JPH07237957A - Heat insulating material composition - Google Patents

Abstract

PURPOSE:To obtain a heat-insulating material composition capable of selecting a dry press method or a wet making method depending on the shape of a part to be used, improving a thermal conductivity irrespective of a production method, providing a heat insulating material having flexibility much more improved than that of a conventional one in a heat insulating material made by a wet making process. CONSTITUTION:This heat insulating material composition is obtained by blending 5-50wt.% of a ceramic inorganic fibers with 50-95wt.% of inorganic powder, optionally 3-5wt.% of an inorganic binder and 3-10wt.% of an organic elastic substance and has 0.35-0.45g/cm<3> bulk density. Silica-alumina fibers and alumina fibers can be used as the ceramic inorganic fibers utilized in this invention and the inorganic powder has 0.5-10mum particle diameter and <=18kcal/m.h. deg.C solid thermal conductivity by itself at a room temperature. Two kinds of powders having different refractive indexes to light rays at >=1mum wavelength are used as the inorganic powder.

Description

Detailed Description of the Invention

[0001]

2. Description of the Related Art Conventionally, as a heat insulating material used in a fuel cell or the like, for example, synthetic silica having an average primary particle size of about 20 mμ (for example, Aerosil, manufactured by Nippon Aerosil Co., Ltd .: trade name Aerosil), titanium oxide and ceramic fiber are dry type. What was obtained by carrying out mixing and press molding and then machining is known.

[0002]

However, in the above conventional heat insulating material, 90% or more of the material used is fine powder, and since it is molded by a dry press, it has extremely poor flexibility and does not bend to a curved surface. There was a problem in that it had to be covered with glass fiber cloth or the like before use.

Therefore, in order to improve the flexibility, the inventors of the present invention have tried to manufacture a conventional product by wet papermaking.
Synthetic silica used in conventional products was remarkably thickened by contact with water and could not be manufactured. Therefore, the inventors have come to the conclusion that it is not possible to improve the flexibility of conventional products. Therefore, the object of the present invention is to select a dry pressing method or a wet papermaking method depending on the shape of the site to be used, and further improve the thermal conductivity as compared with the conventional product regardless of the manufacturing method, and further manufactured by the wet papermaking method. In terms of products, it is to provide a heat insulating material with dramatically improved flexibility compared to conventional products.

[0004]

According to the present invention, the ceramic inorganic fiber is 5 to 50 wt% and the inorganic powder is 50 to 50 wt%.
95 wt% If necessary, an inorganic binder is added in an amount of 3 to 5 wt% and an organic elastic material is added in an amount of 3 to 10 wt%.
It has a bulk density of 0.35 to 0.45 g / cm ³ . The method for producing such a heat insulating material is characterized in that it can be produced by either a dry pressing method or a wet papermaking method.

[0005]

Next, the structure of the present invention will be described in detail. As the ceramic inorganic fiber, silica-alumina fiber, alumina fiber, silica fiber, zirconia fiber and potassium titanate whiskers can be used. The blending amount of such ceramic inorganic fibers is in the range of 5 to 50 wt%, and if the proportion is less than 5 wt%, the reinforcing effect of the fibers cannot be obtained, and the handleability and mechanical strength are remarkably lowered. On the other hand, 50w
If it exceeds t%, the amount of the inorganic powder added decreases, and convective heat transfer, molecular heat transfer, radiative transfer, and the like increase, so that the heat insulating property deteriorates remarkably. Next, the inorganic powder will be described.

In the present invention, two kinds of inorganic powders that meet the following conditions are selected and used. (1) The ratio of the refractive index to light having a wavelength of 1 μm or more (specific refractive index) is 1.25 μm or more. (2) The average particle size is in the range of 0.5 to 10 μm. (3) The solid thermal conductivity of each powder is 18 Kc at room temperature.
al / m. h. It is below ℃. When the inorganic powders that meet the above conditions are divided into two groups and described, a more preferable material having a relatively small refractive index for light having a wavelength of 1 μm or more is a refractive index =
It is an inorganic powder of 1.5 or less. As such powder, S
Examples thereof include iO ₂ , NaF, and LiF, and SiO ₂ is preferable in view of heat resistance. An inorganic powder having a relatively large refractive index with respect to light having a wavelength of 1 μm or more, more preferably an inorganic powder having a refractive index of 2.0 or more.

Examples of such powder include TiO ₂ and BaTi.
₃ , PbS and the like are included, but the inorganic powders in this group have an extremely important role as a radiant heat scattering material, and in order to more effectively scatter the radiant heat, the refractive index is as large as possible. Moreover, it is desirable to use an inorganic powder having a peak having a reflectance of 70% or more for light having a wavelength of 10 μm or more. Therefore, in the present invention, BaTiO ₃ is used.

The above relative refractive index is extremely important for suppressing phonon conduction, and the larger this value, the better. Therefore, in the present invention, the value of the relative refractive index is limited to 1.25 or more. Here, adding a little more about suppression of phonon conduction, as a material that can generally suppress phonon conduction, a material having a lattice defect in the crystal or a material having a complicated structure (Mg
Compared to O and SiO ₂ , MgO / Al ₂ O ₃ and 3Al ₂ O ₃
・ 2SiO ₂ is said to be good).
Thus, BaTiO ₃ described above is coordinated to the position Ti atoms in the crystal slightly shifted from the center, yet, TiO ₂
Since it has a more complicated structure than SiO ₂ and SiO ₂ , it is effective not only for scattering of radiant heat but also for scattering of phonons.

The inorganic powder used in the present invention has an average particle size in the range of 0.5 to 10 μm, and the solid thermal conductivity of each powder is 18 Kcal / m.s. h. ℃ (a
t room temperature) or less. Especially for powders having a large refractive index, 3.0 μm or more is suitable.
If the average particle diameter is 0.5 μm or less, not only the production of the heat insulating material becomes extremely difficult, but also the radiant heat is not sufficiently scattered and the thermal conductivity deteriorates.

On the other hand, if powder having a particle size of 10 μm or more is used, the pores generated in the heat insulating material become extremely large.
Convection and molecular heat transfer increase, and thermal conductivity deteriorates. Also, the solid thermal conductivity is 18 Kcal /
m. h. When a powder having a temperature of ℃ (at room temperature) or higher is used, solid heat transfer becomes dominant in the heat insulating material and the thermal conductivity deteriorates. Therefore, in the present invention, the above-mentioned 3
Two kinds of inorganic powders suitable for one condition are used, and the compounding ratio thereof is in the range of 50 to 95 wt%. The two kinds of inorganic powders within the mixing ratio range of 50 to 95 wt% have a small refractive index powder amount / a large refractive index powder amount = 1.5 to
Each of them will be blended at a ratio of 3.0.

The powder having a large refractive index used in the present invention has a large true specific gravity as compared with the powder having a small refractive index. Therefore, if the compounding amount of this powder is increased (the above compounding ratio is 1.5 or less), the number of powders decreases, so that the pore diameter in the heat insulating material increases, convection and molecular heat transfer dominate, and heat conductivity deteriorates. On the other hand, when the blending ratio is 3.0 or more, the amount of powder having a large refractive index decreases, so that radiant heat is not sufficiently scattered and the thermal conductivity deteriorates. Therefore, in the present invention, the above-mentioned mixing ratio must be within the range of 1.5 to 3.0.

Next, in the present invention, an inorganic binder for the purpose of maintaining the strength at high temperature can be used in a range of 3 to 5 wt% if necessary. Examples of the inorganic binder include colloidal silica, synthetic mica, montmorillonite, and the like. The method of use is to mix the raw material or impregnate the obtained heat insulating material. Further, in the present invention, if necessary, an organic elastic substance may be added in an amount of 3 to 3.
It can be used in the range of 10 wt%. This substance is particularly useful for producing a heat insulating material used in a region requiring flexibility, and for example, emulsion of natural heat rubber and synthetic rubber latex binder such as NBR and SBR are suitable. . Especially in the case of manufacturing by wet papermaking, the flexibility is drastically improved by using such an organic elastic substance. In the present invention, the compounding ratio of the organic elastic material is in the range of 3 to 10 wt%. If this ratio is less than 3 wt%, the flexibility of the obtained heat insulating material will be insufficient, and if it exceeds 10 wt%, the organic elastic material will be burned out when used in a high temperature range of 700 ° C or higher, and the voids will remarkably increase. Sex is reduced.

A composition obtained by molding the composition blended in the above blending ratio into a desired shape by a dry pressing method or a wet papermaking method has a bulk density of 0.35 to 0.45 g / c.
Within the range of m ³ . This bulk density is 0.35 g / cm ^3.
Below, convection and molecular heat transfer increase, while 0.45
If it exceeds g / cm ³ , the solid heat transfer increases, and the thermal conductivity significantly decreases. Next, a method for manufacturing the heat insulating material of the present invention will be described.

In the present invention, the heat insulating material is manufactured by a dry pressing method or a wet papermaking method. First, in the dry pressing method, after mixing the ceramic-based inorganic fibers, the inorganic powder and, if necessary, an inorganic binder with a V-type mixer or the like,
The mixture is put into a predetermined mold and pressed to obtain a molded body. In addition, it is also possible to impregnate the obtained molded body with an inorganic binder. Next, in the wet papermaking method, the ceramic-based inorganic fiber, the inorganic powder and, if necessary, the inorganic binder are dispersed in water, and then an aluminum sulfate aqueous solution is added to the fiber to attach the inorganic powder or the inorganic binder. Let Next, an organic elastic substance is added to the water within a predetermined range, and then a cationic polymer flocculant is added to obtain an aggregate. Here, if the order of addition of the aqueous solution of aluminum sulfate and the organic elastic substance is reversed, it becomes difficult for the inorganic binder to be attached to the fibers, and it becomes extremely difficult to maintain the strength at high temperatures, so it is necessary to exercise caution.

Next, the above-mentioned aggregate is put into a predetermined mold and paper is made to obtain a molded body. The obtained heat-insulating material is obtained by subjecting the obtained molded body to dewatering press, adjusting the water content in the sheet to 100% or less, and then drying.
Here, the water content of the sheet after the dewatering press needs to be 100% or less, and when the water content is 100% or more, shrinkage occurs during drying and it becomes difficult to obtain a predetermined dimension.

In the heat insulating material obtained as described above, the strength is reinforced by the ceramic inorganic fiber, and when an inorganic binder is used, the strength at high temperature is maintained.
In addition, by using two kinds of inorganic powder suitable for the above conditions, air convection and molecular heat transfer in the voids inside the heat insulating material are suppressed, and further radiant heat is scattered, so that the heat insulation With respect to the property, it is possible to obtain a property superior to the conventional one.
In addition, the flexibility of the molded body manufactured by the wet papermaking method using the organic elastic substance can be dramatically improved as compared with the conventional one. Next, examples and comparative examples embodying the present invention will be described below.

[0017]

【Example】

(Example 1) To 25 liters of water, 12 g of so-called de-shot bulk (Ibiden Co., Ltd .: trade name Ibiwool), in which large particles were removed as silica-alumina ceramic fibers, was added and defibrated.

Next, as a powder having a large refractive index, BaTiO _{3 is used.}
(Kyoritsu Kiln Raw Materials Co., Ltd.) 58 g and SiO ₂ (Shionogi Pharmaceutical Co., Ltd .: trade name Carplex) 148 g as a powder having a small refractive index were added to 25 liters of the water and mixed well, and further colloidal silica (Nissan Chemical Co., Ltd .: trade name Snowtex) (23 g) is added, and then an aluminum sulfate aqueous solution is added to obtain a primary aggregate. Then, 17 g of NBR type latex (manufactured by Nippon Zeon Co., Ltd .: trade name Nipol) was added, and finally a cationic polymer coagulant was added to re-aggregate to prepare a slurry.

Next, the slurry is added to 340 mm × 340
It is put into a mm paper machine to make paper, and a wet sheet-like material having a thickness of 8 mm is obtained. The surface pressure of this sheet is 100 kg /
It was pressed at cm ² and dried under the condition of 120 ° C. × 2 Hr. After drying, the end portion of the obtained sheet-shaped material was cut to obtain a sheet-shaped material having a thickness of 5 mm, a 300 mm square, and a bulk density of 0.40 g / cm ³ . Table 1 shows the thermal conductivity, bending strength, and amount of flexure of this sheet.

(Example 2) Among the raw materials used in Example 1, silica-alumina ceramic fiber and BaT
Using only iO ₃ and SiO _2, the same compounding amounts as in Example 1 were mixed by a V-shaped mixer, and then the mixture was put into a predetermined mold, and a thickness of 5 mm and 30 was produced by a dry pressing method.
With respect to a heat insulating material having a 0 mm square and a bulk density of 0.38 g / cm ³ , the same physical property measurement as in Example 1 was performed, and the results are shown in Table 1.

(Example 3) Similar to Example 1, 25 g of water was added to 23 g of ceramic fiber and disentangled, and then 60 g of TiO ₂ powder (manufactured by Toho Titanium Co., Ltd.)
After adding 128 g of SiO ₂ powder to 25 liters of the above water and mixing them well, 27 g of colloidal silica and 28 g of NBR-based latex are further added, and an aqueous solution of aluminum sulfate and a cationic polymer coagulant are added in this order to coagulate. The slurry was adjusted from the above. Next, the slurry was supplied to a 340 mm × 340 mm hand-made paper machine to make a paper, to obtain a wet sheet-like material having a thickness of 8 mm. This sheet-like material is pressed at a surface pressure of 100 Kg / cm ² and at 120 ° C.
It was dried under the condition of × 2Hr. The edge of the sheet-like material obtained after drying was cut to obtain a sheet-like material having a thickness of 5 mm, a 300 mm square, and a bulk density of 0.40 g / cm ³ . The physical properties of this sheet-like material were measured in the same manner as in Example 1, and the results are shown in Table 1.

(Comparative Example 1) The same raw material as that used in Example 1 was used, and the raw material mixture ratio was BaTiO ₃ 104.
g, SiO ₂ 102 g, other raw material ratios and manufacturing methods were the same as in Example 1 to obtain a sheet-like material having a thickness of 5 mm, a 300 mm square, and a bulk density of 0.40 g / cm ³ . The physical properties of this sheet-like product were measured in the same manner as in Example 1, and the results are shown in Table 1.

(Comparative Example 2) The same raw material as that used in Example 1 was used, and the raw material blending ratio was BaTiO ₃ 44 g,
SiO _{2 was} 162 g, and the other raw material ratios and manufacturing methods were the same as in Example 1 to obtain a sheet-like material having a thickness of 5 mm, a 300 mm square, and a bulk density of 0.40 g / cm ³ . The physical properties of this sheet-like product were measured in the same manner as in Example 1, and the results are shown in Table 1.

(Comparative Example 3) Of the raw materials used in Example 1, only SiO ₂ was replaced with TiO ₂ , and the compounding amount and the manufacturing method were the same as in Example 1, and the thickness was 5 mm and 300 mm.
A sheet-like material having a square shape and a bulk density of 0.40 g / cm ³ was obtained. The physical properties of this sheet-like product were measured in the same manner as in Example 1, and the results are shown in Table 1.

(Comparative Example 4) Of the raw materials used in Example 1, only BaTiO ₃ was replaced with NaF, and the compounding amount and the manufacturing method were the same as in Example 1, and the thickness was 5 mm, 300 mm square,
A sheet-like material having a bulk density of 0.40 g / cm ³ was obtained. The physical properties of this sheet-like product were measured in the same manner as in Example 1, and the results are shown in Table 1.

(Comparative Example 5) Among the raw materials used in Example 1, only BaTiO ₃ was replaced with SiC, and the compounding amount and the manufacturing method were the same as in Example 1, and the thickness was 5 mm and 300 mm.
A sheet-like material having a square shape and a bulk density of 0.40 g / cm ³ was obtained. The physical properties of this sheet-like product were measured in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 6 Physical properties were measured in the same manner as in Example 1 with respect to a commercially available heat insulating material molded by conventional dry mixing and dry pressing, and the results are shown in Table 1. As is clear from Table 1, when the mixing ratio of two kinds of inorganic powders is set outside the predetermined range (1.5 to 3.0) as in Comparative Examples 1 and 2, when the ratio is less than 1.5, BaTiO ₃ Of the powder, resulting in a decrease in the total number of powders, which increases convection and molecular conduction and deteriorates the thermal conductivity in the low temperature range. On the other hand, when the ratio exceeds 3.0, the compounding amount of BaTiO ₃ which is a radiant heat scattering material decreases, so that the radiative conduction increases and the thermal conductivity in the high temperature region deteriorates.

Further, when the value of the relative refractive index is reduced to about 1.0 as in Comparative Examples 3 and 4, the thermal conductivity in the low temperature range is remarkably deteriorated in Comparative Example 3 using the powder having a large refractive index. In addition, since the difference in the refractive index is small in the high temperature region, the radiation heat is not sufficiently scattered and the thermal conductivity is slightly lowered. On the other hand, in Comparative Example 4 using a powder having a small refractive index, contrary to Comparative Example 3, good characteristics are exhibited in the low temperature region, but radiant heat is extremely unlikely to scatter in the high temperature region, resulting in an extremely high thermal conductivity. It gets worse.

Further, in Comparative Example 5, the refractive index is BaTiO 3.
_Although SiC larger than ₃ is used, the result is Ba
TiO ₃ is better. It can be considered that this is because the solid thermal conductivity of SiC is about three times higher than that of BaTiO ₃ . Therefore, in the present invention, the solid thermal conductivity at room temperature is 18 kcal / m. h. Inorganic powder below ℃ must be used. The heat insulating material manufactured by the wet papermaking method in the present invention has a thermal conductivity higher than that of the conventional heat insulating material (Comparative Example 6).
It can be seen that the bending strength and the amount of deflection (flexibility) are improved. On the other hand, it can be seen that the heat insulating material manufactured by the dry pressing method has improved thermal conductivity without lowering strength and flexibility as compared with the conventional product.

Therefore, according to the present invention, the thermal conductivity can be improved without lowering the strength and the manufacturing method can be selected according to the shape of the portion to be used. Therefore, the conventional product is coated with glass fiber cloth. Alternatively, since the sheet-shaped article can be used alone as a part of the used sheet by performing the secondary processing, it is possible to significantly reduce the cost. For example, as a heat insulating material for a halogen lamp stove, a high-temperature battery, etc., since it is used for a portion having a curved surface, a conventional product is a product coated with a glass fiber cloth. It can be used alone.
Also, since the heat insulating material on the bottom surface of the electric heating stove is used in the form of a flat plate, the dry press product of the present invention can be used, and the thermal conductivity is superior to the conventional product, so the thickness can be made thinner than the conventional product and the size is small. There is a merit that can be realized.

[Table 1]

Claims (7)

[Claims] 1. A ceramic inorganic fiber in an amount of 5 to 50 wt.
%, 50 to 95 wt% of inorganic powder, and 3 to 5 wt% of inorganic binder and 3 to 10 wt% of organic elastic material as required, and have a bulk density of 0.35 to 0.45 g / c.
An insulating material having m ³ . 2. Silica-alumina fiber, alumina fiber,
The ceramic-based inorganic fiber according to claim 1, comprising silica fiber, potassium titanate whiskers and zirconia fiber. 3. The inorganic powder according to claim 1, wherein the relative refractive index is 1.25 or more by using two kinds of powders having different refractive indexes with respect to light having a wavelength of 1 μm or more. 4. The inorganic powder according to claim 1, which has an average particle size of 0.5 to 10 μm. 5. The solid thermal conductivity at room temperature is 18 Kcal /
m. h. The inorganic powder according to any one of claims 1, 3, and 4, which has a temperature of not higher than ° C. 6. The compounding ratio of the two kinds of inorganic powders is within a range of a powder amount having a small refractive index / a powder amount having a large refractive index = 1.5 to 3.0. The inorganic powder according to any one of 4 and 5. 7. The heat insulating material according to claim 1, which can be produced by either a dry pressing method or a wet papermaking method.