U.S. patent application number 14/668457 was filed with the patent office on 2015-07-23 for method for producing laminated porous sheet comprising polytetrafluoroethylene and carbon particles.
The applicant listed for this patent is Nitto Denko Corporation. Invention is credited to Hiroyuki HIGUCHI, Masayoshi KAWABE, Ryoichi MATSUSHIMA, Takashi WANO, Yoshinori YAMAMOTO, Koichiro YAMASHITA.
Application Number | 20150203646 14/668457 |
Document ID | / |
Family ID | 41255090 |
Filed Date | 2015-07-23 |
United States Patent
Application |
20150203646 |
Kind Code |
A1 |
WANO; Takashi ; et
al. |
July 23, 2015 |
METHOD FOR PRODUCING LAMINATED POROUS SHEET COMPRISING
POLYTETRAFLUOROETHYLENE AND CARBON PARTICLES
Abstract
The method for producing the porous sheet of the present
invention includes the steps of (I) preparing a plurality of sheet
materials that contain polytetrafluoroethylene and carbon particles
and (II) stacking the plurality of sheet materials over one another
and rolling the stacked sheet materials. In the method for
producing the porous sheet of the present invention, step (I) and
step (II) may be repeated alternately. Further, as the sheet
materials to be used in the production method of the present
invention, a base sheet obtained by forming a mixture containing
polytetrafluoroethylene and carbon particles into sheet form also
can be used, or a laminated sheet obtained by stacking a plurality
of base sheets over one another and rolling them also can be used,
for example.
Inventors: |
WANO; Takashi; (Osaka,
JP) ; HIGUCHI; Hiroyuki; (Osaka, JP) ; KAWABE;
Masayoshi; (Osaka, JP) ; MATSUSHIMA; Ryoichi;
(Osaka, JP) ; YAMAMOTO; Yoshinori; (Toyota-shi,
JP) ; YAMASHITA; Koichiro; (Toyota-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nitto Denko Corporation |
Osaka |
|
JP |
|
|
Family ID: |
41255090 |
Appl. No.: |
14/668457 |
Filed: |
March 25, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12989151 |
Oct 22, 2010 |
9017817 |
|
|
PCT/JP2009/058326 |
Apr 28, 2009 |
|
|
|
14668457 |
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Current U.S.
Class: |
521/145 |
Current CPC
Class: |
B29C 43/00 20130101;
B29C 43/26 20130101; Y10T 428/3154 20150401; B29K 2105/04 20130101;
C08J 2327/18 20130101; C08J 9/0066 20130101; B32B 27/28 20130101;
B32B 2307/202 20130101; B29C 43/305 20130101; B29K 2995/0005
20130101; C08J 9/283 20130101; Y10T 156/10 20150115; B29C 43/003
20130101; Y10T 428/249986 20150401; B32B 2264/108 20130101; B29K
2027/18 20130101; C08J 2201/0502 20130101; B29K 2995/001 20130101;
B32B 27/08 20130101; B32B 2305/026 20130101; B32B 2509/00 20130101;
B32B 2419/00 20130101; B32B 2307/51 20130101; Y10T 428/31544
20150401; B32B 27/18 20130101; B32B 2307/21 20130101; B32B 2250/24
20130101; B32B 2307/304 20130101; B32B 2607/00 20130101; B32B
27/322 20130101; B29C 43/46 20130101 |
International
Class: |
C08J 9/00 20060101
C08J009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 2008 |
JP |
2008-119278 |
Claims
1-4. (canceled)
5. A porous sheet containing polytetrafluoroethylene and carbon
particles, the porous sheet having a thermal conductivity in the
thickness direction of at least 0.05 W/mK but not more than 0.1
W/mK and a volume resistivity in the thickness direction of at
least 0.5 .OMEGA.cm but not more than 2 .OMEGA.cm.
6. The porous sheet according to claim 5, the porous sheet having a
compressive elastic modulus at 5% strain in the thickness direction
of at least 0.5 MPa but not more than 2 MPa.
7. A heat insulating sheet produced using the porous sheet of claim
5.
Description
TECHNICAL FIELD
[0001] The present invention relates to a porous sheet and a method
for producing the porous sheet, and a heat insulating sheet.
BACKGROUND ART
[0002] Heat insulators are applied to various products, such as
precision instruments whose functions are significantly affected by
temperature changes, home appliances (e.g. refrigerator), and walls
and ceiling of a clean room. Conventionally polymer foams, such as
urethane foam, and glass wool are used as a heat insulator, for
example. These materials are not only excellent in heat insulating
properties but also lightweight and inexpensive, and therefore are
used as a heat insulator in a wide range of applications. Further,
a fiber reinforced plastic heat insulator formed by impregnating
woven fabric or nonwoven fabric with a matrix resin (see Patent
Literature 1) has been proposed as a high-strength heat
insulator.
[0003] However, these heat insulators have a problem of generation
of static electricity. To deal with this, heat insulators capable
of preventing generation of static electricity have been proposed,
such as a heat insulator formed of heat insulating layers with a
metal plate interposed therebetween, and a heat insulator coated
with an antistatic agent (see Patent Literature 2 and Patent
Literature 3), for example. However, in the case of the heat
insulator formed of heat insulating layers with a metal plate
interposed therebetween, a bonding process is necessary for
interposing the metal plate therebetween, and the bonding strength
between the layers needs to be enhanced in addition. For these
reasons, there has been a problem of an increase in the number of
production processes. On the other hand, the heat insulator that
uses an antistatic agent has a problem of an increase in the number
of production processes since a coating process is necessary for
applying the antistatic agent. Furthermore, they is an additional
problem of the antistatic performance deterioration with time.
CITATION LIST
[0004] Patent Literature 1: JP 2709371 B2
[0005] Patent Literature 2: JP 3-8248 B
[0006] Patent Literature 3: JP 5-25668 B
SUMMARY OF INVENTION
Technical Problem
[0007] Thus, conventionally, it has been difficult to provide a
heat insulator capable of preventing generation of static
electricity using a simple and convenient method.
[0008] It is therefore an object of the present invention to
provide a sheet that is available as a heat insulator and capable
of preventing generation of static electricity, and has sufficient
heal insulating properties.
Solution to Problem
[0009] The method for producing the porous sheet of the present
invention includes the steps of (I) preparing a plurality of sheet
materials that contain polytetrafluoroethylene (hereinafter,
referred to as PTFE) and carbon particles; and CID stacking the
plurality of sheet materials over one another and rolling them.
[0010] The porous sheet of the present invention contains PTFE and
carbon particles, and has a thermal conductivity in the thickness
direction of at least 0.05 W/mK but not more than 0.1 W/mK and a
volume resistivity in the thickness direction of at least 0.5
.OMEGA.cm but not more than 2 .OMEGA.cm.
[0011] The present invention further provides a heat insulating
sheet produced by using the above-mentioned porous sheet of the
present invention or a porous sheet to be obtained by the
above-mentioned production method of the porous sheet of the
present invention.
Advantageous Effects of Invention
[0012] According to the method for producing the porous sheet of
the present invention, a porous sheet having low thermal
conductivity and high electrical conductivity can be obtained.
Further, the porous sheet of the present invention has sufficient
heat insulating properties and high electrical conductivity.
[0013] Accordingly, the present invention makes it possible to
provide, with a simple and convenient method, a porous sheet that
is available as a heat insulator and capable of preventing
generation of static electricity and has sufficient heat insulating
properties.
DESCRIPTION OF EMBODIMENTS
[0014] Hereinafter, the embodiments of the present invention are
described. It should be noted that the following descriptions are
not intended to limit the present invention.
[0015] The method for producing the porous sheet of this embodiment
includes the steps of: (I) preparing a plurality of sheet materials
that contain PTFE and carbon particles; and (II) stacking the
plurality of sheet materials over one another and rolling the
stacked sheet materials.
[0016] An example of step (I) is described.
[0017] First, an example of the sheet materials to be prepared in
step (I) is described. PTFE fine powder, carbon particles and a
forming aid are mixed to produce a mixture in paste form.
Desirably, they are mixed under conditions such that PTFE can be
prevented from becoming fibrous as much as possible. Specifically,
it is desirable to mix them without kneading under conditions in
which the rotation rate is decreased and the mixing time is
shortened. By mixing them in this way, the processing of sheet
materials that contain PTFE as a matrix can be facilitated. Carbon
particles are not particularly limited as long as they can be
supported by the PTFE matrix without falling and can give
sufficient electrical conductivity to the porous sheet to be
obtained. However, the carbon particles desirably have a particle
size of 20 to 60 nm. It should be noted that the particle size
herein means a value to be obtained by a method in which arbitrary
10 sites of the carbon particles are observed to measure the
particle size of 10 particles in each site (100 particles in total)
using an SEM (Scanning Electron Microscope), and thereafter the
mean value is calculated. Examples of the carbon particles that can
be used include carbon black. The addition amount of the carbon
particles, for example, is 60 to 90 wt %. As a forming aid,
saturated hydrocarbons such as dodecane and decane can be used, for
example. The addition amount of the forming aid, for example, is 1
to 1.4 times (weight ratio) with respect to the solid content. Such
a mixture is extruded and rolled into sheet form, and thus obtained
base sheet can be used as a sheet material of the present invention
(the first example of the sheet material). The thus obtained sheet
materials each have a thickness, for example, of 0.5 to 10 mm.
[0018] Further, as another example of the sheet materials to be
prepared in step (I), there can be mentioned a laminated sheet (the
second example of the sheet material) obtained by stacking a
plurality of the above-mentioned base sheets over one another and
rolling them. The number of the layers in the laminated sheet is
not particularly limited, and can be determined appropriately in
consideration of the number of constituent layers of the porous
sheet (the number of layers that form the porous sheet) intended to
be produced.
[0019] Thus, the sheet materials can be prepared.
[0020] Next, an example of step (II) is described.
[0021] In step (II), the plurality of sheet materials prepared in
step (I) are stacked over one another and then rolled.
Specifically, the plurality of sheet materials prepared in step (I)
are stacked, and the stacked product is rolled to form a laminated
sheet. As mentioned above, the sheet material may be the
above-mentioned base sheet (the first example of the sheet
material), or may be a laminated sheet (the second example of the
sheet material) obtained by stacking a plurality of the base sheets
over one another and rolling the stacked sheets. The number of the
sheet materials to be stacked over one another in step (II) is not
particularly limited. For example, about 2 to 6 sheet materials can
be stacked. Desirably, the sheet materials are stacked and rolled
one on one, so that high strength can be achieved.
[0022] In the method for producing the porous sheet of this
embodiment, step (I) and step (II) may be repeated alternately. A
specific example of this case is described below.
[0023] First, a plurality of base sheets (e.g., 2 to 6 sheets) are
prepared (step (I)). Next, the plurality of base sheets are
stacked, and the stacked product is rolled to obtain a laminated
sheet (first laminated sheet) (step (II)). A plurality of first
laminated sheets (e.g., 2 to (3 sheets) as obtained above are
prepared so that the first laminated sheets are used as the sheet
materials in step (I). Next, the plurality of the first laminated
sheets (e.g., 2 to 6 sheets) are stacked, and the stacked product
is rolled to obtain a laminated sheet (second laminated sheet)
(step (II)). Furthermore, a plurality of second laminated sheets
(e.g., 2 to 6 sheets) as obtained above are prepared, and the
second laminated sheets are used as the sheet materials in step
(I). Next, the plurality of second laminated sheets (e.g., 2 to 6
sheets) are stacked, and the stacked product is rolled to obtain a
laminated sheet (third laminated sheet) (step (II)). In this way,
step (I) and step (II) are repeated alternately until the intended
number of the constituent layers of the porous sheet can be
achieved. In the embodiment described above, the laminated sheets
each having the same number of layers (the first laminated sheets,
or the second laminated sheets, for example) are stacked and
rolled. However, laminated sheets with the number of layer's
different from one another also may be stacked and rolled.
[0024] When step (II) is repeated, the rolling direction is
desirably changed. For example, at the time of rolling to obtain
the second laminated sheet, the rolling direction may be changed by
90 degrees from the rolling direction that has been employed to
obtain the first laminated sheet. By rolling with changing the
rolling direction in this way, the network of PTFE extends in every
direction, thereby allowing the sheet strength to be improved and
the carbon particles to be fixed firmly to the PTFE matrix.
[0025] When the number of constituent layers of the porous sheet is
expressed in terms of the total number of the base sheets included
in the porous sheet, the number of constituent layers can be, for
example, 100 to 800 layers. In order to improve the sheet strength,
the number of layers is desirably 100 layers or more. Meanwhile, in
order to obtain a sheet with a reduced thickness (e.g., 1 mm or
less), the number of layers is desirably 800 layers or less. The
more the number of constituent layers, the more the strength of the
sheet to be obtained can be enhanced.
[0026] At an early stage of rolling (at a stage where the total
number of base sheets to be included is small), the strength is low
and therefore the sheet can hardly withstand rolling at high
magnification. However, while repeating the stacking and rolling of
the sheet materials, the upper limit of the rolling magnification
is raised, so that the sheet strength can be improved and the
carbon particles can be attached firmly to the PTFE matrix.
Further, the structure of the laminated (the number of constituent
layers) also has a relation to the heat insulating properties or
compression resistance of the sheet to be obtained. Accordingly the
number of constituent layers is preferably 200 to 600 layers in
order to obtain a sheet with sufficient heat insulating properties
and compression resistance.
[0027] Finally, a sheet with a thickness of about 0.5 to 2 mm is
produced, and thereafter the forming aid is heated and removed.
Thus, the porous sheet of the present invention can be
obtained.
[0028] According to the production method of this embodiment, a
porous sheet having a thermal conductivity in the thickness
direction of at least 0.05 W/mK but not more than 0.1 W/mK and a
volume resistivity in the thickness direction of at least 0.5
.OMEGA.cm but not more than 2 .OMEGA.cm can be produced. Further,
the production method of this embodiment allows a porous sheet
having a porosity of 70 to 80 vol % to be produced.
[0029] Furthermore, in this porous sheet, the compressive elastic
modulus at 5% strain in the thickness direction can be controlled
to at least 0.5 MPa but not more than 2 MPa by appropriately
adjusting, for example, the number of layers of the sheet
materials. The heat insulating properties of heat insulators that
are generally used tend to decrease because of compressive
deformation. However, a porous sheet to be produced by the method
of this embodiment can achieve high compressive elastic modulus as
mentioned above, so that deformation due to compression is small.
As a result, it is possible to avoid a decrease in heat insulating
properties to be caused by compressive deformation. Furthermore,
such a porous sheet has a restoring force against compression, and
therefore has a thermal conductivity that is difficult to change,
even after a compressive force is applied in the thickness
direction. As a heat insulator capable of preventing a decrease in
heat insulating properties due to compression, JP 2709371 B2
(Patent Literature 1) proposes a fiber reinforced plastic heat
insulator produced by alternately stacking a woven fabric or
nonwoven fabric impregnated with a matrix resin and a woven fabric
or nonwoven fabric not impregnated with a matrix resin and pressing
them, for example. However, this heat insulator involves problems,
such as complicated production process and low flexibility, in
addition to the lack of electrical conductivity. In contrast, the
porous sheet to be produced according to the method of this
embodiment has a simple and convenient production process because
it can be produced by stacking sheet materials that contain PTFE
and carbon particles, and rolling them. Further, this porous sheet
has high flexibility, and therefore has high bending strength.
[0030] The porous sheet of this embodiment further has self-bonding
adhesiveness. Therefore, it is possible to avoid the problem of the
sheet shifting from a predetermined position when being placed at
the predetermined position in equipment or the like to serve as a
heat insulating sheet, for example.
[0031] As described above, the porous sheet produced by the method
of this embodiment is formed by stacking sheet materials that
contain PTFE and carbon particles, and therefore has a thermal
conductivity a volume resistivity and a compressive elastic modulus
in the thickness direction that satisfy the above-mentioned
range.
[0032] The porous sheet to be obtained according to this embodiment
can be used as a heat insulating sheet. This porous sheet has good
heat insulating properties and good electrical conductivity as
mentioned above. Therefore, the heat insulating sheet of this
embodiment produced using this porous sheet has good heat
insulating properties and is capable of preventing generation of
static electricity Furthermore, the heat insulating sheet of this
embodiment also has high compressive elastic modulus. Therefore,
even if a compressive force is applied in the thickness direction,
the heat insulating properties are unlikely to decrease.
EXAMPLES
[0033] Next, the porous sheet and the method for producing the
porous sheet of the present invention are described specifically
with reference to examples.
Example 1
[0034] 15 parts by mass of PTFE fine powder (product name: "F104",
manufactured by DAIKIN INDUSTRIES, LTD), 85 parts by mass of
acetylene black (product name: "DENKA BLACK (powdered product)",
manufactured by DENKI KAGAKU KOGYO KABUSHIKI KAISHA), 140 parts by
mass of saturated hydrocarbon (product name: "NS clean 220",
manufactured by Japan Energy Corporation) to serve as a forming aid
were mixed in a blender. The mixing conditions were set to:
rotation rate: 100 rpm; temperature: 20.degree. C.; and mixing
time: 2 minutes. The mixture was compressed at a pressure of 0.3
MPa to form a preform. Next, this preform was extruded at
approximately 10 MPa to form a 15 mm-diameter round bar. Further,
the round bar was rolled by passing though between a pair of metal
rollers (surface temperature: 40.degree. C.). Thus, a base sheet
(sheet material) with a thickness of 5 mm and a width of 25 mm was
obtained.
[0035] First, two base sheets were stacked, and the stacked product
was rolled, so that a laminated sheet (the first laminated sheet)
was produced. Next, two first laminated sheets thus obtained were
prepared as a sheet material. These two first laminated sheets were
stacked over each other and layered, and the stacked product was
rolled. Thus, a new laminated sheet (the second laminated sheet)
was produced. Next, two second laminated sheets thus obtained were
prepared as a sheet material. These two second laminated sheets
were stacked over each other and layered, and the stacked product
was rolled. Thus, a new laminated sheet (the third laminated sheet)
was produced. In this way, by repeating the steps of stacking the
obtained laminated sheets as a sheet material over each other and
rolling them 8 times, a sheet having 256 layers was produced. In
this example, the rolling step of step (II) in the present
invention was repeated 8 times. In each rolling step, the rolling
direction was shifted by 90 degrees from the rolling direction of
the previous rolling step. Such configurations that the rolling
direction is shifted when repeating the rolling step and the angle
of the shift is 90 degrees are not intended to limit the principles
of the present invention. The finally obtained sheet had a
thickness of 1 mm, a width of 250 mm, and a length of 2 m.
Subsequently, this sheet was heated to 150.degree. C. so that the
forming aid was removed.
[0036] The thermal conductivity, the volume resistivity and the
compressive elastic modulus were measured for the porous sheet of
Example 1 as produced above. The measurement methods were as
follows. Further, Table 1 indicates the measurement results.
[0037] <Measurement of Thermal Conductivity>
[0038] The thermal conductivity in the thickness direction was
measured using a thermal conductivity meter (product name:
"QTM-500", manufactured by Kyoto Electronics Manufacturing Co.,
Ltd.) based on the hot wire method.
[0039] <Measurement of Volume Resistivity>
[0040] The volume resistivity was measured using the four-terminal
method. A current of 100 mA was applied to the porous sheet in the
thickness direction, and the voltage was measured. Thus, the volume
resistivity was determined. An electrode probe was brought into
contact with the porous sheet with a pressure of 0.2 MPa, when the
measurement was carried out.
[0041] <Measurement of Compressive Elastic Modulus>
[0042] Using a Tensilon universal testing machine (manufactured by
A&D Company, Limited), the porous sheet was compressed in the
thickness direction at a speed of 0.5 mm/min, and thus the
displacement and stress were measured. The compressive elastic
modulus (E) was calculated taking a stress load of 20 kPa as the
displacement of 0 and applying the measured value of the stress
(.delta.) at 5% strain to the following formula:
E=.delta./0.05.
Example 2
[0043] 30 parts by mass of PTFE fine powder (product name: "F104",
manufactured by DAIKIN INDUSTRIES, LTD), 70 parts by mass of
acetylene black (product name: "DENKA BLACK (powdered product)",
manufactured by DENKI KAGAKU KOGYO KABUSHIKI KAISHA), 100 parts by
mass of saturated hydrocarbon (product name: "NS clean 220",
manufactured by Japan Energy Corporation) to serve as a forming aid
were mixed in a blender. Except for that, the porous sheet of
Example 2 was produced in the same manner as in Example 1.
[0044] The thermal conductivity, the volume resistivity and the
compressive elastic modulus were measured for the porous sheet of
Example 2, in the same manner as in Example 1, Table 1 indicates
the measurement results.
Comparative Example 1
[0045] 15 parts by mass of PTFE fine powder (product name: "F104",
manufactured by DAIKIN INDUSTRIES, LTD), 85 parts by mass of
acetylene black (product name: "DENKA BLACK (powdered product)",
manufactured by DENKI KAGAKU KOGYO KABUSHIKI KAISHA), 140 parts by
mass of saturated hydrocarbon (product name: "NS clean 220",
manufactured by Japan Energy Corporation) to serve as a forming aid
were mixed in a blender. The mixing conditions were set to:
rotation rate: 100 rpm: temperature: 20.degree. C.: and mixing
time: 2 minutes. The mixture was compressed at a pressure of 0.3
MPa to form a preform. Next, this preform was extruded at
approximately 10 MPa to form a plate with a thickness of 5 mm and a
width of 30 mm. Further, the plate product was rolled in the
extrusion direction by passing though between a pair of metal
rollers (surface temperature: 40.degree. C.). Thus, a sheet with a
thickness of 1 mm and a width of 50 mm was obtained. Subsequently,
this sheet was heated to 150.degree. C. so that the forming aid was
removed.
[0046] The thermal conductivity, the volume resistivity and the
compressive elastic modulus were measured for the obtained porous
sheet of Comparative Example 1, in the same manner as in Example 1.
Table 1 indicates the measurement results.
TABLE-US-00001 TABLE 1 Thermal Volume Compressive conductivity
resistivity elastic modulus (W/mK) (.OMEGA. cm) (Mpa) Example 1
0.055 0.8 1.5 Example 2 0.08 1.5 0.5 Comparative 0.12 0.5 0.3
Example 1
[0047] The porous sheet of Example 1 and the porous sheet of
Comparative Example 1, which had been produced at the same material
ratio as the porous sheet of Example 1 (PTFE: 1.5 parts by mass,
carbon particles: 85 parts by mass, forming aid: 140 parts by
mass), were compared to each other. The porous sheet of Comparative
Example 1 that does not have a multilayer structure showed high
thermal conductivity and thus insufficient heat insulating
properties, though its volume resistivity was low (which means high
electrical conductivity). In contrast, the porous sheet of Example
1 achieved low volume resistivity (high electrical conductivity)
and low thermal conductivity (good heat insulating properties)
simultaneously. Further, the porous sheet of Example 2 produced in
the same manner as in Example 1, though the material ratio thereof
was different from that of Example 1, achieved low volume
resistivity and low thermal conductivity simultaneously, as was the
case of Example 1. Further, the porous sheets of Examples 1 and 2
each had higher compressive elastic modulus than the porous sheet
of Comparative Example 1.
[0048] The above results demonstrated that the porous sheet
produced by the production method of the present invention
prevented generation of static electricity due to its high
electrical conductivity, and had sufficient heat insulating
properties.
INDUSTRIAL APPLICABILITY
[0049] The porous sheet according to the present invention has low
thermal conductivity and high electrical conductivity. Therefore,
the porous sheet of the present invention can be used suitably for
a precision instrument or the like as a heat insulator that is
capable of preventing generation of static electricity. Further,
the porous sheet according to the present invention can be used
also as a material that prevents generation of noise caused by
static electricity or dust proof material.
* * * * *