Heat insulating structure and production process thereof

A heat insulating structure comprising a vacuum insulator fixed to a surface on which the vacuum insulator is to be applied is provided for the purpose of improving the workability in fixing the vacuum insulator to the surface to be applied. A thermally adherable layer comprising a thermally adherable material is made between the vacuum insulator and the surface to be applied, and the thermally adherable layer is heated and melted whereby the vacuum insulator is fixed to the surface to be applied.

BACKGROUND OF THE INVENTION 
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. 
SUMMARY OF THE INVENTION 
The present invention has been made to overcome such technical problems. An 
object of the present invention is to improve the process of fixing a 
vacuum insulator to a surface to be insulated. 
A heat insulating structure according to the present invention has a 
thermally adhered layer comprising a thermally adherable material between 
a vacuum insulator and a surface to be applied and insulated, the vacuum 
insulator being fixed to the surface to be applied by heating and melting 
the thermally adherable material. 
A heat insulating structure according to the present invention has, on both 
a vacuum insulator surface and a surface to be insulated, thermally 
adherable layers each comprising a thermally adherable material, both 
thermally adherable layers being adhered closely and thermally melted 
whereby the vacuum insulator is fixed to the surface to be insulated. 
Furthermore, a process for producing a heat insulating structure according 
to the present invention comprises a step where a thermally adherable 
layer comprising a thermally adherable material is formed between a vacuum 
insulator and a surface to be insulated, a step where the thermally 
adherable layer is heated and melted, a step where the melted thermally 
adherable layer is cooled and solidified, and a step where the vacuum 
insulator is fixed to the surface to be applied. Still further, a process 
for producing a heat insulating structure according to the present 
invention comprises a step where thermally adherable layers, each 
comprising a thermally adherable material, are formed on both a vacuum 
insulator surface and a surface on which the vacuum insulator is to be 
applied, a step where both of the thermally adherable layers are closely 
adhered, a step where both of the thermally adherable layers are heated 
and melted, and a step where both of the melted and thermally adhered 
layers are cooled and solidified for fixing the vacuum insulator to the 
surface to be insulated in mutually adhering condition. 
According to the present invention, a vacuum insulator is fixed to a 
surface to be insulated, by melting the thermally adherable layer 
comprising a thermally adherable material with heat; thus, no adhesion 
occurs until the heating, thus simplifying the positioning and handling. 
Thereby, the workability in fixing a vacuum insulator is improved 
significantly. 
Still further, a heat insulating structure according to the present 
invention has a fixed vacuum insulator on a surface to be insulated by 
installing a fixing device that retains the peripheral part of the vacuum 
insulator and setting the fixing device to the surface to be insulated. 
According to the present invention, a fixing device retains the peripheral 
part of the vacuum insulator, thus the fixation to the surface to be 
insulated is firm, and damage to the vacuum insulator is prevented. 
Overall workability in the setting operation is improved significantly 
thereby.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, embodiments of the present invention are explained in details 
referring to in the drawings herein. The reference numerals shown in FIG. 
14 are common in all the drawings. FIG. 1 is a side view of a vacuum 
insulator 1 and an outer panel 4 composing a thermal insulation door D in 
an embodiment of the heat insulating structure according to the present 
invention; FIG. 2 is a side view when the vacuum insulator 1 illustrating 
the position of when it is fixed to the outer panel 4 in FIG. 5; and FIG. 
3 is a perspective view of insulation door D. 
The vacuum insulator 1 comprises two gas barrier films 2 each of which has 
laminated internal thermally adherable layer of polyethylene or 
polypropylene, aluminum and surface protective layer, 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 by removing the gas barrier film 2 partly. 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 mutually seal together. 
One of the gas barrier films 2 (upper side in the drawing) of vacuum 
insulator 1 is molded in the form of a vessel and the other gas barrier 
film 2 (lower side in the drawing) is flat. On the surface (lower surface 
in FIG. 1) of the flat gas barrier film 2, thermally adherable plastic 
sheets or films 6 such as of polyethylene or polypropylene are laminated 
thereto. 
The outer door panel 4, which is the surface to be insulated, is made of a 
coated steel sheet or stainless steel, and has a coating layer 7 thereon 
of thermally adherable plastic, such as polyethylene or polypropylene 
(upper surface in FIG. 1). When the vacuum insulator 1 is fixed to the 
outer door panel 4 as indicated by the arrow marks in FIG. 1, the vacuum 
insulator 1 is superimposed at a predetermined position on the outer door 
panel 4, and the thermally adherable plastic sheet 6 and the thermally 
adherable plastic sheet 7 are closely superimposed as shown in FIG. 2. In 
this step, the thermally adherable plastic sheets 6 and 7 are neither 
melted nor adhered together; the positioning vacuum insulator 1 in 
relation to the outer door panel 4 is simplified. 
Next, the assembly of vacuum insulator 1 and the outer door panel 4 is 
heated by a heating device 41 for 5 to 10 minutes, for example, to a 
temperature ranging from 100.degree. C. to 140.degree. C. During this 
heating step, the thermally adherable plastic sheets 6 and 7 melt. 
Subsequent to the heating, the thermally adherable plastic sheets 6 and 7 
are cooled and solidified, whereby both sheets 6 and 7 are mutually 
adhering to one another. With this adhesion, the vacuum insulator 1 is 
fixed onto the surface of outer door panel 4 as shown in FIG. 3. 
The insulation door D as an embodiment of the heat insulating strucutre is, 
for example, a door of an ultra-deep low temperature freezer not shown in 
the drawing, and the outer door panel 4 is as a whole in the shape of a 
rectangular container. Two sheets of the vacuum insulator are set upper 
and lower in the internal recesses of the rectangular container. After the 
fixation of vacuum insulator 1, an inner sheet, not shown in the drawing, 
is installed, and expanded polyurethane not shown in the drawing, for 
example, is charged into the space, other than the vacuum insulator 1, 
inside the insulator door D by means of foaming in place to complete the 
insulation door D. 
In the embodiment mentioned above, the gas barrier film 2 of the vacuum 
insulator 1 is laminated on the surface (lower surface in FIG. 1) with the 
thermally adherable plastic sheet 6. However, the present invention is not 
limited to this embodiment, and the thermally adherable plastic layer may 
be coated on the gas barrier film 2, as is the case of the outer door 
panel 4, or else the thermally adherable plastic sheet 6 may be adhered to 
the surface of the gas barrier film 2. 
Furthermore, while the whole of vacuum insulator 1 and outer door panel 4 
is heated to adhere the whole of the thermally adherable plastic sheets 6 
and 7, the method of adhesion is not limited to this procedure, and 
heating may be carried out on only a part or spots corresponding to the 
periphery part 2A to cause adhesion. 
FIGS. 4 and 5 illustrate another embodiment of the present invention. In 
this embodiment, one surface (upper surface in FIG. 4) of one (upper side 
of the drawing) of the gas barrier film 2 of the vacuum insulator 1 and 
the other surface, the lower surface in FIG. 4 of the other (lower side of 
the drawing) of the gas barrier films 2 are both laminated with the 
thermally adherable plastic sheet 6. 
As is the case in the previous embodiment, the vacuum insulator 1 is 
thermally adhered to the outer door panel 4; however, in this embodiment, 
the whole surface of the gas barrier film 2 is laminated with the 
thermally adherable plastic sheet 6, this being a very convenient 
structure in case the vacuum insulator 1 is fixed between two panels. 
FIGS. 6 and 7 illustrate still another embodiment of the present invention. 
In this case, the three sides of the periphery part 6A, 6A of two 
thermally adherable plastic sheets 6, are preliminarily adhered to form a 
bag shape, in which bag a vacuum insulator 1 is inserted. Thereafter, a 
vacuum is created inside the bag, then the remaining side is adhered 
thermally. In this way, the thermally adhered plastic sheets 6 are 
provided over the whole surface of the gas barrier film 2. This structure 
also functions as in the previous embodiment. 
Here, such vacuum insulators are subjected to vacuum internally, and the 
surface might not be smoothly flat but become slightly concave and/or 
convex. FIGS. 8 through 13 illustrate heat insulating structures that are 
suitable for such cases. 
The reference numerals in FIGS. 1 through 7 and FIG. 14 are common 
respectively for designating the same parts. FIG. 8 is an enlarged 
cross-sectional view of the corner part of an outer side wall panel 31 in 
a side wall 27, which is an embodiment of the heat insulating structure in 
the mentioned case. FIG. 9 is a perspective view of the vacuum insulator 1 
and the fixing device 11. 
The vacuum insulator 1, as in previous cases, comprises two gas barrier 
films 2, each of which has laminated internal thermally adherable layer of 
polyethylene or polypropylene, aluminum and surface protective layer, 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 by partly removing the gas barrier film 2. The inside 
of vacuum insulator 1 is evacuated to a predetermined pressure. 
Thereafter, the peripheral part of the gas barrier film 2 is heated to 
make the thermally adherable layers mutually seal together. 
A fixing device 11 is set on the peripheral part of vacuum insulator 1 as 
shown in FIG. 9. The fixing device 11 which is made of a plastic by 
extrusion molding into a U-shape, has a flat and smooth surface. The 
dimension of a retaining part 11A that is incorporated in the fixing 
device 11, has an open end, and approximately fits the shape and thickness 
of the vacuum insulator 1. Thereby, the retaining part 11A of fixing 
device 11 encompasses and holds the edge part of vacuum insulator 1 so 
that the gas barrier films 2 are not broken. In addition, on one surface 
(front surface, for example) of fixing device 11, an adhesive tape 12 is 
applied in the lengthwise direction. 
When the vacuum insulator 1 is fixed to the outer side wall panel 31 that 
is made of a coated steel sheet or stainless steel sheet, the vacuum 
insulator 1 is positioned in a predetermined location of the inner surface 
of outer side wall panel 31 and fixed with the adhesive tape 12 of fixing 
device 11 applied to the inner surface of outer side wall panel 31, FIGS. 
8 and 9. 
In this procedure, close adherence to the outer side wall panel 31 is 
sufficiently secured since the surface of fixing device is flat and 
smooth. Thus, the vacuum insulator 1 is firmly fixed to the outer side 
wall panel 31 with substantially improved workability. The outer side wall 
panel 31 having the fixed vacuum insulator 1 is coupled with the inner 
side wall panel that is not shown in the drawing; the space between both 
panels other than the vacuum insulator 1 being filled with expanded 
polyurethane by foaming in place. As a result, a side wall 27, FIG. 12, 
described later herein, is completed as a heat insulating structure. 
Here, the fixing device 11 is not limited to having a U-shaped 
cross-section as shown in FIG. 8 and may have an approximate H-shape as 
shown in FIG. 10. In this case, the fixing device 11 is also formed by 
extrusion molding of a plastic, and the fixing device has a flat and 
smooth surface. The fixing device 11 has a pair of retaining parts 11A, 
which has opposed open ends. The retaining parts 11A retain and hold edge 
parts of the two sheets of vacuum insulator 1, 1 respectively. 
On one surface (front surface, for example) of fixing device 11 as well, an 
adhesive tape 12 is applied in the lengthwise direction. Thus, with the 
fixing device 11 in this case, the two sheets of vacuum insulator 1, are 
connected on the same plane and can be fixed simultaneously on the flat 
surface to be insulated, such as the outer side wall panel 31, by using 
the adhesive tape 12 pasted on the surface to be insulated. 
FIG. 11 illustrates the cross-section of the fixing device 11 in which case 
the retainers 11A, are integrally formed, and wherein retainers have open 
ends nearly perpendicularly to each other. Also in this case, the fixing 
device 11 is formed by extrusion molding of a plastic which has a flat and 
smooth surface. On two surfaces (back and lower surfaces for example), 
adhesive tapes 12 are applied in the lengthwise direction. 
With such fixing device 11, retaining parts 11A retain two sheets of vacuum 
insulators 1, 1, respectively; the two sheets of vacuum insulators 1, 1 
can be simultaneously fixed to the surfaces, perpendicularly crossed, to 
be insulated. 
FIG. 12 is an exploded perspective view of an insulation box 21 comprising 
such vacuum insulator 1. The insulation box 21 constitutes the main body 
of an ultra-deep low temperature freezer, for example, and comprises the 
main insulating wall 26 including a ceiling wall 22, back wall 23 and 
bottom wall 24, and the two side walls 27, 27 fixed to both sides of the 
main insulating wall 26. In the side wall 27, the two sheets of vacuum 
insulator 1, 1 are connected and fitted on the same plane by the fixing 
device 11. In the connecting parts of the ceiling wall 22 to the back wall 
23 and of the back wall 23 to the bottom wall 24, respectively, the two 
sheets of vacuum insulator 1, 1 are connected and fixed nearly 
perpendicular by the fixing device 11 shown in FIG. 11. 
FIG. 13 illustrates another embodiment of the structure for fixing a vacuum 
insulator 1. In this drawing, the reference numerals are common with FIGS. 
8 through 12, respectively, for designating the same parts. In this 
embodiment, a fixing device 11 in a shape of frame having nearly H-shape 
cross-section is fixed on the edge of the vacuum insulator 1, thus 
retaining the vacuum insulator 1. On the other hand, a pair of rails 29, 
29 is preliminarily installed on the upper and lower internal surfaces of 
the outer box 28 of the main insulating wall 26. The fixing device 11 of 
vacuum insulator 1 is inserted like a sliding door and fixed between the 
rails 29, 29, thus retaining the vacuum insulator 1. 
In this structure, the vacuum insulator 1 can be fitted without using an 
adhesive tape, as is the case mentioned above. The fitting work of the 
vacuum insulator 1 becomes much smoother. 
While the vacuum insulator having open cell expanded polyurethane that is 
internally sealed is used in the above embodiments, the vacuum insulator 
is not limited to this type and may use silica or perlite powder for 
general purposes. In the embodiments mentioned above, the vacuum insulator 
is fixed to the outer door panel or the body of insulation box of an 
ultra-deep low temperature freezer. However, the present invention is not 
limited to such embodiments and is useful for application to any other 
surfaces. 
As explained in detail hereinabove, according to the present invention, a 
vacuum insulator is fixed to a surface to be insulated, by melting the 
thermally adherable layer comprising a thermally adherable material with 
heat; thus, no adhesion is made until the heating, and the positioning and 
handling become very easy. Thus, the workability in fixing a vacuum 
insulator is improved significantly. 
Furthermore, according to the present invention, a fixing device retains 
and holds the peripheral part of the vacuum insulator, thus the fixation 
to the surface to be insulated is firm and potential damage to the vacuum 
insulator is prevented. As a result, overall workability in the setting is 
improved significantly thereby.