Note: Descriptions are shown in the official language in which they were submitted.
POUCHES OF ETHYLENE-~-OLEFIN COPOLYMER/
ETHYLENE-VINYL ACETATE COPOLYMER BLENDS
The invention relates to pouches filled with flow-
able materials, e.g. liquids, particularly to pouches made on
so-called vertical form and fill machines.
It is well known to package plowable materials, for
example, milk, on a so-called vertical form and fill machine.
Using such a machine, a flat wok of synthetic -thermoplastic
film is unwound from a roll and formed into a continuous
tube, in a tube-forming section by sealing the longitudinal
edges of the film together to form a so-called lap seal or a
so-called fin seal. The tube thus formed is pulled vertical-
lye downwards to a filling station. The tube is then collapse
Ed across a transverse cross-section of the tube the post-
lion of such cross-section being at a sealing device below
the filling station. A transverse heat seal is made, by the
sealing device, at the collapsed portion of the tube, thus
making an air-tight seal across the tube. The sealing device
generally comprises a pair of jaws, and is described more
fully hereinbelow. After making the transverse seal, but
before the jaws of the sealing device are opened, a priest
quantity of material to be packaged e.g. liquid is allowed to
enter the tube, at the filling station, and fill the tube
upwardly from the aforementioned transverse seal. The tube
is then allowed to drop a predetermined distance under the
influence of the weight of the material in the tube. The
jaws of the sealing device are closed again, thus collapsing
the tube at a second transverse section, which is above,
usually just above, the air/material interface in the tube.
The sealing device seals and severs the tune transversely at
the second transverse section. The material-filled portion
of -the tube is now in the form of a pillow shaped pouch.
Thus the sealing device has sealed the top of a filled pouch,
sealed the bottom of the next-to-be-formed pouch and
US separated the filled pouch from the next-to-be-Eormed pouch,
all in one operation.
',~;,
33
-- 2 --
One vertical form and fill machine o-f the type
described above is a Proposes liquid packaging machine.
A sealing device commonly used is a so-called
impulse sealer which has a sealing element mounted in sealing
jaws and electrically insulated ~herefromO In operation the
sealing jaws are closed and an electrical current is caused
to flow through a sealing element e.g. a wire, for a fraction
of the time that the jaws are closed. The jaws remain closed
during a cooling period in which the seals partially solidify
lo before the sealing jaws are opened. The transverse seal thus
obtained support the weight of the plowable material e.g.
liquid, in the next-to-be-formed pouch.
A sealing element made of round wire e.g. "piano"
wire about lo to 2.5 mm diameter, electrically insulated
lo from a water cooled supporting jaw, may be used but a wire of
rectangular cross-section is preferred. These types of seal-
in elements may be used for making both -the longitudinal and
transverse seals.
The temperature of the sealing element during
passage of the electrical current is largely determined by
the resistance of the sealing element, the voltage applied
across the element, the heat -transfer rate through the film
being sealed and the temperature and mass of the jaw of the
sealing device. A may be seen, operation of the impulse
sealer may affect the seal strength and it is desirable to
optimize such operation.
When a liquid is packaged in pouches as described
above, the liquid, especially ire aqueous, aids in cooling the
transverse seal in the tube after the sealing jaws are open-
Ed because of the liquid's relatively high thermal conduct
tivity. It appears that the cooling effect of the liquid on
the seal takes effect before the weight of the liquid can
weaken or rupture the bottom seal.
USE Patent 3 682 767 issued 1979 August 8 to
Briton et at, discloses liquid filled pouches made from
films of blends of a) 90-50 White of a random copolymer o-f
*denotes trade mark.
. .
ethylene and an oleflnic unsaturated monomer e.g. vinyl
acetate, which is present in -the amount of 2-10 White of toe
copolymer and b) 10-50% ox a linear copolymer of ethylene
and a C3-C20 ~olefin of a density of about 0.930 to 0.960
g/cm3.
It is more common, commercially, to use film made
from a lend containing 70-90% linear ethylene-butene Capella-
men having a density of about OWE g/cm3 and a melt index offbeat 0.75 dg/min and 10-30% high pressure polyethylene i.e.
a homopolymer, having a melt index of about 2 to 10 and a
density of from 0.916 to 0 7 924 g/cm3. Density is determined
by ASTM Procedure D1505-68 and melt index by ASTM Procedure
D1238-79 (Condition Eye Such films having a thickness of
about 76 micrometers, have been used for making pouches con-
twining about 1.3 liters of milk. Pouches made from such film are generally satisfactory from the standpoint of pouch
toughness and puncture resistance, but suffer from a tendency
to have weak transverse end and/or longitudinal weals even
though the operating conditions of the impulse sealer have
been optimized. Defective seals may lead to the phenomenon
known as leakers in which the plowable material e.g. milk,
may escape from the pouch through pinholes which develop at
or close to the seal. It has been estimated that leakers
account for about 1-2% of the 1.3 lithe milk pouch
production.
It has been proposed that increasing the film
thickness would overcome the problem of leakers. however, it
has been shown that even at film thicknesses of up to about
127 micrometers the percentage of leakers is not substantial-
I lye reduced and yet the cost of the unfilled pouch is increase
Ed in proportion to the increase in thickness of the film
It has been suggested that melt strength, hot tack
strength and heat-seal strength would be good measures on
which to select films to produce pouches having improved seal
integrity and therefore reduce the number of leavers. On
-- 4
these bases, however, it appears that one skilled in the art
would not have any reason to believe that other polyolefins
or blends of polyolefins perform any better -than the adore-
mentioned lend owe linear ethylene-butene copolymer and high
pressure polyethylene Surprisingly, however, it has now
been found that pouches made from certain film of linear
copolymers of ethylene and a C~-Clo ~-olefin, admixed wit
ethylene-vinyl acetate copolyrners (EVA resins) jive s~lbstan~
tidally better performance with respect to the problem ox
leakers. Indeed, because of this improved performance it is
possible to make pouches of film with thinner film than was
heretofore possible with the aforementioned film of the blend
of ethylene-butene copolymer and high pressure polyethylene.
Accordingly the present invention provides a pouch
containing a plowable material, said pouch being made from a
sealant lo in tubular form and having transversely heat-
sealed ends, said film being made from a blend of a linear
ethylene-C4-Clo ~-olefin copolymer and an ethylene vinyl
acetate copolymer, said ethylene-C4-Clo ~-olefin copolymer
having a density of prom 0.916 to 0.930 g/cm3 and a melt
index ox from 0.3 to 2.0 dg/min, said ethylene-vinyl acetate
copolymer having a weight ratio of ethylene to vinyl acetate
Eros 2.2:1 to 24:1 and a melt index of from 0.2 to 10 dg/min,
said blend having a weight ratio of linear ethylene-C4-Clo
~olefin copolymer to ethylene vinyl acetate copolymer of
prom 1.2:1 to 9:1.
A preferred blend has a weight ratio of linear
ethylene-C4-Clo ~-olefin copolymer to ethylene-vinyl acetate
copol~mer of 2.33:1 to 9:1.
In a ureter embodiment the blend ox linear ethyl-
ene-C4-Clo ~-olefin copolymer and ethylene vinyl acetate
copolymer has admixed therewith from 13 to 18 parts of a high
pressure polyethylene having a density in the range ox 0.916
to 0.924 g/cm3 and a melt index in the range of 2 to 10
dg/min per 100 parts of said lends of copolymer.
In another embodiment the ekhylene-C~-Clo a-olefin
copolymer is selected from ethylene-butene or ethylene-octene
copolymers, especially ethylene-octene copolymer~
In a further embodiment the film has a thickness
from 38 to ]27 em, preferably from 51 em to 102 em.
In another embodiment the pouch contains from about
1~25 to 2 liters of a liquid or emulsion and the film thick-
news is Eros about 51 to 127 em.
As used herein the term "plowable material" does
not include gaseous materials, but encompasses materials
which are flcwable under gravity or may be pumped. Such
materials include liquids e.g. milk, water, fruit juice, oil,
emulsions e.g. ice cream mix, soft margarine; pastes e.g.
meat pastes, peanut butter; preserves e.g. jams, pie fillings
marmalade; jellies, doughs; ground meat e.g. sausage meat;
powders e.g. gelatin powders, detergents; granular solids
e.g. nuts, sugar; and like materials. The invention is
particularly useful for plowable foods e.g. milk.
In a specific embodiment the pouch contains from
about 0.1 to 5 liters, particularly from 1 to 2 liters, of a
wobbly material. Preferably the plowable material is a
liquid, especially milk, water, fruit juice, or an emulsion,
e.g. ice cream mix, soft margarine.
The present invention also provides a pouch con-
twining a plowable material, said pouch being made from a
film in tubular form and having transversely heat-sealed
ends, said film comprising being a laminate of a base film
and a sealant film, said base film being selected Eros the
group consisting of nylon film, polyethylene terephkhalate
film, polyvinylidene chloride film, polyvinyl chloride film,
polyacrylonitrile film, polystyrene film and saponified
ethylene-vinyl acetate film and said sealant film being made
from a blend of a linear ethylene-C4-C10 a -oleEin copolymer
and a ethylene-vinyl acetate copolymer said ethylene-C4-Clo
~-oleEin copolymer having a density of from 0.916 to 0.930
g/cm3 and a melt index of from 0.3 to I dg/min, said
ethylene-vinyl acetate copolymer having a weight ratio of
ethylene -to vinyl acetate of from 2.2:1 to 24:1 and a melt
index of from 0.2 to 10 dg/min, said blend having a weight
ratio of linear ethylene C~Clo ~-olefin coplanar to
ethylene-vinyl acetate copolymer of from 1.2:1 to 9:1, said
sealant film briny on the inside of the pouch.
In a preferred embodiment the weight ratio of
ethylene-C~-C10 a -olefin copolymer to ethylene vinyl acetate
copolymer is from 2.33:1 to 9:1.
In another embodiment the blend of ethylene-C4-Clo
~-olefin copolymer and ethylene-vinyl acetate copolymer has
admixed -therewith from 13 to 18 parts of a high pressure
polyethylene per 100 parts of said blend, said high pressure
polyethylene having a melt index in -the range of 2 to 10
dg~min and a density of from 0.916 to O.g24 g/cm3.
In a further embodiment -the base film is selected
from nylon 66, nylon 6, nylon 66~6 copolymer, nylon 6/10
copolymer, nylon 6/11 copolymer and nylon 6/12 copolymer.
Preferably the base film is nylon 66~ nylon 6 or nylon 66/6
copolymer.
In yet another embodiment, the base film and the
sealant film have a layer of polyvinyldiene chloride (PVDC~
interposed there between
In another embodiment the laminate comprises a base
film sandwiched between two sealant films.
In a further embodiment -the plowable material is an
oil, especially vegetable oil or motor oil and the base film
it a nylon film.
The present invention also provides, in a process
for making pouches filled with a plowable material on a
vertical form and fill machine, in which process each pouch
is made from a flat web of film by forming a tubular film
therefrom with a longitudinal seal and subsequently flatten-
-- 7 --
in the tubular film at a eeriest position and transversely
heat sealing sail tubular film at the flattened position,
filling the tubular iamb with a predetermined quantity of
plowable material above said first position, flattening the
-tubular film above the predetermined quantity of plowable
material at a second position and transversely heat sealing
said tubular film at the second position, the improvement
comprising making the pouches from a flat web of film made
from 60 to 90 parts ethylene-C~-Clo -olefin copolymer having
a density from 0.916 to 0.930 g/cm3 and a melt index from
0.3 to 2.0 dg/min admixed with 10 to 40 parts ethylene-vinyl
acetate copolymer having a weight ratio of ethylene to vinyl
acetate of prom 2.2 to 24 and a molt index of from 0.2 to 10
dg/min.
In a preferred embodiment the film web used in the
process is made from the blend of the linear ethylene-C4-Clo
~-olefin copolymer and ethylene-vinyl acetate copolymer,
blend has admixed therewith from 13 to 18 parts of a high
pressure polyethylene having a density in the range of 0.916
to 0.924 g/cm3 and a melt index in the range of 2 to 10
dg/min per 100 parts of said blend.
In another embodiment the ethylene-C4-Clo -olefin
is selected from ethylene-butene or ethylene-octene Capella-
men, especially ethylene-octene copolymer.
The linear ethylene-C4-Cloa -olefin copolymer use-
fur in the present invention may be made from ethylene and an
~-olefin by a process disclosed in Canadian patent 856 137
which issued 1970 November 7 to WOE. Baker, IoC~B~ Saunders
and JAM. Stewart. The linear ethylene~C4-Cl~ a-olefin
copolymer may also be made by other processes known to those
skilled in the art.
The ethylene-C4-Clo ~-olefin copolymer, ethylene-
vinyl acetate copolymer and high pressure polyethylene are often available in pellet form.
Blends of the pelleted polymers may be fed into a
film exterior and extruded into film form. A preferred film
manufacturing method is the so-called blown film process disk
closed in Canadian patent 460 963 issued 1949 November 8 to
I Fuller. Films may also be made using an internal or
external cooling mandrel with the blown film process, as disk
closed for example in Canadian patent 893 216 issued 1972
February 15 to M. Boeing and TV Thomas. The internal cool-
in mandrel brown film process is preferred. The copolymers,
and high pressure polyethylene if present, may be blended
prior to feeding to the film extrude hopper, or may be
blended at the time of extrusion just prior to melting in the
extrude, or alternatively may be melt blended in the
extrude.
It will be understood by those swilled in the art
that additives e.g. US stabilizers may be added to the
ethylene polymers from which pouches of the present invention
are made.
The film, after manufacture, is slit longitudinally
into appropriate widths. The width determines the diameter
of the tube formed on the vertical form and fill machine.
Preferably, film having a thickness of 51 to 127 em
in thickness, especially 63 to 76 em in thickness, is used
for the pouches of the present invention.
Pouches containing plowable materials may then be
formed in the general manner described hereinbeEore on a
vertical form and fill machine e.g. Prepay IS-2 or IS-6
liquid packaging machine, using the ethylene-C~-Clo Olin
copolymar/ethylene-vinyl acetate copolymer film described
herein.
When the film is a single layer or comprises a base
film sandwiched between two sealant films, the pouch may have
a fin seal or a lap seal. When the film comprises a base
film and a sealant film, the pouch has a fin seal, and the
sealant film is on the inside of the pouch.
g
When the pouch is made from a laminate as described
herein before, the transverse sealing device may more advent-
ageously comprise two sealing elements and a severing element
as described in US patent 1 377 149 granted 1975 April 9 to
RYE. Petersen. With such a sealing device two transverse
seals are made across the tubular film above and below the
transverse sections described hereinhefore and the tubular
film is severed between the two transverse seals.
Film laminates as described herein, having nylon,
particularly nylon 66, nylon 6 or nylon 66/6 copolymer base
film are particularly desirable for packaging oleagenous
liquids e.g. cooking oil, motor oil. The nylon film may be
cast or oriented.
As indicated herein before examination of melt
strength, hot tax strength and heat seal strength data for
the linear ethylene-C4-Clo ~-olefin copolymer/ethylene-vinyl
acetate copolymer blends used in the present invention leads
one skilled in the art to believe that there would be no
improvement in the number of leakers with pouches from such
blends compared to that experienced with pouches made from a
blend of linear ethylene-butene copolymer and high pressure
polyethylene. In order to illustrate the lack of correlation
between melt strength, hot tack strength and heat seal
strength with pouch performance, several samples of films,
were taken and melt strength, hot tack strength and heat seal
strength were measure. 2 lithe pouches of water were made
using such films and the number of leakers determined by
means of a drop test. In the drop test the pouches were
dropped end-wise 152.4 cm onto a concrete floor.
Melt strength, is the weight of extradite which
will remain suspended for a period of 3 minutes from -the
orifice of a standard melt index tester (ASTM Procedure
D1238-79). Heat seal strength is determined using a peel
strength test similar to that used in ASTM Procedure D903 on
a sample of film sealed using a Sentinel* heat seal apparatus
*denotes trade mark.
33
Hot tack strength may be determined ho ASTM Procedure ~3706.
TABLE I
Heat Seal Hot Tack
smelt Strength Strength %
Strength 12.7mm 25.4mm Seal
Film* (g/3mln) 180C 190CFailures
A 0.31 2080 300 11.6
B 0.63 2040 300 2.3
C 0.38 2300 300 1.7
D 0.29 1950 800 10.3
E 0.49 1397 500 0.4
Film A is 76 em in thickness and is made from a
blend of 85 parts of a linear ethylene-~-butene copolymer
having a density of 0.919 g/cm3 and a melt index of 0.75
dg/min and 15 parts of a high pressure polyethylene having a
density of 0.918 g/cm3 and a melt index of 8.5 dg/min.
Film B is 76 em in thickness and is made from a
blend of 85 parts of the blend of Film A and 15 parts of an
ethylene-vinyl acetate coplanar having a melt index of 0.35
dg/min and a vinyl acetate content of 12 wit%.
Film C is 76 em in thickness and is made from a
blend of 85 parts of the blend of Film A and 15 parts of an
ethylene-vinyl acetate copolymer having a melt index of 0.7
dg/min and a vinyl acetate content of 18 wit%.
Film D is 51 em in thickness and is made from an
ethylene-~-octene copolymer having a density of 0.918 g/cm3
and a malt index of 0c84 dg/min~
Film E is 51 em in thickness and is made from the
ethylene-~-octene copolymer of Film D and 20 wit% of the
ethylene-vinyl acetate of Film B.
Pouches made from Films B, C and F are within the
scope of the present invention.
From the values of melt strength, ho-t tack strung
and heat seal strength data it would be expected that the
ethylene-~-olefin copolymer/ethylene-vinyl acetate copolymer
and, optionally, high pressure polyethylene blend film would
show little, if any, advantage over the ethylene-butene
copolymer/high pressure polyethylene blend film.
The following examples further serve to illustrate
the invention.
Example l
The following resins and/or resin blends were
evaluated for their performance as liquid packaging films:
U. 85 parts of an ethylene-butene coupler having
a density of 0.919 g/cm3 and a melt index of
0.75 dg/min blended with lo parts of a high
pressure polyethylene having a density of 0.918
g/cm3 and a melt index of 8.5 dg/min;
V. 85 parts of the resin blend in U in turn blend-
Ed with 15 parts of an ethylene-vinyl acetate
copolymer having a melt index of 0.35 dg/min
and a vinyl acetate content of 12 wit%;
W. 85 parts of the resin blend in U in turn blend-
Ed with 15 parts of an ethylene-vinyl acetate
copolymer having a melt index of 0.7 dg/min and
a vinyl acetate content of 18 White.
Pouches made from blend U is not within -the scope
of the present invention and exemplifies the prior art.
The resins or resin blends were extruded at a melt
temperature of 232C into films of various gauges at 409
kg/hr using a extrude equipped with a 81.3 cm diameter
circular die and an internal film cooling mandrel.
The films were processed into 2 lithe pouches,
substantially filled with water, using a Prepay IS-6 liquid
packaging machine. The pouches were subsequently tested for
seal integrity by dropping them from a height of 152.4 cm and
determining the percentage seal failures.
% Seal Failures
Film Gauge: 51 em 76 em 102 em
Blend
V 100 11.6 11.3
V 0.9 2.3 2.7
W 1.0 1.7 0.3
Example 2
Resin composition U of Example I above was blended
with a number of ethylene-vinyl acetate copolymers (ETA
resins) outlined below and extruded into films 76 us in
thickness. The resin blonds were extruded at a melt tempera-
lure of 221C, at a rate of 38~6 kg/hr trough a 22.9 cm
diameter circular die The films were processed into 1.3
lithe pouches, substantially filled with water, using a
Prepay IS-6 liquid packaging machine. The pouches were sub-
sequently tested or seal integrity by dropping them from a
height of 152.4 cm. and determining the percentage seal
failures.
-- 13 --
Wit %
EVA resin Vinyl Acetate
Melt Index in the EVA % Seal
Sample _(dg/min) Resin Failures
U - - 50
U~15% EVA I 0.3 12.0 2
U-~15% EYE II 1~2 7.5 40
U+30% EVA II 1.2 7. 5 23
u+a,5~ EVA II 1.2 7.5 5
lo U+30% EVA III 0.8 9.5 38
U~15% EVA IV 3.0 28.0 0
U~15~ EVA V 0.7 18.0 0
U+30% EVA VI 7.0 9.0 7
U-~45% EYE VI 7 . 0 9 . 0 3
U+15% EVA VII 8.0 18.0 5
Example 3
The following resins and/or resin blends were
evaluated for their performance as liquid packaging films:
U, 85 parts of an ethylene-butene copolymer having
a density of 0. 919 gm/cm3 and a melt index of
0.75 dg/min blended with 15 parts of a high
pressure polyethylene having a density of 0. 918
gmfcm3 and a melt index of I 5 dg/min,
Y. 85 parts of an ethylene-octene copolymer having
a density of 0.918 g/cm3 and a melt index of
0 . 84 dg/min blended with 15 pats of an
ethylene-vinyl acetate copolymer having a melt
index owe 3 dg/min and containing 2 8 wit% vinyl
acetate,
Z. 70 parts of an ethylene-octene copolymer having
a density of 0.918 g/cm and a melt index of
0.84 dg/min blended with 30 parts of an
ethylene-vinyl acetate copolymer having a melt
index of I 2 dg/min and containing 7.5 wit%
vinyl acetate.
- 14 -
Pouches made from Blend U it not within the scope
of the present invention and exemplifies the prior art.
The resins were extruded at a melt -temperature of
221C at a rate of 38.6 kg/hr. through a 22.9 cm diameter
circular die, and the resulting blown film was cooled by an
internal cooling mandrel. The films were subsequently
processed into 1.3 lithe pouches containing 103 liters of
water, using a Prepay IS-6 liquid packaging machine. The
pouches were subsequently tested for seal integrity by
dropping them from a height of 152.4 cm. and determining the
percentage failures.
Blend% Seal Failures
U 50
Y O
Z O
