JPH025958B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to powder vacuum insulation. Conventionally, glass fiber,
Rock wool, polyurethane foam, etc. are used.
Glass fiber and rock wool have good heat resistance, but their thermal conductivity is 0.03 to 0.5 kcal/mh℃,
The insulation effect is not very good. Furthermore, foamed resins such as foamed polyurethane and foamed polystyrene are commonly used as low-temperature cold insulation materials for refrigerators and the like. In the case of foamed polyurethane, the thermal conductivity at 24°C has reached 0.015 kcal/mh°C, but it is difficult to improve the thermal insulation properties further. The same applies to expanded polystyrene. Furthermore, as a cold insulation for liquefied petroleum gas tanks and liquid nitrogen tanks, powder vacuum insulation is known, which is made by doubling the tank container and vacuum filling the gap with hollow spherical foamed perlite powder with an average particle size of 100 to 500 μm. However, in order to obtain a good insulation effect,
A vacuum higher than 0.01 Torr is required, and it is not easy to achieve this degree of vacuum industrially. The evacuation capacity of a large Kinney-type single-stage oil rotary vacuum pump commonly used in industry decreases in evacuation speed as the degree of vacuum increases. For example, with commercially available oil rotary pumps, the pumping speed suddenly decreases from around 0.05 Torr. As described above, it takes a considerable amount of time to achieve a vacuum degree of 0.01 Torr, which is disadvantageous from an industrial standpoint. The present invention relates to a powder vacuum insulator that eliminates the above drawbacks, does not require a high vacuum, can be easily manufactured at an industrially easy degree of vacuum of about 0.1 to 1 Torr, and has a thermal conductivity of 0.01. The purpose is to provide an inexpensive heat insulator that is smaller than kcal/mh℃ and has an excellent insulation effect.This insulator is characterized by being filled with diatomaceous earth powder in a vacuum-maintained container. do. Diatomaceous earth consists of fragments of diatomaceous shells with a size of 1 to 100 μm and has countless pores that communicate with the inside and outside. Generally, many kinds of powders are produced by crushing naturally occurring diatomaceous earth ore. Commonly used as an adjuvant. In the present invention, as the diatomaceous earth powder, it is possible to use a dry powder obtained by crushing and drying diatomaceous earth ore, a calcined powder calcined at 600 to 1400°C, and a flux calcined powder to which an inorganic melting agent is added. Fine powder with a particle size of 20 μm or less or a specific surface area of 5 m ² /
By using fine floating particles of g or more, a better heat insulating effect can be obtained. Since diatomaceous earth powder is a light and bulky powder with a bulk specific gravity of 0.05 to 0.5, it is difficult to pack it tightly into a container. On this point, when a deformable film-like plastic container is used, when the inside of the container is sealed in a vacuum state, the film is strongly attracted toward the inside due to the pressure difference between the inside and outside of the vacuum container, and the film is tightly sealed. do. As a result, the packing density of the powder increases, which has the effect of increasing mechanical strength. It also has the advantage of being easily sealed using a heat sealing machine. For film-like plastic containers, it is necessary to use a film with low gas permeability to prevent vacuum leaks, such as polyethylene, polyvinyl alcohol, polyester, polypropylene, polyvinylidene chloride, polyamide, aluminum vapor-deposited film, and aluminum foil. It is desirable to use a laminate film made by laminating several types of . FIG. 1 shows a sectional view showing the basic configuration of an embodiment of the present invention. In FIG. 1, 1 is diatomaceous earth powder, 2 is a container for storing the diatomaceous earth powder, and the space inside container 2 is maintained at a vacuum of 0.1 to 1 Torr. The present invention will be explained in more detail below using Examples. In this example, the thermal conductivity was measured using a K-Matech thermal conductivity measuring device manufactured by Dynatake Co., Ltd. in accordance with ASTM-C518.
The thermal conductivity was measured at a temperature difference between ℃ and 35℃. Example 1 Specific surface area as shown in Table 1 is 2,
5, 22, 95, and 175 m ² /g of diatomaceous earth powder (sample numbers A, B, C, D, and E) were filled into kraft paper bags, and then coated with polyethylene, aluminum vapor-deposited stretched polyvinyl alcohol, and vinylidene chloride. Place it in a laminated film bag made of polypropylene, then place the film bag in a vacuum container (inner volume 50) equipped with a heat-sealing device, and then use an oil rotary pump (evacuation capacity 950/min).
The pressure inside the vacuum container is set to 0.05Torr using
0.1Torr, 0.3Torr, 1Torr, 3Torr, 10Torr,
It was evacuated to a vacuum degree of 30 Torr and 760 Torr. At this time, the inside of the film bag filled with diatomaceous earth has the same degree of vacuum as the vacuum container. In this way, while the vacuum container and the inside of the film bag filled with powder were kept in a vacuum state, the open part of the film bag was pressed and heated using a heat sealing device to seal the film bag. Next, outside air was introduced into the vacuum container to return it to atmospheric pressure (760 Torr), and then the film bag filled with diatomaceous earth powder was taken out and placed in a bag with a width of 30 cm and a height of 30 cm.
Each powder vacuum insulation body with a thickness of 3 cm was obtained. It was confirmed that the obtained film bag of each powder vacuum insulator was strongly attracted to the internally filled powder and adhered tightly to the powder to ensure complete vacuum sealing.
The time required to create a vacuum of 1 Torr, 0.1 Torr, and 0.5 Torr inside the container was 20 seconds, 40 seconds, and 40 seconds, respectively.
It was hot in 900 seconds. The results of measuring the thermal conductivity, density, etc. of each powder vacuum insulation material obtained are shown in Table 1 and Figure ² . In the case of the heat insulators (sample numbers B, C, D, and E), the thermal conductivity at a vacuum of 1 Torr is 0.01 kcal/mh℃ or less, and as the specific surface area increases, the thermal conductivity decreases. It is clear that the heat insulation effect is excellent.

【table】

[Table] Example 2 Average particle diameters of 1 μm, 3 μm, 5 μm, 10 μm,
Each diatomaceous earth powder of 19 nm and 32 μm was filled in a breathable kraft paper bag, and then placed in a 105 μm thick multilayer laminate film bag made of polyethylene, aluminum-deposited polyester, aluminum foil, and polyester. Width by method
Each powder vacuum insulator (sample number F, G, H, I, J,
K) was prototyped. The appearance of the obtained powder vacuum insulators was such that the film bag was strongly attracted to the powder filled inside and adhered tightly to the powder, and the vacuum seal was perfect. Table 2 and FIG. 3 show the characteristics of the obtained powder vacuum insulators when diatomaceous earth powders having respective average particle diameters were used. As is clear from Table 2 and Figure 3, in the case of powder vacuum insulation (sample numbers F, G, H, I, J) using diatomaceous earth powder with an average particle diameter of 20 μm or less,
Thermal conductivity at 1Torr vacuum is 0.01kcal/mh
It is clear that as the average particle diameter decreases, the thermal conductivity decreases and the heat insulating effect is excellent. Comparative Example In contrast, using foamed pearlite powder with an average particle diameter of 300 μm, which is known for powder vacuum insulation,
Table 2 and Figure 3 show the performance of the powder vacuum insulation prototype fabricated using the same method as in Example 2, but the thermal conductivity was
In order to keep it below 0.01kcal/mh℃, the degree of vacuum must be
It can be seen that it needs to be 0.05Torr or less.

[Table] As explained above, the present invention provides a heat insulator characterized by filling a container kept in a vacuum with diatomaceous earth powder, and in particular powder with an average particle size of 20 μm or less or , specific surface area is 5m ² /
By using powder with a weight of more than 1.5 g, there is no need for high vacuum, the thermal conductivity is less than 0.01 kcal/mh℃ at a vacuum degree of about 1 Torr, which is easy to obtain industrially, and it has an excellent heat insulation effect. By constructing the container with a plastic container, it is very easy to seal the container, and a heat insulator with strong mechanical strength can be obtained, which is of great industrial value.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an embodiment showing the basic structure of the heat insulator of the present invention, and FIGS. 2 and 3 are curves showing the relationship between the degree of vacuum and thermal conductivity of the heat insulator of the embodiment of the present invention. It is a diagram. 1...Diatomaceous earth powder, 2...Container.

Claims (1)

[Claims] 1. A heat insulator made by filling a film-like plastic container kept in a vacuum of 0.1 to 1 Torr with diatomaceous earth powder having countless pores with an average particle diameter of 20 μm or less or a specific surface area of 5 m ² /g or more.