AU2015405840B2

AU2015405840B2 - Vacuum thermal insulator and thermal insulation container

Info

Publication number: AU2015405840B2
Application number: AU2015405840A
Authority: AU
Inventors: Shohei ABIKO; Yosuke Fujimori; Kazumasa Fujimura; Takayuki Inuzuka; Yasushi Masuda; Takayoshi MUKAIYAMA; Hiroaki Takai
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2015-08-19
Filing date: 2015-08-19
Publication date: 2019-02-21
Anticipated expiration: 2035-08-19
Also published as: CN107923565B; WO2017029727A1; AU2015405840A1; JPWO2017029727A1; TW201719068A; TWI604150B; CN107923565A

Abstract

This vacuum heat insulation material is provided with a core material holding a vacuum space, an adsorbent that adsorbs moisture, and an outer packaging material that covers the core material and the adsorbent; and the inside of the outer packaging material is depressurized and hermetically sealed. The outer packaging material is composed of a surface protective layer, a gas barrier layer and a thermal fusion layer. The outer packaging material has a sealed part obtained by thermally fusing thermal fusion layers with each other in the peripheral portion of the outer packaging material. The thermal fusion layer has a thickness from 35 μm to 70 μm (inclusive). The adsorbent contains calcium oxide having a moisture absorption rate of from 15 wt%/h to 32 wt%/h (inclusive).

Description

DESCRIPTION

VACUUM THERMAL INSULATOR AND THERMAL INSULATION CONTAINER

Technical Field [0001]

The present invention relates to a vacuum thermal insulator for use with a thermal insulation container, such as a refrigerator, and to a thermal insulation container using the vacuum thermal insulator.

Background Art [0002]

As a related-art vacuum thermal insulator used as a heat insulating material for a refrigerator or any other such device, a vacuum thermal insulator is known that is formed by covering a core configured to secure a vacuum space and an adsorbent configured to adsorb water vapor with two sheets of enclosure, and depressurizing and sealing an inside of the enclosure. The enclosure includes a surface protective layer, a barrier layer, and a thermal fusion layer, and the enclosure is configured to maintain a vacuum in the inside, to thereby reduce a thermal conductivity of the vacuum thermal insulator. As the enclosure, for example, in Patent Literature 1, it is proposed that a linear low-density polyethylene film having a thickness of, for example, 50 micrometers be used for the thermal fusion layer in order to prevent bag rupture due to pinhole occurrence. Further, for example, in Patent Literature 2, it is proposed to use calcium oxide having a rate of moisture adsorption of, for example, 13.2 wt%/h, for the adsorbent configured to adsorb water vapor, in order to achieve a vacuum state of the inside.

Citation List

Patent Literature [0003]

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2006-38122

Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2015-59642 [0003a]

Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant and/or combined with other pieces of prior art by a person skilled in the art.

Summary [0003b]

As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps.

[0004]

In a vacuum thermal insulator, a penetration path by which water vapor penetrates into its inside may be a surface of an enclosure, and a thermal fusion layer formed by fusion of two sheets of enclosure. When the thickness of the thermal fusion layer is increased to, for example, 50 micrometers as in Patent Literature 1, the penetration path of water vapor is consequently expanded, and hence the amount of water vapor penetrating into the inside is expected to increase. In this case, even if bag rupture due to pinhole occurrence can be suppressed, water vapor that can penetrate through the fused thermal fusion layer increases in amount, and hence it is not possible to maintain the vacuum state of the inside of the vacuum thermal insulator over a long period of time to suppress a rise in thermal conductivity.

[0005]

Further, the adsorbent of Patent Literature 2 has a rate of moisture adsorption of 13.2 wt%/h, and hence the rate of moisture adsorption is insufficient for adsorbing both of water vapor that has entered through the thermal fusion layer, and water vapor that has entered through a defective portion generated in a gas barrier layer. Also in this case, it is difficult to suppress a rise in thermal conductivity of the vacuum thermal insulator over a long period of time.

[0006]

The present invention has been made in light of the above-mentioned problems, and an object of the present invention is to provide a vacuum thermal insulator and a thermal insulation container each of which is capable of suppressing the occurrence of bag rupture due to the occurrence of a pinhole caused by piercing with particles of a core, and capable of maintaining heat insulating performance over a long period of time. An additional or alternative object is to provide the public with a useful choice.

[0007] A vacuum thermal insulator according to one embodiment of the present invention includes: a core configured to secure a vacuum space; an adsorbent configured to adsorb moisture; and an enclosure configured to cover the core and the adsorbent, the vacuum thermal insulator having a depressurized inside enclosed and sealed by the enclosure, the enclosure including a surface protective layer, a gas barrier layer, and a thermal fusion layer, the enclosure including a sealing portion in which parts of the thermal fusion layer at a peripheral edge portion of the enclosure are fused to each other, the thermal fusion layer having a thickness of 35 micrometers or more and 70 micrometers or less, the adsorbent containing calcium oxide having a rate of moisture adsorption of 15 wt%/h or more and 32 wt%/h or less.

[0008]

According to the vacuum thermal insulator disclosed within the following, by virtue of adopting the above-mentioned configuration, the occurrence of bag rupture due to the occurrence of a pinhole caused by piercing with the core is sufficiently suppressed by increasing the thickness of the thermal fusion layer, and besides, water vapor penetrating through the thermal fusion layer is quickly adsorbed by the adsorbent. With this, the degree of vacuum of the inside of the vacuum thermal insulator can be maintained to suppress a rise in thermal conductivity, and hence the following effect is exhibited: the heat insulating performance of the vacuum thermal insulator can be maintained for a long period of time.

Brief Description of Drawings [0009] [Fig, 1] Fig. 1 is a sectional view for illustrating a schematic configuration of a vacuum thermal insulator according to Embodiment 1 of the present invention.

[Fig. 2] Fig. 2 is a scatter plot for showing a relationship between the amount of increase in thermal conductivity of the vacuum thermal insulator of Fig. 1 and the rate of moisture adsorption.

[Fig. 3] Fig. 3 is a scatter plot for showing a relationship between the relative piercing strength of the vacuum thermal insulator of Fig. 1 and the thickness of its thermal fusion layer.

[Fig. 4] Fig. 4 is a scatter plot for showing a relationship between the number of pieces with bag rupture due to pinhole occurrence of the vacuum thermal insulator of Fig. 1 and the thickness of its thermal fusion layer.

[Fig. 5] Fig. 5 is a scatter plot for showing a relationship between the amount of increase in thermal conductivity of the vacuum thermal insulator of Fig. 1 and the thickness of its thermal fusion layer.

[Fig. 6] Fig. 6 is a sectional view for illustrating a schematic configuration of a thermal insulation container according to Embodiment 2 of the present invention.

Description of Embodiments [0010]

Embodiment 1 A vacuum thermal insulator according to Embodiment 1 of the present invention is described. Fig. 1 is a sectional view for illustrating a schematic configuration of a vacuum thermal insulator 1 according to Embodiment 1. In the drawings including Fig. 1, the dimensional relationship, shape, and other conditions of each constituent member are different from actual ones in some cases. The specific dimensions and other conditions of each constituent member should be determined in view of the following description.

[0011]

As illustrated in Fig. 1, the vacuum thermal insulator 1 is a heat insulating material capable of achieving low thermal conductivity by making its inside a vacuum, and includes: a core 2 configured to secure a vacuum space; an adsorbent 3 configured to adsorb at least moisture; and an enclosure 4 configured to cover the core 2 and the adsorbent 3. The vacuum space defined by the enclosure 4 is depressurized and sealed by fusion of its opening by heat sealing or any other method under a depressurized state. The vacuum thermal insulator 1 has a substantially rectangular plate shape as a whole.

[0012]

An uneven shape is formed on a surface of the vacuum thermal insulator 1 for avoiding interference with a copper pipe for heat transfer and other problems. Unevenness only needs to be formed as necessary, and the difference between a surface of a depressed portion and a surface of a projected portion, that is, the depth of a groove only needs to be 2 mm or more and 10 mm or less because the diameter of the copper pipe is about 4 mm.

[0013]

The core 2 is used for securing the vacuum space. As the core 2, a fiber assembly, for example, glass wool is generally used. Further, the fiber assembly forming the core 2 may be subjected to: heating pressure forming; hermetic sealing with an inner packaging material; or binding with a binder.

[0014]

The adsorbent 3 is configured to adsorb water vapor in the inside of the vacuum thermal insulator 1 to keep its degree of vacuum, to thereby suppress a rise in thermal conductivity. Calcium oxide (CaO) having a rate of moisture adsorption of 15 wt%/h or more and 32 wt%/h or less is used as the adsorbent 3. The rate of moisture adsorption refers to a value calculated from the rate of weight increase when the adsorbent 3 is left to stand still under an atmosphere having a temperature of 25 degrees centigrade and a relative humidity of 90%.

[0015]

The adsorbent 3 may be packaged with a packaging material having air permeability. The packaging material having air permeability is formed of a member having air permeability selected from paper, a nonwoven fabric, a plastic film, and a mesh cloth, and can be expected to improve workability. The packaging material may be a product obtained by laminating two or more kinds of members selected from those members having air permeability.

[0016]

The enclosure 4 is formed of two laminate films each having a multi-layer structure of a surface protective layer 41, a gas barrier layer 42, and a thermal fusion layer 43. The thermal fusion layers 43 are fused to each other and bonded at a sealing portion 43a, and thus the core 2 and the adsorbent 3 are covered. At this time, the enclosure 4 is depressurized and sealed by fusion of the sealing portion 43a in a state of being depressurized to a degree of vacuum of from about 1 Pa (pascal) to about 3 Pa (pascals).

[0017]

The surface protective layer 41 has a thickness of, for example, 25 micrometers, and a material therefor is desirably a thermoplastic resin having a melting point of 150 degrees centigrade or more and excellent in mar resistance, or any other such material. For example, oriented polyamide, such as oriented nylon, polyethylene terephthalate, oriented polypropylene, or any other such material may be used. Oriented nylon is abbreviated as ONY, polyethylene terephthalate is abbreviated as PET, and oriented polypropylene is abbreviated as OPP in some cases.

[0018]

As a material for the gas barrier layer 42, a thermoplastic resin or a metal film excellent in barrier properties against water vapor and air is selected, and the gas barrier layer 42 is formed, for example, of a single layer having a thickness of 24 micrometers, or by laminating two layers each having a thickness of 12 micrometers. As the material for the gas barrier layer 42, aluminum vapor-deposition polyethylene terephthalate, aluminum vapor-deposition ethylene vinyl alcohol, an aluminum foil, or a combination thereof, or any other such material may be used. Further, an inorganic material for vapor-depositing a thermoplastic resin is not limited to aluminum, and may be alumina, silica, or a combination thereof. Ethylene vinyl alcohol is sometimes abbreviated as EVOH.

[0019]

The thermal fusion layer 43 only needs to be as follows: a thickness t of the thermal fusion layer 43 is set to 35 micrometers or more and 70 micrometers or less, and a thickness T of the sealing portion 43a to be formed by fusion of parts of the thermal fusion layer 43 to each other is 70 micrometers or more and 140 micrometers or less. As a material therefor, a thermoplastic resin having a melting point of 150 degrees centigrade or less, or any other such material, for example, is selected, but the material is not particularly limited. As the thermal fusion layer 43, for example, low-density polyethylene, linear low-density polyethylene, or any other such material is used. High-density polyethylene or cast polypropylene having high elastic modulus and excellent in barrier property against water vapor is more desired. Low-density polyethylene is abbreviated as LDPE, linear low-density polyethylene is abbreviated as LLDPE, high-density polyethylene is abbreviated as HDPE, and cast polypropylene is abbreviated as CPP in some cases. In the following description, the above-mentioned abbreviations are described in parentheses.

[0020]

Next, the rate of moisture adsorption of the adsorbent 3 is described in detail with reference to Fig. 2.

Fig. 2 is a scatter plot for showing a relationship between the rate of moisture adsorption and the amount of increase in thermal conductivity for the vacuum thermal insulator 1 of Fig. 1. In Fig. 2, the case of using linear low-density polyethylene (LLDPE) as the thermal fusion layer 43 is represented by filled circles, and the case of using cast polypropylene (CPP) is represented by filled squares. As shown in Fig. 2, in the case of using calcium oxide (CaO) as the adsorbent 3, when the rate of moisture adsorption of calcium oxide (CaO) is changed, a state in which the amount of increase in thermal conductivity is small is maintained in the range of the rate of moisture adsorption of 15 wt%/h or more. This is because, when the rate of moisture adsorption is 15 wt%/h or more, a vacuum is maintained for a long period of time to suppress the rise in thermal conductivity. Meanwhile, when the rate of moisture adsorption is 15 wt%/h or less, the amount of increase in thermal conductivity significantly rises at a borderline around 15 wt%/h. This is because the rate of moisture adsorption of the adsorbent is not sufficient, and hence the water vapor has increased in amount, resulting in a rise in thermal conductivity. Even when the material to be used for the thermal fusion layer 43 is changed, a similar tendency is shown without dependence on the material.

[0021]

In view of the foregoing, it may be considered that, when calcium oxide (CaO) having a rate of moisture adsorption of 15 wt%/h or more is used as the adsorbent 3, high thermal conductivity of the vacuum thermal insulator 1 can be maintained over a long period of time. Further, the amount of moisture that calcium oxide (CaO) can theoretically adsorb is 32 wt%, and hence 32 wt%/h is the upper limit value of the rate of moisture adsorption that the adsorbent 3 can take. Further, when the rate of moisture adsorption is 17 wt%/h or more, a state in which the amount of increase in thermal conductivity is low can be stably maintained, and when the rate of moisture adsorption is set to 22 wt%/h or less, deactivation of the adsorbent 3 due to moisture adsorption in a manufacturing process of the vacuum thermal insulator 1 is suppressed. It is therefore more preferred that the rate of moisture adsorption of the adsorbent 3 be set to 17 wt%/h or more and 22 wt%/h or less.

[0022]

The rate of moisture adsorption is measured by the following method. First, calcium oxide (CaO) is measured for its weight with an electronic balance, and is used as a sample. Then, the sample is left to stand still in a thermo-hygrostat chamber having an atmosphere having a temperature of 25 degrees centigrade and a relative humidity of 90% for 1 hour, and then the weight of the sample is immediately measured with the electronic balance. The rate of moisture adsorption is calculated from a change in weight between before and after standing still in the thermohygrostat chamber. When the calcium oxide (CaO) has already been used, the rate of moisture adsorption may be calculated by a similar method after heating in an electric furnace at a temperature of 1,000 degrees centigrade for 4 hours.

[0023]

Next, the thermal fusion layer 43 is described in detail with reference to Fig. 3 to Fig. 5.

Fig. 3 is a scatter plot for showing a relationship between the relative piercing strength of the vacuum thermal insulator 1 of Fig. 1 and the thickness t of its thermal fusion layer 43. Fig. 4 is a scatter plot for showing a relationship between the number of pieces with bag rupture due to pinhole occurrence of the vacuum thermal insulator 1 of Fig. 1 and the thickness t of its thermal fusion layer 43. Further, Fig. 5 is a scatter plot for showing a relationship between the amount of increase in thermal conductivity of the vacuum thermal insulator 1 of Fig. 1 and the thickness t of its thermal fusion layer 43. Also in Fig. 3 to Fig. 5, the case of using linear low-density polyethylene (LLDPE) as the thermal fusion layer 43 is represented by filled circles, and the case of using cast polypropylene (CPP) is represented by filled squares.

The relative piercing strength refers to piercing strength relative to 100% of the strength of 30-micrometer linear low-density polyethylene (LLDPE) against piercing with a needle having a diameter of 0.4 mm. Further, in Fig. 4, the number of pieces with bag rupture due to pinhole occurrence represents the number of pieces of the vacuum thermal insulator 1 having bag rupture due to the occurrence of a pinhole, out of groups of the vacuum thermal insulators, each group consisting of 1,000 pieces of produced vacuum thermal insulators 1 different from each other in thickness t of the thermal fusion layer 43.

[0024]

When attention is focused on the thickness t of the thermal fusion layer 43, as shown in Fig. 3, irrespective of which material is used for the thermal fusion layer 43, at a thickness t of the thermal fusion layer 43 of 35 micrometers or more, the relative piercing strength rapidly increases to reach as high as twice that at a thickness t of 30 micrometers. Further, as shown in Fig. 4, at a thickness t of the thermal fusion layer 43 of 35 micrometers or more, the number of pieces with bag rupture due to pinhole occurrence abruptly reduces as compared to that at a thickness t of 35 micrometers.

In addition, at a thickness t of 50 micrometers or more, the relative piercing strength is maintained, and a state in which the number of pieces with bag rupture due to pinhole occurrence is small is stably maintained.

[0025]

Meanwhile, when attention is focused on the amount of increase in thermal conductivity, as shown in Fig. 5, while the thickness t of the thermal fusion layer 43 ranges from 20 micrometers to 80 micrometers, the amount of increase in thermal conductivity shows a slow rise, but the amount of increase in thermal conductivity abruptly rises at a thickness t of around 80 micrometers. At a thickness t of the thermal fusion layer 43 of 80 micrometers, the amount of increase in thermal conductivity shows a value close to twice that at a thickness t of 20 micrometers. In the range of the thickness t of the thermal fusion layer 43 of from 20 micrometers to 80 micrometers, the adsorbent 3 can adsorb water vapor that has entered, and hence low thermal conductivity is maintained. However, as the thickness t of the thermal fusion layer 43 increases, the amount of entering water vapor increases along with an increase in thickness T of the sealing portion 43a, and the rate of moisture adsorption of the adsorbent 3 decreases. Consequently, with time, the degree of vacuum of the inside decreases, resulting in an increase in thermal conductivity.

[0026]

In view of the foregoing, on the basis of the descriptions of Fig. 2 to Fig. 5, it is decided that the thickness t of the thermal fusion layer 43 is 35 micrometers or more and 70 micrometers or less and the thickness T of the sealing portion 43a in which parts of the thermal fusion layer 43 are fused to each other is 70 micrometers or more and 140 micrometers or more. Further, it is decided that the rate of moisture adsorption of the adsorbent 3 is 15 wt%/h or more and 32 wt%/h or less.

[0027]

Next, a manufacturing process of the vacuum thermal insulator 1 according to Embodiment 1 is described.

In the manufacturing process of the vacuum thermal insulator 1 according to Embodiment 1, first, the core 2 is covered with the enclosure 4 formed of the multilayer structure of the surface protective layer 41, the gas barrier layer 42, and the thermal fusion layer 43. At this time, the thickness t of the thermal fusion layer 43 is set to 35 micrometers or more and 70 micrometers or less. Then, the core 2 and the enclosure 4 are dried. The core 2 covered with the enclosure 4 is subjected to heat treatment at 100 degrees centigrade for 2 hours to remove moisture from the core 2 and the enclosure 4.

[0028]

Next, the adsorbent 3 is arranged between the core 2 and the enclosure 4.

The adsorbent 3 has a rate of moisture adsorption of 15 wt%/h or more and 32 wt%/h or less. Then, an inside of the enclosure 4 is depressurized to a degree of vacuum of from about 1 Pa to about 3 Pa, and the inside of the enclosure 4 is depressurized and sealed by fusing its opening by heat sealing or any other method under the depressurized state. At this time, as a result of the depressurization and sealing of the enclosure 4, there occurs piercing with the core 2 into the thermal fusion layer 43. However, by virtue of the setting of the thickness t of the thermal fusion layer 43 to 35 micrometers or more and 70 micrometers or less, the occurrence of bag rupture due to the occurrence of a pinhole caused by the piercing is suppressed.

[0029]

Water vapor is liable to enter into the vacuum thermal insulator 1 obtained through the above-mentioned steps owing to the thickness of the sealing portion 43a formed by fusion of parts of the thermal fusion layer 43 to each other. However, the water vapor that has entered is quickly adsorbed by the adsorbent 3 having a rate of moisture adsorption of 15 wt%/h or more and 32 wt%/h or less. Accordingly, the degree of vacuum of the inside of the vacuum thermal insulator 1 is maintained, and a state in which the amount of increase in thermal conductivity is suppressed can be maintained over a long period of time. In particular, when the rate of moisture adsorption of the adsorbent 3 is 17 wt%/h or more and 22 wt%/h or less, a rise in thermal conductivity is stably reduced, and besides, a decrease in moisture adsorbability during the manufacturing process can be avoided.

[0030]

The vacuum thermal insulator 1 may be subjected to press working in order to impart an uneven shape thereto for avoiding interference with a copper pipe for heat transfer and other problems. In this case, the height difference of projected portions and depressed portions of the unevenness to be formed by the press working may be, for example, 2 mm or more and 10 mm or less.

[0031]

Further, in the enclosure 4, the respective thermal fusion layers 43 may have different thicknesses, and it is only necessary that the thickness T of the sealing portion 43a to be formed by fusion of the thermal fusion layers 43 each having a thickness t of 35 micrometers or more and 70 micrometers or less to each other be 70 micrometers or more and 140 micrometers or less. Further, as the enclosure 4 configured to cover the core 2 and the adsorbent 3, two sheets of enclosure 4 may be used, or one sheet of enclosure 4 may be used by being folded. As long as the core 2 and the adsorbent 3 can be depressurized and sealed, the number of the enclosures 4 is not limited.

[0032]

Next, the vacuum thermal insulator 1 according to Embodiment 1 was produced, and Examples 1 to 3 were compared to Comparative Examples 1 to 3.

The results of the comparison are described below.

[0033] <Example 1>

In Example 1, a relationship between the number of pieces with bag rupture due to the occurrence of a pinhole and the thickness t of the thermal fusion layer 43 was investigated. In the vacuum thermal insulator 1, the core 2 was formed of glass wool, in the enclosure 4, oriented nylon (ONY) having a thickness of 25 micrometers was used as the surface protective layer 41, and aluminum vapor-deposition polyethylene terephthalate (PET) having a thickness of 12 micrometers and aluminum vapor-deposition ethylene vinyl alcohol (EVOH) having a thickness of 12 micrometers were each used as the gas barrier layer 42. In addition, a laminate film in which the surface protective layer 41, the gas barrier layer 42, and the thermal fusion layer 43 were laminated was formed as the enclosure 4. In addition, the core 2 was covered with the enclosure 4 to produce the vacuum thermal insulator 1.

For samples of Example 1, vacuum thermal insulators 1 including a thermal fusion layer 43 having a thickness t of 35 micrometers and a thermal fusion layer 43 having a thickness t of 50 micrometers were used. Materials for the thermal fusion layers 43 were linear low-density polyethylene (LLDPE) and cast polypropylene (CPP) having an elastic modulus higher than that of the low-density polyethylene (LLDPE). In addition, 1,000 pieces each of the samples of different thicknesses and materials were prepared.

[0034]

In a sample used in Comparative Example 1, the thermal fusion layer 43 of the enclosure 4 of the vacuum thermal insulator was linear low-density polyethylene (LLDPE) having a thickness of 30 micrometers, and the other configurations were the same as those in the samples of Example 1. As with the samples of Example 1, 1,000 pieces were prepared also for the sample of Comparative Example 1.

[0035]

In Table 1, the results of comparison of the numbers of pieces with bag rupture due to pinhole occurrence in the samples of Example 1 and Comparative Example 1 are shown.

Table 1

[0036]

As shown in Table 1, in the case of Comparative Example 1, in which the thickness t of the thermal fusion layer 43 of linear low-density polyethylene (LLDPE) was set to 30 micrometers, the number of pieces with bag rupture due to pinhole occurrence was 42, and the frequency of occurrence was 4.2%.

[0037]

In contrast, in the case of the sample of Example 1 in which the thickness t of the thermal fusion layer 43 of linear low-density polyethylene (LLDPE) was set to 35 micrometers, the number of pieces with bag rupture due to pinhole occurrence was 19, and the frequency of occurrence was 1.9%. In other words, in the sample of Example 1, the frequency of occurrence of a pinhole reduced by as much as 2.3% as compared to that of Comparative Example 1. Further, when the thickness t of the thermal fusion layer 43 was set to 50 micrometers, the number of pieces with bag rupture due to pinhole occurrence reduced to 14, but reduction was only by 5 as compared to that in the case of setting the thickness t to 35 micrometers.

[0038]

It was found that, when the thickness t of the thermal fusion layer 43 was increased from 30 micrometers to 35 micrometers, the number of pieces with bag rupture due to pinhole occurrence significantly reduced, and when the thickness t was increased from 35 micrometers to 50 micrometers, no great change was observed in the number of pieces with bag rupture due to pinhole occurrence.

[0039]

Also in the sample of Example 1 in which the thickness t of the thermal fusion layer 43 was set to 35 micrometers and cast polypropylene (CPP) was adopted, the number of pieces with bag rupture due to pinhole occurrence reduced to 7. The occurrence of a pinhole was further suppressed by forming the thermal fusion layer 43 of a material having high elastic modulus. Further, the number of pieces with bag rupture due to pinhole occurrence in the case of setting the thickness t to 50

micrometers is 5, reduced only by 2 from when the thickness is 35 micrometers.

Also when cast polypropylene (CPP) was adopted as the material for the thermal fusion layer 43, no great change was observed in the number of pieces with bag rupture due to pinhole occurrence between the case of setting the thickness t to 35 micrometers and the case of setting the thickness t to 50 micrometers.

[0040] <Example 2>

In Example 2, a relationship between the amount of increase in thermal conductivity of the vacuum thermal insulator 1 and the rate of moisture adsorption of the adsorbent 3 was investigated. In samples used in Example 2, the same configurations as those of Example 1 were adopted except for the configurations described below. The rate of moisture adsorption was defined as a value calculated from the rate of weight increase when the adsorbent 3 was left to stand still under an atmosphere having a temperature of 25 degrees centigrade and a relative humidity of 90%. Further, with regard to the amount of increase in thermal conductivity, thermal conductivity immediately after manufacture, and thermal conductivity after storage under an atmosphere having a temperature of 25 degrees centigrade and a relative humidity of 60% for 30 days were investigated, and the difference therebetween was calculated as the amount of increase.

[0041]

Immediately after the manufacture of the vacuum thermal insulator 1 of Example 2 and the vacuum thermal insulator of Comparative Example 2, each of the samples had a thermal conductivity of the same value, i.e., 1.8 mW/(m K), and no difference in thermal conductivity due to the rate of moisture adsorption of the adsorbent 3 was observed.

[0042]

In Example 2, as samples, vacuum thermal insulators 1 in each of which the adsorbent 3 was covered with the enclosure 4 together with the core 2 were produced. The adsorbent 3 had a rate of moisture adsorption of 15 wt%/h, 18 wt%/h, and 32 wt%/h. Further, as in Example 1, linear low-density polyethylene (LLDPE) and cast polypropylene (CPP) were adopted as the materials for the thermal fusion layers 43 of the samples. The thickness t of the thermal fusion layer 43 was set to a constant value of 50 micrometers, and hence the thickness T of the sealing portion 43a was 100 micrometers.

[0043]

In Comparative Example 2, calcium oxide having a rate of moisture adsorption of 14 wt%/h was used as the adsorbent 3, and the other configurations were the same as those of the vacuum thermal insulator 1 of Comparative Example 1.

Further, also in Comparative Example 2, as in Example 2, the thickness t of the thermal fusion layer 43 was set to a constant value of 50 micrometers, and the thickness T of the sealing portion 43a was 100 micrometers.

[0044]

In Table 2, the results of comparison of the amounts of increase in thermal conductivity of the vacuum thermal insulators 1 in the samples of Example 2 and Comparative Example 2 are shown.

Table 2

[0045]

As shown in Table 2, the vacuum thermal insulator of Comparative Example 2 had an amount of increase in thermal conductivity of 0.4 mW/(mK). In contrast, the vacuum thermal insulator 1 of Example 2 showed an amount of increase in thermal conductivity of 0.2 mW/(nrK) for all the adsorbents 3 each having a rate of moisture adsorption of 15 wt%/h or more. The sample in which cast polypropylene (CPP) was adopted for the thermal fusion layer 43 had an even lower amount of increase in thermal conductivity, i.e., 0.1 mW/(mK).

[0046]

As apparent from the foregoing, when the rate of moisture adsorption of the adsorbent 3 was 15 wt%/h or more, the amount of increase in thermal conductivity was maintained at a low value over a long period of time. Further, when cast polypropylene (CPP) was adopted for the thermal fusion layer 43, an even lower amount of change in thermal conductivity was obtained.

[0047] <Example 3>

In Example 3, a relationship between the number of pieces with bag rupture due to the occurrence of a pinhole of the vacuum thermal insulator 1 and the rate of moisture adsorption was investigated. In samples used in Example 3 and Comparative Examples 3, the same configurations as described in Example 1 were adopted except for the configurations described below.

[0048]

In Example 3, the thickness t of the thermal fusion layer 43 was set to 50 micrometers. Further, in Comparative Example 3, the thickness t of the thermal fusion layer 43 was set to 30 micrometers, which was below the lower limit value for the thermal fusion layer 43, and to 80 micrometers, which was above the upper limit value for the thermal fusion layer 43. In each of the samples, linear low-density polyethylene (LLDPE) was used as the material for the thermal fusion layer 43, and the rate of adsorption of the adsorbent 3 was set to a constant value of 18 wt%/h. [0049]

In Table 3, the results of comparison of the numbers of pieces with bag rupture due to pinhole occurrence and the amounts of increase in thermal conductivity of the vacuum thermal insulator 1 in the samples of Example 3 and Comparative Example 3 are shown.

Table 3

[0050]

As shown in Table 3, in the sample of Comparative Example 3 in which the thickness t of the thermal fusion layer 43 was set to 30 micrometers, which was below the lower limit value, the number of pieces with bag rupture due to pinhole occurrence was 42. Further, the amount of increase in thermal conductivity was 0.2 mW/(m'K), and the number of pieces with bag rupture due to pinhole occurrence was not able to be suppressed.

[0051]

In the sample in which the thickness t of the thermal fusion layer 43 was set to 80 micrometers, which was above the upper limit value, the number of pieces with bag rupture due to pinhole occurrence was 15, and the amount of increase in thermal conductivity was 0.3 mW/(nrK), and hence the amount of increase in thermal conductivity was not able to be suppressed.

[0052]

In contrast, in Example 3, the number of pieces with bag rupture due to pinhole occurrence was 14, and the amount of change in thermal conductivity was 0.2 mW/(nrK). That is, the occurrence of bag rupture due to a pinhole was suppressed, and the amount of increase in thermal conductivity was also suppressed.

[0053]

In view of the foregoing, it was found that, when the thickness t of the thermal fusion layer 43 was set to 35 micrometers or more and 70 micrometers or less and the rate of moisture adsorption of the adsorbent 3 was set to 15 wt%/h or more and 32 wt%/h or less, the vacuum thermal insulator 1 capable of suppressing the occurrence of bag rupture due to a pinhole, and capable of adsorbing water vapor that has entered into its inside was able to be obtained.

[0054]

In the vacuum thermal insulator 1 according to Embodiment 1 described above, the thickness t of the thermal fusion layer 43 is set to 35 micrometers or more and 70 micrometers or less. Accordingly, the thermal fusion layer 43 has a thickness capable of sufficiently suppressing the occurrence of bag rupture due to the occurrence of a pinhole caused by piercing with the core 2. Further, the adsorbent 3 has a rate of moisture adsorption of 15 wt%/h or more and 32 wt%/h or less, and hence has a rate of moisture adsorption that can sufficiently adsorb water vapor that has entered through the sealing portion 43a in which parts of the thermal fusion layer 43 are fused to each other and which has a thickness T of 70 micrometers or more and 140 micrometers or more. With this, the degree of vacuum of the vacuum space is maintained to suppress a rise in thermal conductivity, and thus the heat insulating performance can be maintained for a long period of time.

[0055]

In particular, when the rate of moisture adsorption of the adsorbent 3 is set to 17 wt%/h or more and 22 wt%/h or less, a rise in thermal conductivity can be stably reduced, and besides, a decrease in moisture adsorbability in the manufacturing process can be suppressed.

[0056]

Further, when the thermal fusion layer is formed of high-density polyethylene or cast polypropylene having high elastic modulus and being excellent in barrier property against water vapor, the occurrence of bag rupture due to the occurrence of a pinhole caused by piercing with the core 2 is further suppressed, and the penetration amount of water vapor can be reduced.

[0057]

Further, when unevenness in which the difference between a surface of a depressed portion and a surface of a projected portion is 2 mm or more and 10 mm or less is formed on the surface of the vacuum thermal insulator 1, heat exchange between the vacuum thermal insulator 1 and a copper pipe for heat transfer can be promoted.

[0058]

Further, when the adsorbent 3 is covered with a packaging material formed of any one of paper, a nonwoven fabric, a plastic film, and a mesh cloth, workability can be improved while the air permeability of the adsorbent 3 is ensured. The packaging material may be formed by laminating a plurality of layers each formed of paper, a nonwoven fabric, a plastic film, or a mesh cloth.

[0059]

The core 2 is desirably a fiber assembly having low thermal conductivity and being easy to handle, in particular, glass wool or any other such material.

[0060]

Embodiment 2

Fig. 6 is a sectional view for illustrating a schematic configuration of a thermal insulation container 100 according to Embodiment 2 of the present invention. The thermal insulation container 100 is, for example, a refrigerator or any other such device, which is required to have heat insulating performance over a long period of time.

[0061]

As illustrated in Fig. 6, the thermal insulation container 100 includes an inner box 110 and an outer box 120. In addition, in a space between the inner box 110 and the outer box 120, the vacuum thermal insulator 1 described in Embodiment 1 is arranged to perform heat insulation between the inner box 110 and the outer box 120. The position at which the vacuum thermal insulator 1 is arranged is, for example, a position in close contact with an outer wall surface of the inner box 110 or any other such position, and the vacuum thermal insulator 1 is arranged at a position allowing heat insulation to be performed between the inner box 110 and the outer box 120. [0062]

As described above, the thermal insulation container 100 includes the vacuum thermal insulator 1 having low thermal conductivity. With this, a state in which the thermal conductivity between the inner box 110 and the outer box 120 is low is maintained, and hence high heat insulating performance of the thermal insulation container 100 can be maintained over a long period of time. This leads to a reduction in power consumption in a refrigerator or any other such device including the thermal insulation container 100.

[0063]

The vacuum thermal insulator 1 has heat insulating performance higher than that of a urethane foam heat insulating material 130 or other materials, and hence the thermal insulation container 100 can obtain heat insulating performance higher than that of a thermal insulation container 100 using only the urethane foam heat insulating material 130. However, the urethane foam heat insulating material 130 may be filled into an area other than the vacuum thermal insulator 1 in the space between the inner box 110 and the outer box 120.

[0064]

Further, in the foregoing description, the vacuum thermal insulator 1 of the thermal insulation container 100 is in close contact with the outer wall surface of the inner box 110, but the vacuum thermal insulator 1 may be in close contact with the inner wall surface of the outer box 120. The vacuum thermal insulator 1 may be arranged in the space between the inner box 110 and the outer box 120 so as not to be in close contact with any of the inner box 110 and the outer box 120 through use of a spacer or other members.

In the foregoing description, illustration and description are omitted for parts equivalent to those of a thermal insulation container to be used for a general refrigerator or any other such device.

[0065]

The vacuum thermal insulator 1 according to the present invention may be variously modified without being limited to the above-mentioned embodiments, and the embodiments described above and modification examples may be carried out in combination with each other.

[0066]

For example, in the foregoing, there is exemplified a case in which the drying of the core 2 and the enclosure 4 in the manufacturing process is performed by heat treatment at 100 degrees centigrade for 2 hours. However, the temperature and time period of the heat treatment are not limited thereto as long as the temperature and the time period allow the moisture in the core 2 and the enclosure 4 to be removed. Further, although the drying of the core 2 and the enclosure 4 is performed under a state in which the core 2 is covered with the enclosure 4, the core 2 may be covered with the enclosure 4 after the core 2 and the enclosure 4 have been separately dried.

[0067]

Further, in the above-mentioned manufacturing process of the vacuum thermal insulator 1 according to Embodiment 1, the adsorbent 3 is arranged between the core 2 and the enclosure 4 after the drying of the core 2 and the enclosure 4. However, the adsorbent 3 may be arranged before the drying of the core 2 and the enclosure 4. [0068]

Further, in Embodiment 2, the configuration in which the vacuum thermal insulator 1 is used in the thermal insulation container 100 of a refrigerator including a cooling source is given as an example, but the present invention is not limited thereto. The vacuum thermal insulator 1 may also be used in a thermal insulation container of a heat retention tank including a heating source or a thermal insulation container, such as a cooler box, not including a cooling source or a heating source. Further, the vacuum thermal insulator 1 may also be used as a heat insulating member of cooling equipment or heating equipment in, for example, an air-conditioner, an air-conditioner for vehicles, and a hot water dispenser, as well as the thermal insulation container 100. Further, the shape of the vacuum thermal insulator 1 is not limited to a predetermined shape, and the vacuum thermal insulator 1 may also be used in a heat insulating bag including an outer bag and an inner bag that can change in shape freely, and other heat insulating containers.

Reference Signs List [0069] 1 vacuum thermal insulator 2 core 3 adsorbent 4 enclosure 41 surface protective layer 42 gas barrier layer 43 thermal fusion layer 43a sealing portion 100 thermal insulation container 110 inner box 120 outer box 130 urethane foam heat insulating material T thickness of sealing portion

Claims

CLAIMS [Claim 1] A vacuum thermal insulator comprising: a core configured to secure a vacuum space; an adsorbent configured to adsorb moisture; and an enclosure configured to cover the core and the adsorbent, the vacuum thermal insulator having a depressurized inside enclosed and sealed by the enclosure, the enclosure including a surface protective layer, a gas barrier layer, and a thermal fusion layer, the enclosure including a sealing portion in which parts of the thermal fusion layer at a peripheral edge portion of the enclosure are fused to each other, the thermal fusion layer having a thickness of 35 micrometers or more and 70 micrometers or less, the adsorbent containing calcium oxide having a rate of moisture adsorption of 15 wt%/h or more and 32 wt%/h or less. [Claim
2] The vacuum thermal insulator of claim 1, wherein the adsorbent has a rate of moisture adsorption of 17 wt%/h or more and 22 wt%/h or less. [Claim
3] The vacuum thermal insulator of claim 1 or 2, wherein the thermal fusion layer comprises high-density polyethylene or cast polypropylene. [Claim
4] The vacuum thermal insulator of any one of claims 1 to 3, wherein the vacuum thermal insulator has, on a surface thereof, unevenness comprising projected portions and depressed portions, wherein a height difference between the projected portions and the depressed portion is 2 mm or more and 10 mm or less. [Claim
5] The vacuum thermal insulator of any one of claims 1 to 4, wherein a packaging material for the adsorbent comprises a member selected from a first group consisting of paper, a nonwoven fabric, a plastic film, and a mesh cloth, or a member obtained by laminating two or more kinds of members selected from the first group. [Claim
6] The vacuum thermal insulator of any one of claims 1 to 5, wherein the core comprises a fiber assembly. [Claim
7] The vacuum thermal insulator of any one of claims 1 to 6, wherein the core comprises glass wool. [Claim
8] Athermal insulation container, comprising the vacuum thermal insulator of any one of claims 1 to 7.