U.S. patent application number 13/924042 was filed with the patent office on 2013-12-26 for deposition of ultra-thin inorganic oxide coatings on packaging.
The applicant listed for this patent is Frito-Lay North America, Inc.. Invention is credited to Robert GODFROID, Glenn JORDAN, Anthony Robert KNOERZER, Kenneth Scott LAVERDURE, Eldridge M. MOUNT, III.
Application Number | 20130340673 13/924042 |
Document ID | / |
Family ID | 49769728 |
Filed Date | 2013-12-26 |
United States Patent
Application |
20130340673 |
Kind Code |
A1 |
GODFROID; Robert ; et
al. |
December 26, 2013 |
DEPOSITION OF ULTRA-THIN INORGANIC OXIDE COATINGS ON PACKAGING
Abstract
An apparatus and method for depositing an ultra-thin inorganic
coating on to a packaging film substrate is disclosed. Flame
pretreatment enhances the quality of the inorganic coating.
Multiple coating layers may be deposited onto the substrate by
passing the substrate over various one or more flame head
configurations in either a stand-alone or in-line manufacturing
environment.
Inventors: |
GODFROID; Robert; (McKinney,
TX) ; JORDAN; Glenn; (Prosper, TX) ; KNOERZER;
Anthony Robert; (Parker, TX) ; LAVERDURE; Kenneth
Scott; (Plano, TX) ; MOUNT, III; Eldridge M.;
(Canandaigua, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Frito-Lay North America, Inc. |
Plano |
TX |
US |
|
|
Family ID: |
49769728 |
Appl. No.: |
13/924042 |
Filed: |
June 21, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61663555 |
Jun 23, 2012 |
|
|
|
Current U.S.
Class: |
118/47 |
Current CPC
Class: |
C23C 16/453 20130101;
B65D 65/42 20130101; C23C 16/545 20130101 |
Class at
Publication: |
118/47 |
International
Class: |
B65D 65/42 20060101
B65D065/42 |
Claims
1. A system for coating a packaging film substrate with an
inorganic oxide layer comprising: at least one flame treatment
flame head assembly supplied with no inorganic oxide precursor; one
or more deposition flame heads supplied with at least one inorganic
oxide precursor placed in series on at least one deposition flame
head assembly; wherein said substrate passes through said flame
treatment flame head assembly before said substrate passes through
said deposition flame head assembly, and wherein said at least one
flame treatment flame head assembly and said one or more deposition
flame heads are at open atmosphere.
2. The system of claim 1 wherein said at least one flame treatment
flame head assembly or said at least one deposition flame head
assembly comprises multiple flame head assemblies oriented in
parallel rows perpendicular to a substrate movement direction.
3. The system of claim 1 wherein said at least one flame treatment
flame head assembly or said at least one deposition flame head
assembly comprises a square or rectangular shaped flame head
assembly.
4. The system of claim 1 wherein said at least one flame treatment
flame head assembly or said at least one deposition flame head
assembly comprises multiple flame heads assemblies oriented in rows
parallel to a substrate movement direction.
5. The system of claim 1 wherein said at least one flame treatment
flame head assembly or said at least one deposition flame head
assembly comprises a curved flame head assembly.
6. The system of claim 1 wherein said at least one flame treatment
flame head assembly or said at least one deposition flame head
assembly is oriented at an angle relative to a surface of said
substrate.
7. The system of claim 1 wherein said substrate passes through said
flame head assemblies as it passes over a portion of said at least
one chill roll.
8. The system of claim 1 wherein said inorganic precursors are fed
into a flame fuel line of said deposition flame heads prior to
being mixed with air from an air line and combusted at said flame
heads.
9. The system of claim 1 wherein said inorganic precursors are fed
into an air line of said deposition flame heads prior to being
mixed with fuel from a fuel line and combusted at said flame
heads.
10. The system of claim 1 wherein said inorganic precursors are fed
into an air line and a fuel line of said deposition flame heads
prior to being mixed and combusted at said flame heads.
11. The system of claim 1 wherein said inorganic precursors are
mixed with an air/fuel mixture prior to being fed to said
deposition flame heads.
12. The system of claim 1 wherein said inorganic precursors is
injected into a flame produced by said deposition flame heads.
13. The system of claim 1 further comprising an air knife flame
redirect.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of provisional U.S.
Application No. 61/663,555 entitled "Deposition of Ultra-Thin
Inorganic Oxide Coatings on Packaging" filed Jun. 23, 2012.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates to an elemental layer on a
packaging substrate and the method and apparatus for applying the
elemental layer. More specifically, the invention disclosed herein
pertains to an ultra-thin inorganic metal oxide layer that serves
as an oxygen and water vapor barrier layer and/or to serve as an
interface for future functionalization when applied to a packaging
substrate. This layer can be formed during the manufacture of the
packaging substrate or in later processing stages by use of known
chemical vapor deposition apparatus and methods in a commercial
packaging substrate manufacturing context.
[0004] 2. Description of Related Art
[0005] Multi-layered packaging substrates made from petroleum-based
products, polymers, copolymers, bio-polymers and/or paper
structures are often used where there is a need for advantageous
barrier, sealant, and graphics-capability properties. Barrier
properties in one or more layers comprising the packaging substrate
are important in order to protect the product inside the package
from light, oxygen and/or moisture. Such a need exists, for
example, for the protection of foodstuffs that may run the risk of
flavor loss, staling, or spoilage if sufficient barrier properties
are not present to prevent transmission of light, oxygen, or
moisture into or out of the package. A graphics capability may also
be required so as to enable a consumer to quickly identify the
product that he or she is seeking to purchase, which also allows
food product manufacturers a way to label information such as the
nutritional content of the packaged food, and present pricing
information, such as bar codes, to be placed on the product.
[0006] In the packaged food industry, protecting food from the
effects of moisture and oxygen is important for many reasons,
including health, safety, and consumer acceptability (i.e.,
preserving product freshness and taste). Conventional methods to
protect food contents incorporate specialized coatings or layers
within or on a surface of the packaging substrate, which function
as an impervious barrier to prevent the migration of light, water,
water vapor, fluids and foreign matter. These coatings may consist
of coextruded polymers (e.g., ethyl vinyl alcohol, polyvinyl
alcohol, polyimides, polyamides (i.e. nylons and polyvinyl acetate)
and/or a thin layer of metal or metal oxide, depending on the level
of barrier performance required to preserve the quality of the
product stored within the package volume.
[0007] Coatings produced by chemical vapor deposition are known to
provide certain barrier characteristics to the coated substrate.
For example, an organic coating such as amorphous carbon can
inhibit the transmission of elements including water, oxygen and
carbon dioxide. Accordingly, carbon coatings have been applied to
substrates, for example, polymeric films, to improve the barrier
characteristics exhibited by the substrate. Another example of
coatings applied to substrates to improve barrier adhesion
performance includes coatings comprised of inorganic materials such
as inorganic metal oxides. Ethyl vinyl alcohol and other polymer
skin layers are widely used to prime or improve the wettability of
film substrates for the application of a barrier layer also
referred to herein as "metallization primer". Aluminum metal,
aluminum oxide, and silicon oxide are widely used for the
application of barrier layer(s) directly to the substrates also
referred to herein as "metallization".
[0008] The inorganic coatings described above may be deposited onto
substrates through various techniques as known in the art. Such
techniques include physical vapor deposition (PVD) or chemical
vapor deposition (CVD) processes. Examples of PVD include ion beam
sputtering and thermal evaporation. Examples of CVD include glow
discharge, combustion chemical vapor deposition (CCVD) and plasma
enhanced chemical vapor deposition (PECVD) by generation of flame
plasma or in strong electric fields.
[0009] The most commonly known and utilized method for depositing
barrier layers on packaging substrates for metallization requires
the use of a vacuum chamber to provide the vacuum environment for
the deposition of inorganic atoms/ions on to the film substrate
surface. This known technique, as used in the food packaging
industry, consists of processing packaging substrate rolls that are
from less than one to three meters wide and 500 to 150,000 meters
in length running at industry speeds of 60-600 meters/min and
higher in a vacuum metallization chamber. This equipment is highly
specialized, requires a great deal of electrical power and requires
large capital expense. Current vacuum chamber processes for
metalizing films is inefficient in many respects due to the high
operational costs and limited production capacity associated with
the use of such equipment. Moreover, higher quality film
substrates, requiring additional capital expenditure, must
typically be used to achieve the desired barrier properties.
[0010] Combustion chemical vapor deposition (CCVD) and plasma
enhanced chemical vapor deposition (PECVD) apparatus and methods
are known in the art, as disclosed in U.S. Pat. Nos. 5,997,996 and
7,351,449, the disclosures of which are hereby incorporated by
reference. Typically, a combustion flame or plasma field provides
the environment required for the deposition of the desired coating
(via the vapors and gases generated by the combustion or plasma)
onto the substrate. The elemental precursors (e.g. organometallics)
may be vaporous or dissolved in a solvent that may also act as a
combustible fuel. The deposition of organic and inorganic oxides
may then be carried out under standard and/or open atmospheric
pressures and temperatures without the need of a vacuum chamber,
furnace and/or pressure chamber.
[0011] As described above, the application of barrier to food
packaging is required to protect food and food products from the
effects of moisture and oxygen. It is well known in the art that
metalizing a petroleum-based polyolefin such as OPP or PET reduces
the moisture vapor and oxygen transmission through specialty film
by approximately three orders of magnitude. Conventional technology
employs an inorganic layer of metal or ceramic on a specialized
polymer film. The inorganic layer may be aluminum, silicon, zinc,
or other desired element in a metal or oxide form. However, the
surface of the substrate onto which the barrier layer will be
applied is typically primed to increase its surface energy so as to
be receptive to the metal barrier to be deposited thereon and/or to
"smooth" the surface to be metalized so as to reduce the surface
gauge variation or surface roughness of the film to be metalized.
The term "wettability" is defined herein to include surface energy,
metal adhesion bond strength, and any other associated
characteristic that would increase the receptiveness of the film
layer surface for deposition of an inorganic ultra-thin as
disclosed herein.
[0012] For example, the utilization of aluminum metal as a barrier
layer on low energy plastics, such as biaxially oriented
polypropylene (BOPP) film, requires a metallization primer to
reduce the gauge variation of the film substrate surface and/or to
improve the adhesion or bond between the metal and film substrate.
Various chemical methods are employed to prime the substrate
surface layer for improving the substrate surface and/or bonding of
the metal barrier layer to the film substrate. With polymer film
substrates, one method to prime the substrate for metallization is
to co-extrude a specialized polymer as a skin layer on the
substrate film. These skin layers may comprise ethyl vinyl alcohol
(EVOH), polyvinyl alcohol (PVOH), and polyvinyl acetate (PVA),
ethyl vinyl acetate (EVA), polyethylene terephthalate glycol
(PETG), amorphous polyethylene terephthalate (aPET), among other
polymers used in the industry. Unfortunately, these materials are
quite expensive and add additional cost to the manufacture of
metallization ready films. Plastic film cores, such as oriented
polypropylene (OPP), polystyrene (PS), and polyethylene
terephthalate (PET) are typically treated with corona discharge or
flame treatment. However, these treatments tend to create
undesired, adverse impacts on film substrate characteristics such
as the formation of pin holes, chemical degradation of the surface
through cross linking or intra-molecular chain scission that can
adversely affect downstream metallization and heat sealing
processes.
[0013] As such, there exists a need for an improved apparatus and
method for depositing an ultra-thin inorganic oxide layer onto a
packaging substrate to prime a substrate for metallization.
Likewise, a need exists in the art for an improved apparatus and
method for depositing multiple ultra-thin layers of an inorganic
oxide layer on to a packaging substrate to enhance the barrier
properties of a packaging substrate, which is less expensive and
more energy efficient than tradition metallization while achieving
and maintaining high quality barrier characteristics.
SUMMARY OF THE INVENTION
[0014] The inventive embodiments disclosed herein include a
packaging substrate with an ultra-thin barrier layer and an
apparatus and method for applying an ultra-thin inorganic metal
oxide barrier layer to a film substrate. In one embodiment, the
apparatus and method disclosed herein use the direct combustion of
liquids, gases and/or vapors that contain the chemical precursors
or reagents capable of producing inorganic oxides which are
deposited on to the surface of a film substrate at open atmosphere.
Chemical precursors, for example tetraethyl orthosilicate,
tetramethyl disiloxane, silicon tetrachloride, silane,
trimethylaluminium, triethylaluminium,
methylaluminiumdichlorid-diethyletherate,
trimethylaluminium-diethyletherate,
ethylaluminiumdichlorid-diethyletherate,
diethylaluminium-dimethylamide, aluminum trichloride, and other
aluminum halides may be sprayed or atomized in an oxidant and
combusted resulting in a vapor and/or gas that is directed on to
the surface of the substrate via one or more flame heads for
forming the desired coating or multiple coatings thereon. Multiple
coating layers may be deposited onto the substrate by passing the
substrate through the system in either a stand-alone or in-line
manufacturing environment, or by passing the substrate over various
one or more flame head configurations in either a stand-alone or
in-line manufacturing environment as disclosed herein.
[0015] One embodiment of the present invention comprises a
packaging substrate surface with an inorganic metal oxide layer of
less than 50 nm thickness that is constructed by depositing
multiple ultra-thin layers of inorganic metal oxide on to a surface
of the packaging substrate. In various embodiments, a preferred
process that can accomplish deposition of an inorganic oxide layer
onto the packaging substrate surface is CCVD or PECVD in an open
atmosphere utilizing novel flame head assembly designs and
orientations to provide and adjust as for various precursor
concentrations and coating thicknesses that are deposited on to the
film substrate.
[0016] In one embodiment of the invention, a method of coating a
film substrate with at least one inorganic oxide layers comprises
pretreating said substrate by passing said substrate through at
least one flame treatment flame head assembly supplied with no
inorganic oxide precursor, and after said pretreating step,
depositing one or more inorganic oxide layers on said substrate by
passing said substrate through one or more deposition flame heads
on at least one deposition flame head assembly supplied with at
least one inorganic oxide precursor, wherein said pretreating and
depositing steps occur at open atmosphere.
[0017] In another embodiment, the at least one inorganic oxide
precursor comprises at least one of tetraethyl orthosilicate,
tetramethyl disiloxane, silicon tetrachloride, silane,
trimethylaluminium, triethylaluminium,
methylaluminiumdichlorid-diethyletherate,
trimethylaluminium-diethyletherate,
ethylaluminiumdichlorid-diethyletherate,
diethylaluminium-dimethylamide, aluminum trichloride, and aluminum
halides.
[0018] In one embodiment, the pretreating step comprising passing
said substrate over a portion of at least one chill roll. In
another embodiment, the pretreating step comprises passing said
substrate over a portion of multiple chill rolls. The chill roll
can comprise a temperature of 40.degree. C. to 80.degree. C.
[0019] In one embodiment, the depositing step comprises depositing
multiple inorganic oxide layers on said substrate by passing said
substrate through two or more deposition flame heads in series. In
another embodiment, the pretreating and depositing steps occur as
said film substrate is unwound from one roll and wound onto a
second roll. The pretreating and depositing steps may occur in-line
during manufacturing of said film substrate.
[0020] In one embodiment, the film substrate is cooled during said
pretreating step by spraying cooling fluid on said film
substrate.
[0021] In one embodiment of the invention, a system for coating a
packaging film substrate with an inorganic oxide layer comprises at
least one flame treatment flame head assembly supplied with no
inorganic oxide precursor, one or more deposition flame heads
supplied with at least one inorganic oxide precursor placed in
series on at least one deposition flame head assembly, wherein said
substrate passes through said flame treatment flame head assembly
before said substrate passes through said deposition flame head
assembly, and wherein said at least one flame treatment flame head
assembly and said one or more deposition flame heads are at open
atmosphere.
[0022] In another embodiment, the at least one flame treatment
flame head assembly or said at least one deposition flame head
assembly comprises multiple flame head assemblies oriented in
parallel rows perpendicular to a substrate movement direction.
[0023] In one embodiment, the at least one flame treatment flame
head assembly or said at least one deposition flame head assembly
comprises a square or rectangular shaped flame head assembly. In
another embodiment, the at least one flame treatment flame head
assembly or said at least one deposition flame head assembly
comprises multiple flame heads assemblies oriented in rows parallel
to a substrate movement direction. In still another embodiment, the
at least one flame treatment flame head assembly or said at least
one deposition flame head assembly comprises a curved flame head
assembly.
[0024] In one embodiment, the at least one flame treatment flame
head assembly or said at least one deposition flame head assembly
is oriented at an angle relative to a surface of said substrate. In
another embodiment, the substrate passes through said flame head
assemblies as it passes over a portion of said at least one chill
roll.
[0025] In one embodiment, the inorganic precursors are fed into a
flame fuel line of said deposition flame heads prior to being mixed
with air from an air line and combusted at said flame heads, into
an air line of said deposition flame heads prior to being mixed
with fuel from a fuel line and combusted at said flame heads, into
an air line and a fuel line of said deposition flame heads prior to
being mixed and combusted at said flame heads, or mixed with an
air/fuel mixture prior to being fed to said deposition flame heads.
In another embodiment, the inorganic precursors is injected into a
flame produced by said deposition flame heads.
[0026] The inventive embodiments described herein may be
implemented in stand-alone configurations, retrofitted to existing
film production lines, or installed into an in-line film substrate
manufacturing and/or processing system. The substrate material to
be coated does not need to be heated or treated in a furnace or
reaction chamber, or placed under vacuum or non-standard
atmospheric conditions to effect coating deposition. The heat of
combustion provides the needed conditions for the reaction of the
chemical precursors. The substrate material being coated is
likewise heated by the combustion flame, which creates and/or
enhances the kinetic environment for surface reactions,
wettability, diffusion, film (coating) nucleation and film
(coating) growth. The chemical precursors utilized need to be
properly reactive to form the desired coating. While inorganic
metal oxides are the preferred material for the coating applied to
the packaging substrate, other elemental coatings and compounds,
for example metals, nitrides, carbides, and carbonates may also be
used as desired.
[0027] Other aspects, embodiments and features of the invention
will become apparent from the following detailed description of the
invention when considered in conjunction with the accompanying
figures. The accompanying figures are schematic and are not
intended to be drawn to scale. For purposes of clarity, not every
component is labeled in every figure, nor is every component of
each embodiment of the invention shown where illustration is not
necessary to allow those of ordinary skill in the art to understand
the invention. All patent applications and patents incorporated
herein by reference are incorporated by reference in their
entirety. In case of conflict, the present specification, including
definitions, will control.
BRIEF DESCRIPTION OF THE FIGURES
[0028] The novel features believed characteristic of the invention
are set forth in the appended claims. The invention itself,
however, as well as a preferred mode of use, further objectives and
advantages thereof, will be best understood by reference to the
following detailed description of illustrative embodiments when
read in conjunction with the accompanying figures, wherein:
[0029] FIG. 1 depicts a cross-section view of a typical prior art
food packaging film substrate;
[0030] FIGS. 2A-2I depict various embodiments of the apparatus and
method employed in the present invention disclosed herein;
[0031] FIGS. 3A-3E are depictions of the apparatus and method as
integrated into in-line packaging substrate production and
manufacturing equipment according to one embodiment of the
invention disclosed herein;
[0032] FIG. 4 is a cross-sectional depiction of a film substrate
with multiple coating nanolayers according to one embodiment of the
invention disclosed herein; and,
[0033] FIGS. 5A-5I are depictions of various apparatus embodiments
which may be employed in the present invention disclosed
herein.
[0034] FIG. 6 is a graph showing, for a single deposition pass of
silica, the amount of silica deposited as determined by signal
strength via information collected by XPS.
[0035] FIG. 7 is a graph showing a signal strength (CPS) vs.
binding energy (eV) from XPS for multiple passes; and
[0036] FIG. 8 is a graph showing the atomic percentage of silicon
atoms on the film surface, WVTR, and OTR values plotted versus the
number of silica deposition passes.
DETAILED DESCRIPTION
[0037] FIG. 1 depicts a schematic cross-section of a typical,
currently used food packaging multi-layer or composite film
substrate 10. Film 10 is constructed of various intermediate layers
that act in concert to provide the film 10 with the required
performance characteristics. For example, a graphics layer 14
allows a graphic to be printed or otherwise disposed thereon and is
protected by transparent exterior base layer 12 which may consist
of oriented polypropylene (OPP) or polyethylene terephthalate
(PET). A glue or laminate layer 16, which is typically a
polyethylene extrusion, acts to bind the exterior base layer 12
with the inner, product-side base layer 18. A metal layer may be
disposed upon inner base layer 18 by means of metallization known
in the art. Sealant layer 20 is disposed upon the OPP or PET
interior base layer 18 to enable a hermetic seal to be formed at a
temperature lower than the melt temperature of the interior base
layer 18. Each layer described is formed as a roll of film that is
then unwound and laminated together to form the composite film.
Each film being laminated together forms the composite films, which
are film structures composed of multiple layers when originally
extruded or fabricated.
[0038] Alternative materials used in the construction of packaging
film substrates may include polyesters, polyolefin extrusions,
cellulosic polymers, acetate polymers, adhesive laminates,
bio-films such as polylactic acid (PLA) films and
polyhydroxy-alkanoate (PHA) films, produced in various combinations
resulting in composite, multi-layered film structures. The film
substrate may be formed by typical coextrusion, lamination, or
extrusion coating techniques as known in the art. The film
substrate can also be composed of polyimide, liquid crystal,
polyethylene, or other materials normally used in electronic, optic
or specialty packaging or multilayer applications.
[0039] In both PECVD and CCVD processes described herein, the
localized environment required for coating deposition to occur is
provided by the flame, plasma or other energy means. With CCVD and
PECVD no furnace, auxiliary heating, or reaction chamber is
necessary for the reaction to occur. Further, both CCVD and PECVD
can be carried out in open-atmosphere conditions. The plasma or
flame supplies the energy needed for coating deposition in the
forms of the kinetic energy of the species present and radiation.
This energy creates the appropriate thermal environment to form
reactive species and coincidentally heats the substrate, thus
providing the kinetic conditions for surface reactions, diffusion,
nucleation, and growth to occur. When using combustible solutions,
the solvent plays two primary roles. First, the solvent conveys the
coating reagents into the vicinity of the substrate where coating
deposition occurs, thereby allowing the use of low cost soluble
precursors. Uniform feed rates of any reagent stoichiometry can be
produced easily by simply varying the reagents' concentrations in
solution and the solution flow rate. Second, the combustion of the
solvent produces the flame required for CCVD and PECVD.
[0040] In general, the deposition processes described herein are
performed under ambient conditions in the open atmosphere to
produce an inorganic film on a substrate. The film preferably is
amorphous, but may be crystalline, depending on the reagent and
deposition conditions. The reagent, or chemically reactive
compound, is dissolved or carried in a solvent, typically a liquid
organic solvent, such as an alkene, alkide or alcohol. The
resulting solution is sprayed from a nozzle using oxygen-enriched
air as the propellant gas and ignited. A substrate is positioned at
or near the flame's end. Flame blow-off may be prevented by use of
a hot element such as a small pilot light. The reactants are
combusted in the flame and the ions or radicals generated from the
combustion are deposited on the substrate as a coating. For the
present invention, the formation and rate of deposition of the
inorganic oxide layer(s) are important to the quality of the
coating produced and the invention disclosed herein describes in
various embodiments and examples of the equipment and processes for
producing such quality coatings.
[0041] The methods and apparatus utilized to perform the inventive
methods disclosed herein provide a less-energy intensive and more
efficient method for the surface treatment of film substrates for a
variety of applications. For example, priming a substrate for
metallization is usually required to enhance the wettability of the
substrate surface for the reception of a metalized layer. As
previously discussed, prior art methods of priming a substrate for
metallization typically require the addition of a skin layer via
coextrusion or solution coating of chemical additives such as EVOH
and/or treatment by flame or Corona discharge prior to
metallization. The apparatus and methods herein provide a novel
method by which the surface energy of the film substrate is raised
typically between 1 and 10 dynes by the addition of the inorganic
primer nanolayer, thereby enhancing the wettability of the
substrate surface and thus improving the adhesion between the
deposited metal barrier coating and the substrate.
[0042] It is also important for the inorganic oxide layer(s) to
enable future vapor deposition of barrier, printing or adhesive
layers applied to the film substrate to adhere well and for hot
seal processes to still function as desired. An integral aspect of
the invention includes application of the inorganic oxide layer to
the film substrate so as to improve the surface wettability of the
substrate surface for future applications.
[0043] By using different inorganic materials, additional
properties can be created to enhance the use of the film for
various applications. For example, use of silver can provide
antimicrobial/disinfection properties. In other embodiments,
ultraviolet radiation blocking inorganics, including zinc oxides
and tin oxides may be utilized to form a clear ultra-violet light
and gas barrier layer. Other transparent materials, for example
silica oxide, may be used to form and/or act as ultra-thin barrier
layer(s).
[0044] A key economic feature in using polymer-based products is
maintaining low cost. As a result, the inorganic materials used as
nanolayer coatings are typically selected from low cost inorganic
elements. Also, the health aspect of the materials used in the
formation of films for packaging is very important since the
polymer films are used most often in consumer products including
food and medical packaging. Thus, health safe materials, for
example silica-based inorganics, may be utilized in various
embodiments. Silica is the most common oxide of the earth's crust
and soil and long-term storage in glass containers has extensive
proven history as a safe and effective storage medium with regard
to human health requirements.
[0045] The use of current surface modifying materials in film
production represents a significant volume and weight fraction of
the end product thus reducing its recyclability. The present
invention greatly reduces the material required to form the desired
barrier thickness, resulting in a more recyclable and/or
compostable product. In one an embodiment, the inorganic oxide
layer is generally less than 10 nm thick and more preferably less
than 5 nm average thickness. Due to the small thickness of such a
layer, the inorganic oxide layer more readily breaks into smaller
pieces resulting in a higher grade of recyclable material. In fact,
silica is often used as an enhancement additive to polymers to
improve strength and durability. One embodiment of the invention
includes an inorganic oxide layer that alters the bulk physical
properties of film base polymer, as compared to reprocessing of
neat polymer, by less than 1%.
[0046] For biodegradable polymers, such as PLA and PHA, a barrier
layer applied to a film substrate incorporating PLA and/or PHA or
other bio-polymer may in fact detract from the desired
degradability of the packaging material resulting therefrom. Such a
barrier layer reduces the transmission of moisture or oxygen that
can affect the degradation process of the film package. Multiple
layers of barrier can result in a package that does not degrade due
to the core film substrate material (barrier on both sides) never
being exposed to the proper environment for decomposition. An
embodiment of the present invention includes forming an inorganic
oxide coating that alone does not provide an impervious barrier,
but enables subsequent printing, adhesion layers, or quality
barrier layer(s) to be deposited upon the inorganic oxide coating
in an online manufacturing context or a secondary downstream
facility. In one embodiment, the inorganic oxide layer can be
deposited on both sides of the packaging substrate for a variety of
contemplated end uses.
[0047] One of the key uses of the smooth inorganic ultra-thin layer
is subsequent barrier layer formation thereon. Thin film
metallization or oxide barrier layers adhere to and perform better
on smooth surfaces with low defects. Polymer films readily form
such surfaces during manufacturing, but the addition of anti-block
agents as currently used in the industry cause an increase in the
film's surface roughness and defects, with RMS generally greater
than 100 nm. A key aspect of the present invention results in
packaging substrates with surface roughness than 30 nm RMS, and
more preferably less than 10 nm RMS, and in some cases less than 5
nm RMS.
[0048] In another embodiment, the invention disclosed herein
produces the ability to maintain low surface RMS values while
controlling the surface wetting properties. The surface tension can
be controlled by a combination of the inorganic ultra-thin layer's
surface roughness and also the termination material on the surface.
To improve the adhesion of inorganic barrier layer materials to the
substrate, it is desired that a surface of the substrate be
receptive to metal or inorganic oxide ionic or covalent bonding.
Inorganic oxide surfaces provide excellent bonding sites for both
metal and oxide layers, along with a smooth surface coating. It has
been discovered that surface smoothness enhances the formation of
barrier layer(s) on the substrate. For barrier deposition
applications, it is preferred that the substrate surface to be
coated has a smooth, low texture surface on both the nanometer and
micrometer scale.
[0049] One key to successful application of such interface layers
is to form and apply the primer and barrier layers to the substrate
prior to winding or rolling of the film. Films are made by a number
of processes including cast and blown films. These processes are
typically performed at ambient atmosphere and pressure on large
production lines. The introduction of prior art vacuum deposition
equipment into such a line makes such processes economically
impractical. Thus, a method for forming films online with an
inorganic ultra-thin layer at ambient pressure on low temperature
polymers is a better pathway to accomplish such an inventive
ultra-thin layer. Aspects of how to do this with a process such as
CCVD are disclosed in U.S. Pat. No. 5,652,021 (Hunt et al.) and
U.S. Pat. No. 5,863,604 (Hunt et al.), the disclosures of which are
incorporated herein by reference.
[0050] In order to form an effective barrier layer in subsequent
processing operations, it is important for the film substrate
surface to be smooth. Thin film barrier requires a smooth substrate
surface without features that can shadow or inhibit the thin film
material from being deposited onto the vast majority of the entire
surface. It is preferred that at least 90% of the substrate surface
be coated and even more preferred that over 99% be accessible to
vapor deposition material without surface roughness that can cause
shadowing or thin film defects. It is also important that the
inorganic primer layer is very smooth so that it will not impact
the dense uniform continuous growth of additional inorganic oxide
layer(s) deposited thereon to build an effective thin film barrier
layer. Columnar growth on the inorganic primer layer will have a
negative impact on the subsequent growth of a vacuum deposited or
other thin film barrier layer applied thereto. The end effect is
that a subsequent barrier layer can be grown to yield a Oxygen
Transmission Rate (OTR) of less than 10 cc/m.sup.2/day @ 23.degree.
C. and 0% RH and a Water Vapor Transmission Rate (WVTR) of less
than 2 g/m.sup.2/day @ 38.degree. C. and 90% RH, more preferably
OTR<2 cc/m.sup.2/day @ 23.degree. C. and 0% RH and WVTR<1
g/m.sup.2/day @ 38.degree. C. and 90% RH, and even more preferably
OTR<1 cc/m.sup.2/day @ 23.degree. C. and 0% RH and WVTR<0.2
g/m.sup.2/day @ 38.degree. C. and 90% RH on substrates where an
inorganic primer layer is deposited prior to the barrier layer. In
one embodiment, the primer and/or barrier layer is transparent to
light in the visible spectrum. In alternative embodiments, the
subsequent primer and/or barrier layers may be translucent or
opaque as appropriate for effective utilization of the coated
substrate for flexible packaging or other contemplated end
uses.
[0051] The current invention also has minimal environmental impact
and yields a safer packaging material as a result of the reduction
in the number of organic chemicals blended into the polymer film
substrate. Such additives can cause health concerns or can reduce
the quality of recyclable material. Silica, alumina, and the other
elements of the present invention are common in the earth's crust,
are often used as food additives, and have been used safely in
glass containers for many years. As a result, the invention
disclosed herein utilizes plentiful and non-toxic, safe inorganic
materials with essentially no detrimental environmental impact.
[0052] Multilayer packaging substrates may be produced with
excellent bonding characteristics provided by application of one or
more ultra-thin inorganic oxide layers as described herein. In
various embodiments, moisture, oxygen and light can pass through
the inorganic oxide layer(s) so that compostable polymer film
structures can still be decomposed under typical environmental
conditions. The inorganic oxide coating with proper selection of
metalloid or metal element, such as silicon or aluminum, creates a
thin coating that will not inhibit composting of the film substrate
and has absolute minimal impact on the environment.
[0053] In one embodiment disclosed herein, a PECVD or CCVD
apparatus is used to deposit one or more ultra-thin layers of
silica oxide (SiO.sub.x) and/or other inorganic oxides on the
surface of the substrate in an open atmosphere environment thereby
increasing the substrate surface energy and improving the adhesion
of the metal barrier layer with the substrate, effectively
"priming" the substrate for metallization. In one embodiment
disclosed herein, a PECVD or CCVD apparatus is integrated "in-line"
with a packaging substrate manufacturing line there for priming the
substrate for metallization before being wound into a roll.
[0054] Various embodiments of the present invention disclosed
herein also comprise apparatus and methods for applying a barrier
layer to the surface of a packaging substrate at open atmosphere.
The apparatus and method disclosed herein provide for the direct
combustion of liquids and/or vapors that contain the chemical
precursors or reagents to be deposited on to the surface of a
substrate material at open atmosphere. Metal oxides, for example,
aluminum oxides, are formed from the combustion of materials, such
as organo-aluminum compounds with an oxidant, and combusted
resulting in a vapor and/or gas at open atmosphere that is directed
on to the surface of the substrate and resulting in the deposition
of the desired coating thereon.
[0055] In accordance with an embodiment of the invention disclosed
herein, FIG. 2A depicts a flame CCVD apparatus that is supplied
with combustible chemical precursors for the deposition of an
inorganic oxide coating on to a substrate. The system operates to
break the chemical precursors into micron and sub-micron sized
droplets in the combustion zone for the application of the
ultra-thin coating process disclosed herein.
[0056] Turning to FIG. 2A, a general schematic of the apparatus 40
that is utilized to carry out the coating deposition process is
shown. Chemical precursors 42 may comprise a solvent-reagent
solution of flammable or non-flammable solvents mixed with liquid,
vaporous, or gaseous reagents supplied to flame head assembly 44 or
other flame-producing device. The term "flame head assembly" is
used to refer generally to describe any apparatus that is capable
of producing a flame from a fuel feed, including flame treaters,
flame burners and flame head devices as described herein and which
are commercially available from various manufacturers. Chemical
precursors 42 are ignited in the presence of an oxidant 46
resulting in a flame 48. As the chemical precursors 42 solution or
mixture burn, the reagent reacts to form an inorganic vapor and
leaves the flame 48 along with other hot gases 50 and combustion
products. The substrate 52 to be coated is located proximal to
flame 48 within the region of gases 50. In one embodiment,
substrate 52 is oriented tangentially to the flame 48, or as shown
in FIG. 2B substrate 52 is oriented obliquely to the flame 48, or
at any angle facing the flame end 54 of flame 48 such that the hot
gases 50 containing the reagent vapor will contact the substrate
surface 56 to be coated. In various embodiments, substrate 52 may
consist of a film or composite film comprising oriented
polypropylene (OPP), polyethylene (PE), polylactic acid (PLA),
polyhydroxy-alkanoate (PHA), polyethylene terephthalate (PETP),
other polyesters, or other known polymer, biopolymer, paper or
other cellulosic substrates, alone or in combination, as known in
the art.
[0057] FIG. 2B is similar to the apparatus 40 shown in FIG. 2A, but
is configured for a non-turbulent flame methodology, suitable for
chemical precursors comprising gaseous precursors 42 and
non-flammable carrier solutions 46. Flame 48 produced by the flame
head assembly 44a typically has the flame characteristics of an
inner flame 48a defining the reducing region where the majority of
oxidizing gas supplied with the reagent burns and an outer flame
48b defining the oxidizing region where the excess fuel oxidizes
with any oxidizing gas in the atmosphere. In this example
embodiment, the substrate is positioned at an oblique angle
proximate to the flame end 54 of the flame 48 such that the hot
gases and/or vapors 50 containing the reagent vapor will contact
the substrate surface 56 of substrate 52.
[0058] Referring back to FIG. 2A, the precursor mixture 46 is
supplied to the flame head assembly 44. Oxidant 46 is also supplied
to the flame head assembly 44 in some fashion, via a separate feed,
or is present in the process atmosphere, or the oxidant may be
supplied by a separate feed to the process atmosphere or flame
ignition point, or the oxidant may be present in the reagent
mixture. In the depicted embodiment, the chemical precursor
solution 42 is ignited in the presence of oxidant 46 and combust in
flame 48 resulting in the generation of heat, gases and/or vapors
50. The generation of heat causes any liquid reagent solutions
present to vaporize and increase the temperature of the substrate
52 so as to result in improved surface diffusion of the coating
resulting in a more uniform coating deposited onto the substrate
surface 56.
[0059] In performing CCVD or PECVD coating deposition on film
substrates, certain deposition conditions are preferred. First, the
substrate needs to be located in a zone such that it is heated by
the flame's radiant energy and the hot gases produced by the flame
sufficiently to allow surface diffusion. This temperature zone is
present from about the middle of the flame to some distance beyond
the flame's end. The temperature of the flame can be controlled to
some extent by varying the oxidant-to-fuel ratio as well as by
adding non-reactive gases to the feed gas or non-combustible
miscible liquids to the feed solution. Secondly, the metal-based
precursors need to be vaporized and chemically changed into the
desired state. For oxides, this will occur in the flame if
sufficient oxygen is present. The high temperatures, radiant energy
(infrared, ultraviolet and other radiant energy), and plasma of the
flame also aid in the reactivity of precursors. Finally, for single
crystal films, the material being deposited should be in the vapor
phase, with little or no stable particle deposition. Particle
formation can be suppressed by maintaining a low concentration of
solutes, and by minimizing the distance, and therefore time,
between locations where the reagents react and where the substrate
is positioned. Combining these different factors predicts the best
deposition zone to be located in proximity of the flame's tip. If a
solution is sprayed, droplets can strike a substrate located too
far into the flame proximity, possibly resulting in some spray
pyrolysis characteristics in the resulting film. In fact, in some
configurations, with large droplets or with some reactants, it may
be impossible to not have some spray pyrolysis occur.
[0060] In various embodiments of the invention disclosed herein, a
plasma torch may also be used in a manner similar to a flame
apparatus to achieve similar results. Chemical precursors are
sprayed through a plasma torch and deposited on to the substrate.
The reagents and other matter fed through the plasma torch are
heated and, in turn, heat the substrate surface, much in the same
manner by the flame embodiment described herein. In plasma enhanced
chemical vapor deposition, lower plasma temperatures may be used as
compared to conventional plasma spraying, as lower heat is required
to cause the chemical precursors to react. As a result, the
chemical precursor reactions occur at lower temperatures thereby
allowing substrates with low melt points to take advantage of
PECVD. The deposition of the coating on to the substrate results
from directing of the plasma gas vapor containing the charged ions
in the direction of the substrate. For example, a chemical
precursor gas mixture or solution is fed into a plasma flame
resulting in the formation of a chemical vapor. The chemical
precursor solution may comprise inorganic metal oxides such as
aluminum oxide or silicon oxide. Once oxidized, the resulting ions
in substantially vapor form are directed onto the surface of the
substrate resulting in the formation of a solid coating formed on
the surface of the substrate and which are typically formed with
thicknesses in the 1 to 50 nanometer range.
[0061] In general, as long as a flame is produced, CCVD or PECVD
can occur independently of the flame temperature or substrate
surface temperature. The flame temperature is dependent on the type
and quantity of reagent, solvent, fuel and oxidant used, and the
substrate shape and material, and can be determined by one skilled
in the art when presented with the particular reagent, solvent,
fuel, oxidant and other components and conditions for deposition.
The preferred flame temperature near the deposition surface on a
moving web line is between about 800.degree. C. and 1300.degree. C.
As flames may exist over a wide pressure range, CCVD can be
accomplished at a pressure from about 10 torr to about thousands of
torr, but it is preferred to be at ambient pressure to ease its use
on the polymer film processing line. Likewise, if plasma is formed
for depositing the coating, the temperature of the plasma can range
from about 400.degree. C. to about 1200.degree. C. The temperature
of the substrate during the CCVD process also can vary depending on
the type of coating desired, the substrate material, and the flame
characteristics. Generally, a substrate surface temperature of
between about 40.degree. C. and 80.degree. C. is preferred for
temperature sensitive polymer films.
[0062] The deposition rate of the coating onto the substrate can
vary widely depending on, among other factors, the coating quality,
the coating thickness, the reagent, the substrate material and the
flame characteristics. For example, increasing the exposure period
of the film substrate to the vapor stream emanating from a flame
head can result in thicker coatings deposited on the film
substrate, assuming a relatively constant precursor feed flow rate
to the flame generated at the flame nozzle. Less porous coatings
are possible assuming a relatively lower feed flow rate to the
flame generated at the flame nozzle or more porous coatings
assuming a relatively greater feed flow rate to the flame generated
at the flame nozzle. Likewise, if a higher quality coating is
desired, a longer exposure time at a lower precursor feed flow rate
may be necessary, while a gross or textured coating can be produced
relatively quickly using a greater precursor feed flow rate. One
skilled in the art can determine the precursor feed flow rates and
exposure periods necessary to produce a desired coating on the film
substrate. Typical deposition rates on product made using the
apparatus and methods disclosed herein range from about 10 nm/min
to about 1000 nm/min with the film surface being normally exposed
to the flame for 0.1 to 10 seconds. As discussed above, the
chemical precursor solution in one embodiment is a liquid reagent
dissolved in a liquid solvent. However, solid, liquid, vaporous and
gaseous reagents can be used, with a liquid or gaseous solvent, as
long as the chemical precursor feed to the flame is typically
liquid or gaseous in nature.
[0063] Referring to FIG. 2C, one embodiment of the invention
disclosed herein is shown wherein a flame redirect source is shown.
The flame redirect technique employs an air knife 49 situated at an
angle to the flame 48 to redirect the gases and/or vapors 50 from
the process. The air knife 49 directs an air stream into the vapor
stream 50 coming from the flame 48. This effectively redirects the
vapor stream 50 in the desired direction of the substrate surface
56 while at the same time deflecting the heat stream associated
with flame 48 from overheating or melting the substrate 52 being
coated with the vapor 50. This method results in the dissipation of
heat directed on to the substrate 52 from the flame 48 heat stream
thereby resulting in the deposition of desired coating on to the
substrate surface 56 at lower temperatures.
[0064] The redirect flame embodiment also acts to disperse the gas
and/or vapor stream 50 emanating from the flame 48 resulting in a
wider deposition stream 50 being directed on to the substrate
surface 56 and enlarging the coating area of same. In an
alternative embodiment, an electromagnetic or "electro-redirect"
method may be employed to redirect the deposition of ions and/or
particles emanating from a flame and/or plasma source on to the
substrate surface. In this embodiment, the flame and/or plasma
source initially directs the ion and/or particle stream and any
associated heat in a substantially parallel direction to the film
substrate to be coated. A field with an electrical potential is
generated by means as is known in the art that passes through a
portion of the film substrate resulting in the redirection and/or
acceleration of the ion and/or particle stream emanating from the
flame or plasma source on to the film surface. The chemical bonds
within the polymer molecules are more readily broken which results
in the rapid formation of free radicals. This results in the
deposition of the desired ultra-thin coating on to the film surface
without the associated heat being transferred to the film surface
thereby preventing potential melting of the film substrate during
the deposition process.
[0065] With reference to FIG. 2D, one embodiment of the invention
disclosed herein is shown with multi-flame head system 60. In this
embodiment, system 60 includes a flame head assembly 62 comprising
a pipe with spaced holes or nozzles for emitting flames and
referred to as flame heads 64 integrated therewith. In various
embodiments, such flame head assembly 62 may comprise commercially
available flame burner heads manufactured by Flynn Burner
Corporation of New Rochelle, N.Y. Chemical precursors 61, which may
also include an oxidant, are fed into flame head assembly 62 and
when ignited result in lit flames emanating from flame heads 64
resulting in the generation of hot gases and/or vapors 66. The
substrate 52 to be coated is located proximal to flame heads 64
within the region of hot gases and/or vapors 66, such that hot
gases and/or vapors 66 containing the reagent vapor will contact
the substrate surface 56 resulting in a coating deposited thereon.
The multi-head flame head deposition system 60 improves the
continuity and thickness of coating deposition across the substrate
surface 56 as the hot gas and/or vapor region 66 is expanded by the
use of multiple flame sources. System 60 depicted in FIG. 2D is
shown with flame head assembly 62 aligned with multiple flame heads
positioned in a planar and/or linear orientation. However, other
embodiments are contemplated wherein one or more flame head
assemblies may be designed in various two-dimensional and
three-dimensional geometries such as square, rhomboid, cylindrical
shapes which may be fashioned and positioned relative to the film
being processed according to the necessity of the user as depicted
in FIGS. 2E, 2F, 2G, 2H and 2I. In these alternative contemplated
embodiments, one or more precursor(s) may be fed to select flame
heads in the individual flame head assembly providing the user with
the ability to vary the type, characteristics and thickness of the
coating deposited on to a substrate. As can be readily seen in
these figures, the shape of the individual flame heads and flame
head assemblies and their orientation relative to the substrate may
be configured to achieve differential types, concentrations and/or
thicknesses of ultra-thin coating deposition on to the substrate by
the apparatus and methods described herein.
[0066] For example, FIG. 2E discloses multiple flame head
assemblies 68 oriented in parallel rows perpendicular to the
direction of the packaging substrate 52 movement. By orienting the
flame head assemblies 68 in this fashion, multiple coatings may be
deposited on the substrate 52 in one pass along the indicated
direction of substrate 52 travel. In one embodiment, various
concentrations, gradients of precursor concentrations or different
precursors may be fed to each individual flame head assembly 68, or
to each individual flame head integrated into each flame head
assembly 68 to vary the type of coating layers and/or concentration
of coating layers and/or thickness of coating layers deposited on
to substrate 52. In one embodiment, one or more of the flame head
assemblies 68 emit a flame for purposes of priming the film
substrate 52 via flame treatment. After passing through the flame
treatment flame head assemblies, the substrate encounters one or
more of the latter positioned flame head assemblies 68 which may be
supplied with a precursor or various precursors for application of
an ultra-thin coating on the flame-treated substrate 52 as desired
by the user.
[0067] FIG. 2F discloses a curved flame head assembly 70 that
provides for deposition of an ultra-thin inorganic oxide layer on
to a substrate 52 as it passes over a portion of chill roll 72 and
is held in relative contact with chill roll 72 via placement of nip
rollers 74. In one embodiment, various concentrations, gradients of
precursor concentrations or different precursors may be fed to the
curved flame head assembly 70, or to each individual flame head
integrated into the curved flame head assembly 70, to vary the type
of coating layers and/or concentration of coating layers and/or
thickness of coating layers deposited on to substrate 52.
[0068] FIG. 2G depicts a square or rectangular shaped flame head
assembly 76 that provides for deposition of an ultra-thin inorganic
oxide layer on to substrate 52. In one embodiment, various
concentrations, gradients of precursor concentrations or different
precursors may be fed to the flame head assembly 76, or to each
individual flame head integrated into the flame head assembly 76,
to vary the type of coating layers and/or concentration of coating
layers and/or thickness of coating layers deposited on to substrate
52.
[0069] FIG. 2H discloses multiple flame heads integrated into flame
head assemblies 68 oriented in parallel rows parallel to the
direction of the packaging substrate 52 travel. In one embodiment,
various concentrations, gradients of precursor concentrations or
different precursors may be fed to each individual flame head
assembly 68, or to each individual flame head integrated into each
flame head assembly 68 to vary the type of coating layers and/or
concentration of coating layers and/or thickness of coating layers
deposited on to substrate 52.
[0070] Turning to FIG. 2I, one embodiment of the invention
disclosed herein depicts a flame head assembly 78 oriented at an
angle relative to the substrate 52 surface. In this configuration,
one end of the flame head assembly 78 is closer to the substrate
surface as the substrate 52 moves in the longitudinal direction
parallel to the flame head assembly 78. In one embodiment, the
"lower" end of the flame head assembly 78 is positioned at
substantially 20 mm above the surface of substrate 52 and serves to
precondition the substrate 52 as it provides a more intensive heat
treatment upon introduction of the substrate 52 to the proximity of
flame head assembly 78 and would serve to clean off dirt, dust and
other contaminants that may be on the substrate surface. As the
substrate 52 moves along, the "upper" end of the flame head
assembly 78 is positioned substantially 40 mm above the surface of
substrate 52 and resulting in lower intensity heat treatment
applied to the substrate 52 due to the increasing distance between
the surface of substrate 52 and the flame head assembly 78.
Therefore, various concentrations of precursor could be fed to
select or all of the remaining flame heads in the flame head
assembly 78 resulting in the differential application of inorganic
oxide layers to the surface of substrate 52 as it moves along the
length of the flame head assembly 78. In one embodiment, the flame
head assembly 78 is oriented at a 2 mm distance from the substrate
52 surface at the initial encounter between the flame/plasma with
the substrate 52 surface and oriented at an inclined angle to
produce a 4 mm distance between the substrate 52 and the last flame
head in the flame head assembly 78 as shown. In alternative
embodiments, the flame head assembly 78 may be oriented at inclined
angles perpendicular or along a radial arc relative to the
direction of the substrate 52 to achieve flame pretreatment or
variegated organic oxide layer deposition on the substrate 52 as
desired.
[0071] Such configurations and shapes would increase the film
surface area exposed to the flame in a single pass of the film
substrate past the burner. In turn, these geometric configurations
increase the dwell time the flame or plasma has in contact with the
film substrate surface thereby altering the coating properties
imparted to the film substrate. Therefore, the embodiments depicted
herein are not to be construed as limiting to the disclosure
herein.
[0072] Turning to FIG. 3A, one embodiment of a CCVD and/or PECVD
coating assembly as described herein is shown "in-line" with a
roll-to-roll winding/coating assembly 80 in a typical manufacturing
context. In the depicted embodiment, an unwinding unit 86 unwinds
film 88 from roller 96 as winding unit 84 winds film 88 on to
winding core 94. A flame chamber 82 housing a CCVD and/or PECVD
coating assembly 92 as described herein is integrated in-line with
the unwinding/winding units 86 and 84. The flame chamber 82
constitutes an unpressurized enclosure in which at least one CCVD
and/or PECVD flame head assembly 92 is housed for the safety of the
user and surrounding equipment and materials. During the
unwinding/winding process, a film substrate 88 is drawn from
unwinding unit 86 through various rollers and on to drum 90. After
receiving a coating and exiting the flame chamber 82, film
substrate 88 is wound around winding core 94. Drum roller 90
rotates and winds and/or draws substrate 88 in proximity to the hot
gases and/or vapors generated by the flame head assembly 92. In the
depicted embodiment, drum roller 90 is positioned above flame head
assembly 92 so as to maximize the surface area contact between the
rising hot gases and/or vapors generated by flame head assembly 92
thereby resulting in efficient deposition of the coating material
carried by the hot gases and/or vapors on to substrate 88. In
various contemplated embodiments, drum roller 90 may comprise a
temperature control roll or "chill roll" so as to impart a thermal
temperature to the substrate and a differential between the
substrate 88 to be coated and the heat generated by the flame head
assembly 92 which would facilitate coating substrates with low melt
points without heat damage to the substrate according the inventive
method and apparatus disclosed herein. In the embodiment depicted
in FIG. 3B, multiple flame assemblies 82 are integrated in-line to
provide multiple coating layers to the substrate 88. In this
configuration, multiple layers of ultra-thin inorganic coatings of
variable type, concentration and/or thickness may be applied to the
substrate at each flame head assembly 82 station as desired and
configured by the user.
[0073] With reference to FIGS. 3A and 3B and without being bound by
theory, it has been discovered that better quality deposition
coatings (i.e. improved coating layer coverage uniformity over the
substrate surface and enhanced RMS smoothness of the deposited
coating layer) may be achieved by passing the substrate film
multiple times through the flame treatment system or past multiple
flame heads and/or flame head assemblies, with low concentrations
of precursor, as opposed to a single pass of the substrate through
a flame treatment system using a high concentration of precursor
resulting in one thick deposition layer. In one example embodiment,
a stand alone roll-to-roll coater was equipped with a single burner
plasma flame treatment system. A combustible inorganic precursor,
tetraethyl orthosilicate (TEOS), was metered into the fuel stream
at a controlled rate. As the film was unwound and passed over the
plasma flame, low concentration levels of silica were deposited
onto the surface of the film substrate. Collected data revealed
that the SiO.sub.2 deposition quality was poor where the TEOS
concentration was greater than 22 mg/min, SiO.sub.2 deposition
quality was rated as good where the TEOS concentration was less
than 11 mg/min, and SiO.sub.2 deposition quality was rated as
excellent where the TEOS concentration level was less than 2
mg/min. As the film was passed multiple times (between two to five
passes) over a plasma flame fed with low concentration TEOS,
multiple layers of SiO.sub.2 were deposited on the film substrate
which resulted in the development of a barrier layer with a
thickness of 50 nm and exhibiting an OTR<10 cc/m.sup.2/day and a
WVTR<0.5 g/m.sup.2/day.
[0074] The metallization primer process described herein may be
conducted either during ("in-line") or after film manufacturing.
The film surface manufacture in-line is commonly pristine and free
of contaminants thereby making it ideal for surface priming due to
the challenges of keeping the film surface clean after the
manufacturing process is complete. For example, dust, anti-block
particles, or additives in the polymer film may "bloom" to the
surface of the film substrate in a post-manufacturing environment.
These conditions can make it difficult to achieve a uniform primer
coating during the priming process conducted after the film has
been manufactured and stored for a period of time. Blooming
additives can also migrate over the inorganic nanolayer, as it is
not a barrier layer in itself, thus it is desired not to have these
additives in the film.
[0075] Turning to FIG. 3C, one embodiment of the invention
disclosed herein is shown wherein a flame CCVD or PECVD unit is
installed in-line with a biaxial film substrate production line
100. In the depicted embodiment, a biaxial film substrate 102 is
formed by an extrusion unit 104. The film substrate 102 is then
passed through a cooling unit 106 and is stretched in the machine
(longitudinal) direction in machine stretching unit 108 and in the
transverse direction in transverse stretching unit 110. The film
substrate is then passed through the flame head assembly 112
wherein it is coated with the desired inorganic primer and/or
barrier coating according to the apparatus and processes described
herein. The coated film substrate is then wound into a
transportable roll in winding unit 114 for further processing or
distribution.
[0076] With reference to FIG. 3D, an embodiment of the invention
disclosed herein is depicted wherein a flame CCVD or PECVD coating
tower unit 118 is installed in-line with a biaxial film substrate
production line 100 as similar to the production line depicted in
FIG. 3C. In this embodiment, multiple flame head assemblies 120 are
placed in series with each delivering a low concentration of
inorganic precursor as the substrate 102 passes through the line
over various chill rolls and nip rolls in a single pass through the
system. The flame head assembly geometry, substrate line speed,
chill roll temperature and precursor types and concentration could
be configured in various contexts to produce the desired type,
concentration and/or thickness(es) of ultra-thin inorganic
coating(s) to be deposited on the particular packaging substrate.
Typical processing conditions are as follows: line speeds from 200
to 1500 ft/min (60 m/min to 450 m/min); chill roll temperatures of
40 to 80.degree. C.; the flame pretreatment with burner to film
distance of 5 mm for flame pretreatment, a fuel to air ratio of
0.90 to 0.95 for the flame treatment step, a natural gas flow rate
of 100 liters/min for a 1 meter wide line; the deposition step with
burner to film distances of 5 to 45 mm, a fuel to air ratio 1.0,
gas flow rates of 70 to 105 liters/min for a 1 meter wide line, a
precursor concentration of 0.0001 mole % to 0.01 mole % of the gas
stream. The plasma temperatures have exhibited good results at
1200.degree. C. with a range covering 650.degree. C. to
1450.degree. C. The above conditions will produce a coating with a
WVTR of <0.2 g/m.sup.2/day and an OTR<20 cc/m.sup.2/day.
[0077] Managing heat buildup in the substrate from exposure to
PECVD or CCVD flame head is of great concern as such heat buildup
will distort or melt the substrate being coated. As described in
various embodiments shown and disclosed herein, chill roll
technology is used to dissipate heat buildup in the substrate.
However, the diameter of the chill roll or number of multiple chill
rolls required to accomplish certain coatings may be cost or space
prohibitive due to size/space limitation in the manufacturing
environment. Alternatively, spray coolants may be utilized to
dissipate heat buildup in the substrate as it is treated according
to the apparatus and methods herein that are practiced in limited
space environments. As depicted in FIG. 3E, one embodiment of the
invention disclosed herein depicts an "off line" inorganic coating
deposition apparatus that could be used to coat a substrate
produced at a different facility. For example, in one embodiment
the equipment design shown in FIG. 3E may be incorporated into a
stand-alone process step at a converter. In this embodiment, a
packaging substrate 102 is unwound from unwind roll 96, passed over
a series of flame head assemblies 82 which may flame treat and/or
deposit an ultra-thin coating(s) on to the exposed surface of the
substrate 102, while concurrently the opposite exposed surface of
the substrate 102 is being cooled with spray coolant from coolant
nozzles 130 to dissipate heat and control or prevent degradation or
melting of the substrate 102. In this embodiment, chill rolls or
other thermal applicators are not required to keep the substrate
102 from degrading or overheating due to the thermal inputs from
exposure to the burners 82. The flame head assembly geometry,
substrate line speed, coolant spray temperature and precursor
concentration could be configured in various contexts to produce
the desired thickness(es) of ultra-thin coating(s) to be deposited
on the particular packaging substrate. Industrial spray coolants
that may be utilized in this embodiment may include aromatics,
silicate-ester (COOLANOL 25R), Aliphatic (PAO), silicone (SYLTHERM
XLT) or others as known in the art. Typical processing conditions
are as follows: line speeds from 200 to 1500 ft/min (60 m/min to
450 m/min); chill roll temperatures of 40 to 80.degree. C.; the
flame pretreatment with burner to film distance of 5 mm for flame
pretreatment, a fuel to air ratio of 0.90 to 0.95 for the flame
treatment step, a natural gas flow rate of 100 liters/min for a 1
meter wide line; the deposition step with burner to film distances
of 5 to 45 mm, a fuel to air ratio 1.0, gas flow rates of 70 to 105
liters/min for a 1 meter wide line, a precursor concentration of
0.0001 mole % to 0.01 mole % of the gas stream. The plasma
temperatures have exhibited good results at 1200.degree. C. with a
range covering 650.degree. C. to 1450.degree. C. The above
conditions will produce a coating with a WVTR of <0.2
g/m.sup.2/day and an OTR<20 cc/m.sup.2/day.
[0078] It should be noted that the embodiments shown in FIGS. 2A-3E
and FIGS. 5A-5I may utilize plasma-enhanced chemical vapor
deposition (PECVD) apparatus and methods to accomplish the coating
process as described herein. As such, the depicted embodiments are
not be construed as being limited to flame CCVD methods. Whenever
the term "flame" or its analogues such as "flame head" or "flame
head assembly" are used herein, it is interpreted as including
"plasma" and its analogues, and equivalent laser ablation
equipment. The plasma may be manipulated by an electromagnetic
field in proximity to the plasma source so as to direct the ions
generated from the plasma reaction on to the substrate surface to
be coated. Thus CCVD is not limiting to the product made, but is
just one enabling method used to accomplish making of the described
product on the film fabrication line. As previously described
herein, alternative embodiments of the apparatus and systems
disclosed in FIGS. 2A-3E may be independently be configured to
provide flame treatment of the substrate, to apply a primer coating
and/or to apply barrier coatings at open atmosphere to the
substrate as it moves along the manufacturing line.
[0079] FIG. 4 is a structural diagram depicting an embodiment of a
coated substrate 120. In the depicted embodiment, a film or paper
substrate 122 is primed with a pure or substantially pure silica
layer 124. The substrate 122 with silica layer 124 is then coated
with additional oxide layer 126 and a subsequent metal or oxide
layer 128. Oxide layers 126, 128 may be comprised of silica mixed
with an additional chemical additive or "dopant" for purposes of
enhancing the reactivity of the primed surface 124 with additional
desired coatings. In one embodiment, the metal barrier layer
deposited by the apparatus and method described herein has a
thickness between 5 and 50 nm, with an optical density of over 30%.
The metal barrier layer may comprise aluminum, copper, iron,
manganese, zinc and/or other metals as dictated by the needs of the
user. In other embodiments, layer 128 is an oxide layer deposited
via CCVD or layer 128 is a metal layer deposited by conventional
vacuum metallization technology.
[0080] FIGS. 5A-5I depict various apparatus in which various
embodiments of the invention disclosed herein may be configured as
desired by the user. FIG. 5A discloses a configuration wherein the
chemical precursors 504 are fed into the flame fuel line 502 prior
to being mixed with air from the air line 506 and combusted at the
flame head 508 as shown. FIG. 5B depicts a configuration wherein
the chemical precursors 504 are fed into the air line 506 prior to
being mixed with fuel from the fuel line 502, which in this
embodiment is natural gas, and combusted at the flame head 508 as
shown. FIG. 5C discloses a configuration were chemical precursors
504 are fed into an air line 506 and a fuel line 502 prior to being
mixed at a fuel/air mixer 510 and combusted at the flame head 508
as shown. In this embodiment, different chemical precursors may be
utilized and fed into the air line and fuel line prior to mixing at
the fuel/air mixer. FIG. 5D discloses wherein a chemical precursor
is introduced after the fuel and air constituents have mixed at the
fuel/air mixer as shown. The resulting mixture is then combusted at
the flame head as described herein. FIG. 5E discloses a
configuration wherein one or more chemical precursors may be mixed
at the fuel/air mixer prior to the introduction of an additional
chemical precursor downstream and which is thereafter combusted at
the flame head as shown. FIG. 5F discloses a configuration where
the chemical precursor is introduced at the point where the fuel
and air are mixed. The resulting mixture is then combusted at the
flame head as described herein. FIG. 5G discloses a configuration
wherein the chemical precursor is sprayed or otherwise injected
into the existing flame produced by the flame head as shown. FIG.
5H discloses a configuration where in the chemical precursor is
combusted into the flame head burner as shown. FIG. 5I discloses a
configuration wherein a laser ablation apparatus 512 is used to
generate the vapors and/or ion stream 514 which is directed to a
substrate for coating thereon. In the embodiments disclosed in
FIGS. 5A-5I, it will be evident to one of ordinary skill in the art
that various fuel, air and chemical precursor species may be
utilized to generate the desired coatings upon the film substrate
passing in the desired proximity of the flame head as described
herein. The various embodiments shown in FIGS. 5A-5I may be
integrated into the various in-line and standalone film substrate
manufacturing and processing environments as disclosed herein.
[0081] To describe certain embodiments of the inventive apparatus
and methods disclosed herein, the following examples are provided.
Once having understood the examples set forth herein, one of
ordinary skill in the art should be able to apply the apparatus and
methods disclosed herein to other chemical deposition methods, and
such applications are deemed to fall within the scope of the
invention disclosed herein. The following examples are for
illustrative purposes and are not to be construed as limiting the
scope of the invention. In the examples, the primer coating
deposition was performed using CCVD in an open atmosphere
environment. The chemical precursors consisted of TEOS in a methane
air feed through a film flame treater with a flame temps of
800.degree. C. to 1200.degree. C. unless otherwise indicated.
Example 1
SiO.sub.2 Deposition on OPP Polymer by Roll Coater
[0082] As an example and for comparative purposes, a biaxially
oriented OPP polymer film substrate was flame treated first on the
inside surface of the roll. Conditions for the flame treatment of
film include: line speed of about 184 feet/min, a burner to film
distance of about 5 mm, and a fuel to air ratio of about 1.0.
Following flame treatment step, the film was run through the roll
coater a second time to deposit a silica layer. Conditions for the
silica layer deposition include: line speed of about 184 feet/min,
a burner to film distance of about 5 mm, and a fuel to air ratio of
about 1.0, TEOS concentration of about 0.00379 mole percentage for
both of the flame treatment and silica deposition runs.
[0083] The deposition of silica is greatly enhanced by the flame
treatment step prior to the treatment with silica. This is
demonstrated in FIG. 6 for a single deposition pass of silica via
information collected by XPS. The amount of silica, as determined
by signal strength, has a 70% increase in silica deposited. Signal
without flame pretreatment is 290 counts per second (CPS) at a peak
maximum, while the max signal is 500 counts per second for a single
pass of silica after flame treatment. In other words, the silica
content increased from 0.18 atomic % silicon without flame
pretreatment to 0.23 atomic % silicon.
[0084] The pretreatment was so successful that multiple laps of
silica were deposited after a flame pretreatment was utilized. This
is shown in FIG. 7 for signal strength (CPS) vs. binding energy
(eV) from XPS. The amount of silica increase during each pass, as
can be clearly seen. In terms of atomic % of silicon present, 1, 2,
and 3 deposition passes of silica result in 0.23%, 0.26%, and
0.44%, respectively.
[0085] The ultimate arbiter of effectiveness is barrier of the
deposited silica layer. All of the samples from above in this
example were metallized under standard vacuum metallization
conditions to an optical density of 2.3. The atomic percentage of
silicon atoms on the film surface, WVTR, and OTR values are shown
in FIG. 8 and plotted versus the number of silica deposition
passes. All samples were flame treated before the silica deposition
passes except for the first sample labeled with a black oval, which
had no flame pretreatment before a single silica deposition. Flame
treatment and increasing number of silica passes result in lower
WVTR and OTR, or increasing barrier. This increasing barrier
results from a higher quality or more effective layer of aluminum
metal deposited on the silica primed film.
Example 2
High Speed Deposition on OPP Film
[0086] The current example is a biaxially oriented polypropylene
(BOPP) placed on a roll to roll coater as disclosed herein for a
single pass flame treatment and single layer silica coating
deposited in one pass. Typical processing conditions are as
follows: line speed at about 900 ft/min (275 m/min); chill roll
temperatures at about 54 degrees Celsius; the flame pretreatment
with burner to film substrate distance of about 5 mm for flame
pretreatment, a fuel to air ratio of about 0.95 for the flame
pretreatment step, a natural gas flow rate of about 100 liters/min
for a 1 meter wide line; the silica coating deposition step with
burner to film distances of about 5 to 10 mm, a fuel air ratio of
about 1.0, gas flow rates of about 75 to 100 liters/min for a 1
meter wide line, a precursor concentration of in the range of about
0.0001 mole % to 0.01 mole % of the gas stream and plasma
temperatures at 1200 degrees Celsius. The film samples were then
metallized under standard conditions to an optical density of 2.5.
The above described operating conditions produced a film substrate
with a WVTR of <0.2 g/m.sup.2/day and an OTR of <20
cc/m.sup.2/day. WVTR and OTR data for a variety of working
distances (flame burner to film substrate distance), gas flow rate,
and precursor concentration (TEOS) are given in Table 1.
TABLE-US-00001 TABLE 1 Working Precursor Sample Distance, Conc, Gas
Flow, WVTR, OTR, Number mm Mole % l/min g/m.sup.2/day
cc/m.sup.2/day 1 5.00 0.0038 75.00 0.05 10.9 2 5.00 0.0038 100.00
0.12 12.8 3 10.00 0.0038 75.00 0.08 10.5 4 10.00 0.0038 100.00 0.08
6.86 5 5.00 0.0049 75.00 0.09 9.09 6 5.00 0.0049 100.00 0.12 17.7 7
10.00 0.0049 75.00 0.15 10.5 8 10.00 0.0049 100.00 0.09 9.75 9 5.00
0.0095 75.00 0.07 11.8 10 5.00 0.0095 100.00 0.13 10.1 11 10.00
0.0095 75.00 0.09 10.1 12 10.00 0.0095 100.00 0.16 25.2
[0087] The data in Table 1 demonstrates the robustness of the
silica deposition and primer process. The speeds employed in this
example are similar, if not identical, to the line speeds in the
typical film substrate production process.
Example 3
Multiple Layer Silica Deposition on OPP Film
[0088] Experiments were conducted with multiple laps over a film to
produce pure silica coating between 10 to 50 nm. The coatings were
produced under the following conditions: line speeds of about 600
to 900 FPM (180 m/min to 275 m/min), the flame treatment with flame
burner to film substrate distance of about 5 mm for the flame
treatment step, a fuel to air ratio of about 0.95, and a natural
gas flow rate of about 100 liters/min for a 0.3 meter wide line.
For the coating deposition step, a flame burner to film substrate
distance of about 5 to 15 mm, a fuel to air ratio of about 1.0, gas
flow rates of about 75 to 100 liters/min for a 0.3 meter wide line,
and a precursor concentration in the range of 0.0001 mole % to 0.01
mole % of the gas stream. The plasma temperatures were about 1250
degrees Celsius. A number of silica laps were made between about 36
and 72.
[0089] Unless otherwise indicated, all numbers expressing
quantities of ingredients, properties such as molecular weight,
reaction conditions, and so forth used in the specification and
claims are to be understood as being modified in all instances by
the term "about." Accordingly, unless indicated to the contrary,
the numerical parameters set forth in the following specification
and attached claims are approximations that may vary depending upon
the desired properties sought to be obtained by the present
invention. At the very least, and not as an attempt to limit the
application of the doctrine of equivalents to the scope of the
claims, each numerical parameter should at least be construed in
light of the number of reported significant digits and by applying
ordinary rounding techniques. While the invention has been
particularly shown and described with reference to a preferred
embodiment, it will be understood by those skilled in the art that
various changes in form and detail may be made therein without
departing from the spirit and scope of the invention.
* * * * *