JPH0820031B2 - Decompression insulation board - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure reducing heat insulating plate used for a heat insulating box heat insulating wall of a refrigerator, a freezer, a freezer showcase and the like.

2. Description of the Related Art FIG. 3 shows a conventional pressure-reducing heat insulating plate. The structure of this conventional example will be described below.

In the figure, 1 is a reduced pressure heat insulating plate, 2 is an air-permeable inner bag made of paper or the like, and 3 is powder such as synthetic silica fine powder. 4 is an outer bag made of a laminated film of plastics or the like, and an inner bag 2 in which powder 3 is filled in the outer bag 2
Is inserted and the inside pressure is reduced to 0.1 Torr or less, and then the opening of the outer bag 4 is sealed by heat fusion.

The thermal conductivity of the reduced pressure heat insulating plate 1 configured as described above is
It is 0.0050 to 0.0070 kcal / mh ° C, and has a heat insulation performance that is more than twice as high as that of hard polyurethane foam that is generally used as a heat insulation material for refrigerators and the like. Further, the thermal conductivity of air in the depressurized heat insulating plate 1 is expressed by the following equation.

λg ': Thermal conductivity of air in a vacuum insulation plate (kcal / mh ℃) λg (1atm): Thermal conductivity of static air at 1 atm (kcal)
/ mh ° C) d: Distance between powder particles (m) L: Average free path of air under pressure in the reduced pressure insulating plate (m) Therefore, the smaller the particle size of the powder 3 used for the reduced pressure insulating plate 1 is, Heat transfer by air can be reduced. Therefore, the powder 3 having an average particle size of 10 μm or less is used so that the heat conduction by air becomes almost negligible at a pressure of about 0.1 Torr.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above-mentioned configuration, since the particle size of the powder 3 is small, the voids between the particles of the powder 3 are narrow, and a very large exhaust resistance when decompressing the inside of the outer bag 4. Becomes Therefore, there is a problem that it takes a long time to depressurize the inside of the outer bag 4. Further, when the pressure is reduced, the inside of the inner bag 2 filled with the powder 3 has a large exhaust resistance and the pressure drop is much slower than that of the outside of the inner bag 2. Therefore, the pressure difference between the inside and the outside of the inner bag 2 becomes large, and often the inner bag 2 There was also an accident that the bag was broken.

Therefore, the present invention reduces the exhaust resistance in the powder-packed layer to shorten the decompression time and prevent the inner bag from breaking.

Means for Solving the Problems In order to solve the above problems, the pressure-reducing heat insulating plate of the present invention is used as a powder material and has a primary particle size of 500, which is the minimum unit of particles.
Å or less, and the secondary condensed particle diameter of the aggregate is 20-80μ
m synthetic silica powder is used.

Action The action of the above technical means is as follows.

That is, in the present invention, since the secondary agglomerated particle diameter of the synthetic silica powder is relatively large, 20 to 80 μm, the voids between the particles of the powder are large, the exhaust resistance at the time of depressurization is small, and the depressurization time can be shortened. Also, since the exhaust resistance of the powder packed bed is small,
At the time of depressurization, the pressure drop inside the inner bag is sufficiently fast, the pressure difference inside and outside the inner bag does not become large, and the inner bag does not break.

Further, after the pressure reduction is completed and the opening of the outer bag is sealed, the powder is densely compressed, so that the voids between the particles of the powder are reduced. Therefore, the interparticle distance related to the thermal conductivity of gas in the reduced pressure heat insulating plate is the distance between the primary particles. Since the primary particle size is less than 500Å, the distance between particles is also several 100Å
Therefore, the thermal conductivity of air represented by Formula 1 is extremely small, and a very excellent heat insulating performance can be obtained.

Example A depressurized heat insulating plate according to an example of the present invention will be described below with reference to the drawings.

In FIG. 1, 5 is a depressurized heat insulating plate, 6 is an air-permeable inner bag made of paper or the like, 7 is an aggregate having a primary particle size of 500 Å or less, which is the smallest unit of particles, 2 It is a granular synthetic silica powder having a secondary condensed particle diameter of 20 to 80 μm. 8 is an air-impermeable outer bag made of a plastic slaminate film. The inner bag 6 filled with the powder 7 is inserted into the outer bag 8 to reduce the pressure to 0.1 Torr or less, and then the outer bag 8
The opening is formed by sealing by heat fusion.

The operation of the reduced pressure heat insulating plate 5 configured as described above will be described below with reference to FIG.

Fig. 2 shows synthetic silica with various secondary particle sizes (1 for each).
The secondary particle size is 500 Å or less) and the thermal conductivity of the reduced pressure heat insulating plate 5 using the powder 7 and the time required to reduce the pressure from atmospheric pressure to 0.1 Torr are shown.

As shown in the figure, the average particle size was 20 μm or more, the depressurization time was within 2 minutes, and the inner bag did not break. Regarding the thermal conductivity, 0.0060 kcal / mh ° C or less can be obtained when the average particle size is 80 μm or less.

That is, when synthetic silica having an average particle size of 20 μm or more is used as the powder 7, the decompression time is shortened because the voids between the particles of the powder 7 are large and the exhaust resistance is small. Further, when synthetic silica having an average particle size of 80 μm or less is used, after the pressure reduction is completed and the opening of the outer bag 8 is sealed, the powder 7 is densely compressed, so that the voids between the particles of the powder 7 are very small. It will be small. Therefore, the interparticle distance related to the thermal conductivity of gas in the reduced pressure heat insulating plate 5 is the distance between the primary particles. Since the primary particle size is less than 500Å, the distance between particles is also several 100Å, the thermal conductivity due to air shown in equation 1 is extremely small, and the thermal conductivity of the decompression insulation plate is 0.0060 kcal.
/ mh ℃ or less.

As described above, by using the synthetic silica having the primary particle diameter of 500 Å or less and the secondary agglomerated particle diameter of 20 to 80 μm as the powder 7, the decompression time can be shortened while suppressing the thermal conductivity to be low. It is possible to prevent the bag from breaking.

In addition, dust generation can be suppressed to be much smaller than that of the conventional powder having an average particle size of 10 μm or less, so that workability other than depressurization and work environment can be improved.

In this example, the powder 7 was made of granular synthetic silica, but if the primary particle size is 500Å or less and the secondary agglomerated particle size is 20 to 80 μm, the granular synthetic silica having a larger particle size is used. The same effect can be obtained by using, as the powder 7, synthetic silica obtained by roughly pulverizing the.

EFFECTS OF THE INVENTION As described above, the present invention has a primary particle size of 500 as powder.
Since the synthetic silica having a secondary agglomerated particle diameter of 20 to 80 μm is used, the following effects can be obtained.

(A) Since the powder has a primary particle size of 500 Å or less, the voids between the primary particles are narrow, and heat conduction by gas can be almost eliminated, so that a very excellent heat insulating performance can be obtained.

(B) Since the secondary agglomerated particle diameter is as large as 20 to 80 μm, the exhaust resistance at the time of depressurizing operation is small, the depressurizing time can be shortened, the man-hours can be reduced, and the productivity can be improved.

(C) Since the exhaust resistance is small as described above, the pressure difference between the inside and the outside of the breathable inner bag filled with powder does not become large during the depressurization operation, and the inner bag does not break.

(D) Since the secondary agglomerated particle size of the powder is as large as 20 to 80 μm, less dust is generated, and workability other than depressurization operation and work environment can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a reduced pressure heat insulating plate in one embodiment of the present invention, and FIG. 2 is a thermal conductivity and a reduced pressure time when powders having various secondary agglomerated particle sizes are used in the reduced pressure heat insulating plate of FIG. FIG. 3 is a cross-sectional view of a conventional vacuum insulation material. 5 ... decompression insulation board, 6 ... inner bag, 7 ... powder, 8 ... outer bag.

Claims (1)

[Claims] 1. A non-breathable inner bag having air permeability, a powder of synthetic silica filled in the inner bag, and a plastic slaminate film for containing and depressurizing the inner bag filled with the powder. Characterized in that the synthetic silica powder has a primary particle size of 500 Å or less, which is the smallest unit of particles, and a secondary condensed particle size of 20 to 80 μm, which is an aggregate. Reduced pressure insulation board.