U.S. patent application number 09/837102 was filed with the patent office on 2002-04-11 for filter cartridge and process for producing the same.
This patent application is currently assigned to Chisso Corporation. Invention is credited to Nobuhara, Hideo, Yamaguchi, Osamu.
Application Number | 20020042236 09/837102 |
Document ID | / |
Family ID | 26590892 |
Filed Date | 2002-04-11 |
United States Patent
Application |
20020042236 |
Kind Code |
A1 |
Nobuhara, Hideo ; et
al. |
April 11, 2002 |
Filter cartridge and process for producing the same
Abstract
An object of the present invention is to provide a filter
cartridge having an high filtering accuracy, a long filter life and
a good liquid-passing property, in which an initial trapped
particle diameter little changes, a pressure loss is small and
neither bubbling nor falling of the filter material is observed.
Such a filter cartridge is obtained by a production process, which
comprises winding a non-woven fabric strip comprising a
thermoplastic fiber around a perforated cylinder in a twill form,
wherein a non-woven fabric strip satisfies the following equation
(A): log.sub.10Y<3.75-0.6(log.sub.10X) (A) wherein X
(cm.sup.3/cm.sup.2/sec) is an airflow amount of the non-woven
fabric strip, and Y (g/m.sup.2) is a basis weight thereof; or a
production process, which comprises winding in a twill form,
wherein a number (W) of winding a non-woven fabric strip around a
perforated cylinder from one end to the other end is one to 10 per
a length of 250 mm in the perforated cylinder.
Inventors: |
Nobuhara, Hideo;
(Moriyama-shi, JP) ; Yamaguchi, Osamu;
(Moriyama-shi, JP) |
Correspondence
Address: |
Mr. Curtis B. Hamre
MERCHANT, GOULD, P.C.
3100 Norwest Center
90 South Seventh Street
Minneapolis
MN
55402-4131
US
|
Assignee: |
Chisso Corporation
|
Family ID: |
26590892 |
Appl. No.: |
09/837102 |
Filed: |
April 18, 2001 |
Current U.S.
Class: |
442/327 ;
442/361; 442/400; 442/401 |
Current CPC
Class: |
B01D 2275/206 20130101;
Y10T 442/681 20150401; B01D 39/163 20130101; Y10T 442/637 20150401;
Y10T 442/60 20150401; Y10T 442/68 20150401; B01D 46/24
20130101 |
Class at
Publication: |
442/327 ;
442/361; 442/400; 442/401 |
International
Class: |
D04H 003/00; D04H
005/00; D04H 013/00; D04H 001/56; D04H 003/16 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 2000 |
JP |
2000-126531 |
May 16, 2000 |
JP |
2000-143672 |
Claims
What is claimed is:
1. A filter cartridge which is prepared by winding a non-woven
fabric strip comprising a thermoplastic fiber around a perforated
cylinder in a twill form, wherein the non-woven fabric strip
satisfies the following equation (A):
log.sub.10Y<3.75-0.6(log.sub.10X) (A) wherein X
(cm.sup.3/cm.sup.2/sec) is an airflow amount of the non-woven
fabric strip measured in accordance with JIS L 1096-A (1990), and Y
(g/m.sup.2) is a basis weight thereof.
2. A filter cartridge which is prepared by winding a long fiber
non-woven fabric strip comprising a thermoplastic fiber around a
perforated cylinder in a twill form, wherein the non-woven fabric
strip satisfies the following equation (B):
log.sub.10Y<3.75-0.75(log.sub.10X) (B) wherein X
(cm.sup.3/cm.sup.2/sec) is an airflow amount of the non-woven
fabric strip measured in accordance with JIS L 1096-A (1990), and Y
(g/m.sup.2) is a basis weight thereof.
3. A filter cartridge which is prepared by winding a non-woven
fabric strip comprising a thermoplastic fiber around a perforated
cylinder in a twill form, wherein in winding in a twill form, a
number (W) of winding the non-woven fabric strip from one end to
the other end in a longitudinal direction of the perforated
cylinder is one to 10 per a length of 250 mm in the perforated
cylinder.
4. The filter cartridge as claimed in claim 3, wherein when a
2-fold value (2W) of the winding number (W) is represented by a
fraction having a denominator of two figures or less which is a
non-reducible approximate value, the denominator is 4 to 40.
5. The filter cartridge as claimed in any one of claims 1 to 3,
wherein at least a part of fiber intersections of the non-woven
fabric strip is thermally bonded.
6. The filter cartridge as claimed in any one of claims 1 to 3,
wherein the non-woven fabric strip has a width of 0.5 to 40 cm.
7. The filter cartridge as claimed in any one of claims 1 to 3,
wherein a product of a width (cm) and a basis weight (g/m.sup.2) of
the non-woven fabric strip is 10 to 200.
8. The filter cartridge as claimed in any one of claims 1 to 3,
wherein the non-woven fabric strip has a thickness of 0.02 to 1.20
mm.
9. The filter cartridge as claimed in any one of claims 1 to 3,
wherein the non-woven fabric strip is thermal compression bonded by
means of a heat embossing roll having an embossing area rate of 5
to 25%.
10. The filter cartridge as claimed in any one of claims 1 to 3,
wherein the filter material of the filter cartridge has a void rate
of 65 to 85%.
11. The filter cartridge as claimed in claim 1 or 3, wherein the
non-woven fabric strip is of a long fiber non-woven fabric.
12. The filter cartridge as claimed in claim 11, wherein the long
fiber non-woven fabric is produced by a spun bonding method.
13. The filter cartridge as claimed in claim 1 or 3, wherein the
non-woven fabric strip is of a melt blown non-woven fabric.
14. The filter cartridge as claimed in any one of claims 1 to 3,
wherein the thermoplastic fiber is a composite fiber comprising a
low melting resin and a high melting resin, a difference of the
melting points between these resins being 10.degree. C. or
more.
15. The filter cartridge as claimed in any one of claims 1 to 3,
wherein the thermoplastic fiber is a fiber formed from at least one
thermoplastic resin selected from the group consisting of a
polyester resin, a polyamide resin, a polyethylene resin and a
polypropylene resin.
16. A process for producing a filter cartridge, which comprises
winding a non-woven fabric strip comprising a thermoplastic fiber
around a perforated cylinder in a twill form, wherein the non-woven
fabric strip satisfies the following equation (A):
log.sub.10Y<3.75-0.6(log.sub.10X- ) (A) wherein X
(cm.sup.3/cm.sup.2/sec) is an airflow amount of the non-woven
fabric strip measured in accordance with JIS L 1096-A (1990), and Y
(g/m.sup.2), and Y (g/m.sup.2) is a basis weight thereof.
17. A process for producing a filter cartridge, which comprises
winding a non-woven fabric strip comprising a thermoplastic fiber
around a perforated cylinder in a twill form, wherein in winding in
a twill form, a number (W) of winding the non-woven fabric strip
from one end to the other end in a longitudinal direction of the
perforated cylinder is one to 10 per a length of 250 mm in the
perforated cylinder.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a filter cartridge and a
process for producing the same, specifically to a cylindrical
filter cartridge which is prepared by winding a non-woven fabric
strip comprising thermoplastic fibers on a perforated cylinder in a
twill form and which is excellent in a liquid-passing property, a
filter life and stability of a filtering accuracy, and a process
for producing the same.
BACKGROUND OF THE INVENTION
[0002] Various filters for clarifying a fluid are presently
developed and produced. Among them, cartridge-type filters
(hereinafter called filter cartridges) are widely used in the
industrial field, for example, for removing suspended particles in
industrial liquid materials, removing cakes flowing out of a cake
filtering apparatus and clarifying industrial water.
[0003] Several kinds of structures of a filter cartridge have so
far been proposed. The most typical one is a bobbin winder-type
filter cartridge, which is a cylindrical filter cartridge prepared
by winding a spun yarn as a filter material on a perforated
cylindrical core in a twill form and then fluffing the spun yarn.
This type has long been used due to inexpensiveness and easiness in
production. Another type of structure includes a non-woven
fabric-laminated type filter cartridge. This is a cylindrical
filter cartridge prepared by winding several kinds of non-woven
fabrics such as a carding non-woven fabric stepwise and
concentrically on a perforated cylindrical core. A recent advanced
technique in a non-woven fabric production has allowed some of them
to be put to practical use.
[0004] However, the above-mentioned filter cartridges have several
defects. For example, in the bobbin winder-type filter cartridge
for trapping foreign matters by means of fluffs of fluffed spun
yarns and also in gaps of the spun yarns, it is difficult to
control the size and form of the fluffs and gaps. This limits size
and amount of the foreign matters that can be trapped. Further,
constitutional fibers of a spun yarn, which is made from short
fibers, fall away when fluid flows onto the filter cartridge.
[0005] Furthermore, in producing a spun yarn, a trace amount of a
surfactant is often applied onto a surface of material short fibers
to prevent the short fibers from sticking to a spinning machine by
electrostatic charge or the like. Filtering a liquid by means of a
filter cartridge using surfactant-coated spun yarns may bring
adverse effects on the cleanness of liquid, such as foaming of the
liquid, and increase in TOC (total organic carbon), COD (chemical
oxygen demand) and the electric conductivity. In addition, a spun
yarn is produced by spinning short fibers as already mentioned, for
which at least two steps of forming and spinning short fibers are
required. Thus, use of the spun yarn will sometimes increase a
price of the product.
[0006] A performance of a non-woven fabric-laminated type filter
cartridge depends on the non-woven fabric used. A non-woven fabric
is produced mostly by a method in which short fibers are confounded
by means of a carding machine or an air laid machine and then
subjecting them, if necessary, to heat treatment by means of a
hot-air heater or a heating roll, or a method in which a non-woven
fabric is directly prepared, such as a melt blowing method and a
spun bonding method. However, any machines used for producing
non-woven fabrics, such as a carding machine, an air laid machine,
a hot-air heater, a heating roll, a melt blowing machine and a spun
bonding machine, may cause, for example, uneven basis weights of a
non-woven fabric in a lateral direction of a machine. Accordingly,
a filter cartridge of poor quality will be produced. Also, use of a
more advanced manufacturing technique to avoid such unevenness
sometimes raises the production cost. Moreover, production of one
kind of non-woven fabric-laminated type filter cartridges needs two
to six kinds of non-woven fabrics, and different non-woven fabrics
are needed depending on the kind of a filter cartridge. Thus, the
production cost will increase in some cases.
[0007] Several methods have been proposed in order to solve such
problems of conventional filter cartridges. For example, Japanese
Utility Model Publication No. 6-7767 proposes a filter cartridge in
which a filter material obtained by squashing a tape-shaped paper
having porosity while twisting, thereby squeezing it to control a
diameter thereof to about 3 mm is wound around a porous internal
cylinder in a close twill. This method is advantageous in that a
winding pitch can be gradually increased from the porous internal
cylinder toward the outside. However, the filter material needs to
be squashed and squeezed, so that foreign matters are trapped
primarily between the winding pitches of the filter material.
Accordingly, it is less expected to trap foreign matters by the
filter material itself as is the case of a conventional bobbin
winder type filter using spun yarns which traps foreign matters by
means of fluffs. This blocks the surface of the filter to shorten
the filter life or brings about the poor liquid-passing property in
a certain case.
[0008] JP-A 1-115423 proposes a filter in which strings obtained by
slitting a cellulose spun bonded non-woven fabric into strips and
passing them through narrow holes to twist them are wound around a
bobbin having a lot of drilled pores. It is considered that this
method shall make it possible to prepare a filter having a higher
mechanical strength and being free of dissolution in water and
elution of a binder, as compared with a conventional roll tissue
filter prepared by winding tissue paper in a roll form, which is
produced from a-cellulose prepared by refining a coniferous
pulp.
[0009] However, the cellulose spun bonded non-woven fabric used for
this filter has a papery form and thus a too high rigidity, so that
it is less expected to trap foreign matters by the filter material
itself as is the case of a conventional bobbin winder type filter
using spun yarns which traps foreign matters by means of fluffs.
Further, the cellulose spun bonded non-woven fabric is liable to
swell in a liquid due to its papery form. Swelling may bring about
various problems such as a decrease in a filter strength, a change
in a filtering accuracy, a deterioration in a liquid-passing
property, a reduction in a filter life and the like. Adhesion at
fiber intersections of the cellulose spun bonded non-woven fabric
are mostly conducted by a certain chemical treatment. Such adhesion
is often unsatisfactory, causing a change in a filtering accuracy
or falling of fiber chips, so that a stable filtering performance
is difficult to achieve.
[0010] Further, JP-A 4-45810 proposes a filter prepared by winding
a slit non-woven fabric comprising composite fibers in which 10% by
weight or more of structural fibers is divided ones of 0.5 denier
or less on a porous core cylinder to provide the fiber density of
0.18 to 0.30. This method is advantageously used to trap fine
particles contained in a liquid by means of fibers having a high
fineness. However, in order to divide the composite fibers, a
stress needs to be applied using, for example, high-pressure water,
and it is difficult to evenly divide the fibers all over the
non-woven fabric by means of high-pressure water processing. If not
evenly divided, there occurs a difference in a trapped particle
diameter between a well-divided portion and an insufficiently
divided portion of the non-woven fabric, and this may lower the
filtering accuracy. Further, the stress applied for dividing
sometimes lowers a strength of the non-woven fabric, and this may
cause reduction of the resulting filter strength and frequent
deformation of the filter during use; or possible change of the
void ratio of the filter may reduce the liquid-passing
property.
[0011] Further, the reduced strength of the non-woven fabric makes
it difficult to control a tension in winding around a porous core
cylinder, and hence the difficulty in exact control of the void
rate may arise. Further, a spinning technique required for
producing easily divisible fibers and an increased operation cost
in producing thereof lead to an increased production cost of the
filter. Such a filter would be usable in a certain field such as
the pharmaceutical industry and the electronic industry which
require a high filtering performance, if the above mentioned
problems of the filtering performance are solved. However, such a
filter is considered to be difficult to use in cases in which
inexpensive filters are requested such as the filtering of swimming
pool water and a plating liquid for the plating industry.
[0012] An object of the present invention is to provide a
cylindrical filter cartridge which is excellent in a liquid-passing
property, a filter life and stability of a filtering accuracy.
[0013] An object of the present invention is to solve the problems
described above. It has been found, as a result of investigations,
that a cylindrical filter cartridge which is excellent in a
liquid-passing property, a filter life and a stability of a
filtering accuracy can be obtained by winding a long fiber
non-woven fabric comprising thermoplastic fibers on a perforated
cylinder in a twill form.
SUMMARY OF THE INVENTION
[0014] The present inventors have conducted intensive researches
and, as a result, found that the problems described above can be
solved by a cylindrical filter cartridge, which is prepared by
winding a non-woven fabric strip on a perforated cylinder in a
twill form, in which the strip is a long fiber non-woven fabric
and/or a melt blown non-woven fabric comprising thermoplastic
fibers and an airflow amount (air permeability) is specially
related to a basis weight; or by specifying a number of winding in
producing the filter cartridge. This finding has led to the present
invention.
[0015] The present invention is composed of:
[0016] (1) A filter cartridge which is prepared by winding a
non-woven fabric strip comprising a thermoplastic fiber around a
perforated cylinder in a twill form, wherein the non-woven fabric
strip satisfies the following equation (A):
log.sub.10Y<3.75-0.6(log.sub.10X) (A)
[0017] wherein X (cm.sup.3/cm.sup.2/sec) is an airflow amount of
the non-woven fabric strip measured in accordance with JIS L 1096-A
(1990), and Y (g/m.sup.2) is a basis weight thereof.
[0018] (2) A filter cartridge which is prepared by winding a long
fiber non-woven fabric strip comprising a thermoplastic fiber
around a perforated cylinder in a twill form, wherein the non-woven
fabric strip satisfies the following equation (B):
log.sub.10Y<3.75-0.75(log.sub.10X) (B)
[0019] wherein X (cm.sup.3/cm.sup.2/sec) is an airflow amount of
the non-woven fabric strip measured in accordance with JIS L 1096-A
(1990), and Y (g/m.sup.2) is a basis weight thereof.
[0020] (3) A filter cartridge which is prepared by winding a
non-woven fabric strip comprising a thermoplastic fiber around a
perforated cylinder in a twill form, wherein in winding in a twill
form, a number (W) of winding the non-woven fabric strip from one
end to the other end in a longitudinal direction of the perforated
cylinder is one to 10 per a length of 250 mm in the perforated
cylinder.
[0021] (4) The filter cartridge as described in the item (3),
wherein when a 2-fold value (2W) of the winding number (W) is
represented by a fraction having a denominator of two figures or
less which is a non-reducible approximate value, the denominator is
4 to 40.
[0022] (5) The filter cartridge as described in any one of the
items (1) to (3), wherein at least a part of fiber intersections of
the non-woven fabric strip is thermally bonded.
[0023] (6) The filter cartridge as described in any one of the
items (1) to (3), wherein the non-woven fabric strip has a width of
0.5 to 40 cm.
[0024] (7) The filter cartridge as described in any one of the
items (1) to (3), wherein a product of a width (cm) and a basis
weight (g/m.sup.2) of the non-woven fabric strip is 10 to 200.
[0025] (8) The filter cartridge as described in any one of the
items (1) to (3), wherein the non-woven fabric strip has a
thickness of 0.02 to 1.20 mm.
[0026] (9) The filter cartridge as described in any one of the
items (1) to (3), wherein the non-woven fabric strip is thermal
compression bonded by means of a heat embossing roll having an
embossing area rate of 5 to 25%.
[0027] (10) The filter cartridge as described in any one of the
items (1) to (3), wherein the filter material of the filter
cartridge has a void rate of 65 to 85%.
[0028] (11) The filter cartridge as described in the item (1) or
(3), wherein the non-woven fabric strip is of a long fiber
non-woven fabric.
[0029] (12) The filter cartridge as described in the item (11),
wherein the long fiber non-woven fabric is produced by a spun
bonding method.
[0030] (13) The filter cartridge as described in the item (1) or
(3), wherein the non-woven fabric strip is of a melt blown
non-woven fabric.
[0031] (14) The filter cartridge as described in any one of the
items (1) to (3), wherein the thermoplastic fiber is a composite
fiber comprising a low melting resin and a high melting resin, a
difference of the melting points between these resins being
10.degree. C. or more.
[0032] (15) The filter cartridge as described in any one of the
items (1) to (3), wherein the thermoplastic fiber is a fiber formed
from at least one thermoplastic resin selected from the group
consisting of a polyester resin, a polyamide resin, a polyethylene
resin and a polypropylene resin.
[0033] (16) A process for producing a filter cartridge, which
comprises winding a non-woven fabric strip comprising a
thermoplastic fiber around a perforated cylinder in a twill form,
wherein the non-woven fabric strip satisfies the following equation
(A):
log.sub.10Y<3.75-0.6(log.sub.10X) (A)
[0034] wherein X (cm.sup.3/cm.sup.2/sec) is an airflow amount of
the non-woven fabric strip measured in accordance with JIS L 1096-A
(1990), and Y (g/m.sup.2) is a basis weight thereof.
[0035] (17) A process for producing a filter cartridge, which
comprises winding a non-woven fabric strip comprising a
thermoplastic fiber around a perforated cylinder in a twill form,
wherein in winding in a twill form, a number (W) of winding the
non-woven fabric strip from one end to the other end in a
longitudinal direction of the perforated cylinder is one to 10 per
a length of 250 mm in the perforated cylinder.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 is a conceptual diagram of a spun bonded non-woven
fabric.
[0037] FIG. 2 is a conceptual diagram of a short fiber non-woven
fabric.
[0038] FIG. 3 represents the equation (A) showing a relation of a
basis weight to an airflow amount of the non-woven fabric.
[0039] FIG. 4 is an illustration of winding a non-woven fabric
strip as it is, without processing.
[0040] FIG. 5 is an illustration of winding a non-woven fabric
strip with twisting.
[0041] FIG. 6 is an illustration of winding a non-woven fabric
strip with traversing.
[0042] FIG. 7 is an illustration of trapping foreign matters by
means of an embossing pattern of a non-woven fabric.
[0043] FIG. 8 is a perspective of the filter cartridge according to
the present invention.
[0044] Explanation of Codes
[0045] 1: Long fiber constituting spun bonded non-woven fabric
[0046] 2: Foreign matters
[0047] 3: Bobbin
[0048] 4: Perforated cylinder
[0049] 5: Traverse guide
[0050] 6: Non-woven fabric strip or converged matter thereof
[0051] 7: Filter cartridge
[0052] 8: Part where strong thermal compression bonding by an
embossing pattern is applied.
[0053] 9: Part where only weak thermal compression bonding by
deviating from an embossing pattern is applied
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0054] The embodiment of the present invention shall be explained
below in detail.
[0055] The filter cartridge of the present invention is prepared by
winding a non-woven fabric strip comprising a thermoplastic fiber
on a perforated cylinder in a twill form.
[0056] In the present invention, the non-woven fabric strip means a
non-woven fabric having a narrow width, which is prepared by
slitting (cutting) a wide non-woven fabric or produced directly in
a narrow width. It is preferable that a wide non-woven fabric is
slit in order to obtain the stable quality at low cost. An optimum
width and basis weight of a non-woven fabric to be used shall be
described later.
[0057] In the present invention, the thermoplastic fiber means a
fiber produced from a thermoplastic resin. All thermoplastic resins
capable of being melt-spun can be used for the thermoplastic resin
used in the present invention.
[0058] Examples include polyethylene resins such as low density
polyethylene, high density polyethylene and linear low density
polyethylene; polypropylene resins such as polypropylene and
copolymerized polypropylene (for example, binary or multi-component
copolymers comprising propylene as a primary component with
ethylene, butene-1, 4-methylpentene-1 and the like); other
polyolefin resins than the above polyethylene and polypropylene
resins; polyester resins such as polyethylene terephthalate,
polybutylene terephthalate and low melting polyesters copolymerized
with addition of isophthalic acid besides terephthalic acid as an
acid component; polyamide resins such as nylon 6 and nylon 66; and
thermoplastic resins such as polystyrene, polyurethane elastomers,
polyester elastomers and polytetrafluoroethylene.
[0059] Functional resins can also be used so as to provide a filter
cartridge with a biodegradability derived from biodegradable resins
such as a lactic acid base polyester. Further, polyolefin resins
and polystyrene resins which can be polymerized using metallocene
catalysts are preferably used for a filter cartridge, taking
advantage of the characteristics of metallocene resins such as
improvements in a strength of a non-woven fabric and a chemical
resistance, and a reduction in a production energy.
[0060] Also, those resins may be blended for use in order to
control a heat adhesion property and a rigidity of a non-woven
fabric. When a filter cartridge is used for filtering an aqueous
solution of room temperature, polyolefin resins such as
polypropylene and polyethylene are preferably used from the
viewpoints of a chemical resistance and a cost. When used for a
solution of a relatively high temperature, polyester resins and
polyamide resins are preferred.
[0061] These thermoplastic resins can be blended, if necessary,
with publicly known additives.
[0062] The non-woven fabric strip used in the present invention is
preferably a long fiber non-woven fabric or a melt blown non-woven
fabric, and the resulting filter cartridge reduces a risk that
fibers fall off and are mixed in a filtrate when used for
filtering.
[0063] The long fiber non-woven fabric or melt blown non-woven
fabric described above can be used separately as a non-woven fabric
strip or in the form of a laminated non-woven fabric of the
both.
[0064] In the filter cartridge of the present invention, the melt
blown non-woven fabric as the non-woven fabric strip has a higher
fineness than that of the long fiber non-woven fabric, and the
texture thereof can easily be homogenized. Accordingly, the
resulting filter cartridge can be improved in a filtering
accuracy.
[0065] An average fiber diameter of the above melt blown non-woven
fabric varies depending on uses of the filter cartridge and kinds
of the resin, and is 0.5 to 1000 .mu.m, preferably 1 to 50 .mu.m.
If the average fiber diameter is less than 0.5 .mu.m, it is
difficult to produce the non-woven fabric, which may result in a
high-cost filter cartridge. On the other hand, the average fiber
diameter exceeding 1000 .mu.m expands a distribution of the fiber
diameter and deteriorates a texture of the resulting non-woven
fabric. Further, the average fiber diameter exceeding 50 .mu.m may
allow the adjacent fibers to bond each other by remaining heat, but
it makes no difference especially as long as it does not prevent
the effects of the present invention.
[0066] The non-woven fabric strip used in the present invention is
preferably a long fiber non-woven fabric, a melt blown non-woven
fabric or a laminated non-woven fabric thereof, in which at least a
part of fiber intersections thereof is thermally bonded. Among
them, preferred is the long fiber non-woven fabric in which at
least a part of fiber intersections thereof is thermally
bonded.
[0067] In particular, a non-woven fabric obtained by a spun bonding
method is preferred as the long fiber non-woven fabric described
above. The spun bonding method is a non-woven fabric production
technique in which a thermoplastic fiber discharged from a nozzle
is sucked and drawn by an air gun, spread on a conveyor and then
thermally bonded. The long fiber non-woven fabric comprising
thermoplastic fibers produced by the spun bonding method has a
fiber direction aligned along a machine direction as shown in FIG.
1, so that a hole constituted by fibers 1 becomes long and narrow,
and a maximum size of the passing particle 2 is rather small. In
contrast with this, a non-woven fabric comprising short fibers
obtained by a carding method and the like has a fiber direction not
fixed as shown in FIG. 2, so that a hole constituted by fibers 1
has a shape close to a circle or a square, and a maximum size of
the passing particle 2 is larger than that of a long fiber
non-woven fabric produced by the spun bonding method, even the two
has the same fiber diameter and void rate.
[0068] In the present invention, other fibers than the
thermoplastic fiber, for example, cotton, glass fibers and metallic
fibers can be used in combination as structural fibers of the
non-woven fabric strip as long as they do not impair a filter life,
a liquid-passing property and the functions such as preventing
matters from falling off the filter cartridge which are
characteristics of the present filter cartridge.
[0069] In the non-woven fabric strip used for producing the filter
cartridge which is the first embodiment of the present invention,
an airflow amount X (cm.sup.3/cm.sup.2/sec) and a basis weight Y
(g/m.sup.2) which are measured by a JIS L 1096-A method satisfy the
following equation (A) by bonding the fiber intersections
thereof.
log.sub.10Y<3.75.times.0.6(log.sub.10X) (A)
[0070] The filter cartridge of the present invention which is
prepared by winding the non-woven fabric strip around a perforated
cylinder in a twill form exhibits an excellent filtering
accuracy.
[0071] A relation of the equation (A) is shown in FIG. 3. The
equation (A) represents a shaded area in FIG. 3 and exhibits a
basis weight range corresponding to the respective airflow amounts
of the non-woven fabric strip. When the airflow amount and the
basis weight do not have a relation represented by the shaded area,
it means that the basis weight is too large, and a rigidity of the
non-woven fabric strip becomes too high, so that it is difficult to
minutely wind the non-woven fabric strip around the perforated
cylinder, and the resulting filter cartridge may have a reduced
filtering accuracy.
[0072] If the production process of the present invention is a spun
bonding process in which a non-woven fabric is prepared directly
from a formed fiber, the resulting filter cartridge reduces a risk
that the fibers fall off and are mixed in the filtrate when used
for filtering. Further, it is relatively low in cost, and
therefore, it is preferable.
[0073] In the second embodiment of the present invention, the
non-woven fabric strip is a long fiber non-woven fabric, and the
airflow amount X (cm.sup.3/cm.sup.2/sec) and the basis weight Y
(g/m.sup.2) satisfy the following equation (B). In such a case, the
filter cartridge is excellent in a non-woven fabric strength and a
property of preventing the fibers from falling off the filter
cartridge, and therefore it exhibits a particularly excellent
filtering accuracy.
log.sub.10Y<3.75-0.75(log.sub.10X) (B)
[0074] Next, a method for winding the non-woven fabric strip around
a perforated cylinder shall be explained. One example of the
processes is shown in FIG. 4. A winder conventionally used for a
bobbin winder type filter cartridge can be used for the winding
machine. A perforated cylinder 4 having a diameter of about 10 to
40 mm and a length of 100 to 1000 mm is installed to a bobbin 3 of
this winder. A non-woven fabric strip 6 passes through a yarn
passage and a hole of a traverse guide 5 of the winder to be
converged and wound around the perforated cylinder one to two
times. The perforated cylinder may be thermally bonded to an end
part of the non-woven fabric strip in order to accurately wind the
strip. The yarn passage of the winder is waved in each longitudinal
direction in a twill form by means of the traverse guide 5 disposed
parallel to the bobbin, so that the non-woven fabric strip is wound
around the perforated cylinder in a twill form by rotation of the
bobbin, whereby a filter cartridge 7 is produced. A diameter of the
hole disposed in the traverse guide 5 varies depending on a basis
weight and a width of the non-woven fabric strip used and falls
preferably in a range of 3 to 10 mm. If this diameter is less than
3 mm, a friction between the non-woven fabric strip and the hole is
increased, so that the winding tension becomes too high. On the
other hand, the value larger than 10 mm may not render the
converging size of the non-woven fabric stabilized. Various
traverse guides having a narrow hole can be used for the traverse
guide 5. For example, those in an almost circular form, an almost
elliptical form and an almost flat form can be used. Further, those
having an aperture part at one end of a narrow hole can be used as
well.
[0075] The perforated cylinder functions as a core of a filter
cartridge, and the material and the form thereof shall not
specifically be restricted as long as it has a strength which is
endurable to external pressure applied in filtering and the
pressure loss is not markedly high. It may be, for example, an
injection-molded article obtained by processing polyethylene or
polypropylene into a net type cylinder as is the case with a core
used for a conventional filter cartridge or ones obtained by
processing ceramics and stainless steel in the same manner.
Alternatively, other filter cartridges such as a filter cartridge
subjected to pleat-folding processing and a filter cartridge of a
non-woven fabric-winding type can be used as a perforated
cylinder.
[0076] The winding conditions in this case can be set up according
to those in producing a conventional bobbin winder type filter
cartridge. Initial speed of the bobbin may be set to, for example,
1000 to 2000 rpm, and the feeding speed may be controlled to apply
a tension in winding the non-woven fabric. The void rate of the
filter cartridge can be changed by the tension in this case.
[0077] On the other hand, this non-woven fabric strip can be
twisted and then wound. One embodiment of the production process is
shown in FIG. 5. Also in this case, a winder conventionally used
for a bobbin winder type filter cartridge can be used for the
winding machine. The non-woven fabric becomes apparently thick by
twisting, and therefore a traverse guide 5 has preferably a larger
hole diameter than that in the case of FIG. 4. By twisting a
non-woven fabric, an apparent void rate of the non-woven fabric can
be changed depending on a twisting number per unit length or a
twisting strength, so that the filtering accuracy can be
controlled. The twisting number in this case falls preferably in a
range of 50 to 1000 times per meter of the non-woven fabric strip.
If this value is smaller than 50 times, the twisting effect is
scarcely obtained. On the other hand, the value larger than 1000
times will provide the filter cartridge produced with a inferior
liquid-passing property. Accordingly, both are not preferred.
[0078] It is more preferred to converge the non-woven fabric strip
by any method and then wind it around a perforated cylinder. Such a
method include one in which the non-woven fabric strip may be
passed merely through a small hole to be converged or one in which
the cross-sectional form of the non-woven fabric strip may be
pre-molded by means of a pleat-forming guide and then passed
through a small hole to be processed into a pleated matter. Use of
the latter method makes it possible to control a ratio of a
traversing speed of the traverse guide to a rotating speed of the
bobbin to change the winding pattern, so that filter cartridges
having various performances can be produced from the same kind of
the non-woven fabric strip.
[0079] One embodiment of a production process in which the
non-woven fabric is passed merely through a small hole for
converging the strip is shown in FIG. 6. Also in this case, a
winder conventionally used for a bobbin winder type filter
cartridge can be used for the winding machine. In FIG. 6, the hole
of a traverse guide 5 turned into a small hole, thereby converging
the non-woven fabric strip, but a guide of a small hole may be
provided at a yarn passage in front of the traverse guide 5. The
diameter of the small hole varies depending on the basis weight and
the width of the non-woven fabric used and falls preferably in the
range of 3 to 10 mm. If this diameter is smaller than 3 mm, a
friction between the non-woven fabric and the small hole is
increased, so that the winding tension becomes too high. On the
other hand, the value larger than 10 mm may not render the
converging size of the non-woven fabric stabilized.
[0080] Further, when producing the above non-woven fabric
strip-converged matter, granular activated carbon or ion exchange
resins may be present as long as they do not damage the effects of
the present invention. In this case, in order to fix granular
activated carbon or ion exchange resins, they may be bonded by
means of a suitable binder either prior to or after converging the
non-woven fabric strip or processing it into a pleated matter, or
they may be first added and then thermally bonded to the structural
fibers of the non-woven fabric by heating.
[0081] The yarn passage of the winder is waved in twill form by
means of a traverse cam disposed parallel to the bobbin, so that
the non-woven fabric strip is wound around the perforated cylinder
while waving in a twill form. The winding conditions in this case
can be set up according to those in producing a conventional bobbin
winder type filter cartridge. Initial speed of the bobbin may be
set to, for example, 1000 to 2000 rpm, and the feeding speed may be
controlled to apply a tension in winding the non-woven fabric. The
void rate of the filter cartridge can be changed by the tension in
this case.
[0082] Further, the tension in winding is controlled to make the
void rate of an internal layer small, and the void rate of an
intermediate layer to an external layer gradually large as the
non-woven fabric is wound around. In particular, when the non-woven
fabric strip is first formed into the pleated matter and then is
wound around the perforated cylinder, there can be provided a
filter cartridge having an ideal filtering structure owing to a
difference in rough and dense structures formed in the external
layer, the intermediate layer and the internal layer in combination
with a deep layer-filtering structure formed by the pleats of the
pleated matter.
[0083] The filtering accuracy can be changed by controlling a ratio
of the traversing speed of the traverse cam to the rotating speed
of the bobbin, thereby changing a number (hereinafter referred to
as a winding number and represented by W) of winding the non-woven
fabric strip around the perforated cylinder from one end to the
other end in a longitudinal direction when winding the non-woven
fabric strip in a twill form. That is, the winding number means a
rotation number of the bobbin 3 while the traverse guide 5 moves
from one end to the other end of the perforated cylinder 4 in a
longitudinal direction. Accordingly, a value of W is not
necessarily a natural number. The winding number should be very
accurate, and therefore, a moving distance of the traverse guide
has to be geared to a rotation number of the bobbin so that this
value should not get out of order.
[0084] In the filter cartridge of the present invention, a winding
number W is 1 to 10, preferably 2 to 8 and more preferably 3 to 5
per 250 mm of the perforated cylinder used for the filter
cartridge. If this value is less than one, an angle of traversing
becomes too large, and therefore the non-woven fabric strip is
liable to get out of the perforated cylinder. On the other hand, if
this value exceeds 10, an angle of traversing becomes too small,
and the non-woven fabric strip is liable to get out of the
perforated cylinder also in this case. Further, if the value
deviates from the range of 1 to 10, an initial trapped particle
diameter becomes extremely large, resulting in an inadequate filter
cartridge.
[0085] A relation of the winding number to the filtering accuracy
is well known in the case of a wound filter in which a spun yarn is
used as a filtering material. In a conventional wound filter in
which a spun yarn is used, a winding yarn (that is, a spun yarn)
generally has a circular cross-sectional form, and a yarn diameter
thereof is about 3 mm at the largest. Thus, the winding number and
the pitch of the yarn in winding in a twill form can be represented
by the following equations (1) and (2):
2.times.W=2.times.W.sub.0.+-.1/N (1)
N=T/W.sub.0/P (2)
[0086] wherein W is a winding number; W.sub.0 is a natural number
approximate to the winding number W; N is an ordered number; T is a
traverse width; and P is a pitch of the yarn. Among the above
variables, W.sub.0 and N are natural numbers, and W, P and T are
arbitrary positive numbers. In general, as the pitch of the yarn
becomes smaller, the wind filter having a finer accuracy is
prepared. This equation can be applied to a yarn other than a spun
yarn, for example, a split yarn.
[0087] On the other hand, in the filter cartridge of the present
invention, the non-woven fabric strip is used as a filter material
in place of a spun yarn, and therefore the equations (1) and (2)
cannot be applied as they are. The non-woven fabric is converged in
winding as described above, so that a thickness of the yarn becomes
far large as compared with that of a conventional spun yarn.
Accordingly, even if the conditions of the equations (1) and (2)
are satisfied, the yarns themselves are superposed and a filter
cartridge having the intended accuracy is not obtained.
[0088] As the third embodiment of the present invention, we have
found that a filter cartridge, which is prepared by winding a
non-woven fabric strip around a perforated cylinder in a twill
form, exhibits an excellent filtering performance when a
denominator M.sub.n is a specific value the winding number
approximated by the following equation (3):
2.times.W.apprxeq.X/M.sub.n (3)
[0089] wherein X/M.sub.n represent a non-reducible fraction, X and
M.sub.n are each independently natural numbers, and n represents a
maximum figure of the number; for example, M.sub.2 is an integer of
1 to 99.
[0090] In the present invention, when a 2-fold value (2W) of the
winding number (W) is represented by an approximate fraction having
a non-reducible denominator of two figures or less, M.sub.2 in the
equation (3), i.e., a value of the denominator is 4 to 40,
preferably 5 to 20. As the value of M.sub.2 becomes larger, the
filter cartridge having a finer texture is prepared. If this value
is less than 4, a texture of the resulting filter cartridge is
roughened too much, and it is likely that a filter cartridge end
face is not smooth. On the other hand, if the value of M.sub.2
exceeds 40, a texture of the filter cartridge becomes too fine, and
it is likely that the liquid-passing property is reduced and the
filter life is shortened.
[0091] In this case, it is important that the value of 2W is
approximate to a fraction having a denominator of a natural number
of two figures or less. For example, when the winding number is
1.893, 2.times.W is 3.786. When this 3.786 is approximated to a
fraction having a denominator of one figure, it is 3 and 4/5 (this
means a mixed fraction consisting of 3 and four fifths, and the
same shall apply unless otherwise described). Accordingly, when the
winding number is 1.893, M.sub.1 is 5 which is the denominator of 3
and 4/5. Similarly, when 2W is approximated to a fraction having a
denominator of two figures or less, a value thereof is 3 and
{fraction (11/14)}, and therefore M.sub.2 is 14 which is a
denominator of 3 and {fraction (11/14)}. Similarly, when 2W is
approximated to a fraction having a denominator of three figures or
less, it is 3 and {fraction (393/500)}, and therefore M.sub.3 is
500. Accordingly, in this case, a value of M.sub.2 in the equation
(3) is 14 which is the denominator when approximated to a fraction
having a denominator of two figures. When 2W is approximated to a
fraction having a denominator of two figures or less, 3 and
{fraction (22/28)} and 3 and {fraction (33/42)} are also the most
approximate values, but these number are reduced to 3 and {fraction
(11/14)}, so that a value of M.sub.2 is 14 in this case.
[0092] The value of M.sub.2 described above is varied in a range of
4 to 40, whereby filter cartridges having various accuracies can be
prepared even if the same non-woven fabric strip is used. Further,
it can also be combined with a method of varying a width, a basis
weight or a fiber diameter of the non-woven fabric strip.
[0093] A deep layer-filtering structure of the filter cartridge can
further be optimized by winding the non-woven fabric with M.sub.2
set to a specific value until the major diameter becomes a certain
degree, and by further winding the non-woven fabric with the value
of M.sub.2 changed.
[0094] In the filter cartridge of the present invention, the
non-woven fabric strip is wound around the perforated cylinder 2 to
form a filter cartridge having a major diameter 1.5 to 3 times as
large as that of the perforated cylinder. Even when wound in the
same winding number, a space between the non-woven fabric strips is
varied depending on a major diameter of the perforated cylinder 4.
A major diameter of the perforated cylinder 4 is usually decided
according to use conditions, and the filtering performance is not
controlled by a major diameter of the perforated cylinder 4. If the
winding number is the same, as the major diameter of the filter
cartridge becomes larger, the particle diameter of the initial
particles trapped on the filter cartridge becomes smaller.
[0095] A fiber diameter of the long fiber used for the long fiber
non-woven fabric described above varies depending on uses of the
filter cartridge and kinds of the resin, and it is preferably in a
range of 5 to 680 .mu.m. If the fiber diameter exceeds 680 .mu.m,
it makes no difference between continuous yarns merely bound into a
bundle and the long fiber non-woven fabric. On the other hand, even
if the fiber diameter is less than 5 .mu.m, the resulting long
fiber non-woven fabric can be used for a filter cartridge. However,
when the long fiber non-woven fabric is a non-woven fabric prepared
by a spun bonding method as described above (hereinafter referred
to as a spun bonded non-woven fabric), spinning of fibers having a
fiber diameter of less than 5 .mu.m by the spun bonding method
reduces a production efficiency and is not practical. The fiber
diameter is more preferably 9 to 150 .mu.m.
[0096] In the filter cartridge of the present invention, a
non-woven fabric prepared by laminating a long fiber non-woven
fabric and a melt blown non-woven fabric may be used for the
non-woven fabric strip. In this case, it can make good use of both
advantages of the long fiber non-woven fabric and the melt blown
non-woven fabric. A particle-trapping performance of the filter
cartridge is influenced a great deal by a fiber diameter of the
melt blown non-woven fabric, and this is particularly preferred
when preparing the filter cartridge with a high accuracy.
[0097] The laminating method shall not specifically be restricted.
A fiber aggregate of the melt blown non-woven fabric and that of
the long fiber non-woven fabric (long fiber web) may be produced
respectively at different steps and then superposed, or
alternatively, fibers may be melt-blown directly on the long fiber
non-woven fabric or the long fiber web and laminated. Examples of
combinations of the fibers for the laminated non-woven fabric
include two layers of melt blown fiber/long fiber, three layers of
long fiber/melt blown fiber/long fiber, and three layers of melt
blown fiber/melt blown fiber/long fiber which comprise two melt
blown fibers having different fiber diameters.
[0098] In the present invention, yarns having different cross
sections can be used. They can provide a filter cartridge having
the same liquid-passing property and a higher accuracy, as compared
with the fibers having a circular cross section, because an amount
of trapped fine particles increases as a surface area of the filter
becomes larger.
[0099] In the present invention, the thermoplastic resin used for
producing the thermoplastic fiber can be blended with a hydrophilic
resin such as polyvinyl alcohol, or a surface of the non-woven
fabric strip can be subjected to plasma treating, in order to
improve the liquid-passing property when using the filter cartridge
for filtering a water-based liquid.
[0100] In the present invention, a heat bonding method is preferred
as a method for bonding fiber intersections for preparing the
non-woven fabric from the thermoplastic fiber. The method includes
a thermal compression bonding method by means of an apparatus such
as a thermal embossing roll and a heat flat calender roll; and a
method using a heat treating machine of a hot blast-circulating
type, a heat through-air type, an infrared heater type or a
vertical hot blast-blowing type. Among them, a method using a
thermal embossing roll is preferred, because it can elevate a
production rate of a non-woven fabric, provides a good productivity
and can reduce a cost.
[0101] As shown in FIG. 7, a non-woven fabric produced by the
method using a thermal embossing roll has part 8 where strong
thermal compression bonding by an embossing pattern is applied and
part 9 where only weak thermal compression bonding by deviating
from an embossing pattern is applied. This makes it possible to
trap a lot of foreign matters 2 in the part 8, and a part of the
foreign matters in the part 9, while the remaining foreign matters
can pass through the long fiber non-woven fabric to move to the
following layer. Preferred is this deep layer-filtering structure,
in which even the inside of the filter is utilized. In this case,
an embossing patterned area is preferably from 5 to 25%. Setting
the lower limit of this area to 5% can enhance the filtering effect
exerted by the part 8 and 9, and setting the upper limit to 25% can
control the rigidity of the non-woven fabric not to become too
high. Further, a part of foreign matters are allowed to pass
through the non-woven fabric strip.
[0102] A composite fiber comprising a low melting resin and a high
melting resin, wherein the melting point difference is 10.degree.
C. or more, preferably 15.degree. C. or more, is preferred as the
fiber constituting the non-woven fabric strip. The melting point
difference of 10.degree. C. or more stabilizes a heat adhesion
property in the fiber intersections of the non-woven fabric. In the
case of a resin having no melting point, the flow-starting
temperature is defined as a melting point. Stabilized heat adhesion
in the fiber intersections of non-woven fabric strips will allow
less particles which have been trapped in the vicinity of the fiber
intersections to flow out of filter cartridges, when a filtering
pressure and a flow amount of a solution are elevated, and will
result in a less deformation of the filter cartridge. Further, even
if a substance contained in a filtrate deteriorate the fibers, the
stabilized heat adhesion can reduce probability of the fibers
falling, and thus it is desirable.
[0103] The composite fiber described above may be in any forms such
as a parallel type and a sheath-core type, wherein a low-melting
resin is present on at least a part of a fiber surface.
[0104] A combination of the low melting resin and the high melting
resin in the composite fibers shall not specifically be restricted
as long as the melting point difference is 10.degree. C. or more,
preferably 15.degree. C. or more, which includes linear low density
polyethylene/polypropylene, high density
polyethylene/polypropylene, low density polyethylene/polypropylene,
copolymer of propylene with other a-olefin/polypropylene, linear
low density polyethylene/high density polyethylene, low density
polyethylene/high density polyethylene, various
polyethylenes/thermoplastic polyester, polypropylene/ thermoplastic
polyester, copolymerized low melting thermoplastic
polyester/thermoplastic polyester, various polyethylenes/nylon 6,
polypropylene/nylon 6, nylon 6/nylon 66 and nylon 6/thermoplastic
polyester. Among them, a combination of linear low density
polyethylene/polypropylene is preferably used, since rigidity and a
void rate of the non-woven fabric strip can readily be controlled
during a step of adhesion of fiber intersections in producing the
non-woven fabric. When a filter cartridge is used for filtering a
solution of a relatively high temperature, a combination of low
melting polyester/polyethylene terephthalate can suitably be used,
the polyester being prepared by copolymerizing with isophthalic
acid.
[0105] In the present invention, other fibers than the
thermoplastic fibers may be contained in the non-woven fabric strip
as long as the effect of the present invention is not damaged.
Examples of the fibers other than the thermoplastic fibers include
rayon, cupra, cotton, hemp, pulp and carbon fiber. The content of
the thermoplastic fiber may preferably be at least 30% by weight,
and it can be 100% by weight. If it is less than 30% by weight, a
strength of the non-woven fabric is reduced when thermally bonded
by a thermal compression bonding method and a through-air heat
treating method, so that the fibers are liable to fall off and to
be mixed in the filtrate while filtering.
[0106] For preparing the non-woven fabric strip used for the filter
cartridge of the present invention, a non-woven fabric-producing
set-up, for example, a spinning width may be controlled to directly
prepare the non-woven fabric strip, but preferably, a wide
non-woven fabric is slit into strips.
[0107] A width of the non-woven fabric strip used for the filter
cartridge of the present invention is preferably 0.5 to 40 cm. If
this width is less than 0.5 cm, the wide non-woven fabric is likely
to be broken when the non-woven fabric is slit into strips, and it
is difficult to control a tension in winding around a perforated
cylinder in a twill form. Further, when preparing a filter
cartridge having the same void rate, the winding time is extended
and the productivity is reduced. On the other hand, if the width
exceeds 40 cm, a friction in a yarn passage of a winder including a
traverse guide may be larger or the converged non-woven fabrics may
be irregular in size.
[0108] A basis weight of the non-woven fabric strip, i.e., a weight
per unit area of the non-woven fabric is preferably 5 to 200
g/m.sup.2. If the value is smaller than 5 g/m.sup.2, an amount of
the fiber is reduced, resulting in an increased unevenness in the
non-woven fabric or a reduced strength of the non-woven fabric, or
occasionally difficulty in thermal bonding of the fiber
intersections. On the other hand, the value larger than 200
g/m.sup.2 will render the rigidity of the non-woven fabric too much
increased, so that the fabric is difficult to wind around a
perforated cylinder in a twill form at the later stage.
[0109] An upper limit of a width of the non-woven fabric strip
varies depending on the basis weight, and a product of a width (cm)
and a basis weight (g/m.sup.2) of the non-woven fabric strip is
preferably 10 to 200 cm g/m.sup.2. The value larger than 200 will
render the rigidity of the non-woven fabric excessively increased,
so that winding of the non-woven fabric on a perforated cylinder in
a twill form becomes difficult at the later stage. Further, the
non-woven fabric becomes too thick in converging, so that it
becomes difficult to wind it densely. On the other hand, if the
product is less than 10, the non-woven fabric may be cut.
[0110] In the present invention, an airflow amount
(cm.sup.3/cm.sup.2/sec) of the non-woven fabric strip measured by
JIS L 1096-A (1990) method varies depending on uses of the filter
cartridge, and it is preferably 1 to 6000
cm.sup.3/cm.sup.2/sec.
[0111] In the present invention, a thickness of the non-woven
fabric strip is 0.02 to 1.20 mm, preferably 0.05 to 0.90 mm. If a
thickness of the non-woven fabric strip is less than 0.02 mm, a
strength of the non-woven fabric is reduced, and the non-woven
fabric may be cut when wound around a perforated cylinder in
producing a filter cartridge. On the other hand, if a thickness of
the non-woven fabric strip exceeds 1.20 mm, the rigidity may become
too high, so that the non-woven fabric is difficult to be wound
around a perforated cylinder densely in a twill form.
[0112] The non-woven fabric strip is wound and processed into a
form of a filter cartridge by the method mentioned above. This may
be used for a filter cartridge as it is, or a gasket of foamed
polyethylene having a thickness of approx. 3 mm may be stuck on an
end surface of the filter cartridge to improve an adhesion property
to housing.
[0113] In the filter cartridge of the present invention, divided
fibers can also be used for the fibers of the non-woven fabric
strip. However, since it is actually difficult to evenly divide
fibers into divided fibers, a melt blown non-woven fabric having a
similar average fiber diameter is more preferably used as described
above.
[0114] When the non-woven fabric strip is made hydrophilic by
incorporating a hydrophilic resin such as polyvinyl alcohol into a
raw material resin for the fabric or subjecting the surface thereof
to plasma treatment, the liquid-passing property of the resulting
filter cartridge can be enhanced in case of filtering an aqueous
solution. Accordingly, a filter cartridge using such resin is
preferred for filtering an aqueous solution.
[0115] In the present invention, the filter cartridge thus prepared
has a void rate preferably in a range of 65 to 85%. The value
smaller than 65% will render the fiber density too high, so that
the liquid-passing property is reduced. On the contrary, the value
larger than 85% will render the strength of the filter cartridge
reduced and often cause deformation of the filter cartridge
unfavorably when a high filtering pressure is applied.
[0116] The liquid-passing property can be improved by providing the
non-woven fabric strip with notch or by perforating it. In this
case, the number of the notch is preferably 5 to 100 per 10 cm of
the non-woven fabric, and the perforation area is preferably 10 to
80%. The filtering performance can be controlled by winding plural
non-woven fabric strips, or winding it together with other yarns
such as a spun yarn. A wide non-woven fabric may be wound in a
layer form while winding the non-woven fabric strip in a traversing
manner, whereby the maximum flow-out diameter of particles can be
controlled when a filter cartridge having a rough accuracy is
prepared.
[0117] The filter life can be improved by winding a non-woven
fabric having a high fineness in an internal layer of the filter
cartridge and then winding a non-woven fabric having a low fineness
in an external layer thereof. In this case, a fineness of the
external layer is set suitably 2 to 8 times as low as that of the
internal layer. Further, the filter life can be improved as well by
winding a non-woven fabric having a wide slit width for the
internal layer and winding a non-woven fabric having a narrow slit
width for the external layer. In this case, a non-woven fabric
strip width of the internal layer is set suitably 1.5 to 10 times
as large as that of the external layer. Other methods for improving
the filter life include a method of winding a non-woven fabric
having a large basis weight for the internal layer and then winding
a non-woven fabric having a small basis weight for the external
layer, and a method of winding a weakly twisted non-woven fabric
for the internal layer and then winding a strongly twisted
non-woven fabric for the external layer. It is suitable to set a
basis weight of the non-woven fabric in the internal layer 2 to 10
times as large as that of the external layer and to set a twist of
the non-woven fabric in the external layer 2 to 10 times as much as
that of the internal layer. A dense and rough structure of the
filter cartridge can be formed by these methods, and a filter life
of the filter cartridge is improved.
[0118] In the present invention, an end face of the filter
cartridge may preferably be smoothened by heat adhesion, which
forms smooth end-sealing parts at both ends of the filter cartridge
and elevates the sealing property. The non-woven fabric strip
constituting both end parts of the filter cartridge is molten by
heat, a solvent, a supersonic wave, etc. and then solidified while
forming the smooth end faces. Since the non-woven fabric strip
comprising the thermoplastic fiber is used in the present
invention, a heating method is preferred.
EXAMPLES
[0119] The present invention shall be explained below in detail
with reference to examples and comparative examples, but the
present invention shall not be restricted to these examples. In the
respective examples, the physical properties and the filtering
performances of the filters were evaluated by the methods described
below.
[0120] Winder and Winding Number
[0121] A winder had a traverse width (width of traversing) of 250
mm, in which a hole of a traverse guide 5 shown in FIG. 6 had a
diameter of 5 mm. An initial speed of a bobbin was set up to 1500
rpm. A winding number (W), that is, a number of winding the
non-woven fabric strip around a perforated cylinder from one end to
the other end was controlled by interlocking a reciprocating motion
of the traverse guide with a rotary motion of the perforated
cylinder by means of several gears having an appropriate number of
gear teeth.
[0122] Basis Weight and Thickness of Non-woven Fabric
[0123] The non-woven fabric having the area of 625 cm.sup.2
(Examples 1 to 15 and Comparative Examples 1 to 5) or 500 cm2
(Examples 16 to 25 and Comparative Examples 6 to 9) was cut off and
weighed. The weight was converted to a weight per square meter to
define a basis weight. Further, the thickness of the cut non-woven
fabric was measured optionally at 10 points, (Examples 1 to 15 and
Comparative Examples 1 to 5) or 12 points (Examples 16 to 25 and
Comparative Examples 6 to 9), and the values of 8 points (Examples
1 to 15 and Comparative Examples 1 to 5) or 10 points (Examples 16
to 25 and Comparative Examples 6 to 9) excluding the maximum value
and the minimum value were averaged to define the thickness of the
non-woven fabric. The thickness at the respective points was
measured on the conditions of a load of 196 Pa and a measuring
speed of 2 mm/sec by means of "Digithickness Tester (trade name)"
manufactured by Toyo Seiki Seisaku-Sho, Ltd.
[0124] Fiber Diameter of Fiber Constituting Non-woven Fabric
[0125] The non-woven fabric was sampled at 5 spots at random, and
they were photographed through a scanning type electron microscope.
20 fibers per spot were selected at random to measure the diameters
of the fibers, and an average value thereof was defined as the
fiber diameter (.mu.m) of the non-woven fabric.
[0126] Airflow Amount
[0127] Measured according to JIS L 1096-A (1990) method. When the
airflow amount exceeded 790 cm.sup.3/cm.sup.2/sec, a measured area
of the test sample was reduced.
[0128] Void Rate of Filter Material for Filter Cartridge
[0129] The major diameter, the minor diameter, the length and the
weight of the filter cartridge were measured to determine the void
rate using the following equation. In order to determine the void
rate of the filter material itself excluding a perforated cylinder,
the major diameter of the perforated cylinder was used for the
value of the minor diameter, and a value obtained by deducting the
weight of the perforated cylinder from the weight of the filter
cartridge was used for the value of the weight:
(Apparent volume of filter material)={(Major diameter of filter
material).sup.2-(Minor diameter of filter material
).sup.2}/4.times..pi..times.(Length of filter material);
(Real volume of filter material)=(Weight of filter
material)/(Density of raw material of filter material);
(Void rate of filter material)={1-(Real volume of filter
material)/(Apparent volume of filter material)}.times.100 (%).
[0130] Initial Trapped Particle Diameter, Initial Pressure Loss and
Filter Life
[0131] One filter cartridge was mounted to a housing of a
circulating type testing machine for filtering performance, and
water was passed to circulate, controlling a flow rate to 30
dm.sup.3/minute by means of a pump. A difference in pressures at
the inlet and outlet of the filter cartridge was set as an initial
pressure loss. Next, a cake prepared by mixing 8 kinds of testing
powder I prescribed in JIS Z 8901 (1995) (abbreviated as JIS 8
kinds; intermediate diameter: 6.6. to 8.6 .mu.m) with 7 kinds of
the same powder (abbreviated as JIS 7 kinds; intermediate diameter:
27 to 31 .mu.m) in a weight ratio of 1:1 was continuously added at
0.4 g/minute, (Examples 1 to 15 and Comparative Examples 1 to 5),
or the JIS 7 kinds were continuously added at 0.2 g/minute
(Examples 16 to 25 and Comparative Examples 6 to 9), and the
original solution and the filtrate were sampled 5 minutes after
starting of the addition. They were diluted to appropriate
concentrations, and then the numbers of particles contained in the
respective solutions were measured by means of a light shielding
type particle detector to calculate an initial trapping efficiency.
Further, the value thereof was interpolated to determine a particle
diameter showing a trapping efficiency of 80%. The addition of the
cake was still continued until the pressure loss of the filter
cartridge reached to 0.2 MPa, and the original solution and the
filtrate were again sampled to determine a trapped particle
diameter. Time consumed from starting addition of the cake until
reaching to 0.2 MPa was defined as a filter life. When the pressure
difference did not reach to 0.2 MPa even the filter life reached to
1000 minutes, the measurement was discontinued at that point of
time.
[0132] Bubbling and Fiber Falling of Initial Filtrate
[0133] One filter cartridge was mounted to a housing of a
circulating type testing machine for filtering performance, and
ion-exchanged water was passed, controlling a flow rate to 10000
cm.sup.3/minute by means of a pump. 1000 cm.sup.3 of an initial
filtrate was sampled, and 25 cm.sup.3 thereof was taken into a
calorimetric bottle and stirred vigorously to observe bubbling 10
seconds after stopping the stirring. When a volume of bubble
(volume from a liquid surface up to the top of bubble) was 10
cm.sup.3 or more, it was judged poor and shown by a symbol "C";
when a volume of bubble was less than 10 cm.sup.3, it was judged
fair and shown by a symbol "B"; and when less than 5 bubbles having
a diameter of 1 mm or more were observed, it was judged good and
shown by a symbol "A". Further, 500 cm.sup.3 of the initial
filtrate was passed through a nitrocellulose filter having a pore
diameter of 0.8 .mu.m to judge fiber falling. When the number of
fibers having a length of 1 mm or more per cm.sup.2 of the filter
paper were 4 or more, it was judged poor and shown by "C"; the
number of 1 to 3 was judged fair and was shown by "B"; and the
number of 0 was judged good and shown by "A".
[0134] Deformation of Filter Cartridge
[0135] One filter cartridge was mounted to a housing (transparent)
of a circulating type testing machine for filtering performance,
and water was passed to circulate, controlling a flow rate to 30
dm.sup.3/minute by means of a pump. An appearance of the filter
cartridge was photographed. The JIS 7 kinds were added until the
pressure loss before and after the housing reached 0.5 MPa. Then,
an appearance of the filter cartridge was photographed on the same
conditions (object distance, magnification, etc.) when the pressure
loss before and after the housing reached 0.5 MPa. The major
diameter of the filter cartridges shown in the two photographs was
measured by image analysis to determine a shrinkage percentage. A
shrinkage less than 10% was judged good and shown by "A"; a
shrinkage 10% or more and less than 20% was judged fair and shown
by "B" and a shrinkage 20% or more was judged poor and shown by
"C".
Example 1
[0136] Used as a non-woven fabric was a polypropylene melt blown
non-woven fabric having a basis weight of 50 g/m.sup.2, a thickness
of 0.8 mm and a fiber diameter of 82 .mu.m, in which fiber
intersections were thermally bonded by remaining heat of spinning
and an airflow amount was 1400 cm.sup.3/cm.sup.2/sec. Used for a
perforated cylinder was a polypropylene injection-molded article
having a minor diameter of 30 mm, a major diameter of 34 mm and a
length of 250 mm, and also having 180 holes of 6 mm square. The
above melt blown non-woven fabric was slit to a width of 2.5 cm to
obtain a non-woven fabric strip. The strip was passed through a
traverse hole of the winder to be converged and wound around the
perforated cylinder with a winding number set to 4.429 until the
major diameter reached to 62 mm to obtain a cylindrical filter
cartridge 7 as shown in FIG. 8.
Example 2
[0137] A cylindrical filter cartridge was obtained in the same
manner as in Example 1, except that used as a non-woven fabric was
a polypropylene melt blown non-woven fabric having a basis weight
of 20 g/m.sup.2, a thickness of 0.2 mm and a fiber diameter of 3
.mu.m, in which fiber intersections were thermally bonded by
remaining heat of spinning and an airflow amount was 38
cm.sup.3/cm.sup.2/sec. This filter cartridge had a higher filtering
accuracy than that of the filter cartridge described in Example
1.
Example 3
[0138] Used as a non-woven fabric were the same polypropylene melt
blown non-woven fabric as in Example 2 and a polypropylene spun
bonded long fiber non-woven fabric having a basis weight of 20
g/m.sup.2, a thickness of 0.2 mm, a fiber diameter of 18 .mu.m and
an airflow amount of 560 cm.sup.3/cm.sup.2/sec. One melt blown
non-woven fabric and one spun bonded long fiber non-woven fabric
each described above were superposed and the fiber intersections
were thermal compression bonded by means of a heat embossing roll
at a heat bonded area rate of 13% to prepare a laminated non-woven
fabric. A cylindrical filter cartridge was obtained in the same
manner as in Example 1, except that this non-woven fabric was used
to prepare a non-woven fabric strip having a width of 5 cm. This
filter cartridge had almost the same filtering accuracy and an
excellent filter life as compared with the filter cartridge
described in Example 2.
Example 4
[0139] Used as a non-woven fabric was a polypropylene spun bonded
long fiber non-woven fabric having a basis weight of 20 g/m.sup.2,
a thickness of 0.19 mm and a fiber diameter of 18 .mu.m, in which
fiber intersections were thermal compression bonded by means of a
heat embossing roll at a heat bonded area rate of 13% and an
airflow amount was 490 cm.sup.3/cm.sup.2/sec. The same perforated
cylinder as in Example 1 was used. The spun bonded long fiber
non-woven fabric was slit to a width of 5 cm to obtain a non-woven
fabric strip. The strip was not converged and wound around the
perforated cylinder by means of a winder with a winding number set
to 4.429 until the major diameter reached to 62 mm to obtain a
cylindrical filter cartridge.
Example 5
[0140] The same non-woven fabric strip and perforated cylinder as
in Example 1 were used. The non-woven fabric strip was passed
through a traverse hole of a winder and converged. It was wound
around the perforated cylinder on the same conditions as in Example
4 to obtain a filter cartridge. This filter cartridge had a lower
filtering accuracy, a better liquid-passing property and a longer
filter life than those of the filter cartridge described in Example
4.
Example 6
[0141] A cylindrical filter cartridge was obtained in the same
manner as in Example 5, except for changing the raw material resin
of the spun bonded long fiber non-woven fabric to polyethylene
terephthalate. This filter cartridge showed almost the same
filtering performance as that of the filter cartridge described in
Example 5.
Example 7
[0142] A cylindrical filter cartridge was obtained in the same
manner as in Example 5, except for changing the raw material resin
of the spun bonded long fiber non-woven fabric to nylon 66. This
filter cartridge showed almost the same filtering performance as
that of the filter cartridge described in Example 5.
Example 8
[0143] A cylindrical filter cartridge was obtained in the same
manner as in Example 5, except that sheath-core type composite
fibers comprising high density polyethylene as a low melting
component and polypropylene as a high melting component in a weight
ratio of 5:5 were used as the structural fibers for the spun bonded
long fiber non-woven fabric. This filter cartridge had a more
excellent accuracy than that of the filter cartridge described in
Example 5 and showed such an excellent stability in the filtering
accuracy that the trapped particle diameter at 0.2 MPa scarcely
changed from the initial trapped particle diameter.
Example 9
[0144] A cylindrical filter cartridge was obtained in the same
manner as in Example 8, except that linear low density polyethylene
was used as the low melting component for the sheath-core type
composite fiber. This filter cartridge had almost the same
filtering accuracy as that of the filter cartridge obtained in
Example 8 and had a more excellent liquid-passing property than
that of the filter cartridge described in Example 8.
Example 10
[0145] A cylindrical filter cartridge was obtained in the same
manner as in Example 9, except that the thermal bonding method for
the fiber intersections was changed from the thermal compression
bonding method by a hot embossing roll to a heat treating method by
a hot blast-circulating type heating apparatus. This filter
cartridge had a little lower filtering accuracy than that of the
filter cartridge described in Example 9.
Example 11
[0146] A cylindrical filter cartridge was obtained in the same
manner as in Example 5, except that the long fiber non-woven fabric
was slit to a width of 1 cm and that the winding number was changed
to 3.476. This filter cartridge showed almost the same performance
as that of the filter cartridge described in Example 5. However,
time required for winding was longer than in Example 2.
Example 12
[0147] A cylindrical filter cartridge was obtained in the same
manner as in Example 11, except that the long fiber non-woven
fabric was slit to a width of 9 cm and that the winding number was
changed to 3.714. This filter cartridge had a lower filtering
accuracy than that of the filter cartridge described in Example 11,
and this may be because the non-woven fabric strip-converged matter
became extremely thick.
Example 13
[0148] A cylindrical filter cartridge was obtained in the same
manner as in Example 5, except that a fiber diameter of the fiber
constituting the non-woven fabric strip was changed to 40 .mu.m.
This filter cartridge had a lower filtering accuracy than that of
the filter cartridge described in Example 5.
Example 14
[0149] A cylindrical filter cartridge was obtained in the same
manner as in Example 5, except that a basis weight of the non-woven
fabric strip was changed to 44 g/m.sup.2. This filter cartridge had
a lower filtering accuracy than that of the filter cartridge
described in Example 5.
Example 15
[0150] A cylindrical filter cartridge was obtained in the same
manner as in Example 5, except that the non-woven fabric strip was
twisted 100 times per one meter instead of converging. This filter
cartridge showed almost the same filtering performance as that of
the filter cartridge described in Example 12.
Comparative Example 1
[0151] A cylindrical filter cartridge was obtained in the same
manner as in Example 2, except that polypropylene spun yarns having
a diameter of 2 mm prepared by spinning fibers having a fiber
diameter of 22 .mu.m was used in place of the non-woven fabric
strip. This filter cartridge had an initial trapped particle
diameter larger than that of the filter cartridge described in
Example 5 and almost the same as that of the filter cartridge
described in Example 12. However, it had an inferior liquid-passing
property and a shorter filter life than those of the filter
cartridge described in Example 12. Further, bubbling was observed
in the initial filtrate, and falling of the filter material was
observed as well.
Comparative Example 2
[0152] A cylindrical filter cartridge was obtained in the same
manner as in Example 2, except that a filter paper No. 1 prescribed
in JIS P 3801 (1995), which was cut to a width of 5 cm, was used in
place of the non-woven fabric strip. This filter cartridge had an
initial trapped particle diameter smaller than that of the filter
cartridge described in Example 5, but the trapped particle diameter
at an elevated pressure was changed from the initial one to a large
extent. Further, the filter life was extremely short, and falling
of the filter material was observed in the initial filtrate.
Comparative Example 3
[0153] Short fibers comprising polypropylene and high density
polyethylene which were dividable to eight parts and had a fiber
diameter of 25 .mu.m were webbed by means of a carding machine, and
the webbed matter was subjected to fiber division and fiber
entanglement by high pressure water processing to obtain a divided
short fiber non-woven fabric having a basis weight of 22 g/m.sup.2.
This non-woven fabric was observed under an electron microscope to
carry out image analysis, which showed that 50% by weight of the
whole fibers was divided into a fiber diameter of 9 .mu.m. A
cylindrical filter cartridge was obtained in the same manner as in
Example 5, except that this non-woven fabric was cut to a width of
5 cm and used in place of the non-woven fabric strip. An initial
trapped particle diameter in this filter cartridge was smaller than
that in the filter cartridge described in Example 5, but a trapped
particle diameter at 0.2 MPa was larger. Further, a little bubbling
in the initial filtrate was observed as well as falling of the
fibers.
Comparative Example 4
[0154] A cylindrical filter cartridge was obtained in the same
manner as in Example 11, except that used as a non-woven fabric was
a polypropylene melt blown non-woven fabric having a basis weight
of 100 g/m.sup.2, a thickness of 1.5 mm and a fiber diameter of 140
.mu.m, in which fiber intersections were thermally bonded by
remaining heat of spinning and an airflow amount was 1400
cm.sup.3/cm.sup.2/sec. It was difficult to wind the non-woven
fabric densely around the perforated cylinder so that the filtering
accuracy could not be measured.
Comparative Example 5
[0155] A cylindrical filter cartridge was obtained in the same
manner as in Example 11, except that used as a non-woven fabric was
a polypropylene melt blown non-woven fabric having a basis weight
of 140 g/m.sup.2, a thickness of 0.5 mm and a fiber diameter of 90
.mu.m, in which fiber intersections were thermally bonded by
remaining heat of spinning and an airflow amount was 600
cm.sup.3/cm.sup.2/sec. It was difficult to wind the non-woven
fabric densely around the perforated cylinder as was the case with
Comparative Example 4 so that the filtering accuracy could not be
measured.
Comparative Example 6
[0156] Used as a non-woven fabric was a polypropylene spun bonded
long fiber non-woven fabric having a basis weight of 90 g/m.sup.2,
a thickness of 0.80 mm and a fiber diameter of 80 .mu.m, in which
fiber intersections were thermally bonded by a heat embossing roll
at a heat bonded area rate of 13% and an airflow amount was 1000
cm.sup.3/cm.sup.2/sec. This spun bonded long fiber non-woven fabric
was slit into a non-woven fabric strip having a width of 5 cm. The
same perforated cylinder as in Example 1 was used. The strip was
passed through a traverse hole of the winder to be converged and
wound around the perforated cylinder with a winding number set to
4.429 until the major diameter reached to 62 mm to obtain a
cylindrical filter cartridge as shown in FIG. 8. In this case,
neither equation (A) nor equation (B) was satisfied. As compared
with the filter cartridge of Example 4 which had such a high
filtering accuracy that an initial trapped particle diameter was 7
.mu.m, this filter cartridge had an initial trapped particle
diameter of 103 .mu.m, which proved that it could not trap fine
particles.
Comparative Example 7
[0157] Used as a non-woven fabric was a polypropylene spun bonded
long fiber non-woven fabric having a basis weight of 50 g/m.sup.2,
a thickness of 0.86 mm and a fiber diameter of 500 .mu.m, in which
fiber intersections were thermally bonded by a heat embossing roll
at a heat bonded area rate of 13% and an airflow amount was 3000
cm.sup.3/cm.sup.2/sec. This spun bonded long fiber non-woven fabric
was slit into a non-woven fabric strip having a width of 5 cm. The
same perforated cylinder as in Example 1 was used. The strip was
passed through a traverse hole of the winder to be converged and
wound around the perforated cylinder with a winding number set to
4.429 until the major diameter reached to 62 mm to obtain a
cylindrical filter cartridge as shown in FIG. 8. In this case,
neither equation (A) nor equation (B) was satisfied. As compared
with the filter cartridge of Example 4 which had such a high
filtering accuracy that an initial trapped particle diameter was 7
.mu.m, this filter cartridge had an initial trapped particle
diameter of 349 .mu.m, which proved that it could not trap fine
particles.
1 TABLE 1 Example 1 2 3 4 5 Non-woven fabric strip Raw material of
fiber*.sup.1 PP PP PP PP PP Fiber diameter .mu.m 82 3 18 & 3 18
18 Production process Melt blow Melt blow S + M*.sup.2 Spun bonding
Spun bonding Method for bonding fiber Remaining Remaining Embossing
Embossing Embossing intersections heat heat Basis weight g/m.sup.2
50 20 40 20 20 Width cm 2.5 5 5 5 5 Thickness mm 0.8 0.2 0.35 0.19
0.19 Airflow amount 1400 38 35 490 490 cm.sup.3/cm.sup.2/sec
Fitness of equation (A) A A A A A Filter cartridge Processing of
non-woven Converging Converging Converging None Converging fabric
Void rate of filter % 78 80 81 77 81 material Initial trapped .mu.m
80 8 8 7 13 particle diameter Initial pressure loss MPa 0.001 0.025
0.025 0.013 0.003 Trapped particle .mu.m 80 9 9 8 14 diameter in
0.2 MPa Filter life min. >1000 20 30 70 215 Bubbling A A A A A
Fiber falling A A A A A 6 7 8 9 10 Non-woven fabric strip Raw
material of fiber*.sup.1 PET Nylon 66 HDPE/PP LLDPE/PP LLDPE/PP
Fiber diameter .mu.m 15 16 18 18 18 Production process Spun Spun
Spun Spun bonding Spun bonding bonding bonding bonding Method for
bonding fiber Embossing Embossing Embossing Embossing Hot-air
intersections circulating Basis weight g/m.sup.2 20 20 20 20 20
Width cm 5 5 5 5 5 Thickness mm 0.27 0.23 0.19 0.19 0.19 Airflow
amount 600 580 470 470 450 cm.sup.3/cm.sup.2/sec Fitness of
equation (A) A A A A A Filter cartridge Processing of non-woven
Converging Converging Converging Converging Converging fabric Void
rate of filter % 81 81 80 80 81 material Initial trapped .mu.m 13
13 12 12 13 particle diameter Initial pressure loss MPa 0.002 0.002
0.003 0.002 0.001 Trapped particle .mu.m 14 14 12 12 13 diameter in
0.2 MPa Filter life min. 210 210 220 220 240 Bubbling A A A A A
Fiber falling A A A A A *.sup.1Raw material for sheath/core in the
case of composite fiber *.sup.2Lamination of spun bonded non-woven
fabric and melt blown non-woven fabric
[0158]
2 TABLE 2 Example 11 12 13 14 15 Non-woven fabric strip Raw
material of fiber*.sup.1 PP PP PP PP PP Fiber diameter .mu.m 18 18
40 18 18 Production process Spun bonding Spun bonding Spun bonding
Spun bonding Spun bonding Method for bonding fiber Embossing
Embossing Embossing Embossing Embossing intersections Basis weight
g/m.sup.2 20 20 20 44 20 Width cm 1 9 5 2.5 5 Thickness mm 0.19
0.19 0.19 0.39 0.19 Airflow amount cm.sup.3/cm.sup.2/sec 490 490
780 260 490 Fitness of equation (A) A A A A A Filter cartridge
Processing of non-woven Converging Converging Converging Converging
Converging fabric Void rate of filter % 80 82 82 80 80 material
Initial trapped .mu.m 12 18 30 17 13 particle diameter Initial
pressure loss MPa 0.003 0.003 0.001 0.003 0.003 Trapped particle
.mu.m 13 19 30 18 14 diameter in 0.2 MPa Filter life min. 210 630
>1000 620 210 Bubbling A A A A A Fiber falling A A A A A
Comparative Example 1 2 3 4 5 Non-woven fabric strip (Spun yarn)
(Filter paper) Raw material of fiber*.sup.1 PP Cellulose HDPE/PP PP
PP Fiber diameter .mu.m -- -- 9 140 90 Production process -- --
(Fiber Melt blow Melt blow confounding) Method for bonding fiber --
-- (High pressure Remaining Remaining intersections water) heat
heat Basis weight g/m.sup.2 -- 90 22 100 140 Width cm -- 1.5 5 1 1
Thickness mm -- 0.2 0.2 1.5 0.5 Airflow amount
cm.sup.3/cm.sup.2/sec 150 1400 600 Fitness of equation (A) -- -- A
C C Filter cartridge Processing of non-woven -- None None
Converging Converging fabric Void rate of filter % 76 72 77 -- --
material Initial trapped .mu.m 18 11 10 -- -- particle diameter
Initial pressure loss MPa 0.005 0.022 0.010 -- -- Trapped particle
.mu.m 22 20 13 -- diameter in 0.2 MPa Filter life min. 280 30 80 --
-- Bubbling C A B -- -- Fiber falling C C C -- -- *.sup.1Raw
material for sheath/core in the case of composite fiber
Example 16
[0159] Used as a non-woven fabric was a polypropylene long fiber
non-woven fabric obtained by a spun bonding method. The fiber
intersections were thermally bonded by a thermal compression
bonding method by means of a heat embossing roll. The non-woven
fabric had a basis weight of 22 g/m.sup.2, a thickness of 200 .mu.m
and an average fiber diameter of 17 .mu.m. The long fiber non-woven
fabric was slit to a width of 50 mm to prepare a non-woven fabric
strip. Further, used for a perforated cylinder was a polypropylene
injection-molded article having a minor diameter 30 mm, a major
diameter of 34 mm and a length of 250 mm, and also having 180 holes
of 6 mm square. A winding number (W) of a winder was set up to
3.1875 (M.sub.2 in the equation (3) is 8 in this case). The
non-woven fabric strip was passed through a hole of a traverse
guide in the winder and converged, and it was wound around the
perforated cylinder until a major diameter reached to 60 mm to
obtain a cylindrical filter cartridge. Both end faces thereof were
welded by heating for 5 seconds by means of a hot plate having a
surface temperature of 175.degree. C. to obtain a cylindrical
filter cartridge as shown in FIG. 8. Neither bubbling nor falling
of the filter material was observed and the pressure loss was
small, and thus, the filter cartridge was proved excellent.
Examples 17 to 21
[0160] Cylindrical filter cartridges were obtained in the same
manner using the same non-woven fabric strip and perforated
cylinder as in Example 16, except that the winding numbers (W) were
set to 3.2778 (Example 17), 3.2917 5 (Example 18), 3.3847 (Example
19), 3.4118 (Example 20) and 3.1885 (Example 21), respectively.
When the 2-fold values (2W) of these winding numbers (W) are
approximated to fractions having denominators (M.sub.2) of two
figures or less, the denominators are 9, 12, 13, 17 and 61,
respectively. As these filter cartridges had larger M.sub.2, the
initial trapped particle diameters became smaller. Accordingly, the
value of M.sub.2 correlates with the initial trapped particle
diameter. When 2W are approximated to fractions having denominators
(M.sub.3) of three figures or less, the initial trapped particle
diameter does not decrease in proportion to the denominator
(M.sub.3). For example, M.sub.3 is larger in Example 20 than in
Example 21, but the initial trapped particle diameter is smaller in
Example 21. Thus, it proves that M.sub.3 in the equation (3) does
not correlate with the filtering accuracy. The winding number W is
smaller in Example 20 than in Example 21, but the initial trapped
particle diameter is smaller in Example 21. Thus, it proves that
the initial trapped particle diameter does not increase in
proportion to the winding number W. The filter described in Example
21 had a relatively large pressure loss and a little poor
liquid-passing property as compared with the other filters.
Examples 22 and 23
[0161] Cylindrical filter cartridges were obtained in the same
manner as in Example 19, except that a width of the non-woven
fabric strip was changed to 2 cm (Example 22) or 3 cm (Example 23).
These filter cartridges had large initial trapped particle
diameters as compared with that of the filter cartridge described
in Example 19.
Example 24
[0162] A cylindrical filter cartridge was obtained in the same
manner as in Example 19, except that used as a non-woven fabric
strip was a melt blown non-woven fabric having an average fiber
diameter of 2 .mu.m, a basis weight of 22 g/m.sup.2 and a width of
5 cm. This filter cartridge had a small initial trapped particle
diameter as compared with that of the filter cartridge described in
Example 19.
Example 25
[0163] A cylindrical filter cartridge was obtained on the same
conditions as in Example 19, except that used as a non-woven fabric
strip was a laminated non-woven fabric obtained by thermal
compression bonding by means of a heat embossing roll, which
comprised three kinds of non-woven fabrics: a polypropylene long
fiber non-woven fabric having a basis weight of 5 g/m.sup.2 and a
fineness of 2 dtex which was obtained by a spun bonding method, a
melt blown non-woven fabric having an average fiber diameter of 2
.mu.m, a basis weight of 22 g/m.sup.2 and a width of 5 cm, and a
polypropylene long fiber non-woven fabric having a basis weight of
5 g/m.sup.2 and a fineness of 2 dtex which was obtained by the spun
bonding method. This filter cartridge had a small initial trapped
particle diameter as compared with that of the filter cartridge
described in Example 19.
Comparative Example 8
[0164] A polypropylene short fiber having a fineness of 2 dtex, a
cut length of 51 mm and a crimp number of 14 was formed by
conventional melt spinning, and it was spun to obtain a spun yarn.
The spun yarn was wound around the same perforated cylinder as in
Example 16 with a winding number (W) set to 3.2252 to obtain a
filter cartridge. Both end faces thereof were welded by heating for
5 seconds by means of a hot plate having a surface temperature of
175.degree. C. to obtain a filter cartridge. This filter cartridge
was uneven on the end face and inferior in a sealing property of
the end face. The initial trapped particle diameter thereof was
in-between of the initial trapped particle diameters in Examples 19
and 20, but it had a larger pressure loss than those of both
Examples 19 and 20 and an inferior liquid-passing property.
Further, bubbling and the fibers fallen off the filter material
were observed in the filtrate, and therefore, it was not preferred
as a filter cartridge. Comparative Example 9.
[0165] A filter cartridge was obtained in the same manner using the
same materials as in Example 16, except that the winding number (W)
was changed to 0.6538. The wound non-woven fabric strip was liable
to come off this filter cartridge, and it was not suited for a
filter cartridge.
Comparative Example 10
[0166] A filter cartridge was obtained in the same manner using the
same materials as in Example 16, except that the winding number (W)
was changed to 10.1923. The wound non-woven fabric strip was liable
to come off this filter cartridge, and it was not suited for a
filter cartridge.
Comparative Example 11
[0167] Used as a structural fiber for the non-woven fabric strip
were short fibers comprising polypropylene and high density
polyethylene which were dividable into eight parts in a fiber cross
section and had a fineness of 2 dtex and a fiber length of 64 mm.
This dividable short fiber was webbed by processing by means of a
carding machine, and the webbed matter was processed by means of a
heat embossing roll to prepare a non-woven fabric. The non-woven
fabric was treated twice by means of a water jet apparatus to
divide the fiber into a divided non-woven fabric having a basis
weight of 22 g/m.sup.2 and a thickness of 210 .mu.m. The non-woven
fabric was slit to a width of 50 mm to prepare a non-woven fabric
strip. Further, a winding number (W) of a winder was set up to
3.1875 (M.sub.2 in the equation (3) is 8 in this case). The
non-woven fabric strip was passed through a hole of a traverse
guide in the winder and converged, and it was wound around a
perforated cylinder until a major diameter reached to 60 mm to
obtain a cylindrical filter cartridge. Both end faces thereof were
welded by heating for 5 seconds by means of a hot plate having a
surface temperature of 175.degree. C. to obtain a filter cartridge.
The filter cartridge thus obtained had a little reduced filtering
accuracy as compared with Example 16. A little bubbling and falling
of the filter material were observed in the filtrate, and the
pressure loss was large. Further, the filter cartridge was liable
to be deformed, and it was judged that its use needs a lot of
attention in case of the large pressure.
Comparative Example 12
[0168] Used as a non-woven fabric was the same polypropylene spun
bonded long fiber non-woven fabric as in Example 16. This fabric
was slit into a non-woven fabric strip having a width of 5 cm. The
same perforated cylinder as in Example 16 was used. The strip was
passed through a hole of a traverse guide in the winder to be
converged and wound around a perforated cylinder with a winder
number set to 0.8077 until a major diameter reached to 62 mm to
obtain a cylindrical filter cartridge as shown in FIG. 8. As
compared with the filter cartridge of Example 16 having an initial
trapped particle diameter of 59 .mu.m, this filter cartridge had an
initial trapped particle diameter of 300 .mu.m, which proved that
it could not trap fine particles.
Comparative Example 13
[0169] Used as a non-woven fabric was the same polypropylene spun
bonded long fiber non-woven fabric as in Example 16. This fabric
was slit into a non-woven fabric strip having a width of 5 cm. The
same perforated cylinder as in Example 16 was used. The strip was
passed through a hole of a traverse guide in the winder to be
converged and wound around a perforated cylinder with a winder
number set to 10.0381 until a major diameter reached to 62 mm to
obtain a cylindrical filter cartridge as shown in FIG. 8. As
compared with the cartridge filter of Example 16 having a initial
trapped particle diameter of 59 .mu.m, this cartridge filter has a
initial trapped particle diameter of 500 .mu.m, which proved that
it could not trap fine particles.
3 TABLE 3 Approximation of 2W Approximation of 2W Basis with
denominator of with denominator of Non-woven Width weight W two
figures M.sub.2 three figures M.sub.3 fabric cm g/cm.sup.2 Example
16 3.1875 6 and 3/8 8 6 and 3/8 8 S 5 22 Example 17 3.2778 6 and
5/9 9 6 and 5/9 9 S 5 22 Example 18 3.2917 6 and 7/12 12 6 and 7/12
12 S 5 15 Example 19 3.3847 6 and 10/13 13 6 and 347/451 451 S 5 22
Example 20 3.4118 6 and 14/17 17 6 and 691/839 839 S 5 22 Example
21 3.1885 6 and 23/61 61 6 and 118/313 313 S 5 22 Example 22 3.3847
6 and 10/13 13 6 and 347/451 451 S 2 22 Example 23 3.3847 6 and
10/13 13 6 and 347/451 451 S 3 22 Example 24 3.3847 6 and 10/13 13
6 and 347/451 451 M 5 22 Example 25 3.3847 6 and 10/13 13 6 and
347/451 451 SMS 5 32 Comparative 3.2252 6 and 9/20 13 6 and 168/373
373 Spun yarn 0.3 -- Example 8 Comparative 0.6538 1 and 4/13 13 1
and 255/829 829 S 5 22 Example 9 Comparative 10.1923 20 and 5/13 13
20 and 5/13 13 S 5 22 Example 10 Comparative 3.1875 6 and 3/8 8 6
and 3/8 8 Divided 5 22 Example 11 yarns 80% trapped Width .times.
Void particle Pressure Falling basis weight rate diameter loss of
filter cm .times. g/cm.sup.2 % .mu.m MPa Bubbling material
Deformation Example 16 110 85 59 0.003 A A A Example 17 110 82 39
0.004 A A A Example 18 75 76 8.3 0.018 A A A Example 19 110 81 27
0.006 A A A Example 20 110 76 7.5 0.020 A A A Example 21 110 74 5
0.030 A A A Example 22 44 81 28 0.005 A A A Example 23 66 78 17
0.009 A A A Example 24 110 81 20 0.006 A A A Example 25 160 81 20
0.006 A A A Comparative -- 70 10 0.030 C C B Example 8 Comparative
110 -- -- -- -- -- -- Example 9 Comparative 110 -- -- -- -- -- --
Example 10 Comparative 110 85 50 0.004 B B C Example 11 S: Spun
bonded non-woven fabric M: Melt blown non-woven fabric SMS: Spun
bonded non-woven fabric/melt blown non-woven fabric/spun bonded
non-woven fabric
[0170] Effects of the Invention
[0171] The filter cartridge of the present invention has a high
filtering accuracy, a long filter life and a good liquid-passing
property, in which an initial trapped particle diameter little
changes, a pressure loss is small and neither bubbling nor falling
of the filter material is observed, as compared with a conventional
bobbin winder type filter cartridge.
* * * * *