JPH08320179A - Vacuum heat insulation material and refrigerator - Google Patents

Abstract

PURPOSE: To increase strength and restrict an increase of heat conductivity due to secular deterioration and hence ensure a heat insulation state stable over a long period of time by forming a core material inserted into an airtight container with urethane foam subjected to a high temperature high humidity processing. CONSTITUTION: In a vacuum heat insulation material wherein a core material is inserted into an airtight container and the inside of the container is reduced in its pressure and the container is sealed, the core material is formed with urethane foam subjected to a high temperature high humidity processing. Urethane foam used as the core material is desirably hard open cell urethane foam. With the high temperature high humidity processing, a non-reaction isocyanate group remaining in the hard open cell urethane foam is inactivated and hence it does not produce carbon dioxide gas even it reacts with water. Hereby, strength is increased, and increased heat conductivity due to secular deterioration is restricted, and hence a heat insulation state stable over a long period of time is ensured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum heat insulating material and a refrigerator using the same.

[0002]

2. Description of the Related Art In a conventional refrigerator, a space formed by combining an inner box made of a plastic molded body and an outer box made of a metal plate is filled with a polyurethane foam insulating material to form a heat insulating box body. In order to secure the space inside the refrigerator by improving the thickness of the refrigerator, and to improve the initial and temporal insulation performance,
A vacuum heat insulating material, which inserts a core material into an airtight container, decompresses the inside, and then seals it, has come to be used in refrigerators.
A general vacuum heat insulating material is, for example, a core material such as precipitated silica, fine powder perlite, continuous urethane foam, etc., which is surrounded by a container having a high gas barrier property made of a laminated film in which a metal foil and a plastic film are laminated, After being decompressed, it has a shape in which the peripheral portion is sealed by heat fusion.

In such a vacuum heat insulating material, the thermal conductivity showing the performance as a vacuum heat insulating material is as follows: heat conduction of gas in voids inside the core material, contact heat conduction between substances constituting the core material,
It is expressed as the sum of the four elements of heat transfer due to radiation transfer and convection. In particular, it has been proved that the thermal conductivity of gas is dominant, and theoretically, the smaller the gap between the substances constituting the core material and the lower the pressure inside the gas barrier container, the smaller the thermal conductivity. For example, it is known that when a precipitated silica fine powder (having a void size of 10 μm or less) is used as a core material, a low thermal conductivity can be obtained at a relatively high internal pressure. A lower internal pressure is required for perlite and continuous urethane foam, which have a larger particle size than the precipitated silica fine powder.

As described above, since the thermal conductivity of the vacuum heat insulating material is determined by the internal pressure, it is necessary to keep the internal pressure below a certain value in order to maintain the heat insulating performance. Factors that increase the internal pressure of the vacuum heat insulating material are 1) gas leakage from the outside of the vacuum heat insulating material, 2) generated gas from the inside of the vacuum heat insulating material, and suppressing gas leaks and generated gas based on these factors. Is important.

[0005]

However, the factor 1) can be eliminated by changing the structure of the airtight container, but the factor 2) has a large void and a low boiling point residue. It was difficult to use the internal material or the urethane foam which may decompose / react as the core material. Urethane foam is usually produced by using polyol and polyisocyanate as main raw materials. That is, a polyol having a plurality of hydroxyl groups (-OH) and a plurality of isocyanate groups (-NC
When a foaming agent or a catalyst is added to and mixed with polyisocyanate having O), a hydroxyl group and an isocyanate group undergo a chemical reaction to form a urethane bond (-NHCOO-), which is cured while foaming to form a urethane foam. .

On the other hand, the strength of the urethane foam thus formed is influenced by the mixing ratio of the hydroxyl group (-OH) in the polyol and the isocyanate group (-NCO) in the polyisocyanate. This mixing ratio is defined as an index. When the index is 90, it indicates that the urethane foam is a mixture of isocyanate groups in an amount of 90% of hydroxyl groups. The relationship between the index and the compressive strength of urethane foam is shown in FIG. As shown in Fig. 1, the compressive strength of urethane foam is closely related to the index, and if the desirable compressive strength for the core material of the vacuum heat insulating material is 100, a rigid continuous urethane foam with an index of 100 or more is desirable. become. Therefore, in the case of rigid continuous urethane foam, which requires more strength, it often has a high index, in which case the isocyanate group (-N
Since CO) increases, the amount of gas generated from the inside of the vacuum heat insulating material increases with time, as will be described later, and as a result,
There is a problem that the thermal conductivity increases due to deterioration over time.

[0007] The present invention has been made to address such a problem, and enhances and maintains the strength, and
An object of the present invention is to provide a vacuum heat insulating material capable of suppressing an increase in heat conductivity due to aging deterioration to a small extent and obtaining a stable heat insulating state for a long time, and a refrigerator using the same.

[0008]

According to a first aspect of the present invention, in a vacuum heat insulating material in which a core material is inserted into an airtight container, the inside of the container is depressurized and then sealed, the core material is a urethane subjected to high temperature and high humidity treatment. It is characterized by consisting of a form.

According to a second aspect of the present invention, in a refrigerator in which a heat insulating material is provided in an outer box, the heat insulating material is formed by inserting a core material made of urethane foam that has been subjected to high temperature and high humidity treatment into an airtight container, It is a vacuum heat insulating material that is sealed after depressurization.

The urethane foam used as the core material according to claims 1 and 2 is preferably a rigid continuous urethane foam. When the amount of isocyanate groups (-NCO) remaining in the rigid continuous urethane foam increases, it becomes easy to generate carbon dioxide gas by reacting with water as shown in the following formula after vacuum sealing.

[0011]

Embedded image Especially in the case of urethane foam with an index exceeding 100, the unreacted isocyanate group increases, so
The increase in internal pressure after vacuum sealing is dominated by the generation of carbon dioxide gas due to the above reaction. In the inventions according to claims 1 and 2, unreacted isocyanate groups that react with moisture after vacuum sealing and cause generation of carbon dioxide gas are reduced or eliminated in advance by high temperature and high humidity treatment before vacuum sealing.

In the inventions according to claims 1 and 2, the high-temperature and high-humidity treatment means a treatment for inactivating the unreacted isocyanate group. Specifically, carbon dioxide gas is generated even when it reacts with water. It means to lose. Although the treatment conditions can be arbitrarily selected as long as they are the conditions for inactivating unreacted isocyanate groups, practical treatment conditions include 40 ° C to 100 ° C, relative humidity 50% to 90%, and treatment time 10 The range of hours to 100 hours is preferred.

As the urethane foam raw material, known polyol components and polyisocyanate components capable of forming urethane bonds can be used. Examples of the polyol component include polyethers, polyesters and glycols, and examples of the polyisocyanate component include tolylene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI), and derivatives thereof. In addition to the foaming aid, additives such as a foaming aid, a foam stabilizer, a reaction catalyst, a flame retardant, an antistatic agent, and a colorant may be added to the above-mentioned polyurethane foam raw material, if necessary.

The airtight container according to claims 1 and 2 is a container formed of a material having a high gas barrier property,
For example, a container composed of a laminated film of a plastic film and a metal foil can be used.

[0015]

[Function] A vacuum heat insulating material that uses a core material that has been subjected to a high temperature and high humidity treatment in advance to reduce or eliminate the amount of residual isocyanate groups makes it possible to suppress the gas generated from the inside and reduce the heat due to deterioration over time. The deterioration of conductivity can be prevented. In addition, since the heat insulation performance does not deteriorate, a refrigerator using such a vacuum heat insulating material has excellent durability.

[0016]

【Example】

Examples 1 to 6 and Comparative Examples 1 to 3 Hard communicating urethane foams having different indexes were subjected to high temperature and high humidity treatment to prepare core materials. On the other hand, insert the above core material into an airtight container in which a polypropylene film layer is used as a sealing layer on three sides of a laminated film made of polyethylene terephthalate film, aluminum foil and polypropylene film, and evacuate and leave under reduced pressure. A vacuum heat insulating material was produced by sealing one side.

With respect to the obtained vacuum heat insulating material, the thermal conductivity was evaluated over time. There are 3 types of index, 85, 100 and 110, 2 types of high temperature and high humidity treatment at a temperature of 70 ° C and 95% relative humidity for 4 days, and a temperature of 60 ° C and 90% relative humidity for 4 days. I went there. All urethane foams had the same formulation, and were used as a core material of a vacuum heat insulating material after being sufficiently dried after being subjected to high temperature and high humidity treatment. The condition for evaluating the vacuum heat insulating material over time is to leave it at room temperature.

Table 1 shows the indexes and processing conditions, and Table 2 shows the evaluation results of the thermal conductivity.

[Table 1]

[Table 2] As shown in Tables 1 and 2, by using the hard continuous urethane foam subjected to the high temperature and high humidity treatment as the core material of the vacuum heat insulating material, deterioration of the thermal conductivity of the vacuum heat insulating material with time can be reduced.

As the index increases, the thermal conductivity of the vacuum heat insulating material using untreated urethane foam as the core material deteriorates with time. However, the effect of high temperature and high humidity treatment is particularly high for urethane foam with a large index. Is also large, and the deterioration of thermal conductivity can be greatly improved.

In the above embodiment, the conditions of high temperature and high humidity are
Although only two conditions are described, the amount of isocyanate groups remaining in the urethane foam varies depending on the foam formulation and the foaming process, so it is necessary to set the conditions suitable for the urethane foam. In that case, the isocyanate group is measured by an infrared spectrophotometer, or the urethane foam is heated to 100 ° C or higher in the presence of water, and the gas generated at this time is introduced into the gas chromatography GC-FID to generate the gas. The conditions of high temperature and high humidity treatment can be set by using the method of measuring the carbon dioxide concentration.

Further, the vacuum heat insulating material obtained in the above-mentioned embodiment is arranged on both sides and back surface of the refrigerator main body, and the refrigerator is filled with the closed cell urethane foam heat insulating material, and a continuous test operation is conducted. As a result, the power consumption changed as shown in Table 3.

[0022]

[Table 3] As shown in Table 3, in the refrigerator of the present invention, the amount of change in power consumption was small and the heat insulating effect was maintained for a long time.

[0023]

In the vacuum heat insulating material according to the first aspect of the present invention, since urethane foam which has been subjected to high temperature and high humidity treatment is used as the core material, generation of gas generated inside the vacuum heat insulating material can be suppressed. As a result, deterioration of the thermal conductivity over time can be significantly suppressed, and the heat insulating effect can be maintained for a long period of time.

In the refrigerator according to the second aspect, since the vacuum heat insulating material which uses the urethane foam subjected to the high temperature and high humidity treatment as the core material is arranged in the outer box, the heat insulating effect can be maintained for a long period of time and the durability is improved. Is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an index and strength of urethane foam.

Front Page Continuation (72) Inventor Kumiko Takeshima 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa, Ltd.

Claims (2)

[Claims] 1. A vacuum heat insulating material in which a core material is inserted into an airtight container, the inside pressure is reduced, and then sealed, wherein the core material is made of urethane foam subjected to high temperature and high humidity treatment. Insulation. 2. A refrigerator in which a heat insulating material is provided in an outer box, wherein the heat insulating material is a hermetically-sealed container in which a core material made of urethane foam subjected to high-temperature and high-humidity treatment is inserted, and the inside is depressurized and then sealed. A refrigerator characterized by being a vacuum heat insulating material that stops.