U.S. patent application number 15/816229 was filed with the patent office on 2018-06-07 for heat insulation material and device using same.
The applicant listed for this patent is Panasonic Intellectual Property Management Co., Ltd.. Invention is credited to DAIDO KOHMYOHJI, KAZUMA OIKAWA, TATSUHIRO OOSHIRO, SHIGEAKI SAKATANI, KEI TOYOTA, TOORU WADA.
Application Number | 20180156550 15/816229 |
Document ID | / |
Family ID | 62163699 |
Filed Date | 2018-06-07 |
United States Patent
Application |
20180156550 |
Kind Code |
A1 |
OIKAWA; KAZUMA ; et
al. |
June 7, 2018 |
HEAT INSULATION MATERIAL AND DEVICE USING SAME
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.
Inventors: |
OIKAWA; KAZUMA; (Osaka,
JP) ; TOYOTA; KEI; (Osaka, JP) ; SAKATANI;
SHIGEAKI; (Osaka, JP) ; KOHMYOHJI; DAIDO;
(Nara, JP) ; OOSHIRO; TATSUHIRO; (Hokkaido,
JP) ; WADA; TOORU; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Intellectual Property Management Co., Ltd. |
Osaka |
|
JP |
|
|
Family ID: |
62163699 |
Appl. No.: |
15/816229 |
Filed: |
November 17, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28F 21/04 20130101;
F28F 21/02 20130101; F16L 59/06 20130101; F16L 59/029 20130101;
C09K 21/02 20130101; F28F 2270/00 20130101; F16L 59/145 20130101;
F28F 13/003 20130101 |
International
Class: |
F28F 13/00 20060101
F28F013/00; F28F 21/04 20060101 F28F021/04; F28F 21/02 20060101
F28F021/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 2016 |
JP |
2016-235629 |
Sep 6, 2017 |
JP |
2017-170791 |
Claims
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.
Description
TECHNICAL FIELD
[0001] 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
[0002] 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.
[0003] 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.degree. C. They have been problematic when employed in a high
temperature range (e.g., 100.degree. 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.
[0004] 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
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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
[0010] FIGS. 1A and 1B are cross-section views of flame retardant
heat insulation materials according to embodiments.
[0011] FIG. 2 is a diagram that shows a two-component layer
including a silica xerogel and a carbon material in an
embodiment.
[0012] FIG. 3 is a three-component composite layer including a
silica xerogel, a carbon material, and unwoven fabric fibers in an
embodiment.
[0013] FIGS. 4A to 4F are diagrams that shows carbon materials in
embodiments.
[0014] FIG. 5 is a diagram that describes a method for producing a
flame retardant heat insulation material according to an
embodiment.
[0015] 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.
[0016] FIG. 7 is a diagram that shows detailed conditions and
evaluation results for examples and comparative examples.
[0017] 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
[0018] Next, embodiments according to the disclosure will be
described with reference to one preferable embodiment.
Examples of Structures of Heat Insulation Materials 108
[0019] FIGS. 1A and 1B shows cross-section views of heat insulation
materials 108 according to embodiments.
[0020] 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.
[0021] The three-component composite layer 103 includes a silica
xerogel 115, a carbon material 114, and unwoven fabric fibers
116.
[0022] 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.
[0023] The one-component single layer 101 is formed of the silica
xerogel 115.
[0024] 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.
[0025] The role of each layer will be described below.
[0026] 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.
[0027] 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 O.sub.2 present in the atmosphere,
thereby producing a larger amount of CO.sub.2. The produced
CO.sub.2 dilutes combustible gases, and contributes to flame
retardancy.
[0028] 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.
[0029] 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.
[0030] 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 CO.sub.2 will be produced from the either
side. Thus, effective flame retardancy can be delivered.
[0031] 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.
[0032] Components found in FIGS. 1A and 1B are shown in Tables 1
and 2, respectively.
TABLE-US-00001 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-US-00002 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
[0033] 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
[0034] 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.
[0035] 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.
[0036] 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.
[0037] Furthermore, the carbon material 114 that is located inside
the heat insulation material 108 does not contribute to production
of carbon dioxide.
[0038] 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
[0039] 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
[0040] 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.
[0041] 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.degree. 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.
[0042] 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 m.sup.2/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.degree. C. or
higher, although it depends on the unit weight.
Structure of the Two-Component Composite Layer 102
[0043] The structure of the two-component composite layer 102 is
shown in FIG. 2.
[0044] 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
[0045] 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.degree. C. or higher, the
carbon material 114 reacts with O.sub.2 in the atmosphere so as to
produce CO.sub.2, thereby contributing development of flame
retardancy. That is, the carbon material 114 serves as a flame
retardant.
Carbon Material 114
[0046] The carbon material 114 used in the present embodiment has
at least one condensed ring compound having aromaticity, and reacts
with O.sub.2 in the atmosphere to produce CO.sub.2, at high
temperature, e.g., 300.degree. C. or higher. With regards to
conditions for the carbon material 114 producing CO.sub.2 at
300.degree. 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.degree. 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 O.sub.2 in the atmosphere. A condensed
ring compound having aromaticity and satisfying these conditions is
preferably employed for the carbon material 114.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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 %.
[0055] 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 .lamda.s 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
[0056] 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.
[0057] 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
[0058] 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.
[0059] 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
[0060] A unit weight of the unwoven fabric fibers 116 may be from 5
g/m.sup.2 to 500 g/m.sup.2. 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
[0061] The bulk density of the unwoven fabric fibers 116 is
preferably within a range from 100 kg/m.sup.3 to 500 kg/m.sup.3 in
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.
[0062] 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/m.sup.3. Furthermore, if the
bulk density of the unwoven fabric fibers 116 is larger than 500
kg/m.sup.3, 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
[0063] 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
[0064] 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.degree. 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.
[0065] 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 m.sup.2/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.degree. C. or higher, although
it depends on the unit weight.
[0066] 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.degree.
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
[0067] An outline of a method for producing the three-component
composite layer 103 is shown in FIG. 5.
(i) Sol Preparation
[0068] 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 (SiO.sub.2 concentration:
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.
[0069] 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.
[0070] 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.
[0071] 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
[0072] The sol solution is poured into unwoven fabric fibers 116
(material: glass papers, thickness specification: 600 um, unit
weight: 110 g/m.sup.2, 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.
[0073] 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
[0074] The unwoven fabric fibers 116 impregnated with the sol
solution is held between PP films (50 um thick.times.2, dimension:
B6), and this is allowed to stand at room temperature (23.degree.
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.degree. C. or higher
and a linear thermal expansion coefficient of 100
(.times.10.sup.-6/.degree. 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
[0075] 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
[0076] 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)
[0077] The gel sheet is immersed in hydrochloric acid (4-12 N), and
then, is allowed to stand at ordinary temperature (23.degree. C.)
for 5 minutes or more, to incorporate hydrochloric acid into the
gel sheet.
(vii) Second Hydrophobization (Siloxane Treatment)
[0078] 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.degree. 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
[0079] The gel sheet is transferred into a thermostatic bath at
150.degree. C., and is dried therein for 2 hours.
[0080] 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
[0081] 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.
[0082] 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.
[0083] 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
[0084] Hereinafter, the disclosure will further be described with
reference working examples. However, the disclosure is not
limited
[0085] to the working example described below. All of reactions
described below were carried out under the atmosphere.
Evaluations
[0086] 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
[0087] 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
[0088] 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)
[0089] 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
[0090] 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.
[0091] In the test, while samples 10 cm square are exposed to
radiation heat of 50 kW/m.sup.2, 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.
[0092] 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.
[0093] 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.
[0094] 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
[0095] 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.
[0096] 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
[0097] For thermal decomposition temperatures, 400.degree. C. or
higher was considered as acceptable. If decomposition temperature
of organic modifying groups were lower than 400.degree. C., large
amounts of trimethyl silanol serving as a flammable gas were easily
produced, and this could cause ignition.
(iii) Evaluations on Flame Retardancy
[0098] 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:
[0099] After any of occasions of flame contact, there are no
samples that continue to burn for 10 seconds or more. [0100] For
ten flame contacts of five samples, the total combustion times do
not exceed 50 seconds. [0101] There are no samples that burn to
positions where the fixing clamps are present. [0102] There are no
samples that drop burning particles causing ignition of absorbent
cottons placed below the samples. [0103] After second flame
contact, there are not samples that continue to glow for 30 second
or more.
[0104] Samples satisfying these conditions were graded as V-0.
V-1:
[0105] After any of occasions of flame contact, there are no
samples that continue to burn for 30 seconds or more. [0106] For
ten flame contacts of five samples, the total combustion times do
not exceed 250 seconds. [0107] There are no samples that burn to
positions where the fixing clamps are present. [0108] There are no
samples that drop burning particles causing ignition of absorbent
cottons placed below the samples. [0109] After second flame
contact, there are not samples that continue to glow for 60 second
or more.
[0110] Samples satisfying these conditions were graded as V-1.
V-2:
[0111] After any of occasions of flame contact, there are no
samples that continue to burn for 30 seconds or more. [0112] For
ten flame contacts of five samples, the total combustion times do
not exceed 250 seconds. [0113] There are no samples that burn to
positions where the fixing clamps are present. [0114] Dropping of
burning particles are tolerated. [0115] After second flame contact,
there are not samples that continue to glow for 60 second or
more.
[0116] Samples satisfying these conditions were graded as V-2.
(iv) Cone Calorimeter-Based Exothermic Test
[0117] 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/m.sup.2 or less in the flame retardant
material test (20 minutes) were considered as acceptable.
(v) Comprehensive Evaluations
[0118] Samples that satisfied all of the conditions were considered
as acceptable in the comprehensive evaluations.
Overall
[0119] 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
[0120] Self-dispersible type oxidated graphene (SIGMA-ALDRICH, 4
mg/ml in H.sub.2O) and water were added to water glass (TOSO SANGYO
CO., LTD.) to prepare a starting material (SiO.sub.2 concentration:
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.
[0121] Subsequently, by pouring the sol solution into unwoven
fabric fibers 116 (material: glass paper; thickness: 600 um; weight
per area: 100 g/m.sup.2; 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.times.2 pieces), and allowed to stand
at room temperature (23.degree. 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.
[0122] 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.degree. 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.degree. 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.degree. C., and was dried in the atmosphere for 2 hours to
obtain the sheet.
[0123] 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.degree. C., and thus, the high temperature
side was shifted by more than 190.degree. 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/m.sup.2 in the
flame retardant material test for 20 minutes.
Example 2
[0124] Self-dispersible type oxidated graphene (SIGMA-ALDRICH, 4
mg/ml in H.sub.2O) and water were added to a water glass aqueous
solution (TOSO SANGYO CO., LTD.) to prepare a starting material
(SiO.sub.2 concentration: 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%.
[0125] 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.degree. C., and thus, the high temperature
side was shifted by more than 190.degree. 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/m.sup.2 in the
flame retardant material test for 20 minutes.
Example 3
[0126] Self-dispersible type carbon black (TOKAI CARBON CO., LTD.,
Aqua black 162, and 19.2 wt % in H.sub.2O) and water were added to
a water glass aqueous solution (TOSO SANGYO CO., LTD.) to prepare a
starting material (SiO.sub.2 concentration: 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.
[0127] 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.degree. C., and thus, the high temperature
side was shifted by more than 190.degree. 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/m.sup.2 in the
flame retardant material test for 20 minutes.
Example 4
[0128] Self-dispersible type carbon black (TOKAI CARBON CO., LTD.,
Aqua black 162, and 19.2 wt % in H.sub.2O) and water were added to
a water glass aqueous solution (TOSO SANGYO CO., LTD.) to prepare a
starting material (SiO.sub.2 concentration: 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%.
[0129] 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.degree. C., and thus, the high temperature
side was shifted by more than 190.degree. 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/m.sup.2 in the
flame retardant material test for 20 minutes.
[0130] 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
[0131] 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.
(SiO.sub.2 concentration: 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.
[0132] 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.degree. C., and thus, the high temperature
side was shifted by more than 190.degree. 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/m.sup.2 in the
flame retardant material test for 20 minutes.
Example 6
[0133] 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
(SiO.sub.2 concentration: 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.
[0134] 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.degree. C., and thus, the high temperature
side was shifted by more than 190.degree. 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/m.sup.2 in the
flame retardant material test for 20 minutes.
Example 7
[0135] 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 (SiO.sub.2 concentration: 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.
[0136] 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.degree. C., and thus, the high temperature
side was shifted by more than 190.degree. 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/m.sup.2 in the
flame retardant material test for 20 minutes.
Example 8
[0137] One part by weight of self-dispersible type carbon black
(TOKAI CARBON CO., LTD., Aqua black 162, and 19.2 wt % in H.sub.2O)
was added to a water glass aqueous solution (TOSO SANGYO CO., LTD.)
to prepare a starting material (SiO.sub.2 concentration: 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.
[0138] Conditions for the impregnation and thickness control were
the same as those in EXAMPLE 1, and the sample was heated to
90.degree. 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.
[0139] 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.degree. C., and thus, the high temperature
side was shifted by more than 190.degree. 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/m.sup.2 in the
flame retardant material test for 20 minutes.
Comparative Example 1
[0140] 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.
[0141] 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.degree. 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.degree. 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/m.sup.2 in the flame retardant material test for 20 minutes. In
the comprehensive evaluations, the sample was unacceptable.
Comparative Example 2
[0142] 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.).
[0143] 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.degree. 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.degree. 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/m.sup.2 in the flame retardant material test for 20 minutes. In
the comprehensive evaluations, the sample was unacceptable.
Comparative Example 3
[0144] 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/m.sup.2 and 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
[0145] 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
[0146] 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.degree. 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.
[0147] Furthermore, the samples were subjected to flame retardant
material test (20 minutes) in the cone calorimeter-based exothermic
test.
[0148] 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/m.sup.2,
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/m.sup.2, 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)
[0149] 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.
[0150] 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).
* * * * *