a shape as to collect heat such as a heat sink is preferably provided for a portion, exposed to the hot air, of the base  73  (which is made of a material with good thermal conductivity). This also enables heating the bag  40  from both sides more easily, thus making it easier to heat the first intermediate film  31  and the second intermediate film  32  uniformly. Still alternatively, the bag  40  loaded with the laminate  41  is also preferably heated in an upright position. This also allows the bag  40  to be heated more easily from both sides thereof, thus making it easier to heat the first intermediate film  31  and the second intermediate film  32  uniformly. 
     Naturally, even if both the first intermediate film  31  and the second intermediate film  32  are made of the EVA resin, the ionomer resin, the cycloolefin resin, or the polyolefin resin, the glass panel unit  10 , the first transparent plate  21 , and the second transparent plate  22  may also be bonded together by the same vacuum bagging process as the one adopted for the first embodiment. 
     For example, if the first intermediate film  31  and the second intermediate film  32  are made of different materials, then assembling the glass panel unit  10  and the first transparent plate  21  and assembling the glass panel unit  10  and the second transparent plate  22  are preferably performed separately from each other. The reason is as follows. Specifically, if the first intermediate film  31  and the second intermediate film  32  are made of different materials, then there may be a difference between the heating temperature required for bonding with the first intermediate film  31  and the heating temperature required for bonding with the second intermediate film  32 . Thus, if the first intermediate film  31  and the second intermediate film  32  made of different materials are heated simultaneously, then the bond strength may be insufficient or the intermediate films  30  may be deformed, for example. In this respect, assembling the glass panel unit  10  and the first intermediate film  31  separately from assembling the glass panel unit  10  and the second intermediate film  32  may reduce the chances of the bond strength becoming insufficient or the intermediate films  30  being deformed or damaged, for example. 
     Specifically, one intermediate film, requiring the higher heating temperature for bonding, out of the first intermediate film  31  and the second intermediate film  32  is preferably bonded earlier than the other intermediate film. For example, if the heating temperature of the first intermediate film  31  is higher than the heating temperature of the second intermediate film  32 , then the glass panel unit  10  and the second transparent plate  22  are preferably assembled together via the second intermediate film  32  by the vacuum bagging process after the glass panel unit  10  and the first transparent plate  21  have been assembled together via the first intermediate film  31  by the vacuum bagging process. Alternatively, if the heating temperature of the second intermediate film  32  is higher than the heating temperature of the first intermediate film  31 , then the glass panel unit  10  and the first transparent plate  21  are preferably assembled together via the first intermediate film  31  by the vacuum bagging process after the glass panel unit  10  and the second transparent plate  22  have been assembled together via the second intermediate film  32  by the vacuum bagging process. 
     For example, if the first intermediate film  31  is made of the PVB resin and the second intermediate film  32  is made of the EVA resin, then the heating temperature required for bonding with the first intermediate film  31  made of the PVB resin may be higher than the heating temperature required for bonding with the second intermediate film  32  made of the EVA resin. In that case, the glass panel unit  10  and the second transparent plate  22  are preferably assembled together by the vacuum bagging process via the second intermediate film  32  made of the EVA resin after the glass panel unit  10  and the first transparent plate  21  have been assembled together by the vacuum bagging process via the first intermediate film  31  made of the PVB resin. 
     As can be seen from the foregoing description of the first and second embodiments, a method for manufacturing a multi-layer laminate ( 100 ) according to a first aspect has the following features. The multi-layer laminate ( 100 ) includes a glass panel unit ( 10 ), an intermediate film ( 30 ), and a transparent plate ( 20 ). The transparent plate ( 20 ) is assembled to the glass panel unit ( 10 ) via the intermediate film ( 30 ). The glass panel unit ( 10 ) includes a first glass panel ( 1 ), a second glass panel ( 2 ), and an evacuated space ( 3 ). The evacuated space ( 3 ) is interposed between the first glass panel ( 1 ) and the second glass panel ( 2 ). The method for manufacturing the multi-layer laminate ( 100 ) includes a step (assembling step). The step includes exhausting a gas from a bag ( 40 ), loaded with the glass panel unit ( 10 ), the intermediate film ( 30 ), and the transparent plate ( 20 ), to cause the bag ( 40 ) to shrink and thereby assembling, using the bag ( 40 ) thus shrunk, the glass panel unit ( 10 ) and the transparent plate ( 20 ) via the intermediate film ( 30 ). The step includes raising a pressure inside the bag ( 40 ) from a pressure at an initial stage of heating while increasing a temperature of the intermediate film ( 30 ) to a predetermined temperature at which the intermediate film ( 30 ) softens. 
     This aspect enables manufacturing a multi-layer laminate ( 100 ) which has excellent thermal insulation properties and mechanical strength and in which the transparent plate ( 20 ) is assembled onto the glass panel unit ( 10 ) via the intermediate film ( 30 ). In addition, the glass panel unit ( 10 ) and the transparent plate ( 20 ) are assembled to each other using the bag ( 40 ) that has been caused to shrink by exhausting gases therefrom. This enables applying pressure uniformly to the intermediate film ( 30 ) and reducing the chances of the intermediate film ( 30 ) losing its transparency or producing bubbles therein. Furthermore, raising the pressure inside the bag ( 40 ) while increasing the temperature of the intermediate film ( 30 ) to a predetermined temperature at which the intermediate film ( 30 ) softens enables assembling the glass panel unit ( 10 ) and the transparent plate ( 20 ) together with an appropriate pressure while reducing the chances of the intermediate film ( 30 ) sticking out from the gap between the glass panel unit ( 10 ) and the transparent plate ( 20 ). 
     A method for manufacturing a multi-layer laminate ( 100 ) according to a second aspect may be implemented in conjunction with the first aspect. In the second aspect, the step includes changing a pressing pressure applied from the bag ( 40 ) onto a laminate ( 41 ) including the glass panel unit ( 10 ), the intermediate film ( 30 ), and the transparent plate ( 20 ) within a range from 0.02 atm to 3 atm. 
     This aspect enables assembling the glass panel unit ( 10 ) and the transparent plate ( 20 ) together with a more appropriate pressure while further reducing the chances of the intermediate film ( 30 ) sticking out from the gap between the glass panel unit ( 10 ) and the transparent plate ( 20 ). 
     A method for manufacturing a multi-layer laminate ( 100 ) according to a third aspect may be implemented in conjunction with the first or second aspect. In the third aspect, the step includes setting, when the temperature of the intermediate film ( 30 ) is equal to the predetermined temperature, the pressure inside the bag ( 40 ) at the atmospheric pressure and then lowering the temperature of the intermediate film ( 30 ). 
     According to this aspect, setting, when the temperature of the intermediate film ( 30 ) is equal to the predetermined temperature, the pressure inside the bag ( 40 ) at the atmospheric pressure enables further reducing the chances of the intermediate film ( 30 ) sticking out from the gap between the glass panel unit ( 10 ) and the transparent plate ( 20 ). 
     A method for manufacturing a multi-layer laminate ( 100 ) according to a fourth aspect may be implemented in conjunction with any one of the first to third aspects. In the fourth aspect, the step includes raising the pressure inside the bag ( 40 ) stepwise while increasing the temperature of the intermediate film ( 30 ) to the predetermined temperature at which the intermediate film ( 30 ) softens. 
     According to this aspect, raising the pressure inside the bag ( 40 ) stepwise in the assembling step enables assembling the glass panel unit ( 10 ) and the transparent plate ( 20 ) together with an appropriate pressure while reducing the chances of the intermediate film ( 30 ) sticking out from the gap between the glass panel unit ( 10 ) and the transparent plate ( 20 ). 
     A method for manufacturing a multi-layer laminate ( 100 ) according to a fifth aspect may be implemented in conjunction with any one of the first to fourth aspects. The fifth aspect has the following features. The intermediate film ( 30 ) is made of a PVB resin. The step includes assembling, using the bag ( 40 ), the glass panel unit ( 10 ) and the transparent plate ( 20 ) via the intermediate film ( 30 ) while setting a moisture content of the intermediate film ( 30 ) at a value equal to or greater than 0.1% by weight and equal to or less than 0.5% by weight. 
     According to this aspect, making the intermediate film ( 30 ) of a PVB resin enables reducing the chances of causing a decline in the anti-penetration ability of the intermediate film ( 30 ) and/or the intermediate film ( 30 ) losing its transparency or producing bubbles therein. In addition, setting a moisture content of the intermediate film ( 30 ) at a value equal to or greater than 0.1% by weight and equal to or less than 0.5% by weight when assembling the glass panel unit ( 10 ) and the transparent plate ( 20 ) via the intermediate film ( 30 ) enables assembling the glass panel unit ( 10 ) and the transparent plate ( 20 ) via the intermediate film ( 30 ) while reducing the chances of causing damage, deformation, and other inconveniences to the first glass panel ( 1 ) and the second glass panel ( 2 ). 
     REFERENCE SIGNS LIST 
     
         
           1  First Glass Panel 
           2  Second Glass Panel 
           3  Evacuated Space 
           10  Glass Panel Unit 
           20  Transparent Plate 
           30  Intermediate Film 
           40  Bag 
           100  Multi-Layer Laminate