JPH07167376A - Vacuum heat insulating material and manufacture thereof - Google Patents

Abstract

PURPOSE:To dissolve vacuum degradation over a long period of time without deformation such as waviness and recess by binding mutual inorganic fibers at the respective intersections by components eluted from these fibers. CONSTITUTION:Inorganic fibers of 2 mum or less in average fiber diameter are collected into the cotton state, and after the attachment of an acid aqueous solution, compression-dehydrated and dried, the eluted components of the inorganic fibers are then collected to the intersections of the inorganic fibers and hardened. If the average fiber diameter exceeds 2mum, recessions become large at the time of evacuation. Because of being formed only of such inorganic fiber without containing organic substance, there is no generation of gas, carbonization or the lowering of strength due to the burning of organic substance even during use under high temperature, nor is vacuum degradation generated at the time of use for a long period of time. Because of not using an inorganic binder, an obtained compact is made into the hard board state, so that cracking and chipping caused by compression during evacuation are not generated, nor is compression restoring performance damaged. In addition, air bubbles are not left inside heat insulating material.

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 a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as this kind of vacuum heat insulating material, a needling mat, felt, blanket and the like made of inorganic fibers are housed in a heat insulating container or bag, then vacuumed and sealed, or inorganic fibers are used. It is known that it is strongly molded with an inorganic binder.

[0003]

However, in the former case, when the inorganic fibers are put into a heat insulating container or bag and evacuated, the heat insulating container or bag is formed due to the uneven density of the mat or felt or the compressive deformability of the fiber mat. Rippling,
Alternatively, it has a problem of depression. Further, when it is stored in an aluminum foil, it has a problem that when it is used at high temperature, the heat insulating property is impaired by radiation from aluminum itself. Further, in the latter case, although there are few dents during vacuum evacuation, since it is hardened with an inorganic binder, it is not elastic like unglazed porcelain, cracks occur during vacuum evacuation, and heat insulation performance deteriorates. In addition, since the film is formed by the inorganic binder, it is difficult to degas from the bubbles inside the molded body during vacuum exhaust, and when used as a vacuum heat insulating material for a long time, the gas generated from these bubbles causes vacuum deterioration and heat insulation performance. However, there is a problem that the life of the device is shortened. On the other hand, a thick inorganic fiber having an average fiber diameter of 4 to 15 μm may be used as a core material in a bag and evacuated. In this case, the vacuum thermal conductivity is 0.01 kcal in addition to the depression during vacuum evacuation. / M ・
It has a drawback that it can be obtained only up to about h · ° C. The present invention solves these problems, does not include an organic binder and an inorganic binder, does not crack or chip during vacuum evacuation, does not dent, and does not deteriorate in vacuum even when left for a long time,
It is an object of the present invention to provide a desired shape of vacuum heat insulating material having high vacuum thermal conductivity and a method for manufacturing the same.

[0004]

The vacuum heat insulating material of the present invention comprises:
In order to achieve the above-mentioned object, it is characterized in that the inorganic fibers are bound to each other at each intersection by a component eluted from the fibers.

As the inorganic fibers constituting the vacuum heat insulating material, glass fibers, ceramic fibers, slag wool fibers, rock wool fibers and the like can be used. From the viewpoint of easily obtaining an average fiber diameter of 2 μm or less, glass fibers are preferred. preferable. In addition, the fiber diameter of the inorganic fiber is the average fiber diameter 2
When the average fiber diameter exceeds 2 μm, the dents become large during vacuum evacuation, and the vacuum thermal conductivity is 0.01 kcal / m · h ·
This is because it does not fall below ℃. The smaller the fiber diameter is, the more preferable. However, since fibers having an average fiber diameter of less than 0.5 μm have no general versatility at present, the average fiber diameter of inorganic fibers is in the range of 0.5 to 1.0 μm. Is preferred.

[0006] In the production method of the present invention for obtaining the above vacuum heat insulating material, inorganic fibers having an average fiber diameter of 2 µm or less are collected and treated with an acidic aqueous solution, followed by compression dehydration and drying. Is collected at the intersection of the inorganic fibers and cured.

The cotton collecting of the inorganic fibers is, for example, 20 to 1.
The cotton is collected with a static pressure of about 00 mmH ₂ O, or the collected cotton product is transported into a mold capable of collecting cotton while suctioning with the same static pressure. Next, an acidic aqueous solution is applied to the collected cotton material, and the pH of the acidic solution to be applied is preferably 5 or less. This is because the binding of the inorganic fibers to each other hardly occurs in the neutral to alkaline regions where the pH exceeds 5. As the acid added to adjust the pH to 5 or less, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid and the like can be used, but sulfuric acid is preferable from the stability and handling of the liquid. In addition, the adhesion-treated product is generally 2
It is compressed and dehydrated at a pressure of about 10 kg / cm ² to obtain a wetted compact having a desired thickness and shape. Then, a vacuum heat insulating material is obtained by appropriately selecting and drying from drying methods such as natural drying, hot air drying, contact drying, high frequency drying and far infrared ray drying.

[0008]

Since the vacuum heat insulating material of the present invention is composed only of inorganic fibers and does not contain organic substances, it does not cause strength reduction due to gas generation or carbonization or organic substance burning even when used at high temperatures. Also, vacuum deterioration does not occur during long-term use. Further, since no inorganic binder is used, the obtained molded product becomes a hard board, and cracks and chips do not occur due to compression during vacuum evacuation, and the compression recoverability is not impaired. In addition, air bubbles are not left behind inside the heat insulating material. In the production method of the present invention, in the step of drying the wet-molded body to which the acidic aqueous solution has been attached, the acidic aqueous solution gathers at the contact points between the fibers due to the surface tension as the water covering the entire fiber evaporates. And at the same time concentrated
The lower pH value erodes the fiber surface at the intersection. Then, the surface fibers gelled by the eluted component SiO ₂ are further dried and solidified, and the fibers are bound at the fiber intersections. In addition, since the inorganic fibers are oriented in a two-dimensional direction when collecting cotton, the vacuum heat insulating material can be controlled so that the direction of the inorganic fibers is oriented perpendicular to the heat transfer direction, improving the heat insulating effect and increasing the thermal conductivity. The value becomes smaller.

[0009]

EXAMPLES Next, examples of the present invention will be described together with comparative examples. Example 1 First, C glass short fibers (alkali-containing silicate glass) having an average fiber diameter of 0.8 μm were collected by a cotton collecting machine.
Next, an aqueous sulfuric acid solution adjusted to pH 3 was applied to the collected cotton product, and compression dehydration was performed to obtain a molded product having a predetermined shape in a wet state. This was dried with hot air to obtain a molded body having a thickness of 30 mm. When this molded product was evaluated, the average fiber diameter was 0.8 μm, the average fiber length was 10 mm, and the organic matter content was 0.
It was less than 01%, and neither cracking, chipping nor peeling occurred. Further, even when it was used at a high temperature of about 550 ° C., there was no decrease in strength, and the compression recovery by pressing at 0.5 kg / cm ² was 100% and did not change. The vacuum heat insulating material was placed in a bag and evacuated to 10 ^-3 Torr. At this time, the vacuum heat insulating material did not have waviness or dents, nor did it crack or chip. Moreover, as a result of measuring the thermal conductivity at room temperature, it was 0.002.
It was kcal / m · h · ° C., and there was almost no vacuum deterioration even in the vacuum deterioration accelerated test corresponding to 10 years, and the value of the thermal conductivity did not change.

Comparative Example 1 A mat made of C glass fibers having an average fiber diameter of 7 μm and having a thickness of 50 mm and a density of 0.09 g / cm ³ was placed in a bag and evacuated to 10 ⁻³ Torr.
At this time, the mat shrank to 10 mm, and waviness and warpage due to uneven density of the mat occurred. The thermal conductivity was 0.012 kcal / m · h · ° C.

(Comparative Example 2) A mat similar to Comparative Example 1 was impregnated with water glass as an inorganic binder to obtain 1 kg / cm ^2.
It was pressed under the pressure of and dried to obtain a mat having a thickness of 10 mm. When this mat was placed in a bag and evacuated to 10 ^-3 Torr, the mat was cracked and the surface was not smooth. The thermal conductivity is 0.008 kcal / m.
Although it was h · ° C., it was 0.
It had deteriorated to 02 kcal / m · h · ° C.

[0012]

As described above, the vacuum heat insulating material according to the present invention has no deformation such as waviness and dents during vacuum evacuation, and
Since it does not contain an organic binder or an inorganic binder, it does not deteriorate in vacuum for a long time. Furthermore, when inorganic fibers having an average fiber diameter of 2 μm or less are laminated so as to be oriented in a direction perpendicular to the direction of heat conduction, the value of the vacuum thermal conductivity is small at a temperature of 550 ° C. or less. It also has good heat insulation properties. Further, according to the method for manufacturing a vacuum heat insulating material of the present invention, the vacuum heat insulating material can be easily manufactured.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kazuhiro Kitamura 630 Tarui-cho, Fuwa-gun, Gifu Japan Inorganic stock company Tarui factory (72) Inventor Yuji Katagiri 630 Tarui-machi, Fuwa-gun Gifu Japan Inorganic stock company Tarui Factory

Claims (5)

[Claims] 1. A vacuum heat insulating material, characterized in that inorganic fibers having an average fiber diameter of 2 μm or less are bound at each intersection by a component eluted from the fibers. 2. The vacuum heat insulating material according to claim 1, wherein the inorganic fibers are laminated so as to be oriented in a direction perpendicular to a heat conduction direction. 3. The vacuum heat insulating material according to claim 1, wherein the inorganic fiber is any one of glass fiber, ceramic fiber, slag wool fiber and rock wool fiber. 4. The method for producing a vacuum heat insulating material according to claim 1, wherein the inorganic fibers having an average fiber diameter of 2 μm or less are collected, treated with an acidic aqueous solution, compressed and dehydrated, and dried. A method for producing a vacuum heat insulating material, comprising collecting elution components at intersections of inorganic fibers and curing them. 5. The method for manufacturing a vacuum heat insulating material according to claim 4, wherein the pH value of the acidic aqueous solution is 5 or less.