Note: Descriptions are shown in the official language in which they were submitted.
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1MACEINE AND NETHOD OF MAIONG A FILTER
Field of the Invention
This invention relates to fluid filters and
particularly, though not necessarily exclusively, to
thin bed filters comprising a random fiber web having
sorptive particles uniformly distributed through and
locked in the web, and to methods of making such a web.
Background of the Invention
For a sorptive type filter, i.e., one which
filters by adsorption or absorption, of particulate
material, maximum efficiency and life span are attained
when the sorptive particles are packed together in a
bed. For a thin bed filter, i.e., from less than 1/2"
to 2 or more inches thick, this can be obtained by
simply filling the space between two spaced apart
perforated sheets with loose carbon particles. Such
filters, herein referred to as "filled filters", have
been manufactured and sold by D-Mark, Inc. of
Chesterfield Township, Michigan as well as by others.
While resulting in a high capacity filter, the particles
tend to settle resulting in channelling and shedding of
the sorptive particle dust such as carbon dust.
Shedding and channelling is overcome as
disclosed in U.S. Patent 3,019,127 but only a very low
carbon loading results, somewhere on the order of 4% of
particulate material per unit volume of the web.
Increased carbon loading, while avoiding shedding and
channelling, is disclosed in U.S. Patent 4,227,904
wherein carbon particles are glued to the face of a
perforated substrate to provide a layer of particles on
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the substrate. Two such substrates are then placed
together with the carbon covered faces in opposition and
a border frame is secured about the edges to hold the
substrates together. This results in a medium loaded
product which has enjoyed substantial commercial
success.
Finally, heavily loaded thin bed filters which
avoid channelling and the other drawbacks of the prior
art and methods of making them are disclosed in U.S.
Patents 5,124,177 and 5,338,340. These filters have a
maximum loading of approximately 90-100 grams per square
foot with a 3/8" thick mat, and up to 300 grams per
square foot with a mat approximately 3/411 thick. These
loadings have a very acceptable pressure drop, and with
roll-coating, "driving" and/or rolling techniques, they
have been able to achieve extremely good adhesion with
a minimum of shedding during handling and final
assembly. From a performance point of view, the carbon
is not totally encapsulated during the manufacturing
process, and therefore the vast majority is available
for first pass absorption.
While such filters are enjoying commercial
success, these products do not always contain a uniform
loading of the particulate throughout the web or pad and
the density or porosity may vary from pad to pad or
throughout the same pad. This is not the fault of the
methods disclosed in such patents, but rather the pad as
received from the pad manufacturer varies. The prior
art does not offer a solution that resolves the problem, =
and provides a uniform particulate loading in the pad.
Accordingly, a different method of constructing the
filter disclosed in U.S. Patent 5,338,340 is needed, one
that provides uniformity in loading and density of the
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finished filter, and which allows an increase in the
loading.
Suanmarp of t:he Invention
It is an object of the present invention to
provide a fluid filter having a fiber web which has a
uniform distribution of sorptive particles.
It is another object to provide a method of
locking sorbent or sorptive particles in a uniform
distribution within a fiber web.
It is yet another object to provide a method
of constructing a filter wherein the sorptive particles,
~~~~'h ac n~rl+nn -F4" dust 'a'~ not "i""'a 'a"-----~
uual. l1v nvl.. y11CC1 C1VWilb'La method that does not require the need for a
carbon
capturing filter layer.
In meeting the above object, advantages and
features, the present invention is directed to a method
of making a random fiber web having sorbent or sorptive
particles distributed therethrough which includes the
steps of: introducing fibers into an air stream;
introducing sorbent particles into the air stream;
mixing the particles and fibers in the air stream; and
directing the air stream with contained fibers and
sorbent particles against a foraminate condenser to form
a sorbent containing random fiber web.
The invention also discloses a method of
making a thin web filter from a sorbent containing
random fiber web comprising the steps of: containing
sorptive particles with an adhesive; introducing fibers
into a moving air stream; introducing the sorbent
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particles and adhesive into the air stream; mixing the
sorbent particles and adhesive with the fibers in the
air stream; condensing the fibers and sorbent particles
and adhesive in the air stream into a web; and treating
the adhesive within the web to use sorbent particles to
be retained in the web.
Additionally, the invention discloses a method
for making a thin bed filter from a sorbent containing
random fiber web having a first and second side
comprising the steps of: introducing fibers into a
moving air stream; introducing sorbent particles into
the air stream; mixing the sorbent particles and fibers
in the air stream; condensing the fibers and sorbent
particles in the air stream into a web; and treating the
'web to cause the sorbent particles to be retained in the
web.
The invention further discloses a machine for
making a sorbent containing random fiber web.
Disclosed herein is a method of constructing
a filter by inserting the sorptive particles into the
web or pad at the time the web is being formed. Not
only is uniformity in the final product achieved, but
the filter may be made in one continuous process rather
than first making the web and thereafter inserting the
carbon. Such requires several separate steps which
could be avoided if the sorptive particles are combined
in the web simultaneously with its formation. In
addition, by building the particulates into the web at the time of its
formation, the amount and uniformity of
the sorbent (carbon or other material) can be adjusted
to increase or decrease. With this type of control the
performance of the filter can also be controlled,
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allowing a wide range of products, from the "getter" type to
HVAC, medical, industrial, automotive, aircraft and similar
products.
With this improved process, first pass efficiency and
capacity can be designed or controlled in the filter, and
different sorptive particle sizes can be combined into one
substrate. By using different denier fibers, a combination
product is possible that would allow both gases to be absorbed
or adsorbed and finite particles to be removed.
To carry out the disclosed method, processes shown in U.S.
Patents 3,194,822, 3,918,126 or 3,972,092, are modified as herein
disclosed. More particularly, and with reference to U.S. Patent
3,972,092 (hereafter the 1092 patent) this invention introduces
into the air stream passing down through the duct 310 past the
lickerin 303 and through the duct 324, sorptive particles of the
type and size one wishes to have in the web. After the sorptive
particles are introduced, such particles are mixed in the air
stream with the fibers, and collected on an endless condensing
screen conveyor 326 to form a loose web of randomly arranged
fibers with the sorbent particles uniformly distributed
therethrough. Thereafter the loose web is treated to lock the
fibers together and the sorbent particles therein. Utilizing the
teachings of U.S. Patent 3,914,822 multiple lickerins and
correspondingly different denier or length fibers may be
incorporated in the web to vary the characteristics thereof
and/or the retention of the sorptive particles therein. Sorptive
particles of different types and sizes may be introduced in the
same
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air stream to provide different sorptive actions in the
filter web being formed.
The treatment of the web to lock the fibers
together and the sorptive particles therein may involve
spraying adhesive on the web with or without subsequent
rolling thereof, or the fibers may be precoated with an
adhesive before entering the lickerin and the adhesive
then activated by ultraviolet light or heat in the web.
Dow melting fibers may be used and UV hardenable
adhesives may be introduced and then cured. Needling of
the web may also be utilized to lock fibers together and
the sorptive particles therein. If desired, the needling
may be utilized in combination with the application of
adhesive.
In accordance with one aspect of the present
invention, there is provided a method of making a random
fiber web with sorbent particles distributed
therethrough comprising the-steps of: introducing fibers
into an air stream; introducing sorbent particles into
the air stream containing the fibers at an area
downstream from the point at which the fibers are
introduced; mixing the particles and fibers in the air
stream; and directing the air stream with entrained
fibers and sorbent particles against a foraminate
condenser to form a sorbent containing random fiber web.
In accordance with another aspect of the present
invention, there is provided a method of making a thin
bed filter comprising the steps of: combining sorbent
particles with an adhesive; introducing fibers into a
moving air stream; introducing the sorbent particles and
adhesive into the air stream containing the fibers at an
area downstream from the point at which the fibers are
introduced; mixing the sorbent particles and adhesive
with the fibers in the air stream; condensing the fibers
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and sorbent particles and adhesive in the air stream
into a web; and treating the adhesive within the web to
cause the sorbent particles to be retained in the web.
Brief Description of the Drawings
Fig. 1 is a schematic view of a portion of the
machine shown in Fig. 6 of U.S. Pat. No. 3,972,092
modified to carry out the method described herein;
Fig. 2 is a schematic view of a modified form of
the apparatus shown in Fig. 1;
Fig. 3 shows a detail of the expansion chamber or
duct of the apparatus of either Figs. 1 or 2 at the
endless condenser screen;
Fig. 4 is similar to Fig. 3 with arrangements for
accelerating the air flow in the expansion chamber at
the point of mixing the fibers and sorptive particles to
improve mixing thereof;
30
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Fig. 5 is a schematic view of a portion of the
= machine shown in Fig. 1 of U.S. Patent 3,914,822
modified to carry out the method described herein;
Fig. 5A shows a detail of the expansion
chamber of Fig. 5; and
Fig. 6 shows a modification of the apparatus
of Fig. 5.
Brief Description of Preferred Embodiments
Fig. 1 depicts a schematic drawing, similar to
Fig. 6 of U.S. Patent 3,972,092, a portion of a machine
for forming a random fiber web W. Reference should be
made to such patent for details of construction and
operation of the machine. Fibers F for making the web
are introduced in the direction of arrows 10 into a duct
12 which communicates with a rotating condensing roll 14
having a foraminous periphery through which air is drawn
by a partial vacuum V to form the fibers into a mat at
the periphery of the roll. The mat (not shown) on the
periphery of the condensing roll 14 is removed therefrom
by a doffing bar 16 and delivered by a feed roll 18 to
the rotating lickerin 20. The teeth of the lickerin
separate the fibers and by a combination of the high
speed of the lickerin creating a strong centrifugal
action, doffing by a doffing bar 24 and the movement of
an air stream 26 passing over the face of the lickerin
in the throat area 28 causes the fibers to fly off the
lickerin 20 and become airborne in the air stream.
The air stream is contained in a duct 22 of
generally venturi shape which extends across
substantially the width of the machine. The lickerin
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and the other rolls are coextensive therewith. The
fibers enter the air stream at the throat area 28 of the
venturi shaped duct. The entrained air borne fibers move
with the air stream into an expanding area 30 of the
duct where they mix with sorbent particles P introduced
into the duct transversely across the width of the duct
(i.e. the machine) from a hopper 32 through one or more
feed pipes 34 extending through the side wall of the
duct. The hopper and/or feed pipe may be vibrated as
needed to induce proper feed of the particles. A movable
gate 33 may be provided at the bottom of the hopper to
control the flow rates of the sorptive particles.
The location at which the particles enter the
duct may be varied as desired. For example, the feed
tubes may enter the duct farther up, closer to the
lickerin 20, as long as the particulate does not
adversely contaminate the lickerin. A movable wall 36
opposite the exit of the feed tubes 34 is pivoted at 38
and may be positioned as desired to vary the rate of
expansion of the air stream in the expansion chamber to
modify the mixing of the fibers and the sorptive
particles.
At the lower end of the expansion chamber an
endless condensing screen conveyor 40 having a suction
chamber 42 therein draws the air stream with its
airborne fibers and sorptive particles against the
screen conveyor to form a loose random fiber web W
thereon. The loft or thickness of the web may be
controlled by thickness control 44 as discussed in
Patent '092.
Adjustable air jets or atmospheric air inlets
(see openings 70 in Figure 3) may be provided in the
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walls of duct 22 at one or more suitable point along its
length as required for adequate mixing of the fibers and
sorptive particles. In addition, the hopper 32 may have
its interior exposed to atmospheric air, or
superatmospheric pressure or sealed from atmospheric
pressure as desired to vary the feed of particles into
the duct or control entry of air into the duct with the
particles.
Side walls 35 and 37 of the duct are
adjustable toward and away from each other to adjust the
air flow and mixing of the fibers and sorptive
particles. The adjustment of these walls, the location
of supplementary air inlets in the walls of the duct,
the location of the entry point of the particle tube or
tubes 34 through the wall of the duct are all related to
the objective of effecting a uniform mixing of the
sorptive particles and fibers so that the final web will
have the particles uniformly distributed therethrough.
In addition, these adjustments in flow rate of the air
stream and the volume of sorbent particles introduced
allow variations in the sorbent loading of the web being
formed. Thus the greater the quantity of the sorbent
particles introduced into the air stream in a given time
interval the greater the loading of the resulting web,
and vice versa. The particle loading expected to be
produced by the methods disclosed herein should be at
least similar to those produced by the methods of U.S.
Patent 5,338,340 and theoretically even greater.
As described in Patent '092, suction air from
the condenser 42 may be returned to the air tube 46 from
which it exits through a slot 47 within a feed plenum 48
having distribution screens 50 and 52 through which the
air enters duct 22.
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In practicing the method, it is desirable to
screen all sorptive particles prior to filling the feed
hopper 32 to eliminate fines from the air system of the
machine, and to isolate air used in the fiber feed side
of the apparatus, i.e., the air used in delivering the
fibers F as at arrows 10, and on through the condenser
roll and the lickerin 20, from the air circulating in
the plenum 48 and the endless condenser chamber 42, to
avoid contaminating the lickerin and other condenser
rolls 14.
Carbon and other sorptive particles useable in
the methods disclosed herein may be on the order of
from 4/6 or 6/16 mesh down through 20/50 particles. Much
finer particles may be utilized, such as powders in the
300/400 mesh range. In connection with carbon
particles, blends may be utilized to combine a very high
first pass efficiency (small carbon) with larger carbon
particles which would offer long life, capacity, and
higher retentivity.
Fig. 2 depicts an apparatus generally similar
to that of Fig. 1. In Fig. 2, for simplicity, the
plenum box 48 with its screens 50 and 52 have not been
shown. Primed reference numerals within Fig. 2 indicate
corresponding parts from Fig. 1.
Air from the delivery tube 46' moves
downwardly through duct 60 and splits at the apex 62 of
the air divider 64, a portion passing between the
adjustable divider wall 66 and the lickerin 20' with fibers F becoming
airborne and entering the mixing and
expansion chamber. The other portion of the downwardly
moving air passes through a particle entrainment chamber
68 between the air divider 64 and the opposed wall 65 of
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the duct where the sorbent particle delivery tube or
tubes 34' opens into the duct.
While Fig. 2 depicts the tube 34' located
substantially opposite the apex of the air divider, it
should be understood that the tube may be positioned
lower down along the duct as shown in Fig. 3 where it is
substantially opposite the lower end of the divider. By
varying the pivoted position of the air divider 64 the
cross-section of the entrainment chamber 68 may be
varied to increase or decrease the air velocity and
velocity of the sorptive particles as they enter the
mixing chamber 30' where they commingle with the fibers
F. The wall 66 may also be pivotally adjusted about the
apex 62 to vary the air speed across the lickerin 20'
and thus vary the fiber introduction into the mixing
chamber.
Walls 35' and 37' may be adjusted toward and
from each other to vary the mixing action in the chamber
30'. As with the Fig. 1 embodiment, the fibers and
sorptive particles are deposited on the endless
condenser 40' which is driven by the motor M' to thereby
form the loose web W which is then treated to lock the
fibers together and lock the sorptive particles therein.
As shown in the modification in Fig. 3,
atmospheric air may be introduced into the duct 30" at
the adjustable ports 70. In Fig. 4 accelerator bumps 72
and 74 are shown which "push" the sorptive particles
into the air stream and increase the mixing with the
fibers. As pointed out in U.S. Patent '092 the thickness
of the fiber stream as it passes downwardly through the
mixing and expansion chamber should not exceed more than
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about 12 to 25 mm as it approaches the condenser screen
4011.
In Fig. 5 apparatus of the kind shown in U.S.
Patent 3,914,822 is shown, modified to enable the
formation of a web from two different length and/or
denier fibers and two different size and/or types of
sorptive particles. Assuming an understanding of the
machine disclosed in Patent 3,914,822 the different
fibers are delivered to the machine through the infeed
chutes 80 and 82 which correspond generally to ducts 10
and 12 of such patent. The fibers are first matted on
the condenser rolls 84 and 86 and are delivered to the
lickerins 88 and 90 as disclosed in the patent where the
fibers are doffed into the air streams 92 and 94 on
opposite sides of the air splitter 96 and then enter the
mixing and expansion chamber 98. If the apparatus is to
form a web containing carbon particles of two different
sizes, the particles are placed in the two bins 100 and
102 having feed tubes 104 and 106 which open into the
mixing chamber one above the other as shown. As with the
Fig. 1 embodiment, the hoppers 100 and 102 and the feed
tubes 104 and 106 may be vibrated, and moveable gates
may be provided to control the feed rate and ensure
proper mesh size. For example particles of a 6/8 mesh
may be placed in one bin and particles of a 20/50 size
in the other. These particles may then combined with
the fibers in whatever ratio desired by merely
controlling the feed from the bins. As before, the web
is formed on an endless condenser screen 40 and which is
thereafter treated to lock the fibers and particles in
the web.
In Fig. 5A the lower end of the expansion
chamber of Fig. 5 is shown having been modified by the
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addition of air accelerating bumps 72' and 74' whose
action is similar to that of the bumps in Fig. 4.
Fig. 6 shows an apparatus based on the
disclosure of Fig. 5 of U.S. Patent 3,918,126 modified
as hereinafter described. This apparatus is designed to
blend different sizes or types of sorbents with two
dissimilar fibers to form a uniform nonwoven
filter/sorbent web. The sorbents are added to the air
stream below the lickerins 88' and 90' as by the
vibrated tubes 104' and 106' delivering sorbent
particles from associated hoppers or bins 100' and 102'.
Fibers are fed into the machine at 80' and 82', pass to
the condensing rolls 84' and 86' and from there to the
lickerins 88' and 90' and thence doffed into the
expansion chamber 98' where they are mixed randomly
together and with the sorptive particles from the
hoppers 100' and 102'. To assist the mixing and promote
uniformity of the resulting product, accelerator bumps
72" and 74" may be provided. In addition, the walls 110
and 112, hinged at 114 and 116, may be adjusted toward
and from each other to vary the expansion of the
entrained fiber/sorbent air stream. Fibers different
from those entering at 80' and 82', or wood pulp or
other fibrous product may be fed to the lickerins 88'
and 90' as at 118, 120, 122 and 124 to provide a random
fiber web of virtually any desired characteristic. With
the diversity of fibers possible with this arrangement,
a contaminant particle and odor removing filter web may
be easily formed, combining in it a single pass filter
based on the use of a fine mesh carbon particle, for
example. Other variations will readily occur to those
skilled in the filter art.
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Shown in phantom outline at 126 is yet another
vibratory tube which may be optionally utilized to
deliver a different sorbent to the mixing chamber than
those from tubes 104' or 106'. Sorbents from all tubes
need not be delivered simultaneously to the mixing
chamber, but rather may be selectively delivered in
accordance with the requirements of the filter web to be
produced.
Various kinds of sorbents may be utilized in the
methods and apparatus herein disclosed. Carbon
particles, oxidizing agents, Zeolites, activated
aluminum impregnated with potassium permanganate,
molecular sieves, or combinations of these materials
with or without carbon could be blended for specific
applications. Blends of carbons, and/or impregnated
carbons could also be utilized for specific
applications, efficiency, capacity, or life.
After the web has been formed on the endless
condenser screen 40, it is very fragile and must be
treated to lock the fibers together and the sorbent
particles therein, thereby allowing it to be handled,
cut and used in a filter. This locking of the fibers of
the web together may be carried out in several ways as
explained hereinafter.
According to one method of locking the web fibers
together, the web may be sprayed on one side with an
adhesive, then processed through a curing over, turned
over and sprayed on the other side and then again passed
through either the same or a second oven. Spraying
techniques are disclosed in U.S. Pat. 5,338,340 ('340
patent). Adhesives which may be suitable for this
purpose are also disclosed in the'340 patent. A suitable
adhesive for use with the spraying application is a
PVAC-polyvinylacitate latex formulation. This is termed
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a cross-linking polymer 50% water content which cures at
3250 F. in about one minute. The adhesive is available
from National Starch or Sequa Division of Sun Chemicals.
It is a common material used in the trade for bonding
non-woven fibers.
In a second method the fibers may be locked
together by treating the fibers with an adhesive or
resin prior to forming the web. Adhesives suitable for
this method can vary in size from granular adhesives to
powder adhesives. In one embodiment, "MICROTHENETM" a
product of Quantum U.S.I. based in Cincinnati, Ohio may
be utilized. MICROTHENETM is a dry, polyolefin-based
adhesive that has spherically shaped particles ranging
from 20 microns to 40 microns. MICROTHENETM may be
combined with the sorptive particles. Accordingly, the
MICROTHENETM particles can be fed into hopper 32 and thus
transported through one or more feed pipes 34 which
would then carry both the sorptive particles and the
MICROTHENETM particles to the expanding area 30 of the
duct where the fibers would be mixed with the sorptive
and MICROTHENETM particles.
The benefit associated with the use of MICROTHENETM
particles is that by using such a fine, dry adhesive the
adhesive does not settle to the bottom to the extent
that a denser adhesive would likely settle. As a result,
the MICROTHENETM particles remain dispersed randomly
throughout the Web as it is formed. During the curing
stage, the MICROTHENETM adhere to lock in the sorptive
particles within the fiber web. The use of a dry
adhesive also eliminates the need for spraying of an
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adhesive or needling processes and the like. In sum, the use of
a dry adhesive during the formation of a web results in a more
uniformly loaded web with sorptive particles locked within the
matrix of fibers.
After the web is formed utilizing such treated fibers with
the sorptive particles distributed therethrough, bonding of the
fibers together and securement of the particles therein may be
effected by a combination of heat, light and/or pressure and a
finished web or mat can be made that will be superior to the one
formed by spraying. This form of product would be uniform even
with regard to the amount of adhesive therethrough and would have
improved first pass absorption properties and lower pressure drop
since the only adhesive on the carbon would be at the point where
it touched or bonded to the fibers.
A fourth method of locking the fibers together is to needle
punch the web. This approach is more feasible with smaller
carbon such as 20/50 mesh and finer denier fibers such as 6 to
15 denier, since these particles will tend to be pushed aside by
the needles as they penetrate the web. The process need not
utilize any adhesive and therefore may be the best from the point
of first pass absorption efficiency. The needling will increase
the pressure drop but this should be well within acceptable
ranges to obtain the highest possible adsorption efficiency.
In a fifth method, a UV hardenable solvent-free prepolymer
binder composition, such as that disclosed in U.S. Patent
4,300,968 ('968 patent), may be applied to the fibrous web. As
disclosed in the
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'968 patent, a UV prepolymer binder composition can
include a combination of a prepolymer and a thinner for
the prepolymer. Suitable prepolymers include low
molecular weight polyurethane, polyester or polyepoxy
prepolymers. Suitable thinners include tri- or
tetrafunctional acrylate monomers or multifunctional
acrylate oligomers. The prepolymer binder composition
may be cured by exposing the treated fibrous web to
ultraviolet light.
One advantage of using UV light is that the
binder is solidifed upon irradiation in its original
plane, such that no web delamination occurs. The
application of the binder can thus be readily
controlled. For the present invention, the Uv binder can
be applied in stages onto the fibrous web or
alternatively applied to the external surfaces of the
fibrous web when it is fully formed. In the former
case, the mixture of sorptive particles and fibers can
be dropped onto the conveyor in stages, such that only
a part of the overall fibrous mixture is released at one
time. Following each partial release of the fibrous
mixture, the W binder is applied and immediately cured.
This two-step partial release step process occurs until
the fibers and sorptive particle mixture are fully
dropped down and the UV binder is fully dispersed and
cured within the fibrous web. With the latter method,
after the web is fully formed, the UV binder may be
applied to the external surfaces and cured to provide
additional strength thereto.
In an additional method, the fibers can
include low melting fibers which when activated by heat
have a lower melting temperature than the other fibers.
Upon application of heat, the low melting fibers
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adhesively bond to connect the fibers to one another and
lock in the sorptive particles. U.S. Patent 4,917,943
discloses low melting fibers for use within a fiber
containing aggregate to place a mixture of spherically
entangled fibers into a desired form and bond the fibers
together. The low melting fibers can be made of a low
melt thermoplastic material such as polyester,
polyethylene and polyamide. U.S. Patent 5,301,400
teaches the use of a three-dimensional non-woven fabric
with a thermally adhesive surface for covering a fibrous
mat. The '400 patent provides a specific example of a
satisfactory low melt polyester fiber, sold by Du Pont
Canada Inc,. under the code D1346.
The invention has been described in terms of
specific embodiments set forth in detail herein. It
should be understood, however, that these are by way of
illustration only and that the invention is not
necessarily limited thereto. Modifications and
variations will be apparent from this disclosure and may
be resorted to without departing from the spirit of the
invention, as those skilled in the art will readily
understand. Accordingly, such variations and
modifications are considered to be within the scope of
this invention and the following claims.
