U.S. patent number 3,862,867 [Application Number 05/374,003] was granted by the patent office on 1975-01-28 for process for producing reinforced nonwoven fabrics.
This patent grant is currently assigned to The Kendall Company. Invention is credited to Preston F. Marshall.
United States Patent |
3,862,867 |
Marshall |
January 28, 1975 |
PROCESS FOR PRODUCING REINFORCED NONWOVEN FABRICS
Abstract
Textile-length fibers are subjected to a centrifugal force which
orients them in a lateral direction, in which orientation they are
deposited upon and mechanically engaged with a set of spaced-apart
warp strands to form novel nonwoven fabrics.
Inventors: |
Marshall; Preston F. (Walpole,
MA) |
Assignee: |
The Kendall Company (Walpole,
MA)
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Family
ID: |
26945545 |
Appl.
No.: |
05/374,003 |
Filed: |
June 27, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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256711 |
May 25, 1972 |
3816231 |
|
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Current U.S.
Class: |
156/62.2; 19/299;
156/74; 264/121; 19/304; 156/181 |
Current CPC
Class: |
D04H
5/08 (20130101) |
Current International
Class: |
D04H
5/00 (20060101); D04H 5/08 (20060101); D01g
025/00 () |
Field of
Search: |
;156/62.2,62.4,62.6,74,62.8 ;264/121 ;425/80,81,82,83
;19/145,155,156-156.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Fritsch; Daniel J.
Parent Case Text
This application is a division of Ser. No. 256,711, filed May 25,
1972, now U.S. Pat. No. 3816231.
Claims
Having thus described my invention, I claim:
1. The process of making a nonwoven fabric which comprises passing
a fluid-borne stream of textile-length fibers through a passageway
having a transversely-extended smoothly curved surface curved in
the direction of said stream,
thereby changing the direction of said fluid-borne stream along
said surface and causing centrifugal force on said fibers to align
said fibers in a transverse direction along said surface and
concentrating said fibers thereat in a narrow,
transversely-extended band,
collecting said fibers of said band on a set of parallel,
spaced-apart warp strands,
said warp strands extending continuously in the longitudinal
direction of said fabric,
and causing a portion of said fibers to entangle with said warp
strands in mechanical engagement by passing over certain of said
warp strands and under other of said warp strands,
and causing an additional portion of said fibers to entangle with
said warp strands by having a portion of their length wrapped
around at least a portion of the perimeters of certain of said
strands.
2. The process according to claim 1 wherein a thermoplastic binder
material is diffused into said fluid-borne stream of fibers.
3. The process according to claim 2 wherein the thermoplastic
binder material is a powder.
4. The process according to claim 2 wherein the thermoplastic
binder material is thermoplastic fibers.
Description
This invention relates to novel nonwoven fabrics, and to a process
therefor. More particularly it relates to nonwoven fabrics
comprising a spaced-apart set of warp strands running along the
length of the fabric, with a web of textile-length fibers disposed
substantially normal to said warp strands, a substantial number of
said textile-length fibers being interlaced or otherwise
mechanically engaged with said warp strands.
DISCUSSION OF PRIOR ART
In the preparation of nonwoven fabrics wherein a substantial degree
of tensile strength, toughness, and opacity are desired, as for use
in disposable garments, hospital drapes, and the like, it is common
practice to laminate together nonwoven fabrics composed of
textile-length fibers with other sheet material such as cellulose
tissue, plastic films, paper, or other continuous sheet material.
Such laminates, however, are usually deficient in tensile strength
unless semi-rigid binder materials are employed in the lamination,
in which case the laminate is liable to be unpleasantly stiff and
papery, lacking in drape and esthetic appeal. In such cases, in
order to combine adequate tensile strength with soft polymeric
binder material in a product with suitable drape and
conformability, recourse is frequently had to the use of an
internal reinforcing layer or layers of textile yarns, spun or
continuous filament.
Such a reinforcing layer may be in the form of woven gauze or
scrim, but due to the relative expense of woven fabrics, a more
frequent reinforcement expedient is the use of a layer of warp
strands crossed physically by, but not interwoven with, a layer or
layers of filling strands which may be normally disposed to the
warp strands, or disposed at an angle or angles thereto. In order
to impart stability to such an array, the multiple sets of yarns
are commonly bonded to each other at at least a portion of their
crossover points.
Prior art yarn-reinforcing devices of this nature, however, are
intricate, expensive, difficult to maintain, and are rarely capable
of operating at the speed at which it is desired to produce
nonwoven fabrics in order to make them economically feasible for
use in disposable garments.
BACKGROUND OF THE INVENTION
One obvious way to facilitate the processing of nonwoven fabrics
and laminates with strand reinforcement would be to omit the
time-consuming need for cross-strand reinforcement, using only a
set of spaced-apart warp strands. However, unless the warp strands
are spaced very closely together, there is no support for that
portion of an overlay, such as a tissue, lying between the warp
strands. Spacing the warp strands closely together is economically
inexpedient: furthermore, no cross-direction (C.D.) strength is
provided.
It is an object of this invention to provide a primarily
two-dimensional nonwoven fabric comprising a set of spaced-apart
warp strands, reinforced in the cross direction by a planar web of
textile-length fibers, the textile length fibers being
predominantly oriented normal to the warp strands and a portion of
said fibers being mechanically engaged with said warp strands.
Further objects of the invention will be apparent from the
following description and drawings, in which:
FIG. 1 is a perspective view of a product of this invention.
FIG. 2 is a similar view of the product of FIG. 1 showing in detail
the nature of the mechanical engagement of fibers and warp
strands.
FIG. 3 is an enlarged view of another embodiment of the
invention.
FIG. 4 is a side elevation of an apparatus suitable for carrying
out the process of the invention.
FIG. 5 is a top elevation of the apparatus of FIG. 4.
FIG. 6 is a side elevation of the centrifugal or horn section of
FIG. 4.
Basically, the process comprises the formation of a high-velocity
fluid stream of textile-length fibers, diffusion and deceleration
of the fibrous stream in a chamber that is of substantial width in
comparison with its thickness, to form a relatively wide but
shallow fibrous stream, and then deflecting the fluid stream of
fibers along a transversely extended smoothly curved surface curved
in the direction of the stream, the curved surface forming what
will herein be termed a horn.
In this manner, centrifugal force is exerted on the fibers, causing
them to align in a transverse direction along the curved surface
and to concentrate in a narrow transversely extended band along the
forward edge of the curved surface.
The above process, with a description of the apparatus and the
operating parameters, is set forth in detail in copending U.S.
Patent Application Ser. No. 248,106, filed Apr. 27, 1972 now U.S.
Pat. No. 3,812,553, of common assignee, and incorporated herein by
reference, said application being a continuation-in-part of U.S.
Ser. No. 196,709, filed Nov. 8, 1971.
The essence of the present invention is the interposition of a set
of spaced-apart warp strands which traverse the lower edge of the
centrifuge or horn, in a direction substantially normal to the flow
of the narrow band of transversely-aligned fibers. The spacing of
the strands and the length of the fibers are so chosen that at
least a portion of the fibers, traveling at high velocity as they
reach the forward exit edge of the horn, become mechanically
engaged with the warp strands and with each other. Thus a set of
parallel warp strands, having no crosswise tensile strength per se,
is converted into a nonwoven fabric, with a strand warp and a
fibrous filling substantially normal thereto. The nature of the
mechanical engagement will be more fully explained below.
TECHNICAL DISCLOSURE
By warp strands is meant herein a spaced-apart non-interconnected
set of supportive and reinforcing strands, of substantial tensile
strength, running in the machine (M.D.) or longitudinal direction
of the fabric. Exemplary but not restrictive illustrations are spun
yarns, continuous filament yarns, narrow ribbons of film, fine
wires, and bands of spread-apart tow comprising continuous
synthetic filaments.
By textile-length fibers is meant fibers between 1 1/2 and about 6
inches in length, capable of being formed into a fluid stream of
substantially individualized fibers under the influence of an air
jet.
Referring to FIG. 4 there is shown a fluid-powered jet or
aspirator, 10, capable of converting a top or sliver of
staplelength fibers into a high-velocity fluid stream of
substantially individualized fibers. Such jets, their parameters,
and their function are described in detail in my copending
applications Ser. Nos. 159,229, filed July 2, 1971, now U.S. Pat.
No. 3,793,679 and 164,255, filed July 20, 1971, now U.S. Pat. No.
3,727,270, and there are also commercially available aspirators
capable of performing a similar function.
The high-velocity fluid stream of fibers is directed into the entry
chamber 12, and thence is diffused into a guiding chamber 14,
which, as seen by comparing FIGS. 4 and 5, reforms the fibrous
stream into a stream which is wider and shallower than the diffuse
stream emerging from the aspirator. The wide and shallow fibrous
stream flows then then through the chamber 16 and preferably to a
constricting region 18, which acts as a Venturi. While not
absolutely mandatory, this constriction 18 serves to iron out or
minimize local disruptive pressure differences or vortices, thus
evening out the flow of fibers.
From the Venturi section 18 the fibrous stream passes into the
curved centrifuge section 22, where the actual reorientation takes
place. The majority of the fibers are thrown against the leading or
forward contour of the centrifuge 22, causing them to become
reoriented from their previous orientation parallel to the fluid
stream, or long axis of the apparatus, to a position in which they
lie predominantly across or normal to the direction of fluid
flow.
Immediately adjacent to and preferably in contact with the exit
section of the horn, a warp of spaced-apart strands 25, from supply
roll 23, is caused to traverse the exit section in a direction
normal to the fiber flow. As seen more clearly in FIG. 6, the
reoriented fibers are flowing in a narrow band traversing
downwardly along the forward section of the horn. This band is
customarily so narrow as to be less in width than the length of an
individual fiber.
In preferred operation, the operating air pressures and apparatus
configuration are such that the air velocity in the Venturi section
18 is about 88 to 176 feet per second, and at the forward edge of
the exit section of the horn, where the fibers are grouped in a
narrow transverse band, the air velocity is from about 44 to 88
feet per second. In this manner the fibers are strongly impelled
onto the warp strands, and become mechanically engaged therewith as
explained more fully below.
It should be appreciated that when the fibrous web is described as
being oriented substantially normal to the warp strands, this does
not mean that the fibers are laid down absolutely straight and
parallel, like a row of matchsticks, since the length of the fibers
being dealt with herein is so much greater than their diameter, and
the fibers are so flexible, that practically without exception
every fiber will lie in a twisted and cursive path, with curves and
direction reversals along its path. The mean orientation of the
fibers, therefore, is measured by the ratio of M.D. to C.D.
strength of the fibrous web per se. By the statement herein that
the fibers are predominantly oriented normal to the warp strands is
meant that the ratio of C.D. to M.D. strength in the fibrous web
alone is at least 4 or 5 to 1.
As desirable auxiliary equipment, means may be supplied to prevent
excessive downward deflection of the warp strands as they traverse
the exit section of the horn. This preferably is in the form of an
air-permeable conveyor, such as a screen, 24, driven by drive rolls
36 and 38. In order to bleed off excess air, and to allow high air
volumes and velocities to be employed in the horn, a conventional
suction box 27 may be mounted immediately below the screen, as
shown in FIG. 4.
Also, in order to prevent leakage of air into the exit section of
the horn, as shown in FIGS. 4 and 6, a sealing roll 28 may rotate
across the leading edge of the exit section of the horn, contacting
the warp strands, and a curved plastic strip may make similar
contact with the warp strands along the rear edge of the exit
section.
The warp strand-textile length fiber combination may conveniently
be doffed by means of take-off rolls 32 and 34, whence it is wound
up by conventional means, not shown.
The size of the apparatus will naturally vary with the width of
fabric to be produced, the volume of fiber to be processed, and
with other factors. A typical set of dimensions might involve an
entry chamber 12 in the form of a 10 inch cube. The guiding chamber
14 may taper down to a 4.5 inch depth, while widening out to 40
inches for the purpose of producing a 40 inch-wide web. The chamber
16 may be 40 inches square and 4.5 inches deep, with a capacity of
180 cubic inches.
The outlet slot of the Venturi section 18 may taper down to a depth
of about 1.2 inches, ejecting a fibrous stream into the 2 inch deep
opening of the centrifugal section 22. The guiding surfaces of this
centrifugal section 22 are curved in a 15 inch radius through a
90.degree. turn, terminating in an outlet section 6 inches wide,
thus giving a 240 square inch screen deposition area.
The above dimensional parameters are illustrative only, and not
restrictive. Engineering details for modifications of the apparatus
may be made, bearing in mind that the centrifugal force developed
is proportional to the square of the velocity of the air stream,
and inversely proportional to the radius of curvature.
NATURE OF THE PRODUCT
The products of this invention are in general planar nonwoven
fabrics of substantial length and breadth in comparison with their
thickness. As shown in FIG. 1, they comprise a set of warp
streands, strands, and a superimposed web or fleece of
textile-length fibers 42, lying principally on and normal to the
warp strands.
As mentioned previously herein, a portion of the fibers are
mcehanically engaged with the warp strands. This is shown more
clearly in FIG. 2, wherein it may be assumed that that portion of
the fibers of FIG. 1 which are not engaged with the warp strands,
but are merely lying across the strands, has been removed for
clarity. The nature of the mechanical engagement with the warp
strands is of three principal types. First, there is a plain
interlacing, as shown at 44, where a textile-length fiber passes
above certain warp strands and below certain other warp strands.
Second, there is a wrapping action of one end of a fiber around a
strand, as shown at 46. Third, as shown at 48, certain portions of
the length of a fiber may be formed into a loop or series of loops,
which loops are then at least in part wrapped around one or more
wrap strands.
Additionally, there is a certain degree of entanglement and
wrapping of some fibers, which are not in mechanical engagement
with the warp strands as described above, with and around certain
other fibers which are so engaged. It will be appreciated that the
greatest degree of mechanical engagement of fibers with warp
strands occurs with the fibers initially deposited on the strands,
and that as more and more textile fibers are deposited, they tend
to lie upon the initially deposited portion of the fleece. Light
weight nonwoven fabrics of this invention, therefore, will
generally show greater tensile strength per unit of fabric weight
than fabrics with a heavier deposit of fibers.
In general, in the practice of this invention, a set of warp
strands of, for example, spun cotton yarns, will be spaced from 0.5
to 1.5 inches apart, and will have applied thereto a fleece or web
of textile-length fibers of from 1.5 to 6.0 inches in length,
weighting from 5 or 6 to 60 or 70 grams per square yard. The
invention will be illustrated by the following examples.
EXAMPLE 1
The apparatus employed was that shown in FIG. 4, wherein the warp
strands were 40's 2 ply cotton yarns spaced approximately 0.75
inches apart.
The chamber 12 of FIGS. 4 and 5 was fed by 4 aspirator jets of the
type described as Type C in copending application Ser. No. 164,255,
referred to above. The throat diameter of each jet was 0.562 inches
in-diameter, the taper was 2.7.degree., and the exit section
diameter was 0.600 inches. Each jet was powered by air at 75
P.S.I.G., which, as set forth in Ser. No. 164,255, develops a
maximum vacuum in the tube, of approximately 24 inches of
mercury.
Each jet was fed by a 60 grain rayon sliver, 1.5 denier per
filament, 1 9/16 inches long. The total denier of the four ends of
sliver was 153,060, and the feed rate was 4 feet per minute.
The 40 inch wide beam of cotton warp strands traversed the exit
section of the horn at a speed of 8 feet per minute, in the manner
shown in FIG. 4.
The product resembled that shown in FIG. 1, with a portion of the
cross-deposited fibers mechanically engaged with the warp strands,
as shown in FIG. 2. The yarn-fiber product weighed 8.7 grams per
square yard, of which 2.9 grams was cotton yarn and 5.8 grams was
rayon fiber. When a 1-inch wide strip was cut across the 40 inch
width of the fabric and suspended by one end, the strip remained
integral and self-sustaining in the absence of binder, indicating
internal cohesion due to fiber-yarn interengagement.
If it is desired to produce stronger products, or to provide a
potential adhesive property to fabrics of this invention, auxiliary
binding material may be deposited within the product by the same
air-deposition process. Such binding material may be in the form of
thermoplastic fibers, or thermoplastic powders, or both, and the
fiber-warp strand composite may be further unified by developing
the adhesive properties of the auxiliary binding material, or the
composite may be laminated to another planar sheet material, as
shown in the following example.
EXAMPLE 2
The same apparatus, jets, rayon sliver, and cotton warp strands
were used as in Example 1. In addition, two auxiliary aspirators
were set up to feed into chamber 12 of FIGS. 4 and 5. These were a
commercially available type, CP 200, from Clevepak Pollution
Control Systems. These aspirators consist of a straight pipe
approximately 9 inches long and 2.75 inches I.D., with an air
supply delivered through four holes 0.089 inches in diameter
distributed around the periphery of the central air chamber and
inclined at about 30.degree. to the axis of the pipe. Aspirators of
this type are designed to operate at from 5 to 150 P.S.I.G.,
depending on the degree of vacuum it is desired to establish.
One CP 200 aspirator was fed with a supply of 3 denier 0.25 inch
long Vinyon fibers (Union Carbide trademark for a copolymer of
vinyl chloride-vinyl acetate in fiber form), at 75 P.S.I.G.,
delivering 6 grams of short thermoplastic fiber to each square yard
of product. The other CP 200 aspirator, operating at 20 P.S.I.G.,
delivered to each square yard of product approximately 5 grams of a
thermoplastic powder, 35 mesh, a copolymer of
polyethylene-polyethylacrylate.
The composite product, after leaving the take-off roll 32 of FIG.
4, was plied with a layer of cellulose tissue weighing 20 grams per
square yard, and was passed through a 3-roll calender. The bottom
steel roll was heated to about 420.degree.F: the center silicone
covered roll equilibrated at about 360.degree.F., and the top steel
roll at about 120.degree.F. The tissue side made contact with the
heated steel roll, and the pressure was about 70 pounds per inch of
nip.
The final compodite product weighed 59 grams per square yard, of
which 25 grams was rayon fiber, 20 grams tissue, 3 grams cotton
yarn, 6 grams fused thermoplastic fiber, and 5 grams fused
thermoplastic powder. It has a tensile strength of 6.4 pounds per
inch-wide strip cut to include one cotton warp strand, and a
filling strength of 1.45 pounds.
Under the conditions of hot calendering, the thermoplastic fibers
and thermoplastic powder granules were found, under microscopic
examination, to have fused to binder globules unifying the rayon
fibers, principally at their points of intersection, as shown at 50
in FIG. 30. Both thermoplastic components also served to bond the
sheet of tissue to the assembly.
It will be apparent to those skilled in the art that any desired
sheet material, such as film, foil, paper, or other nonwoven
fabric, may be thus laminated to the basic fiber-warp strand-binder
composite.
* * * * *