JPH0446348B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a vacuum insulation structure with excellent insulation performance.

BACKGROUND ART Generally, in structures that require high-performance insulation, such as refrigerated containers and liquefied gas storage tanks, it is well known that the insulation walls are made into vacuum structures in order to improve the insulation performance.

However, when forming an insulating wall in a vacuum structure, a vacuum load (1Kg/cm ² ) is applied to the inner and outer walls (metal container) forming the vacuum structure, and therefore, the metal container cannot withstand the vacuum load sufficiently. You will need to use thicker material to obtain the desired results. However, if a thick material is used for the metal container, it will not only be heavy and require an extremely large amount of labor to process.
In the vacuum heat insulating structure constructed of thick material as shown in FIG. 2, although little heat is transmitted through the vacuum space 1, it is transmitted from the surface portion 2a or 2b, through the forehead portions 3a and 3b, and then to the surface portion 2b or 2a. The drawback was that the amount of heat escaping increased. For this reason, various vacuum insulation structures have been developed that can use thin-walled metal containers. This type of vacuum insulation structure receives a vacuum load between the inner and outer walls, so it is loaded with compression-resistant molded insulation material as a support material, but those that satisfy compression resistance generally have a bulk specific gravity. As the size increased, the thermal conductivity increased, causing problems in terms of insulation performance.

Due to the current situation as described above, compression-resistant, lightweight inorganic material moldings with a continuous open pore structure such as calcium silicate are used as supporting materials, and 10 ^-2 torr
The following vacuum insulation structures have been proposed.

This molded product has a compressive load resistance of 2 kg/cm ² or more, a light bulk specific gravity of about 0.1 g/cc, and has a continuous open pore structure, so it has a remarkable vacuum evacuation effect.

Problems to be Solved by the Invention However, in calcium silicate molded bodies, burr crystals with a diameter of several tens of micrometers grow and intertwine in number.
Because it has relatively large air holes of 10 μm or less, its radiation prevention ability is low, and solid heat conduction between crystals and heat conduction between crystals and metal containers are relatively large, resulting in a temperature of 10 ^-2 torr. The following thermal conductivity under vacuum is approximately 0.01Kcal/mh℃ (under normal pressure
0.03Kcal/mh℃), which is relatively large.

Insulating materials with low thermal conductivity include fine powders such as perlite, shirasu balloons, and glass balloons (thermal conductivity in a vacuum of 10 ^-2 torr or less).
0.002Kcal/mh℃, however, 0.02Kcal/mh under normal pressure
mh℃), fibrous materials such as glass wool, silica alumina wool, silica wool, and carbon wool (thermal conductivity in a vacuum of 10 ^-2 torr or less
0.003Kcal/mh℃, however, 0.03Kcal/mh under normal pressure
mh℃). However, fibrous materials cannot withstand vacuum loads, and even powder insulation materials cannot withstand vacuum loads.
Powder such as barlite has closed cells and contains gas, and when subjected to a vacuum load, the bubbles burst and release the built-in gas, making it impossible to bear the load. For this reason, when these heat insulating materials are used under vacuum, it is necessary to use a thick material for the metal container, which inevitably increases the weight.

The present invention aims to improve the drawbacks of such a vacuum insulation structure, and aims to provide a vacuum insulation structure that is inexpensive, has excellent insulation performance, is easy to perform evacuation operation, and is lightweight. It is something.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a method for reducing the primary particle size, which is obtained by a wet method which is much cheaper than a dry method such as heat treatment or thermal decomposition of a silane derivative. The main material is ultrafine silica particles of submicron size or less, which are intertwined with fibrous substances and molded.
A heat insulating material with low thermal conductivity is used as the supporting material.

That is, in a vacuum insulation structure formed by filling a metal container with a support material, sealing the metal container, and then evacuating the interior of the metal container, a method of decomposing the support material with sodium silicate using an acid; Mixing ultrafine silica and fiber reinforcement obtained by wet methods such as decomposing alkaline earth metal silicate with acid or decomposing acid clay with acid,
It is constructed from a compressed molded body.

In addition, especially when the temperature difference between the inner and outer walls of the vacuum insulation structure is large, it is possible to mix a fine emulsifier with the ultrafine particle silica and fiber reinforcing material, compression mold it, and use it as a support material to radiate radiation. This is designed to increase the prevention effect.

Function It is difficult to mold ultrafine silica particles alone into a porous body. Furthermore, when molded using a binder, solid heat conduction increases. Therefore, it is well known that ultrafine silica particles and a fibrous material are stirred and mixed at high speed and compression molded.

According to this method, a microporous support material having a compressive strength of 2 Kg/cm ² or more and nearly 90% of submicron or smaller pores can be obtained.

Since the particles of this support material are submicron or smaller, even when only ultrafine silica particles are used without adding an emulsifier, the radiation prevention effect is greater than that of a calcium silicate molded body. If the temperature difference between the inner and outer walls is large, the radiation prevention effect can be further improved by mixing an emulsifier with a particle size that does not affect the heat insulation performance of the original support material or the size of the pores. be able to.

In addition, because this support material is formed by point contact between particles and point contact between particles and fibers, the porosity is smaller than about 95% of calcium silicate.
Heat conduction between solids is small.

However, like calcium silicate, this support material adsorbs 5 to 10% of water at normal pressure, so its thermal conductivity is not so good at about 0.03Kcal/mh℃, but it is less susceptible to the effects of adsorbed water. At no reduced pressure, it exhibits much better thermal insulation performance than calcium silicate.

On the other hand, the above-mentioned supporting material is composed of continuous pores with a diameter of submicron or less, and the pores are much smaller than the calcium silicate molded body. Heat conduction between molecules disappears.

Examples Examples of the present invention will be specifically described below.

The ultrafine particle silica used as the main material of the support material of the present invention is amorphous silica obtained by decomposing sodium silicate with acid, and is generally called wet process ultrafine particle silica or wet process white carbon. For example, there is Tokusil manufactured by Tokuyama Soda.

As fiber reinforcement materials, silica alumina wool,
There are silica wool, glass wool, alumina fiber, etc., but silica alumina wool is preferred because it allows the evacuation temperature to be as high as possible, is inexpensive, and has a small fiber diameter.

The emulsifier may basically be one of three different types or a combination of such types. These basic types are: (a) Reflective type, such as metal powder (b) Scattering type, such as titanium oxide, zircon, etc.
Potassium titanate whisker (c) Absorption type For example, carbon black.

In the case of using only wet process ultrafine particle silica and fiber reinforcement, 93 to 98 parts by weight of wet process ultrafine particle silica and 2 to 7 parts by weight of fiber reinforcement are stirred and mixed at high speed, press-molded in a mold, and the bulk density is determined. The supporting material should be 0.22 to 0.35 Kg/m ² (porosity 83 to 89%).

On the other hand, when mixing an emulsifier, 60 to 75 parts by weight of ultrafine silica, 2 to 7 parts by weight of fiber reinforcement, and 25 to 40 parts by weight of emulsifier are stirred and mixed at high speed, press-molded in a mold, and the bulk density 0.29～0.46Kg/ ^m2 (porosity
83-89%) as a supporting material.

The above two types of ultrafine particle silica molded bodies have a heat resistance of approximately 850℃ and a thermal conductivity of 0.025Kcal/mh at normal pressure.
℃～0.035Kcal/mh℃(50℃), compression resistance 2Kg/
^cm2 or more, and has a continuous open pore structure.

Now, the ultrafine silica molded body is produced by stirring, mixing, and press molding as described above, and the gas released is only moisture absorbed from the atmosphere.
When the ultrafine silica molded body as described above is used as a support material for a vacuum heat-insulated container, first, the ultrafine silica molded body having a predetermined shape is preliminarily dried in a heating furnace. The drying conditions for this ultrafine silica molded product are usually about 200° C. for about 2 hours, so that the weight becomes almost constant. Through this treatment, the silanol groups remain, but the moisture adsorbed within the molded article is almost certainly removed. Furthermore, if a high temperature is used, the heating time can be significantly shortened.

Next, a thin metal surface portion 11 as shown in FIG.
The preheated support material 13 is filled into a container composed of metal frames 12a and 12b. The metal surface parts 11a, 11b and the metal forehead part 1
2a and 12b are hermetically sealed by attaching them at their respective ends by welding or seaming. A sealing valve 14 is provided on the metal surface portion 11b.
An exhaust pipe 15 having a diameter is attached by an embedded structure.

After this, the chamber is heated from the outside at a temperature as high as 100°C or higher and evacuated for a short time. By this operation, most of the water in the support material 13 is released, and other gases are also released, and the support material 13 is released.
The inside is maintained at a high degree of vacuum. and the sealing valve 1
By sealing 4, the supporting material 1 is placed inside the metal container.
A vacuum insulation structure is manufactured in which the support material 13 is filled with the support material 13 and the inside thereof is maintained in a vacuum. In this case, the insulation performance can be sufficiently exhibited at a maintained vacuum level of 1 Torr.

Next, two embodiments of the present invention will be described.

Example 1 Raw materials with the following composition were produced by Nippon Airitzhi Co., Ltd.
The mixture was mixed at 5,000 rpm using a high-speed backflow mixer manufactured by Yamaha Motor Co., Ltd.

Wet method ultrafine particle silica (Tokusil manufactured by Tokuyama Soda)
P) 62 parts by weight Titanium oxide (Titanium Oxide P manufactured by Tegusa)
-25) 33 parts by weight Silica alumina wool (IBIDEN's IBI WOOL bulk) 5 parts by weight The above mixture was put into a mold and press-molded, and the width
1000mm, length 2000mm, thickness 50mm, bulk density 0.31g/
The supporting material 13 was cm ³ . This support material 13 has a continuous open pore structure and has a compression resistance of 2 kg/cm ² or more.

The thermal conductivity of the support material 13 as-formed as described above at normal pressure is 0.030 Kcal/mh℃ (50℃)
This is not particularly superior to calcium silicate molded bodies. This is thought to be because it absorbs moisture from the atmosphere. However, the thermal conductivity in a vacuum without the influence of moisture is 0.005 Kcal/at 50°C.
Excellent at 0.008Kcal/mh℃ even at mh℃ and 200℃.

Therefore, the supporting material 13 was placed in an oven at 200°C.
Heat treatment was performed for 2 hours to dehumidify. This supporting material 13 is connected to the metal surface portions 11a and 1 of SUS304 with a thickness of 0.2 mm.
1b and a metal frame part 12a of SUS304 with a thickness of 0.08mm,
12b is filled.

The inside of the metal container filled with the support material 13 is 100
A vacuum insulation structure with a degree of vacuum of 1 Torr or less was created in a short time at a high temperature of ℃ or higher.

(Example 2) Raw materials having the following composition were mixed in the same manner as in Example 1.

Wet method ultrafine particle silica (Tokusil manufactured by Tokuyama Soda)
P) 95 parts by weight Silica alumina wool (IBIDEN's IBI WOOL bulk) 5 parts by weight The above mixture was put into a mold and press-molded, and the width
1000mm, length 2000mm, thickness 50mm, bulk density 0.24g/
The supporting material 13 was cm ³ . This support material 13 has a continuous open pore structure and has a compression resistance of 2 kg/cm ² or more.

The thermal conductivity of the supporting material 13 as-formed as described above at normal pressure is 0.028 Kcal/mh℃ (50℃)
The thermal conductivity in vacuum without the influence of moisture is
0.0045Kcal/mh at 50℃, at 200℃,
0.012Kcal/mh℃. Although these are superior to conventional calcium silicate molded bodies, when the influence of radiation becomes large in a high-temperature atmosphere, the heat insulation performance is inferior to that of Example 1 in which an emulsifier is added.

The molded support material 13 is preheated in the same manner as in Example 1 to release the adsorbed water, and then the metal face parts 11a and 11b of SUS304 with a thickness of 0.2 mm and the metal frame part of SUS304 with a thickness of 0.08 mm are formed. A container composed of 12a and 12b was filled with the mixture, and the inside of the container was kept in a high-temperature atmosphere for a short time to form a vacuum insulation structure with a degree of vacuum of 1 Torr or less.

The heat resistance of the support material 13 in both Examples 1 and 2 is approximately 850°C.
However, considering the oxidation coloration of stainless steel,
It can be used up to 250℃ without any temper color.

Effects of the Invention As described above, according to the present invention, since an ultrafine silica molded body with low thermal conductivity and excellent compression resistance is used as a support material, a thin metal container can be used, and as a result, it is lightweight and has high heat insulation performance. An excellent vacuum heat insulating structure can be obtained, and since the present invention uses wet method ultrafine silica particles, an inexpensive vacuum heat insulating structure can be obtained.

On the other hand, when a conventional calcium silicate molded body is used as a support material, the degree of vacuum needs to be 10 ^-2 torr or less, but since the pores of the ultrafine silica molded body are submicron or less, a vacuum level of 1 Torr or less is sufficient. , vacuuming work is easier. In addition, because the degree of vacuum is low, there is less gas released from the metal container.
Furthermore, due to the getter action of ultrafine silica particles, there is extremely little change in thermal insulation performance over time.

Furthermore, by adding an emulsifier, it is possible to provide a vacuum insulation structure with excellent insulation performance even at high temperatures.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a vacuum insulation structure showing an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional vacuum insulation structure. 11a, 11b...metal surface part, 12a, 12b
...Metal forehead part, 13...Supporting material.

Claims (1)

[Scope of Claims] 1. A vacuum insulation structure in which a metal container is filled with a support material, the metal container is sealed, and then the interior of the metal container is evacuated. A vacuum insulation structure made of a molded product obtained by mixing and compressing the resulting ultrafine particle silica and fiber reinforcement. 2. The vacuum heat insulating structure according to claim 1, wherein the support material is a molded body containing an emulsifier.