JPH06172010A - Insulation material and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Structure] An inorganic fiber mixture of 65 to 85% by weight of silica fiber and 15 to 35% by weight of mullite fiber is mixed with cellulose powder, B ₂ O ₃ -forming boron compound powder and silicon carbide heat radiation material in water. And the resulting slurry mixture is dehydrated and molded, dried, and then fired at a temperature at which the boron compound melts to obtain a low-density heat insulating material. [Effect] It is possible to reliably and easily manufacture a low-density heat insulating material having excellent physical properties, heat insulating properties, heat resistance, and the like, which is suitable as a surface protective material for a space vehicle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is suitable as a heat insulating material to be used under severe temperature conditions exceeding 1200 ° C.,
The present invention relates to a plate-shaped low-density heat insulating material having a high degree of heat resistance and thermal shock resistance, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Like NASA's space shuttle and space shuttle surface protection materials, it withstands extremely high temperatures and severe thermal shocks, has a low density and excellent heat insulation properties, and has a certain level of strength and machining. As a typical example of the plate-shaped heat insulating material required to have heat resistance, a porous heat insulating material containing a heat-resistant inorganic fiber as a main material is known.

The first materials of this type used were:
It is a material called silica tile, which is made by firing a molded product of a mixture of colloidal silica as a binder and high-purity silica fiber at about 1300 ° C. However, this material is low in strength and has a rapid deterioration in physical properties, and has a defect that it is chipped by a mechanical impact during use or the adhered material is peeled off. In order to solve the above-mentioned drawbacks of the silica tile by using the binder, in the invention of JP-A-55-37500, a mixture of silica fiber, aluminosilicate fiber and boron oxide, or silica fiber and aluminoborosilicate fiber is used. It is proposed that the mixture of fibers is molded and then fired to cause interfiber fusion. In addition, JP-A-60-15
The invention of No. 1269 discloses a fusion of silica fiber and alumina fiber having a specific fiber diameter with boron oxide. Further, in the invention of Japanese Patent Laid-Open No. 4-119958, a production in which interfiber fusion is caused by mixing organic fiber and boron oxide into a mixture of silica fiber, aluminosilicate fiber and aluminoborosilicate fiber, followed by molding and firing The law is disclosed.

[0004]

The low-density heat insulating materials according to the above inventions have already achieved quite high performance levels.
Needless to say, a heat insulating material that is used under extremely harsh conditions and requires a high degree of reliability, such as a space shuttle, is required to have a high performance. Therefore, an object of the present invention is to provide a heat insulating material having higher performance than the conventional low density heat insulating material, and to provide a method for reliably and easily manufacturing the high performance low density heat insulating material. .

[0005]

The heat insulating material successfully provided by the present invention is composed of 65 to 85% by weight of silica fibers, 15 to 35% by weight of mullite fibers, and a glass-like material for fixing the entanglement points of the fibers. It has a three-dimensional network structure including a boron compound and cellulose powder burned voids of fine and uniform size uniformly distributed in the product.

Further, in the method of manufacturing the heat insulating material according to the present invention, the silica fiber is 65 to 85% by weight and the mullite fiber is 15 to 3% by weight.
A slurry obtained by dispersing 5 wt% of the inorganic fiber mixture in water together with 5 to 40 wt% of the cellulose powder and ₃ to 4 wt% of the boron compound powder in terms of B ₂ O ₃ with respect to the inorganic fiber mixture. After dehydration molding the mixture and drying,
It is characterized by firing at a temperature at which the boron compound melts.

The heat insulating material of the present invention can have further excellent heat insulating performance by containing a silicon carbide based heat radiation material in an amount of about 20% by weight or less with respect to the inorganic fiber.

[0008]

In the heat insulating material according to the present invention, silica fiber constitutes the basic composition of the heat insulating material, and is particularly effective in obtaining a heat insulating material having a low coefficient of thermal expansion and good spalling resistance. If the amount of this fiber is less than 65% by weight, the heat insulating material has a high coefficient of thermal expansion, and cracks due to rapid heating and quenching are likely to occur. If it exceeds 85% by weight, the desired 1200
The heat resistance at ℃ decreases and the shrinkage due to heating increases. Therefore, the content of silica fiber is preferably 65 to 85% by weight. The silica fiber is a high-purity silica fiber having a SiO ₂ content of 95% by weight or more, and an average fiber diameter of 0.1.
It is desirable to use one having an average fiber length of 3 to 3 μm and an average fiber length of about 1 to 5 mm.

Mullite fiber is a fiber composed of orthorhombic aluminous crystals having a SiO ₂ / Al ₂ O ₃ molar ratio of 2/3, which improves heat resistance and maintains a low coefficient of thermal expansion. It is effective for If the amount of this fiber is less than 15% by weight, the ratio of silica fiber becomes relatively large, and the heat resistance is lowered as described above. On the other hand, if it exceeds 35% by weight, the silica fiber is relatively insufficient, and the rapid heating and rapid cooling resistance is deteriorated as described above. Therefore, it is desirable that the content rate of the mullite fiber is 15 to 35% by weight. As the mullite fiber, it is desirable to use one having an average fiber diameter of about 2 to 10 μm and an average fiber length of about 2 to 10 mm.

By adopting both the silica fiber and the mullite fiber having the above-mentioned suitable fiber diameter and suitable fiber length, it is possible to obtain a heat insulating material having a low density and a small thermal conductivity, and at the same time, a layered structure of the fibers in the molding step. It is possible to reduce the orientation and avoid the occurrence of remarkable directionality in the physical properties.

The boron compound oxidizes and melts when the raw material mixture is molded and fired, and then reacts with silicon oxide to form a borosilicate compound. The produced borosilicate compound is
After cooling, it is vitrified to fix the entanglement points of the inorganic fibers. As the boron compound as a raw material, boron oxide, boron nitride,
Boron carbide and the like are particularly preferable.

The amount of the boron compound used as a raw material in the production method of the present invention is B ₂ O _{3 with} respect to the total weight of the above fibers.
It is preferable to be 3 to 5% by weight in terms of conversion. If the amount is less than 3% by weight, the vitrification and fusion bonding points at the entanglement points of the fibers are reduced and the strength is lowered. On the other hand, if it exceeds 5% by weight, shrinkage during firing of the molded body becomes large, and the product has a high density. Especially the target density is 0.08 ~ 0.15g / cm ³
If it is set to, it will be extremely difficult to achieve the target unless the content is within the above range. If the content is too large,
The resulting glass coats the fibers, which not only impairs the heat insulating properties, but also prevents each inorganic fiber from exerting its properties to its fullest, thus degrading the heat resistance.

The voids in the insulation material have a great influence on the performance of the insulation material. In the present invention, fine and uniform voids are uniformly distributed in the heat insulating material. Due to the above inorganic fibers and voids, the heat insulating material of the present invention has a three-dimensional network structure. A suitable void is a vanishing void of cellulose powder. A preferable amount of voids, that is, a porosity is 92 to 97% by volume.

Cellulose powder is easily dispersed in water due to its hydrophilicity and does not become entangled like defibrated pulp or organic fiber, and a dehydrated molded product is obtained when a slurry-like raw material mixture is molded. Evenly distributed throughout. And the mixed cellulose powder is
Since it is extremely fine, it easily flows in the process of dehydration molding, so that it does not hinder the movement of the inorganic fibers in their natural arrangement. As a result, when the cellulose powder is burnt out in the firing process of the molded product, fine and evenly sized voids are uniformly distributed in the product, and naturally, the inorganic fiber is also uniformly distributed. The physical properties of (the defibration-treated pulp or organic fibers are used, since the lumps of undefibrated fibers that remain do not interfere with the natural arrangement of the inorganic fibers, the voids formed after firing are not uniform, Moreover, some unnatural curvature remains in the inorganic fibers.)

The content of the cellulose powder in the raw material for production is suitably 5 to 40% by weight. If it is less than 5% by weight, the target porosity cannot be achieved, while it exceeds 40% by weight. And, vitrification fusion at the entanglement point of fibers is hindered, resulting in a decrease in strength.

Cellulose powder (powder fibrin)
Among them, particularly preferred is a highly bleached pulp that has been subjected to acid hydrolysis treatment and taken out as high-purity cellulose crystals, which is a fine powder that does not stop the original form of pulp fiber (commercially available product). An example is KC Flock from Sanyo Kokusaku Pulp Co., Ltd.). As a similar product, there is a product obtained by finely pulverizing the selected pulp only by mechanical pulverization without chemically cutting and refining the fiber by acid hydrolysis, and this can also be used as a raw material in the present invention ( An example of a commercially available product is Sanyo Kokusaku Pulp Co., Ltd.'s pulp floc).

The silicon carbide-based heat radiation material impedes the transmission of radiant heat to further improve the heat insulation performance of the product, but if it is excessively compounded, the density of the product will be increased to an undesired level. Therefore, when compounding this, considering the effect of reducing the thermal conductivity of the product and the effect on the density, the compounding ratio is 20 relative to the total amount of silica fiber and mullite fiber.
It is desirable that the amount is not more than 5% by weight, especially 5 to 20%.
Specific examples of preferable silicon carbide-based heat radiation materials include silicon carbide powder and silicon carbide whiskers.

The above-mentioned inorganic fibers, cellulose powder, and boron compound are uniformly mixed in water together with a silicon carbide-based heat radiation material to be contained to form a slurry. Here, the solid content concentration of the slurry is preferably about 1 to 2% by weight. This slurry is dehydrated and molded into a desired shape by a conventional method. A press is generally used for the dehydration molding. After drying the obtained molded product, the temperature is raised and baking is performed. Drying is usually carried out below the carbonization temperature of the cellulose powder, that is, below about 150 ° C. When firing is performed in the air, the cellulose powder is first burned off, and when the temperature further rises, the boron compound is oxidized and melted into glass,
Interfiber fusion occurs. It is desirable that the calcination for the oxidative melting is usually performed in the range of about 1100 to 1400 ° C. The molded product after firing is cooled and then cut if necessary to obtain a desired heat insulating material.

In a product in which silica fibers and mullite fibers, which are main raw materials, are fused and fixed at a confounding point of them with a boron compound in a borosilicate glass form, a large amount of fine voids formed by burning away the cellulose powder are formed. Exists in. The voids are very uniform in size and distribution as compared with the case where pulp and other organic fibers are mixed. Further, the distribution of the inorganic fibers is extremely uniform and natural, so that the utilization rate of the inorganic fibers as the skeleton is high. Therefore, even when a low-density product having a bulk density of about 0.08 to 0.15 g / cm ³ is manufactured, it has excellent mechanical properties such as strength and thermal properties.

[0020]

【Example】

Examples 1 and 2 Raw material used: Silica fiber 98% by weight of SiO ₂ , average fiber diameter 0.9μ
m, average fiber length 2 mm mullite fiber average fiber diameter 4 μm, average fiber length 2 mm boron nitride powder average particle size 1 μm silicon carbide powder average particle size 0.26 μm cellulose powder KC Flock W-50 (product of Sanyo Kokusaku Pulp Co., Ltd.) average particle Major axis 1 mm, average particle minor axis 7
5 μm

The above raw materials were poured into a large amount of water at the ratio shown in Table 1 and mixed sufficiently to form a slurry. Here, the solid content concentration of the slurry was 1%. The obtained slurry was formed into a plate by dehydration press forming, and the obtained formed product was dried at 105 ° C. for 16 hours. The molded product was further calcined in the air at 1300 ° C. for 2 hours to burn out the cellulose powder and cause interfiber fusion by B ₂ O ₃ which became glassy as a result of the oxidation of the boron compound. After cooling, the fired product is cut to a thickness of 50 mm and a side of 20
A 0 mm plate-shaped heat insulating material was obtained.

Comparative Example 1 A plate-like heat insulating material was produced in the same manner as in Example 1 except that alumina fiber (Al ₂ O ₃ 95% by weight, average fiber diameter 3 μm, average fiber length 2 mm) was used instead of mullite fiber. did.

Comparative Example 2 A plate-like heat insulating material was produced with the same raw material composition as in Example 1 except that bleached kraft pulp for papermaking (softwood material) was used instead of cellulose powder. In this case, at first, only the pulp was put into water, and after vigorous stirring with a stirrer, the pulp was well defibrated, then the other raw materials were put and further stirred to prepare a slurry in which the raw materials were uniformly mixed. .

Comparative Example 3 In the same production method as in Comparative Example 2, a combination of inorganic fiber as a raw material, silica fiber, alumina fiber, and aluminoborosilicate fiber (average fiber diameter of about 10 μm) (compounding ratio is as shown in Table 1). ) Was changed. The characteristic values of the products according to each of the above examples are shown in Table 1 together with the raw material composition.

As shown in Table 1, this example has a bulk density of 0.08 to 0.1 which is suitable as a surface material for space equipment.
The thermal conductivity and the thermal expansion coefficient are sufficiently small while being kept within the range of 5 g / cm ³ . In particular, the coefficient of thermal expansion is required to be about 2.50 × 10 ^-6 / ° C or less for space equipment,
All of the present embodiments have cleared it sufficiently.
Moreover, although the strength has never been high, the strength of this example is generally higher than that of the comparative example.

As a result of observing the structure with a microscope, the heat insulating materials of Examples 1 and 2 of the present invention had the entanglement points of silica fibers and mullite fibers fixed by vitreous borosilicate glass and were uniformly and finely distributed in the product. It has a three-dimensional network structure in which voids of uniform size are formed. The size of this void is
It corresponds to the burned voids of cellulose powder, and it is considered that excellent product characteristics were obtained depending on the size and degree of dispersion of the voids.

[0027]

[Table 1] Note 1 The amount of boron nitride powder is the equivalent of B ₂ O _3. Note 2 The thermal conductivity is the value at atmospheric pressure of 850 ° C; Unit: kcal
/ m ・ h ・ ℃

[0028]

As described above, according to the present invention, a mixture of silica fiber and mullite fiber in a specific ratio is dispersed in water together with a cellulose powder, a boron compound powder and a silicon carbide-based heat radiation material as an optional additional component. The resulting slurry-like mixture is dehydrated, dried, and then fired to obtain a product in which the heat-resistant inorganic fibers are highly uniformly distributed. A product excellent in heat resistance and the like can be reliably and easily manufactured.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomohiko Hara, 1-5-21 Tsurumi, Tsurumi-ku, Yokohama (72) Toshiyuki Aji 2-38-3, Aizawa, Seya-ku, Yokohama

Claims (6)

[Claims] 1. A silica fiber of 65 to 85% by weight, a mullite fiber of 15 to 35% by weight, a glassy boron compound for fixing the entanglement points of the fibers, and a fine and uniform size uniformly distributed in the product. A heat insulating material that has a three-dimensional mesh structure with a cellulose powder burned void. 2. The heat insulating material according to claim 1, which has 20% by weight or less of a silicon carbide based heat radiation material therein. 3. The heat insulating material according to claim 1, which has a porosity of 92 to 97% by volume. 4. The average fiber diameter of the silica fibers is 0.3 to 3 μm.
The heat insulating material according to claim 3, wherein m, the average fiber length is 1 to 5 mm, the average fiber diameter of the mullite fiber is 2 to 10 µm, and the average fiber length is 2 to 10 mm. 5. An inorganic fiber mixture containing 65 to 85% by weight of silica fibers and 15 to 35% by weight of mullite fibers is contained in an amount of 5 to 40% by weight based on the inorganic fiber mixture of cellulose powder and _{3 in} terms of B ₂ O 3. A method for producing a low-density heat insulating material, which comprises: dispersing in a water content of up to 5% by weight of a boron compound powder in water; dehydrating and molding the resulting slurry mixture; and drying and firing at a temperature at which the boron compound melts. 6. An inorganic fiber mixture containing 65 to 85% by weight of silica fibers and 15 to 35% by weight of mullite fibers, 5 to 40% by weight of cellulose powder based on the inorganic fiber mixture, and _{3 in} terms of B ₂ O 3. Dispersing in water together with ~ 5% by weight of a boron compound powder and 20% by weight or less of a silicon carbide-based heat radiation material, dehydrating and molding the resulting slurry-like mixture, and then baking at a temperature at which the boron compound melts. A method for manufacturing a low-density heat insulating material characterized by: