JP5640591B2 - Thermal insulation sheet - Google Patents

Description

  The present invention relates to a heat insulating material comprising a porous skeleton structure having nano-level pores.

  In buildings such as ordinary houses and office buildings, most of the energy in and out of air conditioning is through glass windows and glass doors. In order to reduce the energy transfer between the building interior and the outside air, for example, double windows and double glazing are used, but the heat insulation effect is insufficient, and the vacuum heat insulation windows have high performance. However, it is difficult to maintain a vacuum for a long time.

  In addition, as a method for achieving heat insulation by using an existing glass window or the like as it is, for example, a method for improving heat insulation by applying a heat insulating film having a void structure on the glass surface has been proposed. Since the included pore diameter is larger than the wavelength of visible light, daylighting is possible, but there is a drawback that the function of transparency as a window is significantly impaired (Patent Document 1).

  In addition, a heat insulating sheet in which fine bubbles are formed by foaming in a resin sheet has been proposed, but since the porosity is small and conduction heat transfer from the resin cannot be suppressed, the heat insulating property and transparency are insufficient. (Patent Document 2).

  On the other hand, silica airgel, which is a dry gel body of extremely low density silica, has been studied as a transparent heat insulating material with excellent heat insulation and light transmission properties, but its mechanical strength is extremely high due to its low density and brittleness. Since it is small and inflexible, sheeting is not realized.

  As an attempt to improve the mechanical strength, a means for improving the mechanical strength and handling property by impregnating the silica airgel skeleton with a polymer has been studied (Non-patent Document 1). In this case, the mechanical strength is improved. However, the transparency of the structure has been lost and the density has increased, so it is considered that the thermal conductivity has been greatly increased, and the transparency is excellent in transparency and heat insulation and is easy to handle. A heat insulating sheet was desired.

JP-A-10-205236 JP 2004-66638 A

Nano Letters, 2000, Vol. 2, 957

  An object of the present invention is to provide a transparent heat insulating sheet that is excellent in heat insulating properties and transparency and easy to handle.

  The object of the present invention is achieved by the following configurations.

  1. A heat insulating sheet having a porous skeleton having an average pore diameter of 10 nm or more and 70 nm or less and a porosity of 90 to 99%.

  2. 2. The heat insulating sheet according to 1 above, wherein the porosity of the porous skeleton is 96 to 99%.

  3. 3. The heat insulation according to 1 or 2, wherein the porous skeleton is an organic material or a porous skeleton composed of at least two kinds of materials selected from the following materials 1) to 3). Sheet.

1) Organic material, 2) Inorganic material, 3) Organic / inorganic hybrid material 4. The heat insulating sheet according to any one of 1 to 3, wherein the porous skeleton includes a fibrous three-dimensional network structure having an average fiber diameter of 1 nm to 10 nm.

  5. 5. The heat insulation according to any one of 1 to 4, wherein the porous skeleton includes hollow particles having shells having a number average thickness of 2 nm or more and 10 nm or less and a number average inner diameter of 10 nm or more and 70 nm or less. Sheet.

  6). The heat insulating sheet according to any one of 1 to 5, wherein the porous skeleton includes organic / inorganic hybrid silica hollow particles.

  7). 6. The heat insulating sheet according to any one of 1 to 5, wherein the porous skeleton includes an organic / inorganic hybrid silica network structure and organic / inorganic hybrid silica hollow particles.

  8). The heat insulating sheet according to any one of 1 to 5, wherein the porous skeleton includes an organic / inorganic hybrid silica network structure and silica hollow particles.

  9. The heat insulating sheet according to any one of 1 to 5, wherein the porous skeleton includes a silica network structure and organic / inorganic hybrid silica hollow particles.

  According to the present invention, it is possible to achieve both high heat insulation performance and light transmittance, and the glass window or glass door to which the glass window is attached can greatly improve heat insulation while maintaining transparency, and mechanically. A heat insulating sheet that is imparted with strength and easy to form and handle is obtained.

  Hereinafter, although this invention is demonstrated based on embodiment, it is not limited to these.

  The present invention relates to a transparent heat insulating sheet characterized in that it is formed from a porous skeleton structure having pores with an average pore diameter of 10 nm to 70 nm and a porosity of 90 to 99% by volume. It is about.

  Hereinafter, the present invention will be described in more detail, but the present invention is not limited to the following embodiments.

(Configuration of thermal insulation sheet)
The heat insulating sheet of the present invention has a porous skeleton having pores having an average pore diameter of 10 nm or more and 70 nm or less on a substrate and a porosity of 90 to 99% by volume. It is.

  The porous skeleton is made of many fine pores and a material surrounding the pores, and forms a heat insulation layer having heat insulation properties.

  The porous skeleton has a structure in which one structural unit (hereinafter referred to as a cell structure) that forms the pores is connected, and the average pore diameter of the pores is 70 nm or less. With this configuration, since the heat insulating layer has a low density, the heat conduction is extremely small, and the vacancies are mesopores lower than the mean free path (70 nm) of the air component gas. High heat insulation can be expressed by reducing the conduction heat transfer of the structure composed of the sex skeleton.

  In addition, since the average pore diameter of the pores is 10 nm or more, a structure composed of the porous skeleton having low thermal conductivity and high strength can be produced stably.

  The average pore diameter is 70 nm or less, preferably 50 nm or less, more preferably 30 nm or less in order to suppress heat conduction by air.

  Further, the porosity is 90% or more, preferably 96% or more, in order to reduce the conduction heat transfer of the structure composed of the porous skeleton. Moreover, if the porosity is 99% or less, the strength of the structure is high and it is easy to maintain the sheet shape.

  Examples of the porous skeleton constituting the cell structure include those in which pores having an average pore diameter of 70 nm or less are formed in the continuous phase of the resin by foam molding using a foaming agent or supercritical carbon dioxide, and average fibers Examples include those in which a fibrous three-dimensional network structure having a diameter of 10 nm or less is formed, or those composed of hollow particles having shells having an average thickness of 10 nm or less and an average inner diameter of 70 nm or less. One or a plurality of skeletons are preferable, and the skeleton including the three-dimensional network structure and the hollow particles is more preferable.

In the present invention, the material constituting the porous skeleton is an organic material (organic resin) or a material formed of a porous skeleton made of two materials selected from the following materials 1) to 3). Preferably
1) Organic materials, 2) Inorganic materials, 3) Organic / inorganic hybrid materials In order to ensure mechanical strength and obtain a sheet with good handling properties, the material composition including organic materials or organic / inorganic hybrid materials is required. preferable. Examples of organic materials include styrene resin, acrylic resin, polyvinyl alcohol resin, polyvinyl acetal resin, polyvinyl butyral resin, urethane resin, polyester polyurethane resin, polyether polyurethane resin, polycarbonate polyurethane resin, polyester resin, polyether resin, polyamide resin, Examples thereof include, but are not limited to, rubber resins such as amino resins, styrene-butadiene resins, and butadiene-acrylonitrile resins.

  As the inorganic material, a resin material such as a silicone resin, a metal oxide such as alumina, titania, silica, zirconia, or the like is used, but is not limited thereto. Among these, silica is preferably used because it is easy to control the particle size and the size of the structure when forming fine pores. The organic / inorganic hybrid is a compound in which an organic group and an inorganic component are combined. For example, an inorganic component is bonded to the resin with a silane coupling agent such as methyl silicate or ethyl silicate, or an oligomer thereof. And those obtained by condensing a silane coupling agent having an organic group bonded thereto, or those obtained by bonding an alkoxide such as titanium or zirconia to an organic group, but are not limited thereto. Among these, a material obtained by condensing a silane coupling agent to which an organic group is bonded is preferably used because it is easy to control the particle size and the size of the structure when forming fine pores.

  When the porous skeleton is formed, a material obtained by converting the skeleton material itself into an organic-inorganic hybrid may be used, or a composite structure in which structural units composed of organic components and structural units composed of inorganic components are connected may be used.

  In the heat insulating sheet of the present invention, the heat insulating layer is formed on a transparent base material such as glass or a transparent resin, the mechanical strength is ensured and handling is easy, and the heat insulating performance is greatly improved. It is preferable because a heat insulating sheet is obtained.

The present invention preferably comprises a transparent substrate and a heat insulating layer of a porous skeleton, for example,
1. A form in which a heat insulating layer is formed on a transparent substrate,
2.2 Form in which a heat insulating layer is sandwiched between two transparent substrates,
However, it is not limited to these. Moreover, these heat insulation layers may be formed on both surfaces of the transparent substrate.

(Three-dimensional network structure)
The three-dimensional network structure refers to a structure in which fibrous substances are branched and spread into a three-dimensional fine network.

  Examples of the three-dimensional network structure forming the porous skeleton of the present invention include those in which a three-dimensional network structure is formed by cross-linking between fibers using organic fibers having an average fiber diameter of 10 nm or less; Nanoparticles (secondary particles) having a particle size of 10 nm or less using a structure formed by dissolving a resin in a fiber and then using a sol-gel reaction of a silane coupling agent such as a metal alkoxide or alkoxysilane Are formed with a three-dimensional network structure in which fibrous skeletons having an average fiber diameter of 10 nm or less are intertwined, and pores formed by the network. A structure having an average pore diameter of 70 nm or less can be preferably used.

  When organic fibers are used, cellulose fibers obtained by defibrating natural cellulose, polymer solutions such as PMMA and polycarbonate, organic fibers obtained by electrospinning molten polymers, or special nozzles Examples include, but are not limited to, organic fibers that are formed by extruding molten polymer from (1) to obtain sea-island structure fibers and then dividing the fibers. Among these, it is preferable to use cellulose fibers that have been defibrated in that the average fiber diameter can be further reduced and high transparency can be obtained.

  There are no particular restrictions on the method of defibrating cellulose fibers. Physical methods such as high-pressure homogenizers, ultrahigh-pressure homogenizers, refiners, grinders, and stone mills, and the primary hydroxyl groups of cellulose amorphous regions are oxidized and chemically disassembled. You may use the method of fibering. As a specific example, cellulose fibers such as pulp are introduced into a dispersion container containing water so as to be 0.1 to 3% by mass, and this is defibrated with a high-pressure homogenizer to obtain an average fiber diameter of 0.1 to 3%. An aqueous dispersion of cellulose fibers defibrated to about 10 μm microfibrils is obtained. Furthermore, by repeatedly grinding with a grinder or the like, nano-order cellulose fibers having an average fiber diameter (short axis diameter) of about 2 to 10 nm can be obtained. In addition, by using 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) as a catalyst, primary hydroxyl group of cellulose amorphous region is oxidized and carboxyl is introduced, and electrostatic repulsion between fibrils is utilized. It can also be chemically defibrated. As the fiber forming the three-dimensional network structure of the present invention, a surface-modified fiber is preferably used. A nanoporous skeleton structure composed of fibers used as a heat insulating material can be obtained by drying the solvent dispersion of the fibers, but the fibers may aggregate due to the interfacial tension when the solvent dries. Thus, the cohesive force between fibers can be suppressed by introducing a hydrophobic group on the fiber surface. For example, when modifying a cellulose fiber, it is preferable to chemically modify the hydroxyl group using a modifying agent such as an acid, an alcohol, a halogenating reagent, an acid anhydride, an isocyanate, or a silane coupling agent.

  When utilizing a sol-gel reaction of a metal alkoxide, it is preferable to use an alkoxysilane as the metal alkoxide because of easy control of the reaction.

As an alkoxysilane used for forming a three-dimensional network structure of silica, a tetraalkoxysilane monomer or oligomer (condensation product) is preferable. A tetrafunctional alkoxysilane is advantageous for obtaining a sol of colloidal silica particles having a relatively large average particle size. Tetraalkoxysilane is represented by Si (OR) ₄ . R is preferably an alkyl group having 1 to 5 carbon atoms (such as methyl, ethyl, propyl, or butyl) or an acyl group having 1 to 4 carbon atoms (such as acetyl). Specific examples of tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, diethoxydimethoxysilane and the like. Of these, tetramethoxysilane and tetraethoxysilane are preferred. Further, a small amount of trifunctional or lower functional alkoxysilane may be added to the tetraalkoxysilane as long as the effects of the present invention are not impaired.

  When the inorganic component of the organic-inorganic hybrid three-dimensional network structure is silica, it can be produced by hydrolyzing and polymerizing an alkoxy group of a compound in which an alkoxy group and an organic group are bonded to a silicon atom.

  Preferred compounds in which an alkoxy group and an organic group are bonded to the silicon atom include trialkoxysilane in which one alkyl group such as methyltriethoxysilane, methyltrimethoxysilane, and ethyltriethoxysilane is bonded, and dimethyldiethoxysilane, Examples include dialkoxysilane having two alkyl groups bonded such as diethyldiethoxysilane and dimethyldimethoxysilane, and trialkoxysilane having one alkyl group bonded is particularly preferable.

  In the present invention, the average fiber diameter of the fibrous skeleton forming the three-dimensional network structure is preferably 1 nm or more and 7 nm or less, in order to ensure heat insulation and transparency and to maintain sheet strength. More preferably, it is 5 nm or less. If it is 10 nm or less, it is excellent in heat insulation and transparency, and if it is 1 nm or more, the strength of the structure is high.

  The average fiber diameter when the sol-gel reaction is used can be adjusted by the concentration of metal alkoxide and the reaction temperature.

(Hollow particles)
The hollow particles that can preferably form the porous skeleton of the present invention can be used without limitation as long as the structure has a hollow structure having an average thickness of 10 nm or less and an average inner diameter of the shell of 70 nm or less. It is preferable. In order to form the porous skeleton, it is preferable to use hollow particles because the inner diameter of the hollow structure and the thickness of the shell of the structure can be easily controlled. As hollow particles to be used, a template using a sol-gel solution or a reactive resin monomer solution such as a metal alkoxide or a silane coupling agent in which a template of inorganic nanoparticles having a predetermined particle size (substance that becomes a hollow mold) is dispersed is used. After the surface is coated with an inorganic material such as a metal oxide, an organic material such as a resin, or an organic / inorganic hybrid material, the inner template can be dissolved and hollowed. The inner diameter of the hollow particles can be adjusted by the particle size of the template. The thickness of the shell of the hollow particles can be adjusted by the addition amount of a sol-gel solution such as the metal alkoxide or silane coupling agent or a reactive resin monomer.

  The hollow particles are not limited to those in which the shell is entirely closed, but may have a structure in which a part is opened. Moreover, as a material used for the shell, silica, metal oxide, organic resin material and the like can be used without limitation, but silica or organically modified silica is preferable in order to secure the mechanical strength of the sheet. As a reaction raw material for forming a shell made of silica or organically modified silica, a silane coupling agent is preferably used.

  If the number average inner diameter of the hollow particles is 70 nm or less, heat insulation and transparency can be ensured. Furthermore, in order to improve heat insulation and transparency, 50 nm or less is preferable and 30 nm or less is more preferable.

  The number average thickness of the shell is preferably 1 nm or more and 7 nm or less, more preferably 1 nm or more and 5 nm or less. When the thickness of the shell exceeds 10 nm, the transparency of the sheet is lowered. When the thickness is smaller than 1 nm, the mechanical strength of the particles is lowered and it is difficult to maintain the sheet shape.

(Average hole diameter)
The average pore diameter of the porous skeleton is measured by small angle X-ray scattering. Whether the porous skeleton is composed of a three-dimensional network structure or the hollow particles are contained, the average pore diameter can be similarly determined by small angle X-ray scattering.

  The porous skeleton has pores having an average pore diameter of 10 nm or more and 70 nm or less. By setting the average pore diameter to 70 nm or less, since the pores become mesopores below the mean free path (70 nm) of the gas of the air component, convective heat transfer is also reduced, and conduction heat transfer of the structure is reduced. As a result, high heat insulation can be expressed. Further, since it is necessary to secure a fiber diameter capable of forming a three-dimensional network structure, a thickness of the shell of the hollow particles, and a sufficient porosity, the average pore diameter is 10 nm or more. The average pore diameter is preferably 50 nm or less, more preferably 30 nm or less.

  Examples of the method for adjusting the average pore diameter include a method for adjusting the concentration of the material forming the skeleton. When the concentration is low, the average pore diameter increases, and when the concentration is high, the average pore diameter decreases.

(Porosity)
The porosity is a ratio of the volume of voids to the volume of the heat insulating layer, and is obtained by the following formula.

Porosity = ((C−B) / C) × 100 (%)
Here, B is the density (mass / volume) of the heat insulation layer, and C is the mass average density (mass / volume) of the material (network fiber or hollow particle shell) constituting the heat insulation layer.

  For example, when the heat insulating layer has a hollow particle and a network structure, and the shell of the hollow particle and the fiber of the network structure are different, the density of the shell is x, the density of the fiber is y, and the shell for the material of the entire heat insulating layer The mass average density is xz + y (1-z), where z is the mass ratio of the material and (1-z) is the mass ratio of the fiber material to the material of the entire heat insulating layer.

  When the heat insulating sheet has a base material, the volume and mass of the heat insulating sheet composed of the base material and the heat insulating layer are measured, and the volume and mass of the base material from which the heat insulating layer is peeled are measured and subtracted, respectively. Mass is calculated | required and the density B of a heat insulation layer is calculated | required.

  The density C of the material can be known from literatures.

  The porosity is adjusted by adjusting the concentration of the material.

  For example, when a resin is impregnated with carbon dioxide in a supercritical state to form pores in the continuous phase of the resin, the porosity increases as the time for cooling to room temperature increases. In the case of a porous skeleton containing a three-dimensional network structure and hollow particles by a silane coupling agent, the porosity is adjusted by the shell thickness, particle size, hollow particle concentration, and silane coupling agent concentration of the hollow particles. The

(Stabilizer)
When the heat insulating sheet of the present invention has a three-dimensional network structure with organic fibers, at least one kind selected from a phenol-based stabilizer, a hindered amine-based stabilizer, a phosphorus-based stabilizer, and a sulfur-based stabilizer during the production of organic fibers. Additional stabilizers may be added. By appropriately selecting and adding these stabilizers, it is possible to highly suppress deterioration of the heat insulating layer or changes in physical properties such as heat resistance and light resistance of the heat insulating layer in the use environment.

  As a preferable phenol-based stabilizer, conventionally known ones can be used, for example, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2 , 4-di-t-amyl-6- (1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl) phenyl acrylate and the like, and JP-A Nos. 63-179953 and 1-168643. Acrylate compounds described in Japanese Patent Publication No. 1; octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3,5 Di-t-butyl-4-hydroxybenzyl) benzene, tetrakis (methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenylpropionate)) methane [ie pentaerythrmethyl- Tetrakis (3- (3,5-di-t-butyl-4-hydroxyphenylpropionate))], triethylene glycol bis (3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionate) Alkyl-substituted phenolic compounds such as 6- (4-hydroxy-3,5-di-t-butylanilino) -2,4-bisoctylthio-1,3,5-triazine, 4-bisoctylthio-1, 3,5-triazine, 2-octylthio-4,6-bis (3,5-di-t-butyl-4-oxyanilino) -1,3,5-triazine, etc. Triazine group-containing phenol compound; and the like.

  Preferred hindered amine stabilizers include bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (2,2,6,6-tetramethyl-4-piperidyl) succinate, bis ( 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis (N-octoxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-benzyloxy-2, 2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-cyclohexyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6) -Pentamethyl-4-piperidyl) 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-butylmalonate, bis (1-acryloyl-2,2,6 6-tetramethyl-4-piperidyl) 2,2-bis (3,5-di-t-butyl-4-hydroxybenzyl) -2-butylmalonate, bis (1,2,2,6,6-pentamethyl) -4-piperidyldecanedioate, 2,2,6,6-tetramethyl-4-piperidylmethacrylate), 4- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxy]- 1- [2- (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy) ethyl] -2,2,6,6-tetramethylpiperidine, 2-methyl-2- (2 , 2,6,6-tetramethyl-4-piperidyl) amino-N- (2,2,6,6-tetramethyl-4-piperidyl) propionamide and the like.

  Further, the preferable phosphorus stabilizer is not particularly limited as long as it is usually used in the general resin industry. For example, triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris (nonyl) Phenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite, 10- (3,5-di-t-butyl-4-hydroxybenzyl) -9 Monophosphite compounds such as 1,4-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; 4,4'-butylidenebis (3-methyl-6-tert-butylphenyl-di-tridecyl phosphite ), 4,4'-isopropylidenebis (phenyl-di-alkyl (C12-C15) phosphine) Ito) diphosphite compounds such as and the like. Among these, monophosphite compounds are preferable, and tris (nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite and the like are particularly preferable.

  Further, preferable sulfur stabilizers include, for example, dilauryl 3,3-thiodipropionate, dimyristyl 3,3′-thiodipropionate, distearyl 3,3-thiodipropionate, lauryl stearyl 3,3- Thiodipropionate, pentaerythritol-tetrakis (β-laurylthio-propionate), 3,9-bis (2-dodecylthioethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane, etc. It is done.

  Although the compounding quantity of these stabilizers is suitably selected in the range which does not impair the objective of this invention, it is 0.01-2 mass parts normally with respect to 100 mass parts of organic fibers, Preferably 0.01-1 mass part It is.

(Transparent substrate)
As a transparent base material preferably used in the present invention, a flexible glass substrate or a resin substrate is suitable. Examples of the resin used for the resin base include vinyl chloride-vinyl acetate copolymer, vinyl chloride resin, vinyl acetate resin, copolymer of vinyl acetate and vinyl alcohol, and partially hydrolyzed vinyl chloride-vinyl acetate copolymer. , Vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, ethylene-vinyl alcohol copolymer, chlorinated polyvinyl chloride, ethylene-vinyl chloride copolymer, ethylene-vinyl acetate copolymer, etc. Polymer or copolymer, nitrocellulose, cellulose acetate propionate (preferably acetyl group substitution degree 1.8-2.3, propionyl group substitution degree 0.1-1.0), diacetyl cellulose, cellulose acetate butyrate Copolymerization of cellulose derivatives such as rate resins, maleic acid and / or acrylic acid Acrylate copolymer, acrylonitrile-styrene copolymer, chlorinated polyethylene, acrylonitrile-chlorinated polyethylene-styrene copolymer, methyl methacrylate-butadiene-styrene copolymer, acrylic resin, polyvinyl alcohol resin, polyvinyl acetal Resin, polyvinyl butyral resin, urethane resin, polyester polyurethane resin, polyether polyurethane resin, polycarbonate polyurethane resin, polyester resin, polyether resin, polyamide resin, amino resin, styrene-butadiene resin, butadiene-acrylonitrile resin, etc. However, it is not limited to these.

  The thickness of the transparent substrate is 50 to 1000 μm, preferably 70 to 500 μm in consideration of handling as a heat insulating sheet.

(Insulation sheet manufacturing method)
Next, the manufacturing method of the heat insulation sheet of this invention is demonstrated.

  The heat insulating sheet of the present invention is obtained by forming a layer of a heat insulating material made of a porous skeleton on a transparent substrate. The method for forming the porous structure is not particularly limited as long as a porous skeleton having pores with an average pore diameter of 10 nm to 70 nm and a porosity of 90 to 99% by volume can be formed. A method for obtaining a porous skeleton by applying a foam dispersion molding method, or a method for obtaining a three-dimensional structure by applying a dispersion of the above-mentioned fibers and drying, or applying a dispersion of hollow particles onto a transparent substrate. The method of forming etc. are mentioned.

  When using foam molding of resin, foaming agent is mixed in the resin and the foaming agent is thermally decomposed to generate gas, or the mixed degradable resin is used as active energy rays such as electromagnetic waves, electron beams, and ion beams. , Or a chemical method that decomposes with heat, microorganisms, enzymes, acids, alkalis, etc. to form closed cells, carbon dioxide, nitrogenous substances such as carbon dioxide, nitrogen, supercritical state, thermoplastic resin A physical method of foaming by dissolving in a thermoplastic resin at a high temperature near the glass transition temperature and supercritical high temperature, and then cooling and reducing the pressure. A method for forming a sheet by forming pores by performing an orientation treatment such as stretching at the time of film formation or after the film formation is included.

  In order to control the pore diameter obtained by foaming to 70 nm or less, the partition between the pores to 10 nm or less and the porosity to be 90% or more, the molding pressure during foaming is set to 9 Mpa or more to control the pore diameter of the foamed bubbles. It is only necessary to solidify the resin faster than the coalescence rate of the bubbles to fix the bubbles. After the foaming agent is dissolved at a temperature higher than the melting temperature of the resin, the pore diameter obtained by foaming can be adjusted by adjusting the cooling temperature and the pressure reduction rate. Can be controlled at the nano level, and a heat insulating layer made of a structure having a high porosity can be formed. At this time, in order to obtain a sufficient amount of foaming that can ensure the porosity, it is preferable to foam by dissolving the foaming agent in the resin together with the supercritical fluid.

  As the foaming agent used, the substance of the substrate can be used in a supercritical state at normal temperature and pressure, such as carbon dioxide, and as a compound that decomposes by heating to generate gas, azodicarboxylic acid amide, azobisisobutyro Azo compounds such as nitriles, hydrazide compounds such as benzosulfonyl hydrazide, toluenesulfonyl hydrazide, p, p'-oxybis (benzenesulfonyl hydrazide), nitroso compounds such as dinitrosopentamethylenetetramine, hydrogen carbonates such as sodium bicarbonate and sodium carbonate Examples thereof include alkali metal salts, alkali metal carbonates, and mixtures thereof.

  Moreover, you may use a foaming adjuvant with these foaming agents as needed. Examples of the foaming aid include organic acids such as zinc oxide, zinc stearate, calcium stearate, salicylic acid, phthalic acid, oxalic acid and citric acid. The amount of the foaming agent to be added may be 1.0 to 20 times, preferably 1.0 to 18 times, more preferably 1.1 to 10 times as the expansion ratio.

  In order to form a structure composed of a porous skeleton composed of nanofibers and hollow particles, a coating liquid in which these are dispersed in a suitable solvent is prepared, and after the dispersion is coated on a transparent substrate, the solvent Is obtained by drying.

  Also, when forming a three-dimensional network structure using a metal alkoxide or silane coupling agent, a water-based or alcohol-water mixed solution of the metal alkoxide or silane coupling agent is applied onto the substrate to form a sol-gel. After the reaction is advanced to form a fibrous structure, it is obtained by drying the solvent.

  The drying method is not particularly limited, but it is preferable to use a supercritical drying method in order to suppress aggregation between fibers based on interfacial tension accompanying drying. The solvent that is a supercritical fluid used for performing supercritical drying is not particularly limited. For example, a single system such as ethanol, methanol, isopropanol, dichlorodifluoromethane, carbon dioxide, water, or a mixed system of two or more types Can be mentioned.

  When supercritical drying is performed, a sheet coated with a solution of the porous skeleton-forming composition that has undergone solvent substitution is placed in an autoclave, and after raising the temperature and pressure above the critical point of the solvent, the solvent is added. What is necessary is just to dry by removing gradually and finally returning to the state of normal temperature normal pressure.

  In the present invention, in order to ensure heat resistance and transparency as well as mechanical strength, it is preferable to form a heat insulating layer composed of a porous skeleton containing both components of a three-dimensional network structure and hollow particles. After applying a coating liquid in which hollow particles are added to a coating liquid capable of forming a three-dimensional network structure, the solvent is dried.

  Although the thickness of a heat insulation layer is suitably selected in consideration of the required heat insulation, transparency, etc. For example, when using as a transparent heat insulation sheet for window glass, 10 micrometers-5 mm are suitable. If the thickness is less than 10 μm, the heat insulating property is insufficient, and if it is thicker than 5 mm, the handling becomes worse, and there is a possibility that the operation of attaching to the window becomes difficult.

(Method for measuring physical properties of heat insulation layer)
Hereafter, it describes about the physical-property measuring method of a heat insulation layer.

(1) Number average fiber diameter Measurement of the average fiber diameter of the fiber was obtained after observing the obtained organic fiber at a magnification of 10,000 times using a transmission electron microscope, H-1700FA type (manufactured by Hitachi, Ltd.). Randomly select 100 fibers for the obtained image, analyze the fiber diameter for each fiber using image processing software (WINROOF), and determine their simple number average value.

(2) Number average thickness and number average inner diameter of shells of hollow particles The hollow particles are observed by the same operation as in (1). First, 100 hollow particles are selected at random, and the number average value is obtained by analyzing the thickness of 10 shells per particle using image processing software. Further, the number average value of all the selected particles is calculated. The number average thickness of the hollow particle shell is obtained.

  Using a transmission electron microscope, model H-1700FA, the number average outer diameter of 100 hollow particles is obtained, and the number average inner diameter is obtained by subtracting twice the number average thickness of the shell.

(3) Average pore diameter The pore diameter of the transparent heat insulating sheet is measured by small-angle X-ray scattering measurement. An average value of 10 points is used as the measurement value.

  The measurement apparatus and measurement conditions for small-angle X-ray scattering are as follows.

Device: RIGAKU small-angle X-ray scattering device (RU-200B)
Measurement conditions: λ (CuKα) = 0.154 nm, 45 kV, 70 mA
Analysis method: Measurement is performed in the small-angle region (2θ <10 °) using the above-described measuring device, and the average pore diameter (nm) in the heat insulating layer is calculated from the scattered light profile.

(4) Porosity The porosity A of the heat insulating layer is calculated from the density B obtained from the volume and mass of the heat insulating layer and the density C of the material itself constituting the heat insulating layer.

A = ((C−B) / C) × 100 (%)
(Insulation sheet evaluation method)
Below, it describes about the evaluation method of a heat insulation sheet.

(1) Light transmittance The light transmittance is measured with an ultraviolet-visible spectrophotometer (JASCO V-570), and the light transmittance is obtained based on JIS R 3106.

(2) Thermal conductivity Measurement is performed using a hot-wire probe type thermal conductivity measuring device (QTM-500 manufactured by Kyoto Electronics Co., Ltd.).

(3) Bending characteristics The sheet obtained in the production example was bent with a radius of curvature of 10 mm so that the inside of the sheet forms an angle of 120 degrees with the center of the sheet as a fulcrum and the heat insulating layer as the outside. Evaluation is made by visually confirming the occurrence of cracks.

  Examples of the present invention are shown below, but the present invention is not limited to these Examples.

(Production Example 1)
Polystyrene was introduced into a single screw type tension critical extruder. The supercritical impregnation extruder is introduced with carbon dioxide gas in a supercritical state at a temperature of 200 ° C. and a pressure of 90 MPa from a substance supply port that is a gas at room temperature, and polystyrene is impregnated with carbon dioxide gas over 15 minutes. I got a thing. This is introduced from the discharge port of the impregnation composition into the foam formation extruder through the introduction port of the impregnation composition of the foam formation extruder having a single screw, and after foaming through the die from the discharge port After being extruded as a sheet so as to have a thickness of 200 μm, a foam was produced by cooling to room temperature over 3 hours and reducing the pressure to normal pressure. The foam and a polyethylene terephthalate sheet having a thickness of 50 μm were bonded to obtain a transparent heat insulating sheet 101.

(Production Example 2)
In the production example 1, when extruding polystyrene impregnated with carbon dioxide gas from a foam-forming extruder, a transparent heat insulating sheet 102 was obtained by the same operation except that the cooling time was 2 hours 30 minutes.

(Production Example 3)
In Production Example 1, when extruding polystyrene impregnated with carbon dioxide gas from a foam-forming extruder, a transparent heat insulating sheet 201 was obtained by the same operation except that the cooling time was 30 minutes.

(Production Example 4)
A suspension obtained by adding sulfite bleached pulp obtained from conifers to 0.1% by mass in pure water is rotated using a stone mill grinder (Pure Fine Mill KMG1-10; manufactured by Kurita Machinery Co., Ltd.). 50 times (50 passes) grinding process (passage: 1500 revolutions / minute) passing between the disks to the outside from the center, the cellulose fibers are defibrated, filtered, washed with pure water, and then cellulose An aqueous dispersion of fibers was obtained. Next, the cellulose fiber was added to and dispersed in 500 parts by mass of an acetic anhydride / pyridine (molar ratio 1/1) solution so as to be 10 parts by mass, and stirred at room temperature for 3 hours. Next, the dispersed fiber was filtered, washed three times with 500 parts by mass of water, and then washed twice with 200 parts by mass of ethanol. Furthermore, after washing twice with 500 parts by mass of water, it was dried at 70 ° C. to obtain surface-modified cellulose fibers. Next, after adding a cellulose fiber in pure water so that a fiber component might be 1 mass%, it processed for 1 minute using the homogenizer (made by Sanwa Machine Co., Ltd.), and prepared the fiber dispersion liquid. Next, on a polyethylene terephthalate sheet having a thickness of 50 μm, the fiber dispersion was applied to a thickness of 200 μm using a wire bar coater, and then moisture was dried by a supercritical drying method. A heat insulating layer made of a porous skeleton having a three-dimensional network structure of cellulose fibers was formed to obtain a heat insulating sheet 103.

(Production Example 5)
A heat insulating sheet 202 was obtained in the same manner as in Production Example 4 except that the drying operation after coating the fiber dispersion was changed from the supercritical drying method to the freeze drying method.

(Production Example 6)
To 170 parts by mass of a 10% by mass calcium carbonate aqueous dispersion prepared using calcium carbonate having an average particle diameter of 50 nm, 8 parts by mass of 28% by mass of aqueous ammonia is added and stirred for 10 minutes. Tetraethoxysilane: methyltriethoxysilane = 19 parts by mass of 1: 1 (mass ratio) was added, and the mixture was stirred at room temperature for 1 hour. Thereafter, the temperature was raised to 60 ° C., the mixture was stirred for 3 hours, cooled to room temperature, and a silica-coated calcium carbonate dispersion was obtained.

  190 parts by mass of methanol was added to 200 parts by mass of the obtained silica-coated calcium carbonate dispersion, 180 parts by mass of a 10% by mass nitric acid aqueous solution was added, and calcium carbonate was eluted. Next, 200 parts by mass of distilled water was added, and 200 parts by mass of the aqueous solution was discharged using an ultrafiltration membrane. This operation is repeated three times to form organic-inorganic hybrid silica hollow particles having a number average thickness of 3 nm and a number average inner diameter of 50 nm in a shell formed of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio). Obtained. Next, after mixing 1.5 parts by mass of tetraethoxysilane and 70 parts by mass of methanol, 3 parts by mass of an aqueous ammonia solution (3N) was added and stirred at room temperature for 15 hours to give a tetraethoxysilane sol (solid content 2% by mass). After that, the hollow particles were added thereto so as to be 17% by volume to prepare a hollow particle-containing sol. Next, the sol was coated on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then water was dried by a supercritical drying method. A heat insulating layer composed of a porous skeleton formed from a network structure and organic / inorganic hybrid silica hollow particles was formed to obtain a heat insulating sheet 104.

(Production Example 7)
According to the method described in Production Example 6, a shell formed from tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio) having an average thickness of 3 nm, a number average thickness of 3 nm, and a number average inner diameter Obtained 50 nm of organic-inorganic hybrid silica hollow particles. Next, after preparing a sol of tetraethoxysilane (solid content: 2% by mass), the hollow particles were added thereto so as to be 15% by volume to prepare a hollow particle-containing sol. Next, the sol was coated on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then water was dried by a supercritical drying method. A heat insulating layer made of a porous skeleton formed from a network structure and organic / inorganic hybrid silica hollow particles was formed to obtain a heat insulating sheet 105.

(Production Example 8)
According to the method described in Production Example 6, hollow silica particles having a number average thickness of 3 nm and a number average inner diameter of 50 nm were obtained from a shell formed from tetraethoxysilane. Next, after preparing a sol (solid content: 2% by mass) of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), the hollow particles are added to the sol so that the volume becomes 17% by volume. A particle-containing sol was prepared. Next, the sol was applied on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then the moisture was dried by a supercritical drying method. A heat insulating layer made of a porous skeleton formed from an inorganic hybrid silica network structure and silica hollow particles was formed to obtain a heat insulating sheet 106.

(Production Example 9)
According to the method described in Production Example 6, hollow silica particles having a number average thickness of 3 nm and a number average inner diameter of 50 nm were obtained from a shell formed from tetraethoxysilane. Next, after preparing a sol (solid content 2% by mass) of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), the hollow particles are added to the volume so as to be 15% by volume. A particle-containing sol was prepared. Next, the sol was applied on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then the moisture was dried by a supercritical drying method. A heat insulating layer made of an inorganic hybrid silica network structure and a porous skeleton formed from silica hollow particles was formed to obtain a heat insulating sheet 107.

(Production Example 10)
According to the procedure of Production Example 6, hollow particles having a number average inner diameter of 50 nm with a shell made of silica having a number average thickness of 3 nm were obtained, and this was obtained as tetraethoxysilane: methyltriethoxysilane = 1: 1 ( The heat insulating sheet 108 is formed by forming a heat insulating layer made of a porous skeleton formed from an organic-inorganic hybrid silica network structure and silica hollow particles by the same operation except that it is added to a sol having a solid content of 2% by mass. Got.

(Production Example 11)
According to the procedure of Production Example 6, hollow particles having a number average inner diameter of 30 nm with a shell made of silica having a number average thickness of 2 nm were obtained, and this was obtained as tetraethoxysilane: methyltriethoxysilane = 1: 1 ( In the same manner except that it is added to a sol having a solid content of 2% by mass, a heat insulating layer 109 made of a porous skeleton formed from an organic-inorganic hybrid silica network structure and silica hollow particles is formed. Got.

(Production Example 12)
According to the procedure of Production Example 6, hollow particles having a number average inner diameter of 30 nm with a shell made of silica having a number average thickness of 2 nm were obtained, and this was obtained as tetraethoxysilane: methyltriethoxysilane = 1: 1 ( A heat insulating sheet comprising a porous skeleton formed from an organic-inorganic hybrid silica network structure and silica hollow particles is formed in the same manner except that it is added to a sol having a solid content of 3% by mass. 110 was obtained.

(Production Example 13)
In accordance with the method described in Production Example 6, a shell formed from tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), an organic-inorganic hybrid having a number average thickness of 2 nm and a number average inner diameter of 30 nm Silica hollow particles were obtained. Next, after preparing a sol (solid content: 2% by mass) composed of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), the hollow particles were added to the volume so as to be 15% by volume. A sol containing hollow particles was prepared. Next, the sol was applied on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then the moisture was dried by a supercritical drying method. A heat insulating layer composed of a porous skeleton formed from an inorganic hybrid silica network structure and organic / inorganic hybrid silica hollow particles was formed to obtain a heat insulating sheet 111.

(Production Example 14)
In accordance with the method described in Production Example 6, a shell formed from tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), an organic-inorganic hybrid having a number average thickness of 2 nm and a number average inner diameter of 30 nm Silica hollow particles were obtained. To this, the cellulose fiber obtained in Production Example 3 was added to water at 1% by mass, and the hollow particles were added at 3% by volume to prepare a hollow particle-containing sol. Next, the sol was coated on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then water was dried by a supercritical drying method. A heat insulating layer made of a porous skeleton formed of a network structure and organic / inorganic hybrid silica hollow particles was formed to obtain a heat insulating sheet 112.

(Production Example 15)
In accordance with the method described in Production Example 6, a shell formed of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), an organic inorganic material having a number average thickness of 5 nm and a number average pore diameter of 80 nm Hybrid silica hollow particles were obtained. Next, after preparing a sol of tetraethoxysilane (solid content: 2% by mass), the hollow particles were added thereto so as to be 15% by volume to prepare a hollow particle-containing sol. Next, the sol was coated on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then water was dried by a supercritical drying method. A heat insulating layer made of a porous skeleton formed of a network structure and organic / inorganic hybrid silica hollow particles was formed to obtain a heat insulating sheet 203.

(Production Example 16)
After preparing a tetraethoxysilane sol (solid content: 2% by mass) according to the method described in Production Example 6, the cellulose fiber obtained in Production Example 3 was added to 1% by mass. A cellulose fiber-containing sol was prepared. Next, the sol was coated on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then water was dried by a supercritical drying method. A heat insulating sheet 113 having a heat insulating layer made of a porous skeleton formed of a network structure and cellulose fibers was obtained.

(Production Example 17)
In accordance with the method described in Production Example 6, a shell formed of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), an organic-inorganic hybrid having a number average thickness of 12 nm and a number average inner diameter of 50 nm Silica hollow particles were obtained. Next, after preparing a sol of tetraethoxysilane (solid content: 2% by mass), the hollow particles were added thereto so as to be 15% by volume to prepare a hollow particle-containing sol. Next, the sol was coated on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then water was dried by a supercritical drying method. A heat insulating layer composed of a porous body skeleton formed from a network structure and organic / inorganic hybrid silica hollow particles was formed to obtain a heat insulating sheet 204.

(Production Example 18)
In Production Example 6, hollow particles having silica with a number average thickness of 2 nm as hollow particles and having a number average inner diameter of 30 nm are obtained, and tetraethoxysilane: methyl is used so that the hollow particles become 14% by volume. An organic-inorganic hybrid is prepared in the same manner except that it is added to a sol having a solid content of 3% by mass consisting of triethoxysilane = 1: 1 (mass ratio), and drying on a polyethylene terephthalate sheet is performed by freeze drying. A heat insulating layer composed of a porous skeleton formed from a silica network structure and silica hollow particles was formed, and a heat insulating sheet 205 was obtained.

(Production Example 19)
According to the procedure of Production Example 6, hollow particles having a number average inner diameter of 30 nm are obtained with a shell made of silica having a number average thickness of 2 nm, and tetraethoxysilane: A porous skeleton formed from an organic-inorganic hybrid silica network structure and silica hollow particles by the same operation except that it is added to a sol having a solid content of 4% by mass comprising methyltriethoxysilane = 1: 1 (mass ratio). The heat insulation layer 206 was formed and the heat insulation sheet 206 was obtained.

(Production Example 20)
In accordance with the operation of Production Example 6, hollow particles having a number average inner diameter of 30 nm with a shell made of silica having a number average thickness of 2 nm are obtained, and tetraethoxysilane: A porous skeleton formed from an organic-inorganic hybrid silica network structure and silica hollow particles in the same manner except that it is added to a sol having a solid content of 3% by mass comprising methyltriethoxysilane = 1: 1 (mass ratio). The heat insulation layer which consists of was formed and the heat insulation sheet 207 was obtained.

(Production Example 21)
In accordance with the operation of Production Example 6, hollow particles having a number average inner diameter of 30 nm are obtained with a shell made of silica having a number average thickness of 2 nm, and tetraethoxysilane: A porous skeleton formed from an organic-inorganic hybrid silica network structure and silica hollow particles in the same manner except that it is added to a sol having a solid content of 2% by mass comprising methyltriethoxysilane = 1: 1 (mass ratio). A heat insulating layer 208 was formed to obtain a heat insulating sheet 208.

(Production Example 22)
In Production Example 6, an organic-inorganic hybrid silica network structure and silica were obtained in the same manner except that the concentration of the sol of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio) was changed to 1% by mass. A heat insulating layer made of a porous skeleton formed of hollow particles was formed to obtain a heat insulating sheet 209.

(Production Example 23)
After preparing a sol of tetraethoxysilane (solid content 5 mass%) according to the method described in Production Example 6, the wire bar coater was used on a polyethylene terephthalate sheet having a thickness of 50 μm without adding hollow particles. After coating the sol so as to have a dry film thickness of 200 μm, the moisture is dried by a supercritical drying method to form a heat insulating layer made of a porous skeleton in which a silica network structure is formed. Obtained.

(Production Example 24)
According to the method described in Production Example 6, hollow silica particles having a number average thickness of 2 nm and a number average inner diameter of 30 nm were obtained from a shell formed from tetraethoxysilane. Next, after preparing a sol (solid content: 3.5% by mass) consisting of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), the hollow particles are added to the volume so as to be 17% by volume. Thus, a hollow particle-containing sol was prepared. Next, the sol was applied on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then the moisture was dried by a supercritical drying method. A heat insulating layer composed of a porous skeleton formed from an inorganic hybrid silica network structure and silica hollow particles was formed to obtain a heat insulating sheet 114.

(Production Example 25)
According to the method described in Production Example 6, hollow silica particles having a number average thickness of 2 nm and a number average inner diameter of 30 nm were obtained from a shell formed from tetraethoxysilane. Next, after preparing a sol (solid content: 2% by mass) consisting of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), the hollow particles were added to the volume so as to be 13% by volume. A sol containing hollow particles was prepared. Next, the sol was applied on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then the moisture was dried by a supercritical drying method. A heat insulating layer made of a porous skeleton formed of an inorganic hybrid silica network structure and silica hollow particles was formed to obtain a heat insulating sheet 115.

(Production Example 26)
According to the method described in Production Example 6, hollow silica particles having a number average thickness of 2 nm and a number average inner diameter of 30 nm were obtained from a shell formed from tetraethoxysilane. Next, after preparing a sol (solid content: 3% by mass) composed of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), the hollow particles were added thereto so as to be 19% by volume. A sol containing hollow particles was prepared. Next, the sol was applied on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then the moisture was dried by a supercritical drying method. A heat insulating layer composed of a porous skeleton formed from an inorganic hybrid silica network structure and silica hollow particles was formed to obtain a heat insulating sheet 116.

(Production Example 27)
According to the method described in Production Example 6, hollow silica particles having a number average thickness of 2 nm and a number average inner diameter of 30 nm were obtained from a shell formed from tetraethoxysilane. Next, after preparing a sol (solid content: 2% by mass) composed of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), the hollow particles were added thereto so as to be 16% by volume. A sol containing hollow particles was prepared. Next, the sol was applied on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then the moisture was dried by a supercritical drying method. A heat insulating layer consisting of a porous skeleton formed from an inorganic hybrid silica network structure and silica hollow particles was formed to obtain a heat insulating sheet 117.

(Production Example 28)
According to the method described in Production Example 6, hollow silica particles having a number average thickness of 2 nm and a number average inner diameter of 30 nm were obtained from a shell formed from tetraethoxysilane. Next, after preparing a sol (solid content: 3.7% by mass) consisting of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), the hollow particles are added to the volume so as to be 18% by volume. Thus, a hollow particle-containing sol was prepared. Next, the sol was applied on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then the moisture was dried by a supercritical drying method. A heat insulating layer made of a porous skeleton formed from an inorganic hybrid silica network structure and silica hollow particles was formed to obtain a heat insulating sheet 211.

(Production Example 29)
According to the method described in Production Example 6, hollow silica particles having a number average thickness of 2 nm and a number average inner diameter of 30 nm were obtained from a shell formed from tetraethoxysilane. Next, after preparing a sol (solid content: 1.5% by mass) consisting of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), the hollow particles are added so as to be 12% by volume. Thus, a hollow particle-containing sol was prepared. Next, the sol was applied on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then the moisture was dried by a supercritical drying method. A heat insulating layer made of a porous skeleton formed from an inorganic hybrid silica network structure and silica hollow particles was formed to obtain a heat insulating sheet 212.

(Production Example 30)
According to the method described in Production Example 6, hollow silica particles having a number average thickness of 2 nm and a number average inner diameter of 30 nm were obtained from a shell formed from tetraethoxysilane. Next, after preparing a sol (solid content: 3% by mass) composed of tetraethoxysilane: methyltriethoxysilane = 1: 1 (mass ratio), the hollow particles were added to the mixture so as to be 19.5% by volume. Thus, a hollow particle-containing sol was prepared. Next, the sol was applied on a polyethylene terephthalate sheet having a thickness of 50 μm using a wire bar coater so as to have a dry film thickness of 200 μm, and then the moisture was dried by a supercritical drying method. A heat insulating layer made of a porous skeleton formed from an inorganic hybrid silica network structure and silica hollow particles was formed to obtain a heat insulating sheet 213.

(Production Example 31)
After preparing a sol of tetraethoxysilane (solid content: 4.5% by mass) according to the method described in Production Example 6, the sol is dried on a 50 μm thick polyethylene terephthalate sheet using a wire bar coater. After coating to a thickness of 200 μm, moisture was dried by a supercritical drying method to form a heat insulating layer made of a porous skeleton having a silica network structure, and a heat insulating sheet 118 was obtained.

(Method for measuring physical properties of heat insulation layer)
Hereinafter, it describes about the physical-property measuring method of the heat insulation layer of the heat insulation sheet produced above.

(1) Number average fiber diameter Measurement of the average fiber diameter of the fiber was obtained after observing the obtained organic fiber at a magnification of 10,000 times using a transmission electron microscope, H-1700FA type (manufactured by Hitachi, Ltd.). 100 fibers were randomly selected from the obtained images, and the fiber diameter of each fiber was analyzed using image processing software (WINROOF), and a simple number average value thereof was obtained.

(2) Number average thickness and number average inner diameter of shells of hollow particles The obtained hollow particles were observed by the same operation as (1). First, 100 hollow particles are selected at random, and the number average value is calculated by analyzing the thickness of 10 outlines per particle by image processing software. Further, the number average value of all the selected particles is calculated. The average thickness of the hollow particle outer shell was determined.

  Using a transmission electron microscope, model H-1700FA, the number average outer diameter of the hollow particles was determined, and by subtracting twice the number average thickness of the shell, the number average inner diameter was determined.

(3) Average pore diameter The pore diameter of the transparent heat insulating sheet was measured by small-angle X-ray scattering measurement. The average value of 10 points was used as the measurement value.

  The measurement apparatus and measurement conditions for small-angle X-ray scattering are as follows.

Device: RIGAKU small-angle X-ray scattering device (RU-200B)
Measurement conditions: λ (CuKα) = 0.154 nm, 45 kV, 70 mA
Analysis method: Measurement was performed in the small-angle region (2θ <10 °) using the above-described measuring device, and the average pore diameter (nm) in the heat insulating layer was calculated from the scattered light profile.

(4) Porosity The porosity A of the heat insulating layer was calculated from the density B obtained from the volume and mass of the heat insulating layer and the density C of the material itself constituting the heat insulating layer.

A = ((C−B) / C) × 100 (%)
(Insulation sheet evaluation method)
Below, it describes about the evaluation method of the heat insulation sheet produced above.

(1) Light transmittance The light transmittance was measured with an ultraviolet-visible spectrophotometer (JASCO V-570), and the light transmittance was determined based on JIS R 3106.

(2) Thermal conductivity It measured using the hot wire probe type thermal conductivity measuring apparatus (QTM-500 by Kyoto Electronics).

(3) Bending characteristics The sheet obtained in the production example was bent with a radius of curvature of 10 mm so that the inside of the sheet forms an angle of 120 degrees with the center of the sheet as a fulcrum and the heat insulating layer as the outside. The presence or absence of cracks was visually confirmed, and the bending characteristics were evaluated based on the following criteria.

○: No cracking occurred in the bent part Δ: Partial cracking occurred in the bent part ×: Cracking occurred in the entire bent part The above results are shown in Table 1.

  As is clear from the physical property evaluation results in Table 1, the heat insulating sheets 101 to 118 according to the present invention are excellent in mechanical strength (bending characteristics), ensure handling as a sheet, and have high heat insulating properties and transparency. It can be seen that

Claims (2)

It has a porous skeleton having an average pore diameter of 10 nm or more and 70 nm or less and a porosity of 90 to 99%, and satisfies at least one of the following requirements (1) to (5): Thermal insulation sheet;
(1) The porous skeleton includes hollow particles having shells having a number average thickness of 2 nm or more and 10 nm or less, and a number average inner diameter of 10 nm or more and 70 nm or less;
(2) The porous skeleton contains organic / inorganic hybrid silica hollow particles;
(3) The porous skeleton includes an organic / inorganic hybrid silica network structure and organic / inorganic hybrid silica hollow particles;
(4) The porous skeleton includes an organic / inorganic hybrid silica network structure and silica hollow particles;
(5) The porous skeleton includes a silica network and organic / inorganic hybrid silica hollow particles.   The heat insulating sheet according to claim 1, wherein the porosity of the porous skeleton is 96 to 99%.