U.S. patent application number 16/198236 was filed with the patent office on 2019-06-13 for heat insulator.
The applicant listed for this patent is Panasonic Intellectual Property Management Co., Ltd.. Invention is credited to HIROHISA HINO, TAICHI NAKAMURA, KAZUMA OIKAWA, SHIGEAKI SAKATANI.
Application Number | 20190177911 16/198236 |
Document ID | / |
Family ID | 66629275 |
Filed Date | 2019-06-13 |
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United States Patent
Application |
20190177911 |
Kind Code |
A1 |
HINO; HIROHISA ; et
al. |
June 13, 2019 |
HEAT INSULATOR
Abstract
A heat insulator is provided that has a coating structure
preventing separation of silica aerogel in a composite sheet. The
heat insulator includes: a composite layer having silica aerogel
enclosed in a nonwoven fabric; and a coating film containing a
hydrophilic resin and a lipophilic resin and coating a surface of
the composite layer. The nonwoven fabric resides in the coating
film. In the coating film, the heat insulator includes the
lipophilic resin which is present in the hydrophilic resin in the
form of a plurality of islands.
Inventors: |
HINO; HIROHISA; (Osaka,
JP) ; NAKAMURA; TAICHI; (Osaka, JP) ; OIKAWA;
KAZUMA; (Osaka, JP) ; SAKATANI; SHIGEAKI;
(Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Intellectual Property Management Co., Ltd. |
Osaka |
|
JP |
|
|
Family ID: |
66629275 |
Appl. No.: |
16/198236 |
Filed: |
November 21, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D06M 15/507 20130101;
D06N 3/12 20130101; D06N 2209/065 20130101; D06N 3/0011 20130101;
D06N 3/0059 20130101; D06M 2400/02 20130101; D06M 15/55 20130101;
F16L 59/06 20130101; D06M 11/79 20130101; F16L 59/00 20130101; B32B
5/16 20130101 |
International
Class: |
D06N 3/00 20060101
D06N003/00; D06N 3/12 20060101 D06N003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 8, 2017 |
JP |
2017-235639 |
Claims
1. A heat insulator comprising: a composite layer having silica
aerogel enclosed in a nonwoven fabric; and a coating film
containing a hydrophilic resin and a lipophilic resin and coating a
surface of the composite layer.
2. The heat insulator according to claim 1, wherein the nonwoven
fabric resides in the coating film.
3. The heat insulator according to claim 1, wherein the lipophilic
resin is present in the hydrophilic resin in the form of a
plurality of islands.
4. The heat insulator according to claim 3, wherein the nonwoven
fabric is lipophilic, and resides on the lipophilic resin present
in the form of islands.
5. The heat insulator according to claim 1, wherein the hydrophilic
resin is a hydrophilic coating material-base resin.
6. The heat insulator according to claim 1, wherein the lipophilic
resin is a thermosetting resin.
7. The heat insulator according to claim 1, wherein the hydrophilic
resin is a hydrophilic polyester resin, and the lipophilic resin is
an epoxy resin.
8. The heat insulator according to claim 1, wherein the coating
film has a thickness of 1 to 100 .mu.m.
9. The heat insulator according to claim 3, wherein the plurality
of islands each have a diameter of 0.1 to 50 .mu.m.
10. The heat insulator according to claim 1, wherein the lipophilic
resin is 5 to 50 weight % of the coating film.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a heat insulator,
particularly to a heat insulator having a surface coating film.
BACKGROUND
[0002] There is an ongoing trend for lighter, thinner, and higher
performance mobile devices. A user of a mobile device usually holds
and operates the device with a hand for certain lengths of time. It
is accordingly important for a mobile device to keep low surface
temperature.
[0003] A method is available that prevents temperature increase of
a mobile device surface with a heat insulator installed directly
above a heat generating component of a mobile device. Silica
aerogel, one of many heat insulators currently available, is a
material having high heat insulating performance.
[0004] Silica aerogel is known as a nanoporous material having a
porosity of 90% or more. In terms of aging and heat resistance,
silica aerogel is more desirable than other heat insulators, and
has a desirable thermal conductivity of about 15 mW/mK. However,
silica aerogel lacks high mechanical strength because of its
network structure of fine point-contact silica particles of several
tens of nanometers. In order to overcome the weakness of silica
aerogel, Oikawa et al. has proposed to improve strength by forming
a sheet of silica aerogel with other materials such as a fiber, a
nonwoven fabric, and a resin.
[0005] The network structure of fine silica aerogel particles is
intrinsically weak, and there are cases where the individual
particles break away from the network structure of silica aerogel.
These free silica aerogel particles float inside a mobile device,
and cause malfunctions in the device.
[0006] A common approach to preventing this drawback is to enclose
and pack a silica aerogel composite sheet by covering it with
laminate films (hereinafter, referred to as "laminate packing"), as
disclosed in, for example, Japanese Patent Number 6064149.
[0007] However, the method of related art involves the following
problem. Laminate packing is essentially a custom-made process made
to individual shapes and sizes, and greatly increases cost. This
pushes up the cost of the product mobile device, and the product
loses some competitiveness in the market.
SUMMARY
[0008] The present disclosure is intended to provide a solution to
the foregoing problem of related art, and it is an object of the
present disclosure to provide a silica aerogel-containing heat
insulator without using laminate packing.
[0009] According to an aspect of the disclosure, a heat insulator
is used that includes: a composite layer having silica aerogel
enclosed in a nonwoven fabric; and a coating film containing a
hydrophilic resin and a lipophilic resin and coating a surface of
the composite layer.
[0010] With the coating structure of the nonwoven fabric-silica
aerogel composite layer of the aspect of the disclosure, a
protective film can be formed on the silica aerogel composite layer
by applying a coating material to a surface of the silica aerogel
composite layer, regardless of the shape of the coating applied
portion. The film has high adhesion, and can provide a heat
insulator having excellent heat insulation. A device using such a
heat insulator, and a method for forming a coating structure for
such a heat insulator also can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1A is a cross sectional view of a heat insulator formed
by applying a coating material of an embodiment.
[0012] FIG. 1B is a plan view of a coating film of the
embodiment.
[0013] FIG. 2 is a diagram showing an appearance of the coating
film of the embodiment.
DESCRIPTION OF EMBODIMENTS
[0014] An embodiment of the present disclosure is described below,
with reference to the accompanying drawings.
[0015] FIG. 1A shows a cross section of a heat insulator 110 with
an applied coating according to an embodiment. FIG. 1B is a plan
view of a coating film of the embodiment. FIG. 2 is a diagram
showing an appearance of the coating film of the embodiment.
[0016] Heat insulator 110 has a structure in which coating film 111
is formed around composite layer 102 of nonwoven fabric 106 and
silica aerogel 105. The fibers of nonwoven fabric 106 sticking out
of composite layer 102 are adhering to hydrophilic resin 112 and
reactive lipophilic resin 113 in coating film 111.
[0017] Composite Layer 102
[0018] Composite layer 102 is a sheet enclosing silica aerogel 105
of a nanosize porous structure in the nonwoven fabric 106 having a
thickness of 0.05 to 1.0 mm. The thermal conductivity is 0.01 to
0.1 W/mK.
[0019] The thermal conductivity of nonwoven fabric 106 is typically
0.030 to 0.060 W/mK, and this value can be regarded as about the
same as the sum of the thermal conductivity of the solid component
of nonwoven fabric 106, and the thermal conductivity of the air
(nitrogen molecules) component present in the spaces of the
nonwoven fabric.
[0020] The low thermal conductivity specified above can be achieved
by enclosing silica aerogel 105 as a low thermal conductivity
material having a commonly agreed thermal conductivity of 0.010 to
0.015 W/mK--in these spaces.
[0021] The thermal conductivity of still air at ordinary
temperature is said to be typically about 0.026 W/mK, and a value
thereof is smaller than the thermal conductivity of nonwoven fabric
106.
[0022] A characteristic of composite layer 102 is that it is a
sheet having a smaller thermal conductivity than still air.
[0023] Composite layer 102 has water repellency and sound
absorbability, in addition to heat insulation. Composite layer 102
also can be imparted with heat resistance and flame retardancy by
appropriately selecting the type of nonwoven fabric 106.
[0024] In the present embodiment, an oxidized acryl is used as
nonwoven fabric 106 to impart heat resistance and flame retardancy.
It is, however, possible to use glass fiber paper.
Thermal Conductivity of Composite Layer 102
[0025] Composite layer 102 used in the present embodiment has a
thermal conductivity of 0.01 to 0.1 W/mK. The heat insulating
effect of composite layer 102 increases as the thermal conductivity
becomes smaller, and the thickness needed for composite layer 102
to show the same heat insulating effect can be reduced when the
thermal conductivity is smaller.
[0026] The heat insulating effect becomes smaller when the thermal
conductivity increases above 0.1 W/mK. This is not desirable as it
necessitates thicker composite layer 102 to obtain the necessary
heat insulating effect.
Thickness of Composite Layer 102
[0027] Composite layer 102 has a thickness of 0.05 mm to 2 mm,
preferably 0.5 mm to 1 mm. When composite layer 102 has a thickness
of less than 0.05 mm, the heat insulating effect becomes small in
thickness direction, and the heat conduction across the thickness
from one side to the other side of the layer cannot be desirably
reduced unless a low heat conductive material of extremely low
thermal conductivity (even lower than the lowest thermal
conductivity currently available) is selected.
Method of Production of Composite Layer 102
[0028] An example of a method for producing composite layer 102 is
described below.
(1) Mixing Raw Materials
[0029] A sol solution is prepared by adding 1.4 wt % of
concentrated hydrochloric acid (12 N) as a catalyst to a high-molar
sodium silicate (silicate aqueous solution; Si concentration of
14%), and stirring the mixture.
(2) Impregnation
[0030] The sol solution is poured onto nonwoven fabric 106 (the
material is oxidized acryl; the thickness is 0.4 .mu.m; the basis
weight is 50 g/m.sup.2; and the dimensions are 12 mm.times.12 mm),
and nonwoven fabric 106 is impregnated with the sol solution under
the pressure of rollers.
(3) The nonwoven fabric impregnated with the sol solution is
sandwiched between two PP films (each having a thickness of 40
.mu.m), and allowed to stand at room temperature (23.degree. C.)
for about 20 minutes to transform the sol into a gel.
(4) Thickness Control
[0031] After checking that the gel has formed, nonwoven fabric 106
with the films is passed through a preset gap of 650 .mu.m
(including the film thickness) between two-axis rollers to squeeze
out the excessive gel from nonwoven fabric 106 and achieve a target
thickness of 700 .mu.m.
(5) Curing
[0032] The gel sheet with the films is put in a container, and kept
in a 85.degree. C./85 RH % constant temperature and humidity vessel
for 3 hours to prevent drying, and silica particles are allowed to
grow (through dehydrocondensation reaction of silanol) and form a
porous structure.
(6) Removing Films
[0033] The sheet is taken out of the curing container, and the
films are removed.
(7) Hydrophobization 1 (Dipping in Hydrochloric Acid)
[0034] The gel sheet is dipped in hydrochloric acid (6 to 12 N),
and allowed to stand at ordinary temperature (23.degree. C.) for 1
hour to incorporate hydrochloric acid in the gel sheet.
(8) Hydrophobization 2 (Siloxane Treatment)
[0035] The gel sheet is dipped in, for example, a mixture of
octamethyltrisiloxane (silylation agent) and 2-propanol (IPA;
amphiphatic solvent), and placed in a 55.degree. C. thermostat bath
to allow reaction for 2 hours. As soon as the trimethylsiloxane
bond starts to form, the gel sheet releases hydrochloric acid
water, and the solution separates into two layers (the silylation
agent is on the top, and the hydrochloric acid water is at the
bottom).
(9) Drying
[0036] The gel sheet is transferred to a 150.degree. C. thermostat
bath, and dried for 2 hours.
Coating of Composite Layer 102
[0037] Composite layer 102 is a composite of nonwoven fabric 106
and silica aerogel 105, with some of the fibers of nonwoven fabric
106 sticking out of the surface and end portions. Any method may be
used to form the structure in which the fibers of the nonwoven
fabric 106 are sticking out of composite layer 102, and the method
is not limited.
[0038] As an example, the surface and end portions of composite
layer 102 obtained after the steps (1) to (9) of producing
composite layer 102 above are roughened with, for example, an
adhesive roller or a brush to expose fibers.
[0039] Alternatively, composite layer 102 with sticking fibers may
be obtained without grinding by optimizing the thicknesses of
silica aerogel 105 and nonwoven fabric 106 in such a way as to
expose fibers of nonwoven fabric 106 in the steps of producing the
gel sheet.
Coating Material
[0040] The coating material that coats composite layer 102 is
configured from at least a hydrophilic base coating material, and
thermosetting lipophilic resin 113.
[0041] The mainstream base coating material is a hydrophilic
coating material containing particulate hydrophilic resin 112
dispersed in water solvent. Because of the unique structure
resulting from the hydrophobization, silica aerogel 105 of the
present embodiment, unlike its original form, blends well with
lipophilic resin, and the network structure is destroyed by
blending with lipophilic resin. It is accordingly necessary that
the coating material be basically a hydrophilic material.
[0042] The hydrophilic coating material is required to blend well
with water solvent, and can be classified into a self-emulsion type
having a hydrophilic functional group attached to the skeleton of
hydrophilic resin 112, and a forced-emulsion type in which the
resin is forcibly dispersed with the use of an emulsifier. Examples
of hydrophilic resin 112 as a base material include acrylic resins,
polyurethane resins, polyester resins, epoxy resins, silicone
resins, and fluororesins.
[0043] As to the characteristics of each type of hydrophilic resin
112, acrylic resins typically have desirable properties including
lightfastness, weather resistance, monomer variety, relatively low
cost, colorlessness and transparency, and glossiness.
[0044] Polyurethane resins have different types of bonds within the
molecule, such as urethane bonds and urea bonds, and are configured
from a strongly aggregated hard segment and a flexible soft
segment. This makes polyurethane resins desirable in properties
such as adhesion for a substrate, coating hardness, abrasion
resistance with high elasticity, durability, waterfastness, and
chemical resistance.
[0045] The polyester resins used in the embodiment are alkyd
resins, which have a fatty acid side chain linked by ester linkage
to the main chain of a copolyester or a polyester of reduced
crystallinity. Because the backbone of the main chain has the ester
bond formed by reaction of a carboxyl group with a hydroxyl group,
the polyester resins have high adhesion for a substrate, high
coating strength, and desirable heat resistance.
[0046] The coating materials containing hydrophilic resin 112 as a
base are inferior to common solvent-based coating materials with
respect to the following, for example.
[0047] (1) The coating properties are poor because of the
relatively low molecular weight (mesh structure).
[0048] (2) Because the base of the coating is a hydrophilic group,
the waterfastness is intrinsically poor.
[0049] (3) Because of a lack of crosslinking reaction, the coating
has a small Tg, and the adhesion is poor.
[0050] As a countermeasure against these shortcomings, the coating
material used in the present embodiment has a unique structure in
which thermosetting lipophilic resin 113 is added and finely
dispersed in the form of islands ("island-in-sea structure") in
hydrophilic resin 112.
[0051] Thermosetting lipophilic resin 113 blends well with fibers
of water repellent nonwoven fabric 106, and was found to exhibit
strong adhesion upon being joined to nonwoven fabric 106 and
thermally cured. Various surfactants and alcohols capable of
improving blendability for both hydrophilic resin 112 and
lipophilic resin 113 were found to be effective at finely
dispersing thermosetting lipophilic (=water repellent) resin 113 in
base coating material hydrophilic resin 112. 2-Propanol (IPA) is
one such alcohol. Being an amphiphatic solvent, 2-propanol was
found to be capable of controlling the particle size of the
thermosetting lipophilic resin 113, and the adhesion for fibers of
nonwoven fabric 106 improved when thermosetting lipophilic resin
113 had a smaller particle size.
[0052] Suited as hydrophilic resin 112 used to disperse lipophilic
resin 113 of the present embodiment in the form of islands
(hereinafter, such a structure will be referred to as
"island-in-sea structure") are water-based acrylic resins,
water-based urethane resins, and water-based polyester resins, of
which the water-based polyester resins are most suited.
[0053] A reactive one-component epoxy resin was found to be
suitable as lipophilic resin 113. When adding a lipophilic resin to
a water-based coating material, it is typical to use a hydrophilic
resin having high compatibility with the water-based coating
material. The present embodiment, however, is intended to improve
adhesion for coating film 111 by causing lipophilic resin 113 to
adhere to fibers of nonwoven fabric 106 sticking out of composite
layer 102, and, in order to enable pin-point bonding and
reinforcement of fibers, it is important that lipophilic resin 113
does not dissolve into the water-based coating material. To this
end, a lipophilic one-component epoxy resin needs to be selected,
and finely dispersed in the water-based coating material in the
form of an island-in-sea structure.
Island-in-Sea Structure
[0054] Heat insulator 110 formed upon application of the coating
material has a structure in which fibers of nonwoven fabric 106 are
sticking out of the surface layer of composite layer 102 formed by
attachment and integration of silica aerogel 105 into nonwoven
fabric 106 through aggregation.
[0055] In heat insulator 110, nonwoven fabric 106 binds to coating
film 111, and lipophilic resin 113 is present in coating film 111
by being dispersed in a scattered fashion in the form of an
island-in-sea structure. Coating film 111 has a thickness of
preferably 1 to 100 .mu.m, more preferably 10 to 30 .mu.m. When the
thickness is less than 1 .mu.m, the film strength weakens, and the
film easily breaks. When coating film 111 is thicker than 100
.mu.m, the heat insulating performance deteriorates.
[0056] Lipophilic resin 113 has a particle size of preferably 0.1
.mu.m to 50 .mu.m, and the epoxy content in the coating film is
preferably 5 to 50 weight %.
[0057] When the particle size is less than 0.1 .mu.m,
hydrophilicity increases, and the film becomes weaker. When the
particle size is larger than 50 .mu.m, lipophilic resin 113 adheres
to fibers of nonwoven fabric 106 at fewer points, and the adhesion
weakens.
[0058] When the epoxy content (lipophilic resin 113) in coating
film 111 is less than 5 weight %, lipophilic resin 113 contacts
fibers of nonwoven fabric 106 at fewer contact points, and the
adhesion weakens.
[0059] When the epoxy content is higher than 50 weight %,
lipophilic resin 113 readily blends with lipophilic silica aerogel
105, and destroys the fine structure of silica aerogel 105. This
leads to poor heat insulation. The epoxy content is further
preferably 10 to 30 weight %.
EXAMPLES
[0060] Examples of hydrophilic resin 112 and thermosetting
lipophilic resin 113 used in the embodiment are described below. It
is to be noted that the heat insulator structure presented in the
embodiment is not limited to the following exemplary materials.
[0061] A hydrophilic polyester resin Pluscoat Z-880 (Goo Chemical
Co., Ltd.) was used as hydrophilic resin 112. A Novacure HX3941HP
(Asahi Kasei) was used as thermosetting lipophilic resin 113.
2-Propanol (IPA) (amphiphatic solvent) was used as a
compatibilizing agent.
(1) Exemplary Composition of Coating Material Forming Island-in-Sea
Structure
(a) Hydrophilic Resin 112
[0062] Water-based polyester resin Pluscoat Z-880 (solid content of
25 wt %): 100 parts
(b) Lipophilic Resin 113
[0063] One-component epoxy resin Novacure HX3941HP (imidazole
fraction=1/3 wt %, epoxy fraction=2/3 wt %): 10 parts
(c) Compatibilizing Agent
[0064] 2-Propanol (IPA): 10 parts
(2) Production of Coating Material
[0065] The components (a) to (c) were weighed, and mixed and
stirred with a disper for 15 minutes to make a coating material for
forming an island-in-sea structure.
(3) Application of Coating Material
[0066] The coating material is applied by printing on composite
layer 102 having fibers of nonwoven fabric 106 sticking out of the
surface portion, using a printing mask and a squeegee. After
application, the coating material is heat cured to form coating
film 111.
[0067] Coating film 111 may cover the whole composite layer 102
with the coating material applied to not only the surface portion
but end portions of composite layer 102. All surfaces of the
composite layer 102 can be coated by applying the coating material
to both surfaces and end portions in the same fashion.
[0068] When the area to be coated is small, composite layer 102 may
be completely dipped in the coating material using a dipping
method.
(4) Curing of Coating Material
[0069] Composite layer 102 after the application of the coating
material to both surfaces is dried in a 120.degree. C. thermostat
bath for 15 minutes. This causes water to evaporate, and the
particles of the epoxy resin (lipophilic resin 113) to cure in a
curing reaction, forming coating film 111.
(5) Shape of Coating Film 111
[0070] Coating film 111 had a thickness of 30 .mu.m, and
thermosetting lipophilic resin 113 had a particle size of 5 .mu.m.
The particle fraction of thermosetting lipophilic resin 113 was
about 20%.
Structure and Properties of Composite Layer 102 Coated with Coating
Material
[0071] Nonwoven fabric 106 of composite layer 102 had some of its
fibers sticking out of the surface layer of composite layer 102,
and these fibers, which are lipophilic, blended well with
lipophilic resin 113 of coating film 111 in the outermost layer,
and strongly bonded itself to lipophilic resin 113 in a reaction
that provided excellent adhesion.
[0072] In coating film 111, reactive lipophilic resin 113 is
dispersed in the form of islands in an island-in-sea structure, and
strong adhesion occurs as lipophilic resin 113 chemically reacts
with fibers of nonwoven fabric 106.
[0073] In some applications, the heat insulating effect of heat
insulator 110 is exploited by placing heat insulator 110 over a
curved surface of a heat generating component. Here, the base
polyester resin is flexible, and the foregoing structure provides
high adhesion. This prevents detachment of coating film 111 from
composite layer 102, and heat insulator 110 can exhibit desirable
heat insulating performance. The fine particles of silica aerogel
105 enclosed in composite layer 102 also can be prevented from
being exposed on the surface.
Adhesion Force Between Composite Layer 102 and Coating Resin
Film
[0074] Coating film 111 measuring 10 mm in width and 30 .mu.m in
thickness was formed on composite layer 102, and tensile strength
was measured using a 90-degree peeling method.
(a) 0.7 N with no sticking nonwoven fabric 106 (b) 5.5 N with
sticking nonwoven fabric 106 (c) 2.3 N with no thermosetting resin
in (b)
Thermal Conductivity of Heat Insulator 110
[0075] Heat insulator 110 formed by coating a 30 .mu.m-thick
coating film 111 on composite layer 102 had a thermal conductivity
of 0.07 W/mK, confirming that heat insulator 110 had excellent heat
insulating performance comparable to that of composite layer 102
alone.
[0076] The heat insulator of the embodiment can prevent separation
of silica aerogel particles, and, because the heat insulating
performance is maintained, the heat insulator can be used for heat
insulating purposes in applications such as in mobile devices.
* * * * *