Abstract:
This flexible thermal-control material ( 10 A) is obtaining by stacking: a reflective layer ( 12 ) which reflects sunlight; and an infrared-ray emission layer ( 13 ) which emits infrared rays. The infrared-ray emission layer ( 13 ) is configured from a silicone material. Accordingly, a flexible thermal-control material is achieved which exhibits excellent optical characteristics such as solar absorption (α).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a flexible thermal-control material. 
       BACKGROUND ART 
       [0002]    In order to prevent an increase in temperature of an airframe due to incidence of solar light, a surface of an artificial satellite or a rocket used in space is coated with a thermal-control material having a function of reflecting the solar light and radiating thermal energy of the solar light to space. 
         [0003]    A flexible thermal-control material, a so-called flexible optical solar reflector (OSR), having flexibility which is easily processed according to a surface shape of the airframe or a structure to be coated, is paid attention as the thermal-control material. 
         [0004]    PTL 1 discloses a flexible thermal-control material including a metal layer on a polyimide film. In PTL 1, the surface of the polyimide film is subjected to roughening treatment, and accordingly secondary reflection of solar light is prevented and reflectivity and diffuseness are improved. 
       CITATION LIST 
     Patent Literature 
       [0005]    [PTL 1] Japanese Unexamined Patent Application Publication No. 2007-253399 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    However, in the flexible thermal-control material used in space, applicability in various space missions and particularly low optical properties in a solar absorptance coefficient (α) are required. 
         [0007]    It is required that a low solar absorptance coefficient (α) and a high total semi-sphere infrared emissivity (ε) are satisfied, and in order to realize long-term use in space, it is required that all conditions of high tolerance to radiation and high tolerance to atomic oxygen in space are satisfied. 
         [0008]    However, the flexible thermal-control material disclosed in PTL 1 does not satisfy the conditions of the optical properties. 
         [0009]    The present invention has been made to address the aforementioned problems and provide a flexible thermal-control material having excellent optical properties when it is used in space. 
       Solution to Problem 
       [0010]    The invention provides a flexible thermal-control material configured by laminating a reflection layer which reflects solar light and an infrared radiation layer which radiates infrared light, and the infrared radiation layer is configured with a silicone material. 
         [0011]    In the flexible thermal-control material, it is preferable that the infrared radiation layer includes a silicone layer configured with a silicone material and a pressure sensitive adhesive layer, and the pressure sensitive adhesive layer is provided between the silicone layer and the reflection layer. 
         [0012]    In the flexible thermal-control material, it is preferable that the pressure sensitive adhesive layer is a silicone-based pressure sensitive adhesive layer. 
         [0013]    In the flexible thermal-control material, it is preferable that a support layer is further laminated on a surface of the reflection layer on the side opposite to the surface where the infrared radiation layer is laminated. 
         [0014]    In the flexible thermal-control material, it is preferable that a protection layer is further laminated on a surface of the infrared radiation layer on the side opposite to the surface where the reflection layer is laminated. 
         [0015]    In the flexible thermal-control material, it is preferable that a conductive layer is further laminated on the protection layer. 
         [0016]    In the flexible thermal-control material, it is preferable that an antioxidant layer is further laminated on a surface of the reflection layer on the side opposite to the surface where the infrared radiation layer is laminated. 
         [0017]    In the flexible thermal-control material, it is preferable that the antioxidant layer is provided between the reflection layer and the support layer. 
         [0018]    In the flexible thermal-control material, it is preferable that the flexible thermal-control material is fixed to a surface of an adherend by a bonding layer or a fastening member. 
         [0019]    In the flexible thermal-control material, it is preferable that the adherend is a propellant tank of a rocket or an artificial satellite used in space. 
         [0020]    In the flexible thermal-control material, it is preferable that the propellant tank is a liquid hydrogen tank. 
         [0021]    In the flexible thermal-control material, it is preferable that a surface of the adherend is any one of a polyisocyanurate foam (PIF) heat insulating layer and a polyimide foam heat insulating layer or a heat insulating layer of a laminated body thereof. 
         [0022]    In the flexible thermal-control material, it is preferable that the surface of the adherend includes a degassing groove in any one of a polyisocyanurate foam (PIF) heat insulating layer and a polyimide foam heat insulating layer or a heat insulating layer of a laminated body thereof. 
       Advantageous Effects of Invention 
       [0023]    The invention exhibits an effect of providing a flexible thermal-control material having excellent optical properties such as a solar absorptance coefficient (α). 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0024]      FIG. 1  is a schematic sectional view showing a configuration example of a flexible thermal-control material according to Example 1. 
           [0025]      FIG. 2A  is a schematic sectional view showing a configuration example of a flexible thermal-control material according to Example 2. 
           [0026]      FIG. 2B  is a schematic sectional view showing a configuration example of another flexible thermal-control material according to Example 2. 
           [0027]      FIG. 3  is a schematic sectional view showing a configuration example of a flexible thermal-control material according to Example 3. 
           [0028]      FIG. 4  is a schematic sectional view showing a configuration example of a flexible thermal-control material according to Example 4. 
           [0029]      FIG. 5  is a schematic sectional view showing a configuration example of a flexible thermal-control material according to Example 5. 
           [0030]      FIG. 6  is a schematic sectional view showing a configuration example of a flexible thermal-control material according to Example 6. 
           [0031]      FIG. 7  is a schematic view showing an example of applying the flexible thermal-control material on an adherend. 
           [0032]      FIG. 8  is an enlarged schematic sectional view showing an enlarged A part of  FIG. 7 . 
           [0033]      FIG. 9  is an enlarged schematic sectional view showing an enlarged A part of  FIG. 7 . 
           [0034]      FIG. 10  is an enlarged schematic sectional view showing an enlarged A part of  FIG. 7 . 
           [0035]      FIG. 11  is a diagram showing an example of a schematic view of a rocket. 
           [0036]      FIG. 12A  is a sectional view in a longitudinal direction of a flexible thermal-control material which is applied on a liquid hydrogen tank. 
           [0037]      FIG. 12B  is a B-B line sectional view of  FIG. 12A . 
           [0038]      FIG. 13  is a sectional view of another flexible thermal-control material of the example which is applied on a liquid hydrogen tank. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0039]    Hereinafter, the invention will be described with reference to the accompanied drawings. The invention is not limited to the following embodiments or examples. In addition, constituent elements Of the following embodiments or examples include constituent elements which can be and are easily replaced by a person skilled in the art, or the same constituent elements. 
       EXAMPLE 1 
       [0040]      FIG. 1  is a schematic sectional view showing a configuration example of a flexible thermal-control material according to Example 1. As shown in  FIG. 1 , a thermal-control material  10 A according to the example includes a reflection layer  12  and an infrared radiation layer  13 . In the example of  FIG. 1 , the reflection layer  12  is provided on an adherend side (lower side of the drawing) and the infrared radiation layer  13  is provided on the outer side (upper side of the drawing) of the reflection layer  12 . That is, in the example of the drawing, the reflection layer  12  is provided on an airframe side  20  which is the adherend and the infrared radiation layer  13  is provided as a surface of a space side  21 . That is, in this example, the infrared radiation layer  13  is set as a layer exposed to space. 
       &lt;Reflection Layer&gt; 
       [0041]    The reflection layer  12  is preferably a high-reflectivity material layer. Accordingly, it is possible to reduce heat input to the airframe, by reflecting solar light. Herein, the high-reflectivity material layer is a layer configured with a material called high-reflectivity metal. As specific examples of such high-reflectivity metal, silver (Ag), aluminum (Al), and gold (Au) can be used, for example, but the specific examples are not limited thereto. In addition, as the high-reflectivity metal, an alloy, a compound, or a composite material thereof can be used, in addition to the simple substance of metal elements. 
       &lt;Infrared Radiation Layer&gt; 
       [0042]    The infrared radiation layer  13  is a layer having a function of radiating heat to space without absorbing solar light which is reflected by the reflection layer  12 . Since space is in a vacuum state without oxygen, heat transfer due to radiation which does not require a heat transfer medium, is dominantly performed. Heat of the airframe side  20  is more easily radiated to space, as infrared emissivity increases. Accordingly, in the infrared radiation layer  13 , as absorption of a solar light wavelength region is small and infrared emissivity is great, it is possible to prevent an increase in temperature of the airframe. 
         [0043]    The infrared radiation layer  13  is a layer configured with a silicone layer such as a silicone resin. As one silicone material, a polymer substance having a siloxane bond (Si—O—Si) as a main skeleton, such as a silicone resin, a silicone rubber, or silsesquioxane are also included. Here, a silicone resin and a silicone rubber are provided as a material including an organic group in both ends of silicon (Si) and silsesquioxane is provided as a material including an organic group and oxygen in respective ends of silicon (Si). 
         [0044]    By using the silicone material as the infrared radiation layer  13 , it is possible to ensure sufficient transparency for solar light to be incident to the reflection layer  12  and to ensure radioactive properties for radiating heat of the flexible thermal-control material to space. In addition, the silicone material has excellent radiation resistance and resistance to atomic oxygen, and accordingly, it is possible to realize a flexible thermal-control material which hardly causes performance degradation due to the space environment, by using the silicone material as the infrared radiation layer  13 . 
         [0045]    A thickness of the infrared radiation layer  13  is preferably from 50 μm to 150 μm. In this range, excellent 
         [0046]    balance between a solar absorptance coefficient (α) and a total semi-sphere infrared emissivity (ε) is obtained. 
         [0047]    According to the configuration described above, it is possible to realize a flexible thermal-control material having excellent balance in which the solar absorptance coefficient (α) is equal to or less than 0.2 and the total semi-sphere infrared emissivity (ε) is equal to or greater than 0.8. Although the control effect of an increase in temperature of the airframe decreases, it is also possible to set the thickness of the infrared radiation layer  13  to be smaller than 50 μm, if it is in an acceptable range in thermal design. 
         [0048]    By using a silicone material having excellent radiation resistance and resistance to atomic oxygen, it is possible to improve radiation resistance and resistance to atomic oxygen of the entire thermal-control material (thermal-control film) and to provide a flexible thermal-control material which hardly causes performance degradation in space. 
         [0049]    According to the configuration described above, it is possible to provide a flexible thermal-control material which is excellently adhered to various structures which is an adherend. In addition, by setting a roll molded body by winding the sheet-like flexible thermal-control material around a core, it is possible to perform the application to an adherend having a cylindrical outer shape. 
       EXAMPLE 2 
       [0050]      FIG. 2A  is a schematic sectional view showing a configuration example of a flexible thermal-control material according to Example 2. As shown in  FIG. 2A , the infrared radiation layer  13  of a flexible thermal-control material  10 B- 1  of the example includes a silicone layer  13   a  and a pressure sensitive adhesive layer  13   b . The pressure sensitive adhesive layer  13   b  is provided between the silicone layer  13   a  and the reflection layer  12  and is a layer for bonding both layers. In the example, the same reference numerals are used for the same constituent elements as those in Example 1 and the description thereof will be omitted. 
         [0051]    The silicone layer  13   a  is a layer having a silicone material such as a silicone resin as a component. By using the silicone layer  13   a  as the infrared radiation layer  13 , it is possible to ensure sufficient transparency for solar light to be incident to the reflection layer  12  and to ensure radioactive properties for radiating heat energy of solar light to space. In addition, the silicone material has excellent radiation resistance and resistance to atomic oxygen, and accordingly, it is possible to realize a flexible thermal-control material  10 B- 1  which hardly causes performance degradation due to the space environment, by using the silicone layer  13   a  containing a silicone material as the infrared radiation layer  13 . 
         [0052]    The pressure sensitive adhesive layer  13   b  is preferably configured with a silicone-based pressure sensitive adhesive. This is because the silicone-based adhesive has excellent adhesiveness with the silicone layer  13   a  and excellent heat resistance, radiation resistance, and resistance to atomic oxygen in space. 
         [0053]    The silicone-based pressure sensitive adhesive is a pressure sensitive adhesive having silicone as a base. Any of an addition reaction type and a peroxide-curing type may be used. 
         [0054]    The silicone layer  13   a  and the pressure sensitive adhesive layer  13   b  are common in that both layers have a polymer substance having a siloxane bond as a main skeleton, as a material, and both layers may be configured as separate bodies or may be integrally configured. The layers are integrally configured in the example of  FIG. 1  and the layers are configured as separate bodies in the example of  FIG. 2 . 
         [0055]    A thickness of the pressure sensitive adhesive layer  13   b  is, for example, from 10 μm to 100 μm, when the thickness of the entire infrared radiation layer  13  is from 50 μm to 300 μm. 
         [0056]    According to the configuration described above, it is possible to realize a flexible thermal-control material having excellent balance between the solar absorptance coefficient (α) and the total semi-sphere infrared emissivity (ε). By setting the pressure sensitive adhesive layer as a silicone-based pressure sensitive adhesive layer, it is possible to excellently bond the infrared radiation layer and the reflection layer to each other without disturbing solar absorptance coefficient (α), the total semi-sphere infrared emissivity (ε), radiation resistance, and resistance to atomic oxygen which are properties of the silicone material-made infrared radiation layer. 
         [0057]      FIG. 2B  is a schematic sectional view showing a configuration example of another flexible thermal-control material according to Example 2. As shown in  FIG. 2B , in the infrared radiation layer  13  of a flexible thermal-control material  10 B- 2  of the example, a silsesquioxane layer  13   c  is provided on the outer side (upper side of the drawing) of the reflection layer  12 . 
         [0058]    By using the silsesquioxane layer  13   c  as the infrared radiation layer  13 , it is possible to ensure sufficient transparency for solar light to be incident to the reflection layer  12 . Accordingly, by using the silsesquioxane layer  13   c  as the infrared radiation layer  13 , it is possible to realize the flexible thermal-control material  10 B- 2  which hardly causes performance degradation due to the space-environment. 
         [0059]    The silsesquioxane layer  13   c  can be applied to the reflection layer  12  to form a coating layer by ultraviolet curing or thermal curing, for example. A coating thickness of the silsesquioxane layer  13   c  can be set to be equal to or smaller than 10 μm, the solar absorptance coefficient (α) is equal to or less than 0.1, and low cost can be realized. 
         [0060]    It is preferable to form the silsesquioxane layer  13   c,  because resistance to atomic oxygen is high in the silicone material and no tackiness is obtained. 
       EXAMPLE 3 
       [0061]      FIG. 3  is a schematic sectional view showing a configuration example of a flexible thermal-control material according to Example 3. As shown in  FIG. 3 , a flexible thermal-control material  10 C is formed by further laminating an antioxidant layer  14  on a surface of the reflection layer  12  on the side opposite to the surface where the infrared radiation layer  13  is laminated, in the flexible thermal-control material  10 B- 1  according to Example 2. That is, the antioxidant layer  14  is further provided on the lower side of the reflection layer  12  (lower side of the drawing), that is, on the airframe side  20  of the structure coated with the flexible thermal-control material  10   c.  In the example, the same reference numerals are used for the same constituent elements as those in Example 1 or Example 2 and the description thereof will be omitted. 
         [0062]    The antioxidant layer  14 , for example, can be configured with a nickel-base super-alloy (inconel or the like), chromium, nickel, and gold (vapor deposition on an aluminum surface). Among these, a nickel-base superalloy is particularly preferable, from viewpoints of anti-oxidation properties and corrosion resistance. 
         [0063]    According to the configuration described above, it is possible to further improve an anti-oxidation effect by atomic oxygen in space. In addition to the configuration of the example, in a case of providing a support layer, the antioxidant layer is preferably provided between the reflection layer and the support layer. 
       EXAMPLE 4 
       [0064]      FIG. 4  is a schematic sectional view showing a configuration example of a flexible thermal-control material according to Example 4. As shown in  FIG. 4 , a flexible thermal-control material  10 D is formed by further laminating a support layer  15  on a surface of the reflection layer  12  on the side opposite to the surface where the infrared radiation layer  13  is laminated, in the flexible thermal-control material  10 A according to Example 1. That is, the support layer  15  is further provided on the lower side of the reflection layer  12  (lower side of the drawing), that is, on the structure (adherend) side coated with the flexible thermal-control material  10 D. 
         [0065]    If a tensile force is loaded when applying the flexible thermal-control material onto the adherend, cracks may be generated on the infrared radiation layer  13  or the reflection layer  12 . The support layer  15  has a function and an effect of preventing generation of such cracks. This is for improving hardness or strength of the entire flexible thermal-control material  10 D by the support layer  15 . 
         [0066]    As the support layer  15 , it is preferable to use a polyimide material such as a polyimide resin from viewpoints of strength and heat resistance. Alternatively, a polyester material such as polyethylene-telephthalate (PET), which is a material having a function and an effect of preventing generation of cracks or tears on the reflection layer and the infrared radiation layer may be used. 
         [0067]    According to the configuration described above, it is possible to apply suitable hardness ox strength to the flexible thermal-control material so as to be applied. Accordingly, it is possible to prevent generation of cracks on the reflection layer  12 , when attaching or bonding the flexible thermal-control material to a structure (airframe) such as a rocket or an artificial satellite. 
       EXAMPLE 5 
       [0068]      FIG. 5  is a schematic sectional view showing a configuration example of a flexible thermal-control material according to Example 5. As shown in  FIG. 5 , a flexible thermal-control material  10 E is formed by further laminating a protection layer  16  on a surface of the infrared radiation layer  13  on the side opposite to the surface where the reflection layer  12  is laminated, in the flexible thermal-control material  10 D according to Example 4. That is, the protection layer  16  is further provided on the upper side of the infrared radiation layer  13  (upper side of the drawing), that is, on the space side  21 . 
         [0069]    The protection layer  16  covers the surface of the silicone material having high tackiness (stickiness) so as to provide a function and an effect of preventing surface contamination of the flexible thermal-control material  10 E. For example, when applying the flexible thermal-control material to a rocket, a propellant tank of the rocket becomes an adherend, and the outer surface of the propellant tank of the rocket is coated with the flexible thermal-control material. In this case, the protection layer  16  is provided on the surface of the silicone material layer so as to provide a function and an effect of preventing surface contamination of the flexible thermal-control material  10 E from the application of the material to the rocket fire. 
         [0070]    As the protection layer  16 , it is preferable to configure silsesquioxane having higher resistance to atomic oxygen among the silicone materials. It is possible to obtain higher resistance to atomic oxygen, by coating the surface of the flexible thermal-control material with silsesquioxane. 
       EXAMPLE 6 
       [0071]      FIG. 6  is a schematic sectional view showing a configuration example of a flexible thermal-control material according to Example 6. As shown in  FIG. 6 , a flexible thermal-control material  10 F is formed by further laminating a conductive layer  17  on the protection layer  16  in the flexible thermal-control material  10 E according to Example 5. That is, the conductive layer  17  is further provided on the surface of the protection layer  16 , that is, the outermost surface on the space side  21 . 
         [0072]    The conductive layer  17  has a function and an effect of preventing damage to the flexible thermal-control material  10 F due to an electric discharge. In addition, the conductive layer  17  is preferably a transparent conductive layer having transparency so as to allow solar light to be incident to the reflection layer  12 . 
         [0073]    As the conductive layer  17 , a metal compound material having conductivity such as indium tin oxide (ITO), antimony tin oxide (ATO), or TiO 2  (titanium dioxide) doped with Nb, or carbon-based material such as carbon nanotube can be used. 
         [0074]    According to the configuration described above, it is possible to provide a flexible thermal-control material having reduced risk of damage due to an electric discharge. 
       EXAMPLE 7 
     Application Example (1) of Flexible Thermal-Control Material 
       [0075]      FIG. 7  is a schematic view showing an example of applying the flexible thermal-control material on an adherend. In the example of the drawing, an adherend is a propellant tank (for example, liquid hydrogen tank) of a rocket.  FIGS. 8 to 10  are enlarged schematic sectional views showing an enlarged A part of  FIG. 7 . 
         [0076]    In the example of the laminated body shown in  FIG. 7 , a surface of a tank main body  30   a  of a propellant tank  30  such as a liquid hydrogen tank is coated with the flexible thermal-control material  10 D according to Example 4. Herein, a polyisocyanurate foam (PIF) heat insulating layer (hereinafter, referred to as a “PIF heat insulating layer”)  31  is formed on the surface of the propellant tank and the flexible thermal-control material  10 D is applied to the surface thereof. 
         [0077]      FIG. 8  is a diagram specifically illustrating a relationship between the surface of the propellant tank of  FIG. 7 , that is, the PIF heat insulating layer  31 , and the flexible thermal-control material  10 D. As shown in  FIG. 8 , the flexible thermal-control material  10 D in which the reflection layer  12  is laminated on the support layer  15  and the infrared radiation layer  13  is further laminated on the surface thereof, is adhered onto the PIF heat insulating layer  31  through a bonding layer  18  and covers the tank main body  30   a.    
         [0078]    The bonding layer  18  is a layer configured with a pressure sensitive adhesive or an adhesive, for example. As a pressure sensitive adhesive or an adhesive, a material which hardly causes generation of gas in a vacuum environment as in space is preferable. 
         [0079]    In the embodiment, the flexible thermal-control material  10 D is adhered to the PIF heat insulating layer  31  on the surface of the liquid hydrogen tank by the bonding layer  18 , but the flexible thermal-control material  10 D can also be adhered to the surface of the liquid hydrogen tank by a fastening member. As the fastening member, a fastener for fastening and fixing a component to another component can be used, for example. A rivet can be used, for example, as the fastener. 
         [0080]      FIG. 3  is a diagram in which the flexible thermal-control material  10  ( 10 A to  10 F) is provided by the bonding layer  18  using a polyimide foam heat insulating layer  41 , instead of the PIF heat insulating layer  31  of  FIG. 8 . The polyimide foam heat insulating layer  41  is a foam in which air bubbles have an open-cell structure and exhibits an effect of vacuum insulation. A thickness of the polyimide foam heat insulating layer  41  is, for example, preferably approximately from 10 mm to 50 mm. 
         [0081]      FIG. 10  is a diagram in which the flexible thermal-control material  10  ( 10 A to  10 F) is provided on a heat insulating layer  42  having a laminated body structure of two layers which are the PIF heat insulating layer  31  of  FIG. 8  and the polyimide foam heat insulating layer  41 . 
         [0082]    The polyimide foam heat insulating layer  41  is a foam in which air bubbles have an open-cell structure and exhibits an effect of vacuum insulation. A thickness of the heat insulating layer  42  of two layers which are the PIF heat insulating layer  31  and the polyimide foam heat insulating layer  41  is, for example, preferably approximately from 10 mm to 50 mm. 
         [0083]    In the example, the PIF heat insulating layer  31  is provided on the tank main body  30   a  side, but the polyimide foam heat insulating layer  41  side may be set as the tank main body  30   a  side and the PIF heat insulating layer  31  may be provided on the upper layer thereof. 
       EXAMPLE 8 
     Application Example (2) of Flexible Thermal-Control Material 
       [0084]      FIG. 11  is a diagram showing an example of a schematic view of a rocket. As shown in  FIG. 11 , a satellite  53  is provided on a head portion side of a liquid hydrogen tank  51  which is a propellant tank through a pedestal  52 . A liquid oxygen tank  55  is provided on a rear side of the liquid hydrogen tank  51  through a rod  54  and performs a supply operation to an engine  56  side. 
         [0085]      FIG. 12A  is a sectional view in a longitudinal direction of a flexible thermal-control material which is applied on a liquid hydrogen tank and  FIG. 12B  is a B-B line sectional view of  FIG. 12A . 
         [0086]    In the example, the PIF heat insulating layer  31  is formed on the surface of the liquid hydrogen tank  51  and the flexible thermal-control material  10  ( 10 A to  10 F) according to Examples described above is coated on the surface of the PIF heat insulating layer  31 . The flexible thermal-control material  10  ( 10 A to  10 E) is the same material as in examples 1 to 6 and the description thereof will be omitted. 
         [0087]    In the example, a degassing groove  32  is formed along an axial direction of the PIF heat insulating layer  31  and perform degassing of exhaust gas (for example, low molecular component)  33  generated in the PIF heat insulating layer  31 . 
         [0088]    Accordingly, negative effects such as vapor deposition due to exhaust gas  33  on the flexible thermal-control material  10  ( 10 A to  10 E) formed on the surface of the PIF heat insulating layer  31  or the satellite  53  are prevented and the satellite  53  is protected. 
         [0089]      FIG. 13  is a sectional view of another flexible thermal-control material of the example which is applied on a liquid hydrogen tank. 
         [0090]    In the example, the heat insulating layer  42  having a two-layered structure of the PIF heat insulating layer  31  and the polyimide foam heat insulating layer  41  is provided on the surface of the tank main body  30   a  of the liquid hydrogen tank  51  and the flexible thermal-control material  10  ( 10 A to  10 E) according to Examples described above is coated on the surface of the heat insulating layer  42  having a two-layered structure. 
         [0091]    In the example, the degassing groove  32  is continuously formed along an axial direction of in a boundary between the PIF heat insulating layer  31  and the polyimide foam heat insulating layer  41  and performs degassing of exhaust gas (for example, low molecular component) generated in the heat insulating layer  42 . The degassing groove  32  is formed by setting a boundary surface between the PIF heat insulating layer  31  and the polyimide foam heat insulating layer  41  as an approximate gear wheel structure, but the invention is not limited thereto. 
         [0092]    As described above, it is possible to suitably realize heat insulation in space which was insufficiently realized with only the PIF heat insulating layer, by coating the outer surface of the propellant tank of the rocket with the flexible thermal-control material according to the invention. In the related art, in a structure used in space such as a rocket or an artificial satellite, heat input from the outside is prevented by the PIF heat insulating layer and evaporation of liquid hydrogen which is propellant is prevented, but in space in a vacuum state without oxygen, heat input due to radiation is dominantly performed and sufficient heat insulating performance cannot be obtained with only the PIF heat insulating layer. It is possible to prevent problems regarding heat input due to radiation in space to improve heat insulating performance, by further coating the PIF surface with the flexible thermal-control material according to the invention. 
       REFERENCE SIGNS LIST 
       [0093]      10  ( 10 A to  10 F) Flexible thermal-control material 
         [0094]      12  Reflection layer 
         [0095]      13  Infrared radiation layer 
         [0096]      14  Antioxidant layer 
         [0097]      15  Support layer 
         [0098]      16  Protection layer 
         [0099]      17  Conductive layer 
         [0100]      18  Bonding layer 
         [0101]      20  Airframe side (adherend side) 
         [0102]      21  Space side 
         [0103]      30  Propellant tank (adherend) 
         [0104]      31  PIF heat insulating layer 
         [0105]      41  Polyimide foam heat insulating layer