U.S. patent application number 10/962222 was filed with the patent office on 2005-04-21 for heat insulating container and manufacture method therefor.
Invention is credited to Baba, Naoho, Fujii, Takafumi, Watanabe, Isao.
Application Number | 20050084633 10/962222 |
Document ID | / |
Family ID | 29996464 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050084633 |
Kind Code |
A1 |
Baba, Naoho ; et
al. |
April 21, 2005 |
Heat insulating container and manufacture method therefor
Abstract
A heat insulating container is described, including an outer
glass container and an inner glass container housed therein with a
gap formed in-between as a heat insulating layer. A radiant heat
preventive film containing a metal oxide is disposed on at least
one of the external surface of the inner container or the internal
surface of the outer container, wherein the radiant heat preventive
film has a reflectivity of 35% or higher with a wavelength of 15
.mu.m. When the thickness of the radiant heat preventive film is
3000 .ANG., the Hall mobility "x" (cm.sup.2/V.multidot.s) and the
carrier concentration "y" (cm.sup.-3) of the same satisfy the
following formulae: y.gtoreq.-5.times.10.sup.20x+2.t-
imes.10.sup.21 and y.gtoreq.-6.times.10.sup.18x+3.times.10.sup.20.
When the thickness of the radiant heat preventive film is 5000
.ANG., x and y satisfy the following formulae:
y.gtoreq.-5.times.10.sup.20x+3.times.10.s- up.21 and
y.gtoreq.-6.times.10.sup.18x+7.times.10.sup.20. Such radiant heat
preventive films can have high reflectivity.
Inventors: |
Baba, Naoho; (Tokyo, JP)
; Fujii, Takafumi; (Tokyo, JP) ; Watanabe,
Isao; (Tokyo, JP) |
Correspondence
Address: |
J C PATENTS, INC.
4 VENTURE, SUITE 250
IRVINE
CA
92618
US
|
Family ID: |
29996464 |
Appl. No.: |
10/962222 |
Filed: |
October 8, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10962222 |
Oct 8, 2004 |
|
|
|
10459109 |
Jun 10, 2003 |
|
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|
Current U.S.
Class: |
428/34.4 ;
427/376.2; 427/383.1; 428/432 |
Current CPC
Class: |
Y10T 428/131 20150115;
Y10T 428/277 20150115; Y10T 428/1317 20150115; A47J 41/0077
20130101; A47J 41/024 20130101 |
Class at
Publication: |
428/034.4 ;
427/376.2; 427/383.1; 428/694.0TM; 428/432 |
International
Class: |
B05D 007/22; B05D
003/02; B32B 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 13, 2002 |
JP |
2002-173104 |
Claims
1-8. (canceled)
9. A manufacture method of a heat insulating container, comprising:
forming a film which contains a metal oxide on at least one of an
external surface of an inner glass container and an internal
surface of an outer glass container; and heating the metal oxide
film at a temperature of about 400.degree. C. or higher in a
non-oxidative environment for 10 minutes or longer to form a
radiant heat preventive film.
10. A manufacture method of a heat insulating container, comprising
housing an inner glass container in an outer glass container with a
gap formed in between; integrally joining the inner glass container
and the outer glass container; adhering a raw material of a metal
oxide to at least one of an external surface of the inner glass
container or an internal surface of the outer glass container;
heating the integrally joined inner glass container and outer glass
container at a temperature of about 400.degree. C. or higher in an
oxidative environment for 10 minutes or longer; and heating the
integrally joined inner glass container and outer glass container
at a temperature of about 400.degree. C. or higher in a
non-oxidative environment for 10 minutes or longer to form a
radiant heat preventive film.
11. A manufacture method of a heat insulating container,
comprising: forming a metal oxide film on at least one of an
external surface of an inner glass container and an internal
surface of an outer glass container housing the inner glass
container in the outer glass container with a gap formed in
between; integrally joining the inner glass container and the outer
glass container; heating the integrally joined inner glass
container and outer glass container at a temperature of about
400.degree. C. or higher in a non-oxidative environment for 10
minutes or longer to form a radiant heat preventive film.
12. The manufacture method of claim 9, the non-oxidation
environment is a vacuum environment, an environment filled with
inactive gas, or an environment filled with inactive gas and
hydrogen.
13. The manufacture method of claim 10, the non-oxidation
environment is a vacuum environment, an environment filled with
inactive gas, or an environment filled with inactive gas and
hydrogen.
14. The manufacture method of claim 11, the non-oxidation
environment is a vacuum environment, an environment filled with
inactive gas, or an environment filled with inactive gas and
hydrogen.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The invention relates to a heat insulating container having
a double-wall structure and a manufacture method therefor. More
specifically, the invention relates to a heat insulating container
that includes an inner glass container and an outer glass container
with a gap formed in-between.
[0003] 2. Description of Related Art
[0004] A heat insulating container comprising an inner glass
container and an outer glass container, such as a vacuum flask, has
been in common use. The heat insulating container has a structure
comprising an inner glass container housed in an outer glass
container with a gap formed in-between. In such a heat insulating
container, the gap is in a vacuum, or a low-thermal-conductivity
gas (for example, argon, krypton or xenon) having a thermal
conductivity lower than that of air is sealed within the gap, so
that the gap can serve as a heat insulating layer. Furthermore, in
this type of heat insulating container, a radiant heat preventive
film is usually formed on the outer surface of the inner container
or the inner surface of the outer container by utilizing a silver
mirror reaction or the like.
[0005] To manufacture the above heat insulating container, for
example, the following method may be adopted. The inner container
and the outer container are integrally joined together at the ends
of the container opening. Next, a silver-containing solution is
injected into the gap such that the silver-containing solution gets
adhered to predetermined surfaces of the inner and the outer
containers. Next, the resulting structure is heated at a
temperature of about 200.degree. C. to dry the silver-containing
solution and thereby form a silver film. Subsequently, the gap is
made vacuum by exhausting the gap of air through a tip tube
provided on the outer glass container. Otherwise, a
low-thermal-conductivity gas is sealed within the gap. In both
cases, the gap is transformed into a heat insulating layer.
[0006] Japanese Patent Application Laid Open Publication No.
2001-505088 discloses a heat insulating container, in which a
radiant heat preventive film made of metal oxide (SnO.sub.2,
In.sub.2O.sub.3, ZnO, etc.) with a resistivity of 10.sup.-4
.OMEGA..multidot.cm or less is formed on the surfaces of the inner
container and the outer container. The heat insulating container
disclosed in the above publication has an advantage that the
contents of the container can be seen because the radiant heat
preventive film is highly transparent.
[0007] However, a radiant heat preventive film formed from a metal
oxide usually has a low performance in preventing radiant heat
because of the restrictions of the manufacturing conditions.
Therefore, it is difficult to produce a heat insulating container
that is excellent in heat insulating capability.
SUMMARY OF THE INVENTION
[0008] Accordingly, in the light of the foregoing description, it
is an object of the present invention to provide a heat insulating
container that is excellent in thermal insulating capability and a
manufacture method of the same.
[0009] To achieve these and other advantages and in accordance with
the purpose of the invention, as embodied and broadly described
herein, the invention provides a heat insulating container that has
a radiant heat preventive film containing a metal oxide on at least
one of the external surface of the inner container or the internal
surface of the outer container. The reflectivity of the radiant
heat preventive film to a radiation with a wavelength of 15 .mu.m
is 35% or higher.
[0010] The Hall mobility "x" (cm.sup.2/V.multidot.s), the carrier
concentration "y" (cm.sup.-1) and the thickness "t" (.ANG.) of the
radiant heat preventive film satisfy the following formulae:
y.gtoreq.-5.times.10.sup.20x+5.times.10.sup.17t+0.5.times.10.sup.21
y.gtoreq.-6.times.10.sup.18x+2.times.10.sup.17t-3.times.10.sup.20
[0011] wherein 1 .ANG.=10.sup.-10 m (0.1 nm).
[0012] That is, for example, when the thickness "t" (.ANG.) of the
radiant heat preventive film is 3000 .ANG., the Hall mobility "x"
(cm.sup.2/V.multidot.s) and the carrier concentration "y"
(cm.sup.-3) satisfy the following formulae:
y.gtoreq.-5.times.10.sup.2x+2.times.10.sup.21
y.gtoreq.-6.times.10.sup.18x+3.times.10.sup.20
[0013] Similarly, when the thickness "t" (.ANG.) of the radiant
heat preventive film is 5000 .ANG., the Hall mobility "x"
(cm.sup.2/V.multidot.s) and the carrier concentration "y"
(cm.sup.-3) satisfy the following formulae:
y.gtoreq.-5.times.10.sup.20x+3.times.10.sup.21
y.gtoreq.-6.times.10.sup.8x+7.times.10.sup.20
[0014] The carrier concentration of the radiant heat preventive
film is preferably within a range of 1.5.times.10.sup.21/cm.sup.3
to 1.times.10.sup.22/cm.sup.3.
[0015] To achieve these and other advantages and in accordance with
the purpose of the invention, as embodied and broadly described
herein, the invention provides a manufacture method of the heat
insulating container, including forming a metal oxide film on at
least one of the external surface of an inner glass container or
the internal surface of an outer glass container. The metal oxide
film is heated at a temperature of 400.degree. C. or higher in a
non-oxidative environment for 10 minutes or longer to form a
radiant heat preventive film.
[0016] The metal oxide film may be formed with the following
process. Firstly, the inner container and the outer container are
integrally joining together. Then, materials for forming the metal
oxide film is injected into the gap between the inner container and
the outer container. Next, the resulting structure is heated at a
temperature of about 400.degree. C. or higher in an oxidative
environment for 10 minutes or longer to form a metal oxide film. In
an alternative embodiment, the metal oxide film is formed before
the inner container and the outer container are integrally joining
together.
[0017] The non-oxidative environment is preferably a vacuum
environment, an environment filled with an inactive gas, or an
environment filled with an inactive gas that is added with
hydrogen.
[0018] It is to be understood that both the foregoing general
description and the following detailed description are exemplary,
and are intended to provide further explanation of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention. In the
drawings,
[0020] FIG. 1 illustrates a sectional view of a heat insulating
container according to an embodiment of the present invention.
[0021] FIG. 2 illustrates a manufacture method of a heat insulating
container according to an embodiment of this invention in a
perspective view.
[0022] FIG. 3 is a graph showing respective resistivities of the
metal oxide films of Samples 1-5.
[0023] FIG. 4 is a graph showing respective carrier concentrations
of the metal oxide films of Samples 1-5.
[0024] FIG. 5 is a graph showing respective Hall mobilities of the
metal oxide films of Samples 1-5.
[0025] FIG. 6 is a graph showing the reflection spectrum of the
metal oxide film of Sample 1.
[0026] FIG. 7 is a graph showing the reflection spectrum of the
metal oxide film of Sample 2.
[0027] FIG. 8 is a graph showing the reflection spectrum of the
metal oxide film of Sample 3.
[0028] FIG. 9 is a graph showing the reflection spectrum of the
metal oxide film of Sample 4.
[0029] FIG. 10 is a graph showing the reflection spectrum of the
metal oxide film of Sample 5.
[0030] FIG. 11 is a graph showing an example of the relationship
between the Hall mobility and the carrier concentration of a metal
oxide film having a thickness of 3000 .ANG..
[0031] FIG. 12 is a graph showing an example of the relationship
between the Hall mobility and the carrier concentration of a metal
oxide film having a thickness of 5000 .ANG.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] Refer to FIG. 1, which illustrates a sectional view of a
heat insulating container according to a preferred embodiment of
the present invention. In the heat insulating container 1 of the
preferred embodiment, an inner glass container 2 is housed in an
outer glass container 3 with a gap 4 formed in-between as a heat
insulating layer.
[0033] The inner container 2 and the outer container 3 are joined
together at respective opening ends 2b, 3b and integrated. In a
preferred embodiment, both containers are joined together in an
airtight manner by heating and softening the opening ends 2b and
3b, so as to make the gap 4 airtight.
[0034] The shape of the inner container 2 or the outer container 3
is not specifically restricted, and can be a cylinder shape, a ball
shape or the like. However, in order to keep the width of the gap 4
between the inner container 2 and the outer container 3
approximately uniform, it is preferred that the inner container 2
and the outer container 3 have similar shapes.
[0035] The material of the inner container 2 and the outer
container 3 can be soda-lime glass (soda glass), borosilicate
glass, quartz glass or the like. Particularly, soda glass is
inexpensive and therefore preferable. It is preferable to use a
glass with a softening temperature of 500.degree. C. or higher to
constitute the inner and the outer containers 2 and 3. To raise the
softening temperature of glass (soda glass and the like) above
500.degree. C., it is effective to add impurity, such as
B.sub.2O.sub.3, Al.sub.2O.sub.3 or the like, into the glass
composition in a predetermined concentration. If the softening
temperature is lower than 500.degree. C., the inner and the outer
containers 2 and 3 are easily softened and deformed during the
formation of the intermediate film 5 or the radiant heat preventive
film 6, possibly hampering the manufacturing of the intermediate
film 5 and the radiant heat preventive film 6.
[0036] Both the outer surface 2a of the inner container 2 and the
inner surface 3a of the outer container 3 are provided with the
radiant heat preventive film 6, and with the intermediate film 5
between the respective surfaces 2a and 3a and the radiant heat
preventive film 6. That is, the intermediate film 5 is firstly
formed on the outer surface 2a and the inner surface 3a, and then
the radiant heat preventive film 6 is formed on the intermediate
film 5.
[0037] The intermediate film 5 is made of a material containing
SiO.sub.2, and is formed to repair the flaws on the external
surface 2a of the inner container 2 and the internal surface 3a of
the outer container 3 and thereby reinforce the inner container 2
and the outer container 3. However, the intermediate film 5 is not
absolutely necessary for the fabrication of the heat insulating
container 1, and the radiant heat preventive film 6 can be formed
directly on the outer surface 2a of the inner glass container 2
and/or the inner surface 3a of the outer glass container 3 in such
a case.
[0038] The flaws occurring on the inner container 2 or the outer
container 3 usually reaches tens to hundreds of nanometers in
depth. Therefore, the intermediate film 5 is preferably thick
enough to fill the flaws. Moreover, the intermediate film 5 is
preferably formed by stacking several thinner films each having a
thickness such as tens of nanometers, since a single thick film
formed in only one step usually has non-uniform thickness, and
cracks are easily caused thereby. In consideration of the depth of
flaws and the number of times for forming the intermediate film 5,
it is preferable that the intermediate film 5 has a thickness of 50
nm or more, and more preferably, has a thickness within a range of
100 to 500 nm.
[0039] The radiant heat preventive film 6 is made of a material
containing metal oxide. The radiant heat preventive film 6 is
preferably composed of one or more compounds selected from a group
consisting of ITO (Sn-doped In.sub.2O.sub.3), ATO (Sb-doped
SnO.sub.2) IZO (In-doped ZnO), AZO (Al-doped ZnO), GZO (Ga-doped
ZnO), FTO (F-doped SnO.sub.2) and FZO (F-doped ZnO). It is
preferable that the thickness of the radiant heat preventive film 6
is about 150 nm to 500 nm.
[0040] Moreover, the radiant heat preventive film 6 has a
reflectivity of 35% or higher with a wavelength of 15 .mu.m.
Therefore, the radiant heat preventive film 6 has a high
performance in preventing radiant heat, and the heat insulating
container 1 is excellent in thermal insulating capability. When the
radiant heat preventive film 6 has a reflectivity of 35% or higher,
the heat insulating capability of the heat insulating container 1
is higher than that of a conventional heat insulating container
using a solid heat insulation material such as polyurethane.
[0041] Next, the factors that render the radiant heat preventive
film 6 have a reflectivity of 35% or higher with a wavelength of 15
.mu.m are described as follows.
[0042] Generally, reflection of an electromagnetic wave on a
conductive semiconductor film, such as a semiconductive metal oxide
film, is caused by motions of the free electrons in the film under
the influence of the alternating electric field of the
electromagnetic wave. As a result, the more, or the freer, the free
electrons in the film are, the better the reflecting capability of
the film to the electromagnetic wave is. Therefore, lower
resistivity and increased carrier concentration of the radiant heat
preventive film 6 contribute to improvement of the radiant heat
insulation effect. Moreover, when the Hall mobility is sufficiently
high, a high reflectivity can still be obtained even if the carrier
concentration is relatively low.
[0043] For this reason, the thickness "t" (.ANG.), the Hall
mobility "x" (cm.sup.2/V.multidot.s) and the carrier concentration
"y" (cm.sup.-3) of the radiant heat preventive film 6 preferably
satisfy the following formulae:
y.gtoreq.-5.times.10.sup.20x+5.times.10.sup.17t+0.5.times.10.sup.21
y.gtoreq.-6.times.10.sup.18x+2.times.10.sup.17t-3.times.10.sup.20
[0044] under the condition, the radiant heat preventive film 6 can
have a reflectivity of 35% or higher with a wavelength of 15 .mu.m,
wherein 1 .ANG.=10.sup.-10 m (0.1 nm).
[0045] That is, for example, when the thickness "t" (.ANG.) of the
radiant heat preventive film 6 is 3000 .ANG., the Hall mobility "x"
and the carrier concentration "y" satisfy the following
formulae:
y.gtoreq.-5.times.10.sup.20x+2.times.10.sup.21
y.gtoreq.-6.times.10.sup.18x+3.times.10.sup.20
[0046] Analogously, when the thickness "t" (.ANG.) of the radiant
heat preventive film is 5000 .ANG., the Hall mobility "x" and the
carrier concentration "y" satisfy the following formulae:
y.gtoreq.-5.times.10.sup.20x+3.times.10.sup.21
y.gtoreq.-6.times.10.sup.18x+7.times.10.sup.20
[0047] Thus, by specifying the thickness "t" (.ANG.), the Hall
mobility "x" (cm.sup.2/V.multidot.s) and the carrier concentration
"y" (cm.sup.-3), the radiant heat preventive film 6 that has an
outstanding radiant heat prevention effect can be manufactured
easily. The Hall mobility "x" and the carrier concentration "y",
etc., can be measured by using a well-known Hall-effect measuring
instrument.
[0048] If the carrier concentration is higher than
1.5.times.10.sup.21 cm.sup.-3, in almost all cases, it is not
correlated to the Hall mobility and will satisfy all conditions
mentioned above. However, if the carrier concentration reaches the
order of 10.sup.22 cm.sup.-3, the film also reflects visible light
to cause some problems. Therefore, in the radiant heat preventive
film of the heat insulating container, the carrier concentration is
preferably lower than 10.sup.22 cm.sup.-3 and higher than
1.5.times.10.sup.21 cm.sup.-3.
[0049] On the other hand, the higher the Hall mobility is, the
steeper the raise of the reflectivity in a reflection spectrum is,
and thus the resulting reflectivity is higher, wherein the raise of
the reflectivity means a change of the reflectivity from a low
reflectivity region to a high reflectivity region within a narrow
wavelength range. Therefore, the higher the Hall mobility is, the
better the performance is. As the reflectivity is increased
dramatically, the electromagnetic waves having a specific
wavelength range corresponding to the radiant heat to be reflected
can be reflected in high efficiency.
[0050] Next, with reference to FIG. 2, a manufacture method of the
heat insulating container according to a preferred embodiment of
this invention is described.
[0051] Firstly, an inner container 2 is molded with a desired
shape, and an outer container 3 is molded with a shape basically
similar to that of the inner container 2, and with a sufficient
size so that the inner container 2 can be housed therein with a gap
4 between them. The outer container 3 is divided into an upper
outer container 7 including an opening end 3b and a lower outer
container 8 including a tip tube 11.
[0052] Next, an intermediate film 5 is formed on the external
surface 2a of the inner container 2 and the internal surface 3a of
the outer container 3.
[0053] The intermediate film 5 can be formed, for example, by
conducting a sol-gel process.
[0054] Firstly, a starting material, such as
Si(OC.sub.2H.sub.5).sub.4, is mixed with C.sub.2H.sub.5OH, water
and hydrochloric acid as a catalyst in predetermined ratios,
thereby forming an intermediate film material solution. This
intermediate film material solution is made to adhere to overall
surfaces of the external surface 2a of the inner container 2 and
the internal surface 3a of the outer container 3 by using, for
example, a coating process like a spin coating process or a dip
coating process.
[0055] The thickness of the intermediate film 5 can be controlled
to a desirable one by properly adjusting the concentration of the
starting material in the intermediate film material solution and/or
adjusting the number of times of applying the above material
solution. It is preferable to set the above thickness according to
the dimensions (depth, etc.) of the flaws on the inner container 2
or the outer container 3. For example, when the intermediate film
material solution with the aforementioned composition is applied
only once, an intermediate film 5 with a thickness of 0.1 to 0.5
.mu.m is formed. Therefore, if the maximum depth of the flaws is
around 1 .mu.m, it is preferable that the intermediate film
material solution is applied several times, e.g., two times, so
that the flaws are completely filled with the intermediate film
material.
[0056] Next, the inner container 2 and the outer container 3 are
subjected to a heat treatment, by which the intermediate film
material is thermally decomposed to form an intermediate film 5
containing SiO.sub.2 on the external surface 2a of the inner
container 2 and the internal surface 3a of the outer container 3.
The temperature of the heat treatment is preferably within a range
of about 300 to 600.degree. C. If the temperature does not reach
the above range, the decomposition of the intermediate film
material is insufficient, raising a concern of a weak adherence of
the intermediate film 5 to the inner and the outer containers 2 and
3. Meanwhile, if the temperature is over the upper limit, the cost
of the heat treatment is increased. In addition, such a temperature
exceeds the heat-resistant temperature of the inner and the outer
containers 2 and 3, and is therefore not preferable.
[0057] It is desirable to confirm completion of the thermal
decomposition and the drying step of the intermediate film 5 by
performing a Thermogravity/Differential Thermal Analysis (TG-DTA)
and analyzing the characteristic temperatures obtained from the
TG-DTA curve. Moreover, a cross-sectional photograph of the
container can be taken to help to confirm the completion of the
steps.
[0058] Next, a metal oxide film is formed on the intermediate film
5. The metal oxide film is turned into a radiant heat preventive
film 6 containing the metal oxide by performing a heat treatment (a
calcination treatment), which is described later.
[0059] The metal oxide film can be formed by, for example, applying
a material solution that contains a raw material such as a metal
complex with a sol-gel coating process, a spraying process using
hot spray mechanism, a spin coating process or a coating process
using dip coating mechanism, etc., performing an annealing process
at a temperature ranging from 400.degree. C. to 500.degree. C. in
the atmosphere, and then cooling the product at 200.degree. C.
[0060] Besides, the metal oxide film can be also formed by
depositing a metal oxide material on the external surface 2a of the
inner container 2 or the internal surface 3a of the outer container
3 by using a vapor-phase deposition method, such as a vacuum
evaporation method, a sputtering method, and an ion plating
method.
[0061] Next, the inner container 2 and the outer container 3 are
integrally joined together.
[0062] At first, the upper part of the inner container 2 is housed
in the upper outer container 7, and the opening end 3b of the upper
outer container 7 and opening end 2b of the inner container 2 are
melted and joined together in an airtight manner. Next, the lower
outer container 8 is situated cover the lower part of the inner
container 2, and the lower end 7a of the upper outer container 7
and the upper end 8a of the lower outer container 8 are melted and
joined together in an airtight manner. In addition, some pads can
be disposed between the inner container 2 and both the upper outer
container 7 and the lower outer container 8, so that the inner
container 2 and the outer container 3 can be integrally joined
together with a gap 4 between them.
[0063] After the inner container 2 and the outer container 3 are
integrally joined together, the metal oxide film is subjected to a
heat treatment in a non-oxidative environment. The heat treatment
decomposes the metal oxide and thereby eliminates excess oxygen
atoms from the metal oxide film, by which the carrier concentration
and the Hall mobility of the metal oxide film are raised, and its
reflectivity with a wavelength of 15 .mu.m therefore reaches 35% or
higher. That is, the metal oxide film has been converted to a
radiant heat preventive film 6 having a superior radiant-heat
insulating capability.
[0064] The non-oxidative environment is, for example, a vacuum
environment, an environment filled with an inactive gas, or an
environment filled with an inactive gas that is mixed with a
reductive gas such as hydrogen.
[0065] In order to perform a heat treatment in a vacuum, the method
that heats a double-wall container in a vacuum using a
vacuum-heating furnace can be used. Moreover, argon, nitrogen,
krypton and xenon, etc., are mentioned as the inactive gas.
[0066] Moreover, if a mixed gas atmosphere that comprises an
inactive gas added with a reductive gas like hydrogen is used, the
reductive gas can react with the oxygen atoms emitted from the
metal oxide film to prevent the oxygen atoms from reacting with the
metal oxide film again. Moreover, the reductive gas may directly
react with the metal oxide to reduce the latter efficiently.
[0067] The inactive gas can be, for example, argon, nitrogen,
krypton, xenon or the like. Moreover, the reductive gas is
preferably hydrogen. The addition amount of the reductive gas is
preferred 0.01-1% by volume ratio to the whole mixed gas of the
inactive gas and the reductive gas. For example, the addition
amount can be 0.1%.
[0068] In order to successfully establish a non-oxidative
environment around the metal oxide film before the heat treatment,
the air in the gap 4 is exhausted, or an inactive gas is introduced
into the gap through the tip tube 11. Moreover, when the inactive
gas used for the heat treatment is a low-thermal-conductivity gas,
such as argon, krypton or xenon, the low-thermal-conductivity gas
can be retained in the gap 4, and then the gap 4 is sealed up to
act as a heat insulating layer.
[0069] The temperature of the heat treatment is preferably
400.degree. C. or higher, and more preferably from 400 to
600.degree. C. Moreover, the heating time is preferably 10 minutes
or longer. If the heating temperature or the heating time does not
reach the above range, the reduction of the metal oxide film is
insufficient.
[0070] If the heat temperature is over the above range, the cost of
the heat treatment is increased. In addition, such a heating
temperature exceeds the heat-resistant temperature of the inner and
the outer containers 2 and 3, and is not preferable.
[0071] With the heat treatment, the metal oxide film is converted
to a blackish or blueish transparent film that functions as a
radiant heat preventive film 6. The resistivity of the metal oxide
film is drastically decreased with the above heat treatment, so
that the resulting radiant heat preventive film 6 has a resistivity
far lower than that of the original metal oxide film. For example,
when the resistivity of the original metal oxide film is in the
order of 10.sup.-3 .OMEGA..multidot.cm, the resistivity of the
resulting radiant heat preventive film 6 can be decreased to a
value smaller than that of the metal oxide film by one order of
magnitude, which is in the order of 10.sup.-4
.OMEGA..multidot.cm.
[0072] On the other hand, the carrier concentration of the radiant
heat preventive film 6 is significantly higher than that of the
pre-treatment metal oxide film. For example, when the carrier
concentration of the metal oxide film is in the order of 10.sup.19
cm.sup.-3, the carrier concentration of the radiant heat preventive
film 6 can be increased to the order of 10.sup.20 to 10.sup.21
cm.sup.-3.
[0073] Finally, after the radiant heat preventive film 6 is formed,
the gap 4 is made vacuum and the exhausting tip tube 11 is sealed.
It is also applicable to introduce a low-thermal-conductivity gas,
such as argon, krypton or xenon, into the gap 4 and then seal the
exhausting tip tube 11. Thus, with the processes described
heretofore, the heat insulating container 1 of the present
invention is obtained.
[0074] As mentioned above, the heat insulating container 1
according to the preferred embodiment of the invention has the
radiant heat preventive film 6, which has a reflectivity of 35% or
higher with a wavelength of 15 .mu.m and therefore can efficiently
reflect infrared rays and prevent radiant heat. Therefore, the heat
insulating container 1 is excellent in heat insulting capability.
Moreover, the radiant heat preventive film 6 is transparent in the
field of visible light, and therefore has an advantage that the
contents of the container can be seen from the outside.
[0075] Moreover, since the metal oxide film as a precursor of the
radiant heat preventive film 6 is formed before the inner container
2 and the outer container 3 is integrally joined, it is not
restricted to form by pouring a material solution into the gap 4. A
variety of methods are thus possible for forming the film, which is
an advantage of the invention. For example, the film can be formed
by using a vapor-phase method like an evaporation method, but not
restricted to form by using a liquid-phase method like a sol-gel
method. For this reason, the optimal film formation method can be
chosen, the cost of film formation can be reduced, and the
productivity can be improved.
[0076] It is noted, of course, that there are also various methods
for forming the intermediate film 5 on the heat insulating
container 1, and the resulting effects are the same as those
mentioned in the above cases of forming the metal oxide film.
[0077] Next, the second embodiment of fabricating the heat
insulating container 1 of this invention is described. In the
second embodiment, the intermediate film 5 and the metal oxide film
as the precursor of the radiant heat preventive film 6 are formed
after the inner container 2 and the outer container 3 are
integrally joined together. At first, like the previous embodiment
of the manufacture method of the heat insulating container 1, the
inner container 2 and the outer container 3 are formed and
integrally joined together to form a double-wall container.
[0078] Next, an intermediate film 5 is formed on the external
surface 2a of the inner container 2 and the internal surface 3a of
the outer container 3. The intermediate film 5 can be formed by
using a sol-gel method. Then, a radiant heat preventive film 6 is
formed on the intermediate film 5.
[0079] Hereafter, the sol-gel method for forming the radiant heat
preventive film 6 is described.
[0080] At first, a material solution containing a metal complex
like an acetylacetone-metal complex as a starting material of a
metal oxide is prepared. This material solution is poured into the
gap 4 through the tip tube 11, thereby adhering to the overall
surface of the intermediate film 5. The excess material solution is
drawn out through the tip tube 11. By heating the double wall
container as required, the solvent in the material solution and the
volatile by-products generated from the reaction are drawn out
through the tip tube 11. Although the heating temperature depends
on the properties of the material solution used, it is preferable
to heat the container at about 190.degree. C. in general if a
material solution containing an acetylacetone-metal complex is
used.
[0081] Next, the double wall container is heated under an oxygen
containing atmosphere such as air. The heating temperature is
preferably 400.degree. C. or higher, and more preferably from
400.degree. C. to 600.degree. C. The heating time is preferably 10
minutes or higher.
[0082] If the heating temperature and the heating time do not reach
the above ranges, the thermal decomposition of the material
solution is insufficient, and a metal oxide film having a desired
composition is difficult to obtain. Meanwhile, if the heat
temperature is over the above range, the cost of the heat treatment
is increased. In addition, such a heating temperature exceeds the
heat-resistant temperature of the inner and the outer containers 2
and 3, and is therefore not preferable.
[0083] With the heat treatment, the starting material is thermally
decomposed, and a metal oxide film is formed thereby.
[0084] Next, in order to increase the radiant heat prevention
capability of the metal oxide film, the double wall container is
further heated in a non-oxidative environment (e.g., in vacuum) to
implement a heat treatment to the metal oxide film. The steps and
the conditions of the heat treatment are the same as the
above-mentioned.
[0085] With the heat treatment, the metal oxide film can function
as a radiant heat preventive film 6. The resistivity of the metal
oxide film is drastically decreased with the above heat treatment,
so that the resulting radiant heat preventive film 6 has a
resistivity far lower than that of the original metal oxide film.
On the other hand, the carrier concentration of the radiant heat
preventive film 6 is significant higher than that of the
pre-treatment metal oxide film.
[0086] Finally, the gap 4 is made vacuum and the tip tube 11 is
sealed. It is also applicable to introduce a
low-thermal-conductivity gas, such as argon, krypton or xenon, into
the gap 4 and then seal the exhausting tip tube 11. Thus, with the
processes described heretofore, the heat insulating container 1 of
the present invention is obtained.
[0087] Although this invention has been explained with the
embodiments set forth above, various modifications can be made to
the present invention without departing from the scope or the
spirit of the invention.
[0088] For example, although the radiant heat preventive film 6 is
formed on both the external surface 2a of the inner container 2 and
the internal surface 3a of the outer container 3 in the
embodiments, it is not limited to form with the implementation. For
example, the radiant heat preventive film 6 may be form only on
either the external surface 2a of the inner container 2 or the
internal surface 3a of the outer container 3. In such cases, the
radiant heat preventive film 6 can be formed by using the following
method. At first, a metal oxide film is formed on either the
external surface 2a of the inner container 2 or the internal
surface 3a of the outer container 3 before the inner and the outer
containers 2 and 3 is integrally joined together. After the inner
and outer containers 2 and 3 are integrally joined together, the
metal oxide film is subjected to a heat treatment to form the
radiant heat preventive film 6. In such cases, the heat insulating
container 1, which reduces the amount of the expensive metal oxide
materials, and, furthermore, reduces the fabricating cost, is also
excellent in heat insulating capability.
[0089] Moreover, in the manufacture method of the heat insulating
container of the invention, it is also feasible to form the metal
oxide film in two or more steps, wherein some steps are before and
the other steps are after the inner and outer containers 2 and 3
are integrally joined together.
[0090] In addition, it is also possible to form the intermediate
film 5 before the inner and the outer containers 2 and 3 are
integrally joined together, and then form the metal oxide film and
conduct a heat treatment to form the radiant heat preventive film 6
after the inner and the outer containers 2 and 3 are integrally
joined together.
Examples of the Invention
[0091] Firstly, as shown below, five kinds of radiant heat
preventive films (sample 1-5) are produced (Samples 1-5).
[0092] [Sample 1]
[0093] A material solution for a metal oxide film having the
following composition is prepared.
[0094] Acetylacetone-metal complex: 10 wt %
[0095] Free acetylacetone: 10 wt %
[0096] Isopropyl alcohol: 25 wt %
[0097] Ethanol: 25 wt %
[0098] Propylene glycol: 30 wt %
[0099] 4 wt % of Metal (In: Sn=95:5) is contained in this material
solution.
[0100] After the above-mentioned material solution is applied to a
glass substrate, a spin coating process is performed at 500 rpm for
3 seconds, and then at 1000 rpm for 15 seconds. Thereafter, the
glass substrate is heated and dried at 190.degree. C. in the
atmosphere for 30 minutes. Next, thermal decomposition of the
above-mentioned materials is carried out at 400.degree. C. in the
atmosphere, and the resulting film is heated at 400.degree. C. in
vacuum to form a uniform film of 1000 .ANG. in thickness.
[0101] The above-mentioned operation is performed for three times
to form a film of 3000 .ANG. in thickness.
[0102] Furthermore, the obtained film is heated at 500.degree. C.
in the atmosphere for 60 minutes. The metal complex is under
thermal decomposition in the heat treatment, and a metal oxide film
is formed containing sintered and crystallized ITO. Thereafter, the
resistivity, the carrier concentration, the Hall mobility, and the
reflectivity in an infrared domain of the metal oxide film are
measured.
[0103] Then, the film is heated under 600.degree. C. in vacuum for
60 minutes. After the heat treatment in vacuum, the resistivity,
the carrier concentration and the Hall mobility of the metal oxide
film are measured again using a Hall-measuring instrument (BIO RAD
Co. HL-5500), and the reflectivity in an infrared domain of the
metal oxide film is measured using a FT-IR spectrometer.
[0104] [Sample 2]
[0105] Except the metal ratio is changed to 90:10, the radiant heat
preventive film is formed with the same procedure for preparing
Sample 1. In this case, before and after the heat treatment in
vacuum, the resistivity, the carrier concentration, the Hall
mobility and the reflectivity in an infrared domain of the metal
oxide film are measured.
[0106] [Sample 3]
[0107] Except the metal ratio is changed to 85:15, the radiant heat
preventive film is formed with the same procedure for preparing
Sample 1. In this case, before and after the heat treatment in
vacuum, the resistivity, the carrier concentration, the Hall
mobility and the reflectivity in an infrared domain of the metal
oxide film are measured.
[0108] [Sample 4]
[0109] Except the metal ratio is changed to 85:15 and spin coating
are performed for five times to form a film of 5000 .ANG. in
thickness, the radiant heat preventive film is formed with the same
procedure for preparing Sample 1. In this case, before and after
the heat treatment in vacuum, the resistivity, the carrier
concentration, the Hall mobility and the reflectivity in an
infrared domain of the metal oxide film are measured.
[0110] [Sample 5]
[0111] A material having the same metal ratio of Sample 1 is used
to form a metal oxide film containing ITO with a thickness of 3200
.ANG., using an electronic beam evaporation method in replacement
of the above-mentioned spin coating method. Next, the obtained film
is heated at 500.degree. C. in the atmosphere for 60 minutes to
form a film containing sintered and crystallized ITO. Thereafter,
the resistivity, the carrier concentration, the Hall mobility and
the reflectivity in an infrared domain of the metal oxide film are
measured.
[0112] Then, the film is heated at 600.degree. C. in a vacuum state
for 60 minutes. After the heat treatment in vacuum, the same method
for measuring Sample 1 is used to measure the resistivity, the
carrier concentration, the Hall mobility and the reflectivity in an
infrared domain of the metal oxide film.
[0113] [The Measurement Results of the Radiant Heat Preventive
Film]
[0114] The measurement results of the resistivities, the carrier
concentrations, the Hall mobilities, and the reflectivities in an
infrared domain of the metal oxide films of the five samples
mentioned above are respectively shown in FIGS. 3-10. Meanwhile,
the results for resistivity, carrier concentration and Hall
mobility are listed in Table 1.
[0115] It is shown in Table 1 and FIG. 3 that the resistivity is
reduced by about 1 order with the heating treatment, i.e., from the
order of 10.sup.-2 .OMEGA..multidot.cm to the order of 10.sup.-3
.OMEGA..multidot.cm. Meanwhile, the carrier concentration is
increased with the heat treatment, as shown in Table 1 and FIG. 4.
As shown in Table 1 and FIG. 5, the Hall mobility is also increased
with the heat treatment.
[0116] Moreover, as shown in FIGS. 6-10, for all samples, it is
clear that the reflectivity of the film is increased with vacuum
calcination, which means that the manufacture method with vacuum
calcination is more suitable for the radiant heat preventive film
of a heat insulating container.
[0117] In addition, in the reflection spectra of these samples,
although some peaks are present around wavelengths of 9 .mu.m and
22 .mu.m, they are actually caused by the reflection of the glass
substrate, rather than the radiant heat preventive film (ITO film).
The cause of the peaks near the two wavelengths can be confirmed by
practically measuring the reflectivity of the glass substrate
only.
1 TABLE 1 Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Before
Vacuum Calcination Resistivity 2.27E-2 1.48E-2 1.60E-2 1.07E-2
1.24E-2 (.OMEGA. .multidot. cm) Carrier Con- 2.73E+20 2.53E+20
1.90E+20 2.27E+20 4.44E+20 centration (cm.sup.-3) Hall mobility
1.01 1.67 2.04 2.57 11.4 (cm.sup.2/V .multidot. s) After Vacuum
Calcination Resistivity 4.03E-3 2.22E-3 4.26E-3 1.00E-3 8.26E-4
(.OMEGA. .multidot. cm) Carrier Con- 2.68E+20 6.82E+20 6.12E+20
1.19E+21 5.57E+20 centration (cm.sup.-3) Hall mobility 5.70 4.12
3.90 5.24 13.6 (cm.sup.2/V .multidot. s)
[0118] Next, the temperature for the vacuum calcination is lowered,
and the same experiment is conducted using the same samples. When
the temperature for the vacuum calcination is lowered below
400.degree. C., the effect in raising the reflectivity is small. If
the calcination temperature is reduced down below 300.degree. C.,
almost no increase is seen in the reflectivity.
[0119] Next, when the vacuum environment is replaced with an
environment using a mixed gas atmosphere formed by adding 0.1% of
hydrogen into nitrogen, the reflectivity of the metal oxide film is
also increased with the heat treatment, as in the cases of adopting
a vacuum environment. In addition, when the vacuum environment is
replaced with an environment using 100% of nitrogen, the
reflectivity of the metal oxide film is also increased with the
heat treatment, as in the cases of adopting a vacuum
environment.
[0120] FIG. 11 plots the carrier concentration with respect to the
Hall mobility for the metal oxide (ITO) films of several samples,
wherein the ITO films has a thickness of about 3000 .ANG.. The data
points are shown in different marks depending on whether the
corresponding reflectivity of the film is 35% or higher with a
wavelength of 15 .mu.m or not.
[0121] From the figure, it is clearly shown that if the Hall
mobility is more than 3.9 cm.sup.2/v.multidot.s and the carrier
concentration is more than 5.times.10.sup.20/cm.sup.3, the ITO film
can have a reflectivity of 35% or higher with a wavelength of 15
.mu.m, so as to function as a radiant heat preventive film.
Moreover, even if the carrier concentration is lower than
5.times.10.sup.20/cm.sup.3, the reflectivity can still be 35% or
higher if the Hall mobility is sufficiently high. Analogously, even
if the Hall mobility is smaller than 4 cm.sup.2/V.multidot.s, the
reflectivity can still be 35% or higher if the carrier
concentration is sufficiently high.
[0122] According to the above results, when the thickness of the
radiant heat preventive film is 3000 .ANG., the reflectivity can be
35% or higher if the following formulae are satisfied. The formulae
are express as follows:
y.gtoreq.-5.times.10.sup.20x+2.times.10.sup.21 (1)
y.gtoreq.-6.times.10.sup.18x+3.times.10.sup.20 (2)
[0123] wherein "x" is the Hall mobility (cm.sup.2/V.multidot.s),
and "y" is the carrier concentration (cm.sup.-3).
[0124] Next, several samples having a radiant heat preventive film
of 5000 .ANG. in thickness are manufactured, and the relationship
between the Hall mobility and the carrier concentration is shown in
FIG. 12 in a similarly manner. The data points are shown in
different marks depending on whether the reflectivity is 35% or
higher with a wavelength of 15 .mu.m or not.
[0125] As shown in the figure, if the Hall mobility is higher than
3.8 cm.sup.2/V.multidot.s and the carrier concentration is higher
than 7.times.10.sup.20/cm.sup.3, the film can have a reflectivity
of 35% or higher with a wavelength of 15 .mu.m, so as to function
as a radiant heat preventive film. In addition, even if the carrier
concentration is lower than 7.times.10.sup.20/cm.sup.3, the
reflectivity can still be 35% or higher if the Hall mobility is
sufficiently high. Analogously, even if the Hall mobility is lower
than 3.8 cm.sup.2/V.multidot.s, the reflectivity can still be 35%
or higher if the carrier concentration is sufficiently high.
[0126] According to the above results above, when the thickness of
the radiant heat preventive film is 5000 .ANG., the reflectivity
can be 35% or higher if the following formulae are satisfied. The
formulae are express as follows:
y.gtoreq.-5.times.10.sup.20x+3.times.10.sup.21 (3)
y.gtoreq.-6.times.10.sup.18x+7.times.10.sup.20 (4)
[0127] wherein "x" is the Hall mobility (cm.sup.2/V.multidot.s),
and "y" is the carrier concentration (cm.sup.-3).
[0128] According to formulae (1)-(4), when the thickness of the
film is around 3000 .ANG. to 5000 .ANG., the film should have a
Hall mobility "x" (cm.sup.2/V.multidot.s), a carrier concentration
"y" (cm.sup.-3) and a thickness "t" (.ANG.) satisfying the
following formulae to have a reflectivity of 35% or higher. The
formula are derived based on an interpolation or extrapolation
algorithm:
y.gtoreq.-5.times.10.sup.20x+5.times.10.sup.17t+0.5.times.10.sup.21
(5)
y.gtoreq.-6.times.10.sup.18x+2.times.10.sup.17t-3.times.10.sup.20
(6)
[0129] [Examples of Manufacture of a Glass Heat Insulating
Container]
[0130] As shown in FIG. 2, the heat insulating container of the
embodiment is an inner body of a vacuum flask, and is constituted
of an inner glass container 2 and an outer glass container 3.
[0131] Firstly, an inner container 2 is molded with a desired
shape, and an outer container 3 is molded with a shape basically
similar to that of the inner container 2, and with a sufficient
size so that the inner container 2 can be housed therein with a gap
4 formed in-between. The outer container 3 is divided into an upper
outer container 7 including an opening end 3b and a lower outer
container 8 including a tip tube 11. Next, the opening end 2b of
the inner container 2 is housed in the upper outer container 7 with
pads disposed between them for creating a uniform gap 4. The
opening end 2b of the inner container 2 and the opening end 3b of
the outer container 3 are melted and integrally joined together in
an airtight manner. Next, the lower part of the inner container 2
is inserted into the lower outer container 8 with a gap 4
therebetween. Then, the upper outer container 7 and the lower outer
container 8 are melted near their joint and integrally joined
together to form a double wall container.
[0132] Next, a material solution used for forming the intermediate
film 5 is prepared having the following composition:
[0133] Si (OC.sub.2H.sub.5) 4: 28.9 wt %
[0134] C.sub.2H.sub.5OH: 43.897 wt % (remainder)
[0135] H.sub.2O: 27.2 wt %
[0136] HCl: 0.003 wt %
[0137] The obtained material solution is injected into the gap 4
from the tip tube 11, thereby adhering to all surfaces defining the
gap 4. Next, after excess material solution is drawn through the
tip tube 11, the double wall container is heated at 190.degree. C.
for 30 minutes. With the heat treatment, the volatile components
such as ethanol in the material solution are evaporated, and the
material solution is dried. After the inside of the double wall
container is confirmed to be fully dried, the heating temperature
is raised to about 500.degree. C., at which thermal decomposition
of the raw materials of the intermediate film 5 is induced.
[0138] The degree of dryness inside the double wall container and
the time point of completion of the hydrolysis-polycondensation
reaction of the raw materials of the intermediate film 5 are
determined according to the characteristic temperatures obtained
from a pre-confirmed TG-DTA (Thermogravity/Differential Thermal
Analysis) curve. In addition, as the material solution having the
above-mentioned composition is used, the thickness of the film
formed with only one time of the above-mentioned film formation
process is 0.1-0.5 .mu.m. Therefore, the film formation process
should be conducted twice for the desired thickness of the
intermediate film 5.
[0139] Next, a material solution used for forming the radiant heat
preventive film 6 is prepared having the following composition.
[0140] Acetylacetone-metal complex: 10 wt %
[0141] Free acetylacetone: 10 wt %
[0142] (CH.sub.3).sub.2CHOH: 25 wt %
[0143] Ethanol: 25 wt %
[0144] Propylene glycol: 30 wt %
[0145] 4 wt % of Metal (In: Sn=95:5) is contained in this material
solution.
[0146] The obtained material solution is injected into the gap 4
from the tip tube 11, thereby adhering to all surfaces defining the
gap 4. Next, after excess material solution is drawn through the
tip tube 11, the double wall container is heated at 190.degree. C.
The volatile components such as ethanol in the material solution
are evaporated, so that the material solution is dried. After the
inside of the double wall container is confirmed to be sufficiently
dry, the heating temperature is raised to about 500.degree. C., at
which thermal decomposition and crystallization of the raw material
of the radiant heat preventive film 6 occur.
[0147] The metal oxide (ITO) film obtained with thermal
decomposition is yellowish and transparent. Next, the glass
container is placed in a vacuum environment, and then heated at
400.degree. C. to implement a heat treatment of the metal oxide
film. With the heat treatment in vacuum, the metal oxide film is
turned into a blackish or blueish transparent film. After the
radiant heat preventive film 6 is formed, the gap 4 is made vacuum
and the exhausting tip tube 11 is sealed. The whole container is
then cooled, and the vacuum heat insulating container 1 is
manufactured. The volume of the heat insulating container 1 is 1000
cm.sup.3.
[0148] Furthermore, in order to test the heat insulating capability
of the heat insulating container 1 of the embodiment, 950 cm.sup.3
of hot water at 97.degree. C. is loaded into the heat insulating
container 1, which is then located in a thermostatic chamber with
an atmosphere temperature of 20.degree. C. After 6 hours, the
temperature of the hot water is reduced to 69.degree. C.
[0149] For comparison, another heat insulating container is
manufactured with the same procedure except that the container is
not subjected to vacuum calcination. Under the same testing
conditions, the temperature of the hot water is reduced to
50.degree. C. after 6 hours.
EFFECT OF THE INVENTION
[0150] As mentioned above, the heat insulating container of the
invention has a radiant heat preventive film having a reflectivity
of 35% or higher with a wavelength of 15 .mu.m. Since such a
radiant heat preventive film has a high radiant-heat prevention
capability, the heat insulating container is excellent in heat
insulating capability.
[0151] Moreover, in the manufacture method of the heat insulating
container of this invention, a radiant heat preventive film having
a high reflectivity can be formed by heating the heat insulating
container, on which a metal oxide film has been formed, at
400.degree. C. or higher in a non-oxidative environment such as a
vacuum. Therefore, a heat insulating container excellent in heat
insulating capability can be manufactured.
[0152] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *