JP6099029B2 - Thermal insulation paint, thermal insulation method using the paint, and sheet material coated with the paint - Google Patents

Description

  The present invention relates to a heat-insulating paint that imparts heat insulation to an article by being applied to the article, a heat-insulating method using the paint, and a sheet material coated with the paint.

  Refrigerated and frozen products such as pharmaceuticals and food products are usually corrugated cardboard with insulation such as foamed polystyrene containers and urethane foam that have heat insulation properties in environments other than refrigerated and frozen conditions to prevent quality deterioration during transportation. It is housed and transported in an insulated container (for example, Patent Document 1) such as a box. Since such a heat insulating container is bulky as compared with the product to be stored, there has been a problem that the transportation cost of the product is increased. In addition, it is essential to prepare an insulated container separately from the product itself, and to store and pack the product, which has been a factor in complicating the transportation procedure.

  On the other hand, there are many occasions where a container for keeping a product at a high temperature for a relatively long time is required. Such a container is often required to be touched with a bare hand at the same time as the outside does not become hot at the time of use. As such a container, a bulky material container such as foamed polystyrene, a paper container having a laminated structure on the side wall, or the like is used in order to provide heat retention. As a paper container having a laminated structure on the side wall, for example, a paper container having an air layer inside the laminated side wall is known as in Patent Document 2. In any case, the whole is bulky as compared with the inner volume, and a large space is required for transporting and storing the container itself.

  In other fields, in facilities related (architecture, plant, car body, etc.), a technology to improve the heat insulation inside the base material by providing a heat insulating layer such as a heat-foamable polymer on the back side of the base material constituting the inner wall. Is known (for example, Patent Document 3). However, the conventional heat insulating material layer needs to have a certain thickness or more in order to have a higher heat insulating effect, and there are problems that the internal volume is limited and the transportation cost of the base material is increased. It was.

Japanese Patent Laid-Open No. 11-147777 JP 2000-247377 A JP 7-48881 A

  As described above, since most of the conventional heat insulating materials in each field are bulky, it has been a factor of lowering transport efficiency and storage efficiency. In addition, the materials used are limited to glass wool, heat insulation board, foamed urethane, foamed polystyrene, etc., and due to their thickness and structural weakness, fine processing and molding are difficult, and box-shaped heat insulation containers Moreover, the object used, such as a comparatively large base material, was limited.

Therefore, an object of the present invention is to provide a heat insulating material that is less bulky than the prior art, has excellent processability, and can be applied to a fine structure.

  As a result of intensive studies, the inventors have applied a mixture of a water-soluble polymer solution and a low-density powder material, which is mainly used as a water-soluble adhesive, to a desired article, thereby insulating the article. As a result, the present invention has been found. That is, the present invention includes a low-density powder material containing at least one of a porous powder and a hollow powder and a water-soluble polymer solution in a weight ratio of 1 to 7:99 to 93 as a means for solving the above problems. Providing thermal insulation paint. In the present invention, the “coating material” includes an adhesive that gives the applied article an adhesive property and allows other articles to adhere.

  Usually, solvent-based paints (including adhesives) are often used, but the paints of the present invention are also expected to be used for pharmaceuticals and residential building materials. Use is not suitable. In addition, when a solvent-based paint is applied to a resin product or the like, the product may be corroded. In addition to this, the inventors have found that a high heat insulation effect is achieved by using a water-based polymer solution rather than a solvent-based paint, and have reached the present invention.

The low density powder material includes at least one of a porous powder and a hollow powder. When such a powder is contained in the water-soluble paint, air is contained in the paint layer, and a heat insulating effect is generated by the air inside. Here, the "low-density powder", in powder state, and to refer to those less than 25 ° C., less than 0.5 g / cm ³ under the conditions of 1 atm, especially 0.15 g / cm ³ To do.

  As the water-soluble polymer contained in the paint, at least one water-soluble polymer selected from the group consisting of polyvinyl alcohol, polyvinyl acetate, starch, aqueous urethane and the like can be used. Moreover, it is preferable to use these water-soluble polymers as 10-55 weight% aqueous solution. Since the water-soluble polymer solution produced under such conditions has an appropriate viscosity, it can be used as a water-soluble adhesive.

  As the low-density powder material, those having an average particle diameter of 2 to 25 μm are preferably used.

The low-density powder preferably has a specific surface area of 400 m ² / g or more. By using such a low density powder, the weight of the entire coating can be reduced. Moreover, when porous powder is used, it is preferable to use particles having higher porosity, and it is desirable to use particles having a higher specific surface area.

  The viscosity of the paint of the present invention is 500 to 100,000 mPa · S, and the drying time at room temperature natural drying when the film thickness is 10 μm is 2 hours or less at room temperature natural drying. preferable. By setting it as such a structure, the said coating material can also be used as an adhesive agent. Note that “viscosity” in the present invention is the viscosity at 25 ° C.

  The present invention provides a heat insulating method in which the heat insulating coating is applied to a target article so that the thickness of the coating layer is 2 to 200 μm. Since the coating material is a liquid aqueous solution, it can be easily applied even when the object has a fine structure, and can provide a heat insulating effect.

  The present invention also provides a heat insulating sheet material obtained by applying the above heat insulating coating material to a sheet material so that the thickness of the coating layer is 2 to 200 μm. By using such a sheet material as a packaging material or affixing to a target article, a heat insulating effect can be given to the target article.

By applying the coating material of the present invention to a desired article at a low thickness, a low-bulk heat insulating layer can be provided. Further, the present invention can be applied to an article having a fine structure and an article having low solvent resistance, and these articles can also have a heat insulating effect.
This makes it possible to impart heat insulation to the product itself for refrigerated / frozen products that have been separately housed and transported separately. Moreover, even when storing and using a refrigerated / frozen product in a heat insulation container, it is possible to reduce the volume of the heat insulation container, and to improve transport efficiency. On the other hand, as a heat-insulating packaging container, it is possible to manufacture a heat-insulating packaging container having a lower volume than the conventional container as compared with the volume of the contents.
In addition, for example, by applying the heat-insulating paint of the present invention to the back surface of a wallpaper for a house, heat insulation can be imparted to the wall without providing a bulky heat insulating material on the back surface.

It is a schematic sectional drawing which shows the method of the cold preservation function test of a cooler box. It is a graph which shows the average temperature change of a cooler box. It is a photograph which shows the behavior at the time of throwing low density particles in various solvents. (A) Immediately after loading, (B) 6 minutes after loading, (C) 10 minutes after loading. It is a photograph which shows the behavior at the time of throwing low density particles into each polyvinyl alcohol (PVA) aqueous solution. (A) Immediately after loading, (B) 10 minutes after loading.

  Hereinafter, the paint of the present invention, the heat insulation method using the paint, and the heat insulating sheet material using the paint will be described in detail.

<Water-soluble polymer solution>
The paint of the present invention uses a water-soluble polymer solution instead of a solvent-based paint. Although there are many known solvent-based paints containing additives depending on the purpose, the inventors of the present invention are not limited to solvent-based paints for the purpose of imparting the heat insulating effect of the present invention to articles. Then, it discovered that there was no sufficient effect.

  When the inventors mix a porous or hollow low-density powder described later with an organic solvent, depending on the type of the low-density powder, the presence of the powder in the solvent becomes invisible, so-called dissolved state. I discovered the phenomenon of becoming transparent. As shown in FIG. 3, 0.25 g (volume 5 mL) of methyl silicate critical dry gel was added to each 5 mL of thinner (a), anhydrous methanol (b), and purified water (c). (A)), observed 6 minutes later (FIG. 3B), 10 minutes later (FIG. 3C), methyl silicate emits bubbles immediately after being added to the thinner, and by 10 minutes later Became dissolved. Also, methyl silicate charged into anhydrous methanol was suspended in the liquid by 10 minutes. On the other hand, it was confirmed that the methyl silicate charged into the purified water remained at the upper part of the liquid surface, and this state was maintained for one week or more. The cause of the dissolution behavior of methyl silicate in the solvent is not clear, but it is presumed that the three-dimensional structure of the low density powder has infiltrated the solvent into the pores of the three-dimensional structure of the low-density powder, and that the three-dimensional structure of the powder has collapsed. In fact, as described later, a sufficient heat insulating effect was not seen in a paint produced by suspending low density particles in an organic solvent.

  On the other hand, such a dissolution-like phenomenon was not observed when the water-soluble polymer solution was used. As shown in FIG. 4, methyl silicate was mixed with 20 wt% polyvinyl alcohol (PVA) aqueous solution (a), 15 wt% PVA aqueous solution (b), 10 wt% PVA aqueous solution (c), and 5 wt% aqueous solution (d). 0.25 g (volume 5 mL) was added to each 5 mL, and observation was performed immediately after the injection (FIG. 4A) and 10 minutes later (FIG. 4B). In any sample, dissolution or suspension of methyl silicate did not occur. It was confirmed that this state lasted for more than one week. It has been clarified that the use of a water-soluble polymer makes it difficult to reduce the heat insulation effect due to the collapse of the three-dimensional structure of low density particles. The same phenomenon in the solvent, water and PVA aqueous solution was also observed in the critical dry gel of silica.

  It was also found that when zeolite or calcium carbonate was used as a low density powder and mixed with an organic solvent, the solvent was likely to infiltrate the powder and the powder content had to be reduced in order to prepare it as a paint. . The reason for this is not clear, but it is presumed that the solvent easily enters the pores of the powder due to factors such as low surface tension. If the amount of low density particles in the paint is reduced, it will be difficult to sufficiently achieve the heat insulating effect. On the other hand, in the PVA aqueous solution (5 to 20% by weight), such a phenomenon is not observed, and mixing with a sufficient amount of zeolite or calcium carbonate is possible, and therefore a sufficient heat insulating effect can be achieved. .

  From the above events, in order to sufficiently exhibit the performance as a heat insulating paint containing a low density powder, the present invention particularly uses an aqueous solution (especially a water-soluble polymer solution described later) instead of an organic solvent. It has been found that it is suitable.

  In addition to the above performance aspects, the paint of the present invention is also considered to be the key to food and pharmaceutical packaging and residential building materials, and therefore it is not preferred to use a solvent-based paint that may cause adverse effects on the human body. Therefore, the present invention provides a paint that is advantageous in terms of safety and environment as compared with known solvent-based paints.

  Examples of the water-soluble polymer used in the paint of the present invention include PVA, polyvinyl acetate, starch, and aqueous urethane. In particular, PVA can be suitably used because it has wide and high affinity for sheet materials such as paper, cloth, and nonwoven fabric described later, is easy to apply, and has a relatively short drying time after application. . When PVA is used as the water-soluble polymer, it is preferable to use one having a molecular weight of 10,000 to 200,000, particularly 50,000 to 150,000. If the molecular weight is too low, it is difficult to form a stable coating film, and if the molecular weight is too high, it becomes difficult to prepare a desired aqueous solution.

  The concentration of the aqueous solution of the water-soluble polymer is preferably 10 to 55% by weight, particularly 20 to 50% by weight, in order to make the paint suitable for application (described later). It is more preferable to use 10 to 25% by weight when using PVA, 50 to 55% by weight when using polyvinyl acetate, 30 to 38% by weight when using starch, and 45 to 50% by weight when using aqueous urethane.

<Low density powder>
As the raw material of the low density powder used in the present invention, known porous or hollow powders such as silica, methyl silicate, alumina, silica / alumina, ceramic, zeolite, calcium carbonate, zirconia and the like can be used. Regardless of the degree of porosity, the thermal conductivity of the material itself is 0.15 W / (m · K) or less, particularly 0.1 W / (m · K) or less, and further 0.06 to 0.018 W / ( m · K) is preferably used. In particular, a product obtained by aerogelating methyl silicate monomer by atmospheric pressure drying or critical drying is easy to produce at a low density, can form a nano-level porous structure or hollow structure relatively easily, an aqueous solution It can be suitably used because it is difficult to disintegrate.

  As the low density powder material, at least one of a porous powder and a hollow powder is used. When a porous low density powder is used, the porosity is preferably 50.0 to 99.8%, particularly preferably 70 to 99.8%, and more preferably 86 to 99.8%.

  Regardless of the structure of the powder, the average particle size of the powder is preferably 2 to 25 μm, particularly 5 to 23 μm, and more preferably 8 to 17 μm. If the particle diameter of the low-density powder contained in the coating is more than 25 μm, the thickness of the coating layer at the time of application increases, so that the object of the present application of providing a heat insulating effect with low bulk cannot be achieved. Moreover, since the quantity of the air included in a coating layer will decrease that it is less than 2 micrometers, it is difficult to acquire sufficient heat insulation effect.

Low density powder has a specific surface area of 400 meters ² / g or more, particularly 500 to 1000 m ² / g, it is preferable to further use those 600~1000m ² / g. By increasing the specific surface area, the porosity can be increased when the porous powder is used, and the amount of air contained in the particles can be increased when the hollow particles are used. Moreover, it is because the weight of the whole adhesive agent can also be reduced.

<Insulation paint>
The heat-insulating coating material of the present invention is a ratio of 1 to 7:99 to 93, preferably 3 to 7:97 to 93, more preferably, the above-mentioned low density powder and water-soluble polymer solution. Can be produced by mixing at a ratio of 4-5: 96-95. If the blending amount of the low-density powder is too high, the fluidity is poor and it is difficult to apply it to the target article as a paint, and if it is too low, the heat insulation effect that is the object of the present invention cannot be obtained sufficiently.

  The heat insulating paint is preferably in a state suitable for being applied to the target article at a thickness of 2 to 200 μm, particularly 5 to 50 μm, and further 5 to 25 μm. Specifically, the viscosity of the heat insulating paint is preferably 500 to 100,000 mPa · S, and more preferably 10,000 to 30,000 mPa · S. If the viscosity is too high or too low, it is difficult to form a coating layer having the above thickness.

  Further, it is preferable that the heat-insulating coating is configured such that when it is applied to have a thickness of 10 μm, it is naturally dried at room temperature and the drying time is 2 hours or less, particularly 5 minutes to 2 hours. This is because if the drying time is too long, the processability is poor.

  In addition, the heat insulation coating material of this invention has adhesiveness, and can also be used as an adhesive agent by this. In particular, since the heat-insulating paint of the present invention is made of a water-soluble polymer solution, it is easily affected by water wetting. However, a waterproof sheet such as paper coated with a water repellent and a polyethylene sheet is pasted on the paint layer. Further, it may be configured such that moisture does not directly touch the paint layer.

  Moreover, it is good also as a structure which uses the coating material (adhesive) of this invention for the part which requires an adhesive agent not only a sheet | seat, but provides the heat insulation effect simultaneously.

<Thermal insulation method with thermal insulation paint>
The target article to which the heat insulating paint of the present invention is applied is not particularly limited, and can be used for any of paper, plastic, plate material, metal, and the like. Further, since it is liquid, it can be applied to a portion having a fine structure, and the shape of the article is not particularly limited. When applying the heat-insulating coating material to the target article, it is preferable that the coating layer has a thickness of 2 to 200 μm, particularly 5 to 50 μm, and more preferably 5 to 25 μm. If the coating layer is thick, the heat insulation effect is enhanced, but it may be difficult to achieve the object of the invention to obtain the heat insulation effect without significantly increasing the volume of the target article.

<Insulation sheet material>
Since the heat-insulating paint of the present invention is water-soluble as described above, it is preferably used as an adhesive for attaching a waterproof sheet or the like thereon rather than being applied as the outermost layer. Moreover, it is good also as a structure which apply | coats the heat insulation sheet material which apply | coated the adhesive agent to the waterproof sheet etc. to the target article. In the case of using a waterproof sheet or the like, it is possible to enhance visual cosmetics by giving an internal article display, a design image, or the like on the sheet.

  The heat insulating sheet material is preferably produced by applying the heat insulating coating material to the sheet material so that the thickness of the coating layer is 2 to 200 μm, particularly 5 to 50 μm, and further 5 to 25 μm. If the thickness of the coating layer is large, the heat insulation effect is enhanced, but the characteristics such as flexibility and flexibility of the sheet may be lost. By using the sheet material, it is possible to provide a heat insulating effect such as packaging the target article or sticking to the target article.

<1. Preparation of paint>
The coating material which concerns on this invention was prepared as an Example as follows. The paints of Examples and Reference Examples were prepared so that the viscosity was 10,000 to 15,000 mPa · s .
[Example 1]
A heat insulating paint was prepared by mixing 4 g of the low density powder and 96 g of a 20 wt% PVA aqueous solution (blending ratio 4:96). As the low-density powder, a methylsilicate critical dry hydrophobic gel powder (Cabot, Aerogel Enova) having an average particle size of 5 μm and a specific surface area of 750 m ² / g was used. The viscosity of the prepared heat-insulating coating material was 10,000 mPa · s . This was applied to copy paper (Ricoh Co., Ltd., type 6000 (58 W), thickness 87 μm, basis weight 68 g / m ² , 5 cm × 10 cm) so that the thickness of the coating layer would be 10 μm. Sheets of copy paper were stacked and dried. The drying time at the time of application was 30 minutes to 2 hours.

[Comparative Example 1]
A 20% by weight PVA aqueous solution containing no low-density powder was applied to a copy paper so that the coating layer had a thickness of 10 μm, and another copy paper was laminated thereon and adhered and dried. The drying time at the time of application was 30 minutes to 1 hour.

[Examples 2 and 3 and Comparative Examples 2 and 3]
As shown in Table 1, the mixing weight ratio of the PVA aqueous solution and the powder of Example 1 was changed to 2:98, 7:93, 0.5: 99.5, and 10:90, respectively. Similarly, paints of Examples 2 and 3 and Comparative Examples 2 and 3 were prepared. Each paint was applied to a copy sheet, and another copy sheet was stacked thereon and adhered and dried. In addition, as shown in Table 1, since the coating material of Comparative Example 2 was difficult to prepare and Comparative Example 3 had too much powder and did not have adhesiveness, none of the adhesion drying experiments were possible. The thickness of the paint layer and the drying time were as shown in Table 1.

[Examples 5 to 8, Reference Examples 4, 9, and 10 ]
The paints of Examples 5 to 8, Reference Examples 4 , 9 , and 10 were prepared in the same manner as in Example 1 except that the water-soluble polymer aqueous solution of Example 1 was changed as shown in Table 1. Was applied to a copy sheet, and another copy sheet was stacked thereon and adhered and dried. The thickness of the paint layer and the drying time were as shown in Table 1.

[Examples 11 and 12]
Except that the average particle size of the low density powder of Example 1 was changed to 2 μm and 10 μm, respectively, Examples 11 and 12 were prepared under the same conditions as in Example 1, and each paint was applied to a copy sheet. Another copy sheet was stacked on top of each other and dried. The thickness of the paint layer and the drying time were as shown in Table 1.

Example 13
Except that the low density powder of Example 1 was changed to silica powder (manufactured by Eitoku City Dust Force Co., Ltd., product name: airgel, average particle size 5 μm, specific surface area 650 m ² / g), Example 1 and Similarly, the coating material of Example 13 was prepared, applied to a copy sheet, and another copy sheet was stacked thereon and adhered and dried. The thickness of the paint layer and the drying time were as shown in Table 1.

Example 14
A paint of Example 14 was prepared in the same manner as in Example 1 except that methyl silicate atmospheric dry hydrophobic gel (average particle size 5 μm, specific surface area 750 m ² / g) was used as the low-density powder of Example 1. It was applied to a copy sheet, and another copy sheet was stacked thereon and adhered and dried. The thickness of the paint layer and the drying time were as shown in Table 1.

Example 15
The paint used in Example 1 was applied so that the thickness of the paint layer was 20 μm. The drying time was as shown in Table 1.

Example 16
The paint used in Example 1. The coating layer was applied so that the thickness of the coating layer was 5 μm. The drying time was as shown in Table 1.

[Comparative Example 4]
Instead of the water-soluble polymer solution of Example 1, Example 1 was used except that a solvent-based adhesive (product number CA-114 manufactured by Cemedine Co., Ltd.) diluted 3-fold with an organic solvent (acetone, ethanol, etc.) was used. The coating material of Comparative Example 4 was prepared in the same manner as described above, applied to a copy sheet, and another copy sheet was stacked thereon and adhered and dried. The thickness of the paint layer and the drying time were as shown in Table 1.

[Comparative Example 5]
Instead of the water-soluble polymer solution of Example 1, a solvent-based adhesive (bond, manufactured by Konishi Co., Ltd., product number # 13023) diluted 2.3 times with an organic solvent (cyclohexane / n-hexane) was used. In the same manner as in Example 1, the coating material of Comparative Example 5 was prepared, applied to a copy sheet, and another copy sheet was stacked thereon and adhered and dried. The thickness of the paint layer and the drying time were as shown in Table 1.

<2.Measurement of thermal conductivity>
For the samples of Examples 5 to 8, Reference Examples 4, 9, and 10 and Comparative Examples 1, 4 and 5, using a thermal constant measuring apparatus using a probe method (product number QTM-D3, manufactured by Kyoto Electronics Industry Co., Ltd.) Thermal conductivity measurement was performed. The measured values of the thermal conductivity of each sample are as shown in Table 1. The thermal conductivity when two copy sheets were stacked without being bonded was 0.1 W / (m · K).

<3. Cooling effect test of cooler box>
Using cardboard (product number IT-05, manufactured by Imamura Paper Co., Ltd.) coated with the paints of Examples 1 to 3 and Comparative Examples 1, 4 and 5 so as to have a thickness of 10 μm, the coated surface is outside. A 10 cm cubic box was created. In addition, a cubic box with a side of 10 cm was made of 2 cm-thick polystyrene foam, and an existing cooler box was assumed. Five boxes were prepared for each sample. Also, five boxes with nothing applied were prepared. As shown in the schematic cross-sectional view of FIG. 1, a temperature measurement probe 4 is placed in a box 1, the tip of which is within 1 cm in diameter from the center of the top surface (bottom surface) of the box, and the distance a from the box top surface is 3 to 4 cm. Was installed. After placing No. 9 aluminum cup 2 containing 30 g of a cooling agent in the center of the inner bottom of the box 1, each piece was sealed with cellophane tape. The joint of each piece of the cube was sealed with a cellophane tape having a width of 1 cm so as not to generate a gap. The time from placing ice to sealing the box was within 30 seconds, and the change in the temperature inside the box was observed for 30 minutes, starting from the time when sealing was completed.

  The internal air temperature of the boxes to which the paints of Examples 1 to 3 and Comparative Examples 1, 4 and 5 were applied, and the foamed polystyrene box were measured every 5 minutes after 5 to 30 minutes. The average value of the measured temperature is shown in Table 2, and the change in average temperature is shown in FIG. The temperature inside the box in the Styrofoam box was stable at 6.5 to 7.5 ° C. from 5 minutes to 30 minutes, whereas the temperature inside the box made of only cardboard was 13.5 after 30 minutes. It rose to ℃. In the boxes to which the paints of Comparative Examples 1, 4 and 5 were applied, the temperatures inside the boxes became 13.0 ° C, 13.5 ° C and 12.0 ° C after 30 minutes, respectively, and there was almost no change from the boxes without paint. I understood that. In the boxes to which the paints of Examples 1, 2, and 3 were applied, the temperatures after 30 minutes inside the boxes were 10.5 ° C., 11.0 ° C., and 9.5 ° C., respectively. It was found that the increase was significantly suppressed. In <2. Thermal conductivity measurement>, it was found that the temperature rise was suppressed as the paint showed lower thermal conductivity.

  The paint according to the present invention, the heat insulation method using the paint, and the heat insulation sheet coated with the paint are not limited to fields requiring safety and environmental considerations such as pharmaceuticals, foods, and buildings, and use of heat insulation materials. Can be widely used in fields that require

DESCRIPTION OF SYMBOLS 1 ... Cooler box, 2 ... Aluminum cup, 3 ... Coolant, 4 ... Probe for temperature measurement

Claims (5)

Porous powder or Ranaru low density powder material, and a polymer solution, the weight ratio of 1-7: wherein a ratio of 99 to 93,
The polymer solution is a 10 to 55 wt% mixture of at least one polymer selected from the group consisting of polyvinyl alcohol and starch, using water as a solvent;
The low-density powder material has an average particle size of 2 to 25 μm and a specific surface area of 400 m ² / g or more,
The material of the low-density powder material is at least one that is selected from the group consisting of dried hydrophobic gel and airgel of silica of methyl silicate, heat-insulating paint.   The heat insulation paint according to claim 1, wherein the drying time when the viscosity is 500 to 100,000 mPa · s and the film thickness of the coating film is 10 µm is 2 hours or less by natural drying at room temperature.   The thermal insulation paint according to claim 1 or 2, wherein the low-density powder material has a thermal conductivity of 0.15 W / (m · K) or less. The paint according to any one of claims 1 to 3 the thickness of the coating layer is coated to a 2~200μm the article of interest, adiabatic method. Paint according to any one of claims 1 to 3, the thickness of the coating layer is coated to a 2 to 200 .mu.m, the heat insulating sheet material.