US20180156550A1

US20180156550A1 - Heat insulation material and device using same

Info

Publication number: US20180156550A1
Application number: US15/816,229
Authority: US
Inventors: Kazuma Oikawa; Kei Toyota; Shigeaki Sakatani; Daido Kohmyohji; Tatsuhiro Ooshiro; Tooru Wada
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2016-12-05
Filing date: 2017-11-17
Publication date: 2018-06-07
Also published as: DE102017127388A1; CN108146028B; CN108146028A

Abstract

An object of the disclosure is to provide heat insulation materials that combine high heat insulation properties realizing effective heat insulation, and flame retardancy realizing prevention of fire spreading, and devices using the same. In order to achieve this object, disclosed are heat insulation materials, including: a silica xerogel; a carbon material; unwoven fabric fibers that retains the silica xerogel, and the carbon material. Further disclosed are devices, including the above-described heat insulation material, wherein the heat insulation material serves as a part of a heat-insulation or refrigeration structure, or is placed between a heat-producing component and a casing.

Description

TECHNICAL FIELD

The technical field relates to heat insulation materials, and devices using the same. In particular, the technical field relates to flame retardant heat insulation materials, and devices using the same.

BACKGROUND

In recent years in the fields of automobile and industrial equipment that control heat flows, safety, and fire prevention of fires capable of spreading to neighboring areas, it has been required that the equipment be confined to limited and narrow spaces. Therefore, there has been growing demands for non-conventional high-performance heat insulation materials that combine excellent heat-insulation properties, flame retardancy, and heat resistance. Thus, effective heat insulation can be realized even if they are shaped into thin forms.
For this reason, flame retardant polyurethanes that include flame retardants have been developed. Flame retardant polyurethanes, for example brominated flame retardants have been used as flame retardants for resins. These flame retardants are based on a mechanism in which the surfaces are carbonated at the time of combustion, and thus, combustion progression is prevented. However, upper limits for their workable temperatures are around 100° C. They have been problematic when employed in a high temperature range (e.g., 100° C. or higher) (Japanese Patent No. 5785159, Publication). Furthermore, it is difficult to shape them into thin forms having thicknesses equal to or smaller than the foam diameters, since they are foams.
Meanwhile, silica aerogels are known to serve as heat insulation materials. Silica aerogels have network structures in which silica particles on the scale of several tens of nanometers are connected via point contact, and mean pore diameters are equal to or smaller than 68 nm, which is a mean free path of the air. Accordingly, their heat conductivities are lower than the heat conductivity of the still air.

SUMMARY

However, in silica aerogels, organic modification groups may be decomposed by heat under a high-temperature environment, and thus, combustible gases may be produced. Therefore, silica aerogels have problems in flame retardancy and heat resistance.
Hence, an object of the disclosure is to provide heat insulation materials that combine high heat, insulation properties realizing effective heat insulation, and flame retardancy realizing prevention of fire spreading, and devices using the same.
In order to achieve the above-mentioned objectives, according to one aspect of the disclosure, provided is a heat insulation material, including: a silica xerogel; a carbon material; unwoven fabric fibers that retains the silica xerogel, and the carbon material.
Furthermore, according to another aspect of the disclosure, provided is a device, including the above-described heat insulation material, wherein the heat insulation material serves as a part of a heat-insulation or refrigeration structure, or is placed between a heat-producing component and a casing.
Since heat insulation materials according to the disclosure have heat conductivities lower than those exhibited by conventional heat insulation materials, sufficient heat insulation effects can be obtained even in narrower spaces such as inside electronic devices, in-vehicle devices, and industrial equipment. Thus, conduction of heat from heat-producing components to casings can effectively be reduced. Furthermore, since the heat insulation materials according to the disclosure have sufficient flame retardancy, the heat insulation materials possess fire-spreading-prevention effects that make it possible to prevent fire spreading possibly caused in thermal runaway or firing phenomena.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are cross-section views of flame retardant heat insulation materials according to embodiments.

FIG. 2 is a diagram that shows a two-component layer including a silica xerogel and a carbon material in an embodiment.

FIG. 3 is a three-component composite layer including a silica xerogel, a carbon material, and unwoven fabric fibers in an embodiment.

FIGS. 4A to 4F are diagrams that shows carbon materials in embodiments.

FIG. 5 is a diagram that describes a method for producing a flame retardant heat insulation material according to an embodiment.

FIGS. 6A and 6B are diagrams that show a step in which unwoven fabric fibers are impregnated with a carbon material dispersion, in an embodiment.

FIG. 7 is a diagram that shows detailed conditions and evaluation results for examples and comparative examples.

FIG. 8 is a diagram that shows an SEM images of cross-sections of heat insulation materials prepared in EXAMPLE 1 and COMPARATIVE EXAMPLE 1.

DESCRIPTION OF EMBODIMENTS

Next, embodiments according to the disclosure will be described with reference to one preferable embodiment.

Examples of Structures of Heat Insulation Materials 108

FIGS. 1A and 1B shows cross-section views of heat insulation materials 108 according to embodiments.
The heat, insulation material shown in FIG. 1A includes a three-component composite layer 103, two-component composite layer 102, and a one-component single layer 101.
The three-component composite layer 103 includes a silica xerogel 115, a carbon material 114, and unwoven fabric fibers 116.
The two-component composite layer 102 includes no unwoven fabric fibers 116, and includes a silica xerogel 115, and a carbon material 114. The two-component composite layer 102 is placed on the three-component composite layer 103.
The one-component single layer 101 is formed of the silica xerogel 115.
The silica xerogel 115, the carbon material 114, and the unwoven fabric fibers included in each of the layers may be the same. However, different types of materials can also be used therefor.
The role of each layer will be described below.
The three-component composite layer 103 serves as a main layer of the heat insulation material 108, and is the thickest of the three layers. The three-component composite layer 103 includes as a main ingredient the silica xerogel 115, and determines the heat insulation performance of the heat insulation material 108. Additionally, the carbon material, which is one of the ingredients included in the three-component composite layer 103 contributes to flame retardancy, while the unwoven fabric fibers 116 serve as a support that makes it possible to realize the heat insulation material 108 as a self-standing structure.
The two-component composite layer 102 determines flame retardancy performance of the heat insulation material 108. The two-component composite layer 102 is thinner than the three-component composite layer 103. However, the concentration of the carbon material 114 present in the two-component composite layer 102 is higher than the concentration of the carbon material 114 present in the three-component composite layer 103. Accordingly, the carbon material 114 present in the two-component composite layer 102 reacts with O₂present in the atmosphere, thereby producing a larger amount of CO₂. The produced CO₂dilutes combustible gases, and contributes to flame retardancy.
The one-component single layer 101 includes the silica xerogel 115, and is thinner than the three-component composite layer 103. The one-component single layer 101 ensures smoothness of the surface of the heat insulation material 108. If the one-component single layer 101 lacks smoothness, the contact resistance would become larger, and this may influence the heat insulation performance of the heat insulation material 108. The one-component single layer 101 is provided in order to ensure smoothness of the surface of the heat insulation material 108.
On the other hand, FIG. 1B shows a heat insulation material 108 that has a three-layer structure in which a three-component composite layer 103 is placed between two-component composite layers 102.
In FIG. 1B, the two-component composite layers 102 exist on both sides. Therefore, when either the front side or the backside of the heat insulation material 108 comes into contact with fire, high concentrations of CO₂will be produced from the either side. Thus, effective flame retardancy can be delivered.
FIG. 1A, a two-component composite layer 102 is present only on one side. In cases where only one side is possibly brought into contact with flames are expected, such a structure as found in FIG. 1A is preferable.
Components found in FIGS. 1A and 1B are shown in Tables 1 and 2, respectively.

	TABLE 1

	Layer	Components

	Two-component	Including no unwoven fabric fibers 116, but
	composite layer 102	including a silica xerogel 115 and a carbon
		material
114
	Three-component	Including a silica xerogel 115, a carbon
	composite layer
103	material 114, and unwoven fabric fibers 116
	One-component	Including no unwoven fabric fibers 116, but
	monolayer 101	including a silica xerogel 115

	TABLE 2

	Layer	Components

	Two-component	Including no unwoven fabric fibers 116, but
	composite layer 102	including a silica xerogel 115 and a carbon
		material
114
	Three-component	Including a silica xerogel 115, a carbon
	composite layer
103	material 114, and unwoven fabric fibers 116
	One-component	Including no unwoven fabric fibers 116, but
	monolayer 101	including a silica xerogel 115

According to the above structures, filling rates of silica xerogels 115 in the three-component composite layers 103 can be increased so as to secure sufficient heat insulation properties.

Distribution of Carbon

Concentrations of carbon materials 114 in the two-component composite layer 102, the one-component single layer 101, and the three-component composite layer 103 are different. The concentration of carbon materials 114 in the two-component composite layer 102 is the highest, and the concentration of carbon materials 114 in the three-component composite layer 103 is the second-highest. In principle, the one-component single layer 101 does not include any carbon materials 114.
Furthermore, the concentration of carbon materials 114 is preferably varied in the thickness direction as well as inside the three-component composite layer 103. That is, the concentration of carbon materials 114 may become higher to the top side direction, and may become lower to the bottom side direction, so as to provide a concentration gradient thereof in the vertical direction. In addition, the top side refers to a surface of the heat insulation material 108 that is possibly brought into contact with flames.
If a high concentration of the carbon material 114 is evenly dispersed therein, carbon particles would be connected with each other along the thickness direction, and thus, heat conduction paths may be formed, thereby increasing the heat conductivity. In such a case, heat insulation properties of the heat insulation material 108 would be inferior, and therefore is not preferable.
Furthermore, the carbon material 114 that is located inside the heat insulation material 108 does not contribute to production of carbon dioxide.
For this reason, in order to combine sufficient heat insulation properties (heat conductivity) and flame retardancy, instead of evenly dispersing the carbon material 114 therein, the carbon material 114 is preferably localized to the one side at a higher concentration.

Heat Conductivity

Heat conductivity of the unwoven fabric fibers may be from 0.030 to 0.060 W/mK. Heat conductivity of a composite including the silica xerogel 115 and the carbon material 114 may be from 0.010 to 0.015 W/mK. As a result, heat conductivity of the heat insulation material 108 may be from 0.014 to 0.024 W/mK.

Conventional Heat Insulation Materials

Conventional heat insulation materials that include silica xerogel 115 and unwoven fabric fibers 116 have a structure in which only a two-component composite layer including the silica xerogel 115 and the unwoven fabric fibers 116 are present. As a result, cracks can easily form.
Surfaces of silica particles that form the silica xerogel 115 are organically modified, and therefore, exhibit hydrophobicity. However, when the silica xerogel 115 is heated to a high temperature, i.e., 300° C. or higher, the organic modifying groups are thermally discomposed, and thus, trimethyl silanol and the like are dissociated as large amounts of combustible gases.
Since conventional heat insulation materials do not include any carbon materials 114, such combustible gases may act as a combustion improver. For example, substrates of glass papers made of C-glass are not combustible by themselves. However, when silica xerogels 115 having large specific surface areas (800 m²/g or higher) are combined with the glass papers, large amounts of combustible gases produced from the silica xerogels 115 may catch fire, and consequently, the glass papers made of C-glass may be burned. C-glass has lower heat resistance compared with E-glass, and will shrink or deform when it is heated to 750° C. or higher, although it depends on the unit weight.

Structure of the Two-Component Composite Layer 102

The structure of the two-component composite layer 102 is shown in FIG. 2.
In the silica xerogel 115, silica secondary particles 112 that are produced through aggregation of silica primary particles 111 are connected with each other by point contact. Thus, the silica xerogel 115 is formed as a porous structure having pores 113 on the scale of several tens of nanometers. The carbon material 114 has been incorporated into a three-dimensional network of the silica xerogel 115. The carbon material 114 may be connected to the silica primary particles 111 or the silica secondary particles 112, through covalent bonds or based on intramolecular forces.

Structure of the Three-Component Composite Layer 103

FIG. 3 is a perspective view of the three-component composite layer 103 that includes the silica xerogel 115, the unwoven fabric fibers 116, and the carbon material 114. As shown in FIG. 3, in the three-component composite layer 103, the carbon material 114 exists in a state in which the carbon material 114 is adsorbed onto surfaces of the unwoven fabric fibers 116 based on electrostatic interaction. When the heat insulation material is brought into contact with flames, or is exposed to a high-temperature environment, i.e., 300° C. or higher, the carbon material 114 reacts with O₂in the atmosphere so as to produce CO₂, thereby contributing development of flame retardancy. That is, the carbon material 114 serves as a flame retardant.

Carbon Material

114

The carbon material 114 used in the present embodiment has at least one condensed ring compound having aromaticity, and reacts with O₂in the atmosphere to produce CO₂, at high temperature, e.g., 300° C. or higher. With regards to conditions for the carbon material 114 producing CO₂at 300° C. or higher, for example, it may be required that any melting, thermodecomposition, and sublimation not occur in the process of the temperature elevation to 300° C. (thermostability), and it may be required that the carbon material 114 include sp carbon (triple bond) and sp2 carbon (double bond), which easily reacts with O₂in the atmosphere. A condensed ring compound having aromaticity and satisfying these conditions is preferably employed for the carbon material 114.
FIGS. 4A to 4F shows examples of structures of carbon materials 114 that can be employed in the present embodiments. That is, a fullerene 118 depicted in FIG. 4A, a graphene 119 depicted in FIG. 4B, a carbon nanotube 120 depicted in FIG. 4C, an electrically-conductive polymer 121 (e.g., polypyrroles, polyanilines, polythiophenes, and polyacetylenes) depicted in FIG. 4D, a polyacene 122 depicted in FIG. 4E (e.g., polyacene where n=1, naphthacene where n=2, and pentacene where n=3), and carbon black 123 depicted in FIG. 4F can be employed therefor.
Types of the carbon materials 114 are not particularly limited. However, carbon black 123, which has widely been employed for rubber-reinforcing additives and resin coloring agents, is preferably used.
The carbon material 114 employed in present embodiments is not known to be effective as a flame retardant by itself. Meanwhile, general flame retardants used for resins are not employed in present embodiments. Aluminum hydroxide, magnesium hydroxide, red phosphorus, ammonium phosphate, ammonium carbonate, zinc borate, molybdenum compounds, brominated monomers, brominated epoxies, bromine-type ethers, polystyrene, phosphate esters, melamine cyanurate, triazine compounds, guanidine compounds, and silicone polymers are typical examples of flame retardants used for resins. These materials are not suitable for development of flame retardancy in the heat insulation material 108 in present embodiments.
Furthermore, the carbon material 114 used in present embodiments may be added to an aqueous material in advance. Therefore, there are no limitations to the carbon material 114 as long as the carbon material 114 has hydrophilic functional groups in terms of water dispersibility. However, the aromatic carbon compounds that has been subjected to an oxidation treatment based on hydroxyl groups, carboxyl groups, sulfonyl groups, etc. are preferable in terms of economic efficiencies and water dispersibility.
The carbon material 114 that has been subjected to an oxidation treatment is negatively charged, and has self-dispersibility. Therefore, when the carbon material 114 is added to the aqueous material, the carbon material 114 does not easily settle out therein, and thus, can be stored for a relatively longer period of time. Furthermore, when the sol material is impregnated into the unwoven fabric fibers 116, the negatively-charged carbon material 114 is adsorbed onto surfaces of unwoven fabric fibers 116 due to electrostatic interaction, and thus, is effective in forming a structure in which the concentration of the carbon material 114 is localized in the above-described manner.
The average particle size distribution of the carbon material 114 is preferably from 50 to 500 nm. If the average particle size distribution is smaller than 50 nm, productivity may deteriorate. On the other hand, if the average particle size distribution is larger than 500 nm, the carbon material 114 may relatively settle out, and is accumulated in the sol material during mass production. Thus, problems such as unexpected changes in the concentration, pipe clogging, and nozzle clogging may occur.
An amount of the carbon material 114 is preferably from 0.01 wt % to 10.00 wt % relative to gross weight of the heat insulation material 108. If the amount is smaller than 0.01 wt %, sufficient flame retardancy may not be obtained. If the amount is larger than 10.00% wt, heat conductivity may excessively be increased, and thus, sufficient heat insulation properties may not be secured.
With regards to proportions (distributions) of the carbon materials 114 included in the respective layers, the proportion thereof in the two-component composite layer 102 is preferably from about 51 wt % to about 99 wt % relative to the gross amount of the carbon materials 114 included in the heat-insulation materials, and the proportion in the three-component composite layer 103 is preferably from approximately about 1 wt % to about 49 wt %. That is, when 10 wt % of the carbon materials 114 is included in the heat-insulation material, the proportion of the carbon materials 114 included in the two-component composite layer 102 is preferably from 5.1 wt % to 9.9 wt %, which is equivalent to 51% to 99% of the gross amount, i.e., 10%, and the proportion of the carbon materials 114 included in the three-component composite layer 103 is from 0.1 wt % to 4.9 wt %, which is equivalent to 1% to 49% of the gross amount, i.e., 10 wt %.
The carbon material 114 employed in present embodiments has flame retardancy. However, if an excessive amount of the carbon material 114 is added to the heat-insulation material, a heat conduction λs of solids may excessively be increased, and thus, the heat conductivity of the heat insulation material 108 may become large. Therefore, attention should be paid to an amount of the carbon material 114 included herein, and the manner of distribution of the carbon material 114.

Thickness of the Heat Insulation Material 108

A thickness of the heat insulation material 108 may be within a range from 0.03 mm to 5.0 mm. The thickness is preferably within a range from 0.05 mm to 3.0 mm. If the thickness of the heat insulation material 108 is smaller than 0.03 mm, the heat insulation effects may be reduced to the thickness direction. Consequently, the heat transfer to the direction from one side to the other side cannot sufficiently be reduced unless there is a very low heat conductivity such as close to the level realized in vacuum. If the thickness is larger than 0.05 mm, sufficient heat-insulation effects can be secured in the thickness direction.
On the other hand, if the thickness of the heat insulation material 108 is larger than 3.0 mm, it becomes difficult to incorporate the heat insulation material into various devices that have increasingly been smaller and slimmed in recent years.

Content Percentage of the Silica Xerogel 115 in the Heat Insulation Material 108

A thickness of the heat insulation material 108 may be within a range from 0.03 mm to 5.0 mm. The thickness is preferably from 0.05 mm to 3.0 mm. An optimum range for a weight proportion of the silica xerogel 115 relative to the gross weight will vary depending on weight unit, bulk density and thickness of the unwoven fabric fibers 116.
It may be sufficient that the weight proportion of the silica xerogel 115 is at least 40 wt % or higher. If the proportion is less than 40 wt %, it may become difficult to realize low heat conductivity. Furthermore, it may be sufficient that the proportion is 80 wt % or lower. If the proportion is higher than 80 wt %, flexibility and strength may become insufficient, and loss of the silica xerogel 115 heat conductivity may be caused through repetitive use.

Unit Weight of the Unwoven Fabric Fibers 116

A unit weight of the unwoven fabric fibers 116 may be from 5 g/m²to 500 g/m². The values will be described in the section of EXAMPLES below. In addition, the weight unit refers to a weight per unit area.

Bulk Density of the Unwoven Fabric Fibers 116

The bulk density of the unwoven fabric fibers 116 is preferably within a range from 100 kg/m³to 500 kg/m³in order to increase the content percentage of the silica xerogel 115 in the heat insulation material 108, and in order to reduce the heat conductivity.
In order to form unwoven fabric fibers 116 that possess sufficient mechanical strength as a continuous body, the bulk density may need to be at least 100 kg/m³. Furthermore, if the bulk density of the unwoven fabric fibers 116 is larger than 500 kg/m³, volumes of spaces inside unwoven fabric fibers 116 becomes smaller, an amount of the silica xerogel 115 that is filled into the spaces would be reduced, and thus, the heat conductivity may become higher. The values will be described in EXAMPLES below.

Materials of Unwoven Fabric Fibers 116

A material of the unwoven fabric fibers 116 includes at least one type of fibers selected from among aramid fibers, polyimide fibers, novoloid fibers, glass fibers, polyphenylene sulfide (PPS) fibers, oxidated acrylic fibers, graphite fibers, and carbon fibers that have a limiting oxygen index (LOI) of 25 or higher.

Mechanism for Development of Flame Retardancy in the Heat Insulation Material 108

A mechanism for development of flame retardancy will be described. The heat insulation material 108 includes the silica xerogel 115 and the carbon material 114 in the same layer. The silica particle surface that form the silica xerogel 115 are organically modified, and exhibit hydrophobicity. However, when the silica xerogel 115 is heated to a high temperature, e.g., 300° C. or higher, the organic modifying groups are thermally decomposed, a large amount of trimethyl silanol and the like are dissociated as a combustible gas. The combustible gas possibly acts as a combustion improver.
For example, a substrate of a glass paper made of C-glass is not combustible by itself. However, when the silica xerogel 115 having a large specific surface (800 m²/g or higher) is combined with the glass paper, a large amount of the combustible gas produced from the silica xerogel 115 may catch fire, and thus, the glass paper made of C-glass may be burned. C-glass has lower heat resistance compared with E-glass, and therefore, will shrink or deform when it is heated to 750° C. or higher, although it depends on the unit weight.
To the contrary, in the heat insulation material 108 according to the present, disclosure, oxygen in the atmosphere, and the carbon material 114 react with each other to produce a large amount of carbon dioxide, at a high temperature, e.g., 300° C. or higher, under the atmosphere, releasing a large amount of carbon dioxide. Accordingly, the combustible gas dissociated from the silica xerogel 115 is prevented from burning.

Method for Producing the Three-Component Composite Layer 103

An outline of a method for producing the three-component composite layer 103 is shown in FIG. 5.

(i) Sol Preparation

One part by weight of self-dispersible carbon black CB (Aqua-Black (R) 162 supplied from TOKAI CARBON CO., LTD., solid content concentration: 19.2 wt %) may be added to an aqueous water glass solution (TOSO SANGYO Co., Ltd.) to prepare a carbon black CB-dispersed aqueous water glass solution (SiO₂concentration: 6%, and carbon black CB: 1.3%). 3.6 parts by weight of concentrated hydrochloric acid serving as a catalyst is added to the dispersion, and the dispersion is stirred, to prepare a sol solution. However, a material species for silica is not limited to water glass, and alkoxysilanes, high molar ratio silicate soda may be used.
With regards to types of usable acids: inorganic acids (e.g., hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, sulfurous acid, phosphoric acid, phosphorous acid, hypophosphorous acid, chloric acid, chlorous acid, and hypochlorous acid), acidic phosphates (e.g., acidic aluminum phosphate, acidic magnesium phosphate, acidic zinc phosphate), organic acids such as (e.g., acetic acid, propionic acid, oxalic acid, succinic acid, citric acid, malic acid, adipic acid, and azelaic acid) can be used. Although types of catalysts used herein are not limited, hydrochloric acid is preferable in terms of strength of the gel skeleton, and hydrophobicity of the silica xerogel 115.
Then, the sol solution that is obtained by adding an acid catalyst to an aqueous water glass solution is gelatinized. Gelatinization of the sol is preferably carried out inside a sealed vessel from which the liquid medium is not volatinized.
When the high molar ratio silicate solution is gelatinized by adding the acid thereto, the pH preferably from 4.0 to 8.0. If the pH is less than 4.0 or is larger than 8.0, the high molar ratio silicate solution may not be gelatinized, although it depends on the temperature during the process.
(ii) Impregnation of the Sol Solution into Unwoven Fabrics
The sol solution is poured into unwoven fabric fibers 116 (material: glass papers, thickness specification: 600 um, unit weight: 110 g/m², dimension: 12 cm square) so as to impregnate the sol solution into the unwoven fabric fibers 116. An excessive amount of the sol solution impregnated thereinto is employed relative to a theoretical volume of spaces inside the unwoven fabric fibers 116 (>100%). The theoretical volume of spaces inside the unwoven fabric fibers 116 is calculated based on a bulk density of the unwoven fabric fibers 116. Furthermore, as mentioned above, the material, thickness and bulk density of the unwoven fabric fibers are not limited to the above-described specifications. With regards to usable impregnation techniques, a method in which each roll of unwoven fabrics is soaked in the sol solution, or a method in which the unwoven fabric fibers 116 are delivered at a constant rate in a roll to roll system, and then, the sol solution is coated onto the unwoven fabric fibers 116 based on a dispenser or spray nozzle may be employed. However, the roll to roll system 1s preferably employed in terms of productivity.
In the cross-section view of FIG. 6A, a process in which a sol material 124 that is obtained by dispersion of the carbon material 114 is dropwise poured onto the unwoven fabric fibers 116 so as to impregnate the sol material 124 into the unwoven fabric fibers 116 is shown. Molecular surfaces of the carbon material 114 are negatively charged. Therefore, the unwoven fabric fibers 116 are preferably positively charged, such that the carbon material 114 is adsorbed onto surfaces of the unwoven fabric fibers 116, thereby forming a structure in which the carbon material 114 is localized to one side or both sides of the heat insulation material 108 at a high density. Use of such a positively charged unwoven fabric fibers 116 is effective in forming a structure in which the concentration of the carbon material 114 is localized in the above manner, based on adsorption of the carbon material 114 onto surfaces of the unwoven fabric fibers 116 due to electrostatic interaction. As a result, unwoven fabric fibers 116 impregnated with the sol solution, as shown in the cross-section view of FIG. 6B, is produced.
(iii) Placing the Unwoven Fabric Fibers Between Films
The unwoven fabric fibers 116 impregnated with the sol solution is held between PP films (50 um thick×2, dimension: B6), and this is allowed to stand at room temperature (23° C.) for about 3 minutes, thereby gelatinizing the sol solution. The gelatinization time, the thickness control, the materials and thicknesses of the films, between which the impregnated unwoven fabrics are placed, and the aging step, are not limited to the above specifications. For materials of the films, a resin material having a maximum working temperature of 100° C. or higher and a linear thermal expansion coefficient of 100 (×10⁻⁶/° C.) or lower (e.g., polypropylene (PP), and polyethylene terephthalate (PET)) is preferable, since a heating process is required in the aging step.

(iv) Thickness Control

After it is confirmed that the gelatinization is completed, the sol-impregnated unwoven fabric fibers 116 held between the films is caused to pass through a gap between two-shaft rolls where the gap is set to 1.000 mm (including thicknesses of the films) to squeeze out excess gel from the unwoven fabric fibers 116, thereby controlling the thickness to 1.0 mm. In addition, a technique for controlling the thickness is not limited to the above-mentioned technique, and the thickness may be controlled based on techniques using a squeegee, press, or the like.

(v) Film Stripping

An aging vessel is taken out of a thermostatic chamber, and is cooled to room, temperature. Then, the aged sample is removed therefrom, and the films are stripped from the sample.

(vi) First Hydrophobization (Immersion in Hydrochloric Acid)

The gel sheet is immersed in hydrochloric acid (4-12 N), and then, is allowed to stand at ordinary temperature (23° C.) for 5 minutes or more, to incorporate hydrochloric acid into the gel sheet.
(vii) Second Hydrophobization (Siloxane Treatment)
The gel sheet is immersed in, for example, a mixture of octamethyltrisiloxane, serving as a silylating agent, and 2-propanol (IPA), i.e., an alcohol. Then, this is put into a thermostatic bath at 55° C., and is reacted therein for 2 hours. When formation of trimethylsiloxane bonds is started, hydrochloric acid is discharged from, the gel sheet, and two-liquid separation occurs (siloxane in the upper phase, and aqueous hydrochloric acid and 2-propanol in the lower phase).
(viii) Drying
The gel sheet is transferred into a thermostatic bath at 150° C., and is dried therein for 2 hours.
An example of producing a three-component composite layer 103 is described above with reference to FIG. 6, However, production of the three-component composite layer 103 is not limited to this example.

Production of the Heat Insulation Material 108

To produce a heat insulation material 108, in the above-described method for producing a three-component composite layer 103, the type and amount of the carbon material 114 in the above-described sol preparation (i) are varied. That is, while the three-component composite layer 103 is produced, the two-component composite layer 102 or the one-component single layer 101 is also prepared.
Due to interaction between negatively charged molecular surfaces of the carbon material 114 and positively charged surfaces of the unwoven fabric fibers 116, the two-component composite layer 102 containing a higher concentration of the carbon material 114 is formed on the side that has been subjected to the impregnation process. The one-component, single layer 101 that does not contain any carbon materials 114 is formed on the opposite side. As a result, a heat insulation material 108 depicted in FIG. 1A is prepared.
On the other hand, in a case where an amount of the carbon material 114 is increased, two-component composite layers 102 are formed on both sides of the two-component composite layer 102. In cases where an amount of the carbon material 114 included herein is slight, e.g., less than 1 wt % by weight, a structure shown in FIG. 1A is formed, and, in cases where an amount of the carbon material 114 is 1 wt % or higher, a structure shown in FIG. 1B is formed, although it depends on what type of the carbon material is used herein.

EXAMPLES

Hereinafter, the disclosure will further be described with reference working examples. However, the disclosure is not limited
to the working example described below. All of reactions described below were carried out under the atmosphere.

Evaluations

In EXAMPLES, heat insulation materials 108 in which carbon materials 114 are included, and heat insulation materials 110 in which carbon materials 114 are included were prepared, and the heat insulation materials 108 and 110 were subjected to the following measurement s.

Heat Conductivity Measurement

For measurement of heat conductivity, a heat flowmeter HFM 436 Lamda (manufactured by NETZCH), and a TIM tester (manufactured by Analysys Tech) were employed.

UL94 Vertical Combustion Test

UL94 vertical combustion tests were further carried out to evaluate flame retardance of heat insulation materials 108 and 110. “UL” refers to standards for safeness associated with electric equipment, and the standards were established and approved by UNDERWRITERS LABORATORIES INC. in the United States. Accreditation by UL has even been recognized as proof of safeness. UL has been applied to various products such as electric products, fire prevention equipment, plastic materials, lithium batteries, and electric car-associated equipment. The category of UL94 refers to “tests for flammability of plastic materials for appliances and parts in devices”, and there are two types of tests, namely the horizontal flammability test and the vertical flammability test. In the UL94 vertical combustion test, which were carried out for EXAMPLES, samples prepared in predetermined sizes are vertically retained, the tips of the samples are then burned with a burner for a predetermined period of time, and pass/fail is determined based on afterflame times.

Differential Scanning Calorimetry (DSC)

Differential scanning calorimetry (DSC) was carried out for silica xerogels 115, including carbon materials 114, present in surface layers of heat insulation materials 108, and silica xerogels 115 present in surface layers of heat insulation materials 110, and pyrolysis temperatures of organic modifying groups were compared.

Cone Calorimeter-Based Exothermic Test

The cone calorie meter exothermic test has been employed as a fire retardant material test provided in the Japanese Building Standards Act. This test has widely been acknowledged as a testing method involving combustion of materials, across the world. According to this test method, various combustion parameters such as heat release rates, and combustion times can be measured, and therefore, combustion phenomena can be quantified.
In the test, while samples 10 cm square are exposed to radiation heat of 50 kW/m², the samples were burned using an electric spark serving as an ignition source. Heat release rates over time, gross calorific values from start to completion of combustion, combustion times, etc. are obtained, and these parameters were evaluated.
Specifically, with regards to technical standards for fire retardant materials defined in the Order for Enforcement of the Building Standards Act, an exothermic test using a cone calorimeter complying with ISO5660-1ISO5660, ASTM E1354, and NFPA 264A were carried out.
A mechanism for measurements in the cone calorimeter-based exothermic test will be described. In this test, heat release rates and calorific values are obtained based on a method called “oxygen consumption method.” Amounts of heat releases that are caused by combustion significantly vary with types of materials in terms of weights of burning materials. However, amounts of heat releases that are caused by combustion is expressed as a constant value regardless of types of materials, when they are considered in terms of weights of consumed oxygen (13.1 MJ per 1 kg of oxygen), and the cone calorimeter-based exothermic test is based on this insight. That is, by accurately measuring amounts of consumed oxygen in combustions, burning phenomena are quantified.
Detailed conditions for examples and comparative examples will be described below. Also, the conditions and evaluation results were shown in FIG. 7. In FIG. 7, GO refers to Graphene Oxide; CB refers to Carbon Black; SWCNT refers to Single Walled Carbon Nanotube; and PEDOT: PSS refers to Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate).

Acceptance Standards

(i) Evaluations on Heat Conductivity

For heat conductivities of heat insulation materials 108, samples that exhibited heat conductivities of 0.024 W/mK or less were considered as acceptable. It has been recognized that heat conductivity of still air at ordinary temperature is about 0.026 W/mK. Therefore, in order to effectively insulate flows of heat, heat insulation materials 108 need to have heat conductivities smaller than the heat conductivity of still air.
Therefore, an acceptance standard for heat conductivities of heat insulation materials 108 was determined to be 0.024 W/mK or lower, where 0.024 W/mK is about 10% lower than the heat conductivity of still air. When the heat conductivity is higher than 0.024 W/mK, the heat conductivity is not very different from the heat conductivity of still air, and therefore, superiority to the air heat insulation will be deteriorated.

(ii) Decomposition Temperatures of Organic Modifying Groups

For thermal decomposition temperatures, 400° C. or higher was considered as acceptable. If decomposition temperature of organic modifying groups were lower than 400° C., large amounts of trimethyl silanol serving as a flammable gas were easily produced, and this could cause ignition.
(iii) Evaluations on Flame Retardancy
In the UL94 vertical flammability test, V0 was considered as acceptable. That is, in the UL94 flammability test, V0, which is the strictest criterion, was considered as acceptable, while V1, V2, and flammable were considered as unacceptable. The same testing method was employed for three types of criteria, V0, V1 and V2. That is, bottom edges of samples that were vertically retained were brought into contact with flames generated from gas burners for 10 seconds. If burning phenomena stopped within 30 seconds, the samples were further brought into contact with flames for another 10 seconds. Evaluation criteria for V0, V1, and V2 will be shown below.

(Evaluation Criteria)

V-0:

After any of occasions of flame contact, there are no samples that continue to burn for 10 seconds or more.
For ten flame contacts of five samples, the total combustion times do not exceed 50 seconds.
There are no samples that burn to positions where the fixing clamps are present.
There are no samples that drop burning particles causing ignition of absorbent cottons placed below the samples.
After second flame contact, there are not samples that continue to glow for 30 second or more.

Samples satisfying these conditions were graded as V-0.

V-1:

After any of occasions of flame contact, there are no samples that continue to burn for 30 seconds or more.
For ten flame contacts of five samples, the total combustion times do not exceed 250 seconds.
There are no samples that burn to positions where the fixing clamps are present.
There are no samples that drop burning particles causing ignition of absorbent cottons placed below the samples.
After second flame contact, there are not samples that continue to glow for 60 second or more.

Samples satisfying these conditions were graded as V-1.

V-2:

After any of occasions of flame contact, there are no samples that continue to burn for 30 seconds or more.
For ten flame contacts of five samples, the total combustion times do not exceed 250 seconds.
There are no samples that burn to positions where the fixing clamps are present.
Dropping of burning particles are tolerated.
After second flame contact, there are not samples that continue to glow for 60 second or more.

Samples satisfying these conditions were graded as V-2.

(iv) Cone Calorimeter-Based Exothermic Test

For the cone calorimeter-based exothermic test, samples that exhibited combustion times of 10 seconds or less, and peak heat release rates (HRR) of 15 kW/m²or less in the flame retardant material test (20 minutes) were considered as acceptable.

(v) Comprehensive Evaluations

Samples that satisfied all of the conditions were considered as acceptable in the comprehensive evaluations.

Overall

EXAMPLES 1 to 8 correspond to heat insulation materials 108 having the structure shown in FIG. 1A or FIG. 1B. COMPARATIVE EXAMPLES 1 and 2 correspond to conventional heat insulation materials having a one-layer structure. Conventional heat insulation materials only have one layer made of unwoven fabric fibers 116 and a silica xerogel 115. COMPARATIVE EXAMPLE 3 have only unwoven fabric fibers 116. COMPARATIVE EXAMPLE 3 corresponds to a heat insulation material in which the unwoven fabric fibers 116 are made of glass papers. Concentrations mentioned below refer to percentages by weight.

Example 1

Self-dispersible type oxidated graphene (SIGMA-ALDRICH, 4 mg/ml in H₂O) and water were added to water glass (TOSO SANGYO CO., LTD.) to prepare a starting material (SiO₂concentration: 6%, oxidative graphene GO concentration: 0.1%). To 20.5 g of this dispersion was added 3.6 parts by weight (0.74 g) of concentrated hydrochloric acid serving as an acid catalyst, and the resulting mixture was stirred to prepare a sol solution.
Subsequently, by pouring the sol solution into unwoven fabric fibers 116 (material: glass paper; thickness: 600 um; weight per area: 100 g/m²; dimension: 12 cm square), the sol solution was impregnated into the unwoven fabric fibers 116. The unwoven fabric fibers 116 impregnated with the sol solution were held between PP films (50 um thick×2 pieces), and allowed to stand at room temperature (23° C.) for three minutes, so as to convert the sol into a gel. After it was confirmed that the sol was gelatinized, the impregnated unwoven fabric fibers 116, which were placed between the films, into a dual-axis roll in which the gap was set to 1.00 mm (including the film thicknesses), excess gel was squeezed out of the unwoven fabric fibers 116, and thus, the thickness was controlled so as to be 1.00 mm.
Then, the films were peeled, and the gel sheet was immersed in aqueous hydrochloric acid (6 N). Then, by allowing the sample to stand at room temperature (23° C.) for 5 minutes, the gel sheet was allowed to absorb the hydrochloric acid. Subsequently, the gel sheet was immersed in a mixture of octamethyltrisiloxane, which serves as a silylating agent, and 2-propanol (IPA). This was put into a thermostatic chamber at 55° C., and was caused to react for 2 hours. When trimethylsiloxane bonds started to form, aqueous hydrochloric acid was discharged from the gel sheet, and a state of two liquid separation was observed (siloxane in the upper phase, and aqueous hydrochloric acid/2-propanol in the lower phase.) The gel sheet was transferred into a thermostatic chamber 150° C., and was dried in the atmosphere for 2 hours to obtain the sheet.
As a result, a heat insulation material 108 having a mean thickness of 0.89 mm, and a heat conductivity of 0.019 W/mK was obtained. In this case, a filling rate of the silica xerogel 115 was 45.5 wt %. In the UL94 vertical combustion test, the sample was graded as V0. As a result of the DSC measurement, the thermal decomposition temperature (exothermic peak) of organic modifying groups was above 550° C., and thus, the high temperature side was shifted by more than 190° C., compared with cases in which any carbon materials 114 were not included. For the cone calorimeter-based exothermic test, the combustion time was zero seconds, and the peak heat release rate was 2.5 kW/m²in the flame retardant material test for 20 minutes.

Example 2

Self-dispersible type oxidated graphene (SIGMA-ALDRICH, 4 mg/ml in H₂O) and water were added to a water glass aqueous solution (TOSO SANGYO CO., LTD.) to prepare a starting material (SiO₂concentration: 6%; oxidated graphene GO concentration: 0.5%). A sheet was prepared based on the same process conditions as EXAMPLE 1 except that the concentration of the oxidated graphene was increased to 0.5%.
As a result, a heat insulation material 108 having a mean thickness of 0.88 mm, and a heat conductivity of 0.020 W/mK was obtained. In this case, a filling rate of the silica xerogel 115 was 44.6 wt %. In the UL94 vertical combustion test, the sample was graded as V0. As a result of the DSC measurement, the thermal decomposition temperature (exothermic peak) of organic modifying groups was above 550° C., and thus, the high temperature side was shifted by more than 190° C., compared with cases in which any carbon materials 114 were not included. For the cone calorimeter-based exothermic test, the combustion time was zero seconds, and the peak heat release rate was 1.36 kW/m²in the flame retardant material test for 20 minutes.

Example 3

Self-dispersible type carbon black (TOKAI CARBON CO., LTD., Aqua black 162, and 19.2 wt % in H₂O) and water were added to a water glass aqueous solution (TOSO SANGYO CO., LTD.) to prepare a starting material (SiO₂concentration: 6%; carbon black CB concentration: 0.1%). To 20.5 g of this dispersion was added 3.6 parts by weight (0.74 g) of concentrated hydrochloric acid serving as an acid catalyst, and the mixture was stirred to prepare a sol solution. A sheet was prepared based on the same process conditions as EXAMPLE 1 except that the carbon material was switched to the carbon black.
As a result, a heat insulation material 108 having a mean thickness of 0.88 mm, and a heat conductivity of 0.019 W/mK was obtained. In this case, a filling rate of the silica xerogel 115 was 45.9 wt %. In the UL94 vertical combustion test, the sample was graded as V0. As a result of the DSC measurement, the thermal decomposition temperature (exothermic peak) of organic modifying groups was above 550° C., and thus, the high temperature side was shifted by more than 190° C., compared with cases in which any carbon materials 114 were not included. For the cone calorimeter-based exothermic test, the combustion time was zero seconds, and the peak heat release rate was 1.33 kW/m²in the flame retardant material test for 20 minutes.

Example 4

Self-dispersible type carbon black (TOKAI CARBON CO., LTD., Aqua black 162, and 19.2 wt % in H₂O) and water were added to a water glass aqueous solution (TOSO SANGYO CO., LTD.) to prepare a starting material (SiO₂concentration: 6%; carbon black CB concentration: 0.5%). To 20.5 g of this dispersion was added 3.6 parts by weight (0.74 g) of concentrated hydrochloric acid serving as an acid catalyst, and the mixture was stirred to prepare a sol solution. A sheet was prepared based on the same process conditions as EXAMPLE 3 except that the concentration of the carbon black was increased to 0.5%.
As a result, a heat insulation material 108 having a mean thickness of 0.87 mm, and a heat, conductivity of 0.018 W/mK was obtained. In this case, a filling rate of the silica xerogel 115 was 45.7 wt %. In the UL94 vertical combustion test, the sample was graded as V0. As a result of the DSC measurement, the thermal decomposition temperature (exothermic peak) of organic modifying groups was above 550° C., and thus, the high temperature side was shifted by more than 190° C., compared with cases in which any carbon materials 114 were not included. For the cone calorimeter-based exothermic test, the combustion time was zero seconds, and the peak heat release rate was 1.10 kW/m²in the flame retardant material test for 20 minutes.
FIG. 8 shows an observed SEM image of flame retardant heat insulation materials (composites of unwoven fabric fibers 116 made of glass papers and silica xerogels 115) prepared in EXAMPLE 4 and COMPARATIVE EXAMPLE 1. In EXAMPLE 4, an appearance of carbon materials 114 adsorbed on surfaces of the fibers was confirmed.

Example 5

Single-walled carbon nanotubes SWCNT (SIGMA-ALDRICH), which is PEG-modified to enhance dispersibility, and that served as a carbon material 114, and water were added to a water glass aqueous solution (TOSO SANGYO CO., LTD.) to prepare a starting material. (SiO₂concentration: 6%; SWCNT concentration: 0.1%). To 20.5 g of this dispersion was added 3.6 parts by weight (0.74 g) of concentrated hydrochloric acid serving as an acid catalyst, and the mixture was stirred to prepare a sol solution. A sheet was prepared based on the same process conditions as EXAMPLE 1 except, that the carbon material was switched to SWCNT.
As a result, a heat insulation material 108 having a mean thickness of 0.85 mm, and a heat conductivity of 0.018 W/mK was obtained. In this case, a filling rate of the silica xerogel 115 was 45.5 wt %. In the UL94 vertical combustion test, the sample was graded as V0. As a result of the DSC measurement, the thermal decomposition temperature (exothermic peak) of organic modifying groups was above 550° C., and thus, the high temperature side was shifted by more than 190° C., compared with cases in which any carbon materials 114 were not included. For the cone calorimeter-based exothermic test, the combustion time was 10 seconds, and the peak heat release rate was 14.06 kW/m²in the flame retardant material test for 20 minutes.

Example 6

Single-walled carbon nanotubes SWCNT (SIGMA-ALDRICH), which is PEG-modified to enhance dispersibility, served as a carbon material 114, and water were added to a water glass aqueous solution (TOSO SANGYO CO., LTD.) to prepare a starting material (SiO₂concentration: 6%; SWCNT concentration: 0.5%). To 20.5 g of this dispersion was added 3.6 parts by weight (0.74 g) of concentrated hydrochloric acid serving as an acid catalyst, and the mixture was stirred to prepare a sol solution. A sheet was prepared based on the same process conditions as EXAMPLE 5 except that the concentration of SWCNT was increased in the above-mentioned manner.
As a result, a heat insulation material 108 having a mean thickness of 0.86 mm, and a heat conductivity of 0.018 W/mK was obtained. In this case, a filling rate of the silica xerogel 115 was 45.6 wt %. In the UL94 vertical combustion test, the sample was graded as V0. As a result of the DSC measurement, the thermal decomposition temperature (exothermic peak) of organic modifying groups was above 550° C., and thus, the high temperature side was shifted by more than 190° C., compared with cases in which any carbon materials 114 were not included. For the cone calorimeter-based exothermic test, the combustion time was 10 seconds, and the peak heat release rate was 13.02 kW/m²in the flame retardant material test for 20 minutes.

Example 7

poly(3,4-ethylenedioxythiophene)/polysulfonate (PEDOT: PSS) (SEPLEGYDA AS-Q09 supplied from SHIN-ETSU POLYMER CO., LTD.) that served as a carbon material 114, and water were added to a water glass aqueous solution (TOSO SANGYO CO., LTD.) to prepare a starting material (SiO₂concentration: 6%; PEDOT: PSS concentration: 0.5%). To 20.5 g of this dispersion was added 3.6 parts by weight (0.74 g) of concentrated hydrochloric acid serving as an acid catalyst, and the mixture was stirred to prepare a sol solution. A sheet was prepared based on the same process conditions as EXAMPLE 1 except that the carbon material was switched to PEDOT: PSS.
As a result, a heat insulation material 108 having a mean thickness of 0.86 mm, and a heat conductivity of 0.018 W/mK was obtained. In this case, a filling rate of the silica xerogel 115 was 45.9 wt %. In the UL94 vertical combustion test, the sample was graded as V0. As a result of the DSC measurement, the thermal decomposition temperature (exothermic peak) of organic modifying groups was above 550° C., and thus, the high temperature side was shifted by more than 190° C., compared with cases in which any carbon materials 114 were not included. For the cone calorimeter-based exothermic test, the combustion time was zero seconds, and the peak heat release rate was 1.31 kW/m²in the flame retardant material test for 20 minutes.

Example 8

One part by weight of self-dispersible type carbon black (TOKAI CARBON CO., LTD., Aqua black 162, and 19.2 wt % in H₂O) was added to a water glass aqueous solution (TOSO SANGYO CO., LTD.) to prepare a starting material (SiO₂concentration: 14%; carbon black CB concentration: 1.3%). To 20.5 g of this dispersion was added 1.6 parts by weight (0.33 g) of concentrated hydrochloric acid serving as an acid catalyst, and the mixture was stirred to prepare a sol solution.
Conditions for the impregnation and thickness control were the same as those in EXAMPLE 1, and the sample was heated to 90° C. for five minutes to reinforce the gel skeleton. A sheet was prepared based on the same process conditions as EXAMPLE 1, except that the concentration of hydrochloric acid was changed to 12 N.
As a result, a heat insulation material 108 having a mean thickness of 1.3 mm, and a heat conductivity of 0.018 W/mK was obtained. In this case, a filling rate of the silica xerogel 115 was 67.6 wt %. In the UL94 vertical combustion test, the sample was graded as V0. As a result of the DSC measurement, the thermal decomposition temperature (exothermic peak) of organic modifying groups was above 550° C., and thus, the high temperature side was shifted by more than 190° C., compared with cases in which any carbon materials 114 were not included. For the cone calorimeter-based exothermic test, the combustion time was 14.7 seconds, and the peak heat release rate was 10.94 kW/m²in the flame retardant material test for 20 minutes.

Comparative Example 1

A sheet was prepared based on the same process conditions as those in EXAMPLE 1 except that no self-dispersible oxidated graphene was added to an aqueous water glass serving as a starting material.
As a result, a heat insulation material 107 having a mean thickness of 0.86 mm, and a heat conductivity of 0.019 W/mK was obtained. In this case, a filling rate of the silica xerogel 115 was 45.4 wt %. In the UL94 vertical combustion test, the sample was burned, and thus, was not graded as V0. As a result of the DSC measurement, the thermal decomposition temperature (exothermic peak) of organic modifying groups was low, i.e., 360° C. With regards to a reason why the sample was burned in the combustion test, it was considered that a large amount of flammable gases was produced around 360° C., and this caused ignition. For the cone calorimeter-based exothermic test, the combustion time was 12.7 seconds, and the peak heat release rate was 16.39 kW/m²in the flame retardant material test for 20 minutes. In the comprehensive evaluations, the sample was unacceptable.

Comparative Example 2

A heat insulation sheet was prepared based on the same process conditions as those in EXAMPLE 8 except that no carbon material 114 was added to an aqueous high molar ratio silicate soda (TOSO SANGYO CO., LTD.).
As a result, a heat insulation material 107 having a mean thickness of 1.03 mm, and a heat conductivity of 0.020 W/mK was obtained. In this case, a filling rate of the silica xerogel 115 was 63.0 wt %. In the UL94 vertical combustion test, the sample was burned, and thus, was not graded as V0. As a result of the DSC measurement, the thermal decomposition temperature (exothermic peak) of organic modifying groups was low, i.e., 380° C. With regards to a reason why the sample was burned in the combustion test, it was considered that a large amount of flammable gases was produced around 380° C., and this caused ignition. For the cone calorimeter-based exothermic test, the combustion time was 24.8 seconds, and the peak heat release rate was 28.69 kW/m²in the flame retardant material test for 20 minutes. In the comprehensive evaluations, the sample was unacceptable.

Comparative Example 3

Without combining any silica xerogels 115 with unwoven fabric fibers 116 that had a thickness of 0.600 mm, and a unit weight of 100 g/m²and that were made of glass paper, the heat conductivity was measured. As a result, the heat conductivity was 0.033 W/mK. Furthermore, in the UL94 vertical combustion test, the sample was not burned, and thus, was graded as V0. However, since the heat conductivity was higher than 0.024 W/mK, the sample was unacceptable in the comprehensive evaluations.

Results

(i) Comparison Between Example 4 and Comparative Example 1

FIG. 8 refers to observed scanning electron micrographs of heat insulation materials (composites of unwoven fabric fibers 116 made of glass papers, and silica xerogel 115) prepared in EXAMPLE 4 and COMPARATIVE EXAMPLE 1. In EXAMPLE 1, particles of carbon black are adsorbed onto the surface of unwoven fabric fibers 116. To the contrary, in COMPARATIVE EXAMPLE 1, there are no carbon materials 114 that are adsorbed onto the surface of unwoven fabric fibers 116.

(ii) Overall

In EXAMPLES 1 to 8, heat insulation materials 108 in which carbon materials 114 were localized to around the surfaces were prepared. Thus, the decomposition temperatures were shifted above 400° C. Also, the samples were graded V0 in the UL94 vertical flammability test, and also, it was revealed that their heat, conductivities were very low, i.e., below 0.024 W/mK.
Furthermore, the samples were subjected to flame retardant material test (20 minutes) in the cone calorimeter-based exothermic test.
As a result, the heat insulation materials in COMPARATIVE EXAMPLES 1 and 2 in which any carbon materials were included exhibited a peak heat release rate (HRR) higher than 15 kW/m², or a combustion time exceeding 15 seconds, and did not satisfy both of these requirements. To the contrary, EXAMPLES 1 to 8 in which 0.1 wt % or more of carbon materials were included exhibited peak heat release rates (HRR) lower than 15 kW/m², and combustion times less than 15 seconds, and thus, satisfied both of these requirements. With regards to types of carbon materials 114, it was revealed that carbon black, oxidated graphene, single-walled carbon nanotubes, and PEDOT: PSS are effective, and that preferable amounts of these materials are 0.1 wt % to 1.3 wt %.

(Throughout the Whole of the Disclosure)

It should be noted that the disclosure is not limited to the structures shown in FIGS. 1A and 1B as long as the three-component composite layer 103 can produce effects of heat insulation materials and can solve the above-mentioned objectives.
The disclosure will be employed in a wide range of fields since the heat insulation material according to the disclosure can produce sufficient heat insulation effects even in narrow spaces inside electronic devices, in-vehicle devices, and industrial devices. The disclosure is applicable to all types of products associated with heat (i.e., information devices, portable devices, displays, and electric components).

Claims

What is claimed is:

1. A heat insulation material, comprising:

a silica xerogel;

a carbon material; and

unwoven fabric fibers that retains the silica xerogel, and the carbon material.

2. The heat insulation material according to claim 1, wherein the heat insulation material exhibits a combustion time of 15 seconds or less, and a maximum heat generation rate of 15 kW/m or less, in a cone calorimeter-based exothermic test.

3. The heat insulation material according to claim 1, wherein the carbon material reacts with oxygen in the atmosphere at a temperature (i) where the silica xerogel is thermally decomposed, or at a temperature (ii) higher than the temperature (i), to produce carbon dioxide.

4. The heat insulation material according to claim 1, wherein the carbon material is carbon black.

5. The heat insulation material according to claim 1, wherein the carbon material includes at least one condensed ring compound having aromaticity.

6. The heat insulation material according to claim 1, wherein the carbon material has a mean particle size of 50 nm to 500 nm.

7. The heat insulation material according to claim 1, wherein a concentration of the carbon material is from 0.01 wt % to 10 wt %.

8. The heat insulation material according to claim 1, comprising:

a three-component composite layer that includes the silica xerogel, the carbon material, and the unwoven fabric fibers;

a two-component composite layer that is placed on one side of the three-component composite layer, that does not include a same type of unwoven fabric fibers as the unwoven fabric fibers of the three-component composite layer, and that includes a same type of silica xerogel as the silica xerogel of the three-component composite layer, and a same type of carbon material as the carbon material of the three-component composite layer; and

a monolayer that is placed on an other side of the three-component composite layer, and that includes a same type of silica xerogel as the silica xerogel of the three-component composite layer.

9. The heat insulation material according to claim 1, further comprising:

a three-component composite layer that includes a same type of silica xerogel, and a same type of unwoven fabric fibers; and

two-component composite layers that are placed on both sides, respectively, of the three-component composite layer, that does not include a same type of unwoven fabric fibers, and that includes a same type of silica xerogel, and a same type of carbon material.

10. A device, comprising the heat insulation material according to claim 1, wherein said heat insulation material serves as a part of a heat-insulation or refrigeration structure, or is placed between a heat-producing component and a casing.