U.S. patent number 3,740,797 [Application Number 05/108,545] was granted by the patent office on 1973-06-26 for method of forming webs and apparatus therefor.
This patent grant is currently assigned to Johnson & Johnson. Invention is credited to Allan P. Farrington.
United States Patent |
3,740,797 |
Farrington |
June 26, 1973 |
METHOD OF FORMING WEBS AND APPARATUS THEREFOR
Abstract
A process and apparatus for forming an air-laid, nonwoven web
from separate supplies of individualized fibers, such as textile
and papermaking fibers. Supplies of fibers are fed to oppositely
rotating lickerins that are rotated at speeds which are optimum for
the fibers being individualized by the lickerins. The
individualized fibers are doffed from the lickerins by centrifugal
force and high velocity air streams directed against the fibers
clinging to the lickerin clothing. The fibers from each supply are
entrained in their respective air streams, which are impelled at
high rates of speed toward each other, and the air streams come
together in a mixing zone. The doffed fibers are given an initial
trajectory as they leave their respective lickerins, and the
inertia of the fibers in the air streams is sufficient to bring the
fibers to the mixing zone and effect blending of at least a portion
of the fibers from each supply in the mixing zone. In communication
with the mixing zone is a suction actuated condensing means where
the fibers are deposited to produce a nonwoven web of fibers, for
example, an isotropic nonwoven web. The process and apparatus can
be varied to form a variety of nonwoven webs, using as the fibers
of these webs two different fibers of the same, or of different
lengths. A variable that can be introduced to vary the web
construction includes a baffle that can be interposed between the
two separate air streams to control the location where the two air
streams are intermixed.
Inventors: |
Farrington; Allan P.
(Englishtown, NJ) |
Assignee: |
Johnson & Johnson (New
Brunswick, NJ)
|
Family
ID: |
26806009 |
Appl.
No.: |
05/108,545 |
Filed: |
January 21, 1971 |
Current U.S.
Class: |
264/518;
19/145.5; 19/302; 19/306; 264/112; 425/81.1; 425/82.1 |
Current CPC
Class: |
D21H
13/28 (20130101); D21H 5/2628 (20130101); D21H
11/00 (20130101) |
Current International
Class: |
D01G
25/00 (20060101); D01G 9/00 (20060101); D01G
23/00 (20060101); D04H 1/48 (20060101); D04H
1/72 (20060101); D04H 1/70 (20060101); D04H
5/00 (20060101); D04H 1/16 (20060101); D04H
5/08 (20060101); D04H 1/00 (20060101); D21F
11/14 (20060101); D21F 11/00 (20060101); D01g
025/00 () |
Field of
Search: |
;19/155,156-156.4,88,89,204,205 ;156/62.2-62.8,369,370-374 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Newton; Dorsey
Claims
I claim:
1. The method of forming a nonwoven web comprising the following
steps:
1. providing at least two separate sources of fibers,
2. feeding each fiber source to the inlet of a confined separate
fiber flow path, said paths converging toward one another and being
in communication with a common fiber mixing zone and each fiber
flow path having a fiber outlet leading to said common fiber mixing
zone,
3. individualizing the fibers received from each separate source
and introducing the individualized fibers from each separate source
into one fiber flow path through the fiber inlet thereof,
4. providing a restricted opening upstream of the fiber outlet of
each fiber flow path for directing a separate gaseous stream
through each of said restricted openings with an impelling force to
(a) entrain the individualized fibers in their respective streams
while the fibers are in their respective flow paths, and (b) convey
the entrained fibers with an impelling force along said converging
flow paths and beyond said outlets and into said mixing zone to
forcibly intermingle at least some of the fibers in one gaseous
stream with at least some of the fibers in another gaseous
stream,
5. applying centrifugal forces to the fibers from each source in
each fiber flow path and in said mixing zone to aid in entraining
the fibers in their respective gaseous stream and to aid in the
intermingling of the fibers in the common mixing zone,
6. applying a driving force to said gaseous streams to (a) cause
said gaseous streams to flow through said restricted openings, (b)
accelerate the movement of the entrained fibers through their
respective flow paths and impel the fibers into said mixing zone
with at least some of the fibers from each flow path having a
component of motion directed toward fibers from another flow path,
and (c) accelerate the fibers through said mixing zone to a
depositing zone, and
7. collecting the fibers in the depositing zone to form a web of
nonwoven fibers.
2. The method of claim 1 wherein the separate gaseous streams are
controlled so that each stream is in a turbulent condition when it
is directed through its respective restricted opening.
3. The method of claim 1 wherein one source of fibers is textile
length fibers, and the other source of fibers is short fibers.
4. The method of claim 1 including the further step of controlling
the location of the fiber outlet of each separate fiber flow path
relative to said depositing zone to control the configuration of
the common fiber mixing zone and the degree of intermingling of
said at least some fibers and to thus determine the type of web to
be formed.
5. The method of forming a nonwoven web comprising the following
steps:
1. providing at least two separate sources of fibers,
2. feeding each fiber source to the inlet of a confined separate
fiber flow path, each path being in communication with a common
fiber mixing zone and each fiber flow path having a fiber outlet
leading to said common fiber mixing zone,
3. individualizing the fibers received from each separate source
and introducing the individualized fibers from each separate source
into a fiber flow path through the fiber inlet thereof,
4. introducing a separate high speed gaseous stream into each fiber
flow path upstream of the fiber outlet thereof to (a) entrain the
individualized fibers in their respective streams while the fibers
are in their respective flow paths, and (b) convey the entrained
fibers with an impelling force beyond said outlets, into said
mixing zone, and to a depositing zone, with at least some of the
fibers in one gaseous stream entering said mixing zone with a
component of motion directed toward at least some of the fibers in
another gaseous stream to forcibly intermingle said at least some
fibers,
5. controlling the location of the fiber outlet of each separate
fiber flow path relative to said depositing zone to control the
configuration of the common fiber mixing zone and the degree of
intermingling of said at least some fibers and to thus determine
the type of web to be formed, and
6. collecting the fibers in the depositing zone to form a web of
nonwoven fibers.
6. The method of claim 5 wherein said controlling step is performed
by at least partially blocking the intermixing of said gaseous
streams.
7. The method of claim 5 wherein the step of introducing said
gaseous streams is performed by independently controlling
individual gaseous streams for each source of fibers.
8. The method of claim 5 in which one fiber source is a source of
textile length fibers and the other fiber source is a source of
short fibers.
9. The method of claim 5 in which the collecting step is performed
by applying a suction to a foraminous fiber receiving member at
said depositing zone, whereby said fibers are retained at a
relatively high velocity prior to depositing on the fiber receiving
member.
10. Web forming apparatus comprising: frame means; means for
feeding a fibrous material to a first fiberizing station at a first
location on said frame means; means for feeding a fibrous material
to a second fiberizing station at a second location on said frame
means; means defining a mixing zone between said fiberizing
stations, said mixing zone having a fiber inlet end and a fiber
outlet end; a first lickerin located adjacent the inlet end of said
mixing zone; a second lickerin located adjacent the inlet end of
said mixing zone; means mounting said lickerins in spaced parallel
relationship on said frame means; means rotating each lickerin at
its respective fiberizing station in fiber-removing relationship
with respect to its respective fibrous material to open said
fibrous materials and produce supplies of individualized fibers
through the inlet end of said mixing zone; means for providing air
streams for doffing the fibers from the lickerins and for initially
directing said supplies of doffed fibers toward one another and to
said mixing zone; a flow controlling member; means mounting said
flow controlling member for movement relative to said mixing zone
to control the extent to which said gaseous streams intermix,
including means for moving said flow controlling member along a
path that bisects the space between said lickerins; and fiber
collecting means adjacent the fiber outlet end of said mixing zone
for accumulating fibers to form a web.
11. Apparatus for forming a non-woven web of non-woven fibers from
at least two sources of fibers: a pair of lickerins; means
rotatably mounting said lickerins in spaced parallel relationship
with one another, so that the adjacent facing surfaces of said
lickerins define boundary walls of a fiber mixing zone; means for
rotating said lickerins in opposite directions; means for feeding
each source of fibers into contact with its respective lickerin
whereby each lickerin individualizes fibers it receives from its
respective source; means, including a portion of the periphery of
each of said lickerins upstream of the facing surfaces of the
lickerins that define the boundary walls of the mixing zone,
defining separate duct means having a fiber inlet adjacent the
position where the fibers are individualized and a fiber outlet
opening into said fiber mixing zone; means providing a restricted
opening adjacent each lickerin, each restricted opening
communicating with one of said separate duct means upstream of the
fiber outlet thereof; means for impelling separate gaseous streams
through each of said restricted openings and for directing said
gaseous streams into its respective duct means and against the
associated lickerin to (a) doff at least some of the fibers from
each lickerin, (b) entrain the doffed fibers within the said duct
means, and (c) convey the entrained fibers beyond the fiber outlet
of each duct means and into said fiber mixing zone to forcibly
intermingle at least some of the fibers from one gaseous stream
with at least some of the fibers in the other gaseous stream; and
collecting means including a movable foraminous member
communicating with said fiber mixing zone to collect said fibers
and form a web of non-woven fibers.
12. Apparatus as set forth in claim 11 including passage means in
communication with each of said restricted openings, and means in
each of said passage means for controlling the flow therethrough to
insure that the required quantity of gas in turbulent condition is
uniformly provided to its respective lickerin.
13. Apparatus as set forth in claim 11 including generally parallel
wall members located adjacent the source of fibers for its
associated lickerin defining passage means in communication with
each of said restricted opening, and flow restricting means in each
of said passage means for controlling the flow of the gaseous
stream to the lickerin to insure that the required quantity of gas
in the prescribed condition is uniformly provided to its respective
lickerin.
14. Apparatus as set forth in claim 13 including means for varying
the position of at least one of said flow restricting means.
15. Apparatus as set forth in claim 11 including means for
providing a flow control member at a preselected position between
said lickerins to control the intermixing of said gaseous streams
and the intermingling of fibers.
16. Apparatus for forming a now-woven web of fibers from at least
two sources of fibers comprising: means rotatably mounting a
lickerin for each source of fibers; means for rotating said
lickerins; means for feeding each source of fibers into contact
with its respective lickerin whereby each lickerin individualizes
fibers from its respective source; means defining a mixing zone
between said lickerins having a fiber inlet end and a fiber outlet
end; fiber collecting means adjacent the fiber outlet end of said
mixing zone; means for causing gas to flow against each lickerin,
through said mixing zone and to said fiber collecting means to (a)
doff the individualized fibers from each lickerin, (b) introduce
the doffed fibers into the mixing zone through the inlet end
thereof, and (c) to forcibly intermingle at least some of the
fibers in the mixing zone prior to deposition on the fiber
collecting means; a flow controlling member; and means mounting
said flow controlling member at least for vertical movement
relative to said mixing zone between said lickerins to control the
degree of intermingling of said fibers.
17. Apparatus as set forth in claim 16 wherein the mounting means
for said lickerins locates the lickerins with the axes thereof in a
common plane, and wherein the flow controlling member is mounted
for movement perpendicularly with respect to said common plane.
Description
This invention relates to an improved apparatus and process for
air-laying fibers to produce nonwoven webs consisting of a more or
less uniform intermixture of randomly oriented fibers. It is
particularly directed to producing a substantially homogeneous
blend of long and short fibers, i.e., textile length and
paper-making fibers.
Fibers are usually classified according to length, with relatively
long or textile length fibers being longer than about one-fourth
inch and generally between 1/2 and 21/2 inches in length. The term
"long fibers," as used herein, refers to textile fibers having a
length greater than one-fourth inch, and the fibers may be of
natural or synthetic origin. The term "short fibers," as used
herein, refers to papermaking fibers, such as wood pulp fibers or
cotton linters having a length less than about one-fourth inch.
While it is recognized that short fibers are usually substantially
less costly than long fibers, it is also recognized that for some
uses it is desirable to strengthen a nonwoven web of short fibers
by including a blend of long fibers therein.
Nonwoven fabrics are structures consisting of a random assemblage
or web of fibers which are bonded together with an adhesive to
provide the desired strength. Nonwoven fabrics have gained
considerable prominence within the last two decades because of
their low cost to manufacture, as compared to the cost of making
more conventional textile fabrics by weaving or knitting. This has
come about since nonwoven fabrics can be made with physical
properties and appearance more or less comparable with the more
expensive woven fabrics. Nonwoven materials have been used for hand
towels, table napkins, curtains, hospital caps, draperies, etc.
They are usually available in a wide range of fabric weights of
from as little as about 100 grains per square yard to as much as
about 4,000 grains, or more, per square yard.
Nonwoven fabrics may be made up of webs in which the fibers are
either more, or less oriented, or randomly disposed. Webs in which
the fibers are oriented generally have the major proportion of
their fibers aligned in one direction, i.e., in the "machine," or
long direction, with the result that these webs are anisotropic.
Such webs are relatively strong in the machine direction. On the
other hand, isotropic webs are made up of randomly disposed fibers
which extend in all directions and thus have substantially uniform
strength in all directions.
There have been many different processes and apparatuses for
producing nonwoven webs. One of the well known ways for producing
nonwoven webs of textile length fibers is by employing a
conventional carding process which results in an anisotropic web,
since the fibers are aligned predominantly in the machine
direction. Another method that could be used is a garnetting
process, in which the fibers have less orientation than carded
webs. These webs are generally of unsatisfactory uniformity and are
also limited to textile length fibers. The ways in which webs can
be produced by either of these techniques is limited, and these
techniques do not lend themselves for use in making very low cost
nonwoven fabrics, especially embodying the use of relatively
inexpensive wood pulp fibers.
Another current way for producing a random web of textile length
fibers is the "Rando-Webber" process, wherein pre-opened textile
length fiber material is delivered as a loose mat to a web-forming
unit. The web is brought into contact with a lickerin that further
opens the fibers and introduces them into a high velocity, low
pressure air stream. The fibers are subsequently deposited in
random fashion on a condensing screen to produce a substantially
isotropic web. While this process is generally satisfactory to
provide a relatively uniform random web of textile length fibers,
it is generally not suitable for use with short fibers, nor with
blends of short and long fibers. Also, this machine has limited
throughput capacity.
As described in Langdon U.S. Pat. No. 3,512,218, granted May 19,
1970, air-laid, isotropic, nonwoven webs may be formed by placing
two lickerin and rotary feed condenser assemblies in parallel. In
the process of this patent, individual fibers deposit as a mat on
the condenser and are then fed to the lickerins, where the fibers
are individualized. These parallel systems use a single air stream
that is split into two parts to doff the fibers from the lickerins
and deposit them as streams of fibers onto a suction box where the
final web is formed. The same fibers are processed in each assembly
and there is no blending of the fibers in advance of the suction
box. While the apparatus of this patent doubles the flow rate that
can be obtained with a similar single system, it has deficiencies
in that it cannot be employed to homogeneously blend two streams of
fibers.
Wood U.S. Pat. No. 3,535,187, granted Oct. 20, 1970, discloses an
apparatus for producing a nonwoven web comprised of two or more
separate layers of different randomly oriented fibers apparently
joined at the interface of adjacent layers by a relatively small
mixture of the fibers. The webs produced by this apparatus are
comprised essentially of textile length fibers, although the patent
contemplates that continuous filaments and wood pulp fibers can
also be included. In the webs produced by the process of this
patent, textile length fibers extending generally perpendicularly
between the opposed faces of the web serve to knit or tie the fiber
layers together.
The apparatus of the Wood patent, as in the apparatus of Langdon
U.S. Pat. No. 3,512,218, includes two lickerin and rotary feed
condenser assemblies. Individualized fibers from each lickerin are
deposited as layers on separate cylindrical condenser screens, each
related to a lickerin. The two condenser screens are positioned
closely adjacent one another and the layers of fibers on the
condensers are compressed between the condensers to form a
composite nonwoven web having some blending of the fibers at the
interface between the layers.
In the process of the Wood patent, the fibers are doffed from their
respective lickerins by high-speed turbulent air streams that move
faster than the peripheral speeds of the lickerins. The fibers are
entrained in the air streams moving past the lickerins. The
velocities of these air streams are controlled so that when they
are in the vicinity of the condensers, the velocities are reduced
to where the entrained fibers will not be forcibly impacted on the
condensers. A balance must be achieved in the air flows in each of
the condensing chambers so that the individual fibers have only
just enough kinetic energy to deposit themselves in isotropic web
formation. Due to the low velocity of the air streams carrying
entrained fibers from the lickerins to the condensers, there is a
minimum of blending of the fibers in their passage in the regions
adjacent the condensers, and hence the resulting composite nonwoven
web has only a minimal region of intermixed fibers.
The method and apparatus of the present invention can be used to
form nonwoven webs that are a blend of randomly oriented long and
short fibers. This is in sharp contrast to the prior art processes
and apparatuses that were capable of forming nonwoven webs made up
of only all short fibers or all long fibers, or a composite web
made up of layers of both long and short fibers.
In general, the desired characteristics of the nonwoven end
product, as well as its utility dictate the type of fibers and the
relative proportions of long and short fibers to be used. Thus, for
example, the product may require one or more characteristics, such
as tear resistance, abrasion resistance, washability, and
stretchability, burst strength, absorption or nonabsorption to
different liquids, heat sealability, ability to resist
delamination, etc., all of which will influence the type of fiber
or mixture of fibers to be used. Thus, by way of specific example,
absorbent products requiring strength characteristics may be a
combination of two or more different fibers, such as wood pulp
fibers and rayon, or similar fibers in varying percentages.
Likewise, again depending on the nature of the fabric desired, the
mixed fibers in the fabric may possess substantially random
characteristics as opposed to oriented fiber characteristics in
order to provide for balanced properties in both the machine and
cross direction of the fabric. For example, in the case of products
intended for surgical, or similar, uses requiring absorbency
characteristics, such as covering layers for sanitary napkins,
absorbent layers for surgical drapes, etc., mixtures of randomly
oriented short and long fibers are required to provide improved
mechanical characteristics; while in the case of nonwoven materials
suitable for use as disposable items in the field of diapers, short
fibers are generally employed.
Typical of the short fibers in the mixtures of fibers obtained by
the process of the present invention are wood pulp fibers from
various types of woods, cotton linters, asbestos fibers, glass
fibers, and the like; with wood pulp fibers being those which find
most frequent use in a large variety of products due to their ready
availability and economical attributes. Wood pulp fibers are
commercially available in the form of pulpboards, which come in
varying thicknesses and lengths.
Typical of the long or staple length fibers are synthetic fibers,
such as cellulose acetate fibers, vinyl chloride-vinyl acetate
fibers, viscose staple rayon, and natural fibers, such as cotton
wood or silk.
In the case of staple or long length fibers, such as rayon, for
example, they are normally commercially available in bale form in
various fiber lengths. In the present invention, the staple fibers
are generally introduced in a pre-opened oriented condition, such
as in the form of a "carded web" or "carded batt," but these fibers
may be presented to the machine by other means, such as a chute. If
desired, in place of using a carded batt of only rayon, a mixture
of rayon and other fiber, or fibers, or for that matter, a mixture
of any two, or more different long fibers can be employed.
Combinations of any of the short and staple or long fibers may be
employed in this invention. The denier of the fibers used may vary
over a wide range and may be from one-half to 100, depending on the
type of fiber employed and the requirements of the nonwoven
material. Commonly, when using staple fibers, such as rayon, the
denier will vary from 0.75 to 5 or 6 denier.
Those skilled in the art have long recognized the need for a
process and apparatus that can economically produce a non-woven web
of a mixture of long and short fibers, especially one wherein the
mixture of long and short fibers is randomly oriented more or less
uniformly throughout the web, so that the web has substantially
uniform strength characteristics lengthwise and crosswise thereof.
Of particular interest has been the desire to obtain an air-laid
nonwoven web of homogeneously blended, randomly oriented short and
long fibers which combines the cheapness of short fibers with the
strength of long fibers together with substantially uniform
strength characteristics throughout the long and short dimensions
of the web. There has also been the need for a single apparatus
that is flexible enough to produce air-laid nonwoven webs of a
mixture of long and short randomly oriented fibers in which the
webs have a variety of fiber distribution patterns, including, (1)
webs that have outer layers made up each of two different fibers
and an intermediate layer that is a homogeneous blend of the two
fibers, (2) webs that have a predominance of one fiber at one face
of the web and a predominance of a second fiber at the other face
of the web and a mixture of the two fibers in a transition zone
between the faces, wherein the fiber which predominates at one face
diminishes progressively from that face towards the other face, and
vice versa, and (3) a web made of two separate layers of different
fibers that are interlaced only at the region of their
interface.
There have been a number of attempts to produce non-woven webs made
of a homogeneous mixture of randomly oriented short and long
fibers, but these webs, while generally satisfactory for some uses,
are not of sufficiently high quality to permit them to be used
without an outer facing layer. The reason for this is that in the
apparatus used, clumps or hardened particles of broken or compacted
fibers commonly referred to as "salt," were formed and remained
distributed throughout the web. With these clumps and "salt," the
webs were not suitable for making products, such as surgical
towels, dressings, disposable diapers, sanitary napkins, cloths,
cosmetic pads, and the like, although in some instances they could
be used in conjunction with a high quality facing layer.
One apparatus used to make a nonwoven web of a homogeneous mixture
of randomly oriented long and short fibers includes the use of a
milling device, such as a hammer mill, to individualize the short
fibers and a lickerin to individualize the long fibers. The
individualized short fibers are entrained in an air stream leading
to a mixing zone into which the long fibers are introduced, where
the fibers are intermixed. The mixture of fibers is deposited on a
condenser to form a web of a random mixture of long and short
fibers. In these webs, the intermixed fibers are not homogeneously
blended; in fact, in such webs, there is more or less of a
stratification of the fibers in layers, with the long fibers
predominating on one side of the web and the short fibers
predominating on the other side. A particular disadvantage of this
apparatus was that the hammer mill did not completely individualize
the wood pulp fibers and, in consequence, clumps of fibers and/or
"salt" resulted.
Another method used to blend a mixture of long and short fibers
into a nonwoven web of randomly oriented fibers involves the step
of introducing a mixture of preopened long and short fibers to a
single lickerin where the mixture of long and short fibers is
individualized. The individual fibers, but still in admixture, are
introduced into an air stream and conveyed to a condenser where
they were formed into a web. This method has a significant
disadvantage in that in order to prevent degradation of the long
fibers, it is necessary to operate the lickerin at the optimum
speed for the long fibers, which is much below that which is
optimum for short fibers. This necessary compromise seriously
limited the rate at which the fibers could be processed through
this system and this economic disadvantage militates against its
use.
A recent development in this field of air-laying webs has overcome
a number of the aforementioned problems in the apparatus previously
used and makes possible production of a non-woven web of a
homogeneous mixture of long and short fibers, free from
consequential amounts of clumps and "salt." The apparatus and
method of this development are described and claimed in a commonly
owned application Ser. No. 108,547 filed in the name of Ernest
Lovgren on even date herewith.
In the Lovgren apparatus and process, long and short fibers to be
blended are individualized separately and simultaneously by
separate high speed lickerins, one for each type of fiber, that are
operated at speeds optimum for the specific fibers acted upon. For
example, in the case of pulpboard, the lickerin is operated in the
order of 6,000 rpm. to individualize the wood pulp fibers, and the
long fibers, the staple length fibers, for example, rayon, are
individualized by the lickerin acting on these fibers, operated at
a speed in the order of 2,400 rpm. At a speed of 6,000 rpm., rayon
fibers are damaged.
In the Lovgren apparatus, individualized fibers are doffed from
their respective lickerins by separate air streams. The fibers are
entrained in the separate air streams and the air streams are
subsequently intermixed in a mixing zone to homogeneously blend the
fibers entrained therein. The homogeneous blend of fibers is then
deposited in random fashion on a condenser disposed in proximity to
the mixing zone. The air streams generated by the high speed
operation of the lickerins and by a suction fan located in the
condenser, which acts to draw air past the lickerins, convey the
fibers to the condenser.
While the Lovgren apparatus represents a substantial advance in the
art, the apparatus has limitations in that it does not lend itself
for use in making a wide variety of webs.
In accordance with the present invention, there is provided a novel
method and apparatus that can be practiced to produce a wide
variety of nonwoven, air-laid isotropic webs made up of a
substantially uniform mixture of long and short fibers, or of two
different kinds of long or short fibers. Included in these webs are
webs which cannot be made in the Lovgren apparatus, such as, for
example, (1) webs that have outer layers made up of each of two
different fibers and an intermediate layer that is a homogeneous
blend of the two fibers, (2) webs that have a predominance of one
fiber at one face of the web and a predominance of a second fiber
at the other face of the web and a mixture of the two fibers in a
transition zone between the faces, wherein the fiber which
predominates at one face diminishes progressively from that face
towards the other face, and vice versa, and (3) a web made of two
separate layers of different fibers that are interlaced only at the
region of their interface.
An embodiment of the present invention illustrates an apparatus in
which two sources of fibers, such as pulp and rayon, are
individualized by separate lickerins and formed into a web. Each of
the sources of fibers is guided by a nose bar into engagement with
its respective lickerin, each being rotated at a high speed
suitable for the fibers it is to act on, to individualize the
fibers directed thereto. The lickerins are disposed parallel to
each other and are rotated in opposite directions, i.e., toward
each other. When the web is to be made up of long and short fibers,
the lickerin for the short fibers is rotated at the maximum speed
it can be operated without damaging the short fibers. The lickerin
used for individualizing the long fibers is, of necessity, operated
at a much slower speed to prevent degradation of the fibers. The
nose bar and lickerins are set to obtain the optimum opening
relationship for the fibers being processed, by known
techniques.
The fibers that are individualized by the lickerins are acted on by
separate high-velocity, turbulent air streams that are directed
against the lickerin clothing at a junction adjacent its respective
nose bar. The flow of air to each lickerin is regulated to control
the quantity and uniformity thereof. The high velocity air streams
are directed past the lickerins at a faster speed than the
peripheral speed of the lickerins to assist the centrifugal forces
imposed on the fibers by the lickerins in the doffing of the fibers
from the lickerins, and entrain and convey the individualized
fibers. The separate air streams are impelled toward one another
and are subsequently brought together into a common high-speed air
stream in a centrally disposed mixing zone defined by and between
the spaced lickerins. In the mixing zone, the entrained fibers,
still under the inertia set up by the high-velocity air streams and
the centrifugal forces imposed on the fibers due to the high speed
operation of the lickerin, are intermixed uniformly, so that they
can later be air-laid into a nonwoven web of intermixed, randomly
oriented, long and short fibers.
In the process of the present invention, the fibers entrained in
the separate gaseous streams have a trajectory including a
component impelling them toward one another, as well as a component
directing them toward the mixing zone. Although the fibers are
transported by the separate gaseous streams to the mixing zone, the
fibers have sufficient kinetic energy by virtue of their mass and
velocity, so that the fibers continue to travel at least in part in
the direction of the initial trajectory because of their inertia.
In consequence of this, the component of motion of the fibers
toward one another causes them to combine in an intimate mixture of
fibers when the air streams collide and intermix in turbulence into
a common stream.
The common air stream is produced by the cooperative action of the
fast moving air streams drawn through the system by a large suction
generated within a fiber condensing means located at the terminal
end of the mixing zone plus the air generated by the rotary action
of the oppositely rotating high-speed lickerins. The combined
stream in a state of turbulence transports the mixed fibers through
the mixing zone to a condensing means where the fibers are
deposited to build up a web of the desired thickness.
Different types of webs can be obtained with the apparatus of the
present invention by introducing a baffle into the flow paths of
the separate air streams in advance of the intermingling thereof.
The baffle may be positioned to partially block the intermixing of
the air stream and thus affect the blending of the entrained fibers
in the mixing zone.
In one embodiment of the instant invention where the apparatus is
fed wood pulp and rayon fibers and the air volume to fiber volume
ratio in the common air stream is in the order of 5,000 to 1, and
the baffle does not block the separate air streams, a nonwoven web
of randomly oriented pulp and rayon fibers, in substantially
homogeneous intermixture is formed. With the same operating
parameters, except with the baffle partially blocking the
intermixing of the separate air streams, a web is formed having a
layer of randomly oriented wood pulp fibers on one side, a layer of
randomly oriented rayon fibers on the other, and an intermediate
layer that is a homogeneous blend of randomly oriented wood pulp
and rayon fibers.
The position of the baffle in the fiber mixing region determines
the thickness of each of the aforementioned layers. It is possible
to operate the apparatus of the present invention with the baffle
fully extended, i.e., into a position immediately adjacent the
condenser. With this arrangement, there will be no intermediate
layer of homogeneously blended fibers and a web made up of two
separate layers of different fibers that are interlaced only at the
region of their interface will be formed.
The apparatus of the present invention can also be used to form
still different types of webs, depending on the ratio of the volume
of air to the volume of fiber in the duct carrying the common air
stream through the system and the position of the baffle. It has
been found that with the apparatus of this invention used with the
baffle retracted, i.e., so that it does not block the mixing of the
fibers, and a volume of air to volume of fiber ratio in the order
of 12,000 to 1, or greater, a web is formed that has a predominance
of one fiber at one face and a predominance of a second fiber at
the other face of the web and a transition zone between the faces,
wherein the fiber, which predominates at one face diminishes
progressively from that face towards the other face, and vice
versa. When the baffle is introduced into the system and the volume
of air to volume of fiber ratio is in the order of 12,000 to 1, or
more, homogeneously blended, and other types of nonwoven webs can
be formed. The process utilizing such high volume of air to volume
of fiber ratios, i.e., 12,000 to 1, or more, and the novel products
formed thereby are disclosed and claimed in an application entitled
"Web Forming Process and Product Produced Thereby," filed Jan. 21,
1972, in the names of Messrs. Ruffo and Goyal, Ser. No. 108,546,
which application is assigned to the assignee of the present
invention.
It is thus seen that by the practice of the instant invention, one
is able to produce a wide variety of nonwoven webs of randomly
oriented fibers, including one that is a homogeneous mixture of
long or short fibers, or one which has opposed faces having
selective properties, such as cohesiveness, cohesive strength,
abrasion resistance, absorption characteristics, nonabsorbent
characteristics, and so forth. The thickness and weight of the
nonwoven products being produced by the novel apparatus and method
disclosed herein can vary depending on conventionally commercial
requirements, but typically they will in the order of 700 grains to
several thousand grains per square yard and with a thickness of
from about one thirty-second to about 1 inch, or more, prior to any
post-treating operation. The web thickness will vary depending on
the feeding rate of the fibers and the speed at which the web is
removed from the condensing zone.
The foregoing advantages and numerous other features and advantages
of the invention will be more readily understood and appreciated in
light of the following specification, taken in conjunction with the
accompanying drawings, in which:
FIG. 1 is a cross-sectional view showing the main components of the
apparatus forming part of the instant invention as taken along line
1--1 of FIG. 2;
FIG. 2 is an end elevational view of the apparatus illustrated in
FIG. 1;
FIG. 3 is a fragmentary perspective view, partially in section,
showing a portion of the condenser;
FIG. 4 is an enlarged sectional view taken along line 4--4 of FIG.
3;
FIG. 5 is a schematic view of the apparatus showing the baffle
partially extended;
FIG. 6 is a view showing the baffle in a more fully extended
position;
FIG. 7 is a view showing the baffle in the fully extended position
wherein it is located immediately adjacent a condenser;
FIG. 8 illustrates a randomly oriented, fully homogeneous web;
FIG. 9 shows a web having outer layers made of separate fibers and
an intermediate homogeneous mixture of the two fibers;
FIG. 10 is a view showing a two-layered web; and
FIG. 11 is a web having a preponderance of a different type of
fiber on each of the faces and a transition zone, such that the
fiber type which predominates at one face diminishes in
predominance from the face at which it predominates to the face at
which the other fiber type predominates.
DETAILED DESCRIPTION OF THE INVENTION
While this invention is susceptible of embodiment in many different
forms, there are shown in the drawings and will herein be described
in detail only preferred embodiments of the invention and
modifications thereof, with the understanding that the present
invention is to be considered as an exemplification of the
principles of the invention and is not intended to limit the
invention to the embodiments illustrated. The scope of the
invention will be pointed out in the appended claims.
Referring first to FIG. 1, there is illustrated a cross-sectional
view of the web forming apparatus with parts broken away to show
the relationship between the various components thereof. The
apparatus will be illustrated and described as being used for
blending wood pulp fibers and rayon, but it could obviously be used
to blend two different fibers, or identical fibers.
In the drawings, the apparatus includes a main frame and subframe
components, which, for the sake of simplicity and brevity, will be
identified by reference letter F.
Reference will first be made to the left-hand, or wood pulp side of
the system.
Wood pulp is introduced into the system in the form of a pulpboard
310, which is directed between a plate 311 and a wire wound feed
roll 312. Connected to the lower part of the plate 311 is a nose
bar 313 for providing an anvil against which the pulpboard is
directed during the individualizing step. The nose bar 313 has a
sidewall 314 that can be made relatively flat, since, due to the
integrity of the pulpboard, it is unnecessary that the nose bar 313
be designed to more precisely direct the pulpboard to the lickerin
317 that is used to individualize the pulpboard into short fibers.
The bottom wall 315 of the nose bar 313 is angularly disposed
relative to the sidewall 314 and is spaced a short distance from
the teeth 316 of the lickerin 317 to define a passage 318 through
which the pulpboard is moved during the individualizing operation.
The pulpboard is individualized into short wood fibers by the teeth
316 of the lickerin 317 acting on the pulpboard directed into
position to be contacted by the teeth by the nose bar 313.
The feed roll 312 is journalled in a bracket 319 that is
eccentrically mounted at 320 to permit adjustment of the feed roll
relative to the pulp lickerin 317 and nose bar 313. The bracket 319
and feed roll 312 are resiliently biased to direct the pulpboard
toward the nose bar 313 by a spring 322 that is located between
bracket 319 and head 324a of bolt 324 that extends through a hole
in the bracket 319, and is secured in place in plate 311. The
pivotal movement of the bracket 319 is limited by a set screw 328
that is threaded into and through bracket 319 and engages plate
311. The spring 322 biases feed roll 312 into contact with
pulpboard 310 to insure that the pulpboard is fed into position to
be engaged by lickerin teeth 316. This design accommodates varying
thicknesses of material that can be used in this system.
The feed roll 312 is secured to a shaft 330 that is suitably
supported for rotation by a variable drive means, a portion of
which is shown schematically in FIG. 2. The details of the drive
means are not important to the present invention. The speed at
which the feed roll is operated is determined by the rate at which
pulp is to be fed into the system. A number of the mechanisms
employed for supporting the rolls, lickerins, and so forth, are
shown generally in FIG. 2 and they will be referred to when they
will aid in understanding the present invention.
During the operation of the novel apparatus, the pulpboard 310 is
fed into position to be engaged by the lickerin teeth 316 adjacent
the nose bar 313. The lickerin 317 is mounted on shaft 331, which
is driven at a very high speed by suitable drive means to
individualize the pulpboard into short fibers. The drive means,
together with shaft 331, comprises means for rotating lickerin 317.
In an exemplary embodiment, the lickerin 317 is driven at a speed
of 6,000 rpm. and produces a large throughput of pulp fibers
without adversely affecting the fibers.
The lickerin teeth 316 fray the pulpboard until the fibers are
loosened therefrom, after which the teeth comb the short fibers out
of the board. The clothing on the lickerin is designed to act on
the particular fiber and has the optimum tooth profile for the
specific material it is processing. Each successive tooth has more
opening action than the one before, which facilitates
individualizing and when operated at an optimum speed greatly
minimizes, if not totally prevents, clumps and salt from being
extracted from the board.
The pitch and height of the teeth used on the lickerin for the
pulpboard may vary, good results being obtained with a tooth pitch
of about three thirty-seconds inch to about one-half inch and a
tooth height of about three thirty-seconds inch to about one-half
inch. The angle of the teeth of the lickerin for the pulpboard may
also vary, generally within the limits of about -10.degree. to
about +10.degree.. A positive angle for the teeth of the pulpboard
lickerin which is standard in the industry, viz., +10.degree., may
be used in accordance with the invention, but this is not
preferred. In general, it is preferred that the angle of the teeth
be positive and be below +10.degree..
After the wood fibers are individualized by the lickerin 317, they
are entrained in a turbulent air stream and directed through a duct
332 formed between the lickerin teeth 316 and a sidewall 333, which
duct 332 leads into a mixing zone 334.
Referring now to the rayon fiberizing system which is illustrated
on the right side of FIG. 1, there are shown mechanisms that
control the feeding of the rayon to the system. A number of the
mechanisms used in processing the rayon are similar to those used
on the pulp side of the system and where they are identical they
are given the same numbers.
The rayon, which usually comes in the form of a carded batt 335,
has no integrity and must be positively directed to the clothing of
the rayon lickerin 338 to insure that the rayon lickerin teeth 339
will pick the rayon up from a rayon source 335. To this end, the
nose bar 336 used with the rayon wire wound feed roll 337 differs
from the pulp nose bar 313. The nose bar 336 is curved at 336a to
essentially conform to the adjacent circumference of the rayon feed
roll 337. The rayon fibers picked up from the rayon source are
positively maintained in position relative to the feed roll 337
until the fibers are disposed immediately adjacent the teeth 339 of
the rayon lickerin 338, which teeth will then serve to comb the
fibers from the rayon source. The rayon lickerin is mounted on
shaft 341, which is driven at a high speed by suitable drive means
(not shown). The drive means, together with shaft 341, comprises
means for rotating lickerin 338. A speed which can generally be
used without seriously adversely affecting the fibers is 3,000
rpm.
The teeth of the rayon lickerin usually have a lower tooth height
and pitch than the pulp lickerin. The pitch and height of the teeth
used on the lickerin for the rayon may vary, good results being
obtained with a tooth pitch of about one-eighth inch to about
one-fourth inch and a tooth height of about one-eighth inch to
about one-fourth inch. The angle of the teeth of the lickerin for
the rayon may also vary, generally within the limits of about
-10.degree. to about +20.degree.. The individualized rayon fibers
are then air-conveyed into duct 340 located between sidewall 342
and lickerin 338, which duct 340 leads into mixing zone 334. The
randomly oriented wood pulp and rayon fibers in the mixing zone 334
are then directed through duct 352 onto a condenser 350 where they
form a web.
The movement of the air streams flowing through the system and its
action on the fiber particles to effect the doffing, blending and
condensing that takes place subsequent to the individualizing will
be covered in detail hereinafter.
In the process of the present invention, the length of the fibers
in the condensed nonwoven web may be varied as desired by varying
one or more conditions in the process. These conditions include,
(a) the method used to open the fibers, as by adjusting the height
and angle of the teeth, (b) the rate at which the fibers are opened
and entrained, and (c) the method and rate of feeding the fiber
source to the fiber opening and entraining step.
While the lickerins, nose bars, and fiber receiving means have been
shown in a fixed position, These mechanisms may also be made
adjustable relative to the frame F if this is desired.
The doffing of the fibers from the lickerins 317, 338, the air
entrainment of the previously individualized fibers, the conveying
of the fibers through the ducts 332, 340 into the mixing zone 334,
and the conveying of the intermixed fibers through duct 352 to
condenser 350 are accomplished by high velocity, turbulent air that
is introduced into the system by being pulled in through parallel
passages 344, 346 by a suction fan (not shown).
The parallel flow paths 344, 346 lead to lickerins 317, 338,
respectively, to direct high velocity turbulent air in a uniform
flow pattern against the lickerin teeth 316, 339, respectively, to
doff the fibers clinging thereto. The air with entrained particles
therein then flows through ducts 332, 340, respectively, into
mixing zone 334 from where it flows through duct 352 and condenser
350. The blended randomly oriented fiber particles entrained in the
air stream are deposited on the condenser in the form of a web.
The condenser 350 on which the fibers are formed into a web
consists of an endless movable mesh screen conveyor 381 that is
directed over four pulleys 382, 384, 386, and 388. The position of
pulley 388 can be adjusted to provide suitable tension on the
screen. The conveyor is driven by suitable drive means (not shown).
The conveyor 381 slides over the housing 348, which contains an
aperture 349, through which the air is sucked into the housing and
through conduit 389 that leads to the suction fan. The speed at
which the condenser is moved will determine the thickness of the
web being formed. For example, the thickness of the web will be
increased by decreasing the web take-away speed, and vice
versa.
The screen conveyor 381 leads to another conveyor belt 390 on which
the web is carried to Another station for further processing. For
example, the nonwoven webs obtained by the process of the present
invention may be post-treated by any suitable conventional bonding
technique, e.g., mechanical, or chemical, to bond the web and
provide the required strength and coherency characteristics for a
given product. The particular type of bonding technique chosen will
depend on various factors well-known to those skilled in the art,
e.g., the type of fibers, the particular use of the products, etc.
To this end, typical of the conventional techniques are web
saturation bonding, suction bonding, foam bonding, print bonding,
fiber bonding, fiber interlocking, spray bonding, solvent bonding,
scrim bonding, viscose bonding, mercerization, etc.
For further details of the various bonding techniques, including
the binders that can be employed, reference may be made to the
aforementioned Lovgren application.
In order to help seal off duct 352 and maximize the efficiency of
the suction fan being used, a pair of vertically extending plate
members 366, 368 are employed to define two outer wall portions of
the duct 352 between the lickerins and the condenser. The lower
portion of the duct 352 between the plates 366, 368 and the
condenser 350 are essentially sealed off by rollers 369 that are
rotatably mounted on pivotally mounted arms 370, 372 that are
connected at their upper arms to a shaft 374. The weight of the
rollers and arms tends to maintain the rollers in a sealing
condition to minimize the introduction of air between the rollers
369 and the plates 366, 368, and condenser 350.
Referring now to FIG. 4, there is illustrated a sealing mechanism
that acts to seal the flow duct 352 along the edges of the web
being formed. On each side, there is provided a floating seal 376
that is biased into contact with the web by a spring 378. The seal
376 is reciprocately mounted in a recess 379 defined in a side
plate 380. This mechanism is duplicated on the opposite side to
prevent introduction of air into the suction fan other than down
through the flow ducts 352.
The condition and direction of the air flowing through the system
has a very significant effect on the particular webs being formed.
The air must have a uniform flow pattern through the system to aid
in the formation of a uniform web. Also, the air should be in a
turbulent condition and have a velocity greater than the peripheral
speed of the lickerin which aids in doffing the fibers from the
lickerin and prevents fiber clumping.
The ratio between the volume of air and volume of fibers passed
through the system also has a significant bearing on the type of
web that will be formed by the system. The air flow plays the
important role that it does since it is in effect a pneumatic
conveyor that deposits the fibers onto a condenser where they are
formed into a web. The quantities of fibers to be conveyed
determine the amounts of air to be directed against the particular
lickerin used for fiberizing a given material. Thus, for example,
when forming a web of 90 percent (by weight) of wood pulp fibers
and 10 percent (by weight) of rayon, a substantially higher
quantity of air is needed to convey the wood pulp fibers than is
needed to convey the rayon fibers.
In order to control the relative quantities of air directed to the
pulp and rayon lickerins while insuring that the air so introduced
aids in doffing the fibers from the lickerins, the air passages
344, 346 are appropriately designed and located.
Air passage 344 is vertically disposed and the lower end is located
immediately adjacent the teeth 316 of the pulp lickerin 317. The
webs being formed by this system have substantial width and thus it
is important that the air flow across the axial length of the
lickerin be uniform, so that the thickness of the web will be
constant. Also, the air acts to more effectively doff the fibers
from the lickerin if it is in a generally turbulent condition. To
provide for turbulence while insuring that the air is uniformly
distributed across the lickerin a wedge-shaped restrictor 354,
secured to plate 356 that forms a sidewall of passage 344, is
provided at the lower end of passage 344. The restrictor 354
defines a throat 358 through which the air pulled through the
passage 344 must pass. This throat portion 358 brings about a low
pressure drop and raises the velocity of the air before it contacts
the pulp lickerin teeth 316. The high velocity turbulent air
directed into duct 332 from passage 344 in conjunction with the
centrifugal forces imposed on the fibers due to the high speed of
rotation of the lickerin 317 doffs wood pulp fibers from the
lickerin teeth. The air in duct 332 entrains the fibers therein and
conveys them to a mixing chamber 334. The duct 332 is directed
downwardly at an approximately 45.degree. angle and the high
velocity air flowing therethrough will be directed into collision
with the high velocity air flowing past the rayon lickerin, the
path of which will be described below.
In a system where there is substantially less air needed to process
the rayon fibers than to process the wood pulp fibers, it will be
necessary to provide a substantial obstacle to the flow of air
through the passage 346 to provide for the desired unbalanced air
flow through the system.
In the passage 346, there is a restrictor provided in the form of
an adjustable block 360, which has a substantial length and fills
up a major part of passage 346. Between the plate 311 and block 360
there is defined a narrow passage 362. The block 360 results in
setting up a turbulent condition for the air flowing into duct 340
and severely limits the quantity of air flowing thereto, as
compared to the air flowing through the passage 344 and into duct
332. The position of block 360 can be adjusted by mechanism 364.
The width of the passageways 344, 346 can also be adjusted by the
insertion of blocks by varying widths therein.
The high velocity turbulent air in duct 340 is moving faster than
the peripheral speed of lickerin 338 and acts to doff the fibers
from the rayon lickerin teeth 339 and entrain the fibers therein.
Duct 340 is directed downwardly at a 45.degree. angle with the
result that the high velocity turbulent air flowing therethrough
comes into impelling relationship with the entrained wood pulp
fibers in the air stream moving downward through duct 332 into the
mixing chamber 334. These air streams are moving at a very high
rate of speed and the air is in a turbulent condition, with the
result that when these two streams intermix, the fibers entrained
therein will form a homogeneous blend of randomly oriented fibers.
As the fibers are accelerated and entrained in the air streams
flowing through ducts 332, 340, they possess substantial kinetic
energy because of their mass and velocity, and the inertia of the
fiber tends to keep them moving along a path generally in the
direction of their initial trajectory. The blended fibers then move
down through the duct 352 onto the condenser 350, where a job made
up of a mixture of wood pulp and rayon fibers is randomly oriented
more or less uniformly throughout the web, so that the web has
substantially uniform strength characteristics lengthwise and
crosswise thereof.
In practicing the present invention with the illustrated apparatus,
a nonwoven web of homogeneously blended, randomly oriented fiber
has been formed with a volume of air to volume of fiber ratio in
the system being in the order of 5,000 to 1. Other types of webs
can be formed with the illustrated apparatus by introducing a flow
controlling member such as a baffle into the mixing zone, or by
changing the volume of air to volume of fiber ratio.
The baffle 400, when introduced into the mixing zone 334, acts to
at least partially block the intermixing of the separate air
streams flowing through the ducts 332, 340. With the baffle
extended into the mixing zone, the entrained fibers in ducts 332,
340 are prevented from intermixing until they pass below the bottom
of the baffle. This controls the mixing of the high velocity air
streams being impelled towards each other down ducts 332, 340. The
webs that are formed with the baffle extending into the mixing zone
will vary depending on the depth of penetration of the baffle into
the mixing zone.
The baffle 400 is in the form of a plate that extends the full
width of the machine and, as shown, intersects the space between
the lickerins. The baffle 400 is positioned through the action of a
pair of gears 402 that mesh with racks 406 secured to the baffle
400 (FIG. 2). Leakage of air into the system past the baffle is
prevented by sealing and guide members 408, 410. The particular
location of the baffle will determine how much blending will take
place between the streams of fibers in ducts 332 and 340. With the
baffle located at an intermediate position in the mixing chamber
and the volume of air to volume of fiber ratio in the order of
5,000 to 1, an isotropic web will be formed in which the bottom
layer consists of substantially all wood pulp fibers, the upper
layers consists of substantially all rayon fibers, and the
intermediate layer is a homogeneous blend of the two fibers. As the
baffle is moved further and further down toward the condenser, the
intermediate layer of homogeneously blended fibers will become
thinner and thinner and the outer sections of the web
proportionately thicker. With the baffle all the way down, as shown
in FIG. 7, a two-layered web of short and long fibers will be
formed with the separate layers of different fibers interlaced only
at the region of their interface.
The apparatus of the present invention can also be used to form
still different types of webs, depending on the ratio of the volume
of air to the volume of fiber in the duct carrying the common air
through the system and the position of the baffle. It has been
found that the apparatus of this invention used with the baffle
retracted out of blocking relationship with the ducts 332, 340 and
the volume of air to volume of fiber ratio in the order of 12,000
to 1, or greater, the fibers cross each other in the mixing zone
and a web is formed having a preponderance of one fiber on one face
of the web and a preponderance of a second fiber on the other face,
and a mixture of fibers in a transition zone between the faces
wherein the fiber which predominates at one face diminishes
progressively from that face toward the other face, and vice versa.
When the baffle is introduced into the system in which the volume
of air to volume of fiber ratio is in the order of 12,000 to 1, or
greater, other types of nonwoven webs can be formed. For example,
in the position shown in FIG. 5, where the baffle is in line with a
plane drawn through the axis of the lickerins, a homogeneous,
randomly oriented web is formed. The process of utilizing such high
volume of air to volume of fiber ratios and the novel products
formed thereby are disclosed and claimed in the aforementioned
commonly owned Ruffo and Goyal application.
FIGS. 8-10 schematically illustrate some of the various types of
webs that can be formed with the illustrated apparatus. FIG. 8 is
intended to be a graphic illustration of a fully homogeneous web W.
FIG. 9 illustrates a cross section of a non-woven web 412 that is
made up of three layers that are interlaced at their interface to
form a web. The web 412 includes a layer 414 that contains
essentially all staple fibers, a layer 416 of pulp fibers and a
layer 418 which is a homogeneous blend of staple and pulp fibers.
FIG. 10 illustrates a cross section of a web 434 made up of
separate layers of staple fibers 436, and pulp fibers 438 which are
interlaced at their interfaces. FIG. 11 illustrates a cross section
of a web 440 in which the upper layer 442 has a predominance of
pulp fibers and the bottom layer 444 has a predominance of staple
fibers, and a transition zone therebetween in which the
predominance of staple fibers decreases as it approaches the
predominantly pulp layer 442 and the predominance of pulp fibers
decreases as it approaches the predominantly rayon layer 444.
The following examples apply to the illustrated apparatus.
Example 1. A nonwoven web of a homogeneous blend of randomly
oriented short pulp fibers and staple rayon fibers was formed in
which, by weight, 90 percent of the fibers were pulp and 10 percent
of the fibers were rayon.
The short fibers were extracted from pulpboard and the rayon fibers
came from a rayon picker lap in which the average fiber length was
1-9/16 inches, with a denier of 1.5.
Lickerins 317 and 338 were approximately 91/2 inches in diameter
and were rotated at about 6,000 and 3,000 rpm., respectively, and
the lickerins were spaced from one another by about 11/2 inches.
Lickerins 317 and 338 were spaced from duct walls 333 and 342,
respectively, by about three-fourths inch. Lickerins 317 and 338
were about 18 inches long and a total of 700 pounds per hour of
fibers were fed to the lickerins. Deflector plates 366 and 368 were
spaced from one another by about 41/2 inches. The average volume
ratio of air to fiber was approximately 5,000 to 1 in the common
air stream.
With the web take-away mechanism operated at a speed of 125 feet
per minute, and with baffle 400 in the withdrawn position, a
homogeneous web of randomly oriented fibers was produced having a
weight of approximately 4,000 grains per square yard.
Example 2. The basic machine parameters of Example 1 were repeated,
with the exception that the fiber feed was controlled to provide a
feed rate of 180 pounds of fibers per hour 50:50 (by weight)
mixture of wood pulp and rayon fibers, and the process employed a
70,000:1 volume ratio of total gas to total fiber in the combined
stream as disclosed in the above mentioned Ruffo et al.
application. Also, lickerin 317 was rotated at about 5,000 rpm. The
resulting web weighed approximately 550 grains per square yard, and
was removed from the condensation zone at approximately 150 feet
per minute.
With the above volume of air to volume of fiber ratio, and the
divider plate 400 withdrawn, the resulting web was found to consist
of a predominance of rayon fibers at one face of the web and a
predominance of wood pulp fibers at the opposing face of the web,
with a decreasing amount of wood pulp and rayon fibers from the
faces at which they predominate, respectively, to the opposed
faces. This "transition" feature was found to be substantially
uniform from face to face.
Example 3. The machine parameters of Example 3 were essentially the
same as those in Example 2, except that an 80:20 (by weight)
mixture of short wood pulp fibers and staple rayon fibers were fed
to the respective lickerins. The wood pulp feed rate was
approximately 1,000 pounds per hour and the rayon feed rate was
approximately 150 pounds per hour. Also, the baffle 400, having a
thickness of about one-fourth inch, was positioned with the lower
end thereof essentially located at the level of the plane defined
by the axes of the lickerins. The combined air stream had a total
air to total fiber volume ratio of approximately 30,000 to 1, as
disclosed in the above mentioned Ruffo et al. application. The
take-away mechanism was adjusted to provide a take-away speed of
approximately 550 feet per minute, and the resulting web had a
weight of approximately 1,400 grains per square yard.
The resulting web was found to be a homogeneously blended nonwoven
web of randomly oriented fibers. The cross-over product, such as
that obtained in Example 2, was prevented because of the degree of
interference of the baffle 400 with the separate gas streams.
* * * * *