U.S. patent application number 15/564043 was filed with the patent office on 2018-04-05 for nanofiber structure.
This patent application is currently assigned to FUENCE CO., LTD.. The applicant listed for this patent is FUENCE CO., LTD.. Invention is credited to Kozo INOUE, Yutaka NAGASHIMA, Kazuya NITTA, Keizou TANAKA, Shunsuke YAMADA.
Application Number | 20180094362 15/564043 |
Document ID | / |
Family ID | 57006948 |
Filed Date | 2018-04-05 |
United States Patent
Application |
20180094362 |
Kind Code |
A1 |
INOUE; Kozo ; et
al. |
April 5, 2018 |
NANOFIBER STRUCTURE
Abstract
A transparent soluble polyimide resin was dissolved in
N,N-dimethyacetamide, and a sample solution whose concentration was
10 weight percent was produced. This sample solution is put in a
container CNT which is attached to an apparatus shown in FIG. 1,
whereby a nanofiber structure was produced. The produced polyimide
nanofiber structure acquired the excellent water resistance, air
permeability and moisture permeability while maintaining the
physical properties inherent in a polyimide, such as high heat
resistance and insulation. Further, when a nanofiber structure is
produced in a similar manner from a different polyimide resin, the
nanofiber structure maintains excellent adhesiveness.
Inventors: |
INOUE; Kozo; (Wako-shi,
JP) ; NITTA; Kazuya; (Wako-shi, JP) ; TANAKA;
Keizou; (Kimitsu-shi, JP) ; NAGASHIMA; Yutaka;
(Kimitsu-shi, JP) ; YAMADA; Shunsuke;
(Kimitsu-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUENCE CO., LTD. |
Wako-shi, Saitama |
|
JP |
|
|
Assignee: |
FUENCE CO., LTD.
Wako-shi, Saitama
JP
|
Family ID: |
57006948 |
Appl. No.: |
15/564043 |
Filed: |
April 3, 2015 |
PCT Filed: |
April 3, 2015 |
PCT NO: |
PCT/JP2015/060674 |
371 Date: |
November 24, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D01D 5/003 20130101;
D04H 1/32 20130101; B01D 2239/025 20130101; D01D 5/0069 20130101;
D21H 13/26 20130101; D01F 6/74 20130101; D21H 21/52 20130101; B01D
2239/10 20130101; D04H 1/728 20130101; B01D 39/1623 20130101; D04H
1/4326 20130101 |
International
Class: |
D01D 5/00 20060101
D01D005/00; D01F 6/74 20060101 D01F006/74 |
Claims
1. A nanofiber structure comprising: a polyimide resin having a
structure in which (1) a void ratio thereof is 75% or more, and (2)
an average pore diameter distribution thereof is 0.5-2.0 .mu.m.
2. The nanofiber structure according to claim 1, wherein a
formation of nanofibers is carried out by an electrospray
deposition method.
3. The nanofiber structure according to claim 1, wherein a
nanofiber structure is not changed even if heated at 400.degree. C.
for 16 hours.
4. The nanofiber structure according to claim 1, wherein an air
permeability thereof is 4.55 cc/cm2/s or more in a JIS-L1096 air
permeability A method (Frazier method), or 1.68 s/300 cc or less by
a JIS-P8117 Gurley testing machine.
5. The nanofiber structure according to claim 1, wherein a moisture
permeation resistance (RET) thereof in a ISO11092 method is 3.0 (m2
and Pa/W) or less.
6. The nanofiber structure according to claim 1, wherein a water
resistance thereof is 0.01 or more MPa by JIS-L1092
water-penetration-test B method (high-pressure water method).
7. The nanofiber structure according to claim 1, wherein a thermal
conductivity thereof is within a range of 0.04-0.05 W/mK.
8. The nanofiber structure according to claim 1, wherein the
nanofiber structure has an adhesiveness.
Description
TECHNICAL FIELD
[0001] The present invention relates to a nanofiber structure, and
more particularly to a nanofiber structure of a polyimide resin,
which has air permeability, moisture permeability, and water
resistance. That is, the present invention relates to a nanofiber
structure in which a polyimide resin having physical properties
such as high heat resistance is transformed into nanofibers so as
to have air permeability, moisture permeability, and water
resistance.
BACKGROUND ART
[0002] Conventionally, there has been an ePTFE resin (expanded
polytetrafluoroethylene), which has high heat resistance,
insulation, chemical stability, air permeability, moisture
permeability, and water resistance. The ePTFE resin is formed by
thinning a PTFE resin with special stretching technology, thereby
giving it a porous character, and adding air permeability, moisture
permeability, and water resistance thereto. Although the ePTFE
resin is typically used for rain gear which requires both
waterproofness and moisture permeability, outdoor products such as
clothes, and apparel products, uses thereof are not limited thereto
and they are used in a very wide range of industrial fields.
[0003] It is pointed out that the ePTFE resin has the bad balance
of air permeability and water resistance (the ePTFE resin has the
general character in which if the air permeability thereof is
improved, the water resistance thereof becomes very bad), that
still higher heat resistance thereof is called for now, and that a
price thereof is high as industrial material.
[0004] On the other hand, a polyimide resin has the highest heat
resistance, insulation, and chemical stability among
high-performance resins, and is used in many industrial fields
because of these characteristics. However, it was very difficult to
dissolve the polyimide resin in a solvent or to melt it, after
imidization (namely, after manufacturing).
[0005] Moreover, formation of porosity in the polyimide resin,
processing into nanofibers and nanoparticulatation etc. have been
also attempted in order to improve or change the physical
properties of the polyimide resin.
[0006] As patent documents regarding the above-mentioned polyimide
resin-related prior art technology, there are, for example,
Japanese Patent Application Publication No. 2013-513932,
"Electrochemical cell comprising a separator including a nanoweb
consisting essentially of nanofibers of fully aromatic polyimide"
(PATENT DOCUMENT 1), Japanese Patent Application Publication No.
2013-513931, "Multi-layer article comprising polyimide nanoweb"
(PATENT DOCUMENT 2), Japanese Patent Application Publication No.
2009-243031, "Nanofiber, electrolyte film, membrane electrode
assembly, and fuel cell" (PATENT DOCUMENT 3), Japanese Patent
Application Publication No. 2009-270210, "Manufacturing method of
ultrafine nanofibers" (PATENT DOCUMENT 4), and Japanese Patent
Application Publication No. 2007-92078, "Manufacturing method of a
polyimide porous membrane" (PATENT DOCUMENT 5) etc.
[0007] In addition, as nonpatent literature, there are NON-PATENT
LITERATURE 1: Satoshi Yoda et al., "Polyimide having flexibility
and excellence in heat resistance=silica nanocomposite porous
body," and NON-PATENT LITERATURE 2: "polyimide porous membrane."
However, although the polyimide resin is based on such
state-of-the-art technology, no polyimide resin having the air
permeability, moisture permeability, and water resistance Which is
equal to ePTFE resin has been developed.
PRIOR ART DOCUMENTS
Patent Documents
[0008] PATENT DOCUMENT 1: Patent Application Publication No.
2013-513932, "Electrochemical cell comprising a separator
comprising a nanoweb consisting essentially of nanofibers of fully
aromatic polyimide" [0009] PATENT DOCUMENT 2: Patent Application
Publication No. 2013-513931, "Multi-layer article comprising
polyimide nanoweb", [0010] PATENT DOCUMENT 3: Japanese Patent
Application Publication No. 2009-243031, "Nanofiber, electrolyte
film, membrane electrode assembly, and fuel cell" [0011] PATENT
DOCUMENT 4: Japanese Patent Application Publication No.
2009-270210, "Manufacturing method of ultrafine nanofibers" [0012]
PATENT DOCUMENT 5: Japanese Patent Application Publication No.
2007-92078, "Manufacturing method of a polyimide porous
membrane"
[0013] NON-PATENT LITERATURE 1: Satoshi Yoda et al., "polyimide
having flexibility and excellence in heat resistance=silica
nanocomposite porous body", internet website:
http://www.aist.go.jp/aist_j/press_release/pr2013/pr20130121/pr20130121.h-
tml [0014] NON-PATENT LITERATURE 2: "Polyimide porous membrane",
Website: http
://www.ube-ind.co.jp/japanese/rd/polyimide_porous_film.htm
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0015] Although an ePTFE resin is breakthrough material which has
the physical properties of water resistance, and moister
permeability and air permeability in addition to high heat
resistance, insulation, and chemical stability, as mentioned above,
there is a drawback that the balance of air permeability and water
resistance is bad. In order to improve the air permeability
thereof, it is necessary to increase the porosity (to make the hole
density high or to enlarge the diameter of holes). On the other
hand, the water resistance thereof becomes low when the porosity
becomes high. On the contrary, when the porosity is made low in
order to improve the water resistance thereof, the air permeability
thereof becomes low. Thus, the air permeability of the material,
which is the ePTFE resin, and the water resistance thereof have a
trade-off relation.
[0016] As mentioned above, there is a polyimide resin which has
heat resistance far higher than that of the ePTFE resin etc., but
unlike the ePTFE resin, it is very difficult to mechanically extend
the polyimide resin due to the strength of the physical properties
thereof. Therefore, attempts to change the physical properties and
the characteristics of the polyimide resin have been made by using
technology other than the mechanical stretching technology. For
example, although some technologies which increase the porosity of
a polyimide resin have been developed like the conventional
technology mentioned above, no polyimide resin having the air
permeability, moister permeability, and water resistance which
exceeds those of the ePTFE resin, has been developed. Moreover, a
manufacturing cost of the ePTFE resin is high, and the ePTFE resin
is high price material, so that more cost reduction is also called
for.
[0017] Although, for a long time, a polyimide could not be
dissolved in a solvent, a special solvent for melting the polyimide
resin has been developed in recent years. Furthermore, a polyimide
resin which can be dissolved with a general-purpose solvent has
also been developed.
[0018] After researches and contemplation for solving the
above-mentioned problems, the present inventors came up with a
technique for forming a polyimide solution, in which a polyimide
resin is dissolved in a solvent, into nanofibers by the
Electrospray Deposition Method (ESD method). Furthermore, by
researches and developments under various conditions, they found
out that a polyimide resin, which is formed into nanofibers, has
water resistance, moisture permeability, and air permeability with
a sufficient balance, and has the characteristics equivalent to or
more than those of an ePTFE resin. Furthermore, they found out that
it is possible to add adhesion properties to the polyimide resin,
which is formed into nanofibers.
[0019] It is an object of the present invention to offer a
nanofiber structure of a polyimide resin, and in particular to
offer a nanofiber structure which has air permeability, moisture
permeability, water resistance, adhesiveness, etc.
Means of Solving the Problems
[0020] In order to solve the above mentioned problem, a nanofiber
structure according to the first invention comprises a polyimide
resin having the following structure: [0021] (1) A void ratio
thereof is 75% or more. [0022] (2) An average pore diameter
distribution thereof is 0.5-2.0 .mu.m. [0023] (3) A film thickness
thereof is 50 .mu.m or less.
[0024] Moreover, a nanofiber structure according to the second
invention is characterized in that a formation of nanofibers is
carried out by the electrospray deposition method.
[0025] Moreover, a nanofiber structure according to the third
invention is characterized in that any change in a nanofiber
structure does not occur even if it is heated at 400.degree. C. for
16 hours.
[0026] Further, a nanofiber structure according to the fourth
invention is characterized in that the air permeability thereof is
4.55 cc/cm2/s or more in the JIS-L1096 air permeability A method
(Frazier method), or 1.68 or less s/300 cc in the JIS-L1096 air
permeability B method (Gurley method).
[0027] Furthermore, a nanofiber structure according to the fifth
invention is characterized in that a moisture permeation resistance
(RET) is 3.0 (m2Pa/W) or less in the ISO11092 method.
[0028] In addition, a nanofiber structure according to the sixth
invention is characterized in that the water resistance thereof is
0.01 MPa or more in the JIS-L1092 water resistance test B method
(High-pressure water method).
[0029] Moreover, a nanofiber structure according to the seventh
invention is characterized in that the thermal conductivity thereof
is within a range of from 0.04-0.05 W/mK.
[0030] Moreover, a nanofiber structure according to the eighth
invention is characterized in that the nanofiber structure has
adhesion properties.
[0031] As mentioned above, although a nanofiber structure is
explained as the means for solving the problem, the present
invention can be also realized as a manufacturing method of a
nanofiber structure which is substantially equivalent thereto, so
that it should be understood that they are within the scope of the
present invention.
Effects of the Present Invention
[0032] According to the present invention, it becomes possible to
offer a nanofiber structure of a polyimide resin.
BRIEF EXPLANATION OF THE DRAWINGS
[0033] FIG. 1 is a conceptual diagram showing the fundamental
configuration of an electrospray deposition apparatus.
[0034] FIG. 2 shows SEM photographs of a nanofiber structure
produced according to an Example 1, wherein a polyimide resin
KPI-MX 300 F (75) powder is used as material.
[0035] FIG. 3 is graphs showing a pore diameter distribution of the
nanofiber structure produced according to the Example 1, wherein
the polyimide resin KPI-MX 300 F (75) powder is used as
material.
[0036] FIG. 4 shows SEM photographs of a nanofiber structure
produced according to an Example 2, wherein a polyimide resin
KPI-MX300 F (100) powder is used as material.
[0037] FIG. 5 shows graphs showing a pore diameter distribution of
the nanofiber structure produced according to the Example 2,
wherein the polyimide resin KPI-MX300 F (100) powder was used as
material.
[0038] FIG. 6 is a diagram showing physical properties of the
nanofiber structures in the Examples 1 and 2.
[0039] FIG. 7 is a diagram showing a result of study of a high
temperature influence to a nanofiber structure in the Example
2.
[0040] FIG. 8 is a diagram showing a result of study of a high
temperature influence to a nanofiber structure of the Example
2.
[0041] FIG. 9 is a diagram showing a result of study of a high
temperature influence to a nanofiber structure of the Example
2.
[0042] FIG. 10 is a table of measurement of physical properties of
water resistance and air permeability about a nanofiber structure
of the Examples 1 and 2.
[0043] FIG. 11 is a table of measurement of physical properties of
water resistance and air permeability of the nanofiber structure of
the Example 2, and Comparative Examples 3 and 4;
[0044] FIG. 12 is a table of measurement of physical properties of
air permeability of nanofiber structures in the Examples 1 and 2
and a Comparative example 5.
EMBODIMENTS
[0045] Embodiments of the present invention will be explained below
in detail, referring to drawings.
Electrospray Deposition Method
[0046] Before explanation of the embodiments of the present
invention, the principle about the electrospray deposition method
(ESD method) used in the embodiments of the present invention and
an electrospray deposition apparatus (ESD: electrostatic spraying
apparatus) which can carry out the electrospray deposition method
will be explained.
Electrospray Deposition Apparatus
[0047] FIG. 1 is a conceptual diagram showing the fundamental
configuration of the electrospray deposition apparatus. As shown in
the figure, a container CNT contains a sample solution SL. The
sample solution SL is, for example, an organic macromolecular
solution or polymer fluid etc. In this embodiment, the sample
solution is, for example, a polyimide dissolved or dispersed in a
solvent, namely, a polyimide solution.
[0048] The ESD method is a very complicated physical phenomenon,
and although the entire process has not been figured out, it is
generally considered as a phenomenon set forth below. The sample
solution is stored in a nozzle NZL in the shape of a thin
capillary, and thousands to tens of thousands volt voltage is
applied to a target substrate TS (opposite electrode) that faces
this nozzle. At the tip of the capillary, a powerful electric field
is generated due to effects of electric field concentration, so
that charged microdroplets collect on a liquid surface so that a
corn is formed (so-called Taylor Cone). Furthermore, the sample
solution breaks the surface tension at the tip, so as to become a
jet. The jet is heavily charged and serves as a spray due to
repulsion of electrostatic force (coulomb explosion). The droplet
formed by the spray is very small, so that the solvent is
evaporated and dried in a short time, thereby producing fine
nanoparticles or nanofibers. Of course, a deposition thereof is
also possible in a wet state where it is not evaporated and dried.
The fine electrified nanoparticles and nanofibers with small
diameters are drawn to the target substrate TS which functions as
an opposite electrode due to an electrostatic force. A pattern of
deposit can be controlled by an insulator mask or an auxiliary
electrode, which is not illustrated. As long as the sample is in a
liquid form, it is not limited to a solution and may be dispersion
liquid.
[0049] Moreover, suitably, an extrusion pressure towards the nozzle
NZL side is applied to the sample solution in the container CNT by
an air pressure syringe pump and a plunger etc. (a discharge means,
which is not shown in the figures). The extrusion pressure is given
thereto by, for example, a stepping motor and a screw feeding
mechanism (not shown). An inside pressure increases within the
container CNT, so that the sample solution SL which is subject to
the extrusion pressure is discharged from the tip of the nozzle
NZL. As mentioned above, it becomes possible to make adjustment to
a suitable discharge speed by providing adjustment mechanism (a
stepping motor and a screw feeding mechanism) which adjusts the
sample solution discharge speed.
[0050] The nozzle NZL is made of metal, and positive voltage is
supplied through a wire WL made from a conductor from a
high-voltage power supply HPS. A minus side of the high-voltage
power supply HPS is connected to the target substrate TS (a
substrate, which is used as an opposite electrode). A positive
voltage is impressed to the sample solution SL through the nozzle
NZL by impressing voltage from the high-voltage power supply HPS,
whereby the solution is positively charged. In addition, the
polarity of the voltage applied to the sample solution SL may be
negative.
[0051] Moreover, when producing a nanofiber structure, it is
suitable to place a nonwoven fabric on the target substrate TS, and
deposit the nanofiber structure on the nonwoven fabric. Moreover,
various conditions, such as a level of voltage, concentration of
the sample solution, kinds of polyimide as a sample, and a kind of
solvent, are adjusted, so that a nanofiber structure is
produced.
[0052] The material, with which the spraying is carried out becomes
fibers and droplets and is repeatedly divided while flying by
repulsion due to electrification, thereby forming nanofibers or
nanoparticles. Since the material, with which the spraying is
carried out is in nano size so that a surface area thereof is
large, the material with which the spray was carried out will be
almost dried, when they reaches the substrate. The form and size
thereof can be changed according to the spray conditions, so that,
for example, when a macromolecular solution is used, thick
nanofibers can be formed if a molecular weight thereof is made
large and the concentration thereof is made high greatly, and thin
nanofibers or nanoparticles can be formed if the molecular weight
is made small and the concentration is made low. In addition,
various conditions, such as voltage and the distance between the
nozzle and the substrate, ambient temperature, humidity, etc. exert
influence thereon. In this embodiment, various solvent-soluble
polyimide resins were used as samples, and nanofibers were produced
under various conditions, and the heat resistance, the
conductivity, air permeability and moisture permeability and water
resistance etc. were confirmed in a method described as the
embodiments. As the electrospray deposition apparatus, not only the
above-mentioned apparatus but a different type of ESD apparatus can
be also used therefor. Specifically, a method of using air current,
which is disclosed in Re-Publication of PCT International
Publication No. 2009/060898 and which was developed by applicants,
is suitable for a mass-production purpose.
EXAMPLE 1
[0053] A powder of a transparent solvent-soluble polyimide resin
(KPI-MX 300 F (75) manufactured by Kawamura Sangyo Co., Ltd.) in
amount of 10 grams was dissolved in N,N-dimethyacetamide (purity
97.0%, produced by Wako Pure Chemical Industries, Ltd.) in amount
of 90 grams, whereby a sample solution whose concentration was 10
weight percent was produced in amount of 100 grams. This sample
solution in amount of 5 mL was put in the container CNT, which was
a syringe made of polypropylene (PSY-30E-M produced by Musashi
Engineering Inc.), wherein the metal nozzle NZL (MN-23G-13
manufactured by Iwashita Engineering, Inc.) shown in the FIG. 1,
whose inner diameter was 0.34 mm, was attached to the syringe. The
container CNT was attached to an electrospray deposition apparatus
(Esprayer ES-2300 manufactured by Fuence Co., Ltd.). A polyester
mesh (T-N0280T manufactured by NBC Meshtec Inc.) whose size was A3,
was used as base material on the target substrate TS (collector
substrate). As the conditions of this electrospray, the voltage
between the nozzle NZL and the collector (target substrate TS) was
26-30 kV, the distance between the nozzle and the collector was 15
cm, and the liquid feed pressure was 0.010-0.015 MPa, under which
the entire base material was scanned so as to evenly put the spray
thereon from front to back and from side to side, whereby the
nanofiber structure of polyimide was obtained. In addition, other
polyimide nanofiber structures were obtained under the same
conditions except for the solution concentration of 17 weight
percent.
EXAMPLE 2
[0054] A powder of a transparent solvent-soluble polyimide resin
(KPI-MX 300 F (100) produced by Kawamura Sangyo Co., Ltd.) in
amount of 10 grams was dissolved in N,N-Dimethylacetamide (purity
97.0%, produced by Wako Pure Chemical Industries, Ltd.) in amount
of 90 grams, whereby a sample solution whose concentration was 10
weight % was produced in amount of 100 grams. This sample solution
in amount of 5 mL was put in the container CNT, which was a syringe
made of polypropylene (PSY-30E-M manufactured by Musashi
Engineering Inc.), wherein the metal nozzle NZL (MN-23G-13
manufactured by Iwashita Engineering, Inc.) shown in the FIG. 1,
whose inner diameter was 0.34 mm, was attached to the syringe. The
container CNT was put on the electrospray deposition apparatus
(Esprayer ES-2300 manufactured by Fuence Co., Ltd.). A polyester
mesh (T-N0280T produced by NBC Meshtec Inc.) whose size was A3, was
used as base material on the target substrate TS (collector
substrate). As the conditions of this electrospray, the voltage
between the nozzle NZL and the collector (target substrate TS) was
26-30 kV, the distance between the nozzle and the collector was 15
cm, and the liquid feed pressure was 0.010-0.015 MPa, under which
the entire base material was scanned so as to evenly put the spray
thereon from front to back and from side to side, whereby the
nanofiber structure of polyimide was obtained.
[0055] FIG. 2 shows SEM photographs of a nanofiber structure
produced according to an Example 1, wherein a polyimide resin
KPI-MX 300 F (75) powder was used as material. The upper part of
the figure shows a SEM photograph taken at a magnification of
30,000 times wherein a plurality of diameters of nanofibers are
shown. The diameters were 169, 147, 168, 180, 134, and 145 or 151
nm, and a distribution thereof can be observed in a range of from
134 to 180 nm in the photographed portion. The lower part of the
figure shows a SEM photograph taken at a magnification of 3,000
times.
[0056] FIG. 3 is graphs showing a pore diameter distribution of the
nanofiber structure produced according to the Example 1, wherein
the polyimide resin KPI-MX 300 F (75) powder was used as material.
The measurement was carried out by a. pore diameter distribution
measuring device (Automated Perm Porometer CEP-1100A manufactured
by PMI). FIG. 3(A) shows a measurement result of a pore diameter
distribution in a nanofiber structure containing a mesh base
material, and FIG. 3(B) shows a measurement result of a pore
diameter distribution in a nanofiber structure without a mesh base
material. The film thickness of the nanofiber structure of (A),
which included the mesh base material, was 73.2 .mu.m, a base
weight thereof was 4.0 g/m.sup.2, and a void ratio thereof was
75.0%. In addition, the void ratio was obtained by the expression
set forth below.
Void ratio (%)=(1-bulk density/true density).times.100
[0057] The film thickness of a nanofiber structure without the mesh
base material of (B) was 29.8 .mu.m. And the data of the mesh base
material of (A) is set forth below. [0058] Distance between
openings 56 .mu.m [0059] Opening rate 38% [0060] Wire diameter 35
.mu.m [0061] Thickness 53 .mu.m
[0062] It can be found from (A) that the pore diameters were
distributed from about 0.6 .mu.m to 2 .mu.m, and the peak of
distribution was about 1.2-1.3 .mu.m. It can be found from (B) that
the pore diameters were distributed from about 0.5 .mu.m to 2.3
.mu.m, and the peak of distribution (center value) was about
0.7-0.8 .mu.m. Incidentally, the average pore diameter of (A) was
1.25 .mu.m, and the average pore diameter of (B) was 1.02 .mu.m.
Although the peak value in the graph shown in the figure was
obtained after a curve fitting was applied thereto, and data
obtained before the curve fitting was applied thereto shifts a
little therefrom, the peak value of (A) was 1.18 .mu.m and the peak
value of (B) was 0.77 .mu.m.
[0063] According to the present Example and Examples explained
blow, the polyimide nanofiber structure whose physical properties
is controlled as set forth below can be manufactured. [0064] (1) A
void ratio thereof is 75% or more. [0065] (2) An average of the
pore diameter distribution thereof is 0.5-2.0 .mu.m. [0066] (3) A
film thickness thereof is 50 .mu.m or less.
[0067] FIG. 4 shows SEM photographs of a nanofiber structure which
was produced according to the Example 2, wherein a polyimide KPI-MX
300 F (100) powder was used as material. The upper part of the
figure shows a SEM photograph taken at a magnification of 30,000
times wherein a plurality of diameters of nanofibers are shown. The
diameters were 314, 340, 349, 371, 372, and 379 or 385 nm, and a
distribution thereof can be observed in a range of from 314 to 385
nm in the photographed portion. The lower part of the figure shows
a SEM photograph taken at a magnification of 3,000 times,
[0068] FIG. 5 shows graphs showing a pore diameter distribution of
a nanofiber structure which was produced according to the Example
2, wherein a polyimide resin KPI-MX300 F (100) powder was used as
material. The measurement was carried out by the same apparatus as
that shown in FIG. 3. FIG. 5(A) shows a measurement result of a
pore diameter distribution in a nanofiber structure without a mesh
base material, and FIG. 5(B) shows a measurement result of a pore
diameter distribution in a nanofiber structure without a mesh base
material, which was a separate part. A film thickness of the
nanofiber structure of (A) was 37.0 .mu.m, a base weight thereof is
7.9 g/m.sup.2 and a void ratio thereof is 86.4%. A film thickness
of the nanofiber structure of (B) without the mesh base material
was 37.5 .mu.m.
[0069] It can be found from (A) that the pore diameters were
distributed from about 0.2 .mu.m to 2 .mu.m, and the peak of
distribution was about 1.4-1.5 .mu.m. It can be found from (B) that
the pore diameters were distributed from about 0.6 .mu.m to 2.3
.mu.m, and the peak of distribution was about 1.5-1.6 .mu.m.
Incidentally, the average pore diameter of (A) was 1.14 .mu.m, and
the average pore diameter of (B) was 1.57 .mu.m. Although the peak
value in the graph shown in the figure was a value obtained after a
curve fitting was applied, and data obtained before the curve
fitting was applied shifted a little therefrom, the peak value of
(A) was 1.45 .mu.m and the peak value of (B) was 0.55 .mu.m.
[0070] FIG. 6 is a diagram showing physical properties of the
nanofiber structures according to the Examples 1 and 2. The
physical properties of a commercial polyimide film are shown
therein as Comparative Examples 1 and 2. The physical property
values of two kinds of polyimide nanofiber structures according to
Examples 1 and 2 were measured, one of which was heat treated at
200.degree. C. and the other of which was at room temperature. A
DMAc (dimethylacetamide) residual amount was computed from the
weight reduction between 100 and 200.degree. C. using the TGA
method. The surface and volume resistivity was measured by a double
ring electrode method. Moreover, the CTE was measured under the
condition set forth below by the TMA method. "It was calculated
from a change rate in a temperature drop between 80-180.degree. C.
after being heated from 40 to 210.degree. C. (5.degree. C./min) and
then held for 10 minutes at 210.degree. C."
[0071] In the Examples 1 and 2, it can be found that the DMAc
residual amount was in the same range as that of Comparative
Examples 1 and 2 even without a heat treatment. In addition, in
both the Examples 1 and 2, the surface and volume resistivity was
15th to 16th power .OMEGA. even, in 20-30 .mu.m, and thus shows
insulation properties. Further, since deformation was observed in a
monolayer due to the weight of a jig, the coefficient of thermal
expansion (CTE) was measured by using lamination. It is found that
in both the Examples 1 and 2, values of the coefficient of thermal
expansion (CTE) were good, and they had a sufficient heat
resistance even at 200.degree. C. or higher. Thus, the nanofiber
structure of the polyimide resin according to the present Example
had a sufficient heat resistance, but as shown in SEM photographs
of FIGS. 7, 8 and 9, further heat-resistant examinations were
conducted in severer heat environment (400.degree. C.).
[0072] FIGS. 7, 8 and 9 are diagrams showing results of study of a
high temperature influence to a nanofiber structure of the Example
2. FIG. 7 shows SEM photographs at room temperature, FIG. 8 shows
SEM photographs of a nanofiber structure which was placed in an
electric furnace (Ropet Kobata Electric Industries Ltd., electric
furnace post III type) at 400.degree. C. for 8 hours, and FIG. 9 is
SEM photographs of a nanofiber structure placed therein for 16
hours.
[0073] FIG. 7 shows a photograph of a nanofiber structure at room
temperature, wherein the upper part of the figure shows a SEM
photograph taken at a magnification of 30,000 times and a plurality
of diameters of nanofibers are shown. The diameters were 234, 235,
213, and 212 or 225 nm, and a distribution thereof can be observed
in a range of from 212 to 235 nm in the photographed portion. The
lower part of the figure shows a SEM photograph taken at a
magnification of 1,000 times.
[0074] FIG. 8 shows a photograph of a nanofiber structure which was
heat treated at 400.degree. C. for 8 hours, wherein the SEM
photograph shown in the upper part was taken at a magnification of
30,000 times, and a plurality of diameters of nanofibers are shown.
The diameters were 189, 220, and 204 or 186 nm, and a distribution
thereof can be observed in a range of from 186 to 220 nm in the
photographed portion. The lower part of the figure shows a SEM
photograph taken at a magnification of 1,000 times. Even after the
nanofiber structure in FIG. 8 was heat treated at 400.degree. C.
for 8 hours, the nanofiber structure maintains the structure
similar to that of FIG. 7, and thus it was observed that it had a
sufficient resistance in severer heat environment namely at
400.degree. C. for 8 hours.
[0075] FIG. 8 shows a photograph of a nanofiber structure which was
heat treated at 400.degree. C. for "16 hours," wherein the SEM
photograph shown in the upper part was taken at a magnification of
30,000 times, and a plurality of diameters of nanofibers were
shown. The diameters are 163, 179, 192, and 198 or 208 nm, and a
distribution thereof can be observed in a range of from 163 to 208
nm in the photographed portion. The lower part of the figure shows
a SEM photograph taken at a magnification of 1,000 times. Even
after the nanofiber structure in FIG. 8 was heat treated at
400.degree. C. for "16 hours," the nanofiber structure maintained a
structure similar to that of FIG. 7 (room temperature) and that of
FIG, 8 (400.degree. C. for 8 hours), and thus it was observed that
it had a sufficient resistance in the severer heat environment,
namely at 400.degree. C. for 16 hours).
[0076] As shown in these SEM photographs, in the nanofiber
structure according to the present Example, there was no change in
the nanofiber structure after 8 hours and even after 16 hours at
400.degree. C. That is, the nanofiber structure greatly excels in
heat resistance and has high utility value in a use in which it is
placed in severe heat environment for a long time. Moreover, as
described below, the nanofiber structure according to the present
embodiment is very excellent in water resistance and air
permeability, and applications in a very wide range of industrial
uses are expected, Specifically, as the ESD apparatus used in the
embodiment, there is also a mass-produced type in which many
nozzles are provided, so that it is possible to mass-produce
polyimide resin nano.sup.-fiber structures at very low cost.
Waterproof Pressure Measurement
[0077] The measurement was performed in accordance with the
JIS-L1092 water resistance test method B (high water pressure
method) by a manual waterproofing degree testing machine (No. 169
manufactured by Kabushiki Kaisha Yasuda Seiki Seisakusho).
Moisture Permeation Resistance (RET) Measurement
[0078] Under a test environment of 35.degree. C. and 40 % RH, it
was carried out by the ISO11092 method.
[0079] <Air Permeability Measurement>
[0080] A Frazir value and a Gurley value were measured.
[0081] Frazier Value Measurement
[0082] JIS-L1084 air permeability according to the JIS-L1096 air
permeability A method (Frazier method) by using a Frazir Type Air
Permeability Tester (No. 415 manufactured by Kabushiki Kaisha
Yasuda Seiki Seisakusho).
[0083] Gurley Value Measurement
[0084] Measured in accordance with the JIS-L1096 air permeability B
method (Gurley method) and the JIS-P8117 Gurley testing machine
method by using a Gurley style Densometer (No. 323 manufactured by
Kabushiki Kaisha Yasuda Seiki Seisakusho).
[0085] FIG. 10 is a table of measurement of physical properties of
water resistance and air permeability of the nanofiber structures
of the Examples 1 and 2. A film thickness thereof was measured by a
Mitutoyo Digimatic standard outside micrometer. (MDC-25M). The film
thickness was 50 .mu.m or less. In the Example 1, the water
resistance was 0.025-0.045 MPa, and in the Example 2, it was
0.01-0.055 MPa, thus the good numerical values were acquired.
[0086] In the Frazier method, the air permeability thereof was
4.55-13.9 (cc/cm2/sec) in the Example 1 and 8.12-35.3 (cc/cm2/sec)
in the Example 2 and thus the good numerical values thereof were
acquired. Moreover, in Gurley method, it was 0.45-1.68 (sec) in the
Example 1 and 0.023-0.6 (sec) in the Example 2 and thus, the good
numerical values were acquired. Thus, in the Examples 1 and 2, the
nanofiber structures of polyimide excellent in water resistance and
air permeability was produced.
[0087] FIG. 11 is a table of measurement of physical properties of
water resistance and air permeability of the nanofiber structures
according to the Example 2, and those of Comparative Examples 3 and
4. In order to emphasize the excellent characteristic of the
nanofiber structure according to the embodiment of the present
invention, the water resistance and air permeability of two kinds
of commercial polyimide films were measured in the same manner
thereas. As shown in the figure, for example, in the Example 2, the
air permeability thereof was 0.55 second in a Gurley value, that of
the Comparative Examples 3 was 4 to 11.5 seconds, and that of the
comparative example 4 was 242 to 762 seconds, and thus it turns out
that the physical properties of the present invention were notably
excellent. Moreover, when three samples according to the Example 2
were measured by the ISO11092 method, the moisture permeation
resistances (RET) thereof were 2.7, 2.7, and 2.8, and an average of
2.7 (m2 and Pa/W). If this result is compared with data disclosed
at
http://www.gore-tex.jp/news/utmf/2012/activeshell/characteristic.html,
it was equivalent to or more than that of ePTFE products, which
were known as the best. It is fully possible to obtain higher
performance by examining nanofiber production conditions according
to the technology of this application and thus it can be said that
the moisture permeability thereof was superior to that of the ePTFE
products.
[0088] FIG. 12 is a table of measurement of physical properties of
air permeability and water resistance of the nanofiber structures
according to the Examples 1 and 2 and that of a comparative example
5.
[0089] The physical properties which are excellent in air
permeability and water resistance may not be necessarily obtained
by forming any polyimide resin, which are dissolved in a solvent,
into nanofibers. The example thereof will be given below.
Comparative Example 1
[0090] A sample was produced in the same manner as that of the
Examples 1 and 2 by using a NMP solution 6,6-PI-Solpit-A of a
soluble polyimide produced by another company (concentration was 10
weight percent). Since the produced nanofiber nonwoven fabric
contains much solvent, unless it is produced while drying, holes of
the nanofiber are closed due to welding and adhesion. No
improvement was achieved although various spray conditions (the
solution concentration, voltage between the nozzle and the
substrate, the liquid sending speed, the nozzle diameter, the
distance between the nozzle and the substrate) were adjusted.
Moreover, the waterproof pressure thereof was extremely low
although the air permeability thereof, which was almost equivalent
to that of the nanofiber structure according to the Example 1, was
acquired.
[0091] Although the present invention has been explained based on
the figures and the Examples, it should be noted that it is easy
for a person skilled in the art to make various changes and
alterations based on this disclosure. Therefore, it should be noted
that these changes and alterations are within the scope of the
present invention. For example, the conditions of electrospray
deposition, the apparatus used herein, the solvent, polyimide of
material etc. are only examples, and other equivalent materials,
conditions, apparatuses etc. may be replaced with or changed to
other similar ones.
[0092] Moreover, the thermal conductivity of the nanofiber
structure, which was produced in accordance with the Example 2, was
measured in a hot wire method (at atmosphere temperature:
22.degree. C. by Model TCi manufactured by C-THERMI), and 0.046
W/mK was obtained as a result of the measurement. That is, it is
possible to obtain one with the thermal conductivity of 0.04 to
0.05 W/mK. Although this value is a little larger than that of an
urethane foam (0.026 w/mk) etc. which is a high performance foam
insulation, it has a big advantage that it is flexible and thin
material, compared with a heat insulating foam material, which may
not be made thin. The nanofiber structure according to the present
invention with the above-mentioned physical properties can be used
for various purposes. They are various filters, catalyst support
objects, structure materials (especially for high temperature
environment), breathable water resistance outdoor/apparel items,
flexible and thin heat resistance, heat insulation and insulation
material, and medical field, etc.
[0093] Moreover, although the above described Examples show that
the produced nanofiber structure acquired advanced functionality,
such as the air permeability and water resistance, a nanofiber
structure which has another functionality can be produced,
depending on an attribution of polyimide which is raw
material/material. Hereafter, the example is shown below.
[0094] For example, a polyimide (brand name "Solpit-S")
manufactured by Orient Chemical Industries Co., Ltd. has
adhesiveness. In the same manner as that of the above-mentioned
Examples, a polyimide solution containing Solpit-S was formed into
nanofibers by using the electrospray deposition method (ESD method)
according to the technique of the present invention, thereby
producing a nanofiber structure.
[0095] Of course, this nanofiber structure can be given any or all
of characters set forth below, as well as the above-mentioned
Examples. In addition, the following properties are not
indispensable: [0096] (1) A void ratio thereof is 75% or more.
[0097] (2) An average of a pore size distribution is 0.5-2.0 .mu.m.
[0098] (3) A film thickness thereof is 50 .mu.m or less.
[0099] Moreover, it was confirmed that this nanofiber structure
maintained the adhesiveness which the Solpit-S had. For example,
When the nanofiber structure which used a polyimide other than
Solpit-S as raw material was formed on base material, if the
adhesive tape was tried to be removed after an adhesive tape was
brought in contact with the nanofiber structure side, the nanofiber
structure easily fell away from the base material, and thus a unity
which was formed by the substrate and the nanofiber structure was
lost. However, it was confirmed that in case of the nanofiber
structure which used the Solpit-S as raw material, the nanofiber
structure and the base material did not fall away from each other,
so that adhesiveness was shown between the substrate and the
nanofiber structure. That is, it is possible that this nanofiber
structure and other material adhere to each other so as to become
unified. Thus, in formation of nanofibers according to the
technique of the present invention, it was confirmed that the
functionality which raw material has, was not lost and thus
maintained.
REFERENCE SIGNS LIST
[0100] CNT Container [0101] HPS High-voltage power supply [0102]
NZL Nozzle [0103] SL Sample solution [0104] TS Target substrate
[0105] ESD Electrospray deposition apparatus [0106] WL Wire
* * * * *
References