Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention eelates ~enerally to reinforced composite
structures that are formed by combining thermoplastic poly-
meric sheets and polypropylene netting by lamination or extru-
sion coating. The film of this invention has a unique combin-
ation of properties including strength and tear resistance.
It is known to laminate or extrusion coat woven or non-
woven fa~rics with thermoplastic films to increase their
resistance to moisture and gas permeability and to obtain a
reinforced film. However, in the case of polypropylene fab-
rics and netting, most thermoplastic materials that were pre-
viously known to adhere well to the polypropylene fabrics,
such as low molecular weight polypropylene and copolymers or
grat polymers of polypropylene, cause excessive shrinkage and
distortion of the fabrics or netting at the temperature
required for bondin~. In polypropylene fabrics and netting,
the polypropylene components are oriented and will shrink or
become distorted on exposure to the high temperatures required
to coat or laminate them with molten polypropylene or with the
modified polypropylenes that are known to adhere well to such
components. It has now been discovered that crystalline ran-
dom copolymers of propylene and l-butene, melting low enough
so that such fabric distortion can be avoided in preparing
such laminated structures, will adhere well to polypropylene.
Use of such copolymers, therefore, makes possible preparation
of improved reinforced composite structures using polypropyl~
ene netting.
It is also known, for instance, from U.S. Patents
3,914,365 and 4,144,368, to form multilayer products by lami-
nating two or more layers o~ polypropylene netting having the
same or different configurations so that the main filaments
. ~
-- 2 ~
cross in various directions. Another ref~rence which dis-
closes the lamination of extruded net ~abrics under pressure
and heat or by cementing is U.S. 2,919,467. Disadvantages of
such known laminates include low burst, tear and tensile
strength, and a tendency to delaminate when bonded at tempera-
tures at which the orientation strength and configuration of
the polypropylene netting is retained.
According to the invention, a reinforced composite struc
ture comprising a layer of oriented polypropylene netting to
which is bonded a thermoplastic polymer sheet is characterized
in that the sheet consists of a random copolymer having
bet~een 7% and 30~ l-butene and between 93~ and 70% propylene,
the copolymer having an intrinsic viscosity of between 1.1 and
4Ø According to a preferred modification of the invention,
a second layer of oriented polypropylene netting is bonded to
the thermoplastic copolymer sheet so that the said sheet is
between the two layers of netting. ~1hen two layers of ori-
ented netti~g are employed, preferably each netting layer has
main filaments in one direction and smaller connecting fila-
ments in the opposite direction, and the netting layers arearranged so that the main filaments of one of the netting
layers are essentially perpendicular to the main filaments of
the other netting layer.
Also according to the invention, a process of making the
composite structure according to the invention comprises dis-
posing a layer of thermoplastic sheet material in contact with
a layer o~ oriented polypropylene netting and applying heat
and pressure, characterized in that the sheet material is the
copolymer defined in Claim 1 and the temperature of heating is
approximately 5 above the crystalline melting point of the
copolymer and not more than 150C. Preferably, the sheet
material is a film having a thickness between .25 and 4 mils.
The invention may be adapted to provide either an imper-
forate laminate in which the integrity of the sheet material
is maintained, or a netting structure in which the permeabil-
ity of the netting is retalned to a large degree, depending on
whether unoriented or biaxially oriented polymeric sheet
-- 3
material is selected for bonding to the netting. Therefore,
either a netting reinforced film structure or an open-weave
reinforced netting can be produced according to the invention.
If an open-weave reinforced netting is desired, the ori-
ented thermoplastic sheet material shrin~s under the condi-
tions of the lamination and opens up between the strands of
the netting so as to provide an open net in which the shrunken
copolymer sheet acts as a reinforcement to improve tear-resis-
tance. If two or more layers o~ netting are use~, it also
acts as a bonding agent between the layers.
Referring to the drawings in detail, there is illustrated
in FIG. 1 a netting reinforced film structure 10 comprising a
layer of oriented polypropylene netting 12 bonded to a layer
of unoriented propylene/l-butene copolymer film 14. The net-
ting layer 12 preferably has main filaments 16 and tie fila-
ments 18. Combining layers 12 and 14 in a continuous manner
efficiently provides a product that is suitable for applica-
tions requiring strength and low moisture and gas permeabil-
ity, such as bagging, other packaging applications, tarpau-
lins, and geotextiles.
The embodiment of FIG. 2 depicts an open weave reinforcednetting lOA comprising a layer of nonwoven continuous linearly
oriented polypropylene netting 12A bonded to propylene/l-
butene copolymer 14A. The latter is formed from a thin biaxi-
ally oriented film of tlle copolymer under conditions of bond~ing such that the copolymer contracts until it essentially
conforms to the open-weave of the netting. ~etting layer 12A
preferably has main filaments 16A and tie filaments 18A.
Combining layers 12A and 14A in a continuous manner can
provide a product that is suitable for such applications as
kraft paper reinforcement or reinforcing scrim for plastic
film, and that can be used, for instance, as furniture skirt
liners or duster covers.
FIG. 3 shows the use of apparatus for continuously pre-
paring the netting-reinforced film shown in FIG. 1. A poly-
propylene netting layer 22 and a layer of unoriented thermo-
plastic copolymer film 24 being fed from supply rolls 2~ and
28, respectively, to rolls 30l 32 and 34. Preferably, rolls
30 and 32 are made of steel covered with a TeflonR polymer-
glass cloth. They are heated to a temperature within the
range of 100C. to 150C. Roll 32 is a steel roll covered
with silicone rubberO
FIG. 4 shows the apparatus of FIG. 3 being used for con-
tinuously preparing the open-weave reinforced netting shown in
FIG. 2. The thermoplastic netting layer 22 and a layer of
oriented thermoplastic film 36 are fed from supply rolls 26
and 28, respectively, to the rolls 30, 32 and 34, of the ver-
tical calender stack shown in FIG. 3. Under the pressure and
heat supplied by the rolls, the film adheres strongly to the
netting and opens due to shrinkage so that the copolymer is
essentiall~ confinecl to the filaments and crossover points of
the netting.
FIG. 5 shows another embodiment of the subject invention
where a three-layer reinforced structure 38 is shown. The
interlayer 40 represents an unoriented thermoplastic propyl-
ene/l-butene copolymer film. Outer layer 42 is a layer of
polypropylene nonwoven netting having main filaments 44 and
tie filaments 46 which are orthogonal to main filaments 44~
The other outer layer 48 also consists of a polypropylene non-
woven netting. Layer 48 has main filaments 50 and tie fila-
ments 52 which are orthogonal to main filaments 50. Outer
layers 42 and 48 are orthogonally oriented with respect to
each other wherein, for example, the main filaments 44 of
outer layer 42 are at a 90 angle to main filaments 50 of
outer layer 48. Since the main filaments of the nonwoven
netting layers may have higher strength properties as com-
pared to the respective tie filaments, the orientation oflayers 42 and 48 in the reinforced structure 38 can provide
substantially enhanced stren~th characteristics.
FIG. 6 shows, schematically, a method ~7hich can be used
for the manufacture of the reinforced film sho~7n in FIG. 5.
For that purpose, a netting layer 54 is supplied from supply
roll 56 and another netting layer 58, having its main and tie
filaments at a 90 angle to the main and tie filaments of
-- 5 --
layer 54, respectively, is fed from supply roll 60. Unori-
ented or oriented thermoplastic copolymer film 62 is fed from
supply roll 64 to form the bonding member of the laminate.
Optionally~ unoriented film 62 can be supplied directly from
an extruder. The three layers pass over heated roll 66, into
the nip of heated pressure rolls 68 and 70 wherein the three
layers are bonded together. The reinforced structure 72,
which may be a netting-reinforced film as shown, or an open-
weave reinforced netting, if oriented, copolymer film is used,
then is fed to a take-up spool (not shown).
Typically, the process shown in FIG. 6, utilizes tempera-
tures of the first two rolls between 100C. and 150C., at nip
pressures between 50 and 500 pounds per inchO Such a lamina-
tion process, when unoriented film is used, can also be car-
ried out in a compression press at temperatures ln the sameran~e and at moderate pressures, i.e., over 10 p.s.i. for
short periods of time such as 10 seconds or more.
Optionally, a three-layer netting-reinforced film can be
produced with a layer of netting between two layers of film.
Such a reinforced structure might be useful for trash bags,
for instance.
When oriented copolymer film is used in the method shown
in FIG. 6, a blower can be used to blow air on the laminated
fabric 72 after it exits the nip created by rolls 68 and 70.
The air emerging from a blower and impinging on the laminated
fabric 72 while it is still hot, aids in assuring that the
oriented film will open subsequent to the application of heat
and pressure to maintain the permeability of the netting. The
thickness of the layer of the copolymer between or on the fil-
aments of the polypropylene netting is preferably betweenabout 0.25 mils and about 1.0 mil.
FIG. 7 shows a preferred method for preparing a three
layer structure, involving two layers of oriented polypropyl-
ene netting bonded to a propylene/l-butene copolymer. This
method includes extruding the copolymer as a sheet between two
layers of netting and bonding the netting to the copolymer
sheet in the nip of the two rolls. As shown in FIG. 5, net-
ting layer 74 is supplied from supply roll 7~. Netting layer
~ 7~
-- 6 --
78 is fed f~om supply roll 80. Unoriented polypropylene filtn
82 is supplied from extruder (not shown) through ~ie 86. The
film 82 contacts netting layers 74 and 78 in the nip created
by counter-rotating rolls 88 and 90. Roll 88 is preferably
made of rubber and coated with TeflonR polymer. The temper-
ature oE roll 88 and chill roll 90 should be below 150C. to
avoid shrinkage or distortion of the netting layers and to
effect cooling of the film after it is bonded to the layers of
netting. The extrusion temperature should be above the crys-
talline melting point o~ the copolymer and may be as hlgh as250Co A moderate nip pressure, e.g., in excess of S p.s.i.,
between rolls 88 and 90, is desirable to provide effective
contact between the three layers of the composite structure.
The product of the extrusion coating lamination 92 is fed to
a take-up spool (not shown).
A similar extrusion coating lamination process can be
used to form a two-layer structure consisting of a copolymer
sheet extruded onto a single layer of netting.
The thermoplastic film used in this invention, is formed
frorn a copolymer of propylene and l-butene containing approx-
imate 7% to 30% l-butene. This copolymer provides excellent
adhesion between t~70 layers of oriented polypropylene netting
at temperatures which do not cause a significant loss of ori-
entation of the polypropylene. The preferred materia]s are
random l butene/propylene copolymers which have crystalline
melting points significantly below the crystalline melting
points of polypropylene homopolymers, random ethylene-propyl-
ene copolymers containing up to 10% ethylene or block copoly-
mers containing up to 25% ethylene. The C3-C~ copolymers
are compatible with and adhere well to polypropylene and C2-
C3 copolymers and thus form an extremely good bond, without
requiring melting or loss of orientation of the propylene
homopolymers or C2-C3 copolymers. Preferably the l-butene
content may range from 8 to 20%. The crystalline melting
points of the copolymer containing 8~ butene is about 140C,
while the copolymer containing 18Qo butene has a crystalline
melting point of about 130C. The thermoplastic copolymer
7~i
film should hav~ a thickness between about 0.25 and 4 mil,
preferably between about 0.25 mils and 2 mil.
The oriented polypropylene netting or network structures
used in this invention may be of the types disclosed in the
prior art, for example, Mercer (U.S. Patents 4,020,208 and
4,059,713); Larsen (U.S. Patent 4,152,479); Kim et al (U.S.
Patents 3,914,365 and 4,144,368), and Liu (U.S. Patent
4,140,826) D
l'his netting may be composed of either a polypropylene
homopolymer, a propylene-ethylene random copolymer containing
2% to 10% ethylene or a propylene ethylena block copolymer
containing 2% to 25~ ethylene and may be either natural or
pigmented.
Preferably the netting should have uniform n~twork
structure and hole size, spacing and design of the two nets in
a laminate should be similar. Uniform network structure means
that in each layer of netting, there are at least two sets of
strands wherein each set of strands crosses another set of
strands at a fixed angle and the openings in the netting are
~0 uniformly sized. Preerably, the average minimum dimension of
the openings in each layer of netting is between 0.5 millimeters
and 5 millimeters. Preferred types of thermoplastic netting
useful in this invention are disclos0d in U.S. Patents
4,144,368 and 4,207,375 to Kim et al.
The network structure used in this invention may include
one or more layers of nettingO When two or more layers of
netting are employed, the netting may have the same or differ-
ent configurations such that the main filaments cross in vari-
ous directions to provide a multilayer product having certain
desired strength characteristics. For example, orthogonal
constructions can be made wherein the main filaments of one
layer cross at 90 to the main filaments of another layer to
provide high strength and tear resistance in two directions.
Stxuctures may also be madP from three or more layers of net-
works, each having the main filaments in diferent directions
`715
-- 8 ~
thus providing laminates having excellent dimensional stabil-
ity, high strength and tear resistance in all directions and
high hurst strength.
In order to provide the shrinkage properties which assist
in forming an open network structure durlng the lamination
with polypropylene netting, the propylene-butene copolymer
film must be biaxially oriented, i.e., drawn in perpendicular
directions, at a temperature below its crystalline melting
point. Such orientation increases its strength and provides a
thin film which shrinks, on heating to temperatures approach-
ing the orientation temperature and on subsequent melting.
Such orientation can be carried out by sequential operations
which normally involve a combination of machine direction
stretching between differential speed rolls and lateral
stretching using a tenter, or may be carried out simultane-
ously by lateral expansion of a tube of the plastic by air
blowing while it is being drawn linearly. Such processes are
well known and are not part of this invention.
The oriented films may be from about 0.25 mils to about
2 mils in thickness, and preferably from about 0.25 to about
1 mil in thickness.
Shrinkage properties of oriented films of copolymers of
propylene and l-butene are given in Table I, showing the
effect of the composition and of the degree of orientation on
films made from copolymers with various monomer ratios. It
is apparent that the degree of orientation and the orientation
temperature have a significant effect on the strength and
shrinkage properties of the films.
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Having set forth the general nature of the invention, the
following examples lllustrate some specific embodiments of ~he
invention. It is to be understood, however, that this inven-
tion is not limited to these examples since the invention may
be practiced by the use of various modifications.
Example 1
In this example, the netting components were of polypro-
pylene and were in the form of linearly oriented continuous
filament ortho~onal networks. Two layers of the same type of
netting were used in each test, one with strength primarily in
the machine direction (r~D) and one with strength primarily in
the cross-machine direction (TD). The film used in this exam-
ple was made from a propylene/l-butene copolymer containing
14% butene, and having an intrinsic viscosity of 1.1. The
film had a thickness of 2 mil. The netting layers and the
film were arranged to produce the laminate structure shown in
FIG. 3.
The polypropylene netting employed had main filaments 150
microns in diameter and tie filaments 25 microns in diameter.
There were 5 main filaments per centimeter and 10 tie fila-
ments per centimeter so that the openings in the nets were
about 1.3 by 1.2 millimeters across in the two perpendicular
directions. These nets had a weight of 20 grams per square
meter. The Frazier air permeability of the netting was 1144
ft3/min/ft2 (CFM).
This three layer structure was heated in a platen press
at 120C. under 38 p.s.i. pressure for 30 seconds. The pro-
duct so prepared was a strong reinforced film, resistant to
the passage of gas or liquids. A 180 T-peel test made
according to ASTM D1876, giving a value of 3 pounds per inch,
showed that effective adhesion of the two netting layers was
obtained.
Example 2
This example illustrates preparation of a reinforced film
by extrusion coating of a propylene/l-butene copolymer con-
taining 14~ l-butene onto a single layer of oriented polypro-
pylene netting. The netting employed was of the type used in
Example 1~ having main filaments oriented in the machine
direction. The netting layer was 18 inches wide. Using a
2-1/2 inch diameter plastic extruder with a 24:1 length to
diameter ratio and with a coathanger die 18 inches wide, a
random copolymer containing 8% l-butene and 92% propylene with
an intrinsic viscosity of 1.9 was extruded at 235C. The 2
mil thick film so extruded contacted the netting layer at the
nip between two 6 inch diameter rolls which were two feet
long. The roll corresponding to roll 88 in FIG. 5 was heated
to 50C. The other roll, corresponding to chill roll 90 in
FIG. 5, was heated to 30C. The pressure between the rolls
was 10 pounds per inch. The coated netting was wound onto a
take-up roll. The product was a reinforced film, resistant to
the passage of gas and li~uidr which was puncture and tear
resistant.
Examples 3-4
In these examples, the netting components were of poly-
propylene and were in the form of linearly oriented continuous
filament orthogonal networks. Two layers of the same type o~
netting were used in each test, one with strength primarily in
the machine direction (MD) and one with strength primarily in
the cross-machine direction (TD). Films used in each of the
examples other than the control experiment were of propylene/-
l-butene copolymer containing 14% butene with an intrinsic
viscosity of 1.1 which had been oriented six times in each
direction and having the thickness listed in Table II. The
netting layers and the film were arranged to produce the com-
posite structure prior to lamination shown in FIG. 3.
Two weights of polypropylene netting were employed. Type
A nets had main filaments 150 microns in diameter and tie fil-
aments 25 microns in diameter. There were 5 main ~ilaments
per centimeter and 10 tie filaments per centimeter so that the
openings in the nets were about 1.3 by 1.2 millimeters across
in the two perpendicular directions. These nets had a weight
of 20 grams per square meter. The Frazier air permeability
was 1144 ft /min/ft (CF~). The Type 3 nettings had main
filaments 100 microns in diameter and tie Eilaments 25 microns
- 12 -
in diameter. There were 10 main filaments per centimeter and
15 tie filaments per centimeter so the openings that were in
the nets were 0.9 by 0.7 millimeters across in the two perpen-
dicular directions. These nets had a weight of 12 grams per
square meter. The Frazier air permeability was 1240
ft3/min/ft2.
The laminating step was carried out by a continuous pro-
cess. The control sample and Examples l and 2 were processed
using a three roll vertical calender stackt similar to the
diagram of FIG. 4. The calender consisted of three 8-inch
diameter rolls, each of which was 44 inches wide. The rolls
corresponding to roll 68 and roll 70 in FIG. ~ were made of
steel covered with a Teflon-glass cloth. The gap between
these two rolls was adjusted to apply pressure of ~0 pounds
per linear inch. Roll 68 was oil heated to a temperature of
120C, and roll 70 was operated at 150C. The roll corre-
sponding to roll 72 was a steel rod covered with silicon rub-
ber and oil heated to a temperature of 80C. This roll was
adjusted in spatial relationship to roll 70 to provide a lin-
ear pressure of 30 pounds per linear inch. An air blower,which consisted of a pipe with a 25 mil slit, was used to blow
air at 80 psi onto the laminate after it eMerged from the nip
between rolls 70 and 72 in Example 2. Dwell time on the
heated roll surfaces was 10 seconds. The control sample was
processed without film under the same conditions as were used
with film present in the other examples.
Physical tests, the results of which are shown in Table
II, were performed according to ASTM standards, with the
exception of the seam strength test. For the seam strength
test, 2 in. x 4 in. specimens were cut from sheets of the lam-
inate. Then two of the specimens were placed face to face and
the 2 inch~long edges were joined by sewing 6 stitches per
inch, with cotton-wrapped polyester thread. The stitching was
placed a half-inch from the edge of the specimen and the
direction of stitching was the n test direction". The loose
ends of the sewing thread were tied to prevent unraveling.
- 13 -
The force in pounds per inch to cause seam failure was deter-
mined by drawing the test speclmen in a tensile tester at 12
inches per minute.
The results in Table II show that the laminated network
structures of the invention have good adhesion, substantially
improved seam strength and at least 20~ of the permeability of
the unlaminated network structure. In the tests of interlam-
inar adhesion, the netting of the laminated structure actually
tore before any separation of the netting layers occurred.
It is to be understood that the above description and
drawings are illustrative of this invention and not in limita-
tion thereof. As ~7ill be evident to those skilled in the art,
various modifications can be made in light of the foregoing
disclosure and discussion without departure from the spirit or
scope of the disclosure or from the scope of the claims.
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