U.S. patent application number 10/389384 was filed with the patent office on 2004-09-16 for reduced blocking metallized film.
Invention is credited to Gringoire, Bruno R.L..
Application Number | 20040180162 10/389384 |
Document ID | / |
Family ID | 32962264 |
Filed Date | 2004-09-16 |
United States Patent
Application |
20040180162 |
Kind Code |
A1 |
Gringoire, Bruno R.L. |
September 16, 2004 |
Reduced blocking metallized film
Abstract
Low temperature sealable metallized packaging films are found to
have reduced blocking tendencies when an oxidized polyethylene wax
is blended into a low temperature sealing composition including an
ethylene-carboxylic acid copolymer. The films are useful for
high-speed packaging applications requiring sealability at low
temperatures. The films exhibit low blocking performance during
unwinding of the film while maintaining positive low temperature
sealability characteristics.
Inventors: |
Gringoire, Bruno R.L.;
(Ville-Houdlemont, FR) |
Correspondence
Address: |
EXXONMOBIL CHEMICAL COMPANY
P O BOX 2149
BAYTOWN
TX
77522-2149
US
|
Family ID: |
32962264 |
Appl. No.: |
10/389384 |
Filed: |
March 14, 2003 |
Current U.S.
Class: |
428/35.7 |
Current CPC
Class: |
C08J 2423/00 20130101;
Y10T 428/1352 20150115; C08L 23/30 20130101; C08J 7/0427 20200101;
C08L 23/0869 20130101; C08L 23/0869 20130101; C08L 2666/04
20130101 |
Class at
Publication: |
428/035.7 ;
428/692 |
International
Class: |
B65D 001/00 |
Claims
What is claimed is:
1. A film comprising: (a) a substrate having a first surface and a
second surface; (b) a metallic layer on the first surface; and (c)
a coating on the second surface comprised of at least one ethylene
copolymer and at least one oxidized polyethylene wax.
2. The film of claim 1 wherein the coating is comprised of from
about 5 Phr to about 25 Phr of the at least one oxidized
polyethylene wax based upon 100 parts by weight of the ethylene
copolymer.
3. The film of claim 2 wherein the metallic layer is uncoated and
is comprised of a metal selected from the group consisting of
aluminum, copper, silver, chromium, gold, and mixtures thereof.
4. The film of claim 3 wherein the at least one oxidized
polyethylene wax has a drop point from about 85.degree. C. to about
145.degree. C.
5. The film of claim 4 wherein the substrate is comprised of a
material selected from the group consisting of polypropylene,
polyethylene, polybutene, polystyrene, polyvinyl chloride,
polyesters, polyethylene terephtalate glycol, polyethylene
naphthalate, and oriented nylon.
6. The film of claim 5 wherein the ethylene copolymer is selected
from the group consisting of a copolymer of ethylene and a
carboxylic acid and a copolymer of ethylene and an acrylic
ester.
7. The film of claim 6 wherein the at least one ethylene copolymer
has a melting point from about 65.degree. C. to about 105.degree.
C.
8. The film of claim 7 wherein the at least one oxidized
polyethylene wax has a drop point of from about 95.degree. C. to
about 140.degree. C.
9. The film of claim 8 wherein the at least one ethylene copolymer
is a copolymer of ethylene and carboxylic acid and the carboxylic
acid is selected from the group consisting of acrylic acid,
methacrylic acid, maleic acid, crotonic acid, itaconic acid,
citraconic acid, and mixtures thereof.
10. The film of claim 7 wherein the coating is comprised of from
about 7 Phr to about 20 Phr of the at least one polyethylene wax
based upon 100 parts by weight of the at least one ethylene
copolymer.
11. The film of claim 9 wherein the carboxylic acid of the
ethylene-carboxylic acid copolymer is selected form the group
consisting of acrylic acid and methylacrylic acid, and mixtures
thereof.
12. The film of claim 11 wherein the copolymer of ethylene and
carboxylic acid comprises ions selected from the group consisting
of sodium ions, potassium ions, lithium ions, calcium ions, zinc
ions, and mixtures thereof.
13. The film of claim 10 wherein the at least one ethylene
copolymer is a copolymer of ethylene and acrylic ester, wherein the
acrylic ester is selected from the group consisting of
methylacrylate, methylmethacrylate, butylacrylate, and mixtures
thereof.
14. The film of claim 11 wherein the metallic layer is comprised of
aluminum.
15. The film of claim 14 wherein the at least one oxidized
polyethylene wax has a drop point of from about 98.degree. C. to
about 115.degree. C.
16. The film of claim 15 wherein the substrate is comprised of a
biaxially oriented polypropylene film.
17. The film of claim 16 wherein the substrate is a three layer
film.
18. The film of claim 17 wherein the three layer film is comprised
of a core layer comprised of biaxially oriented film and at least
one skin layer.
19. The film of claim 18 wherein the skin layer of the film is
comprised of a polymer selected from the group consisting of a
copolymer of propylene and ethylene and a terpolymer of propylene,
ethylene, and butylene.
20. The film of claim 17 wherein the film is opaque.
21. The film of claim 17 wherein at least one layer of the film is
voided.
22. The film of claim 16 wherein the substrate is a five layer
biaxially oriented film.
23. The film of claim 15 wherein the coating is comprised of from
about 8 Phr to about 18 Phr of the at least one oxidized
polyethylene wax based upon 100 parts by weight of the
ethylene-carboxylic acid copolymer.
24. The film of claim 14 wherein the coating is comprised of about
10 Phr of the at least one oxidized polyethylene wax based upon 100
parts by weight of the ethylene-carboxylic acid copolymer and the
at least one oxidized polyethylene wax has a drop point from about
98.degree. C. to about 110.degree. C.
25. A package comprised of a film comprising: (a) a substrate
having a first surface and a second surface; (b) a metallic layer
on the first surface; and (c) a coating on the second surface
comprised of at least one ethylene copolymer and from about 5 Phr
to about 25 Phr of a polyethylene wax based upon 100 parts by
weight of the at least one ethylene copolymer.
26. The packaged product of claim 25 wherein the at least one
ethylene copolymer is selected from the group consisting of a
copolymer of ethylene and a carboxylic acid and a copolymer of
ethylene and an acrylic ester.
27. The packaged product of claim 26 wherein the substrate is
comprised of a material selected from the group consisting of
polypropylene, polyethylene, polybutene, polystyrene, polyvinyl
chloride, polyesters, polyethylene terephtalate glycol,
polyethylene naphthalate, and oriented nylon and the polyethylene
wax has a drop point of from about 95.degree. C. to about
140.degree. C.
Description
FIELD OF THE DISCLOSURE
[0001] This disclosure relates to metallized films having low
temperature sealability characteristics with improved anti-blocking
properties.
BACKGROUND INFORMATION
[0002] The modern packaging industry requires expertise in many
disciplines. Packaging technology integrates elements of
engineering, chemistry, food science, metallurgy, and other
disciplines to provide the consumer fresh foods and non-food
products. To protect product quality, it is often desirable to
provide packaging films with the ability to provide a hermetic
seal, i.e., a seal which does not permit gases, such as air, to
enter the package.
[0003] Packages produced from flexible film, such as bags and
pouches, are prevalent in the marketplace. In order to utilize
continuous flexible film, the industry generally employs
form/fill/seal packaging techniques. The type of product packaged
dictates whether or not the technique will include horizontal
form/fill/seal packaging (HFFS) or vertical form/fill/seal
packaging (VFFS).
[0004] It is important for the packaging designer to be able to
select a polymeric film having optimum barrier properties for
storage of products and be confident of providing a high quality
seal using high-speed packaging apparatus. For example, it is known
that stereoregular polypropylene, e.g., oriented polypropylene, is
quite useful in the manufacture of packages from flexible films.
Using oriented polypropylene as a core layer, additional layers in
the way of coatings, co-extrusions, laminations, and combinations
thereof are added to improve barrier properties of the film. In
certain cases, films can be prepared which exclude moisture and
oxygen, but permit the passage of light. In other cases, it is also
important to prevent light from passing through the film barrier.
Barrier properties can also be modified and/or enhanced by
treatments such as heat and flame treatment, electrostatic
discharge, chemical treatments, halogen treatment, ultra-violet
light, plasma treatment and combinations thereof.
[0005] An important issue for designing packaging films is to
ensure they can be processed on high speed form/fill/seal
machinery. Form/fill/seal packaging systems operate by unwinding
continuous film from bulk film rolls, followed by forming pouches,
filling the pouches, and, finally, sealing the pouch closed. Thus,
the film must have sufficient flexibility to undergo machine
folding from a flat orientation to a folded condition, and be
subjected to a sealing function, which is part of high-speed
packaging apparatus. In selecting the optimum packaging film for
its barrier properties, high-speed unrolling and folding are the
primary concern. An additional and very important aspect of the
packaging process, however, is the ability to effectively seal the
pouch after it is filled with the product.
[0006] High-speed horizontal and vertical form/fill/seal systems
include sealing functions at various stages of the packaging
process. In a horizontal form/fill/seal apparatus, individual
pouches are formed by folding the multi-layer film in half followed
by providing vertical seals along the length of the folded web and
separating the pouches along the seals formed by vertical sealing.
Optionally, the bottoms of the pouches can also be sealed. After
the pouch is formed and filled, the top of the pouch is sealed.
Similarly, in vertical form/fill/seal apparatus, the continuous web
is formed around a tube and the web is immediately joined together
by a longitudinal sealing jaw as either a lap seal or a fin
seal.
[0007] A second sealing function is present in a vertical
form/fill/seal configuration which consists of a combination top
and bottom sealing section (with a bag cut-off device in between).
The top-sealing portion seals the bottom of an empty bag suspended
from the bag forming tube while the bottom portion seals the top of
a filled bag.
[0008] In most processes for packaging products, the package is
formed and filled by creating a heat-seal between two opposed
layers of film to form a pocket and almost simultaneously sliding
or dropping the product into the pocket. In these form and fill
packaging techniques a continuous flat web of packaging film is fed
around a form which shapes it into a tube, the tube is slipped over
a hollow form and the free edges of the tube are sealed together.
The tube so formed is then passed between a pair of hot sealing
jaws which create a series of discrete packages by collapsing the
film onto itself and forming a seal by the application of heat and
pressure. The product is introduced into each package through the
hollow form in the interval between the heat seals. During high
operating speeds, the product is dropped into the package while the
sealing jaws, which form the seal, are closed. With both vertical
and horizontal form and fill sealing applications the heat seal
should be strong enough to support and retain the product after the
sealing jaws open to release the film. It is often desirable to
release the sealing jaws soon after the seal is formed so a film
which accomplishes this by exhibiting a high "hot tack" is very
useful.
[0009] Additionally, in packaging applications there is a great
demand for heat sealable films which can be subjected to
temperatures high enough to seal the films without causing the
substrate to cockle or pucker. One approach for achieving this is
by coating a film substrate with a layer of heat sealable material
which adheres strongly to the substrate and which can be melted at
a temperature below the softening temperature of the substrate.
Heat-sealable coatings with low melting temperatures are often
preferred because the substrate is less likely to be damaged during
heat sealing. U.S. Pat. No. 5,419,960 discloses a low temperature
sealable coating.
[0010] Cold sealable pressure-sensitive adhesives have been
developed. These adhesives do not require the use of a heated
element to seal the packages. However, these adhesives have high
surface tack characteristics making them adhere to uncoated
surfaces of the packaging film which makes them difficult to use
because of film blocking (i.e., sticking).
[0011] An important feature in many modern packaging films is a
metallic layer or coating that is usually applied by vapor
deposition methods. U.S. Pat. Nos. 5,487,940 and 6,420,041 describe
and refer to numerous exemplary metallized films. Metal layers are
well known in the packaging industry and can be deposited using any
known method, for instance, vacuum deposition, electroplating,
sputtering, etc. Preferably, the metal layer is one of vacuum
deposited aluminum, copper, silver, chromium, gold, and mixtures
thereof, with vacuum deposited aluminum being the most commonly
used.
[0012] Metallized films are widely used for their moisture barrier
properties. A disadvantage of metallized films, when the metallic
layer is on the surface of the films, is the tendency of the
metallic layer to stick or block to seal layers or coatings on the
opposite side of the film structure when the metallized film is
rolled. This sticking or blocking problem is exacerbated when the
opposite seal layer or coating is a low temperature sealing
material. Blocking of a film having a metallic surface layer often
results in damage to or removal of the metallic surface leading to
a decrease in the moisture barrier properties of the film and/or
unpleasing appearance of the metallic layer. To address this
problem, metallic layers are often covered with another film layer
or coating to protect the metallic layer. U.S. Pat. Nos. 5,287,615
and 6,013,353 disclose application of a layer of a low temperature
sealable coating on the surface of a metallic film layer to protect
the metal and to provide high seal strength. The patents disclose
coating an ethylene-unsaturated carboxylic acid copolymer
composition on the metallic surface. The coating may also contain a
dispersed wax. The disclosed films may optionally include the same
type of coating on the side of the film opposite the metal
layer.
[0013] A protective acrylic or other polymeric coating may be
deposited over the metal layer under vacuum conditions as disclosed
in U.S. Pat. No. 4,842,893. As disclosed in U.S. Pat. No.
6,420,041, it is known to laminate a polymeric film layer over the
metal layer of a film to protect the metal from scratching and
scuffing during use. The polymeric layer can improve the gauge,
stiffness and puncture resistance of the overall film, and can
further enhance the barrier properties of the film. The polymeric
layer can be oriented, unoriented, transparent or opaque. The
polymeric layer is laminated to the metal layer using any suitable
adhesive.
BRIEF DESCRIPTION OF THE DISCLOSURE
[0014] This disclosure relates to low temperature sealing
metallized films. A first surface layer of the films is provided
with low temperature sealability with an ethylene-unsaturated
carboxylic acid copolymer coating. A second surface layer of the
film is provided with a metallized layer. An oxidized polyethylene
wax is blended into the copolymer coating material to reduce
blocking between the low temperature sealing coating and the
metallized layer. The film is useful for high-speed packaging
applications requiring sealability at low temperatures. The film
exhibits low blocking performance during unwinding of the film
while maintaining positive low temperature sealability
characteristics.
DETAILED DESCRIPTION OF THE INVENTION
[0015] While metallized films are used widely in the packaging
industry, many disadvantages arise from blocking of the metal layer
to the opposite side of the film. This problem is most evident when
the surface opposite the metallized surface layer is a low
temperature sealable layer or coating. Providing an additional
layer or coating over the metal layer to protect the metal layer
and to reduce blocking is not always an acceptable solution to this
problem. In certain applications, visibility of the metal layer in
the final packaging product is desirable from an aesthetic or
functional viewpoint. Cost considerations may also make a
protective layer or coating undesirable.
[0016] The films described herein address this problem by providing
a low temperature sealing metallized film that allows the metal
layer to remain exposed while reducing the blocking disadvantages
of conventional metallized films. The films include single or
multiple layers having a metallized layer on one surface and a seal
layer on the other surface. The propensity of the metallized
surface layer to block is reduced by inclusion of at least one
oxidized polyethylene wax emulsion in the seal layer.
[0017] The films are comprised of a substrate which may be a single
or multi-layer film. The metallized layer or coating is provided on
one surface of the substrate. The low temperature sealable layer or
coating is provided on the opposite surface of the substrate.
[0018] A variety of ethylene-carboxylic acid copolymer compositions
are useful to provide the low temperature seal functionality on the
surface of the film opposite the metallized layer. The compositions
include at least one ethylene copolymer comprising from about 65
wt. % to about 95 wt. % of ethylene and from about 5 wt. % to about
35 wt. % of an ethylenically unsaturated carboxylic acid or an
ethylenically unsaturated ester. Exemplary suitable carboxylic acid
monomers may be selected from acrylic acid, methylacrylic acid,
maleic acid, crotonic acid, itaconic acid, citraconic acid, and
mixtures thereof. Exemplary suitable ester monomers are acrylic
esters such as methylacrylate, methylmethacrylate, butylacrylate,
and mixtures thereof. In one embodiment, the ethylene copolymer of
the low temperature composition comprises from about 75 wt. % to
about 90 wt. % of ethylene and from about 10 wt. % to about 25 wt.
% of acrylic acid or methacrylic acid. In another embodiment, the
low sealing temperature composition comprises from about 75 wt. %
to about 85 wt. % of ethylene and from about 15 wt. % to about 25
wt. % of acrylic acid or methacrylic acid. The ethylene copolymer
component of the composition may be comprised of one or a mixture
of more than one ethylene copolymer as described above.
[0019] Within the low temperature sealing composition, in one
embodiment, the at least one ethylene copolymer content ranges from
about 75 wt. % to about 95 wt. %. In another embodiment, the at
least one ethylene copolymer content ranges from about 80 wt. % to
about 90 wt. %. In still another embodiment, the at least one
ethylene copolymer content ranges from about 80 wt. % to about 85
wt. %.
[0020] The ethylene copolymer in the low temperature sealable
coating may be obtained as a solution or fine dispersion of an
ammonium salt of the copolymer in an ammoniacal water solution.
When the copolymer is dried, ammonia is given off and the ionized
and water sensitive carboxylate groups are converted to largely
unionized and less water sensitive free carboxyl groups. However,
there may be added to the solution or dispersion of the ethylene
copolymer an amount of ions of at least one metal from Group Ia,
IIa, or IIb of the Periodic Table, such as, sodium, potassium,
lithium, calcium or zinc ions, and mixtures thereof, in the form of
their hydroxides. In one embodiment, sodium hydroxide is used. The
quantity of such metallic ions may be in the range sufficient to
neutralize, for example, about 2% to about 80% of the total
carboxylate groups in the copolymer in one embodiment. In another
embodiment, from about 10% to about 50% of the carboxylate groups
are neutralized. The presence of the metallic ions has been found
in many cases to result in an improvement in certain properties,
e.g., coefficient of friction (COF), hot tack, and blocking,
without an unacceptable sacrifice of other properties such as low
sealing temperatures as described in U.S. Pat. No. 5,419,960.
[0021] Suitable ethylene copolymers have melting points of about
65.degree. C. to about 105.degree. C. in one embodiment. In another
embodiment, the melting points range from about 65.degree. C. to
about 95.degree. C. In a third embodiment, the melting points range
from about 70.degree. C. to about 90.degree. C.
[0022] Exemplary suitable ethylene copolymers for the low
temperature sealing compositions described here are PRIMACOR 59801
available from Dow Chemical Company and ESCOR 5200 from ExxonMobil
Chemical Company.
[0023] A variety of oxidized polyethylene waxes are useful for
inclusion in the low temperature sealing coating compositions
described herein. Polyethylene waxes are made from ethylene
produced from natural gas or by cracking petroleum naphtha.
Ethylene is then polymerized to produce waxes with various drop
points, hardnesses and densities. Oxidized polyethylenes are
readily subjected to emulsification, whereas non-oxidized
polyethylenes largely are not. Inclusion of waxes in the
formulations described herein is typically accomplished through the
use of wax emulsions. However, techniques making use of waxes in
other forms are within the contemplation of this disclosure.
[0024] Useful oxidized polyethylene wax materials include low
molecular weight polyethylenes having a number average molecular
weight of less than about 5000 in one embodiment. In another
embodiment, the number average molecular weight is about 1000 to
about 4000. In still another embodiment, the number average
molecular weight ranges from about 1500 to about 2500.
[0025] The polyethylene waxes should generally be oxidized to an
acid number of about 10 to about 41 in one embodiment. In another
embodiment, the acid number ranges from about 12 to about 28. In
another embodiment, the acid number is from about 12 to about 28.
In a third embodiment, the acid number ranges from about 13 to
about 17. The oxidized polyethylene waxes may also be blended with
non-oxidized waxes.
[0026] The oxidized polyethylene waxes have a drop point range of
about 85.degree. C. to about 145.degree. C. in one embodiment. In
another embodiment, the drop point ranges from about 95.degree. C.
to about 140.degree. C. In a third embodiment, embodiment, the drop
point ranges from about 98.degree. C. to about 115.degree. C. In
still another embodiment, the drop point ranges from about
98.degree. C. to about 110.degree. C. All drop points referred to
herein are as determined by ASTM D3954.
[0027] The oxidized polyethylene waxes have a Brookfield viscosity
at 140.degree. C. of from about 35 centipoises (cps) to about 400
cps in one embodiment. In another embodiment, the Brookfield
viscosity ranges from about 170 cps to about 250 cps.
[0028] Exemplary useful oxidized polyethylene wax materials are
available under the designations AC-629, AC-656, and AC-680 from
Honeywell. These waxes have drop points of 101.degree. C.,
98.degree. C., and 108.degree. C., respectively.
[0029] The oxidized polyethylene waxes may be emulsified in water
by known methods. Exemplary methods are disclosed in U.S. Pat. Nos.
3,850,658 and 4,371,658.
[0030] The particle size of the waxes in the emulsion should
generally be as small as possible. In one embodiment, the oxidized
polyethylene emulsions have wax particle sizes less than one micron
and up to 5 microns. Generally, the wax particles in the emulsions
should not exceed 50 microns in particle size. In one embodiment,
the emulsions comprise from about 10 wt. % to about 60 wt % wax.
The oxidized polyethylene wax component of the composition may be
comprised of one or a mixture of more than one oxidized
polyethylene wax as described above.
[0031] Within the low sealing temperature coating compositions, the
at least one oxidized polyethylene wax content ranges from about 5
parts per hundred ("Phr") to about 25 Phr based upon 100 parts by
weight of the ethylene copolymer. In another embodiment, the
oxidized polyethylene wax content ranges from about 7 Phr to about
20 Phr. In a third embodiment, the oxidized polyethylene wax
content ranges from about 8 Phr to about 18 Phr. In still another
embodiment, the oxidized ethylene content is about 10 Phr. All
references to Phr concentrations used herein are on a dry basis of
the indicated components based upon 100 parts by weight of the
ethylene copolymer component, on a dry basis.
[0032] The low temperature sealable coating compositions may also
contain particulate materials such as amorphous silica to reduce
the tack of the coating at room temperature. Amorphous silica is
composed of particles which are agglomerations of smaller particles
and which have an average particle size of about 2 to about 9
microns in one embodiment. In another embodiment, the particle size
is about 3 to about 5 microns. The silica may be present in the
sealable coating in a concentration of about 0.1 to about 2.0 Phr
in one embodiment. In another embodiment, the concentration is
about 0.2 to about 0.4 Phr. Other types of particulate materials
can be used instead of amorphous silica. Suitable materials include
polymethylmetacrylate spheric particles with an average particle
size of from about 2 .mu.m to about 6 .mu.m in one embodiment. Such
particulates are available under the designations EPOSTAR MA 1002
AND EPOSTAR MA 1004 manufactured by Nippon Shokubai Co., LTD and
CALIBRE CA 6-6 manufactured by Polymer System. Also, silicone
spherical particles with an average particle size of from about 2
.mu.m to about 6 .mu.m in one embodiment are suitable. Exemplary
silicone particles are available under the designation TOSPEARL
manufactured by Toshiba Silicone Co., LTD.
[0033] Other optional additives which may be included in the
sealable coating of the films include other particulate materials
such as talc which may be present in an amount, for example, of
about 0.1 to 2 Phr, cross-linking agents such as melamine
formaldehyde resins which may be present in an amount, for example,
of about 0.1 to 20 Phr, and anti-static agents such as
poly(oxyethylene) sorbitan monooleate which may be present in an
amount, for example, of about 0.1 to 6 Phr. An anti-bacterial agent
may also be present. Sodium hydroxide may be included as well.
[0034] The low temperature sealable coating composition may be
applied in any suitable manner such as by gravure coating, roll
coating, dipping, spraying, etc. Squeeze rolls, doctor knives,
etc., are useful to remove the excess coating solution. The coating
compositions will ordinarily be applied in such an amount that
there will be deposited following drying, a smooth, evenly
distributed layer of from about 0.3 to about 1.8 grams per square
meter of film surface in one embodiment. In another embodiment, the
coating is applied at a thickness of about 0.5 g/m2 to about 1.2
g/m2. In still another embodiment, the thickness is from about 0.6
g/m2 to about 1.0 g/m2. In general, the thickness of the applied
coating is such that it is sufficient to impart the desired
sealability, coefficient of friction (COF), and hot slip
characteristics to the substrate polymer film.
[0035] The coating, once applied to the film may be dried by hot
air, radiant heat or by any other suitable means thereby providing
a non-water soluble, adherent, glossy coated film product useful,
for example, as a packaging film.
[0036] The substrates to which the metallized layer and the low
sealing temperature layers are applied may be any single or
multi-layer thermoplastic material that can be formed into a film.
The substrate can be clear or opaque. The opacity of opaque films
may be achieved by cavitating, creating voids, in one or more
layers of the polymeric film substrate or by other means. Exemplary
thermoplastic materials include any polyolefin such as
polypropylene, polyethylene, polybutene, polystyrene, polyvinyl
chloride, ethylene containing copolymers such as ethylene-propylene
copolymers, ethylene containing terpolymers such as
ethylene-butylene-propylene terpolymers, and blends thereof. Other
suitable film materials include polyethylene terephthalate, other
polyesters (including but not limited to polyethylene terephtalate
glycol [PETG], polyethylene naphthalate [PEN] and liquid
crystalline polymers [LCP]), and nylon, including oriented
nylon.
[0037] In multilayer films, there is one or more skin layer located
on at least one surface of a thermoplastic core layer. Exemplary
skin layers comprise polyethylene, including medium and
high-density polyethylene, polypropylene, copolymers of propylene
and ethylene and terpolymers of propylene, ethylene and butylenes,
and blends thereof.
[0038] Any of the various film layer materials can contain
processing aids or inorganic particulates such as titanium dioxide
or void initiating agents to enhance the whiteness or color of the
substrate or to enhance anti-blocking properties. Exemplary void
initiators and techniques are disclosed in U.S. Pat. Nos. 5,885,721
and 6,168,826.
[0039] As mentioned, the substrate may be a single or multiple
layers. For example, the substrate may be a 3-layer polymeric film
which comprises a core layer and two outer layers, the core layer
comprising polypropylene. In another embodiment, the substrate may
be a 5-layer polymeric film which comprises a core layer, two
intermediate layers contiguous to the central core layer and two
outer layers, the polymer of at least one of the intermediate
layers can comprise polypropylene.
[0040] A particular type of thermoplastic film which can be
advantageously used in the substrate is molecularly oriented
isotactic polypropylene. After extrusion of the substrate, for
example, the base polypropylene film, utilizing conventional
extrusion techniques, the film is heated and molecularly oriented
by stretching it both in the longitudinal and transverse
directions. The resulting oriented film exhibits greatly improved
tensile and stiffness properties. Typically the polyolefin resin,
such as polypropylene, is extruded through a flat sheet extruder
die at a temperature ranging from between about 200.degree. C. to
about 250.degree. C., casting the film onto a cooling drum and
quenching the film. The sheet is then stretched about 3 times to
about 7 times in the machine direction (MD) orienter followed by
stretching about 5 times to about 10 times in the transverse
direction (TD) orienter.
[0041] The substrates may be oriented or hot-blown shrink films
made from any of a number of processes. The oriented films may be
manufactured in a variety of processes including machine direction
orientation (MDO), double bubble, LISIM.RTM., tape bubble, trapped
bubble or tenter framing. The hot-blown films are typically
manufactured in a simple bubble process.
[0042] The following examples are illustrative of specific
embodiments of low temperature sealing metallized films. All parts
and percentages are by weight unless otherwise noted.
EXPERIMENTAL EVALUATIONS
[0043] A useful low temperature sealing metallized film should
demonstrate a variety of favorable characteristics including the
ability to provide an adequate seal at low temperatures and
resistance to blocking following storage and transport. Evaluations
were conducted on six oxidized polyethylene waxes to determine
suitability for inclusion in low temperature sealable coatings on a
flexible substrate opposite a metallized layer. The waxes were
evaluated in the form of aqueous emulsions available from
Michelman, Inc. under the designations indicated in Table I which
also contains physical properties of the emulsions. Table I also
identifies the specific designations of the waxes used to make the
emulsions. All wax designations having the prefix "AC" are
available from Honeywell. Two waxes are available from Carroll
Scientific, Inc. or Eastman Chemical Company, as indicated. The low
temperature sealable coatings are referred to simply as "Coating"
in the following test results.
1TABLE I Wax Emulsion ME ME ME MGRD/PE Micronised ME No emulsion
Designation/Wax 6135E/AC- 74040/East- 10325/AC- from 20325/AC-
designation/ Designation 316 man E/20 629 Caroll Scientific 656
AC-680 Solids % 35 40 25 41 25 25 Particle Size (nm) 40 35 45 12000
45 45 Wax Drop Point 140 111 (softening 101 136 (melting point) 98
108 (.degree. C.) point)
[0044] Selected sealability characteristics of these emulsions as
determined after blending into an ethylene acrylic acid copolymer
("EAA") low temperature sealing coating with a constant wax
concentration of 15 Phr are set forth in Tables II-V. The EAA based
coatings were formulated as follows with all component parts
calculated by weight on a dry basis:
2 Michem Prime 4983 (25% solids EAA formulation) 100 Phr Sodium
hydroxide (10% solids) 1.5 Phr Oxidized polyethylene wax 15 Phr
Syloid 4 .mu.m 0.2 Phr Talc 0.4 Phr
[0045] A comparative formulation was produced with 4 Phr carnauba
wax in place of the 15 Phr oxidized polyethylene wax. A suitable
carnauba wax is available from Michelman, Inc. under the
designation ML 160. The formulations were adjusted to 15% solids
with demineralized water and coated with a kiss coating head, with
the gravure roll turning in reverse to achieve a coating weight of
0.75 g/m.sup.2. The coatings were applied on a 29 .mu.m 3 layer
base film, corona treated and primed with polyethyleneimine. The
base film outer skin layers were a propylene-ethylene-butylene
terpolymer resin.
3TABLE II Flat Jaw Sealability (Coating/Coating) Temperature
(.degree. C.) 90 95 100 105 110 120 130 140 145 Comparative 390 420
500 510 430 390 460 430 400 MGRD 25 0 0 40 40 60 110 220 200 220 ME
10325 0 20 140 140 300 140 240 260 160 ME 74040 300 280 430 370 480
480 480 480 460 ME 61336.E 150 180 180 220 250 340 340 330 330
Sealability determined on one heated flat jaw Asko brand sealer for
2 seconds dwell time at 165.4 kPa. Values are in g/25 mm.
[0046]
4TABLE III Crimp Sealability (Coating/Coating) Temperature
(.degree. C.) 80 85 Comparative 380 410 MGRD 25 220 330 ME 10325
130 475 ME 74040 480 565 ME 61335.E 480 450 Sealbility determined
on a crimp sealer for .75 second dwell time at a pressure of 137.8
kPa. Values are in g/25 mm.
[0047]
5TABLE IV Flat Jaw Sealability (Coating/aluminum foil) Temperature
90 95 100 105 110 120 130 140 145 Comparative 0 30 60 90 220 240
380 270 290 MGRD 25 0 0 0 20 70 70 80 90 80 ME 10325 0 0 0 0 0 0 10
10 10 ME 74040 0 0 20 20 20 150 180 90 60 ME 61335.E 0 0 0 0 10 50
140 80 40 Sealability determined on one heated flat jaw Asko brand
sealer for 2 seconds dwell time at 165.4 kPa. Values are in g/25
mm.
[0048]
6TABLE V Haze Gloss COF Haze Gloss COF Metal Adhesion Comparative
1.9 88 N/A No metal transfer MGRD 25 7.2 78 0.3 No metal transfer
ME 10325 2.2 85 0.35 Metal transfer ME 74040 2.2 86 0.38 No metal
transfer ME 61335.E 2.1 87 0.47 Metal transfer
[0049] Metal adhesion testing was conducted by metallizing the wax
modified coatings and evaluating their affinity towards metal by
testing metal adhesion to the coatings with an adhesive tape after
two pulls. No metal transfer means a high affinity of the coating
to metal and provides an indication about the blocking that can be
expected when the coatings are in contact with metallized surface
on reels. Metal transfer indicates lower blocking tendency to
metal.
[0050] As seen from Tables II-V, all of the polyethylene waxes
contributed to a low sealability between the low temperature
sealing coating and aluminum foil which simulated a metallized
coating. The low sealability was observed over a wide range. The
ME10325 formulation demonstrated the most dramatic reduction in
sealabilty between the low temperature sealing coating and the
aluminum foil.
[0051] To determine the impact of the concentration of the wax in
the EAA blend on the sealability, blocking and general film
characteristics, the concentrations of three of the waxes were
varied and the data in Table VI-XI were observed.
7TABLE VI Flat Jaw Sealability (Coating/Coating) Temperature
(.degree. C.) 90 95 100 105 110 120 130 140 145 Comparative 390 420
500 510 430 390 460 430 400 ME 10325 10 Phr 0 110 370 450 350 420
430 430 370 ME 74040 15 Phr 350 340 410 510 510 490 410 410 400 ME
61335.E 10 Phr 380 380 440 420 430 430 450 400 450 ME 61335.E 15
Phr 320 370 420 450 450 450 450 450 430 Sealability determined on
one heated flat jaw Asko brand sealer for 2 seconds dwell time at
165.4 kPa. Values are in g/25 mm.
[0052]
8TABLE VII Flat Jaw Sealability (Coating/Aluminum Foil) Temperature
(.degree. C.) 90 95 100 105 110 120 130 140 145 Comparative 0 30 60
90 220 240 380 270 290 ME 10325 10 Phr 0 0 0 0 0 0 20 60 20 ME
74040 15 Phr 80 20 50 50 100 170 50 50 40 ME 61335.E 10 Phr 60 40
70 50 60 200 190 150 300 ME 61335.E 15 Phr 10 20 40 50 90 90 100
170 300 Sealability determined on one heated flat jaw Asko brand
sealer for 2 seconds dwell time at 165.4 kPa. Values are in g/25
mm.
[0053]
9TABLE VIII Flat Jaw Sealability (Coating/Metal Side of a
Metallized Film) Temperature (.degree. C.) 90 95 100 105 110 120
130 140 145 Comparative 100 130 170 200 230 240 260 260 270 ME
10325 10 Phr 0 0 0 0 0 0 0 0 0 ME 74040 15 Phr 0 0 20 110 30 40 110
120 250 ME 61335.E 10 Phr 40 30 80 90 110 130 140 170 220 ME
61335.E 15 Phr 0 0 20 20 60 90 130 150 130 Sealability determined
on one heated flat jaw Asko brand sealer for 2 seconds dwell time
at 165.4 kPa. Values are in g/25 mm.
[0054]
10TABLE IX Crimp Sealability (Coating/Coating) Temperature
(.degree. C.) 80 85 Comparative 380 410 ME 10325 10 Phr 370 560 ME
74040 15 Phr 490 610 ME 61335.E 10 Phr 470 560 ME 61335.E 15 Phr
485 495 Sealability determined on a crimp sealer for .75 second
dwell time at a pressure of 137.8 kPa. Values are in g/25 mm.
[0055]
11TABLE X Haze/Gloss Haze Gloss Metal Adhesion Comparative 1.9 88
No metal transfer ME 10325 10 Phr 1.95 86 Metal transfer ME 74040
15 Phr 1.95 86 No metal transfer ME 61335.E 10 Phr 1.9 86 Metal
transfer ME 61335.E 15 Phr 1.9 86 Metal transfer Metal adhesion was
conducted in the same manner as described for the data of Table
V.
[0056]
12TABLE XI Blocking (Coating/Metal Side of a Metallized Film)
Pulled by Peel Tester Metal Transfer Hand (fast) Comparative 100
Yes Tearing ME 10325 10 Phr 7 No Smooth ME 74040 15 Phr 21 Yes
Tearing ME 61335.E 10 Phr 26 Yes Tearing ME 61335.E 15 Phr 18 Yes
Tearing Coating/metal blocking was evaluated in accelerated test
(60.degree. C., 5171 kPa and 1 hour). The test is conducted using a
heated press Model C, manufactured by Carver, Menomonee Falls WI,
USA. The peel tester figures in column 2 indicate the force
recorded for a very slow pulling speed (15 cm/min), column 3
indicates the level of metal transfer from the metallized side to
the Coating side, and column 4 simulates the behavior when
unwinding a reel where separation speed is high. Blocking values
are in g/25 mm.
[0057] It is seen that generally the addition of the wax emulsions
lowered the sealability of the low temperature coating to itself.
However, the reduction was slight. When compared to the Comparative
low temperature seal coating, inclusion of the polyethylene waxes,
resulted in significant reductions in sealability between the low
temperature coating and aluminum at all concentrations. Generally,
the lower the drop point of the wax, the greater the reduction in
sealability between the low temperature coating and the metal. The
metal adhesion test results reported in Table X were determined on
the four low temperature sealable coatings to provide an indication
of the affinity of each coating to metal. Under the severe testing
conditions reported in Table XI, ME 10325 demonstrated the greatest
resistance to blocking. However, the testing conditions are more
severe than likely to be encountered in practical applications.
Therefore, the formulations other than ME 10325 are useful as
antiblocking formulations in many applications, particularly those
benefiting from the other characteristics of a particular
formulation. Comparative formulations incorporating 15 Phr and 25
Phr carnauba wax were also prepared and evaluated. However, no
improvement for these formulations towards metal affinity/blocking
was observed but significant coating to coating sealability
deterioration was observed.
[0058] Emulsion ME 10325 was subjected to additional testing to
evaluate the impact of wax concentration on the performance of this
emulsion. The results of the additional testing are reported in the
following Tables XII-XVI. A new batch of comparative coating was
prepared for these tests in the same manner as described above for
the data in Tables II-XI.
13TABLE XII Flat Jaw Sealability (Coating/Coating) Temperature
(.degree. C.) 90 95 100 105 110 120 Comparative 550 400 550 N/A N/A
N/A ME 10325 8 Phr 300 300 320 450 500 620 ME 10325 10 Phr 300 350
400 500 550 N/A ME 10325 12 Phr 320 340 550 500 N/A N/A Sealability
determined on one heated flat jaw Asko brand sealer for 2 seconds
dwell time at 165.4 kPa. Values are in g/25 mm.
[0059]
14TABLE XIII Flat Jaw Sealability (Coating/Metal Side of a
Metallized Film) Temperature (.degree. C.) 90 95 100 105 110 120
130 140 145 Comparative 140 150 200 200 250 270 250 N/A N/A ME
10325 8 Phr 0 10 20 50 70 80 150 150 270 ME 10325 10 Phr 0 0 0 20 0
80 100 100 250 ME 10325 12 Phr 0 0 0 0 0 0 10 50 130 Sealability
determined on one heated flat jaw Asko brand sealer for 2 seconds
at 165.4 kPa. Values are in g/25 mm.
[0060]
15TABLE XIV Flat Jaw Sealability (Coating/Aluminum Foil)
Temperature (.degree. C.) 90 95 100 105 110 120 130 140 145
Comparative 270 220 300 310 350 450 500 450 500 ME 10325 8 Phr 100
80 130 150 70 140 250 280 150 ME 10325 10 Phr 20 50 40 60 100 50
150 150 200 ME 10325 12 Phr 0 0 0 40 0 20 20 0 20 Sealability
determined on one heated flat jaw sealer for 2 seconds dwell time
at 165.4 kPa. Values are in g/25 mm.
[0061]
16TABLE XV Crimp Sealability (Coating/Coating) Temperature
(.degree. C.) 80 85 Comparative 380 410 ME 10325 8 Phr 370 380 ME
10325 10 Phr 350 440 ME 10325 12 Phr 220 500 Sealbility determined
on a crimp sealer for .75 second dwell at a pressure of 137.8 kPa.
Values are in g/25 mm.
[0062]
17TABLE XVI Blocking (Coating/Metal Side of a Metallized Film)
Comparative 100 Tearing ME 10325 8 Phr 10 Slight sticking, some
metal transfer ME 10325 10 Phr 7 No metal transfer ME 10325 12 Phr
5 No metal transfer These tests were conducted under the same
conditions as for the data of Table XI. Values are in g/25 mm.
[0063] Significant reductions in metal sealability and blocking
were observed at all levels of the ME 10325 emulsion evaluated.
However, it was generally observed that the higher the level of
wax, the greater the reduction in sealability and blocking. In the
next series of evaluations, the ME 10325 wax emulsion was compared
to two similar wax emulsions, ME 20325 and AC-680. These
comparisons are reported in Tables XVII and XVIII.
18TABLE XVII Flat Jaw Sealability (Coating/Metal Side of a
Metallized Film) Temperature Metal 90 95 100 105 110 120 130 140
145 Transfer Comparative 100 130 170 200 230 240 260 260 270 Yes ME
10325 0 0 0 0 0 0 0 0 0 No ME 20325 0 0 0 0 0 0 0 0 0 No AC-680 0 0
50 60 50 90 100 70 80 Yes Sealability determined on one heated flat
jaw Asko brand sealer for 2 seconds dwell time at 165.4 kPa. Values
are in g/25 mm.
[0064]
19TABLE XVIII Blocking Tests Against Metal Side Of a Metallized
Film Comparative 100 Tearing ME 10325 (AC 629) 10 Phr 12 Pinholing
after film separation ME 10325 (AC 629) 12 Phr 10 Pinholing ME
20325 (AC 656) 10 Phr 10 Very slight Pinholing ME 20325 (AC 656) 12
Phr 8 Very slight Pinholing These tests were conducted under the
same conditions as for the data of Table XI. Values are in g/25
mm.
[0065] Once again it was observed that all formulations resulted in
significant reductions of sealability and blocking of the low
temperature coating containing the waxes and metallized films.
However, the reduction was more significant the lower the drop
point of the wax.
[0066] A trial run on a 25 .mu.m film printed on the metallized
side and coated with a low temperature sealable coating formulation
including 10 Phr of ME 20325 wax on the other side provided very
good machinability on a HFFS Rekord machine and showed a slight
increase of 5.degree. C. to 10.degree. C. in minimum sealing
temperature compared to the unmodified low temperature sealable
coating formulation. This testing demonstrates that the formulation
is suitable for use on a reel of a HFFS packaging machine.
[0067] All patents and publications referred to herein are hereby
incorporated by reference in their entireties.
[0068] This application includes references to certain trademarks.
Although the use of trademarks is permissible in patent
applications, the proprietary nature of the marks should be
respected and every effort made to prevent their use in any manner
which might adversely affect their validity as trademarks.
[0069] Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions, and alterations could be made without departing from
the spirit and scope of the invention as defined by the following
claims.
* * * * *