The present invention relates to a heat insulating structure comprising a vacuum insulator that is fixed to a surface and a production process thereof.
Conventionally, inorganic materials such as glass fiber and organic materials such as expanded polyurethane have been used for hot insulators and cold insulators. Glass fiber has excellent heat resistance, but it has a relative thermal conductivity as high as 0.03 through 0.05 kcal/m.h..degree. C. and poor thermal insulation performance. Expanded polyurethane has a thermal conductivity of 0.015 kcal/m.h..degree. C. or so; however, the thermal conductivity is still high in the case of using the material in an insulation box of a freezer that has a temperature inside the box extremely low, for example -90.degree. C. or lower. In such a case the insulation wall would have to be extremely thick to obtain the desired insulation performance.
Thus, recently, vacuum insulators have been used such as disclosed in JP-B 61-17263 (B32B5/18), JP-B 63-35911 (F25D23/06), and JP-B 2-54479 (F16L59/06).
These vacuum insulators are produced by first sealing an insulating material that comprises fine powders of silica or perlite or open cell expanded polyurethane in a bag that has a multilayer laminate structure comprising gas barrier films, and then exhausting the gas (air) inside the bag to create vacuum conditions in the bag. Such vacuum insulators achieve a thermal conductivity as low as 0.005 through 0.010 kcal/m.h..degree. C. These insulators make it possible to reduce the thickness of the insulation wall of a freezer, which curtails the installation area, and enlarges the volume inside the box, as well as reducing power consumption.
On the other hand, conventional ways of fixing such vacuum insulators to the wall of freezers has been used to make a structure as shown in FIG. 14. In this Figure, reference numeral 1 is the vacuum insulator, mentioned above, that comprises two gas barrier films 2, each of which has laminated internal layers of thermally adherable polyethylene or polypropylene, an aluminum and surface protective layer (as disclosed in JP-B 2-54479), and insulation material 5 inserted between the two gas barrier films 2. The insulation material 5 is made of open cell expanded polyurethane for example, and shown in FIG. 14, by partly removing the gas barrier film 2. The inside of vacuum insulator 1 is evacuated to a predetermined pressure; thereafter, the peripheral part 2A of gas barrier films 2 is heated to make the thermally adherable layers seal together. On the surface of vacuum insulator 1 (the upper outside of the surface protective layer), an adhesive sheet 100 is pasted; or an adhesive material, also shown by reference numeral 100, is precoated on the surface of outer door panel 4 to be insulated (for example, the outer door panel of a freezer), and then vacuum insulator 1 is pasted on the outer door panel 4 sheet by sheet.
In such a conventional process, preliminary pasting of an adhesive sheet to vacuum insulator 1 or to the surface to be insulated, such as outer door panel 4 is carried out; or preliminary coating of an adhesive is effected, then the vacuum insulator is pasted onto the surface to be insulated sheet by sheet. Once fixed, adjustment of the postion of the insulation is very difficult in these structures. Thus, the fixation of the insulation at a predetermined position is difficult and handling is troublesome. When the position of the insulation is incorrect, peeling of the insulation may be necessary, and the adhesive has to be again applied. The fixation of vacuum insulation has been very complicated by these procedures. In addition, there is a risk of breaking the gas barrier film 2 when it is necessary to remove the insulation and repaste the door panel.