Note: Descriptions are shown in the official language in which they were submitted.
11~478~
This invention relates to scrim-reinforced plastic film and
a process for the preparation thereof, and particularly to such film
having improved strength properties, the film being advantageously
adapted for use in preparing various types of containers, such as
envelopes, bags etc. The reinforced film material exhibits the looks
and feel of a strong material as well as being stronger than the un-
reinforced material.
Methods for the preparation of scrim-reinforced plastic
sheet are well known in the art. Since plastic materials currently
available commercially lend themselves advantageously to a wide
variety of uses and particularly in the packaging of consumer goods,
there has been an ever-increasing emphasis on developing means to
further enhance the strength properties of such materials. Thus,
tensile strength, tear and impact resistance, moisture-proofing and
the like are especially important properties as regards container
utility. The use of scrims, these usually comprising web material
formed of spaced-apart strands of high strength thermo-plastic res-
inous material~ to reinforce plastic sheets has proved particularly
effective in augmenting tensile strength, tear resistance and the
like. Additionally, it has been found that a reinforced material,
whether in the form of sheet or bags is more appealing to the con-
sumer and more saleable if the reinforcement is readily discernible
both visually and tactilely. One method commonly used for the prep-
aration of scrim-reinforced plastic sheet involves sandwiching a
scrim member between two sheets of thermoplastic material the assem-
bly thereafter being heatbonded by various means, e.g., contacting
opposed sides of the sandwich assembly with heated platens~ radiant
heating etc.
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Thus, one such method involves the radiant heating of the edge
portions of plastic material folded back on a scrim member to
form an envelope portion. Other methods involve, for example,
the application of adhesive to the scrim or web and/or the inner
surfaces of the plastic sandwiching elements and pressure-sealing
the elements together; extruding one or more layers of thermo-
plastic material onto a supported scrim or web i.e., provided
with a thermoplastic backing layer.
Methods of the aforedescribed type entail significant dis-
advantages. Thus, the use of heated rollers invariably results in
an undesirably thin enclosing plastic film; moreover, the combined
heat-pressure effects often causes structural weakening of the
film and particularly in the critical areas situated outside
of the strands. Extrusion of plastic onto a supported web or
scrim requires the use of a plastic backing or supporting sheet.
Thus, there may be significant differences in the strength char-
acteristics as between the opposed plastic members sandwiching
the web. Bonding can occur between the outer plastic elements,
or between each of these and the intermediate web which can pro-
duce sub-optimum strength characteristics in the product.
The foregoing methods require formation of a sandwich
type element wherein the outer plastic layers are separately provided.
This requires rather burdensome techniques for carrying out contin-
uous operations. This aspect combined with the sub-optimum strength
characteristics often obtained in the final product underscore
the need for more effective methods for preparing reinforced plas-
tic sheets. The prior art methods, typically do not provide the
reinforced material with the appearance and feel of reinforce-
ment and therefore might not be appealing to -the consumer.
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Thus, a primary object of the invention is to provide a method
for preparing reinforced plastic sheets wherein the foregoing
and related disadvantages are eliminated or at least mitigated
to a substantial extent.
Another object of the present invention is to provide
such a method particularly advantageously adapted to continuous
processing.
Yet another object of the invention is to provide such
a method wherein any necessity for the use of heated pressure mem-
bers such as platens to effect the bonding operation is eliminated.
Still another object of the invention is to provide such
a method advantageously adapted to be carried out in conjunction
with an extruder.
A further object of the invention is to provide such a
method capable of producing a reinforced plastic sheet having im-
proved strength properties including, tensile strength, tear re-
sistance, impact resistance and the like.
A still further object of the invention is to provide
such a method which can readily be integrated with a process for
producing plastic containers such as envelopes, containers, etc.
Yet a still further object of the invention is to provide a
reinforced plastic sheet material having significantly improved
strength characteristics.
A still further object of the invention is to provide a
scrim reinforced plastic sheet wherein the scrim reinforcement is
apparent both visually and tactilely.
Other objects and advantages of the invention will be-
come more apparent hereinafter as the description proceeds.
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781
The foregoing objects are attained in accordance with
the :invention which in its broader aspects provide a process
for preparing a scrim-reinforced film comprising contacting
molten plastic in a state of high fluidity with an unsupported
scrim, said plast~c flowing into and around the scrim network,
cooling said plastic to solidify same to produce a scrim at
least substantially completely enclosed and surrounded by said
plastic such that the thickness of the plastic material at
intersections of strands in the scrim is at least 50% greater
than the th~ckness of the scrim at such intersections and the
thickness of the plastic material on the strands is from 1/2 mil
greater than the strand thickness, and subsequently shrinking
said plastic material to a greater degree th.an said scrim, the
plastic material being heat shrinkable to a greater degree than
the scrim mater~al.
In accordance with a preferred em~odiment, the molten
plastic comprises the extrudate from the discharge orifice of
an extruder, and is fed to a contact zone to contact the
unsupported scri.m the di.stance between the discharge orifice of
the extruder and the contact zone being such that the tempera-
ture of the ~olten extrudate as it contacts the scrim is at
least about 400F and preferably at least about 600F. Accord-
ing to a preferred embodiment of the invention, the scrim method
comprises two sets of syntheti.c plafitic fibers or strands
disposed at an angle to each other, preferably transversely.
Each. set of strands i.ncludes a plurality of uniformly spaced,
parallel fibers. The strands can be from about 1 to about 20
mils thick in their largest cross sectional di.mension, prefer-
ably from about 3 to about 8 mils. The fibers can be present
in an amount of 1 to 5 fibers per inch per direction.
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In accordance with a further specific aspect of the
invention, there is provided a reinforced plastic sheet material
comprising a scrim including two sets of angularly disposed
intersecting strands, each set comprising a plurality of uni-
form:Ly spaced strands, and a continuous film of plastic material
which is heat shrinkable to a greater degree than the scrim
material covering both sides of said strands and extending
between said strands such that the thickness of the plastic
material at the intexsections of the strands in the scrim is
10 at lea5t 50% greater than the thickness of the scrim at such
intersecti`ons and the thickness of the plastic material on the
strands i5 from 1~2 mil greater th.an the strand thickness, a
plurali.ty of said strands being buckIed between the points of
intersection o~ sald inter5ecting strands and lying out of the
plane of said film.
Preferably, the thickness of the scrim network at
points of inters.ection of the strands is at least about 50
percent greater than the thickness of the strands. To provide
the desixed tactile sensation of reinforcement, according to
this aspect of the invention, the thickness of the film measured
between
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strands i.e. in the interstices formed by the strands is less than the scrim
thickness at the intersection of the strands and at least half as great as
that of the fibers.
In accordance with a further specific aspect of the invention, a
method is provided to import a nubby or rough character to the scrim rein-
forced product that is both visible and tactilely discernible. In this re-
gard, the new method includes the step of heat shrinking the film component
of the scrim reinforced product by heating the product to a temperature be-
tween about 180 F and 225F and cooling to room temperature. The heat
shrinking step functions to bend or distort the scrim fibers, which are of
a non-heat shrinkable material, out of the plane of the film to create a
rough surface that is both tactilely and visually discernible by the user of
the product. The scrim fibers are bent out of the plane of the film because
the shrinking film draws the scrim intersection closer together, thereby
forcing the fibers to bend. According to this aspect of the invention, the
scrim fibers when plastic are made by a process including the step of heat
setting which releases stresses, and result in plastic fibers that exhibit
virtually no shrinkage when exposed to heat and cooled. The film material
which should be a heat shrinkable substance can be supplied as a preformed
film that is heat sealed or adhesively sealed to both sides of the scrim or
it can be extruded onto the scrim according to the invention and subsequently
heat shrunk to bend the scrim fibers and create the desired rough or nubby
surface pattern.
The foregoing characteristics of the new reinforced material pro-
vides not only an actual and substantial increase in the strength of the ma-
terial but also imparts the appearance and "feel" of strength to the product.
The invention is illustrated but not limited by reference to the
accompanying drawing herein:
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47~31
Figure 1 - is a schematic view of an embodiment of the invention
for producing a scrim-reinforced plastic sheet from a molten extrudate,
Figure 2 - is a sectional view taken along the line 2-2 in "Figure
1", before the scrim-reinforced plastic sheet is heat shrunk;
Figure 3 - is a plan view, shGwn partly broken away illustrating
the scrim-reinforced sheet folded longitudinally prior to the cutting
operation for forming the container;
Figure 4 - is a plan view illustrating schematically the cutting
operation for forming the product bag container;
Figure 5 - is a perspective view illustrating the product container;
Figure 6 - is a sectional view taken along the line 2-2 of Figure
1 after the scrim-reinforced plastic sheet of Figure 2 is heat shrunkO
The invention will now be described by reference to the accom-
panying drawing wherein like reference numerals designate similar parts
throughout the views. "Figure l" illustrates an arrangement of apparatus
for carrying out a preferred embodiment of the invention wherein a molten
plastic extrudate lO from the discharge orifice 12 of an extruder (illus-
trated partially) and generally designated 14 is directed onto a scrim
or netting 16 carried by nip roll 18. Molten extrudate 10 contacts scrim
16 shortly prior to the latter entering the bite provided by chill roll
20 and nip roll 18, these members being positioned so as to tangentially
engage opposed sides of the scrim and applied extrudate while the
latter is in molten condition. It is essential in the practice of the
present invention that the molten plastic extrudate, preferably a film-
forming, thermoplastic heat shrunkable polymeric material to be described
in greater detail hereinafter, be in a molten, highly fluid state ~hen it
contacts the scrim material. In general, the "contact" temperature of the
molten plastic extrudate should be at least about 400F and preferably
at least about
~478~
600F for optimum results and particularly for assuring a scrim-reinforced
product wherein the scrim is completely enclosed and surrounded by the solid-
ified plastic extrudate. The upper limiting contact -temperature of the mol-
ten extrudate is not particularly critical apart from the requirement that it
not exceed the decomposition point o~ the particular plastic material em-
ployed. It is generally recommended that the speed of the nip roll be regu-
lated to provide a linear scrim speed of from about 500 to 1,000 ft/min. as
the scrim 16 passes between chill roll 20 and nip roll 18. Within the lower
portion of the linear speed range stated, it is recommended that the temper-
ature of the molten extrudate be maintained within the higher range and/orthe distance between the discharge orifice 12 of extruder 10 and the point of
contacting the molten extrudate with the scrim be decreased. Conversely,
within the higher range of linear scrim speed, it is recommended that the
molten extrudate temperature be maintained within the lower range and/or the
distance between discharge orifice 12 and the scrim-molten extrudate contact
point be increased. These factors can readily be determined in a particular
instance having reference to the type of plastic material employed. Thus,
operation within the aforestated parameters assures that the molten plastic
extrudate in a relatively high state of fluidity flows into and around the
scrim network, i.e., the interstices defined by the strands comprising the
scrim. This results in the scrim being completely enclosed and surrounded
by the extrudate plastic subsequent to cooling and solidification, thereof,
this being illustrated, for example, in Figures "2" and "3". Scrim member 16,
after contacting molten extrudate 10, is passed between the bite provided by
chill roll 20 and nip roll 18 each tangentially engaging opposed sides of the
scrim. The width of the bi-te can be adjusted to provide the desired thick-
ness of the reinforced product 22.
The temperature of chill roll 20 should be such as to cause sub-
stantial solidification of the molten extrudate 10 whereby to render same
substantially non-flowable as the scrim assembly exits from the bite of chill
X
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roll 20 and nip roll 18. The temperature of chill roll 20 is related to the
temperature of molten extrudate 10, the linear or coating speed of scrim 16
as we]l as the distance between the latter and the discharge orifice 12 of
extruc1er 14. As the coating speed and/or molten extrudate temperature is in-
creased, the chill roll temperature is preferably decreased. The scrim-re-
inforced assembly 22 is thereafter removed from chill roll 20 by any suitable
pickup means (not shown) for further processing (optional) such as the con-
tainer-formine operation to be described in more detail hereinafter.
Referring to Figure "2", the scrim-reinforced plastic sheet 22 is
shown prior to heat shrinking of the film component according to the inven-
tion. The product comprises a scrim member 16 that includes two angularly
disposed sets of strands 16a and 16b. Each set includes a plurality of
strands uniformly spaced to provide about 1 to 5 strands per lineal inch.
Each strand 16a, 16b is from about 1 to about 20 mils thick, preferably from
3 to 8 mils. As shown in Figure "2", the thickness of the scrim at the inter-
section of the strands, 16c is at least 50 percent greater than the thickness
of the strands, to provide "~ubs" that are both visible and feelable. In
combination with the increased "~ub" thickness, the thickness of the extruded
film in the interstices between the strands and the thickness of the film
covering the strands is at least 1/2 mil and is preferably from 1/2 the
strand thickness to the strand thickness. The thickness of the film can be
the same in the interstices 16d between strands and on the strands, or differ-
ent within the foregoing limits. The thickness of the extruded film in the
interstices between the strands and the thickness of the film covering the
strands is at least 1/2 mil. The thickness of the film can be the same in
the interstices 16d between strands and on the strands, or different. Refer-
ring to Figure 6, the scrim reinforced plastic sheet 22 of Figure 2 is shown
after the film component thereof has been heat shrunk according to the inven-
tion. Since the scrim fibers according to this aspect of the invention are
substantially less heat shrinkable than the plastic film material, the fibers
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are bent by the shrinking of the film in which they are securely embedded.
In producing the fibers, stresses should be relieved to render the fibers,
virtually non-heat shrinkable or at least substantially less heat shrinkable
than the film material. The film material extruded according to the method
shown in Figure 1 and described herein, is 1aid down in one direction and
would be heat shrinkable in that direction due to the stresses set up during
the extrusion process.
A product similar to that shown in Figure 6 can be alternatively
made from a laminate of preformed outer layers of a heat shrinkable film and
an inner layer of scrim material that is substantially less heat shrinkable
than the film. The film and s^rim layers can be heat or adhesively sealed to
each other and subsequently heat shrunk.
According to this aspect of the invention, the film material is
typically stressed in one direction when produced and accordingly heat shrinks
in that same one direction to relieve these stresses. When preformed film is
utilized the film components on either side of the scrim should be oriented
so that they heat shrink in the same direction. Film extruded onto the scrim
is inherently aligned in the same direction. In this regard, when the film
layers are heat shrunk the fibers of the scrim parallel to the heat shrunk
direction are buckled, while the transversely dispersed fibers are unaffected,
i.e., unbuckled.
The heat shrinking step includes heating the scrim reinforced ma-
terial of Figure 2 to a temperature between about 180 F and 225 F and cooling
to room temperature. The shrinking of the film without a corresponding degree
of shrinking of the fibers results in a bending of the fibers out of the
plane of the film and provides the desired nubby or rough appearance and feel
as shown in Figure 6.
The plastic material used in forming the molten extrudate 10 can
be selected from a wide variety of materials well known in the art generally
including preferably thermoplastic polymeric materials commonly used in the
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manufacture of plastic bag containers. Preferred for use herein are poly-
ethylene and polypropylene materials capable of forming heat sealable films.
Other suitable materials include without necessary limitation polyvinyl
chloride, copolymers of vinylidene chloride with vinyl chloride, polyacryl-
ates, copolymers of styrene and acrylonitrile~ cellulose triacetate, cellu-
lose acetate butyrate, polyurethane elastomers, polystyrene, polyolefins in-
cluding homo and interpolymers; generally, thermoplastic polymeric material
capable of forming a continuous film on drying from a solvent solution thereof
are usable herein, exemplary of synthetic fibers useful herein; useful fi-
bers of the natural type include, without limitation, cotton, wool, hogshair, horse hair, vicuna and the like. Suitable materials available commer-
cially include the plastic netting available under the trademark "Vexar" man-
ufactured by E.I. du Pont de Nemours & Company which may be prepared from
high density polyethylene, low density polyethylene, blends of high and low
density polyethylene, polypropylene, polybutylene copolymers of ethylene and
propylene and blends of polyethylene. The fiber material may comprise twist-
ed and/or untwisted multifilamentary material, the range of twist ranging
from about one-half to 20 turns or more per inch. The strands, as stated,
may be of any desired mesh design such as the rectangular configuration illus-
trated in Figure "3" and may be of the woven or non-woven type. Usually,
there are provided from 1 to about 10 strands per inch with a range of from
3 to 4 strands per inch being particularly preferred. Although scrims of
varying thickness and patterns may be used, it is nevertheless, preferred
that the scrim weight be from about 1 to 2 lbs./Mft. . In accordance with a
particularly preferred embodiment in terms of cost and performance, the
thermoplastic material comprising the molten extrudate is polyethylene while
the scrim material comprise polyæropylene, preferably of the oriented type
as is well known in the art.
As explained, the process is preferably carried out utilizing an
extruder for producing the molten form of the film forming plastic material.
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9L78~
However, it will be understood that other methods may be effectively employed
for provid;ng the requisite form of the molten plastic e.g., in the form of a
molten extrudate. Moreover, other methods for forming the solidified, coated
scrim assembly can be used such as an air knife coating technique utili~ing
cold air to effect cooling and solidification of the mol-ten plastic. In any
event, the essential cri-teria is the fluidity of the molten plastic at the
time it contacts the scrim network. As explained previously, the extruding
parameters should be chosen to effect at least substantial solidification of
the molten plastic by the time it emerges from the bite of chilling roll 20
and nip roll 18. Thus, as the scrim speed and/or molten plastic temperature
is increased, the temperature of the chilling roll should correspondingly be
decreased consistent with the foregoing requirements.
The scrim-reinforced plastic sheet produced as described is par-
ticularly advantageously adapted to be formed into plastic bags of signifi-
cantly improved strength. Thus, by virtue of contacting the molten plastic
as described with an "unsupported" scrim, the quoted term connoting the ab-
sence any backing or support sheet whatsoevér, there is obtained a sheet
product having improved impact strength, tear and -tensile strength. For ex-
ample, when processed as described herein, it is found that the scrim imparts
strength improvements of 33% in impact, doubled tear and quadrupled breaking
strength. Plastic bag containers fabricated with the thus-reinforced plastic
sheet material are accordingly capable of accommodating larger payloads,
under higher stress conditions for longer periods of use. Moreover, since
any requirement for a backing or support sheet is eliminated, the reinforced
sheets are more economical to manufacture than the scrim-reinforced materials
heretofore provided. One of the particularly surprising and unexpected ad-
vantages of the present invention is the fact that the product sheet material
exhibits vastly improved strength properties despite the fac-t that a backing
or support sheet is not used. In addition to reducing cost, this aspect en-
ables the sheet forming processing to be simplified significantly leading to
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~34781
even greater savings.
The scrim-reinforced fllm 22 is collected by any suitable means,
not shown, from chill roll 20 and folded longitudinally upon itself as illus-
trated in Figure "3" into equal half sections. This can be accomplished, for
example, by any conventional folding means as is well known in the art. In
-this manner, the film 22 of original width W (Figure 3) is divided into sec-
tions 28 and 30 (Figure 5) of width W/2 by means of longitudinal fold 32.
The film 22 is transported in the direction indicated by arrow in Figure "3"
to a hot knife member generally designated 34 comprising a blade portion 36
rotatable about an axle portion 38 in the direction indicated. The hot knife
is maintained at a temperature which is sufficient to effect fusing i.e.,
heat bonding of Sections 28 and 30 along the cutting locii of the hot knife
as illustrated at 40 and 42, Figure "5". The rotary speed of Blade 36 and
the linear speed of film 22 in the direction indicated by arrow 34 are con-
trolled so that cutting is effected at predetermined portions of film 22 to
produce plastic bag containers such as illustrated in Figure "5". Thus, heat
sealed side portions 40 and 42 in combination with the bottom portion formed
by longitudinal fold 32 provide a restraining portion 44 for accommodating
various types of articles e.g., as part of a packaging operation, articles
20 normally accumulated during shopping, or as a trash container, etc. ~he di-
mensions of the plastic bag container can be varied as desired by for ex-
ample, appropriately controlling the rotary speed of hot knife 34 and/or the
linear speed of film 22.
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