A thermally-insulated double-walled container is disclosed made of synthetic resin which is formed by joining together an inner container and an outer container in a unitary fashion to form a space therebetween; wherein a thermoinsulating layer is formed in the space between the inner container and the outer container by filling the space with at least one low thermoconductive gas selected from the group consisting of xenon, krypton, and argon; and wherein the inner container and the outer container are multilayer molded from different synthetic resin materials. The container provides an excellent gas-barrier capacity without requiring plating of the outer surface of the inner container or the inner surface of the outer container in the double walled container and maintains its mechanical strength over a long period of time and having an excellent thermoinsulating capacity. The container is suitable as a thermos, cooler box, ice cooler, thermoinsulated cup, insulated lunch box, or the like.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a thermoinsulated double walled container 
that may be employed for a thermos, cooler box, ice cooler, 
thermoinsulated cup, insulated lunch box, or the like. More specifically, 
the present invention relates to a thermally-insulated double-walled 
synthetic-resin container which employs inner and outer containers formed 
by multilayer molding of different synthetic resins in an inner container 
and an outer container. 
2. Description of the Related Art 
Double walled containers made of glass, synthetic resins, or metals such as 
stainless steel or the like have been employed conventionally for this 
kind of thermoinsulated double walled container. A container formed of a 
synthetic resin offers numerous advantages, including being lightweight, 
easily molded, able to assume a variety of shapes, and inexpensive to 
produce. Accordingly, numerous advances have been made in the development 
of these thermally-insulated double-walled synthetic-resin containers. 
Among these thermally-insulated double-walled synthetic-resin containers, 
there is a vacuum double-walled structure in which a vacuum layer is 
created in the space between the double walls, and an thermal insulation 
structure in which insulating material such as foam is used to fill the 
space between the double walls. However, in the case of the former, 
restrictions must be placed on the shape of the container in order to 
obtain a pressure resistant structure, and production costs are high, 
while in the case of the latter, the thermoinsulating capacity is poor and 
the thermoinsulating layer becomes thick causing the effective volume 
ratio to decrease. To resolve these problems, a thermally-insulated 
double-walled synthetic-resin container was proposed in which the space 
between the double walls is filled with a gas which has a low rate of 
thermoconductivity. Furthermore, in order to increase the gas-barrier 
capacity of the thermoinsulating layer, which is formed by filling the 
space between the double walls with a gas of low thermoconductivity, in 
this thermally-insulated double-walled synthetic-resin container, chemical 
or electroplating is used to form a metallic coating to the outer surface 
of the inner container and to the inner surface of the outer container 
which are in contact with the thermoinsulating layer. 
However, when forming a double walled container by joining the mouth 
openings of each of the inner container and the outer container in a 
unitary fashion, it may not be possible to obtain sufficient joining if 
there is metallic coating remaining around the area of joining between the 
inner and outer containers. As a result, when forming the metallic coating 
to the inner surface of the outer container and the outer surface of the 
inner container, it is necessary to perform masking by some method of the 
area of joining in order to prevent formation of the metallic coating 
there. Further, a opening for charging gas provided for introducing a low 
thermoconductive gas into the thermoinsulating layer must be sealed by 
bonding or welding a sealing plate thereto. Thus, in order to ensure that 
bonding or welding can be carried out completely, it is also necessary to 
carry out masking of the opening for charging gas to prevent formation of 
the metallic coating there. Since masking of this type demands a high 
degree of accuracy, it becomes very expensive. Further, an additional 
disadvantage is incurred in that the cost of electroplating or the like 
after masking also becomes expensive. 
Moreover, when a synthetic resin material having a high gas-barrier 
capacity is employed in the formation of a thermoinsulated double walled 
container, it is generally the case that many of these resins are highly 
hygroscopic. When these resins absorb moisture, their capacity to act as a 
gas-barrier deteriorates substantially over time. Further, depending upon 
the type of resin, the mechanical strength may decrease, with resins which 
are highly hygroscopic experiencing a deterioration in mechanical strength 
due to absorption of moisture. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention has as its objective the provision at 
low cost of a thermally-insulated double-walled synthetic-resin container 
wherein an excellent gas-barrier capacity is obtained without requiring 
plating of the outer surface of the inner container or the inner surface 
of the outer container in the double walled container, the container 
maintaining its mechanical strength over a long period of time and having 
an excellent thermoinsulating capacity. 
The thermally-insulated double-walled synthetic-resin container of the 
present invention is provided with inner and outer containers, and is 
formed by joining the inner container and the outer container together in 
a unitary manner to form a space therebetween. A thermoinsulating layer is 
formed in the space between the inner and outer containers by filling the 
space with at least one gas having a low thermoconductivity rate from 
among the gases xenon, krypton, and argon. The inner and outer containers 
are formed by multilayer molding of different synthetic resins. 
In this thermally-insulated double-walled synthetic-resin container, the 
inner container and the outer container may be formed using two-color 
molding wherein each of the containers has a bilayer comprising an inner 
layer and an outer layer. Moreover, these outer layers and inner layers 
may be formed from different synthetic resin materials. 
In the case of a container in which the inner and outer containers are 
two-color molded from synthetic resins in which the inner and outer layers 
are different, synthetic resins are selected which are resistant to the 
respective environments to which the inner and outer layers of the inner 
container and the inner and outer layers of the outer container will be 
exposed. As a result, thermoinsulating capacity and mechanical strength 
can be maintained over a long period of time. 
Further, the outer layer of the inner container and the inner layer of the 
outer container may be formed of a resin having a high gas-barrier 
capacity, with the inner layer of the inner container and the outer layer 
of the outer container formed of a moisture resistant resin. 
In the case of two-color molding in which the outer layer of the inner 
container and the inner layer of the outer container are formed of a resin 
having a high gas-barrier capacity, while the inner layer of the inner 
container and the outer layer of the outer container are formed of a 
moisture resistant resin. As a result, the low thermoconductive gas which 
fills the space between the inner and outer containers cannot readily pass 
though the high gas-barrier synthetic resin layer which is in contact with 
the thermoinsulated layer between the inner and outer containers. At the 
same time, the external atmosphere cannot easily pass through this high 
gas-barrier synthetic resin layer to enter into the thermoinsulating 
layer. In addition, the inner layer of the inner container and the outer 
layer of the outer container which are in contact with the atmosphere 
outside the thermoinsulated double walled container do not readily absorb 
moisture, thus the moisture resistance of the container increases. 
Further, the inner container and the outer container may also be formed by 
means of sandwich molding, wherein each container has an inner layer, an 
outer layer, and an intermediate layer formed between these inner and 
outer layers. The inner and outer layers and the intermediate layer may be 
formed of different synthetic resins. 
In the case of a container wherein a different synthetic resin is sandwich 
molded between the inner and outer layers in each of the inner and outer 
containers, this intermediate layer resin is protected by the inner and 
outer layers of the containers. By selecting a synthetic resin which is 
resistant to the environments to which the inner and outer layers will be 
exposed, the thermoinsulating capacity and the mechanical strength of the 
container can be maintained over a long period of time. 
Moreover, the inner and outer layers of the inner container and the outer 
container may also be formed of a moisture resistant resin, while the 
intermediate layer may be formed of a gas-barrier resin. 
In the case of sandwich molding, the inner and outer layers of the inner 
container and the outer container are formed of a moisture resistant 
resin, while the intermediate layers of the inner container and the outer 
container are formed of a gas-barrier resin. As a result, this prevents 
deterioration in the container's performance caused by the gas-barrier 
resin in the intermediate layer becoming wet. Thus, the resin's high 
gas-barrier capacity can be maintained over a long period of time. As a 
result, the high gas-barrier synthetic resin layer in contact with the 
thermoinsulating layer, or the high gas-barrier synthetic resin layer in 
the intermediate layer are protected by the layer of moisture resistant 
synthetic resin which is in contact with the outside atmosphere. 
Accordingly, a deterioration in mechanical strength and gas-barrier 
capacity due to absorption of moisture by the high gas-barrier synthetic 
resin is prevented. Thus, the container is maintained in a good condition, 
with the thermoinsulating capacity and mechanical strength which the 
thermoinsulated double walled container initially demonstrated being 
maintained over a long period of time. 
Moreover, a opening for charging gas of a diameter of 0.1 to 3 mm is formed 
in the wall of either the inner container or the outer container. This 
opening for charging gas may be designed to be sealed with a sealing plate 
which is multilayer molded using a gas-barrier resin and a moisture 
resistant resin. 
By forming a opening for charging gas of a diameter of 0.1 to 3 mm in the 
wall of either the inner container or the outer container, and sealing the 
opening for charging gas with a sealing plate which is formed by two-color 
molding of a gas-barrier resin and a moisture resistant resin, or with a 
sealing plate which is formed by sandwich molding a gas-barrier resin as 
an intermediate layer between inner and outer layers of a moisture 
resistant resin, the diameter of the sealing area becomes smaller and the 
risk that gas will leak from the sealing area during sealing is reduced. 
Moreover, in the case where employing a two-color molded sealing plate to 
seal a opening for charging gas that is formed in the outer container, the 
inner and outer layers of the sealing plate may be molded from a synthetic 
resin having the same characteristics as the inner and outer layers of the 
outer container. When sandwich molding the sealing plate, the inner and 
outer layers and the intermediate layer of the sealing plate may be molded 
using synthetic resins having the same characteristics as the resins 
employed for the inner and outer layers and the intermediate layer of the 
inner container and outer container. Since the opening for charging gas is 
sealed with a sealing plate of this type, a sealing area having a 
gas-barrier capacity, as well as moisture resistance and mechanical 
strength characteristics identical to those of the inner and outer 
containers can be obtained. Thus, gas does not leak in through or out from 
the sealing plate. Additionally, since the sealing plate is attached to 
the opening for charging gas by bonding or welding, its attachment is 
easy. 
A metallic radiation shielding material may be disposed to at least one of 
either the outer surface of the inner container or the inner surface of 
the outer container, or to the space between the inner and outer 
containers. This metallic radiation shielding material may be one material 
selected from the group comprising aluminum foil, copper foil, or 
metalized tape. 
By disposing a metallic radiation shielding material, and in particular a 
material selected from the group comprising aluminum foil, copper foil and 
metalized tape, to at least one of either the outer surface of the inner 
container or the inner surface of the outer container, or to the space 
between the inner and outer containers, it becomes possible to prevent 
radiant heat transmission at low cost as compared to the case where a 
metallic coating of electroplating or the like is formed to the inner 
surface of the outer container and the outer surface of the inner 
container which are in contact with the thermoinsulating layer. 
Accordingly, it is possible to provide a thermoinsulated double walled 
container having an excellent heat retention capacity at low cost.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 through 3 show a first example of the thermally-insulated 
double-walled synthetic-resin container of the present invention. In this 
example, the thermally-insulated double-walled synthetic-resin container 
of the present invention is suitably employed in a thermoinsulated cup 1 
(thermoinsulated mug) such as shown in FIG. 1. 
In the thermoinsulated cup 1, a space 6 is formed between an inner 
container 2, which is two-color molded into a bilayer of an inner 
container inner layer 2a and an inner container outer layer 2b, and an 
outer container 3, which is two-color molded into a bilayer of an outer 
container inner layer 3a and an outer container outer layer 3b. A double 
walled container 1a is formed by joining inner container 2 and outer 
container 3 in a unitary fashion at a mouth joining area 4 between their 
respective flanges 2c, 3c. Further, a radiation shielding material 7 
consisting of a metal foil is disposed to space 6 between inner container 
2 and outer container 3. A thermoinsulating layer 8 is formed by filling 
space 6 with at least one type of low thermoconductive gas selected from 
the group of xenon, krypton, and argon. This thermoinsulated cup 1 is 
formed in the shape of a cylinder with a bottom, and has an opening 5 
formed at the upper edge thereof. 
A opening 3d for charging gas is formed in the bottom of outer container 3, 
and is sealed by bonding or welding a two-color molded sealing plate 9 
thereto. Additionally, a handle 10 is attached to the side of outer 
container 3. 
Space 6 is filled with at least one type of low thermoconductive gas 
selected from the group of xenon, krypton, and argon. These gases have 
thermoconductivity rates .kappa. which are smaller than that of air 
(.kappa.=2.41.times.10.sup.-2 W.multidot.m.sup.-1 .multidot.K.sup.-1 at 
0.degree. C.), being .kappa.=0.52.times.10.sup.-2 W.multidot.m.sup.-1 
.multidot.K.sup.-1 at 0.degree. C. in the case of xenon, 
.kappa.=0.87.times.10.sup.-2 W.multidot.m.sup.-1 .multidot.K.sup.-1 at 
0.degree. C. in the case of krypton, and .kappa.=1.63 .times.10.sup.-2 
W.multidot.m.sup.-1 .multidot.K.sup.-1 at 0.degree. C. in the case of 
argon. Moreover, these are inert gases. These gases may be used alone or 
in a mixture of 2 or more. By employing these low thermoconductive gases, 
it is possible to provide a thermoinsulated double walled container 1 
having a high thermoinsulating capacity. Moreover, because these gases are 
inert, they do not pose a danger to the environment, making them ideal for 
use. Filling space 6 with these gases is carried out at room temperature 
and atmospheric pressure. 
This thermally-insulated double-walled synthetic-resin container, which is 
formed by joining an inner container and an outer container in a unitary 
fashion and filling the space between these inner and outer containers 
with at least one low thermoconductive gas selected from among xenon, 
krypton, and argon at room temperature and atmospheric pressure to form a 
thermoinsulating layer, resolves the defects encountered in conventional 
products which employ a vacuum double-walled structure or an thermal 
insulation structure where an insulating material is used to fill the 
space between the inner and outer containers. As a result, it is possible 
to provide at low cost a thermally-insulated double-walled synthetic-resin 
container which has an excellent thermoinsulating capacity (heat retention 
capacity), a high effective volume ratio, and which can be freely shaped. 
Inner container 2 and outer container 3 are two-color molded into bilayers 
comprising respective inner and outer layers. A synthetic resin material 
having an excellent gas-barrier capacity (hereinafter, referred to as 
"gas-barrier resin"), and specifically a resin having a gas permeability 
rate (ASTM Z 1434-58) as a film material of not more than 0.1 g/m.sup.2 
/24 hr/atm for O.sub.2, N.sub.2, and CO.sub.2, may be employed for inner 
container outer layer 2b and outer container inner layer 3a. Examples of 
such resins include polyesters like polyethylene terephthalate, 
polybutylene terephthalate, and polyethylene naphthalate, as well as 
various resins such as polyamide, ethylene vinyl alcohol, polyvinylidene 
chloride, polyacrylonitrile, polyvinyl alcohol and the like. The low 
thermoconductive gases xenon, krypton, and argon have an atomic diameter 
which is larger than O.sub.2 and N.sub.2. Accordingly, the permeability 
rate of these low thermoconductive gases through the aforementioned 
gas-barrier resins is smaller than the rates for O.sub.2 or N.sub.2. 
Moreover, a synthetic resin which is heat resistant, moisture resistant 
(rate of resistance to water-vapor transmission) and is equipped with 
mechanical strength (hereinafter, referred to as "moisture resistant 
resin"), and specifically a synthetic resin which is heat resistant with a 
thermal deformation temperature (ASTM D 648) not less than 100.degree. C. 
and a water-vapor transmission rate (JIS Z 0208) not more than 50 
g/m.sup.2 /24 hr or less, may be employed for the inner container inner 
layer 2a and the outer container outer layer 3b. Examples of this type of 
resin include polypropylene, heat and moisture resistant polycarbonate, 
and the like. By forming inner container 2 and outer container 3 by means 
of two-color molding of a gas-barrier resin and a moisture resistant 
resin, a double walled container 1a which is provided with a high 
gas-barrier capacity can be formed without forming a metallic coating such 
as electroplating to the outer surface of inner container 2 and the inner 
surface of outer container 3. Moreover, the layers of inner and outer 
containers 2, 3 which are in contact with the external atmosphere 
demonstrate excellent mechanical strength, as well as resistance to 
moisture and heat. 
Even if a readily moisture absorbent synthetic resin like polyamide is used 
as the gas-barrier resin employed in inner container outer layer 2b and 
outer container inner layer 3a in thermoinsulated double walled container 
1 formed of two-color molded inner container 2 and outer container 3, it 
is possible to prevent a deterioration in performance due to absorption of 
moisture by the gas-barrier resin in contact with thermoinsulating layer 8 
because inner container inner layer 2a and outer container outer layer 3b, 
which are in contact with the external atmosphere, are formed of a 
moisture resistant resin. Accordingly, the escape of the low 
thermoconductive gas through the walls of inner and outer containers 2 and 
3 is prevented, making is possible to maintain the container's excellent 
thermoinsulating capacity over a long period of time. 
As a method for molding inner container 2 and outer container 3 using 
two-color molding, a known two-color molding method (multi-color molding 
method) may be employed, such as, for example, the method disclosed in 
Plastic Molding Techniques, vol. 10, No. 11, pages 9 through 14 (1993), 
which uses a two-color/mixed color molding machine and working method. 
Inner container 2 and outer container 3 can be joined at mouth joining area 
4 between their respective flanges 2c, 3c by employing a heat welding 
method such as vibration welding, spin welding or heat plate welding, or 
by means of a bonding method using a synthetic resin bonding agent. If 
inner container 2 and outer container 3 are joined by means of a heat 
welding method such as vibration welding, spin welding or heat plate 
welding, then the joining strength at mouth joining area 4 is high, and an 
even higher degree of air tightness can be obtained. As a result, the low 
thermoconductive gas which fills space 6 does not leak from mouth joining 
area 4. The joined surface of mouth joining area 4 is formed by joining 
inner container inner layer 2a and outer container outer layer 3b which 
are each formed of a moisture resistant resin. As a result, even if the 
gas-barrier resin of outer container inner layer 3a and inner container 
outer layer 2b around mouth joining area 4 is moisture absorbent, or has 
low mechanical strength, the gas-barrier resin is protected by the 
moisture resistant resin. Thus, there is no concern that a deterioration 
in the container's thermoinsulating capacity will arise from mouth joining 
area 4. 
The opening 3d for charging gas in the bottom of outer container 3 is 
provided with a diameter in the range of 0.1 to 3 mm. When the diameter of 
opening 3d for charging gas is less than 0.1 mm, then the process of 
vacuum evacuating space 6 between inner and outer containers 2 and 3 via 
opening 3d for charging gas and filling the space with the low 
thermoconductive gas becomes difficult. In contrast, when the diameter is 
larger than 3 mm, air can readily mix into the low thermoconductive gas 
during the sealing of opening 3d for charging gas with sealing plate 9 
after filling space 6 with the low thermoconductive gas. Further, opening 
3d for charging gas is tapered in this first example, with the diameter 
getting larger as opening 3d for charging gas extends from the 
thermoinsulating layer 8 side toward the outside of the container. 
Sealing plate 9 is formed by two-color molding a gas-barrier resin and a 
moisture resistant resin which are identical to those employed in inner 
and outer containers 2, 3 into a shape which can be inserted into opening 
3d for charging gas. Sealing plate 9 is then inserted into opening 3d for 
charging gas with the gas-barrier resin (inner layer 9a) directed toward 
thermoinsulating layer 8, and the moisture resistant resin (outer layer 
9b) directed toward the outside of the container, and is then bonded in 
opening 3d for charging gas through the use of a bonding agent. 
Cyanoacrylate type bonding agents are suitably employed as the bonding 
agent used here. This bonding agent provides a high degree of air 
tightness around the area of bonding and provides strong bonding strength 
instantly. Thus, it is suitably employed as the bonding agent for the 
sealing of opening 3d for charging gas by sealing plate 9 which is 
inserted into opening 3d for charging gas immediately following filling of 
space 6 with a low thermoconductive gas. Further, in addition to using a 
cyanoacrylate type bonding agent to bond sealing plate 9 in opening 3d for 
charging gas, joining by means of a heat welding method such as vibration 
welding, spin welding, heat plate welding or the like is also possible. If 
opening 3d for charging gas is sealed by means of this type of welding, 
the strength and durability of the sealed area 3e are improved. Moreover, 
sealing plate 9 can also be formed by forming a suitably thick plate 
member by two-color molding of a gas-barrier resin and a moisture 
resistant resin, cutting this plate member and then working it into a 
shape which can be inserted into opening 3d for charging gas. 
Sealing plate 9 is formed by two-color molding of a gas-barrier resin and a 
moisture resistant resin which are identical to those employed in inner 
and outer containers 2, 3. By inserting this sealing plate 9 in opening 3d 
for charging gas with the gas-barrier resin directed toward the 
thermoinsulating layer 8 side and the moisture resistant resin directed 
toward the outside of the container, then the gas-barrier resin on the 
thermoinsulating layer 8 side can be protected by the moisture resistant 
resin. Thus, the gas-barrier capacity of sealing plate 9 can be maintained 
well, without a deterioration in the thermoinsulating capacity arising 
from around this area. 
A metallic radiation shielding material 7 is disposed inside space 6 so as 
to cover the outer surface of inner container 2. As a result, it is 
possible to form a structure which prevents radiant heat transmission 
which is less expensive than the case where a metallic coating such as 
electroplating or the like is formed to the sides of inner and outer 
containers 2, 3 which are in contact with thermoinsulating layer 8. Thus, 
the thermoinsulating effect of thermoinsulated double walled container 1 
is improved. Aluminum foil, copper foil, or metalized tape are suitably 
employed as the radiation shielding material 7, as well as stainless foil, 
silver foil or paper which has metallic foil attached to both sides 
thereof. 
An explanation will now be made of the method of production of this 
thermoinsulated cup 1. First, an inner container 2 and an outer container 
3 are formed from a gas-barrier resin and a moisture resistant resin using 
two-color molding. A opening 3d for charging gas is punched in the bottom 
of outer container 3 during or after molding. In a separate process, a 
plate member two-color molded from a gas-barrier resin and a moisture 
resistance resin is punched out and a sealing plate 9 which can be 
inserted to exactly fit into opening 3d for charging gas is formed. 
Next, a metallic radiation shielding material 7 is attached so as to cover 
the outer surfaces of the cylindrical portion and the bottom of inner 
container 2. This radiation shielding material 7 is easily affixed to the 
outer surface of inner container 2 by a bonding agent or the like. 
Next, inner container 2 with attached radiation shielding material 7 is 
inserted into outer container 3. The mouth openings thereof are aligned 
and bonded together by means of a heat welding method such as vibration 
welding, spin welding, heat plate welding, or the like, to form a double 
walled container 1a by joining inner container 2 and outer container 3 in 
a unitary fashion at the mouth areas thereof. 
Next, the air inside space 6 between inner and outer containers 2, 3 is 
evacuated via opening 3d for charging gas in the bottom of double walled 
container 1a, and space 6 is filled with a low thermoconductive gas. 
Opening 3d for charging gas is then sealed with sealing plate 9. This 
operation may be carried out by employing a device which can be switched 
between an evacuation system attached to an evacuation pump and a supply 
system for supplying a low thermoconductive gas, in which packing is 
disposed to the ends of the pipe in the device which attaches to 
double-walled container 1a at opening 3d for charging gas. This packing is 
pushed against the vicinity of opening 3d for charging gas, and space 6 is 
evacuated by the evacuation system while opening 3d for charging gas is 
blocked off from the external atmosphere. Next, the device is switched 
over to the low thermoconductive gas supply system, and space 6 is filled 
with a low thermoconductive gas. Once space 6 is filled with a low 
thermoconductive gas, a cyanoacrylate type instant bonding agent is coated 
dropwise to the tapered opening 3d for charging gas using a dispenser. 
Then, sealing plate 9 is engaged in opening 3d for charging gas, and is 
strongly bonded and fixed therein by the hardening of the bonding agent. 
Further, as an alternative method, a gas substitution device may be 
employed which is provided with a chamber which is attached to a vacuum 
pump and a low thermoconductive gas supply means. A double walled 
container 1a is placed inside the chamber of this device, and the chamber 
is vacuum evacuated, thus also evacuating the air inside space 6 between 
inner and outer containers 2, 3 via opening 3d for charging gas which is 
in the bottom of double walled container 1. Next, low thermoconductive gas 
is introduced into the chamber until the pressure is approximately 
atmospheric pressure, thereby supplying the low thermoconductive gas into 
space 6 of double walled container 1a. A sealing plate 9 which has been 
coated with a bonding agent is then engaged in opening 3d for charging 
gas, sealing it. 
As a result, a thermoinsulated cup 1 (thermally-insulated double-walled 
synthetic-resin container) is formed having a space 6 between its inner 
and outer containers 2, 3 which is filled with a low thermoconductive gas. 
FIGS. 4 through 6 show a second example of the present invention's 
thermally-insulated double-walled synthetic-resin container. In this 
example, the present invention's thermally-insulated double-walled 
synthetic-resin container is suitably employed in a thermoinsulated cup 21 
(thermoinsulated mug) such as shown in FIG. 4. 
In thermoinsulated cup 21, a space 26 is formed between a sandwich molded 
inner container 22, wherein an intermediate layer 22b is sandwiched 
between an inner layer 22a and an outer layer 22c, and a sandwich molded 
outer container 23, wherein an intermediate layer 23b is sandwiched 
between an inner layer 23a and an outer layer 23c. A double walled 
container 21a is formed by joining inner container 22 and outer container 
23 in a unitary fashion at the mouth joining area 24 between their 
respective flanges 22f, 23f. Further, a radiation shielding material 27 
consisting of a metal foil is disposed to space 26 between inner container 
22 and outer container 23. A thermoinsulating layer 28 is formed by 
filling space 26 with at least one type of low thermoconductive gas from 
among the group of xenon, krypton, and argon. This thermoinsulated cup 21, 
which is formed in the shape of a cylinder having a bottom, has an opening 
25 at the upper edge thereof. 
A opening 23d for charging gas is formed in the bottom of outer container 
23, and is sealed by bonding or welding a sandwich molded sealing plate 29 
thereto. 
Space 26 is filled at room temperature and atmospheric pressure with at 
least one type of low thermoconductive gas selected from among the group 
of xenon, krypton, and argon. By employing these low thermoconductive 
gases, it is possible to provide a thermoinsulated cup 21 having a high 
thermoinsulating capacity. 
Inner container 22 and outer container 23 are each molded into respective 
sandwich structures comprising an inner layer, intermediate layer and 
outer layer. A gas-barrier resin selected from among various resins such 
as polyesters like polyethylene terephthalate, polybutylene terephthalate, 
and polyethylene naphthalate, as well as various resins such as polyamide, 
ethylene vinyl alcohol, polyvinylidene chloride, polyacrylonitrile, 
polyvinyl alcohol and the like, may be employed in the intermediate layer 
22b of the inner container and the intermediate layer 23b of the outer 
container. 
Further, a moisture resistant resin which is heat resistant, moisture 
resistance (rate of resistance to water-vapor transmission) and is 
provided with mechanical strength, such as polypropylene, heat and 
moisture resistant polycarbonate or the like, may be employed for inner 
layer 22a and outer layer 22c of inner container 22, and for inner layer 
23a and outer layer 23c of outer container 23. 
By forming inner container 22 and outer container 23 by means of sandwich 
molding so that a gas-barrier resin is sandwiched between moisture 
resistant resins, a double walled container 21a can be formed which has a 
high gas-barrier capacity even if a metallic coating such as 
electroplating or the like is not formed to the outer surface of inner 
container 22 and the inner surface of outer container 23. Further, the 
layers which are in contact with the external atmosphere in inner and 
outer containers 22, 23, and the layers which are in contact with the 
thermoinsulating layer 28 in inner and outer containers 22, 23 have 
excellent mechanical strength as well as resistance to heat and moisture. 
In thermoinsulated cup 21 formed of sandwich molded inner and outer 
containers 22, 23, the inner container inner layer 22a and outer container 
outer layer 23c which are in contact with the external atmosphere are 
formed of a moisture resistant resin. Accordingly, even if a synthetic 
resin, such as polyamide, which readily absorbs moisture is used as the 
gas-barrier resin employed for the respective intermediate layers 22b, 23b 
of inner and outer containers 22, 23, a deterioration in the performance 
of the container due to absorption of moisture by the gas-barrier resin of 
intermediate layers 22b, 23b is prevented. Thus, the escape of the low 
thermoconductive gas through the walls of inner and outer containers 22, 
23 is prevented, making is possible to maintain an excellent 
thermoinsulating capacity over a long period of time. Further, because 
inner container intermediate layer 22b and outer container intermediate 
layer 23b are sandwiched by moisture resistant resin, it is possible to 
prevent deterioration in performance due to absorption of moisture by the 
gas-barrier resin portions of inner and outer containers 22, 23 during 
their storage as parts prior to assembly of double walled container 21a. 
Accordingly, the thermoinsulating capacity of the container is improved. 
As a method for molding inner container 22 and outer container 23 using 
sandwich molding, a known sandwich molding method (multilayer molding 
method) may be employed, such as, for example, the method disclosed in 
Plastic Molding Techniques, vol. 10, No. 11, pages 9 through 14 (1993), 
which uses a two-color/mixed color molding machine and working method. 
Inner container 22 and outer container 23 can be joined at the mouth 
joining area 24 between their respective flanges 22f, 23f by employing a 
heat welding method such as vibration welding, spin welding or heat plate 
welding, or by means of a bonding method using a synthetic resin bonding 
agent. 
Moreover, a opening 23d for charging gas of a diameter of 0.1 to 3 mm is 
formed in the bottom of outer container 23. This opening 23d for charging 
gas is tapered with the diameter widening as the hole extends from the 
thermoinsulating layer 28 side toward the outside of the container. 
Sealing plate 29 is sandwiched molded into a shape which can be inserted 
into opening 23d for charging gas by sandwiched molding a gas-barrier 
resin, which will form intermediate layer 29b, between moisture resistant 
resins, which will form inner layer 29a which is in contact with 
thermoinsulating layer 28 and outer layer 29c which is in contact with the 
external atmosphere, these resins being identical to those employed in 
inner and outer containers 22, 23. Sealing plate 29 is then inserted into 
opening 23d for charging gas and bonded with a cyanoacrylate type bonding 
agent. In addition to using a cyanoacrylate type bonding agent to bond 
sealing plate 29 in opening 23d for charging gas, joining by means of a 
heat welding method such as vibration welding, spin welding, heat plate 
welding or the like are also possible. If opening 23d for charging gas is 
sealed by means of this type of welding, the strength and durability of 
sealing area 23e are improved. 
Sealing plate 29 is formed by sandwich molding a gas-barrier resin and 
moisture resistant resins which are identical to those employed in the 
case of inner and outer containers 22, 23. Thus, the gas-barrier resin of 
intermediate layer 29b is protected by inner and outer layers 29a, 29c 
which are formed of a moisture resistant resin, and the gas-barrier 
capacity of sealing plate 29 can be maintained well. Accordingly, there is 
no concern that a deterioration in thermoinsulating capacity will arise 
from around this area. 
A metallic radiation shielding material 27 is disposed inside space 26 so 
as to cover the outer surface of inner container 22. As a result, it is 
possible to form a structure at a lower cost which prevents radiant heat 
transmission as compared to forming a metallic coating such as 
electroplating to the surfaces of inner and outer containers 22, 23 which 
are in contact with thermoinsulating layer 28. Thus, the thermoinsulating 
effect of thermoinsulated cup 21 is improved. Aluminum foil, copper foil, 
or metalized tape are suitably employed as the radiation shielding 
material 27, as well as stainless foil, silver foil or paper to which 
metallic foil has been attached to both sides thereof. 
An explanation will now be made of the method of production of this 
thermoinsulated cup 21. First, an inner container 22 and an outer 
container 23 are formed by means of sandwich molding so that a gas-barrier 
resin is sandwiched between moisture resistant resins. A opening 23d for 
charging gas is punched in the bottom of outer container 23 during or 
after molding. In a separate process, a sealing plate 29 of a shape which 
can be inserted to exactly fit into opening 23d for charging gas is formed 
by punching out a plate member sandwich molded so that a gas-barrier resin 
is sandwiched between moisture resistant resins. 
Next, a metallic radiation shielding material 27 is attached so as to cover 
the outer surfaces of the cylindrical portion and bottom of inner 
container 22. This radiation shielding material 27 is easily affixed to 
the outer surface of inner container 22 by a bonding agent or the like. 
Next, inner container 22 with attached radiation shielding material 27 is 
inserted into outer container 23. The mouth areas thereof are aligned and 
bonded together by means of a heat welding method such as vibration 
welding, spin welding, heat plate welding, or the like, to form a double 
walled container 21a by joining inner container 22 and outer container 23 
in a unitary fashion at the mouth areas thereof. 
Next, the air inside space 26 between inner and outer containers 22, 23 is 
evacuated via opening 23d for charging gas at the bottom of double walled 
container 21a, and space 26 is filled with a low thermoconductive gas. 
Opening 23d for charging gas is then sealed with sealing plate 29. Once 
space 26 is filled with a low thermoconductive gas, a cyanoacrylate type 
instant bonding agent is coated dropwise to the tapered opening 23d for 
charging gas using a dispenser. Then, sealing plate 29 is engaged in 
opening 23d for charging gas, and is strongly bonded and fixed thereto by 
the hardening of the bonding agent. 
As a result, a thermoinsulated cup 21 (thermally-insulated double-walled 
synthetic-resin container) is formed wherein the space 26 between inner 
and outer containers 22, 23 is filled with a low thermoconductive gas. 
Thermoinsulated cups 1, 21 (thermally-insulated double-walled 
synthetic-resin containers) formed in the first and second examples in 
this way have excellent gas-barrier capacity, resistance to heat and 
moisture, and mechanical strength even though the steps of electroplating 
and masking of non-plating areas are omitted. Accordingly, production 
costs can be greatly reduced. Moreover, in the first example, it is 
possible to select the synthetic resins for the inner surface of inner 
container 2 and the outer surface of outer container 3 in response to the 
specifications of the product. Further, in the second example as well, it 
is possible to select the synthetic resins for the inner and outer 
surfaces and intermediate layer of outer container 23 and inner container 
22. As a result, the present invention can be suitably employed in a 
variety of products of varying designs and colors. 
Because a thermoinsulating layer 8, 28 is formed in thermoinsulating cup 1, 
21 in the first and second examples by introducing at room temperature and 
atmospheric pressure a low thermoconductive gas into the space 6, 26 
between the inner and outer containers, it is not necessary to provide 
double walled container 1a, 21a with a pressure resistant structure such 
as is required in the case of a vacuum insulated container. Thus, a 
container constructed with flat walls, such as a square-shaped container, 
becomes possible. 
Additionally, in the first and second examples, an opening 3d for charging 
gas or an opening 23d for charging gas was provided in the bottom of outer 
container 3 or 23. However, an opening 3d for charging gas or opening 23d 
for charging gas can also be provided in the side surface of flanges 2c of 
inner container 2 or in the side surface of flanges 22f of inner container 
22; in the side surfaces of inner container 2 or 22; in the side surface 
of outer container 3 or 23; or in the bottom of inner container 2 or 22. 
Further, the thermally-insulated double-walled synthetic-resin container of 
the present invention is not limited to use in thermoinsulated cup 1, 21, 
but may be employed for a variety of thermoinsulating containers. 
Additionally, there are no particular limitations placed on the 
container's shape, size or applications. 
Example of Production 
To produce the thermoinsulated cup 1 shown in FIG. 1, an inner container 2 
and outer container 3 for a double walled container 1a were produced using 
two-color molding. Polyamide was employed as a gas-barrier resin for the 
inner container outer layer 2b and outer container inner layer 3a, while 
heat and moisture resistant polycarbonate was employed as the moisture 
resistant resin for inner container inner layer 2a and outer container 
outer layer 3b. During formation of outer container 3, a opening 3d for 
charging gas was formed in the bottom thereof, while a handle 10 of 
polycarbonate was formed to the side of outer container 3. 
Sealing plate 9 was formed by two-color molding of polyamide and heat and 
moisture resistant polycarbonate into the shape of a flat plate. 
Radiant heat transmission was prevented by using double sided adhesive tape 
to adhere aluminum foil to the outer surface of inner container 2 as a 
radiation shielding material. Next, inner container 2 with the adhered 
aluminum foil was inserted into outer container 3, with the flanges 2c, 3c 
engaging. The area of these flanges 2c, 3c were joined by vibration 
welding to form a mouth joining area 4. 
Next, with the opening 5 of the obtained double walled container 1a placed 
downward, a device which could be switched between an evacuation system 
connected to an evacuation pump and a krypton gas (low thermoconductive 
gas) supply system and which had packing disposed to the ends of its pipe 
which attaches to double-walled container 1a at opening 3d for charging 
gas was employed. The packing was pushed against the vicinity of opening 
3d for charging gas, and space 6 was evacuated to a pressure of 10 Torr or 
less by the device's evacuation system with opening 3d for charging gas 
blocked off from the external atmosphere. The device was then switched to 
the krypton gas supply system, and space 6 was filled with krypton gas 
until a pressure around atmospheric pressure was reached. After filling 
with krypton gas, a cyanoacrylate type instant bonding agent was coated 
dropwise to tapered opening 3d for charging gas using a dispenser. Sealing 
plate 9 was then engaged in opening 3d for charging gas and affixed 
therein by the hardening of the bonding agent. 
The thermoinsulated mug produced in this way was lightweight, had high 
mechanical strength, and excellent heat retention capacity. Moreover, 
production costs were less than those required to produce conventional 
thermoinsulating containers. Additionally, it was confirmed that this 
thermoinsulating mug maintained the excellent thermoinsulating capacity 
demonstrated initially over a long period of time.