JPH0794949B2 - Vacuum insulation - Google Patents

Description

The present invention relates to a heat insulating material used in refrigerators, freezers, showcases, and the like.

[Prior art and its problems]

Generally, glass wool was initially used as a heat insulating material for refrigerators and freezers, but recently, polyurethane foam has been widely used as a mainstream material. This polyurethane foam is made by injecting polyurethane into the freezer wall, foaming it with Freon, and forming it as a heat insulating material. Its thermal conductivity is 0.02Kcal / mh ℃, and even the best one is 0.017Kcal / mh ℃. Is the limit.

Therefore, application of the vacuum adiabatic method is conceivable as heat insulation aiming at higher performance, and the thermal conductivity is 0.01 Kcal / m.
Those below h. ° C have appeared. The outline is that an inorganic material such as pearlite is covered with a plastic film having a high gas barrier property and vacuum-packed at a vacuum degree of 1 torr or less.

The disadvantages of this heat insulating material in that case are as follows.

A plastic film that is a high barrier against gas and water vapor is used as the outer covering material, but since the heat insulating material is a vacuum, long-term use requires oxygen from the outside.
Water vapor (water) permeates and infiltrates, and the degree of vacuum in the container gradually decreases compared to the initial level. That is, the thermal conductivity is so high that a high degree of heat insulation cannot be maintained.

Therefore, as a conventional technique for solving these problems, as disclosed in JP-A-58-104081 and JP-A-59-225275, as an air adsorbent, for example, a zeolite such as molecular sieves. Also, it is known to use, for example, silica gel, calcium chloride, quick lime or the like as a moisture adsorbing substance in the heat insulating material.

However, the inventions disclosed in the above publications each use an adsorbent for water and air, and these adsorbents remove water and air (oxygen) by changing them to another substance by a chemical change. However, since it is simply removed by adsorption, the adsorbed substance has a drawback of desorbing with time or temperature change.

[Object of the Invention]

The present invention is to improve the above-mentioned problems, and in a vacuum heat insulating material filled with a heat insulating material in a plastic laminate film container and held in a vacuum, the initial thermal conductivity is maintained for a long period of time, and the heat insulating performance is improved. The object is to obtain a vacuum heat insulating material that does not decrease or has a very small decrease.

[Structure of Invention]

The present invention relates to a vacuum heat insulating material in which a plastic laminated film container is filled with the heat insulating material and is held in a vacuum, wherein iron powder is added to the heat insulating material.

According to the present invention, the moisture and oxygen that have penetrated and penetrated into the laminated film container held in a vacuum first adhere to the iron powder, and the oxygen oxidizes the iron powder by the catalytic action of the moisture. That is, the moisture and oxygen permeated and penetrated into the laminated film container are removed, the initial degree of vacuum can be maintained, and the deterioration of the thermal conductivity can be suppressed.

Hereinafter, the heat insulating material using iron powder will be described.

Iron powder (Fe) becomes ferrous hydroxide (Fe (OH) ₂ ) due to the moisture that has passed through the plastic laminate film,
Water (H ₂ O) is desorbed and becomes ferrous oxide (FeO).
The desorbed water adheres to another iron powder and repeats the reaction so that the iron powder becomes ferrous hydroxide. In addition, ferrous oxide is converted to ferric oxide (Fe
₂ O ₃・ 2H ₂ O).

Since this is an irreversible chemical reaction, water and oxygen are not desorbed from ferric oxide.

That is, oxygen and water that have penetrated the plastic laminate film and penetrated into the vacuum heat insulating material are completely removed by the iron powder, and the initial degree of vacuum is maintained.

It should be noted that 1 g of iron powder has the ability to absorb about 250 ml of oxygen, and the plastic laminate film used for this vacuum heat insulating material is provided with at least one metal foil or a metal thin film layer formed by vapor deposition, sputtering or the like. Therefore, the oxygen permeation rate is about 0.02cc / m ² · 24h (at room temperature and normal pressure) or less, and the water permeation rate is the same. That is, when the vacuum heat insulating material having a surface area of 1 m ² contains 1 g of iron powder, it can continue absorbing oxygen for 30 years or more and maintain the initial degree of vacuum.

Next, the plastic laminate film will be described. The plastic laminate film, as a gas / moisture barrier layer, a metal foil, or a film obtained by subjecting polyester, vinyl chloride-vinylidene chloride film or the like to metal vapor deposition, is used at least one layer, and as a sealant material for the innermost layer, A heat-sealable resin such as polyethylene or polypropylene is used.

As the heat insulating material, powders of silica, diatomaceous earth, pearlite, etc. are mainly used, and the thermal conductivity of the vacuum insulating material varies depending on the type of heat insulating material used. The inside of the plastic film container filled with heat insulating material and iron powder is evacuated to a vacuum, but generally, as the pressure decreases, the thermal conductivity decreases, and in order to obtain a thermal conductivity of 0.01 Kcal / mh ° C,
Normally exhausted to a pressure below 1 torr.

Next, the content of the iron powder added will be described.

The iron powder is preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the heat insulating material. If it is 0.5 parts by weight or less, the moisture and oxygen absorption capacity is not sufficient, and if it is 10 parts by weight or more, it is sufficient in terms of absorption capacity, but in general, metal has a high thermal conductivity,
This is unsuitable because the thermal conductivity of the heat insulating material as a whole increases.

Examples will be described below.

〔Example〕

Heat-resistant kraft paper was filled with 100 parts by weight of dried silica powder (manufactured by Fuji Davison Chemical Co., Ltd., trade name Syloid 255, average particle size 1.8μ) and 1 part by weight of iron, and this was deposited with an Al vapor-deposited polyester film Made, Lumirror P-11,12μ)
/ Vinylidene chloride film (Dow Chemical, Saran HB
25μ) / polyethylene film (Tama Poly Co., Ltd., M
-16,60μ) in a laminated film container
In a vacuum packaging machine equipped with a heat fusion device, 0.1 t
With the vacuum degree of orr evacuated, the opening of the film container was heat-sealed and sealed to obtain a vacuum heat insulating material having a thickness of 20 m / m and a size of 300 × 300 m / m.

This vacuum heat insulating material, temperature 40 ℃, relative humidity 90%, oxygen concentration
After leaving it for 50 days under a constant temperature and humidity condition of 80%, an accelerated test was performed to check long-term storage stability (reliability).

At the same time, the same accelerated test was performed on Conventional Example 1 having the same structure as the present invention except that it did not contain iron powder, and Conventional Example 2 having a structure in which 0.5 part by weight of activated carbon was added instead of iron powder. The results are shown in Table-1.

The thermal conductivity was measured using a QTM type thermal conductivity meter manufactured by Showa Denko KK with a temperature difference between 80 ° C and 60 ° C.

As is clear from the above table, when an accelerated test was performed at 40 ° C-90% RHO ₂ concentration of 80%, the vacuum thermal insulation material containing iron powder showed a very small change in thermal conductivity, and the thermal insulation performance was very small. It is clear that it has an excellent effect on the deterioration.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY As described above, the present invention is a vacuum heat insulating material in which a plastic laminate film container is filled with a heat insulating material, and in a vacuum heat insulating material held in vacuum, iron powder is added to the heat insulating material. The moisture and oxygen gradually permeated into the plastic laminate film container cause a chemical reaction with the iron powder and are absorbed and removed, whereby the initial degree of vacuum can be maintained and deterioration of the thermal conductivity can be suppressed. Therefore, the initial excellent heat insulating performance can be maintained for a long period of time, and its practical value is extremely large.

[Brief description of drawings]

 FIG. 1 is a sectional explanatory view showing an embodiment of the present invention. 1 …… Plastic laminated container 2 …… Inner bag 3 …… Insulation material 4 …… Iron powder

Claims (1)

[Claims] 1. A vacuum heat insulating material in which a plastic laminated film container is filled with the heat insulating material and is held in vacuum, wherein iron powder is added to the heat insulating material.