JPH10205687A - Vacuum heat insulating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a good productivity without necessitating a large high vacuum device by forming a molding body which is tobermorite potassium silicate, and which is composed of a particle in which a spheroidal shell is not formed on an external shell by secondary particle as a main component, as a heat insulating core material, vacuum-exhausting the inside of a container filled the heat insulating material therein, and make the inside thereof in low vacuum condition of a specified value and less. SOLUTION: A heat insulating core material is a tobermorite potassium silicate molding body formed by dehydrating and drying tobermorite slurry obtained by hydrothermal synthesis reacting calcareous raw material and siliceous raw material, and is used which is composed of particle in which a spheroidal shell is not formed by secondary particle as a main component. After a molding body composing tobermorite potassium silicate as a main component is housed in a container manufactured by using a gas barrier film, vacuum exhaust treatment is carried out in the container in a pressure reducing condition. At a time point where the pressure reducing condition in the vacuum container attains a predetermined vacuum degree, an opening end of the container is heat-sealed so as to tightly pack the molding body by the container in the pressure reducing condition. The pressure reducing condition is set so as to hold a vacuum degree of 2Torr and less.

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 more particularly, to a vacuum heat insulating material which uses a specific calcium silicate as a heat insulating core so as to exhibit excellent heat insulating properties even in a low vacuum condition. It is related to thermal insulation.

[0002]

2. Description of the Related Art Vacuum insulation materials having a calcium silicate-based molded body as a core material have been known so far. In order to increase the strength of the molded body, it is reinforced with a fibrous substance, and furthermore, has a thermal conductivity. It has been proposed to use a molded body mainly composed of calcium silicate containing a radiation shielding material to reduce
Several manufacturing methods are also known.
For example, a calcium silicate molded article provided with a mixed layer of a radiation shielding material (Japanese Patent Publication No. 4-4998), and a calcium silicate molded article containing a radiation shielding material (Japanese Patent Application Laid-Open No. 58-145)
No. 652), a vacuum heat insulating material having a core obtained by burning and eliminating pulp in a calcium silicate molded body (Japanese Patent Publication No. Hei 4-
No. 60950) and a vacuum heat insulating material having a core of calcium silicate containing a radiation shielding material (WO9514881) has been proposed.

[0003]

However, the compact mainly composed of calcium silicate used in the above-mentioned conventional vacuum heat insulating material has a large degree of vacuum dependency, and is 0.1T.
Unless vacuum packaging is performed at a high vacuum of orr or lower, there is a problem that a vacuum heat insulating material exhibiting stable low thermal conductivity cannot be obtained. In addition, in order to increase the degree of vacuum to 0.1 Torr or less, a large amount of time is required for evacuation, so that productivity must be reduced, and a large-scale vacuum exhaust system must be introduced. Economically disadvantaged. Therefore, there has been a demand for a core material made of a calcium silicate molded body suitable for obtaining a vacuum heat insulating material having a low vacuum of about 2 Torr and a low thermal conductivity equivalent to that achieved by a conventional high vacuum. .

[0004]

Means for Solving the Problems In order to solve such a problem, the present inventors have conducted intensive studies on calcium silicates having various crystal structures. As a result, calcium silicate having a lower vacuum and lower thermal conductivity has been obtained. The present inventors have found out that a core material made of a molded body using calcium silicate of a specific crystal form, that is, a tobermorite-based calcium silicate, is effective as a vacuum heat insulating material having a molded body as a core material, and reached the present invention.

[0005] That is, the gist of the present invention is to provide a heat-insulating core made of a molded body of tobermorite-based calcium silicate whose secondary particles are mainly composed of particles that do not form a spherical shell in the outer shell. A vacuum insulating material formed by tightly wrapping in the container an insulating core material made to be 2 Torr or less by evacuating the enclosed container, preferably,
The inside of the container is 1 Torr or less, and the tobermorite-based calcium silicate is a petal-like secondary particle in a vacuum heat insulating material.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The calcium silicate used in the present invention is a tobermorite-based calcium silicate mainly composed of crystalline material called tobermorite. Tobermorite is known to have a secondary particle having a spherical shell in the outer shell and a particle having no spherical shell in the outer shell.A typical example of the former is a spherical particle called marimo-like. In the latter typical shape, particles such as rose flowers called petals are known. The tobermorite which can be used in the present invention is a particle whose secondary particle does not have a spherical shell on the outer shell, and is particularly preferably a petal-like secondary particle. Further, as the tobermorite used in the present invention, one containing CSH-I or CSH-II as an impurity and also containing an amorphous substance may be used.

The tobermorite-based calcium silicate of the present invention is produced by subjecting a calcareous material and a siliceous material to a hydrothermal synthesis reaction. The siliceous raw material may be either amorphous or crystalline. Specific examples include natural products such as diatomaceous earth, silica stone and quartz, and industrial by-products such as silicon dust. Further, specific examples of the calcareous raw material include quick lime, slaked lime, and the like.In general, the calcareous raw material is used in the form of slaked lime slurry, and sometimes it is sometimes used by preparing into lime milk containing bulky lime particles. is there.

The above-mentioned hydrothermal synthesis reaction is known per se,
Different crystal forms can be obtained by selecting the reaction conditions, for example, Ca / Si ratio, siliceous raw material, reaction temperature, reaction time, etc. In order to obtain the tobermorite of the present invention,
The aqueous slurry in which the molar ratio between the calcareous raw material and the siliceous raw material CaO and SiO ₂ was adjusted so that Ca / Si = 0.6 to 1.0 was heated to 140 ° C. or more while stirring under pressure. A reaction method is employed. In particular, when obtaining petal-like tobermorite, amorphous silicic acid such as fumed silica is used as a siliceous raw material. Reaction time,
Considering the reactivity, it is better to use a mixture of crystalline silicic acid and amorphous silicic acid.The petal size and particle size differ according to the ratio of this crystalline silicic acid material to the amorphous silicic acid material. Some petal-like particles can be obtained.

The calcium silicate molded body used as the heat insulating core material of the present invention can be produced by dehydrating and molding the tobermorite slurry obtained by the above method as it is and drying it. The powder obtained by powdering can be used by adding it to water again. The solid content concentration of calcium silicate in the slurry is not particularly limited, but is preferably 8 (wt)% or less. In particular, when a calcium silicate compact having a low specific gravity is to be obtained, 2 to 7 (wt)
% Is preferred.

The calcium silicate compact of the present invention comprises a mixture of the aqueous slurry containing tobermorite described above and reinforcing fibers such as pulp and glass fiber, and radiant heat absorbing materials such as silicon carbide and carbon, which are added as necessary. It is manufactured by dehydration molding by a pressure dehydration method using a conventionally known filter press or the like, and then drying. Depending on the shape of the dewatering section of the dewatering molding machine, it can be formed into various shapes (such as pipes) having a flat plate (panel) or a curved portion. Drying after dehydration molding is usually performed at a temperature of 100 to 200 ° C. for 5 to 5 minutes.
Performed for 30 hours. The molded article obtained by the above method has an apparent density of 0.05 to 0.15 g / cm ³ and a compression strength of usually 1 kg / cm ² or more, specifically 1.5 to 6 K.
g / cm ² .

As the fibrous substance added to the molded article of the present invention, various conventionally known fibrous substances such as glass fiber, carbon fiber, organic fiber and pulp can be used. These may be used alone or as a mixture of two or more.
Further, as the radiant heat absorbing material, silicon carbide, titanium oxide, carbon and the like are preferably used. These are added, for example, to a calcium silicate slurry in the process of manufacturing the calcium silicate molded body. Further, any substance that does not inhibit the reaction of calcium silicate may be mixed with, for example, a calcareous raw material or a siliceous raw material and subjected to hydrothermal synthesis.

The container (bag) used in the present invention is not particularly limited as long as it is a gas-barrier and flexible container. Generally, a known gas-barrier film is used as long as it has flexibility. Can be manufactured. Examples of the gas barrier film include, for example, a plastic film obtained by laminating a metal foil such as aluminum on a plastic film, a composite film obtained by depositing a metal or metal oxide, a vinylidene chloride-based film, a vinylidene chloride resin-coated film, a polyvinyl alcohol-based film, and the like. However, composite films are preferred.

Examples of the plastic film constituting the composite film include a polyester film, a polypropylene film, and a polyamide film. The layer structure of the composite film may be two layers. A three-layer structure provided with a film is preferable. In the case of a three-layer composite film, the container
In the case of (bag), the outer layer is selected to be a film having excellent scratch resistance such as a polyester film, and the inner layer is selected to be a film made of polypropylene, polyamide or the like having excellent heat sealing properties. The thickness of the film varies depending on the use of the vacuum heat insulating material, but is usually about 10 to 100 mμ. Further, the shape of the container is usually a tubular body having one end or both ends open.

The vacuum heat insulating material of the present invention is manufactured by a method using a known vacuum packaging machine or the like. That is, after the molded body mainly composed of the above-mentioned tobermorite-based calcium silicate is accommodated in the container, the interior of the container is evacuated to a reduced pressure state, and when the predetermined degree of vacuum is reached, the molded body is decompressed. Heat seal the open end of the container so that it is tightly packed by the container. The depressurized state in the vacuum vessel is to maintain a degree of vacuum of 2 Torr or less, preferably 1 Torr or less,
More preferably, by setting the pressure to 0.8 Torr or less, excellent heat insulating performance can be obtained.

In the present invention, the calcium silicate molded body is preferably subjected to a heat treatment at a temperature of 300 ° C. or higher, specifically, a temperature of 300 to 500 ° C., usually for 1 to 5 hours, before being packaged in close contact. . By this heat treatment, the adsorbed water of the calcium silicate molded body is removed, and more excellent heat insulating performance can be exhibited as compared with the case without the heat treatment.

The vacuum heat insulating material of the present invention can exhibit excellent heat insulating performance even at a low vacuum, and the vacuum inside the container is 2T.
Even at orr, the thermal conductivity at 20 ° C. is usually about 0.01
Kcal / mh ° C, and those with a lower vacuum degree have a thermal conductivity of about 0.006 to 0.008 Kcal / mh ° C.

According to the present invention, by using the secondary particles having no spherical outer shell among the tobermorite particles in the core material molded body, the high-performance vacuum heat insulating material as described above can be obtained. However, since neither cocoon-shaped zonotolite having a spherical outer shell and marimo-shaped tobermorite are unsuitable for the molded body to be the core material of the present invention,
It is presumed that the spherical outer shell of the particles hinders deaeration and dehydration during vacuum evacuation, slows the evacuation speed, and does not exhibit sufficient performance. The high-performance vacuum heat insulating material of the present invention can be suitably used as a heat insulating material for, for example, electric refrigerators, refrigerator cars, refrigerated freight cars, and houses (for construction).

[0018]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. In the following Examples and Comparative Examples,% means% by weight unless otherwise specified.

Example 1 Quick lime (produced by Yabashi Kogyo: lightly burnt quick lime CaO 96.20%, Al ₂ O ₃
0.06%, MgO 1.29%, Fe 0.031%, ig.loss 1.12%) 43.1 parts by weight of hot water (690 parts by weight) was added and slaked at 95 ° C for 5 minutes to form slaked lime slurry, and this slurry was ultrasonically dispersed. Ultrasonic waves were irradiated for 20 minutes using a machine (MST, using a 20 mm chip) to obtain slaked lime milk. Silica (Tokai Kogyo: Izu special powder SiO ₂ 96.64%, Al ₂ O ₃ 1.2
3%, Fe ₂ O ₃ 0.107%, ig.loss 0.89%) 28.4 parts by weight
28.4 parts by weight of fumed silica (trade name: Micro Silica 983U SiO ₂ 98%, manufactured by Elchem) were dispersed in water to obtain a silica slurry. The slaked lime milk and the silica stone slurry were combined, and water was added so that the total amount of water became 27 times by weight of the solid content. This slurry was placed in an autoclave for 1 hour.
The reaction was carried out for 3 hours while stirring at a temperature of 90 ° C. (under a steam pressure of about 15 kg / cm ² ) to obtain a slurry of tobermorite calcium silicate hydrate of the petal-like secondary particles. Electron micrograph (SEM) of the obtained tobermorite calcium silicate
Is shown in FIG.

After adding 1% by weight of glass fiber and 1% by weight of pulp to 98% by weight of solid content of calcium silicate to the above-mentioned calcium silicate slurry and mixing them, 22 × 22 cm
^It was supplied to the mold of the drainage molding machine of No. ² . This was pressurized, dehydrated and dried at 105 ° C. for 21 hours to obtain a specific gravity of 0.093 g /
A molded product of cm ³ was obtained. Glass fiber added (GF)
Is a chopped strand cut to 18 mm,
The glass fiber and the pulp were used after being dispersed with a mixer before mixing with the slurry.

The obtained molded body was subjected to a heat treatment at 300 ° C. for 5 hours, and then stored in a film container. Containers were polyethylene terephthalate film (12 μm) / aluminum foil (9 μm) / polypropylene film (60
μm), a cylindrical container having a polypropylene film as an inner layer and open at both ends was used.
The molded body was placed at about the center of the container, and housed in a vacuum packaging machine having a vacuum chamber volume of 20 L (liter) and an exhaust capacity of 500 L (liter) / min to perform an exhaust process. When the vacuum pressure in the vacuum chamber reaches 2 Torr, this degree of vacuum is maintained, and after evacuation is performed for 30 minutes, the openings at both ends of the container are heat-sealed and tightly packaged, and the calcium silicate molded body is used as a heat insulating core material. A vacuum insulation was obtained. The thermal conductivity at 20 ° C. of the above vacuum heat insulating material was measured and is shown in Table 1.

Next, after the sealed heat insulating material is opened and purged to normal pressure, it is again stored in the vacuum packing machine, and the same method as above is used except that the gauge pressure is maintained at 1.00 Torr. A vacuum heat insulating material was obtained, and the thermal conductivity was measured. The results are shown in Table 1. The same operation is repeated below for 0.8
The thermal conductivity was measured for the obtained heat-insulating vacuum materials repeatedly at a vacuum degree of 0 Torr, 0.45 Torr, and 0.05 Torr, and the results are shown in Table 1. It is clear that a sufficiently excellent performance is exhibited in a low vacuum state near 2 Torr.

Example 2 The composition ratio of the calcium silicate molded product was calcium silicate 83 w
t%, 15 wt% of SiC (average particle size 0.7 μm), 1 wt% of pulp, 1 wt% of GF, and a vacuum heat insulating material was manufactured in the same manner as in Example 1 except that SiC was added simultaneously with GF and pulp. did. The thermal conductivity when exhausted at each degree of vacuum was measured, and the results are shown in Table 1. 2Torr
It exhibits sufficiently excellent performance in a low vacuum state near r. FIG. 2 shows an electron micrograph (SEM) of the calcium silicate hydrate obtained during the production of the molded body.

Comparative Example 1 Warm water was added to 49.6 parts by weight of the same quick lime used in Example 1 and slaked at 95 ° C. for 5 minutes to form a slaked lime slurry.
This slurry was irradiated with ultrasonic waves for 20 minutes using an ultrasonic dispersing machine (MST, using a 20 mm chip) to obtain slaked lime milk. or,
50.4 parts by weight of the same silica as that used in Example 1 was dispersed in water to obtain a silica slurry. The slaked lime milk and the silica stone slurry were combined, and water was added so that the total water content was 38 times by weight of the solid content. The slurry was reacted in an autoclave at a temperature of 204 ° C. (under a water vapor pressure of about 17 kg / cm ² ) for 2 hours and 45 minutes to obtain a calcium silicate hydrate of zonotlite. An electron micrograph (SEM) of this calcium silicate hydrate is shown in FIG.

In the same manner as in Example 1, GF was added to the obtained calcium silicate with respect to the solid content of 98% by weight of calcium silicate.
After adding and mixing 1% by weight and 1% by weight of pulp,
It was supplied to a mold of a × 22 cm ² drainage molding machine. A nonwoven fabric was put on the upper and lower draining surfaces of the mold in advance. This was pressurized, dehydrated, and dried at 105 ° C. for 21 hours to obtain a molded product having a specific gravity of 0.064 g / cm ³ . This molded body was subjected to a heat treatment at 300 ° C. for 5 hours. Using this molded body, a vacuum heat insulating material was obtained using a vacuum packaging machine in the same manner as in Example 1. The thermal conductivity when exhausted at each degree of vacuum was measured, and the results are shown in Table 1. 0.05 Torr
Demonstrates excellent performance in high vacuum conditions of about
Excellent performance is not exhibited even near rr.

Comparative Example 2 The composition ratio of the calcium silicate molded product was 83 w
t%, 15 wt% of SiC (average particle diameter 0.7 μm), 1 wt% of pulp, 1 wt% of GF, and a vacuum heat insulating material was manufactured in the same manner as in Comparative Example 1 except that SiC was added simultaneously with GF and pulp. did. The thermal conductivity when exhausted at each degree of vacuum was measured, and the results are shown in Table 1. 2Torr
Excellent performance is not exhibited in a low vacuum state near r. FIG. 4 shows an electron micrograph (SEM) of the calcium silicate hydrate obtained during the production of the molded body.

COMPARATIVE EXAMPLE 3 Warm water was added to 44.1 parts by weight of the same quick lime used in Example 1 and slaked at 95 ° C. for 5 minutes to obtain a slaked lime slurry. This slurry was treated with an ultrasonic disperser (MST, 20 mm chip). Ultrasonic wave was applied for 20 minutes to obtain slaked lime milk. Also, 55.9 parts by weight of the same silica stone used in Example 1 was dispersed in water to obtain a silica stone slurry. The slaked lime milk and the silica stone slurry were combined, and water was added so that the total water content was 38 times by weight of the solid content. This slurry was placed in an autoclave for 1 hour.
The reaction was carried out for 4 hours while stirring at a temperature of 80 ° C. (under a steam pressure of about 10 kg / cm ² ) to obtain marimo-like secondary particles of tobermorite calcium silicate hydrate having a spherical shell. Electron micrograph (SEM) of this calcium silicate hydrate
Is shown in FIG.

Using the obtained calcium silicate hydrate,
A molded body was manufactured in the same manner as in Example 1, and then a vacuum heat insulating material was manufactured using a vacuum packaging machine. The thermal conductivity when exhausted at each degree of vacuum was measured, and the results are shown in Table 1. 2T
Excellent performance is not exhibited near orr.

[0029]

[Table 1]

[0030]

According to the present invention, the vacuum heat insulating material is evacuated in a low vacuum state of about 2 Torr instead of the high vacuum state required when a conventional calcium silicate molded body is used as a core, and the inside of the vacuum chamber is reduced. Excellent heat insulation performance is exhibited only by setting the degree of vacuum to approximately 2 Torr. Therefore, a large-scale high-vacuum facility is not required to exhibit excellent performance, and a long time is not required for evacuation, so that a vacuum heat insulating material excellent in productivity can be supplied.

[Brief description of the drawings]

FIG. 1 is an electron micrograph (SE) showing the crystal structure of petal-like tobermorite calcium silicate hydrate obtained in Example 1.
M).

FIG. 2 is an electron micrograph (SE) showing the crystal structure of petal-like tobermorite calcium silicate hydrate obtained in Example 1.
M).

FIG. 3 is an electron micrograph (SEM) showing a crystal structure of the zonotorite calcium silicate hydrate obtained in Comparative Example 1.

FIG. 4 is an electron micrograph (SEM) showing the crystal structure of the calcium silicate hydrate obtained in Comparative Example 2.

FIG. 5 is an electron micrograph (S) showing the crystal structure of the marimo-like tobermorite calcium silicate hydrate obtained in Example 3.
EM).

Claims (4)

[Claims] (1) Tobermorite-based calcium silicate,
A molded body mainly composed of particles whose secondary shell does not form a spherical shell is used as a heat insulating core material, and the inside of the container in which the heat insulating core material is sealed is evacuated to 2 Torr or less. Vacuum insulation material consisting of a heat insulation core material packed tightly in a container. 2. The vacuum heat insulating material according to claim 1, wherein the inside of the container is 1 Torr or less. 3. The petal-shaped tobermorite-based calcium silicate
The vacuum heat insulating material according to claim 1, wherein the material is secondary particles. 4. The container according to claim 1, wherein said container has a gas barrier property and is made of a flexible composite film.
4. The vacuum heat insulating material according to any one of claims 3 to 3.