Note: Descriptions are shown in the official language in which they were submitted.
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Our patent application Serial No. lgO,207, filed January 15, 1974,
from which this application is divided, relates to new and improved network
struc~ures and methods for making such network structures~ and particularly
to network structures and methods for making them by embossing or forming
ribs in both sides of a thermoplastic polymeric sheet in a par~icular manner
so as to permit spon~aneous fibrillation or opening of the network structure
upon drawing in one direction or in two preferably perplendicular directions ~;
and to provide a uniform open network structure having desirable strength
characteristics. The present invention is concerned with making tapes and
woven fabrics from network structures such as those which are the subject of
application Serial No. 190,207.
In the manufacture of networks, it has previously been proposed to
form continuous diagonal grooves in one direction in one side of a sheet of
plastic material and continuous diagonal grooves in the opposite direction
on khe other side of the sheet so that upon subjecting the sheet to biaxial ~
stretching the thin parts of the sheet, at the crossing points of the grooves, ~;
split and form perforations thereby opening the material into a network. For `
example, see United States Patent 3,488,415 to A. G. Patchell et al. The net
works therein disclosed are formed in such a manner as to have thicker masses
at the points where the ridges cross, which behave as discrete areas of rein~
forcement, since on biaxial stretching or drawing of the embossed sheet the
thick areas where the ridges cross orien~ only to a limited extent if at all.
The tensile strength and tear characteristics of such a network are relatively
poor because the presence of the unoriented thick areas weakens the tensile
strength and tear resistance of the network so prepared, and such a network
is not uniform in appearance. United States Patent 3,500,627 to Charles W.
Kim discloses making yarn by forming on one side of a ribbon of plastic
material a plurality of parallel filament forming ribs and on the other side
a plurality of fibril forming cross-ribs arranged at an acute angle to the
filament forming ribs. The ribbon is then uniaxially oriented and mechani- -~
cally fibrillated by means of a toothed fibrillating device to break the
fibril forming ribs and form a yarn having fibrils extending laterally there-
from. Use of mechanical fibrillation makes reproducing uniform network struc-
tures very difficult.
The invention of application Serial No. 190,2~7 relates to network
structures and methods of making network structures comprising: forming a
sheet having a plurality of parallel continuous main ribs extending in a first
direction on one side thereof and a plurality of parallel continuous tie ribs
on the other side thereof extending in a second direction other than said
first direction; and drawing said sheet in at least one direction to separate
the main ribs into continuously and uniformly oriented main filaments having
a substantially uniform cross section and to separate the tie ribs into con-
tinuous tie filaments interconnecting the main filaments thereby forming a ,~
network structure. The tie ribs are formed at any desired angle to the main
ribs. The main ribs preferably have a cross-sectional area which is at least
1.5 times as great as the cross-sectional area of the tie ribs, and the main
ribs have a height which is at least three times as great as the thickness of
the webs between the main ribs. By forming the main ribs and tie ribs with
a cross-sectional area ratio of at least 1.5:1 and a main rib height to web
thickness ratio of at least 3:1, it is possible, among other things, to spon-
taneously open or fibrillate the ribbed sheet into a network by drawing, and ~ ;
to orient the main ribs continuously and uni~ormly, thereby making the main
ribs very strong. It is this feature which provides a network structure hav-
ing high tensile strength in the direction parallel to the main ribs. Addi-
tionally, by having continuous main ribs which are uniformly oriented, the
tear strength in the direction across the main ribs is greatly enhanced.
After the main and tie ribs are formed in the plastic sheet the
sheet is drawn in a direction to effect orientation of the main ribs continu-
ously and uniformly, and may be drawn in two different, preferably perpendi-
cular, directions to orient both the main and the tie ribs. For example, when
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the main ribs are formed in the machine direction and the tie ribs are formed
in the cross-machine direction a network structure may be formed with only .
one draw, in this instance in the machine direction. Alternatively, a more
open network structure can be formed by sequential or simul~aneous drawing
in both the machine and
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cross-machine directions. In sequential drawing of a sheet hav-
ing main ribs in the machine direction, the first draw is cus-
tomarily in the cross-machine direction~ Upon drawing, the
thinnest areas in the sheet namely the area~; where the webs be-
tween the main ribs cross the webs between the tie ribs, become
oriented and normally open up spontaneouslyy leaving a uniform
pattern of holes or voids in the sheet. Uncler some conditions and
levels of draw the web openings may not occur during the initial
draw but may occur only during the subsequent perpendicular draw.
In any event, the web openings occur spontaneously and thus there
is no need for mechanical fibrillation. This spontaneous fibril~
lation or opening of the webs converts or forms the tie ribs into
tie filaments and the main ribs into main filaments~ Hereinafter,
the term tie ribs shall be used to re~er to the tie ribs embossed
on the sheet which are ordin~rily interconnected by webs. A~ter
the webs split or open up, the tie ribs are separated and will be
referred to as tie filaments. Likewise, the main ribs are re-
ferred to as main ribs while interconnected by webs, but after
the webs split or open, the main ribs are separated and will be
referred to as main filaments. These main filaments are oontin-
uous if in the machine direction, or if at an angle to the machine
direction, are continuous from one edge of the sheet to the other~
It has been found that highly desirable strength char-
acteristics are obtainable in a network structure having main
filaments in one direction crossed by tie filaments in another
direction wherein the main filaments are dominant in si~e so t~at
all, or substantially all, of the orientation at the cross-over
; points of the main and tie filaments is applicable to the main
filaments. The tie filaments are normally smaller and are usu
ally oxiented to provide sufficient structural integrity for the
network structure, tending to keep it flat and prevent folding,
thus maintaining the main filaments in parallel and uniformly
spaced relationO The single layer plastic network structures
thus formed are dimensionally stable, self-supportiny, easy to
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handle, and have high tensile strength in the direction o the
main filaments and high tear resistance in the other direction.
Such nets are particularly useful for reinforcing paper products
and nonwoven fabrics based on staple fibers and for covering
absorbent pads.
Additionally, the network struotures so formed may be
made into multi-layer fabrics by bonding together two or more
layers of network struc~ures having the same or di~ferent config-
urations so that the main filaments cross in various directions
to provide a multi-layered product having certain desired strength
characteristics. For example, orthogonal conskructions can be
made wherein the main filaments of one layer cross at 90 to the
main ~ilaments of another layer to simulate the appearance and
physical properties of woven fabrics and to provide high ~trength
and tear resistance in two directions. Diagonal constructions,
wherein the main filaments of khe two layers cross preferably at
about 90 to each other with the main filaments of both layers
being at an angle to the machine direction of the fabric, possess
stretch and recovery properties in the machine direction similar
to those of knitted fabrics~ Fabrics made ~rom~three or more
layers of networks each having the main filaments in different
directions have excellent dimensional stability, high str~ngth
and tear resistance in all directions and high burst strength.
For example, triaxial constructions, wherein a diagonal constxuc-
tion is utilized having interposed between the two layers a net
work having main filaments formed in the machine direction, pro-
vide hish bursting strength with minimum weightO Isometric con-
structions, wherein the main filaments of at least four layers
are positioned at about 45 angles to each other, provide strength
in all directions with dimensional stability heretofore unattain-
able in woven, knit or other nonwoven fabric structures with
equivalent unit weight.
Additionall~t the subject network structures which have
main filaments in the machine dire~tion can be made into
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monofilaments, tapes or yarns by separating the network structl~re into strips
which may be subsequently fi~rillated and twisted or bulked to entangle the
main filaments of the strips. If desired, the strips may also be crimped or
false ~wisted.
Hence, in one aspect the invention provides a tape comprising two
or more main filaments uniaxially oriented along their longitudinal axes and
having a plurality of continuous transverse tie filaments interconnecting
said main filaments with portions of tie filam nts protruding from the edges
o said tape.
In another aspect the invention provides a method of making a tape
which comprises (1) forming a sheet having a plurality of parallel continu-
ous main ribs extending in a first direction substantially parallel to the
longitudinal axis of the sheet on one side thereof and a plurality of parallel
continuous tie ribs on the other side thereof extending in a second direction
different from the first direction, drawing the sheet in at least one direc-
tion to separate the main ribs into continuously and uniformly oriented main ;
filaments having a substantially uniform cross-section and to separate the
tie ribs into continuous tie filaments interconnecting the main filaments
thereby forming a network structure; and (2~ breaking the tie filaments inter-
connecting main filaments of the network structure to form a plurality of
tapes composed of main filaments, each having portions of tie filaments pro-
truding therefrom.
Other advantages of the present invention will be apparent from
the following detailed description of the invention when considered in con-
junction with the following detailed drawings, which drawings form a part of
the specification. It is to be noted that the drawings illustrate only typi-
cal embodiments of the invention and are therefore not to be considered limit-
ing of its scope, for the invention may admit to other e~ually effective
embodiments. Figures 1 to 20 illustrate the preparation of network structure
in accordance with the parent application. Figures 21 to 26 particularly
illustrate the invention claimed in this application.
Figure 1 is a perspective schematic view illustrating apparatus
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for embossing ribs on both sides of an advancing sheet o plastic material
Figure 2 is an enlarged perspective view of a portion of the em-
bossed sheet shown in Figure 1.
Figure 3 is an enlarged perspective view of a portion of an em-
bossed sheet having main ribs which are spaced relatively far apart and have
relatively deep grooves therebetween and tie ribs which are spaced close to-
gether and have relatively shallow grooves therebetween. ;~
Figure 4 is an enlarged perspective view of a portion of another
embossed sheet having ma m ribs which are spaced relatively close together
and have shallow grooves therebetween and tie ribs which are spaced relatively
far apart and have relatively deep grooves therebetween.
Figure 5 is an enlarged perspective view of a portion of the top
of a network structure obtained after drawing and orienting the embossed
sheet shown in Figure 2 in two directions.
Figure 6 is an enlarged perspective view of the bottom of the net-
work structure shown in Figure 5.
Figure 7 is an enlarged perspective view of the tie ilament side
of an embossed sheet illustrating the product made by a method wherein sub-
stantially all of the polymer on the back side of the sheet directly opposite
the main rib goes into forming the main rib as opposed to being in the tie
rib so that the tie ribs are discontinuous.
Figure 8 is a schematic perspective view illustrating apparatus
for embossing continuous longitudinal main ribs on one side of a sheet and
discontinuous tie ribs on the other side of the sheet.
Figure 9 shows one side of a portion o the network structure made
after stretching in two directions the sheet shown in either Figures 7 or 8.
Figure 10 shows the other side of a portion of the network struc-
ture of Figure 9.
Figure 11 is a plan view illustrating a portion of a network struc-
tute having main filaments in the machine direction and tie filaments in the
cross-machine direction.
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Figure 12 is a plan view illustrating a portion of a network
structure having main filaments in the cross-machine direction and tie fila-
ments in the machine direction.
Figure 13 is a plan view illustrating a portion of a network
structure having main filaments formed at an angle to the machine direction
with tie filaments formed in the machine direction.
Figure 14 is a plan view illustrating a portion of a network
structure having main filaments formed at an angle to the machine direction
with tie filaments formed perpendicular to the main filaments.
Figure 15 is a perspective schematic view illustrating apparatus
for making multi-layer fabric structures.
Figure 16 is a perspecitve schematic view illustrating other appara-
tus for making multi-layer fabric structures.
Figure 17 is a plan view illustrating a portion of a three-layer
triaxial fabric with one layer having main filaments formed in the cross-
machine direction and the other two layers having their main filaments formed
at equal opposite angles to the cross-machine direction main filaments.
Figure 18 is a plan view illustrating a portion of two-layer diago-
nal fabric formed by bonding together two network structures having their
main filaments formed at equal opposite angles to the machine direction and
desirably, but not necessarily, perpendicular to each other~
Figure 19 is a plan view illustrating a portion of a four-layer
isometric fabric made by bonding together in any desired order the two layers
shown in Figurç 15 and the two layers shown in Figure 18.
Figure 20 is a perspective view illustrating apparatus for rein-
forcing paper, foil~ non-woven fabrics or films by utilizing a central net-
work structure.
Figure 21 is a view illustrating apparatus fo~ making network
structures into yarns.
Figure 22 is an enlarged view of the leasing rods of Figure 21
used to separate or tear the network structure into strips.
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Figure 23 is an enlarged plan view of a portion of a strip before
fibrillation.
Figure 24 is an enlarged plan view of the strip of Figure 23 af~er
fibrillation illustrating the broken tie filaments.
Figure 25 is a view of a portion of an air jet interlaced multi- `
filament yarn having protruding side fibers.
' Figure 26 is a view of a portion of a bulked entangled multi-
filament yarn.
Referring now to Figures 1 and 2, there is shown an embossing roll ;
21 having a plurality of grooves 22 formed therein i` -~
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for forming a plurality of transverse main ribs 23 on an advan-
cing sheet of thermoplastic polymer material 24 with the ribs 23
being interconnected by webs 25 of reduced thickness. Another
embossing roll 26 having a plurality of annular or helical
grooves 27 formed therein is positioned opposite roll 21 for
forming a plurality of longitudinal tie ribs 28 on the other
side of the sheet 24 with the tie ribs being interconnected by
webs 30 of reduced thickness. The embossing rolls 21 and 26
rotate in the direction shown by the arrowsO There are a variety
of different ways to effect the double ernbossing des~ribed herein~
One method is to feed a molten plastic sheet, such as 24, coming
directly from an extrusion die into the nip of two courlter-rotating
er~ossing rolls, such as 21 and 26, which are urged toward each
other by facilities which are not shownO The desired separation
between.the rolls and ultimately the thickness of the ernbossed
sheet is readily controlled by regulating thickness of the ex-
truded sheet entering the embossing rolls and the pressure between
the two er~ossing rollsO The roll temperatures typically are in-
ternally controlled and serve to quench and solidify the molten
plastic forming the desired embossed patterns on each sideO
Alternatively, a previously cast flat sheet.or film may
be re-heated to its softening temperature and then advanced ~ .
through a.pair of ernbossing rolls, such as 21 and 26. Another
method may utilize a polymer which is in powder ~orm and which
is introduced into the nip between two heated rolls, not shown,
to permit the heated rolls to melt and soften the polymer and
form it into a.sheet which is then advanced between two emboss-
ing rolls such as 21 and 26. An additional method is to pass a
previously cast flat sheet or film between two ernbossing rolls
pressed together under a sufficiently high pressure that the
er~ossed patterns are pressed into the sheet without having to
melt or soften the sheetO It is evident that many ernbossing
techniques may be utilized to carry out the principles of this
invention. Alternatively, instead of using embossing rolls to
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form the desired ribbed configuration on both sides of a sheet,
such a configuration may also be accomplished by using a pair of
relatively movable concentric dies such as shown and described in
the aforementioned U S 3,488,415.
It has been found that the most advantageous range of
. the ratio of the cross-sectional area of the main ribs, to the
cross-sectional area of the tie ribs is between 1.5~1 to 100:1 ;
with the ratio of the height of the main ribs to the thickness of
the webs between the main ribs ~eing at least 3~1 or greater.
10 This relationship permits subsequent drawing and orientation .
steps to form.the.ribbed sheet into a.network.structure having .:
uniformly spaced main filaments oriented uniformly and continur
ously along their lengths and being quite uni~orm in cross-
sectionO With continuous.tie ribs and cross-sectional area
ratios less than lo 5, uniform continuous orientation of the main
filaments is not obtained, except with special polymers, or
speGial embossing conditions or methods as described hereinater,
because of a tendency for there to be thick areas where the main
. filaments and tie filaments cross and for those areas to remain
either:unoriented or only slightly oriented on drawingO As
shown in FIGo 2, the cross-sectional area Al of the main ribs
an~ the cross-sectional area A2 of the tie ribs each includes the
web area adjacent to the base of each respective rib. Also iden- .
tified in FIG~ 2 is the height Tl of the main ribs and the thick~
ness T2 of the webs interconnecting the main ribs.
The cross-sectional shape of the ribs formed may vary.
They may be semi~circular, rectangular, triangular, truncated,
or any other desired shape. Furthermore, the shapes of the main
and tie ribs may be the same or different. Lik2wise, the shape
and size of the grooves separating the main or tie ribs is not
critical. The grooves may be narrow so that the ribs are close '
together, or wide so that the ribs are more.widely separated.
Furthermore, the tie ribs may be spaced farther apart than the
main ribs or vice versa~ The size of the openings in t:he network
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structure may be conkrolled to some degree by controlling the
spacing of the main and tie ribsO
Referring to FIG. 3, there is shown a porti.on of an em-
bossed sheet identified generally as 36 having a plurality o~ main
ribs 37 ormed on one side of the sheet, and a plurality of tie
ribs 38 formed on the other side of the sheet in a direction per-
pendicular to the direction of the main rib~; 37O The main ribs
37 are spaced ~arther apart than tha tie ribs and have relatively
wide webs 39 of reduced thickness therebetween. The tie ribs 38,
however, have almost no web thereb~tween, but there is an area or
line o~ reduced thickness at 40 between each pair of adjacent tie
ribsO Note that the height 41 of the main rib 37, which is meas-
ured.from the web 39 to the top of the main rib 37, is much
greater than the height of the tie rib 38 which is measured from
the bottom of 40 to the.top of tie rib 38~ However, referring
now to FIGo 4 there is shown an embossed sheet generally desig-
nated. as 43 having a plurality of closely spaced main ribs 44
formed in one direction on one side of the shaet~ and a plurality
of spaced apart tie ribs 46 formed on the other side of the sheet
in another directionO The web which is the line or area of re-.
duced thickness 4~ between the main ribs 44 is now very small,
while.the web 48 between the tie ribs 46 is relatively larger.
Thus, it can be seen that the invention is relatively independent
of the spacing between the ribs and the height of the ribs,
Additionally~ the direction of'the main ribs is not
. criticalO The main ribs may be formed in the machine direction
~- of the sheet, or transverse to the machine direction, i.eO, 90~ ;
thereto, or at any angle in between~ With the main ribs formed
in either the machine direction or the transverse direction,
orienting the main ribs along.their longitudinal axes is easily
: accomplished by use of either a conventional linear differen-
tial speed draw roll device or a conventional tenter. Li.kewiæe,
if the embossed ribs are diagonal to the machine direction, ori-
entation of the ribs and net formation may be achieved using
the same type of equipment~ In oxienting main ribs which are
formed at an angle to the machine direction along their longi-
tudinal axes~ it is sometimes advantageous to utilize a long
draw gap linear drawing unit so that upon drawing in the machine
Airection the sheet is permitted to neck down and cause orienta~- .
tion of the main ribs principally along their longitudinal axes. . .
In drawing in such a manner~ it is usually desirable that the
linear draw be preceded by a cross-machine direction orientation
by passing the sheet through a tenterO
The direction of the tie ribs on the reverse side of
the sheet should be a~ an angle to that of the main ribs, which
in many cases is desirably 90, but can also be other angles.
Any angle between about 15 and 90 between the directions of
the main ribs to the tie ribs is acceptableO
When the embossed sheet having a first pattern of con
tinuous main ribs on one side and a second pattern of continuous
tie ribs on the.other side is drawn, the thin areas.o~ the sheet,
namely.the areas where webs 25 and;30 cross, spontaneously split~
forming openings~ After the second draw is completed, a network
structure such as or similar to that shown in FIGS~ 5 and 6 is
achievedO The main ribs 23 of the embossed sheet shown in FIGS.
1 and 2 have been separated into main filaments 53 which are
oriented continuously and uniformly The tie ribs 28 have also
been.separated and oriented into tie filaments 54 which inter-
connect the main filaments 53 and keep them uniformly spaced
apart. FIGo 6 shows the back side of the network shown in FIG
5 wherein it can be seen that the tie filaments 54 may extend.
continuously and without interruption across the main filaments
53O
Alternatively, the tie filaments 54 may be eliminated
where they cross over the main filaments 53 by either controlled
embossing to obtain a "cave-in" efect or by us.ing a discontin-
uous tie rib embossing roll. Re~erring to FIGo 7, there is shown
a portion of an embossed sheet having continuous main ribs 5 a and
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r
discontinuous tie ribs 5~ made under selected embossing condi- -
tions. Note that on the tie rib side of the sheet there are
cave-ins or discontinuities 60 in the tie ribs 59 where they
cross the main ribs 58, thereby making the t:ie ribs 59 non-
continuous~
In using grooved embossing rolls such as 21 and 26
shown in FIG 1, it is possible to control t:he distribution of
polymer between the main rib and tie rib roJ.ls, among other
things, by control of the melt temperature, the embossing roll
temperatures, pressure between the rolls~ which roll the molten
sheet contacts first, the time of contact of the emhossed sheet
with one roll, and the thickness of the shee~ as it enters the
nip between.the embossing rolls Shrinkage of the polymer as it
cools may also be a factor contributing to the uni~ue results of
thiS method~ Discontinuities in the tie rib embossing pattern
may be obtained by using th~n sheets, relatively low melt tem-
peratures and having the sheet contact the main rib embossing -
roll before entering the nip ~etween the rollsO If the sheet is ~:
thin~ at the points where the. grooves 22 of the main rib emboss- -.
lng roll 21 cross the grooves! 27 of the tie rib embossing roll
26, there will be inadequate polymer. to fill both the relatively.
fine grooves 27 and.the relatlvely coarse grooves.22 because the ;~ available polymer will go into the larger grooves 22. This is
because the polymer tends to flow in the path of least resistance,
namely toward the larger grooves. Even with a thicker sheet
with low pressure the same phenomenon will occur. At low emboss-
ing temperatures, because of higher resistance of the polymer to
flowj a greater tendency toward formation of a discontinuous tie
rib pattern results. Accordingly, by such controls, coarse
grooves 22 of embossing roll 21 will fill uniformly with polymer,
but the fine grooves 27 of embossing roll 26 will not fill com-.
pletely, Thus, the embossed tie ribs are made discontinuous as
shown in FIG 7, there being insufficient polymer flow to com-
plete the kie ribs 59 in the areas 60 where they cross over the
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main ribs 5S. After orientation~ this makes a strong and inex-
j pensive network structure, among other reason~ because it causes
a higher proportion of the polymer to be present ln the main
ribs than under other operating conditions~ Additionally, the
discontinuous tie ribs 59 are further advantageous in that they
permit the main ribs 58 to be completely and uniformly oriented,
since there is essentially no cross-over of the main xibs 58 and
the tie ribs 59.
Discontinuities in the tie rib embossing pattern can
also be obtained in an alternate way, such as by using a contin-
- uous main rib embossing roll 61 and a discontinuous tie xib em-
bossing rall 63 as shown~in FIGr 8. The main rib embossing roll
61 has a plurality of parallel annular grooves 62 formed therein
for forming main ribs 67 in a sheet 700 The tie rib embossing
roll 63 has a pluraliky of discontinuous grooves or recesses 64
formed therein parallel to the longitudinal axis of the roll for
forming discontinuous tie ribs 68. In each row of grooves 64
across the embossing roll 63, each groove or recess 64 is blocked
, from the adjoining recess by a blocking section 66 of the roll
63, Desirably, the width of the blocking section 66 is equal to
or slightly less than the width of the groove 62 of the main rib
embossing roll 610 It is to be noted that the tie ribs are not
continuous across the embossed sheet~ but rather are continuous
only from one main rib 67 to the adjoining main rib having a
discontinuity at area 69 Because of the configuration of the
- roll 63, little or no polymer is left cn the tie rib side of the
sheet directly opposite the main rib 670 By embossing a sheet
70 in .this manner, and subsequently drawing in two directions,
the main ribs can be highly oriented continuously and uniformly.
Using embossing roll 63 in this manner assures that little or
no poly~er is formed across the main ribs 67. This allows for
high orientation of the main ribs and optimi~es the polymer
distribution. In view of the fact that there is little or no
mass of polymer crossing over the main ribs when using either
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the controlled embossing method described above to obtain the
cave-in effect shown in FIG~ 7, or the discontinuous tie rib
forming method as described above and shown in FIG. 8, the ratlo
of cross-sectional areas of the main ribs to the tie ribs is not
significant. Accordingly, a ratio of 1:1 will work satisfactorily.
However, to obtain low unit weights or finer network patterns,
e~g., more square yards of net per ounce of polymex, it may be
desirable to use a pattern having more and/or smaller tie ribs
than main ribs. An advantage of the controlled embossing method -
using two embossing rolls having continuous grooves such as shown
in FIG~ 1, over the discontinuous tie rib forming method using a
special roll such as 63 having discontin~ous grooves 64 as shown
in FIGo 8 j is that there is no need in the former to precisely
and accurately register and align the embossing rolls as is re- `
quired in using the FIG. 8 apparatus~
FIGS~ 9 and 10 show the top and bottom of a portion of
a network structure formed after drawing the emboysed sheet shown
. ~
in either! FIGo 7 or 8 in both the cross-machine and the machine
directionsO Note that the main filaments 71 flatten out somewhat ~s`
after drawing, and that the tie filaments 72 uniformly space the
main filaments 71 apart~ The tie ilaments 72 have their ends
integrally joined to the main filaments 71~ and as shown in ~IGo
9 do not extend across the main filaments 71.
In drawing the embossed sheetJ the pre~erred amount o
draw would depend on such factors as the polymer employed, the
embossing pattern employed, and the degree of separation of the
main filaments desired in the final network structure~ Custom-
arily, the firsk drawing or orientation step involves drawing
the embossed sheet in a direction generally transverse to the
direction of the main ribs to cause orientation of the thinner
areas of plastic material between the main ribsO Referring,
for example, to the embossed sheet shown in FIG o 2, since the
~main ribs 23 are formed in the cross-machine direction, the
first draw would normally be, but is not necessarily, in the
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machine direction ~his draw could be effected by using conven-
tional linear differential speed draw rolls. This orientation,
which is usually 1~5X or greater, generally results in incipient
or actual voids or openings being ormed between the main ribs
with the formation of small tie filaments spanning the openings
between the main, as yet unoriented, ribs or filaments. Drawing
to an extent greater than five times its ori.ginal length ~5X) at
tXis stage is usually undesirable since cross-orientation of the
. polymer at the cross over points of the main ribs and tie ribs
may occur~ This may interfere with the desired uniform orienta-
tion of the main filaments in the subsequent drawing steps.
As an alternative; it may be desirable to carry out an
initial draw such as~ for example, up to 2X, in the direction of
the main ribs prior to the.drawlng.step transverse to this direc-
tion. This initially orients and strengthens the main ribs and
tends to prevent any possible distortion or development of cross
orientation of the polymer in the.cross-over areas during the.
transverse orientationO.
The second orientation step is normally carried out in
a direction generally parallel to the main ribs Thus, refer-
ring again to the embossed sheet shown in FIGo 2, the second.
orientation would be in the cross-machine direction. This trans- -
verse drawing step, could be carried out on a conventional tenter
The transverse draw causes.orientation of the main ribs along
their.longitudinal axes and separation of the smallj connecting
tie filamentsO The amount of draw will determine the strength
. and size of the resulting main filaments. It can vary from as
low as 1.5X to lOX or greater.. The maximum draw will depend on
the orientation characteristics of the polymer employed, among.
other thingsO Temperatures for drawing will vary depending upon
the polymer employed but generally will be sllghtly lower than
those employed for orienting flat sheets of the same polymer.
While reference has been made to first and second sequential
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drawing steps 7 both draws may be carried out simulataneously, if .
desiredO
The network structures produced by the foregoing methods
contain as desired longitudinal, transversa or oblique oriented
main filaments interconnected by normally lower denier, oriented
tie filaments, with tne main filaments having orientation contin-
uously over ~heir lengths~ Examples of the different configur~-
tions of network structures that can be made are shown in FIGS.
11 7 12~ 13 and 14. In FIGo 11, a network structure is shown hav- -
ing main filaments 73 extending in the machine directiont the
direction of the arrow, and tie filaments 74 being formed in the
cross-machine direction 90 to the machine direction n In FIG. .
12, the main filaments 75 are formed t~ansverse to the machine : ~
direction, indicated.by the arrow, and the tie filaments 76 are :
formed par~l].el to the machine direckionO In FIGo 13/ the main
filaments 77 are formed at an angle to the machine direction, ...
shown.by the arrow~ and the tie filaments 78 are fQrmed parallel
to the machine direction Alternatively, the tie ilaments 78
may be formed in the cross-machine direction or so they axe per- :~
20 pendicular to the main filaments such as shown in FIGo 14. Nhen :
the main filaments ~7 are formed at an angle of 75 or less to
the machine direction, in order to orient such filaments, it is
sometimes desirable to draw in the machine direction while per-
mitting necking down o~ the network structure~ Ordinarily, in
making this configuration, the cross-machine draw in a tenter,
if desired~ comes first, followed by the machine direction draw
allowing neck-down It is apparent that many other configura-
tions of network.structures may be made in accordance with the
principles of this invention~ having the main filaments at any
desired angle wherein maximum tensile strength is desired and
the tie filaments formed at an angle relative to the main
filaments~
The network structures descxibed herein have good.
tensile strength in the direction of the main filaments which
- 17 -
~ O~J3'~ r --
reflects the degree and uniformity of orientation along the length
of these filaments~ Thls strength is lower in the opposite di-
rection because of the smaller size of the interconnecting tie
filamentsO The tear s~rength is high in the direction transverse
to the main filaments because of the strength of the main fil~ :`
mentsa. It is to be noted that the networX structures such as
shown in FIGSo 5~ 6, 9 and 10 have tie filaments which either are
continuous and cross over the main filaments or are discontinuous
and integrally join the main filaments~ without in either case
there.being notches at the junctures as is charactexistic of many
network,structures prepared by previous.methodsO Such notches at
the junctions.or cross-overs enable a network.to tear easily in
either direction,
The subject network structures, while useful as single
layer netwo,rk structures, may also be employed to prepare very
useful multi-layer fabric structuresO Referring to FIGo 151
there is shown one ne~work structure, generally designated as
81, having main filam~nts 82 formed in the machine direction and
tie filaments~ not shown~ formed in the cross-machine direction
being laminated or bonded to a second network structure, gener-
ally designated as 83, having main filaments 84 formed in the
cross machine direction~ Tie filaments are not shown.in any of
the network structures shown in FIGSo 15-20 to facilitate il- ~,
lustration and description of the fabric structures. Neverthe~
less, the tie filaments are present in each network and may be
assumed to be as shown in FIGS. 11-14 or as previously described.
One way of bonding the two network structures 81 and 83 together ~ ,
is to pass them through rolls 79 and 80 into a preheater 84 to
heat the networks under tension without adversely affecting the ,~
orlentation thereof and then advance them into the nip o~ two
heated calender rolls 86 and 87 to bond the plastic materials
to each other. Rolls 79 and 80 rotate very slightly slower
than rolls 86 and 87 to maintain the networks 81 and 8~ under
tension during heating to avoid.loss of orientat:ion. Likewise,
! - 18 -
", ~ 3~
.
it may be desirable to use a tenter, a series of closely spaced
~, rolls or other means to prevent lateral shrinkage of the net-
works in this areaD This bonding or lamination process orms a ~ '
two-layer fabric which has the appearance and physica]. proper- '
ties o a woven fabric having high strength and go~d tear re- ~'
sistance in both the machine and cross-machine directions. Such
a fabric has substantially no stretch in the machine and cross-
machine directions, but does stretch on the bias.
-Three or more layer fahrics can also be prapared with
1~ the main filaments.of each.being formed in ~ifferent diractions :
~' to pro~ide.fabrics having excellent dimensional stability, high
,, str ngth in all directions and.hi~h.burst strengthc As shown in
FIG. 16, a first layer or network structure, generally designated.
as 88~ has main filaments 89 formed at an angle to the machlne
~irection which is indicated by the arrowD A second,central
layer or network structure 91 has main filaments 92 formed in the
: machine diraction~ A third layer or network structure 93 has.main
filaments 9~ formed at an acute an~le.to the machine direction
~pposite that of the angle,of layer 88D The three--layers pass, ~:
thxough the.nip.of rolls 85 and,90,.into a preheater 95 and
~, through the nip of two heated calendar rolls 96 and 97 which,
bonds the three layers together at their cross-over.points. The
bonded,fabric may then pass through an annaaling unit 98 and is
, taken up on take-up spool 19D If desi~ed,.a conventional tentex
or other means could be used to maintain tension in the cross,
machine.direction during heati'ng and bondin~O Such three or
m~re layer.fabrics provide strength in all dir~ctions and dimen- -
sional stability unobtainable in woven~ knitted or other non-
woven fabric structures with aquivalent weight. Such fabrics.
provide good.stretchability in the cxoss-machine direction.
Referring to FIG. 17, there is shown a similax three
: layer fabric, except that it has a central layer havirlg its main
filaments 100 in tho cross-machine direction. Such a fabric has
good stretchability in the machine direction. .
.:
-- 19 --
~ 3~
`' `
If the central network layer 91 shown in FIG 16 i9
eliminated, a two-layer fabric such as shown in FIGo 18 i9 pro-
vided havlng the main filaments 89 on one layer 88 extending at
an angle~ such as 45 to the machine direction, and tha second :~
layer 93 having main filamen~s 94 extending oppositely at an
equal angle to the machine direction. If the main filaments 89
and 94 are formed 45 to the machine direction then main filaments
94 will be perpendicular to the main filamen~s 89 Such a netwoxk
structure with the central layer 91 eliminated has stretch and re-
covery properties in ~he machine and cross-machine directi.ons sim-
ilar to those of a knitted fabricO That is, the fabric wi.ll
stretch both in the machine and cross-machine direction~
If desired, the three-layer structure of FIGo 16 could
be made into a four-layer isometri~ fabric structure by bonding.ox
laminating as a top layer, a network structure such as 83 shown
in FIG~ 15 which has main filaments 84 extending in the cross~
machine direction Such a four.layer isometric fabric is shown
in FIG~ l9 o For the most uniform properties in such a fabric, it
is preferred that the main filaments 89 and 94 be formed at 45 :~
angles to the machine directionO This fabric is dimensionally
stable and has substantially no stretch in any direction. -:.
Referring to FIGD 20p a single layer plastic network
structure, generally designated at 101, having its main filaments
102 formed in the cross--machine direction is bonded between two
layers 103 and 104 of paper~ film, foil or nonwo~en web such as
carded, garnetted or air laid fiber webs, or any combinations
thereof by first.passing the network structure 101 and the layer
104 through an adhesive applicator 1060 Then layer 103 is bonded
to the other two layers by curing the adhesive as by passing
them through a heated zone such as calender rolls 107 and 108,
after which the reinforced paper, nonwoven fiber webs, film or
foil structure is taken up on take-up spool lO9o
It can be appreciated that many different multi-layer
fabrics can be prepared in accordance with the principles of
- 20 -
`:
this invention by taking one network structure having main fila-
ments in one direction and bonding -thereto one or more other
net~orks havlng main filaments in different directions. Then
the layers may be bonded toyether into a fabric in many ways in-
cluding applying or spraying an adhesive between the layers and
passing them through an oven and calender rolls to bond the layers
together, or by passing the layers only through a pair o~ heated
calender rolls to heat bond them together, or by using ultrasonic
bonding, or spot bonding or any other known conventional bonding ;~
techni~ue.
Among the many uses of the subject network structures,
either as single or multi-layer fabrics, are sanitary napkins,
diapers, continence pads, tampons, surgical dressings, surgical
sponges, burn dressings, and reinforcing material for paper and
paper products, films and other nonwovens and woven fabrics,
For example, a network may be used to reinforce masking tape or
wallpaper, thereby contributing increased tensile strength and
tear resistance propertiesO In the case of paper and staple
fiber nonwovens, the network structures of the type shown in FIG.
20 having main filaments in the cross-machine direction are par-
ticularly advantageous. This is because in preparing or making
paper or staple fiber nonwovens the fibers therein customarily
become oriented in the machine direction and increased strength
in the cross-machine direction a~ well as increased tear re-
sistance in the machine direction is needed. Additionally, the
thermoplastic networks can be used as an adhesive in bonaing
other materials together under heat and pressure. The networks
are also usable for fusible inner-liners in shirts and the like,
and can be used in place of cheesecloth for the manufacture and
processing of cheeses.
The multi-layer ~abrics described above are useful for
applications similar to those described for the single layer
network structures, and particularly useful for those applica-
tions in which balanced and high strength and tear resistant
- 21 -
~ ~0~3~
propertles are desiredO Multi-layer products are particularly
useful, for example, for the preparation of high impact resis-
tant plastic bags, primary and secondary tufted carpet backings,
plastic coated fabrics, and for other indust:rial fabric appli-
cations. Many other uses are evident for these networks and
fabrics which have such properties as not being absorbent, not
sticking to wounds or other materials, readily passing liquids
therethrough because of the openings in the network structures,
and relatively light weight and high strength~
While emph;~sis has been placed on the high tensile
strength and high tear resistance of the subject networks, it is
of course appaxent that network structures may be made in accor-
dance with the principles of this invention without necessarily
drawing the main filaments to a high degree so that network s~ruc-
tures may have less strength and tear resistance for applications
where those characteristics are not important. In certain appli-
cations, texture and smoothness may be more significant than
strength~ An example of such an application is the use of net-
work structures as a covering in a sanitary napkin wherein it is
highly desirable that the network have a so~t and smooth texture
in order to prevent irritation and also have high permeability to
permit fluids to pass and be absorbed by the absorbent inner-
material of the napkin.
The subject network structures are very smoo~h since
they do not have any reinforced bosses or thick masses at the
cross-over points of the main filaments and tie filaments. Such
smoothness gives the network a soft hand or feel to make it de
sirable for many uses wherein irritation of the user or wearer
may be an important factor. Additionally, the network structures
can be drawn in such a manner as to provide relatively flat
structures, that is, a structure having a relatively uniform
thickness as measured in the plane perpendicular to the plane
of the network. This may be significant for its use as an ad-
hesive where it may be desired to bond two materials together
- 22
~ 3~
:
to provide a laminated or bonded fabric having a uniform thickness.
It is also possible to make novel monofilaments or ~arns
from certain of the network structures described above Referring
to FIGo 21~ there is shown a network structure generally desig-
nated as 110 having main filaments 111 extending in the longitu~
dinal or machine direction and tie filaments 112 extending in the
cross-machine direction, 90 to the main filaments 111 Any net-
work structure having its main filaments formed in the machine
direction and its tie filaments formed at an angle to the machine
direction may be utilized in making monofilaments or yarns. The
network 110 is advanced by nip rolls 115 through a plurality of
lease rods generally designated as 114 to split the network struc- -
tures into individual filaments or relatively narrow tapes or
strips llOa, llOb, llOc~ llOd, etc~ consisting of a number of main
filaments interconnected by tie filamentsO The network 110 can
easily be split into monofilaments or tapes of any desired widthD
This is accomplished by initially cutting or tearing the leading
end of the network 110 into strips of the desired width and feed~ ;
ing adjacent strips differently through the lease rods 114 so
that upon advancement the lease rods tear or split the network as
desiredO For example~ as shown in FIGS ~ 21 and 22, strip llOa is
fed over lease rod 114a~ under lease rod 114b~ and over lease rod
114co The ad~acent strip llOb is fed or passes under lease rod
114a~ over lease rod 114b~ and under lease rod 114co Thus, as
strips llOa and llOb advance~ the lease rods break the tie fila-
ments interconnecting the adjacent strips~ Because of the relative
sizes of the main filaments to the tie filaments, the tie filaments
break easlly upon passing through the lease rods as shown, without
need for any cutting or slitting elements. If desired~ the strips
can then be fibrillated to completely or partially sever the tie
filaments such as by passing the strip over a beater bar 116 sim-
ilar to that described in UOSO Patent 3~495~752O FIGo 23 shows
a portion of strip llOa as it looks prior to fibrillation. Com-
plete fibrillation of the network breaks substantially all of the
- 23 ~
tie filaments, leaving the main filaments intact thereby forming
each strip into a yarn consisting of a plurality of individual
main filaments which are not interconnected and have protruding
portions of tie filaments extending perpendicularly therefrom,
or at some other angle if the tie filaments are initially formed
at some other angle. FIGo 24 shows a portion of strip llOa after
fibrillation with the tie filaments broken. The main filaments
are pulled through another set of nip rolls 117 and then may pass
over a yarn guide 118 for further processingO The fibrillation
by use of a beater bar 116~ or by any other means, converts the
strips:llOa~ llOb, etcO either partially or completely into a
series of multi-filaments each with.protruding normally smaller
side filaments attached. If desired, bulking may be effected by ~ :.
known cri.mping or false twist methodsO Also, bulking may be
e~fected.by heat relaxation if the main filaments have been pre-
: pared from bicomponent polymer sheetsO For example, referring
- again to FIGo 21, the fibrillated strips llOa may be passed from
; the yarn guide 118 into a heater ll9 to provide bulkingO If de~
sired~ a false twist-may be put into.the yarns by use of false ~ .
twisting head 120 after which the yarns are wo-md on a take-up
spool.l21, Alternativelyt i zero twist yarns are desired~ the
unfibrillated or fibrillated strip llOb may be wound directly
onto a take-up apool 122 as shown in FIGo 210 Alternatively, if
desired, a fibrillated strip llOc may be passed through an air-
jet interlacer 123 and then wound on a take-up spool 124 If ::
further desired, the fibrillated strip llOa may pass through a
conventional down twister 126 and then be wound on a take-up
spoolO Conventional air-jet entangling may be employed to convert
the yarns to a.form which can be wound and unwound from a package
30 readilyO FIGo 25 illustrates an air-jet entangled or interlaced
.~ yarn l280 FIG. 26 illustrates a bulked yaxn 129 which is subse-
quently air-jet entangled. Twister take-up packages may also be
used.to form compact, readily handleable yarnsO Of couxse, many
combinations of these steps such as fibrillation followed by heat
- 24 -
relaxation and twisting may be employed
The unfibrillated strips or tape networks are also use- ~ -
ful in untwisted form in weaving or knitting operations where max-
imum coverage in a light weight but strong fabric is desired.
Such weaving or knitting operations can be ca:rried out in line
with the strip or tape forming operation.
The yarn prepared in accordance with these techni~ues
are unique in that the main filaments have protruding tie fila~
ments which contribute bulk~ cover and a desirable appearance.
These yarns are useful for knitting~ weaving, tufting and contin-
uous filament nonwoven applications in general. The presence of
the side tie filament portions provide improved adhesion of plas-
tic, rubber or other coatings when fabrics prepared ~rom these
yarns are subsequently coatedO Furthexmore, because of the pro-
truding side tie filament portions, the yarns and the fabrics have
good abrasion and pilling resistance.
The strips 110 or individual filaments of this invention ~ :
containing spaced side fibrils may also be cut into staple length
fibers. Such staple fibe~rs are of particular advantage for con-
version into spun yarns, prepared for example by conventional cot-
ton, wool or worsted spinning processes, 4r into nonwoven fabrics,
prepared for example by conventional cording or air-laying methods~
Because of the protruding tie filaments on the staple fibers or on
the yarns either made from staple fibers or continuous filaments
as described above the nonwoven fabrics~ or woven, knit or tufted
fabrics prepared from such fibers or yarns are pleasing in appear
.ance~ h ve high thermal insulating value, high moisture absorptionp
and provide good adhesion to othex materials used to bind or coat
the fabrics~
In the preceding discussion of the embossing methods,
customarily one embossing roll drives the other embossing roll
through the melt or sheet with each roll rotating at t:he same
speed~ However, when using polymers that are relatively difficult
to split spontaneously, such as for example, polyesters, polyamides
- 25 -
~ 3~
and vinyl polymers, differential speed embossing rolls can be
used to effect incipient ~plit-ting of these polymers at the em
bossing stageO By differential speed, it is meant that the sur-
face speed of the main rib embossing roll is different, from a
slight difference up to about a 50~ difference, either faster or
slower, than the surface speed of the tie rib embossing roll. By
using differential speed, of the main and tie rib embossing rolls
it is possible to bring about splitting of the thin web areas of
the embossed sheet at the embossing stage~ This facilitates sub-
sequent splitting or opening up into a uni~orm network structureupon drawing.
",
The materials that the above network structures, fab-
rics and yarns can be formed from include any thermoplastic fiber-
forming polymers. Among these are polyethylene, polypropylene
homopolymer, random copolymers of propylene containing up to 10
percent of another olefin, block copolymers of propylene contain- ;
ing up to 25 percent of another olefin, nylon-6, nylon-66, poly-
ethylene terephthalate, other-high molecular weight thermoplastic
~polyesters, and vinyl polymers such as polyvinyl chloride. Con-
jugate or bicomponent plastic sheets in which two or more differ-
ent polymexs are extruded together to form sheets containing
layers of separate polymers are also possibleO For example, two
layers or network structures, each having a portion thereof made
of a relatively high melting point polymer with the remaining
portion being made of a lower melting point polymer, may be
bonded together by placing the lower melting point polymers of
each layer together and heating. Alternatively, a network struc-
ture made of a higher melting point polymer may be bonded to a
network structure made of a lower melting point polymerO Fur-
thermore, a network structure having a portion thereof made ofa relatively high melting point polymer with the remaining por-
tion being made of a lower melting point polymer, may be honded
to another network structure being made only of a higher melt~
ing point polymer~ Particularly desirable are conjugate plastic
- 26 -
~ 3~7~ ~
in which a higher melting point component, such as nylon or poly-
ester, is used to form the main portion of the main fibers. This
permits lamination without adhesive of two layers by bonding with
heat and pressure or self bulking by heating -the network struc-
tures or yarns prepared from such structures, Alloys or mixtures
of polymers may also be employed.
The principles of this invention are exemplified by
the following examples, which are given to illustrate the inven-
tion, and are not to be considered limiting in any way.
E ~
Propylene homopolymer with a melt flow index of 7~5 and
a randon copolymer of propylene with ethylene containing 2 D 5~
ethylene with the same melt index were coextruded through a slit
die at 465F~ to form a conjugate sheet in which the homopolymer
comprised 75% of the thickness of the sheet. The slit die was
12 inches long with an opening 15 mils wide. The molten sheet was
passed into the nip of two chrome-plated steel embossing rolls,
one 4 inches in diameter, the other 3 inches in diameter, each
being 13 inches longO The 4 inch roll had an embossed pattern
consisting of a plurality of grooves extending circumferentially
around the roll with a spacing of 48 grooves per inchu This roll
was internally cooled to maintain its temperature at 70Co The
other 3 inch roll had a pattern of straight grooves extending
parallel to its longitudinal axis having a uniform spacing of 111
grooves per inch, This 3 inch roll was not cooled and assumed a
temperature of about 60Co The molten sheet was passed between
the two rolls at a rate of 15 feet per minute and went around the
48 grooves per inch roll wi~h 180 contactO The homopolymer side
of the conjugate sheet was in contact with the 48 grooves pex
inch roll. The embossed sheet contained 48 main ribs per inch in
the longitudinal direction on one side with the ribs being sep-
arated by grooves 10 mils wideO On the other side of the sh~et
the continuous tie ribs were formed with 111 tie ribs per inch
with each paix of tie ribs being separated by grooves 5 mils wide.
- 27 -
~ 3~
The maximum thickness of the sheets was 15 mil. The ratio of the
cross-sections of the main ribs to the tie ribs was about 2:1 and
the ratio of the height of the main ribs to the thickness of the
webs between the main ribs was 8:1. The embossed sheet was fed
into a tenter heated with circulatiny air to' 110C. at a speed of
20 feet per minute and it was stretched to tw:ice its width. In
this operationJ it opened in-to a uniforrn network structure, the
grooves between the main ribs becoming openin~s or voids crossed ~ -
by oriented tie filaments with the main ribs now beinq separated
by about 30 milsO The sheet was then drawn in ~he linear direc-
tion by passing it in frictional contact with a series of :Ll steel
rolls heated to 120~Co and moving at progressively increasiny
speeds. The sheet was fed in at 15 feet per minute and exited at
105 feet per minute and accordingly was drawn seven times its
length in the machine direction~ The resulting network structure
had a weight of 0,32 ounce per square yard~ The uniformly ori-
ented main filaments were about 45 denier in size. This ne~work
structure had a tensile strength of 11 pounds per inch and an
elongation of 12 percent in the machine direction. The strength
in the cro~s-mAchine direction was about 1.9 pounds per inch and
the elongation 12 percentO The net was very resistant to tearing
in the cross-machine direction, giving a value of 30 pounds when
tested by the Finch edge tear method, ASTM D-827.
Example 2
Propylene homopolymer with a melt flow index of 7 was
extruded at 400Fo through the slit die described above in Ex-
ample 1. The molten sheet was embossed between two rolls, one
being the same as used in Example 1 and containing 111 grooves
per inch extendiny parallel to the rolls longitudinal axis. The
other roll had 36 annular grooves per inch extencling in the cir-
cumferential directionO The ratio of the cross-sectional areas
of the main ribs to the tie ribs formed on both sides of the re-
sulting embos~ed plastic sheet was about 13:1 and the ratio of
the height of the main ribs to the thickness of the webs between
- 28 -
31~4
the main ribs was 5O1. The embossed sheet was then stretched totwice its width in a tenter at 80Co during which operation reg-
ular voids or openings were formed between the main filaments.
The sheet was then drawn linearly 9.2 times its length by passing
it over a series of differential speed rolls heated to 120C.
The weight of the network structure so formed was 0.45 ounce per
square yard~ The uniformly oriented main filaments were about
160 denier in size. This network structure had a tensile strength
of 22 pounds per inch in the machine direction and an elongation
of 12 percent. The strength in the cross~machine direction was
0O8 pound per inch and the elongation was 22 percent~ It had ex-
cellent tear resistance in the cross-machine direction having a `~
value of 50 pounds when tested by the Finch edge tear methodO
E ~
A cross-laid fabric was prepared by bonding the network.
structure of Example l to a similar network structure having-the
main filaments in the cross-machine direction by pressing the two
networks between steel platens in a compression press at a temper-
ature of 270Fo A pressure of 15 p~ s o i o was applied for 15 sec-
2d onds. The fabric so prepared had a weight o 0O7 ounce per.squareyard and a strength of lO pounds per inch in one direction and lO
pounds per inch in the opposite direction, the elongation being
12 percent in each caseO The fabric had excellent tear resistance
in both.directions, giving a value of 25 pounds in the machine
direction and 25 pounds in the cross-machine direction when tested
by the Finch edge tear.method Its Mullen burst strength was 35
p.s.i.
E ~
High density polyethylene with a melt ind~x of lO was
extruded at 450F~ through a slit die 18 inches long and with an
opening 15 mils wide. The molten sheet was passed int.o the nip
of two chrome-plated steel embossing rolls, one 4 inches in di-
ameter, the other 6 inches in diameter, each being 15 inches and
20 inches long respectively~ The 4 inch roll had an embossed
- 29 -
3~7~pattern consisting of a plurality of grooves around the roll with
a spacing of 75 grooves per inch, with the grooves on the roll
being at an angle of 45 to the longitudinal axis of the roll.
The 6 inch roll had an embossed pattern consisting of a plurality
of grooves around the roll with a spacing of 250 grooves per
inch, with the grooves on the roll being also at an angle of 45
to the longitudinal axis of the rollO The temperature of these
rolls was internally controlled to maintain around 150Fo The
molten sheet was then passed between the two rolls at a rate of
20 feet per minute and had a thickness of 5 milsO A sheet was em-
bossed containing 75 main ribs per inch in the oblique direction
on one side with the ribs being separated by grooves 5 mils wide.
On the other side of the sheet the tie ribs were formed with 250
tie ribs per inch with each pair of ribs being separated by grooves
l mil wide~ The ratio of the cross~section of the main ribs to
the tie ribs was about 13 and the ratio of the height of the main
ribs to the thickness of the webs between the main ribs was 3.5:1
The embossed sheet was fed into a linear draw roll which was heated
to 120Co at a speed of 50 feet per minute and it was stretched to
three times its length. The sheet was then fed into a tenter heated
with circulating air to 110Co at a speed of 150 feet per minute
and it was stretched to 3~0 times its width~ In this operation, it
opened into a uniform network structure~ the grooves between the
main ribs becoming openings or voids crossed by oriented tie fil
aments-with the main filaments now separated by abou~ 15 mils. The ! ~,
sheet was then drawn in the linear direction once more by passing
it in frictional contact with a series of 11 steel rolls heated to
120Co and moving at progressively increasing speeds The sheet
was fed in at 115 feet per minute and exited at 150 feet per rnin-
ute and accordingly was drawn 1~3 times in its length in the
machine directionO The resulting network structure had a weight
o~ 0O35 ounce per square yard~ The uniformly oriented main fil-
aments were about 90 denier in siæe.
30 -
31q~ ~
It is to be understood ~hat the above described embod
iments are merely illustrative of applications of the principles
of this invention and that numerous other arrangements and mod-.
ifications may be made within the spirit and scope of the
invention,
::
'
. . '
. - 31 -
