Note: Descriptions are shown in the official language in which they were submitted.
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LAMINATED PACKAGING FILM
This invention relates to polymer film laminates; more
particularly, this invention relates to polymer film laminates
suitable as packaging film; to processes for their
preparation; and to their use with belt-driven packaging
machines.
Certain polymer films, for example oriented
polypropylene, have a number of advantageous properties such
as transparency, stiffness and moisture barrier while having
coefficients of friction (COF) which are unacceptably high for
use as such in modern packaging technology. Treatment of such
polymer films with silicone oils has been found to provide
satisfactory reductions in their COF; but films so treated are
then relatively difficult to treat in other conventional
manners: for example, the bond strengths of such films, when
laminated to themselves or to metallised coatings, may be
unacceptably low; furthermore, corona or flame treatment
reduces their heat sealability and increases their COF.
This invention seeks to provide polymer film laminates
which are sealable on both surfaces with excellent bond
strength and COF thereon; and which permit great flexibility
in combining film layers of selected properties.
In one aspect, this invention provides a polymer film
laminate which comprises:
a first web including an upper surface layer which layer
contains a silicone oil and an anti-blocking agent, and a core
layer wherein the surface of the core layer remote from the
upper surface layer may be ink receptive;
a second web including a lower surface layer which layer
contains an anti-blocking agent but is substantially free from
compounded silicone oil; and
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an adhesive layer bonding the first web to the second web
such that the upper surface layer of the first web and the
lower surface layer of the second web remain exposed and
silicone oil transfers from the upper surface layer of the
first web to the lower surface layer of the second web in
processing.
This invention also provides a process for the
preparation of a polymer film laminate as herein defined,
which process comprises:
i) providing a first web as herein defined;
ii) providing a second web as herein defined;
iii) applying an adhesive layer between the first and
second webs;
iv) bonding the first web to the second web such that
the upper surface layer of the first web and the lower
surface layer of the second web remain exposed; and
v) contacting the upper surface layer of the first web
with the lower surface layer of the second web so that
silicone oil transfers from the upper surface layer of
the first web to the lower surface layer of the second
web.
This invention further provides use of a film laminate as
herein defined in a belt-driven packaging system.
The surface of the first web which is adhered to the
second web may be treated so that it is receptive to ink. The
bonding of the second web to the first web thereby locks in
any printing on this surface so that it cannot be damaged in a
packaging operation.
Figure 1 is a schematic of the polymer film laminate of the
present invention.
Figure 2 is a schematic of an altez°native polymer film
laminate of the present invention.
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A polymer film laminate (10) is provided which includes a
first (or outside) web (12), second (or inside) web (14), an
adhesive layer (16) bonding the webs to each other, the first
web (12) including an upper surface layer (18) containing a
silicone oil, the second web (14) including a lower surface
layer (20) substantially devoid of silicone oil except for oil
which is transferred by contact with upper surface layer (18).
The outer surfaces of the polymer film laminate are preferably
heat sealable, Such a film laminate can be used for packaging
in either belt-driven or non-belt-driven packaging machines
and regardless of whether fin or lap seals are formed thereby.
When polymer films are formed into bags or sacks for
receiving articles, the outer surfaces thereof can become
scratched if the coefficient of friction is relatively high at
the temperature at which such bags are constructed. The
excessive drag which may cause such scratching may also cause
the packaging apparatus to jam. With the advent of belt-driven
packaging apparatus including an inside shaping tube which
allows the belts to engage the film between the tube and
belts, it is now important that both surfaces of the film have
satisfactory hot slip performance. This allows the film to be
processed on both the new belt-driven apparatus as well as
older equipment.
Silicone oils of the types described in U.S. Patent
4,659,612 have been found to impart satisfactory slip
characteristics to oriented polypropylene films. In accordance
with the present invention, the first web (12) of the polymer
film laminate (10) includes and upper surface layer (18)
(about 2 to 6 gauge units in thickness) containing an amount
of silicone oil sufficient to maintain a low coefficient of
friction thereon. The upper surface layer (18) is preferably a
heat seal layer and is preferably a ethylene-propylene random
copolymer and/or ethylene-propylene-butene-1 terpolymer.
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The latter includes from 2 to 9 wt. and preferably from 3
to 7 wt.% ethylene, and from 2 to 9 wt.% and preferably from 3
to 7 wt,% of 1-butene. Suitable polymers generally have a melt
flow rate at 446°F from 1 to 15 and preferably form 2 to 7.
The crystalline melting point is from 245 to 302°F. The
average molecular weight range is from 25,000 to 100,000 and
the density is from 0.89 to 0.90. The silicone oil, preferably
polydimethylsiloxane, is added in an amount form 0.3 wt.% to
. o wt . % of the heat sealable skin layer . The preferred range
is from 1.1 to 1.5 wt.%.
The upper surface layer (18) is compounded with an anti-
blocking agent to help maintain a low coefficient of friction.
A finely divided, particulate, inorganic material is preferred
having a mean particle size from 0.5 to 5 microns. One
commercially available silica has a mean particle size of 0.75
microns and another has a mean particle size of 4.5 microns,
Materials having either particle size or particle sizes within
this range can be employed. Metal silicates, glasses, clays
and numerous other finely comminuted inorganic materials may
also be used. The anti-blocking agent is preferably present in
an amount from 0.05 to 0.5 wt.%, preferably from 0.1 to 0.3
wt.% of each of the skin layers.
The core layer (22) of the first web (12) is preferably
derived from isotactic polypropylene which may contain anti-
static agents as described in U.S. Patent 4,764,425. The
polypropylene homopolymer has a melting point from 321 to
325°F.
The polypropylene core layer (22) provides a moisture
barrier and stiffness to the first web. Other possible core
materials include oriented high density polyethylene, oriented
polystyrene, oriented polyethylene terephthalate,
polycarbonate and nylon.
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An additional layer (24) may be provided having a surface
which is receptive to ink. This layer (24) may comprise the
same copolymer and/or terpolymer blend as layer (18), but is
subjected to corona, flame, plasma or chemical treatment to
impart ink receptivity. This layer (24) may alternatively be
omitted and the inner surface (26) of the core layer (22)
instead subjected to such treatment.
A primer may be added to the layer (24) depending upon
the ink which is to be used thereon. Any of a number of
commercially available primers would be suitable for enhancing
receptivity to ink and/or adhesive, including
poly(ethyleneimine), acrylic styrene copolymers, urethane and
epoxy. The application of several such primers is discussed in
U.S. Patent 4,565,739.
The second web (14) includes a lower surface layer (20), a
core layer (28) and a bonding surface layer (30) for bonding with
tt~~e adhesive. The lower surface layer core and bonding
surface layer, respectively, may be comprised of the same
materials which are mentioned as suitable for the upper
surface layer (18), core layer (22), and additional layers
(24) of the first web. The lower surface layer (20) of the
second web (14) is substantially devoid of silicone oil,
however, which enhances the adhesion of a metallized coating
which may be applied to the second web bonding surface layer.
The latter is preferably between about two and seventeen gauge
units in thickness. It may contain a slip agent (for example,
from 700 to 3,000 ppm oleamide, stearamide, erucamide or a
blend thereof.
While not required, each web is preferably manufactured
by employing commercially available systems for coextruding
resins. A polypropylene homopolymer of comparatively high
stereoregularity is co-extruded with the resins which
constitute one or both skin layers thereof. The polymers can
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be brought into the molten state and co-extruded from a
conventional extruder through a flat sheet die, the melt
streams being combined in an adapter prior to being extruded
from the die. After leaving the die orifice, the multi-layer
film structure is chilled and the quenched sheet then
preferably reheated and stretched, for example, three to six
times in the machine direction and subsequently four to ten
times in the transverse direction. The edges of the web can be
trimmed and the film wound onto a core.
A metallized coating may be applied to the bonding
surface layer of the second (inside) web using any acceptable
method such as that described in U.S. Patent 4, 345, 005 . Other
coatings may alternatively be employed depending on the
properties desired for the film. A PVDC coating may, for
example, be provided to improve the gas and moisture barrier
properties of the web.
The fist toutside) and second (inside) webs are banded to
each other through the use of commercially available adhesives
and conventional bonding processes. The choice of adhesives
depends on the properties which one wishes the laminated film
to have. A urethane adhesive provides mainly only adhesion.
Extruded polymer resins can provide thickness, stiffness and
durability. As discussed above, PVDG provides a gas barrier
and an additional moisture barrier. If a dry bonding technique
is used, the adhesive is applied to one of the webs, the
solvent is evaporated out of the adhesive, and the adhesive-
coated web is combined with the other web by heat and pressure
or pressure only.
Extrusion laminating involves the use of an extruder to
melt and continuously apply a controlled amount of a very
viscous melted resin, usually polyethylene, directly between
the web materials being laminated. The bound is achieved as
the melted resin resolidifies in situ. Primers or precoatings
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may be employed to augment the bound ar improve resistance or
chemical attack.
Once the first (outside) web has been bonded to the
second (inside) web, the resulting laminated film is wound
onto a core and maintained in this form for a period of about
six hours to one week at a temperature of about 80° to about
125°F. The winding of the film causes the upper layer (18) of
the first (outside) web to contact the lower surface layer
(20) of the second (inside) web. The silicone oil, which is
generally substantially uniformly distributed on the exposed
surface of upper layer (18), is responsible for imparting a
reduced coefficient of friction to this surface as well as to
the exposed surface of the lower surface layer (20) when some
of the oil is transferred thereto after these surfaces have
been placed in mutual contact. A sufficient amount of silicone
oil should be employed to provide a coefficient of friction of
layers (18) and (20), following transfer of silicone oil
microglobules to the latter, of about 0.4 to less, preferably
0.25 - 0.3, up to at least about 60°C,
The thickness of the first (outside) web is primarily due
to the thickness of the oriented polypropylene core, The
surface layers (18) and (24) may comprise, for example, a
total of about eight percent of the total thickness of an 80
gauge web. The total outside web thickness is ordinarily in
the range of about 0.35 to 2.0 mils, The total thickness of
the inside and outside webs are not critical to the present
invention.
The following Examples illustrate this invention.
A laminated film comprising an outside web having a coextruded
abc structure, an inside web having a coextruded alblcl structure,
and an adhesive bonding the c layer of .the outside web to the cl
15 layer of the inside web is provided.
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The "a" layer is an ethylene propylene random copolymer
containing about six percent ethylene. This layer is about 2.2
gauge units (0.55 microns) in thickness, is 1.2 wt. percent
polydimethylsiloxane, and includes about 2300 ppm Si02. The "b"
20 layer of the outside web is an isotactic polypropylene containing
about 0.1% N,N bis hydroxyethylamine and is about seventy-five
gauge units in thickness. The "c" layer is about three gauge units
in thickness, is made from the same copolymer as layer "a", is
flame treated and coated with a polyethylenemine primer.
25 The cl layer is made from an isotactic polypropylene
homopolymer and contains about 2300 ppm Si02. It is about three
gauge units in thickness and is flame treated. The bl layer is about
seventy-five gauge units in thickness and is made from isotactic
polypropylene with no additives. Finally, the al layer is fourteen
30 gauge units in thickness (for hermetic sealability) and is formed
from an ethylene-propylene random copolymer (about 6%
ethylene)containing 2300 ppm Si02 and a slip agent (e. g. oleamide,
stearamide,.erucamide and blends thereof).
The urethane adhesive bonds the c layer of the outside web to
the cl layer of the inside web. The laminated film is wound upon a
roll whereupon some of the polydimethylsiloxane within the "a"
S layer is transferred to the al layer.
The same film structure as Example 1 is provided except that
the al layer is four and six gauge units, respectively, in
thickness.
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The same film structure as Example 1 is provided except that
15 the abd al layers are both made from EPB-1 random terpolymers
containing about 5% ethylene, 8% butene-1 and 87% polypropylene.
20 The same film structure as Example 1 is provided except that
the cl layer has a metallized (aluminium) coating deposited thereon.
25 The same film structure as Example 1 is provided except that
the."a" layer is formed from a random copolymer containing about 6%
butene-1 and 94% polypropylene.
