U.S. patent application number 15/000347 was filed with the patent office on 2016-05-19 for filter medium for liquid filter and method for manufacturing same.
The applicant listed for this patent is AMOGREENTECH CO., LTD.. Invention is credited to Jun Sik Hwang, In Yong Seo.
Application Number | 20160136584 15/000347 |
Document ID | / |
Family ID | 53046233 |
Filed Date | 2016-05-19 |
United States Patent
Application |
20160136584 |
Kind Code |
A1 |
Hwang; Jun Sik ; et
al. |
May 19, 2016 |
FILTER MEDIUM FOR LIQUID FILTER AND METHOD FOR MANUFACTURING
SAME
Abstract
Provided are filter media for liquid filters and a method of
manufacturing the same, in which a thin filter layer is formed and
the content of nanofibers weighs light, by laminating a low weight
nanofiber web on a porous nonwoven fabric, and thus a less
differential pressure is applied before and after filtering, to
thereby increase a pass flow rate. The filter medium includes: a
porous support that plays a strength support role; and a nanofiber
web that is laminated on one side of the porous support and is made
of nanofibers of a polymer material, in which the nanofiber web
comprises fine pores of a three-dimensional structure, through
which a liquid to be treated passes, wherein content of the
nanofibers is less than 5 gsm.
Inventors: |
Hwang; Jun Sik; (Incheon,
KR) ; Seo; In Yong; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AMOGREENTECH CO., LTD. |
Gimpo-si |
|
KR |
|
|
Family ID: |
53046233 |
Appl. No.: |
15/000347 |
Filed: |
January 19, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/KR2014/006788 |
Jul 25, 2014 |
|
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15000347 |
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Current U.S.
Class: |
210/483 ;
156/244.17 |
Current CPC
Class: |
B32B 2262/04 20130101;
B32B 2307/732 20130101; B32B 2262/0253 20130101; B32B 2264/0235
20130101; B01D 2239/065 20130101; B32B 2264/0228 20130101; B01D
2239/0654 20130101; B01D 2239/025 20130101; B01D 39/1623 20130101;
B32B 5/022 20130101; B32B 2307/718 20130101; B01D 69/10 20130101;
B32B 2262/0238 20130101; B01D 2323/39 20130101; B32B 2307/726
20130101; B32B 2307/728 20130101; B32B 2264/10 20130101; B32B 5/00
20130101; D01D 5/003 20130101; D04H 1/728 20130101; B29C 70/504
20130101; B01D 2325/42 20130101; B32B 5/08 20130101; B32B 5/26
20130101; B32B 2262/0276 20130101; B32B 2262/12 20130101; B32B
2307/73 20130101 |
International
Class: |
B01D 69/12 20060101
B01D069/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 6, 2013 |
KR |
10-2013-0093196 |
Jul 24, 2014 |
KR |
10-2014-0094114 |
Claims
1. A filter medium for liquid filters, the filter medium
comprising: a porous support that plays a strength support role;
and a nanofiber web that is laminated on one side of the porous
support and is made of nanofibers of a polymer material, in which
the nanofiber web comprises fine pores of a three-dimensional
structure, through which a liquid to be treated passes, wherein
content of the nanofibers is less than 5 gsm.
2. The filter medium of claim 1, wherein the content of the
nanofibers is set to range from 2 to 3 gsm.
3. The filter medium of claim 1, wherein thickness of the nanofiber
web is set to range from 2 to 6 .mu.m, and a pore size thereof is
set to 0.2 to 3 .mu.m.
4. The filter medium of claim 1, wherein diameter of the nanofibers
is set to range from 100 to 800 nm.
5. The filter medium of claim 4, wherein diameter of the nanofibers
is set to range from 150 to 300 nm.
6. The filter medium of claim 1, wherein the porous support is a
nonwoven fabric.
7. The filter medium of claim 6, wherein the nonwoven fabric is
made of a PP/PE nonwoven fabric in which PE is coated on an outer
periphery of a PP fiber as a core, wherein the PP/PE nonwoven
fabric is combined with the nanofibers by melting a PE coating
portion coated on an outside of the PP fiber, and wherein the PP
fiber maintains a porous structure.
8. The filter medium of claim 6, wherein the nonwoven fabric is
made of a PET (polyethyleneterephthalate) nonwoven fabric in which
a low melting point PET is coated on an outer periphery of a
regular PET fiber as a core, wherein the PET nonwoven fabric is
combined with the nanofibers by melting the low melting point PET
coated on the outer periphery of the regular PET fiber, and wherein
the regular PET fiber maintains a porous structure.
9. The filter medium of claim 1, wherein the nanofibers are
configured so that ion exchange resin particles are dispersed
inside or on the surfaces of the nanofibers.
10. The filter medium of claim 8, wherein the ion exchange resin
particles are particles of a porous organic polymer with an ion
exchange capacity or particles of a copolymer of polystyrene and
divinylbenzene.
11. A method of manufacturing a filter medium of liquid filters,
the method comprising: electrospinning a spinning solution that is
formed by mixing a polymer material with a solvent on a transfer
sheet, thereby forming a nanofiber web having fine pores of a
three-dimensional structure; performing a primary calendering
process of combining the nanofibers and simultaneously adjusting
pore sizes and thicknesses of the nanofiber web; and performing a
secondary calendering process of laminating the nanofiber web
having undergone the first calendaring process on a porous support
to thus form the filter medium.
12. The method of claim 11, wherein the primary calendering process
is performed at a higher temperature than that of the secondary
calendering process.
13. The method of claim 12, wherein the primary calendering process
is set at a temperature capable of combining the nanofibers to form
a nanofiber web, and wherein the secondary calendering process is
set at a temperature identical to a melting point of a coating
portion having the melting point lower than that of a core of a
double core fiber forming a porous support, in which the coating
portion is melted and combined with the nanofibers.
14. The method of claim 13, wherein the porous support is a PP/PE
nonwoven fabric in which PE fiber is coated on an outer periphery
of a PP fiber as a core, or a PET (polyethyleneterephthalate)
nonwoven fabric in which low melting point PET is coated on an
outer periphery of a regular PET fiber as a core.
15. The method of claim 11, further comprising preheating the
porous support at a temperature lower than that of the secondary
calendering process before executing the secondary calendaring
process.
16. The method of claim 11, wherein the transfer sheet is any one
of paper, a nonwoven fabric made of a polymeric material that is
not dissolved by the solvent contained in the spinning solution,
and a polyolefin-based film.
17. The method of claim 11, wherein thickness of the nanofiber web
is set to range from 2 to 6 .mu.m, and a pore size thereof is set
to 0.2 to 3 .mu.m.
18. The method of claim 11, wherein content of the nanofibers is
less than 5 gsm.
19. The method of claim 11, wherein the spinning solution further
comprises ion exchange resin particles or Ag salts, in which the
nanofibers are configured so that the ion exchange resin particles
or the Ag metal salts are dispersed inside or on the surfaces of
the nanofibers.
Description
TECHNICAL FIELD
[0001] The present invention relates to filter media for liquid
filters and a method of manufacturing the same, and more
particularly, to filter media for liquid filters and a method of
manufacturing the same, in which a thin filter layer is formed and
the content of nanofibers weighs light, by laminating a low weight
nanofiber web on a porous nonwoven fabric, and thus a less
differential pressure is applied before and after filtering, to
thereby increase a pass flow rate.
BACKGROUND ART
[0002] Recent industrial advancement has required high purity and
high quality of products, and thus a separator (or a membrane)
technology has been recognized as a very important field. In the
environmental sector, especially as the need for clean water and
the awareness of a lack of water increases, a technology of using a
membrane has largely attracted much attention as one of ways to
solve these problems. Processes such as water purification, sewage,
waste water, and desalination using a membrane, are already rapidly
spreading. In addition, the membrane technology has been developed
for applications away from the membrane itself, and has expanded
into surrounding technology development and has also enhanced
membrane performance improvement according to applications as
well.
[0003] The membrane is a substance having a selection capability
that is present between two different materials. In other words,
the membrane means a substance which serves to selectively pass or
to exclude a material. Structures and substances of the membrane,
and conditions and principles of the movement of the materials
passing through the membrane, have no limitations. When a substance
is located between only two materials to isolate the two materials
each other and the selective movement of the materials through the
substance between the two materials occurs, the substance may be
called a membrane.
[0004] The membranes are of a very variety of types and are
classified into several criteria.
[0005] First, a classification by a separation operation is a
classification method depending upon the state of a target material
to be separated, and is classified into a liquid separation method,
a gas-liquid separation method, a gas separation method, and so on.
The liquid separation method is classified into micro filtration,
ultra filtration, nano filtration, reverse osmosis filtration,
etc., in accordance with the size of an object for filtration. The
gas separation method is classified in detail in accordance with
the type of gas to be separated. The gas separation membrane is
classified into an oxygen-enriched membrane for separating the
oxygen gas, a nitrogen-enriched membrane for separating the
nitrogen gas, a hydrogen-enriched membrane for separating the
hydrogen gas, a dehumidifying film for removing humidity, etc.
[0006] The membrane is classified according to a film-like shape,
and is classified into a flat membrane, a hollow fiber membrane, a
tubular membrane, etc. In addition, the membrane is also classified
into a plate-shaped type, a spiral wound type, a cartridge type, a
flat membrane cell type, an immersion type, a tubular type, and so
on, depending on the form of a filter module.
[0007] The membrane is classified according to a material and is
classified into an inorganic film and an organic film using a
polymer film. In recent years, however the inorganic films expand
their use based on the advantages of heat resistance, durability,
etc., most currently commercialized products are occupied by the
polymer membranes.
[0008] In general, filtration means to remove two or more
components from a fluid, that is, it means to separate
non-dissolved particles (that is, solid) from the fluid. Filtering
mechanisms in the separation of the solid materials may be
described as sieving, adsorption, dissolution, diffusion
mechanisms. Except for some membranes such as gas separation
membranes, reverse osmosis membranes, etc., it can be said that
most of the filtering mechanisms depend entirely on the sieving
mechanism.
[0009] Therefore, it is possible to use any materials with pores as
filter media. Nonwoven fabrics (nonwovens), woven fabrics (wovens),
meshes, porous membranes and the like are typical filter media.
[0010] It is difficult to make pores not more than 1 .mu.m in the
case of nonwovens, wovens, meshes, etc. Thus, the nonwovens,
wovens, meshes, etc., are used as a pretreatment filter concept
with a limitation to a particle filtration area. Meanwhile, porous
membranes can make precise and small pores and have been used for a
process requiring a wide range of filtration areas and the highest
precision such as micro filtration, ultra filtration, nano
filtration, reverse osmosis filtration, etc.
[0011] Since the nonwovens, wovens, or meshes are made of fibers
having a thickness from several micrometers to several hundreds of
micrometers, it is difficult to make fine pores not more than 1
.mu.m. In particular, it is not possible actually to create uniform
pores since webs are formed by random arrangement of fibers in the
case of the nonwoven fabrics. The melt-blown nonwoven fabric may be
called a nonwoven fabric made of a very fine fiber having a
diameter of 1.about.5 .mu.m. The pore size before heat calendering
is not less than six micrometers and the pore size after heat
calendering is only three micrometers approximately. The deviation
in the average pore size occurs by .+-.15% or more around a
reference point, and the melt-blown nonwoven fabric has a structure
in which very large pores coexist. Accordingly, the nonwovens,
wovens, or meshes have the difficulty in preventing the leakage of
contaminated materials through relatively large pores and thus have
low filter efficiency. Therefore, the filter media are used in an
inaccurate filtration process or used as a pre-treatment concept of
an accurate filtration process.
[0012] Meanwhile, the porous membrane is prepared by a method such
as a non-solvent induced phase separation (NIPS) process, a
thermally induced phase separation (TIPS) process, a stretching
process, a track etching process, a sol-gel process, etc. The
materials of most of the porous membranes are made of
representative organic polymers, such as polytetrafluoroethylene
(PTFE), polyvinylidene fluoride (PVdF), nylon (Nylon6 or Nylon66),
polysulfone (PS), polyethersulfone (PES), polypropylene (PP),
polyethylene (PE), nitrocellulose (NC) or the like. While the
conventional porous membranes may create pores of precise and small
size, closed pores or blinded pores may be created inevitably in
the manufacturing process. As a result, the conventional porous
membranes have problems such as a small flow amount of filtration,
a high driving pressure, and a short filtration lift cycle, to thus
cause high operating costs and frequent filter replacement.
[0013] Therefore, it is in an urgent situation to develop a
membrane of a long lifetime and a high efficiency having constant
filtering performance and stability according to the pore size as a
thin film of a micro-porous structure so as to be used for the
liquid treatment.
[0014] Korean Patent Application Publication No. 2008-60263 (Patent
Document 1) discloses a filtering medium including at least one
nanofiber layer of polymeric nanofibers having an average fiber
diameter of less than about 1 .mu.m, in which a mean flow pore size
is about 0.5 .mu.m to about 5.0 .mu.m, and also that a solidity is
about 15% by volume to about 90% by volume, and a water flow rate
through the medium at a differential pressure of 10 psi (69 kPa)
exceeds about 0.055 L/min/cm.sup.2.
[0015] The method of manufacturing a filtering medium proposed in
Patent Document 1 discloses spinning nanofibers by an electro-blown
spinning method or an electric blowing method by using a solution
containing nylon of 24 wt % in a formic acid as a polymer solution,
including at least one spinning beam comprising spinnerets, blowing
gas injection nozzles and collectors, to thereby form webs.
[0016] However, the method of forming a fibrous web of nanofibers
in the patent document 1 cannot be referred to a manufacturing
technique that uses a multi-hole spinning pack. In addition, when
manufacturing a nanofiber web by an electrospinning method in an
electrobrown spinning apparatus using a multi-hole spinning the
pack in order to increase productivity, a spinning solution
containing a polymer of 24 wt % increases the viscosity and is
solidified at the surface of the spinning solution, to thus make it
difficult to spin for a long time, and increases the fiber
diameter, to thus cause a problem that it is not possible to make
the fibrous form of not more than a micrometer in size.
[0017] Furthermore, in the case that the ultrafine fiber web
obtained by electrospinning does not go through a pretreatment
process of appropriately adjusting the amount of the solvent and
moisture remaining on the surface of the web before performing
calendering, pores are increased but the strength of the web is
weakened. Otherwise, in the case that evaporation of the solvent is
performed too slowly, a phenomenon of melting the web may
occur.
[0018] Meanwhile, Korean Patent Application Publication No.
2012-2491 (Patent Document 2) discloses a filter medium for a
liquid filter, a method of manufacturing the same, and a liquid
filter using the same, using an electrospun nanofiber web to have a
multi-layer structured three-dimensional micro-porous structure to
thereby have high efficiency and long lifetime and maximize filter
efficiency.
[0019] The filter media made of a multi-layer nanofiber web for
liquid filters are prepared by air-electrospinning a spinning
solution on top of a support to thus form a nanofiber web, in which
the spinning solution is obtained by dissolving a fiber forming
polymer material in a solvent, thermo-compression bonding the
support in which the nanofiber web has been formed, or
air-electrospinning a spinning solution to thus form and
thermo-compression bond a nanofiber web, to then laminate the
support on one side of the thermo-compression bonded nanofiber
web.
[0020] However, the process of thermo-compression bonding the
support in which the nanofiber web has been formed after
air-electrospinning the spinning solution on top of the support to
thus form a nanofiber web, in the method of preparing the filter
media for liquid filters, may use a porous nonwoven fabric having a
high tensile strength as the support, to thereby increase the
tensile strength and have the benefit of increasing the ease of
handling during the production but may cause a problem that
uniformity of the nanofiber web is not high.
[0021] Generally, the electrospun nanofibers are integrated in a
collector, that is, bring about an integration phenomenon, and
laminated along a pattern of an integrated portion, that is, bring
about a lamination phenomenon. For example, when electrospinning is
executed on a diamond pattern, nanofibers starts to be integrated
along a first diamond pattern.
[0022] Therefore, in the case of forming a nanofiber web by
spinning nanofibers directly on a nonwoven fabric, as disclosed in
Patent Document 2, there exist problems that a nanofiber web having
excellent uniformity cannot be obtained in view of a nanofiber web
pore size, permeability, thickness, weight, and so on.
[0023] In Patent Document 2, was proposed filter media that are
laminated with a nanofiber web by using a nonwoven fabric made of a
fiber with a single core structure such as a melt-blown nonwoven
fabric, a spun bond nonwoven fabric, and a thermal bond nonwoven
fabric, but it is difficult to maintain a pore structure in any one
of the nonwoven fabric and the nanofiber web since calendering is
performed at a relatively lower melting point of melting points of
the nonwoven fabric and the nanofiber web when the nonwoven fabric
and the nanofiber web are laminated on each other.
[0024] Further, as disclosed in Patent Document 2, in the case of
making filter media by air-electrospinning a spinning solution to
thus form nanofiber web, thermo-compression bonding the nanofiber
web, and then laminating a support on one surface of the
thermo-compression bonded nanofiber web or in the case of making
filter media with only nanofibers by themselves, the filter media
of a heavy weight of about 10 g/m.sup.2 or more are required in
order to handle the filter media. However, the heavy-weight of the
filter media is a factor directly connected with a production rate,
to thus cause high costs.
[0025] In addition, nanofibers have a large amount of static
electricity in a manufacturing process, and thus when the filter
media include only nanofibers themselves, it is quite difficult to
handle the filter media. It is not possible to remove the static
electricity through a composition such as lamination, but it is
possible to improve handling properties. Furthermore, although
nanofibers may have good relative intensities as compared with the
other fibers, the absolute strengths of nanofibers are prone to be
weak.
[0026] In addition, a porous nanofiber web made of nanofibers may
create a rigid coupling between the fibers through a calendering
process, to thus create a highly matured porous nanofiber web.
However, when performing a calendering process by spinning a
spinning solution directly onto a nonwoven fabric as disclosed in
Patent Document 2, the melting point of the nonwoven fabric is
lower than an inter-fiber bonding temperature of the nanofibers
made of a polymer, to accordingly limit a calendering temperature
control. As a result, a rigid coupling between the nanofibers to
form the nanofiber web cannot be made.
[0027] The property of hydrophilicity is required in the liquid
filtration. However, when preparing the filter media by using the
hydrophilic polymer, there is a problem that the hydrophilic
polymer is weak in the mechanical strength and the chemical
resistance as compared to the hydrophobic polymer and thus should
be used limitedly.
[0028] As a result, the filter media made of a PVdF polymer have a
very suitable strength and chemical resistance to liquid
filtration, but there is a problem that the filter media are
limitedly used in aqueous filtration because of the hydrophobic
property. In addition, in the case that the filter media made of a
hydrophobic polymer are made of a heavy weight of about 10
g/m.sup.2 or more so as to be handled in the manufacture process, a
relatively high differential pressure is applied across the filter
media when an aqueous fluid passes through the filter media.
Accordingly, in the case that the hydrophilic treatment is
performed or not, there is a problem that water does not pass
through the filter media well if an appropriate force is not
applied across the filter media.
[0029] In addition, in the case of making the filter media made of
only nanofibers themselves of a heavy weight of about 10 g/m.sup.2
or more, a thin filter layer cannot be formed. Thus, since a high
differential pressure is applied across the filter media, there is
a problem that a pass flow rate becomes little.
[0030] In general, methods of treating water pollutants may include
a co-precipitation method of using a waste water treatment
coagulant, a flotation method according to a specific gravity
difference, a bioaccumulation method, an ion exchange adsorption
method, etc. However, the ion exchange adsorption method has been
known as the most effective method from among them.
SUMMARY OF THE INVENTION
[0031] To solve the above problems or defects, it is an object of
the present invention to provide a filter medium for liquid filters
and a method of manufacturing the same, in which a light weight
nanofiber web is laminated on a porous nonwoven fabric to thereby
form a thin filter layer and make the content of nanofibers per
unit area into a light weight to thus apply a less differential
pressure across the filter medium before and after filtration to
increase a pass flow rate and as a result a membrane with excellent
air permeability and excellent water permeability can be prepared
even if the hydrophilic treatment may not be performed by using a
nanofiber web made of light weight nanofibers even with the use of
a hydrophobic PVdF polymer.
[0032] It is another object of the present invention to provide a
filter medium for liquid filters and a method of manufacturing the
same, in which a transfer method of spinning nanofibers on a
transfer sheet such as paper and laminating the nanofiber spun
transfer sheet on a porous nonwoven fabric, is used, and thus a
nanofiber web having excellent uniformity can be obtained in view
of a pore size, permeability, thickness, weight, and so on of the
nanofiber web.
[0033] It is still another object of the present invention to
provide a filter medium for liquid filters and a method of
manufacturing the same, in which a transfer method of spinning
nanofibers on a transfer sheet such as paper and laminating the
nanofiber spun transfer sheet on a porous nonwoven fabric, is used,
and thus a calendaring process may be executed at a temperature
above a melting point of the nonwoven fabric to thereby create a
rigid coupling between the nanofibers.
[0034] It is yet another object of the present invention to provide
a filter medium for liquid filters and a method of manufacturing
the same, in which a transfer method of spinning nanofibers on a
transfer sheet such as paper and laminating the nanofiber spun
transfer sheet on a porous nonwoven fabric, is used, and thus a
residual solvent contained in a nanofiber web is absorbed to
thereby prevent a re-melting phenomenon that the nanofibers are
melted again in the residual solvent and to also properly adjust
the amount of the residual solvent.
[0035] It is a still yet another object of the present invention to
provide a filter medium for liquid filters which can use a porous
nonwoven fabric that can be used as a support and available at a
lower cost to thus increase a tensile strength to thereby increase
the handleability during production and to thus greatly reduce a
manufacturing cost by laminating a thin film porous nanofiber web
on the porous nonwoven fabric.
[0036] It is a further object of the present invention to provide a
filter medium for liquid filters and a method of manufacturing the
same, in which a surface filtration and a depth filtration of a
liquid can be performed with a nanofiber web having
three-dimensional fine pores, and particular ions of a chemical
substance contained in the liquid to be treated can be filtered by
ion exchange resin particles dispersed inside or outside nanofibers
of the nanofiber web.
[0037] It is a still further object of the present invention to
provide a filter medium for liquid filters and a method of
manufacturing the same, in which quality of a liquid to be treated
is purified by Ag nanoparticles distributed inside or on the
surfaces of nanofibers of a nanofiber web, and a variety of
pathogens that are present in the filter media are also killed.
[0038] To accomplish the above and other objects of the present
invention, according to an aspect of the present invention, there
is provided a filter medium for liquid filters, the filter medium
comprising: a porous support that plays a strength support role;
and a nanofiber web that is laminated on one side of the porous
support and is made of nanofibers of a polymer material, in which
the nanofiber web comprises fine pores of a three-dimensional
structure, through which a liquid to be treated passes, wherein
content of the nanofibers is less than 5 gsm.
[0039] When the content of the nanofibers is less than 5 gsm, air
permeability and water permeability are ensured even though the
nanofiber web is made by laminating hydrophobic nanofibers, to thus
obtain an excellent pass flow rate, but when the content of the
nanofibers exceeds 5 gsm, a filter layer becomes thick to thereby
cause a phenomenon that a more differential pressure is applied and
a pass flow rate is reduced.
[0040] Preferably but not necessarily, the content of the
nanofibers is set to range from 2 to 3 gsm.
[0041] Preferably but not necessarily, thickness of the nanofiber
web is set to range from 2 to 6 .mu.m, and a pore size thereof is
set to 0.2 to 3 .mu.m.
[0042] Preferably but not necessarily, diameter of the nanofibers
is set to range from 100 to 800 nm, and more preferably diameter of
the nanofibers is set to range from 150 to 300 nm.
[0043] Preferably but not necessarily, the porous support is a
nonwoven fabric, in which the nonwoven fabric is made of a PP/PE
nonwoven fabric in which PE is coated on an outer periphery of a PP
fiber as a core, or a PET (polyethyleneterephthalate) nonwoven
fabric in which low melting point PET is coated on an outer
periphery of a regular PET fiber as a core.
[0044] The PP/PE nonwoven fabric is combined with the nanofibers by
melting a PE coating portion coated on an outside of the PP fiber,
and the PP fiber maintains a porous structure. In addition, the PET
nonwoven fabric is combined with the nanofibers by melting the low
melting point PET coated on the outer periphery of the regular PET
fiber, and the regular PET fiber maintains a porous structure.
[0045] Preferably but not necessarily, the nanofibers are
configured so that ion exchange resin particles are dispersed
inside or on the surfaces of the nanofibers, and the ion exchange
resin particles are particles of a porous organic polymer with an
ion exchange capacity or particles of a copolymer of polystyrene
and divinylbenzene.
[0046] In addition, the nanofibers are configured so that the Ag
metal salts are dispersed inside or on the surfaces of the
nanofibers.
[0047] According to another aspect of the present invention, there
is also provided a method of manufacturing a filter medium of
liquid filters, the method comprising: electrospinning a spinning
solution that is formed by mixing a polymer material with a solvent
on a transfer sheet, thereby forming a nanofiber web having fine
pores of a three-dimensional structure; performing a primary
calendering process of combining the nanofibers and simultaneously
adjusting pore sizes and thicknesses of the nanofiber web; and
performing a secondary calendering process of laminating the
nanofiber web having undergone the primary calendaring process on a
porous support to thus form the filter medium.
[0048] Preferably but not necessarily, the primary calendering
process is performed at a higher temperature than that of the
secondary calendering process.
[0049] Preferably but not necessarily, the primary calendering
process is set at a temperature capable of combining the nanofibers
to form a nanofiber web, and wherein the secondary calendering
process is set at a temperature identical to a melting point of a
coating portion having the melting point lower than that of a core
of a double core fiber forming a porous support, in which the
coating portion is melted and combined with the nanofibers.
[0050] Preferably but not necessarily, the spinning solution
further comprises ion exchange resin particles or Ag metal salts,
in which the nanofibers are configured so that the ion exchange
resin particles or the Ag metal salts are dispersed inside or on
the surfaces of the nanofibers.
[0051] Preferably but not necessarily, the transfer sheet is any
one of paper, a nonwoven fabric made of a polymeric material that
is not dissolved by the solvent contained in the spinning solution,
and a polyolefin-based film.
[0052] As described above, the present invention provides a filter
medium for liquid filters and a method of manufacturing the same,
in which a light weight nanofiber web is laminated on a porous
nonwoven fabric to thereby form a thin filter layer and make the
content of nanofibers per unit area into a light weight to thus
apply a less differential pressure across the filter medium before
and after filtration to increase a pass flow rate and as a result a
membrane with excellent air permeability and excellent water
permeability can be prepared even if the hydrophilic treatment may
not be performed by using a nanofiber web made of light weight
nanofibers even with the use of a hydrophobic PVdF polymer.
[0053] That is, in general, as a filter layer becomes thick, a
phenomenon of generating a lot of differential pressure and
reducing a pass flow rate occurs, but a light weight porous
nanofiber web is laminated on a porous nonwoven fabric to thereby
form a thin filter layer to thus apply a less differential pressure
across the filter medium to thus increase a pass flow rate.
[0054] The present invention uses a transfer method of spinning
nanofibers on a transfer sheet such as paper and laminating the
nanofiber spun transfer sheet on a porous nonwoven fabric, to thus
obtain a nanofiber web having excellent uniformity in view of a
pore size, permeability, thickness, weight, and so on of the
nanofiber web.
[0055] The present invention uses a transfer method of spinning
nanofibers on a transfer sheet such as paper and laminating the
nanofiber spun transfer sheet on a porous nonwoven fabric, and thus
executes a calendaring process at a temperature above a melting
point of the nonwoven fabric before a laminating process to thereby
create a rigid coupling between the nanofibers.
[0056] The present invention uses a transfer method of spinning
nanofibers on a transfer sheet such as paper and laminating the
nanofiber spun transfer sheet on a porous nonwoven fabric, to thus
absorb a residual solvent contained in a nanofiber web to thereby
prevent a re-melting phenomenon that the nanofibers are melted
again in the residual solvent and to also properly adjust the
amount of the residual solvent.
[0057] The present invention uses a porous nonwoven fabric that can
be used as a support and available at a lower cost in which a
tensile strength can be increased, to thereby increase the
handleability during production and greatly reduce a manufacturing
cost by laminating a thin film porous nanofiber web on the porous
nonwoven fabric.
[0058] The present invention uses a porous support made of fibers
of a double core structure and having respectively different
melting points, to thus execute a calendaring process at a melting
point of a low melting point coating portion that surrounds a high
melting point core when executing the calendaring process in order
to laminate a porous support on a nanofiber web, to thereby enable
the porous support to maintain a pore structure a high melting
point core fiber.
[0059] Further, the low melting point coating portion of the porous
support is combined with (bonded with) nanofibers of a nanofiber
web to thereby increase a coupling force.
[0060] The present invention can filter particular ions of a
chemical substance contained in a liquid to be treated by ion
exchange resin particles dispersed inside or outside nanofibers of
a nanofiber web. The present invention can purify quality of a
liquid to be treated by Ag nanoparticles distributed inside or on
the surfaces of nanofibers of a nanofiber web, and eradicate a
variety of pathogens that are present in a filter medium.
DESCRIPTION OF DRAWINGS
[0061] FIG. 1 is a cross-sectional view of a filter medium for
liquid filters according to a preferred embodiment of the present
invention.
[0062] FIG. 2 is a flowchart view showing a manufacturing process
of a liquid filter according to a preferred embodiment of the
present invention.
[0063] FIG. 3 is a schematic diagram showing an apparatus for
manufacturing filter media shown in FIG. 1.
[0064] FIG. 4 is a schematic diagram showing a roll-type liquid
filter according to a preferred embodiment of the present
invention.
[0065] FIG. 5 is a cross-sectional view of a multilayer-type liquid
filter according to a preferred embodiment of the present
invention.
[0066] FIG. 6 is a graph showing pore size distributions of Example
1 according to the present invention and Comparative Examples 1 to
3.
DETAILED DESCRIPTION OF THE INVENTION
[0067] Hereinafter, filter media for liquid filters and a method of
manufacturing the same embodiments of the present invention will be
described with reference to the accompanying drawings. In the
process, the sizes and shapes of components illustrated in the
drawings may be shown exaggerated for convenience and clarity of
explanation. Further, by considering the configuration and
operation of the present invention, the specifically defined terms
may be changed according to user's or operator's intention, or the
custom. Definitions of these terms herein need to be made based on
the contents across the whole application.
[0068] The electrospun nanofibers are collected on a collector and
are laminated along a pattern of the collector. For example, when
the nanofibers are electrospun on a diamond pattern, the nanofibers
start to be collected along the initial diamond pattern.
[0069] Thus, in order to make a nanofiber web having good
uniformity such as a pore size, permeability, thickness, and
weight, paper is more suitable than a nonwoven fabric.
[0070] The present invention uses a transfer method of spinning
nanofibers on a transfer sheet such as paper and laminating the
nanofiber spun transfer sheet on a porous nonwoven fabric, to thus
make a nanofiber web having good uniformity such as a pore size,
permeability, thickness, and weight.
[0071] The porous nanofiber web made of nanofibers may create a
rigid coupling between the fibers through a calendering process, to
thus create a highly matured porous nanofiber web. However, when
performing a calendering process by spinning a spinning solution
directly onto a nonwoven fabric used as a nonwoven fabric, a
calendering temperature control is limited due to the melting point
of the nonwoven fabric.
[0072] A bonding temperature between nanofibers, for example, PVdF
fibers is about 150.degree. C., but a melting point of the nonwoven
fabric is in the range of 110.about.130.degree. C.
[0073] The present invention prepares filter media by using the
transfer method of forming a nanofiber web and then laminating the
nanofiber web on a porous nonwoven fabric.
[0074] Thus, a primary calendering process is executed for the
nanofiber web that is obtained by spinning nanofibers on the
transfer sheet such as paper, at a temperature higher than the
melting point of the nonwoven fabric, preferably at an inter-fiber
bonding in temperature of the nanofibers, to thereby achieve a
rigid coupling between the nanofibers. Then, the nanofiber web
having undergone the primary calendering is laminated on a porous
nonwoven fabric by a secondary calendaring process whose
temperature is set to a melting point of the nonwoven fabric.
[0075] Thus, the primary calendering temperature is a temperature
at which nanofibers to form a nanofiber web can be combined, for
example, is set to 150 to 200.degree. C., and the secondary
calendering temperature is preferably set to 110.about.130.degree.
C. that is the melting point of a coating portion coated on an
outside of a core in a PP/PE nonwoven fabric made of PP/PE fibers
of a double core structure, for example, PE.
[0076] Accordingly, when the secondary calendering is executed, the
PE coating portion coated on the outside of the core in the PP/PE
nonwoven fabric is melted and laminated with the nanofiber web and
a PP core maintains its shape to thus maintain a porous
structure.
[0077] In the present invention, a transfer sheet having a high
tensile strength is continuously fed to the top of a collector of
an electrospinning device from a transfer roll in order to improve
operability of the primary and secondary calendering processes, to
thereby form a laminated porous nanofiber web on top of the
transfer sheet.
[0078] The transfer sheet may employ, for example, paper, a
nonwoven fabric made of a polymer material that is not made soluble
by a solvent contained in a mixed spinning solution during spinning
the mixed spinning solution, or a polyolefin-based film such as PE
or PP. In the case that the transfer sheet is made of only the
porous nanofiber web itself, the transfer sheet has a low tensile
strength, and thus it is difficult to execute a drying process, a
calendaring process and a winding process while the transfer sheet
is fed at a high feed rate.
[0079] Furthermore, it is difficult to consecutively execute a
laminating process with a subsequent support at a high feed rate
after producing the porous nanofiber web, but in the case of using
the transfer sheet, a sufficient tensile strength is provided to
thus significantly increase a processing speed.
[0080] In the case of using only the porous nanofiber web, a
phenomenon that the porous nanofiber web is stuck to other objects
due to static electricity occurs and thus workability falls, but in
the case of using the transfer sheet, the problem such as the
sticking phenomenon can be solved. After the transfer sheet is
subjected to a lamination process with the support, the transfer
sheet is peeled off and removed.
[0081] In addition, the present invention uses a transfer method of
spinning nanofibers on a transfer sheet such as paper and
laminating the nanofiber spun transfer sheet on a porous nonwoven
fabric, to thus absorb a residual solvent contained in a nanofiber
web to thereby prevent a re-melting phenomenon that the nanofibers
are melted again in the residual solvent and to also properly
adjust the amount of the residual solvent.
[0082] In general, as a filter layer becomes thick, a phenomenon of
generating a lot of differential pressure and reducing a pass flow
rate occurs. In order to solve this problem in the present
invention, a light weight porous nanofiber web is laminated on a
porous nonwoven fabric to thereby form a thin filter layer to thus
apply a less differential pressure across the filter medium to thus
increase a pass flow rate.
[0083] In the present invention, when forming a porous nanofiber
web that is laminated to a porous nonwoven fabric, an accumulated
amount of nanofibers is set to less than 5 gsm, preferably in a
range of 2 to 3 gsm. Accordingly, a membrane with excellent air
permeability and excellent water permeability can be prepared even
if the hydrophilic treatment may not be performed by using a
nanofiber web made of light weight nanofibers even with the use of
a hydrophobic PVdF polymer.
[0084] In addition, in the present invention, a spinning solution
that is obtained by mixing a polymer material, ion exchange resin
particles and a solvent is electrospun to one side of the transfer
sheet to thus form a nanofiber web in which ion exchange resin
particles are dispersed inside or outside the nanofibers.
Accordingly, a surface filtration and a depth filtration of a
liquid can be performed with the nanofiber web having fine pores of
a three-dimensional network structure, and particular ions of a
chemical substance contained in the liquid to be treated can be
filtered by ion exchange resin particles dispersed inside or
outside nanofibers of the nanofiber web.
[0085] Furthermore, in the present invention, a predetermined
amount of Ag metal salt are added when forming the aforementioned
spinning solution, and then the spinning solution with the Ag metal
salt is spun, to thus rigidly fix Ag nanoparticles inside or on the
surfaces of the nanofibers of the nanofiber web and uniformly
dispersing the Ag nanoparticles to thereby eradicate a variety of
pathogenic bacteria in the presence of the filter medium by the Ag
nanoparticles having an antimicrobial function.
[0086] The Ag metal salt can employs one or more selected from the
group consisting of silver nitrate is (AgNO.sub.3), silver chloride
(AgCl), and silver sulfide (Ag.sub.2S).
[0087] In general, a nanofiber web that is formed by collecting
nanofibers by electrospinning has a high porosity structure than a
porous support such as a nonwoven fabric.
[0088] As a result, when a liquid filter that is manufactured by
using a filter media in accordance with the present invention is
configured into a filter structure by laminating a filter medium of
a two-layer structure in which a nanofiber web having a relatively
high porosity and a porous support having a relatively low porosity
are stacked over one another into a multi-layer structure, or
winding the filter medium of the two-layer structure in a roll
type, a liquid to be treated is filtered while passing through the
nanofiber web of a light weight structure and having a relatively
high porosity, thereby ensuring a good air permeability and a good
water permeability while improving filtering efficiency.
[0089] The nonwoven fabric that can be used as the porous support
can be made of a PP/PE nonwoven fabric in which PE is coated on an
outer periphery of a PP fiber as a core, or a PET
(polyethyleneterephthalate) nonwoven fabric in which low melting
point PET is coated on an outer periphery of a regular PET fiber as
a core.
[0090] The nonwoven fabric of the double structure maintains the
pore structure since the PP fiber or the regular PET fiber that
forms a core is able to maintain its shape when the calendering
temperature is set according to the melting point of PE or the low
melting temperature of PET at the time of laminating the nanofiber
web with the nonwoven fabric.
[0091] In addition, the PE coating portion and the low melting
point PET is melted and combined with the nanofibers during
calendaring, to thus increase a bonding force between the nonwoven
fabric and the nanofiber web.
[0092] Therefore, the present invention uses the porous support
made of fibers of the double core structure having two respectively
different melting points, to thus keep the pore structure of the
porous support while increasing the bonding strength between the
porous support and the nanofiber web.
[0093] In addition, the present invention may use a porous support
made of fibers that is available at low cost, and that may increase
the handling properties due to the high tensile strength during the
production of filter media, in which the fibers have a double core
structure with two respectively different melting points, as other
nonwoven fabric.
[0094] The polymer material used for the embodiments of the present
invention may include, for example, hydrophilic polymers or/and
hydrophobic polymers that can be electrospun, or may include one
kind of the polymers or a mixture of two or more kinds of the
polymers.
[0095] In the present invention, the hydrophilic properties may be
required in the liquid filtration, but when considering the
hydrophilic polymer has a weak mechanical strength and a weak
chemical resistance as compared to the hydrophobic polymer, a
mixture of the hydrophilic polymer and the hydrophobic polymer may
be used to supplement the disadvantages of each of the hydrophilic
polymer and the hydrophobic polymer and utilize the advantages
thereof.
[0096] Also, even though a hydrophobic polymer such as PVdF is
used, the filter media made of light weight of less than 5 gsm are
manufactured and set to a low differential pressure, and thus may
have a good water permeability by imposing an appropriate driving
force even when hydrophilic treatment has not been performed.
[0097] The polymer materials used in the embodiments of the present
invention may be resins that may be dissolved in an organic solvent
for electrospinning, and that may be capable of forming nanofibers
by electrospinning, but are not specifically limited thereto. For
example, the polymer materials used in the present invention may
be: polyvinylidene fluoride (PVdF), poly(vinylidene
fluoride-co-hexafluoropropylene), a perfluoropolymer, polyvinyl
chloride, polyvinylidene chloride, or a copolymer thereof; a
polyethylene glycol derivative containing polyethylene glycol
dialkylether and polyethylene glycol dialkylester;
poly(oxymethylene-oligo-oxyethylene); polyoxide containing
polyethylene oxide and polypropylene oxide; polyvinyl acetate,
poly(vinyl pyrrolidone-vinyl acetate), polystyrene, and a
polystyrene acrylonitrile copolymer; a polyacrylonitrile copolymer
containing polyacrylonitrile (PAN) and a polyacrylonitrile methyl
methacrylate copolymer; or polymethyl methacrylate, a poly methyl
methacrylate copolymer, or a mixture thereof.
[0098] Also, the polymer material used in the present invention may
be: aromatic polyester such as polyamide, polyimide,
polyamideimide, poly(meta-phenylene isophthal amide), polyester
sulfone (PES), polyether ketone, polyetherimide (PEI), polyethylene
terephthalate, polytrimethylene terephthalate, or polyethylene
naphthalate; polyphosphazene such as polytetrafluoroethylene,
polydifenoxiphosphazene, poly{bis[2-(2-methoxyethoxy)phosphazene]};
polyurethane, and polyurethane copolymer containing polyether
urethane; or cellulose acetate, cellulose acetate butyrate,
cellulose acetate propionate.
[0099] The polymer materials that may be particularly desirably
used as the filter material of the present invention may be
polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), polyester
sulfone (PES), and polystyrene (PS), alone or a mixture of
polyvinylidene fluoride (PVdF) and polyacrylonitrile (PAN), a
mixture of PVdF and PES, or a mixture of PVdF and thermoplastic
polyurethane (TPU).
[0100] Thus, the polymer that can be used in the present invention
is not particularly limited to a thermoplastic polymer and a
thermoset polymer that can be electrospun.
[0101] In order to prepare a spinning solution, it is possible to
use a single-component solvent, for example, dimethylformamide
(DMF), as a solvent mixed with a polymer material. However, in the
case that a 2-component solvent is used as a solvent that is used
in the spinning solution, it is desirable to use a 2-component
solvent that is obtained by mixing a solvent with a relatively high
boiling point (BP) and a solvent with a relatively low boiling
point (BP).
[0102] In the case of a 2-component solvent according to the
present invention, it is preferable that a high boiling point
solvent and a low boiling solvent are mixed at a weight ratio of
about 7:3 to about 9:1.
[0103] In the present invention, the ion exchange resin can employ
a positive ion exchange resin or a negative ion exchange resin.
[0104] That is, the ion exchange resin particles in the present
invention may be defined as having a functional group which has an
ion exchange capacity on the internal surface thereof, and include
a positive ion exchange resin, a negative ion exchange resin, or a
positive/negative exchange resin in accordance with exchanged
ions.
[0105] More specifically, the present invention creates a spinning
solution by making a porous organic polymer having an ion exchange
capacity or PSDVB (Polystyrene Divinylbenzene) that is a copolymer
of polystyrene and divinylbenzene into particles, and mixing the
particles with a solvent.
[0106] (Structure of Filter Media)
[0107] Filter media for liquid filters according to a preferred
embodiment of the present invention will be described below with
reference to the accompanying drawings.
[0108] FIG. 1 is a cross-sectional view of a filter medium for
liquid filters according to a preferred embodiment of the present
invention. FIG. 2 is a flowchart view showing a manufacturing
process of a liquid filter according to a preferred embodiment of
the present invention. FIG. 3 is a schematic diagram showing an
apparatus for manufacturing filter media shown in FIG. 1.
[0109] Referring to FIG. 1, a filter medium 10 for a liquid filter
according to a preferred embodiment of the present invention is
configured so that a porous support 11 such as nonwoven fabric is
laminated on one surface of a porous nanofiber web 13.
[0110] The nanofiber web 13 is configured so that ion exchange
resin particles 15 and Ag nanoparticles 17 are dispersed inside or
on the surfaces of nanofibers 25 collected by electrospinning a
mixed spinning liquid that is obtained by mixing a polymer
material, ion-exchange resin particles, and a solvent, and is
configured to include fine pores of a three-dimensional network
structure to thus perform surface filtration and depth filtration
of a liquid and simultaneously filter certain ions of a chemical
substance contained in the liquid.
[0111] In addition, it is possible to purify quality of the liquid
to be treated and to eliminate various pathogens present in the
nanofiber web 13 by the Ag nanoparticles 17 that are uniformly
dispersed on and fixed to the surfaces of the nanofibers 25.
[0112] The nanofiber web 13 produced by the electrospinning method
is separately prepared preferably by using a transfer sheet, and
then is laminated with the porous support 11 to thus form a filter
medium 10.
[0113] The filter medium 10 of the two-layer structure is rolled to
thus form a roll type liquid filter 100 as shown in FIG. 4, or form
a laminate type liquid filter 100a that is stacked in a multi-layer
structure through a bending process for increasing a specific
surface area, as shown in FIG. 5.
[0114] As described above, referring to FIG. 4, when partitioning
the layer of the filter medium 10 laminated with the porous support
11, water to be treated (A) is filtered while mainly passing
through the nanofiber web 13 having a high porosity instead of the
porous support 11 having a low porosity, to thereby obtain the
purified water (B) from an outlet of the filter 100, and block a
problem that the water to be treated (A) is concentrated and
pressed locally.
[0115] In the present invention, the diameter of each of the
nanofibers constituting the porous nanofiber web 13 is set to 100
to 800 nm, preferably 150 to 300 nm. The thickness of the nanofiber
web is set to 2-6 .mu.m, and the pore size of the nanofiber web is
preferably set to be in a range of 0.2 to 3 .mu.m. When forming the
porous nanofiber web, the accumulated amount of nanofibers is set
to less than 5 gsm so that a low weight is made, preferably set to
range from 2 to 3 gsm.
[0116] The average diameter of the fibers constituting the porous
nanofiber web 13 has a very large effect on the pore size and pore
size distribution. The smaller the fiber diameter becomes, the
smaller the pore size, and the smaller the pore size
distribution.
[0117] In addition, in the present invention, the smaller the
diameter of each of the nanofibers, the average pore size and the
maximum pore size decrease. In addition, the smaller the diameter
of each of the nanofibers, the density of the nanofibers increase.
Accordingly, the basis weight and the average thickness also
increase, and air permeability decreases. However, it is possible
to filter the finer pollutants, to thus increase a filtering
effect.
[0118] Further, the liquid filter including the filter medium
according to the embodiment of the present invention consumes less
energy and has a long life due to the low differential pressure of
the filter before and after the filtering process.
[0119] (Manufacturing of Filter Media)
[0120] Referring to FIGS. 2 and 3, the method of manufacturing the
filter media according to the embodiment of the present invention
will be described below.
[0121] First, a transfer sheet 20 such as paper is supplied from an
unwinder on which the transfer sheet 20 has been wound, to the top
of a collector 23 of an electrospinning apparatus 21.
[0122] Then, a spinning solution is prepared by mixing a polymer
material, ion exchange resin particles, a metal salt and a solvent,
and then electrospun on the transfer sheet 20, thereby forming a
nanofiber web 13 (S11).
[0123] A spinning method that may be used to manufacture a
nanofiber web according to the present invention may employ any one
selected from general electrospinning, electrospray, electrobrown
spinning, centrifugal electrospinning, and flash-electrospinning,
in addition to air-electrospinning (AES).
[0124] The ion exchange resin particles are dispersed inside or on
or the surfaces of the nanofibers 25 of the nanofiber web 13, and
some of the ion exchange resin particles 15 of all the ion exchange
resin particles are exposed to the surfaces of the nanofibers, to
thus be involved to filter specific ions contained in the water to
be treated (A). Further, the Ag nanoparticles 17 that are derived
from the metal salt are stably and uniformly dispersed inside or on
the surfaces of the nanofibers 25.
[0125] In the present invention, a process of adjusting the amount
of the residual solvent and moisture remaining on the surface of
the porous nanofiber web 13 may be undergone (S12) while the porous
nanofiber web 13 passes through a pre-air dry zone by a pre-heater
27. Then, a calendaring process is undergone.
[0126] In the pre-air dry zone by the pre-heater 27, air of 20 to
40.degree. C. is applied to the porous nanofiber web 13 by using a
fan, thereby adjusting an amount of the solvent and moisture
remaining on the surface of the porous nanofiber web 13. As a
result, the porous nanofiber web 13 is controlled so as to be
prevented from being bulky. The air blow of the fan plays a role of
increasing strength of the film and controlling porosity of the
film.
[0127] In this case, if calendering is accomplished at a state
where evaporation of the solvent has been excessively performed,
porosity is increased but strength of the nanofiber web is
weakened. Reversely, if less evaporation of the solvent occurs, the
nanofiber web is melted.
[0128] Meanwhile, the porous nanofiber web 13 may be a low weight
porous nanofiber web 13 directly formed on the porous support 11 by
the input of the porous support 11 such as a nonwoven fabric to the
collector 23 of the electrospinning apparatus 21 instead of the
transfer sheet 20.
[0129] After forming the porous nanofiber web 13 consisting of
ultra-fine nanofibers 25, the resulting porous nanofiber web is
formed by calendering at a temperature below the melting point of
the polymer in a primary calendering unit 31 (S13).
[0130] An inter-fiber bonding temperature of nanofibers, for
example, PVdF fibers is 150.degree. C., and PAN is 160.degree. C.,
PES is 200.degree. C., and the melting point of the nonwoven fabric
(PE) is 110.about.130.degree. C.
[0131] Therefore, when a polymer forming the porous nanofiber web
13 is PVdF, and the primary calendering process is performed at
about 150.degree. C., the porous nanofiber web 13 made of
nanofibers creates a rigid coupling between the fibers through the
primary calendering process thereby creating a highly matured
porous nanofiber web. When the primary calendering process is done,
a coupling is made between the nanofibers to thus control the pore
sizes of three-dimensional pores and thickness of the nanofiber web
formed by the collection of a large number of the nanofibers
25.
[0132] In the present invention, any one method selected from the
group consisting of pressing, rolling, thermal bonding and
ultrasonic bonding may be performed for a combination of the
nanofiber web and the nonwoven fabric, in addition to calendaring
that laminates the nanofiber web with the nonwoven web to then
perform a hot pressing bond.
[0133] In addition, in the present invention, the porous nanofiber
web 13 obtained after having carried out the calendering process as
required preferably undergoes a process of removing the residual
solvent or water by using a secondary hot air dryer 29 at a
temperature of 100.degree. C. and with a velocity 20 msec (S14),
and is wound on a winder as a take-up roll of the porous nanofiber
web 13 in a state in which the transfer sheet 20 is disposed on the
inner side of the porous nanofiber web 13.
[0134] The two-layer laminate of the porous nanofiber web 13 and
the transfer sheet 20 wound around the winder undergoes a
lamination process with the porous support 11 such as the nonwoven
fabric in a secondary calendering unit 33 (S15).
[0135] In this case, when supplying the porous support 11 that has
not been pre-heated for the secondary calendaring unit 33, a
problem of lowering the set temperature of the roll of the
secondary calendering unit 33 by approximately 10-15.degree. C. may
occur. Thus, preferably, the porous support 11 is preheated to a
slightly lower temperature than the secondary calendering
temperature, for example, 80.degree. C., by using a heating roll or
an infrared (IR) lamp (not shown), calendering, for example, after
the second It is supplied to the calendering apparatus 33, and then
is supplied to the secondary calendering unit 33.
[0136] The temperature of the secondary calendering unit 33 is set
to 110.about.130.degree. C. which can melt a PE film layer when
using a PP/PE nonwoven fabric of a PE-coated double structure on
the outer periphery of a PP fiber. As a result, the porous support
11 is laminated with the porous nanofiber web 13 in the secondary
calendering unit 33 (S15), and then the transfer sheet 20 is peeled
off and removed from the laminated filter medium 10 at the rear end
of the secondary calendering unit 33.
[0137] The present invention uses a transfer method of spinning
nanofibers on a transfer sheet 20 such as paper and laminating the
nanofiber spun transfer sheet on a porous nonwoven fabric, and thus
executes a calendaring process at a temperature above a melting
point of the nonwoven fabric before a laminating process to thereby
create a rigid coupling between the nanofibers.
[0138] Subsequently, when the filter medium 10 is rolled as shown
in FIG. 4 (S16), a roll type liquid filter 100 is obtained.
[0139] When the filter medium of the laminated structure of the
nanofiber web 13 and the porous support 11 is rolled in the present
invention, as shown in FIG. 4, the filter medium 10 of the
laminated structure of the nanofiber web 13 and the porous support
11 has a continuously repeated structure from the center of the
rolled chemical filter medium (that is a roll axis) to the
direction of the outer peripheral surface of the rolled chemical
filter medium, or has a repeatedly laminated structure of the
filter media 10 and 10a of the laminated structure of the nanofiber
web 13 and the porous support 11 as shown in FIG. 5, to thereby
implement a lamination type liquid filter 100a.
[0140] Hereinafter, embodiments of the present invention will be
described in more detail with reference to the following Examples.
However, the following Examples are nothing but the illustration of
the invention only, and are not limited to the scope of the
invention.
Example 1
[0141] In Example 1, PVdF (Polyvinylidene fluoride) as a polymer
material was dissolved in a solvent (DMAc:Acetone=7:3) to become 14
wt % to thus prepare a spinning solution. The spinning solution was
moved to a mixing tank of an electrospinning apparatus to set a
voltage applied to the electrospinning apparatus to 100 kV, a
distance from a spinning nozzle and a collector to 20 cm, a
discharge amount per minute to 20 .mu.l/hole, and was electrospun
under a spinning atmosphere of 30.degree. C. and a relative
humidity of 60%, to have prepared a nanofiber web of a weight of 3
gsm with a pore size of 1 .mu.m.
[0142] The thus-obtained nanofiber web was calendered under the
condition of 150.degree. C. and 1 Kgf/cm.sup.2 thereby have formed
a bond between the nanofibers and thus have implemented a fixed
pore structure, and the calendered nanofiber web was laminated with
a nonwoven fabric under the condition of 130.degree. C. and 1
Kgf/cm.sup.2 to have produced a filter medium. The nonwoven fabric
used in this Example 1 was a nonwoven fabric to be produced in
Namyang Nonwoven Fabric Co., Ltd., and used a polyolefin material
of thickness 160 .mu.m and 40 gsm.
[0143] For the filter medium material obtained from Example 1, by
using a Capillary porosimeter of PMI (Porous Materials, Inc.), the
pore size distribution was measured according to the ASTM E1294
standard, and the results were also shown in Table 1 and FIG.
6.
[0144] A PVdF membrane of a pore size of 1 .mu.m made in a phase
transition manner of Merck-Millipore (Comparative Example 1), a
Micro PES membrane of a pore size of 1 .mu.m made in a phase
transition manner of Membrana Inc., (Comparative Example 2), and
melt-blown media of a pore size of 1 .mu.m made by H & V
(Hollingsworth & Vose Company) (Comparative Example 3) were
used as control groups
TABLE-US-00001 TABLE 1 Pore size (.mu.m) The average pore The
maximum pore Example 1 (Nanofibers 1 .mu.m) 1.0 1.3 Comparative
Example 1 1.0 1.7 (PVdF membrane 1 .mu.m) Comparative Example 2 1.0
1.6 (PES Membrane 1 .mu.m) Comparative Example 3 2.2 5.6
(Melt-blown 1 .mu.m)
[0145] As illustrated in Table 1 and FIG. 6, the filter medium of
Example 1 according to the present invention appeared to have an
average pore size of 1.0 .mu.m, and the maximum pore size of 1.3
.mu.m and appeared to have a narrow pore size distribution over the
same level as those of commercially available filter membranes of
Comparative Examples 1 to 3.
[0146] By using FX3300 of TEXTEST for the filter media of Example 1
and Comparative Examples 1 to 3, air permeabilities were measured
according to the ASTM D737 standard and the results were shown in
Table 2.
TABLE-US-00002 TABLE 2 Air permeability (cfm@125 Pa) Example 1
(Nanofibers 1 .mu.m) 2.5 Comparative Example 1 0.8 (PVdF Membrane 1
.mu.m) Comparative Example 2 1.1 (PES Membrane 1 .mu.m) Comparative
Example 3 0.7 (Melt-blown 1 .mu.m)
[0147] As shown in Table 2, the filter medium of Example 1
according to the present invention was measured as the air
permeability of 2.5 cfm@125 Pa, and appeared to have a very high
air permeability compared to the commercially available filter
membranes of Comparative Examples 1-3.
[0148] By using self-made equipment for the filter media of Example
1 and Comparative Examples 1 to 3, filtration was performed
according to ASTM F795 standard, differential pressures across the
filter media were measured, and the results were shown in Table
3.
TABLE-US-00003 TABLE 3 The pressure drop (psid @ 31 pm, 4.9
cm.sup.2) Example 1 (Nanofibers 1 .mu.m) 0.8 Comparative Example 1
2.1 (PVdF Membrane 1 .mu.m) Comparative Example 2 1.7 (PES Membrane
1 .mu.m) Comparative Example 3 6.2 (Melt-blown 1 .mu.m)
[0149] As shown in Table 3, the filter medium of Example 1
according to the present invention was measured as the pressure
drop of 0.8 psid @ 31 pm, 4.9 cm.sup.2, and appeared to have a very
high water permeability as compared to the commercially available
filter membranes of Comparative Examples 1-3. By using self-made
equipment for the filter media of Example 1 and Comparative
Examples 1 to 3, filtrations were performed according to ASTM F795
standard, turbidities for the filtered liquids were measured, and
the results were shown in Table 4. The test particles (Dust) were
used as ISO 12103-1, A2 fine.
TABLE-US-00004 TABLE 4 Turbidity (NTU) Example 1 (Nanofibers 1
.mu.m) 0.4 Comparative Example 1 0.4 (PVdF Membrane 1 .mu.m)
Comparative Example 2 0.7 (PES Membrane 1 .mu.m) Comparative
Example 3 2.1 (Melt-blown 1 .mu.m)
[0150] As shown in Table 4, the filter medium of Example 1
according to the present invention was measured as the turbidity of
0.4 NTU, and appeared to have very excellent turbidity removal
efficiency as compared to commercially available filter membranes
of Comparative Examples 1 to 3.
Example 2
[0151] In Example 2, PVdF (Polyvinylidene fluoride) as a polymer
material was dissolved in a solvent (DMAc:Acetone=7:3) to become 10
wt % to thus prepare a spinning solution. The spinning solution was
moved to a mixing tank of an electrospinning apparatus to set a
voltage applied to the electrospinning apparatus to 100 kV, a
distance from a spinning nozzle and a collector to 20 cm, a
discharge amount per minute to 20 .mu.l/hole, and was electrospun
under a spinning atmosphere of 30.degree. C. and a relative
humidity of 60%, to have prepared a nanofiber web of a weight of 3
gsm with a pore size of 0.45 .mu.m.
[0152] The thus-obtained nanofiber web was calendered under the
condition of 150.degree. C. and 1 Kgf/cm.sup.2 thereby have formed
a bond between the nanofibers and thus have implemented a fixed
pore structure, and the calendered nanofiber web was laminated with
a nonwoven fabric under the condition of 130.degree. C. and 1
Kgf/cm.sup.2 to have produced a filter medium. The nonwoven fabric
used in this Example 2 was the same as that of Example 1.
[0153] For the filter medium material obtained from Example 2, by
using a Capillary porosimeter of PMI (Porous Materials, Inc.), the
pore size distribution was measured according to the ASTM E1294
standard, and the results were also shown in Table 5.
[0154] A PVdF membrane of a pore size of 0.45 .mu.m of
Merck-Millipore (Comparative Example 4), and a Micro PES membrane
of a pore size of 0.45 .mu.m of Membrana Inc., (Comparative Example
5) were used as control groups
TABLE-US-00005 TABLE 5 Pore size (.mu.m) The average pore The
maximum pore Example 2 0.39 0.59 (Nanofibers 0.45 .mu.m)
Comparative Example 4 0.41 0.68 (PVdF membrane 0.45 .mu.m)
Comparative Example 5 0.36 0.57 (PES Membrane 0.45 .mu.m)
[0155] As illustrated in Table 5 and FIG. 6, the filter medium of
Example 2 according to the present invention appeared to have an
average pore size of 0.39 .mu.m, and the maximum pore size of 0.59
.mu.m and appeared to have a narrow pore size distribution over the
same level as those of commercially available filter membranes of
Comparative Examples 4 and 5.
[0156] By using FX3300 of TEXTEST for the filter media of Example 2
and Comparative Examples 4 and 5, air permeabilities were measured
according to the ASTM D737 standard and the results were shown in
Table 6.
TABLE-US-00006 TABLE 6 Air permeability (cfm@125 Pa) Example 2
(Nanofibers 0.45 .mu.m) 1.48 Comparative Example 4 0.31 (PVdF
Membrane 0.45 .mu.m) Comparative Example 5 0.34 (PES Membrane 0.45
.mu.m)
[0157] As shown in Table 6, the filter medium of Example 2
according to the present invention was measured as the air
permeability of 1.48 cfm@125 Pa, and appeared to have a very high
air permeability compared to the commercially available filter
membranes of Comparative Examples 4 and 5.
[0158] By using self-made equipment for the filter media of Example
2 and Comparative Examples 4 and 5, filtrations were performed
according to ASTM F795 standard, differential pressures across the
filter media were measured, and the results were shown in Table
7.
TABLE-US-00007 TABLE 7 The pressure drop (psid @ 31 pm, 4.9
cm.sup.2) Example 2 (Nanofibers 0.45 .mu.m) 3.8 Comparative Example
4 6.2 (PVdF Membrane 0.45 .mu.m) Comparative Example 5 5.1 (PES
Membrane 0.45 .mu.m)
[0159] As shown in Table 7, the filter medium of Example 2
according to the present invention was measured as the pressure
drop of 3.8 psid @ 31 pm, 4.9 cm.sup.2, and appeared to have a very
high water permeability as compared to the commercially available
filter membranes of Comparative Examples 4 and 5.
[0160] By using self-made equipment for the filter media of Example
2 and Comparative Examples 4 and 5, filtration was performed
according to ASTM F795 standard, turbidities for the filtered
liquids were measured, and the results were shown in Table 4. The
test particles (Dust) were used as ISO 12103-1, A2 fine.
TABLE-US-00008 TABLE 8 Turbidity (NTU) Example 2 (Nanofibers 0.45
.mu.m) 0.1 or less Comparative Example 4 0.1 or less (PVdF Membrane
0.45 .mu.m) Comparative Example 5 0.1 or less (PES Membrane 0.45
.mu.m)
[0161] As shown in Table 8, the filter medium of Example 2
according to the present invention was measured as the turbidity of
0.1 NTU or less, and appeared to have the same turbidity removal
efficiency as compared to commercially available filter membranes
of Comparative Examples 4 and 5.
[0162] According to the present invention, a surface filtration and
a depth filtration of water to be treated can be performed with a
nanofiber web having fine pores of a three-dimensional network
structure. In addition, the ion exchange resin particles exposed to
the nanofibers of the nanofiber web filter specific ions of a
chemical substance contained in the water to be treated, to thus
improve the filtering efficiency, and to remove a variety of
pathogens such as bacteria and E. coli multiplied in the filter
media by an antimicrobial activity of Ag nanoparticles.
[0163] As described above, the present invention has been described
with respect to particularly preferred embodiments. However, the
present invention is not limited to the above embodiments, and it
is possible for one who has an ordinary skill in the art to make
various modifications and variations, without departing off the
spirit of the present invention. Thus, the protective scope of the
present invention is not defined within the detailed description
thereof but is defined by the claims to be described later and the
technical spirit of the present invention.
[0164] The present invention may be applied to filter media for
liquid filters in which a thin filter layer is formed and the
content of nanofibers weighs light, by laminating a low weight
nanofiber web on a porous nonwoven fabric, and thus a less
differential pressure is applied before and after filtering, to
thereby increase a pass flow rate.
* * * * *