JPS6361589B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a heat insulator used in refrigerators, frozen prefabricated products, and the like. Prior Art FIG. 3 shows a conventional heat insulator. The configuration of the conventional example will be explained below with reference to FIG. In recent years, attention has been paid to the use of a heat insulator with a reduced internal pressure for the purpose of improving the heat insulation performance of a heat insulating box.
As the core material of this heat insulator, powder such as perlite, honeycomb, foam, etc. are used. For example, as shown in JP-A-57-133870, a proposal has been made to use a hard urethane foam having open cells as the core material. This Japanese Patent Application Laid-open No. 57-133870 is explained with reference to Fig. 3. In the figure, 1 is a heat insulating structure, in which a hard urethane foam 2 with open cells is covered with a container 3 made of an airtight thin film.
The pressure is reduced to 0.001mmHg and it is sealed. The hard urethane foam 2 is characterized in that a commercially available general material with a cell skeleton diameter of about 300 to 1000 μm is vacuum degassed under high temperature and high humidity to burst the cells and obtain open cells. Problems to be Solved by the Invention In such a heat insulating structure 1, since the bubble skeleton diameter of the hard urethane foam 2 is 300 to 1000 μm, the thermal conductivity of the gas is insufficient unless the pressure is 0.001 mmHg or less. Therefore, excellent heat insulation properties cannot be obtained. Basically, the thermal conductivity of a gas decreases rapidly when the distance between the walls of the gas layer (in this configuration, the bubble skeleton diameter) becomes shorter than the mean free path of the gas, but the longer the distance between the walls, the more the same Lower pressures are required to obtain gas thermal conductivity. The general formula is shown by the following formula (1). Kg=AρCr [Lfd/(Lf+d)] ...(1) Kg: Thermal conductivity of gas, A: Constant, ρ: Density [Kg/m ³ ], V: Average molecular velocity [m/s], Lf: Mean free path, Cr: Constant volume specific heat [Kcal/Kg℃], d:
Distance between walls [m] Therefore, in the conventional example, the bubble skeleton diameter is
Since the diameter is 300 to 1000 μm, a pressure of 10 ⁻³ mmHg or less, which is difficult to handle industrially, is required, leading to problems such as the need for large-scale equipment and long exhaust time in mass production. Furthermore, in the pressure range below 10 ^-3 mmHg, it is easily affected by the amount of gas released by the material. In the case of this configuration of an organic substance that tends to contain a monomer component with a low molecular weight, there is a problem that the evacuation time is particularly long, resulting in poor mass production efficiency. In view of the above problems, the present invention aims to shorten the evacuation time and enable mass production by obtaining excellent heat insulation performance in a low vacuum range that is industrially easy to handle. Means for Solving the Problems The present invention uses 3 parts by weight or more of organic polyisocyanate, polyol, catalyst, blowing agent, cell communication agent, and foam stabilizer per 100 parts by weight of polyol, and A rigid urethane foam with an open cell structure obtained by mixing and foaming a silicone surfactant having a hydroxyl group at the end is used as the core material of the heat insulator. Function The present invention has a core material having a fine cell skeleton as described above, and therefore, by covering the core material with a container made of a metal-plastic laminate film and reducing the internal pressure, it is possible to achieve an industrial pressure of about 0.1 to 0.01 mmHg. Excellent heat insulation performance can be obtained even at a pressure that is easy to handle, and mass production efficiency can be greatly improved by shortening the evacuation time. Examples of silicone surfactants having a hydroxyl group at the end of the molecular structure that can be used in the present invention include silicone F-305, F-308, F-
335 (manufactured by Shin-Etsu Chemical Co., Ltd.), Tegostave B-8404
(manufactured by Gold Schmitt Co., Ltd.). Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. In the figure, 4 is a hard urethane foam foamed in a high-pressure urethane foaming machine using the raw materials shown in the table below, cured, aged at room temperature, and then cut into a predetermined size.

【table】

[Table] In the table, polyol A is produced using tolylene diamine as an initiator (hereinafter referred to as propylene oxide).
Hydroxyl value 400 obtained by addition polymerization of (referred to as PO)
mgKOH/g polyether polyol.
Polyol B is a polyether polyol with a hydroxyl value of 450 mgKOH/g obtained by addition polymerization of PO using sucrose-diethylene glycol as an initiator. Foam stabilizer A is silicone surfactant F-338 manufactured by Shin-Etsu Chemical Co., Ltd., which has a hydroxyl group at the end of its molecular structure.
Foam stabilizer B is silicone surfactant F-318 manufactured by Shin-Etsu Chemical Co., Ltd., which has an alkyl group instead of a hydroxyl group at the end of its molecular structure. The blowing agent was Freon R-11 manufactured by Showa Denko KK, the catalyst A was dimethylethanolamine, the catalyst B was dibutyltin dilaurate, and the cell communication agent was calcium stearate manufactured by NOF Corporation.
In addition, the organic isocyanate is manufactured by Nippon Polyurethane Co., Ltd.
crude diphenylmethane diisocyanate (amine equivalent weight 136) from Various combinations of these raw materials are used for foaming, some of which are used as examples.
Nos. 1 to 4 and Nos. A, B, and C as comparative examples are shown in the table. The density of the obtained hard urethane foam 4,
The open cell ratio and cell skeleton diameter are also shown in the table. After this,
The obtained hard urethane foam 4 was heated to about 2 at 120°C.
After heating for a period of time to evaporate the adsorbed moisture, the container 5 is covered with a metal-plastic laminate film made of a laminate of aluminum-deposited polyester film and polyethylene film.
The pressure was reduced to 0.001, 0.01, 0.1, 0.5, and 1.0 mmHg, and the heat insulator 6 was obtained. The exhaust time at this time is
Examples No. 1 to No. 4 are 40 minutes, 5 minutes, and 2 minutes, respectively.
35 minutes, 5 minutes, 2 minutes, 1 minute, and 30 seconds in Comparative Examples Nos. A to C, respectively. The thermal conductivity of the obtained heat insulator 6 immediately after sealing is shown in the table, and the change in thermal conductivity over time after 80 days is shown in Example No.
For Comparative Example No. 1 and Comparative Example No. C, experiments were conducted on samples with an internal pressure of 0.01 mmHg, and the results are also shown in the table. The thermal conductivity was measured using K-Matic manufactured by Shinku Riko Co., Ltd. at an average temperature of 24°C. As is clear from the table, organic polyisocyanate, polyol, catalyst, blowing agent, cell communication agent,
and 3 parts per 100 parts by weight of polyol as a foam stabilizer.
The rigid urethane foam 4 with an open cell structure obtained by mixing and foaming a silicone surfactant that is used in an amount of at least part by weight and has a hydroxyl group at the end of its molecular structure has a very fine cell skeleton. I found out. This is because by using 3 parts by weight or more of the foam stabilizer, the surface tension is sufficiently lowered, and the foam regulating effect exceeds the foam regulating force caused by the foam breaking effect of the cell communication agent. However, the detailed theory has not yet been elucidated. By using the hard urethane foam 4 with this fine cell skeleton as the core material of the heat insulator 6, the gas heat conduction in the heat insulator 6 is reduced to the same level as that of a foam with a larger cell structure even at high pressure. 0.1 to 0.01 mm, which is easy to handle industrially.
Demonstrates excellent heat insulation performance with Hg. As a result, the exhaust time is short, making mass production easier.
The exhaust system can also be produced with a simple device, which greatly contributes to productivity. It should be noted that if the bubble skeleton is made finer, the exhaust resistance will increase and the exhaust time required to reduce the pressure to the specified pressure will become longer; however, in the 0.01 mmHg region,
0.001 with no effect and further dominated by the molecular flow region
The effect appears at mmHg. Therefore, there is no problem with productivity by using a pressure of 0.1 to 0.01 mmHg, which provides sufficient heat insulation performance even when miniaturized. In addition, in the case of a silicone surfactant having an alkyl group at the end, a similarly fine cell skeleton can be obtained, but when used as the core material of the heat insulator 6, the thermal conductivity changes greatly over time, resulting in quality problems. It turned out to be. This is because silicone surfactants with alkyl groups at the end have no reaction activity.
It is dispersed in the hard urethane foam 4 with a low molecular weight without being converted into a resin, and evaporates over time, increasing the internal pressure and deteriorating the thermal conductivity. Silicone surfactants with a hydroxyl group at the end do not have this problem because they react with the organic polyisocyanate and form a resin. Effects of the Invention As is clear from the above description, the present invention has the following advantages:
The following effects can be obtained. a Silicone surfactant that is used as an organic polyisocyanate, polyol, catalyst, blowing agent, cell communication agent, and foam stabilizer in an amount of 3 parts by weight or more per 100 parts by weight of polyol, and has a hydroxyl group at the end of its molecular structure. The rigid urethane foam with an open cell structure obtained by mixing and foaming
Because it has an extremely fine bubble skeleton, if it is covered with a container made of metal-plastic laminate film and the internal pressure is reduced, the heat conduction of the gas will be sufficiently reduced even at a pressure of 0.01 to 0.1 mmHg, which is easy to handle industrially. Excellent heat insulation performance can be obtained. Therefore, mass production can be carried out in a short time and with simple exhaust equipment, contributing to a significant improvement in productivity. b Because silicone surfactants with hydroxyl groups at the ends of their molecular structures are used as foam stabilizers, they react with organic polyisocyanates and turn into resins, resulting in evaporation and increased internal pressure even if the insulation is left for a long period of time. There is no deterioration in thermal conductivity. Therefore, a heat insulator with stable quality can be obtained.

[Brief explanation of drawings]

FIG. 1 is an external perspective view of a rigid urethane foam according to an embodiment of the present invention, FIG. 2 is a sectional view of the same heat insulating body, and FIG. 3 is a sectional view of a conventional heat insulating structure. 4...Hard urethane foam, 5...Container, 6
...Insulator.

Claims (1)

[Claims] 1. Use 3 parts by weight or more of organic polyisocyanate, polyol, catalyst, blowing agent, cell communication agent, and foam stabilizer per 100 parts by weight of polyol,
A hard urethane foam with an open cell structure obtained by mixing and foaming a silicone surfactant having a hydroxyl group at the end of its molecular structure is covered with a container made of a metal-plastic laminate film.
An insulator with reduced pressure inside.