U.S. patent application number 09/952153 was filed with the patent office on 2002-04-11 for gas-impermeable, chemically inert container structure for food and volatile substances and the method and apparatus producing the same.
Invention is credited to Hagenlocher, Arno, Kuehnle, Manfred R., Schuegraf, Klaus, Statz, Hermann.
Application Number | 20020041942 09/952153 |
Document ID | / |
Family ID | 27386061 |
Filed Date | 2002-04-11 |
United States Patent
Application |
20020041942 |
Kind Code |
A1 |
Kuehnle, Manfred R. ; et
al. |
April 11, 2002 |
Gas-impermeable, chemically inert container structure for food and
volatile substances and the method and apparatus producing the
same
Abstract
A method of making a gas-impermeable, chemically inert container
wall structure comprising the steps of providing a base layer of an
organic polymeric material; conducting a pair of reactive gases to
the surface of the base layer preferably by pulsed gas injection;
heating the gases preferably by microwave energy pulses
sufficiently to create a plasma which causes chemical reaction of
the gases to form an inorganic vapor compound which becomes
deposited on the surface, and continuing the conducting and heating
until the compound vapor deposit on the surface forms a
gas-impermeable, chemically inert barrier layer of the desired
thickness on the surface. Various wall structures and apparatus for
making them are also disclosed.
Inventors: |
Kuehnle, Manfred R.; (New
London, NH) ; Hagenlocher, Arno; (Santa Rosa, CA)
; Schuegraf, Klaus; (Torrance, CA) ; Statz,
Hermann; (Wayland, MA) |
Correspondence
Address: |
CESARI AND MCKENNA, LLP
88 BLACK FALCON AVENUE
BOSTON
MA
02210
US
|
Family ID: |
27386061 |
Appl. No.: |
09/952153 |
Filed: |
September 13, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09952153 |
Sep 13, 2001 |
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09550770 |
Apr 17, 2000 |
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09550770 |
Apr 17, 2000 |
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09133847 |
Aug 14, 1998 |
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09133847 |
Aug 14, 1998 |
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08700845 |
Aug 21, 1996 |
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08700845 |
Aug 21, 1996 |
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08421536 |
Apr 13, 1995 |
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08421536 |
Apr 13, 1995 |
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08342368 |
Nov 18, 1994 |
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08342368 |
Nov 18, 1994 |
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08144249 |
Oct 28, 1993 |
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Current U.S.
Class: |
428/35.7 ;
257/E31.051 |
Current CPC
Class: |
C23C 16/515 20130101;
C08K 7/18 20130101; H01L 31/0384 20130101; C08J 7/123 20130101;
Y10T 428/1352 20150115; G02B 5/206 20130101; C23C 16/0245 20130101;
C23C 16/45523 20130101; B29K 2033/00 20130101; B65D 23/02 20130101;
B29K 2025/00 20130101; B29K 2023/00 20130101; C08K 3/34 20130101;
C23C 16/045 20130101; G02B 5/207 20130101; B29B 13/08 20130101 |
Class at
Publication: |
428/35.7 |
International
Class: |
B32B 001/02 |
Claims
1. A method of making a gas-impermeable container wall structure
comprising the steps of providing a base layer of an organic
polymeric material; conducting a plurality of reactive gases to the
surface of the base layer; heating the gases sufficiently to create
a plasma which causes the chemical reaction of said gases to form
an inorganic vapor compound which becomes deposited on said
surface, and continuing the conducting and heating steps until the
vapor compound deposit on said surface forms a gas-impermeable,
chemically inert barrier layer of the desired thickness on said
surface.
2. The method defined in claim 1 wherein the heating step is
accomplished by exposing said gases and said surface to microwave
radiation.
3. The method defined in claim 2 including pulsing the conducting
and exposing steps at a selected frequency to control the
temperature and stoichiometry of the deposited vapor compound.
4. The method defined in claim 1 including the additional step of,
prior to the conducting step, flowing an inert gas to said surface
and ionizing the inert gas to subject said surface to ionic
bombardment in order to clean said surface and render it receptive
to said vapor compound.
5. The method defined in claim 4 including the additional step of
depositing a plasticizer on said surface during said ionic
bombardment so that the molecules of the plasticizer become
crosslinked and form a coherent skin on said surface.
6. The method defined in claim 1 including the step of forming the
base layer into a container before the conducting step.
7. The method defined in claim 1 including the step of forming said
structure into a container after the continuing step.
8. The method defined in claim 1 wherein the providing step
includes providing a base layer containing a dispersal of tiny
radiation blocking particles of an inorganic semiconductor material
which prevents the transmission through said wall structure of
selected electromagnetic radiation frequencies.
9. The method defined in claim 1 including the step of covering
said barrier layer with a relatively thin top layer of a hard,
abrasion-resistant material.
10. The method defined in claim 1 including the steps of forming
said barrier layer of a material selected from the group consisting
of crystalline silicon, amorphous silicon and hydrogenated
amorphous silicon, and controlling the thickness of said barrier
layer so that said barrier layer blocks electromagnetic radiation
below a selected cutoff wavelength.
11. A method of making a gas-impermeable container wall structure
comprising the steps of providing a container of an organic
polymeric dielectric material; creating a relatively high vacuum in
the container; injecting a plurality of inorganic reactive gases
into said container; exposing the container and its contents to
microwave energy sufficient to ionize said gases and produce a
plasma in the container which causes chemical reaction of said
gases thereby forming an inorganic vapor compound which becomes
deposited on the interior wall of the container, and continuing the
injecting and exposing steps until the compound vapor deposit on
said interior wall forms a gas-impermeable, chemically inert
barrier layer of a selected thickness on said interior wall.
12. The method defined in claim 11 wherein, prior to the injecting
step, flowing an inert gas into the container in the presence of
microwave radiation so as to ionize the inert gas whereupon the gas
ions impact and clean the interior wall and render it receptive to
said vapor compound deposit.
13. The method defined in claim 11 including the additional steps
of injecting said plurality of gases into the container as
injection pulses of a selected frequency, and exposing the
container and its contents to microwave energy as energy pulses
having said selected frequency.
14. The method defined in claim 11 including the steps of forming
said barrier layer of a material selected from the group consisting
of crystalline silicon, amorphous silicon and hydrogenated
amorphous silicon, and controlling the thickness of said barrier
layer so that said barrier layer blocks electromagnetic radiation
below a selected cutoff wavelength.
15. A gas-impermeable container wall structure comprising a base
layer of an organic polymeric material, and a gas-impermeable
chemically inert barrier layer on said base layer formed by
conducting a plurality of reactive gases to the surface of the base
layer, heating the gases sufficiently to create a plasma which
causes the chemical reaction of said gases to form an inorganic
vapor compound which becomes deposited on said surface, and
continuing the conducting and heating steps until the vapor
compound deposit on said surface reaches a desired thickness.
16. The wall structure defined in claim 15 and further including a
crosslinked plasticizer between said surface and said barrier
layer.
17. The wall structure defined in claim 15 and further including a
dispersal in said base layer of tiny radiation blocking particles
of an inorganic semiconductor material which prevents the
transmission through said wall structure of selected
electromagnetic radiation frequencies.
18. The wall structure defined in claim 15 and further including a
relatively thin top layer of a hard, abrasion-resistant material
covering said barrier layer.
19. The wall structure defined in claim 15 wherein said barrier
layer is of a material selected from the group consisting of
silicon dioxide, silicon nitride, aluminum oxide and boron
nitride.
20. The wall structure defined in claim 15 wherein said barrier
layer is of a material selected from the group consisting of
crystalline silicon, amorphous silicon and hydrogenated amorphous
silicon, and said barrier layer is of a thickness to block
electromagnetic radiation below a selected cutoff wavelength.
21. The wall structure defined in claim 15 wherein said barrier
layer is selected from the group consisting of silicon dioxide,
silicon nitride and boron nitride.
22. A gas impermeable container wall structure comprising a base
layer of an organic polymeric material, and a gas impermeable,
chemically inert barrier layer on said base layer, said barrier
layer including a carrier material having a refractive index; and
dispersed therein, a silicon particulate material having
substantially uniform particle size and exhibiting an absorption
cross-section greater than 1 below a predetermined cut off point,
the material having a refractive index differing from that of the
carrier and being present in sufficient density per unit of surface
area to substantially block passage of radiation below the
predetermined cut off point.
23. The material of claim 22 wherein the particulate material is
spherical and exhibits an imaginary refractive-index component K
which decreases substantially with wavelength.
24. The material of claim 23 wherein K is at least 0.5 at a
wavelength of 0.4 .mu.m and is less than 0.005 .mu.m at a
wavelength of 0.7 .mu.m.
25. The material of claim 23 wherein the density per unit of
surface area varies inversely with K.
26. The material of claim 22 wherein the particle size is chosen to
minimize scattering of visible radiation.
27. The material of claim 22 wherein the particulate material
consists of uniformly sized spheres having a diameter that ranges
from 0.005 .mu.m to 0.04 .mu.m.
28. The material of claim 22 wherein the particulate material
consists of spheres of diameter less than 0.04 .mu.m.
29. The material of claim 22 wherein the density per unit of
surface area is approximately 10.sup.-4 to 10.sup.-5
g/cm.sup.2.
30. The material of claim 22 wherein the silicon is crystalline
silicon.
31. The material of claim 22 wherein the silicon is amorphous
silicon.
32. The material of claim 22 wherein the silicon is hydrogenated
amorphous silicon.
33. The material of claim 22 wherein the silicon is alloyed with
germanium.
Description
FIELD OF THE INVENTION
[0001] This invention deals with a gas-impermeable, chemically
inert container product and the method and apparatus for producing
that product.
BACKGROUND OF THE INVENTION
[0002] Containers such as bottles, tanks, pouches and the like
which serve for the storage of various materials such as juices,
chemicals, food stuffs, other organic materials including blood,
petroleum products and the like are affected by the physical and
chemical properties at the interface of the container and its
contents. Thus, the contents can be affected by chemical reactions
which take place between the container material and the contents or
by electrochemical effects caused by different ionic potentials at
the interface or by transmission of damaging radiation of short
wavelength ligh and UV through the container walls into the
contents or by the gradual long-term permeation of external
material such as gases or moisture through the container walls into
the interior of the container. Also, permeation of materials inside
the container, e.g., gasolene vapors, ma be harmful to the
invironment.
[0003] The three most damaging forces which impact the stability of
the container contents, and thereby affect its commercial
acceptability, are: 1) ultra-violet radiation reaching the contents
through the container walls; 2) the gradual permeation of oxygen
through the container walls into the contents and 3) the
penetration of moisture through the container walls into the
contents, and penetration of toxic materials in the container into
the environment.
[0004] The classical solution to the above three problems is to
make the container of thick glass or of metal or of multi-layer
laminates which typically contain metal foil to maintain aseptic
conditions within the container and to protect the container
contents. These approaches have been effective in the past.
However, they also pose substantial burdens in terms of container
cost, non-recycleability of the container and/or limited
disposability of the container due to container bulk. Also, some
applications call for optically transparent containers.
[0005] The container material of choice these days is usually a
plastic material or fiberglass reinforced epoxy, both of which can
be molded to produce a container having the desired shape. Using
such materials, even odd-shaped containers such as gasoline tanks
can be fabricated to fit into the contorted narrow spaces of an
automotive chassis.
[0006] Unfortunately, however, certain container contents such as
citrus juices, certain alcohols, benzene or the like will actually
attack the container material and create conditions which lead to
dangerous leakage and even to eventual corrosion and collapse of
the container walls.
[0007] Accordingly, it would be desirable to be able to provide a
container which can fit odd geometric spaces, be lightweight and
rigid or flexible as desired and yet be capable of preventing
damaging interactions of the container contents with the container
material or external agents.
SUMMARY OF THE INVENTION
[0008] Accordingly, it is an object of the present invention to
provide a new protective container whose fabrication has not been
possible heretofore due to the inability to treat the container
surfaces so as to render them gas-impermeable and chemically
inert.
[0009] Another object of the invention is to provide a container
product which offers unusual protective barrier properties at the
interface between the container and the container contents.
[0010] A further object of the invention is to provide a container
of a material which blocks liquids and gases and which may also
have selected radiation blocking properties.
[0011] Another object of the invention is to provide a container
having the above properties which can be shaped as desired.
[0012] Still another object of the invention is to provide a method
of producing a container possessing one or more of the above
properties.
[0013] A further object of the invention is to provide apparatus
for making a container and a container wall structure having one or
more of the above advantages.
[0014] Other objects will, in part, be obvious and will, in part,
appear hereinafter.
[0015] The invention accordingly comprises the several steps and
the relation of one or more of said steps with respect to each of
the others, and the apparatus embodying the features of
construction, combination of elements and arrangement of parts
which are adapted to effect such steps, and the construction which
possesses the characteristics, properties and relation of elements,
all is exemplified in the detailed disclosure set forth
hereinafter, and the scope of the invention will be indicated in
the claims.
[0016] Briefly, our container is formed of a polymeric material
which can be shaped as desired and whose inside surface is coated
entirely with one or more thin layers of a barrier material
deposited either before or after the container is made. In other
words, in one embodiment of the invention, the barrier properties
are imparted to the interior and/or exterior surface of an already
formed container; in another embodiment, the barrier properties are
applied to the surface(s) of a container material after which that
material is formed into a container. By "container", we mean to
include a bottle, tank, pouch, vial, capsule or other such
enclosure having rigid or flexible walls.
[0017] With such constructions, two important goals of the
invention are achieved, namely: the container contents only contact
what appears to be a solid, inert wall which prevents a chemical
reaction between the container contents and the container wall or
the transgression of the container contents through the container
walls to the outside; at the same time deleterious external agents
such as oxygen and moisture are prevented from permeating through
the walls of the container and reaching the container contents.
[0018] In accordance with the invention, the inside surface of the
container may be exposed to intense ion bombardment to clean the
surface prior to application of the barrier coating. Then, the
chemically inert barrier layer is applied to that surface. Due to
the thinness, coherence and firm adhesion of the barrier layer to
the base material, the mechanical characteristics of the overall
container structure do not change. In other words, if the uncoated
container walls are flexible, they remain flexible after the
barrier layer is applied; if the walls are rigid, they have
essentially the same rigidity after being coated. Yet, the addition
of the barrier layer effectively prevents the permeation of gases
and moisture through the container walls in either direction and
eliminates the danger of chemical reaction between the container
and its contents.
[0019] With the ability to place an impermeable layer of inert
material on the inside and/or outside of a container, an additional
requirement will often arise namely, that the container be
transparent in specific wavelength regions and yet block other
wavelength radiation to prevent that other radiation from reaching
the container contents. For example, in food packaging, it is
desirable to prevent ultraviolet light from penetrating through the
packaging and reaching the contents of the package while still
allowing the customer to see what is in the package.
[0020] To achieve this end, the present container may incorporate a
radiation filter in the container walls through the addition in the
container base material of tiny band gap particles or optical
resonator particles as described in the above identified co-pending
application, the contents of which is hereby incorporated by
reference herein. This type of multi-functional container product
is expected to play an important role in the marketing of
environmentally friendly, recyclable packaging for foods, medicines
and other substances.
[0021] In certain applications, a thin layer on the surface of the
container can act as a radiation filter and this surface layer can
even fulfill the dual role of an impervious layer to liquids and
gases as well as have desirable characteristics as a radiation
filter. Silicon films made of polycrystalline or amorphous phases
in the proper thickness can provide a cutoff effect wherein all
wavelengths shorter than the cutoff wavelength will be absorbed.
Also materials such as Ga.sub.x In.sub.1-x N or Al.sub.x In.sub.1-x
N can be used. The mole fraction x determines the cutoff
wavelength.
[0022] As will be described in more detail later, our method of
fabricating the protective container walls utilizes the microwave
transparency of the container base material for high frequency
radiation to transfer intense energy to the inside of the
container. During the fabrication process, one or more containers
are placed inside a vacuum chamber which also functions as a
resonant cavity. The chamber, including the containers, is filled
with an inert gas such as argon. Then, microwave energy is applied
to the chamber and its contents so as to fill the entire space with
multi-mode resonating energy. This produces a plasma in the chamber
both inside and outside the containers. The plasma, being an
ionized gas, produces an intense ionic bombardment of the walls of
the containers which removes adsorbed gases, particulate material
and any condensed moisture from those walls.
[0023] To meet the extreme impermeability requirements for the
containers, prior to application of microwave energy to the
containers, a preparatory surface sealing step may be carried out
by injecting a certain plasticizer (which will corsslink with ion
and electron bombardment) as a vapor into the containers so that
the vapor becomes deposited on the container walls and covers those
surfaces with a coherent skin. Once coated thusly, the subsequent
ion bombardment will crosslink the polymer skin throughout creating
a continuous, chemically pristine undersurface for the barrier
layer(s). In some applications, a highly crosslinked underlayer
may, in itself, prevent the seapage of gases or liquids into the
container walls.
[0024] Following the aforesaid surface preparation, a new type of
plasma is ignited in the containers now filled with specified
reactant gases. Gas vapor reacts because of the plasma excitation
and becomes deposited on the preconditioned container walls and
firmly adheres thereto forming a continuous barrier layer. As will
be described in more detail later, the reactant gases and the
energy are applied to the containers using a special pulsed mode
gas and energy insertion technique which maintains precise control
over the temperature and the stoichiometry (where applicable) of
the reactant gases so as to produce a high quality barrier layer of
the requisite thickness.
[0025] Using our process, the internal surfaces of certain
containers such as fuel tanks can be covered by a multi-layer
compendium of coatings having a relatively large total thickness,
but whose internal stresses and strains are minimized through the
use of intermediate stress-relieving interface layers. In this
manner, containers can be equipped with an internal barrier layer
whose chemical resistance to alcohol, acid, solvents and the like
is optimal, but which derives its hardness from a special top or
outer coating, while elasticity and shock absorptivity are
furnished by a relatively thick under-layer that bonds well to the
container walls.
[0026] As will be seen, containers can even be made having a
multi-layer wall structure in which the barrier layer is located in
the middle of the walls.
[0027] All of these container structures are vastly superior to
present day containers because they weigh less and require less
material, yet they are still readily disposable and recyclable.
Additionally, if desired, the structures may be fully transparent
in the visible portion of the spectrum so that it is possible to
clearly see the container contents.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] For a fuller understanding of the nature and objects of the
invention, reference should be had to the following detailed
description taken in connection with the accompanying drawings, in
which:
[0029] FIG. 1 is a sectional view of a container incorporating our
invention;
[0030] FIGS. 2A to 2C are fragmentary sectional views taken along
line 2-2 of FIG. 1 showing different wall structures that may be
present in the FIG. 1 container;
[0031] FIGS. 3 to 5 are graphical diagrams showing the radiation
and reflection properties of certain wall structures embodying the
invention;
[0032] FIG. 6 is a longitudinal sectional view of apparatus for
making the FIG. 1 container;
[0033] FIG. 7 is a vertical section on a larger scale showing a
portion of the FIG. 6 apparatus in greater detail;
[0034] FIG. 8 shows the wall temperature of a FIG. 1 container
during the operation of the FIG. 6 apparatus;
[0035] FIG. 9 is a fragmentary sectional view taken along 2-2 of
FIG. 1 showing a container wall structure having an internal
barrier layer, and
[0036] FIG. 10 is a view similar to FIG. 6, of apparatus for making
a container having the FIG. 9 wall structure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] FIG. 1 of the drawings shows a container 10 having a wall 12
of polymeric material. The container is illustrated as being a
bottle or jar; however, it could just as well be an oddly shaped
tank, bowl, vial or other article which provides access to the
interior of the article.
[0038] As shown in FIG. 2A, usually wall 12 comprises a transparent
base layer 14 of a polymeric material such as polypropylene, but it
may also be of an opaque material such as fiberglass--reinforced
epoxy. Typically, layer 14 has a thickness in the order of 300
.mu.m. The outer and inner surfaces 14a and 14b of base layer 14
may be subjected to a plasma to render those surfaces chemically
pure as shown by the hatching. These enable the outer surface 14a
to be printed on with a hot melt ink (not shown) and makes the
inner surface 14b chemically receptive so that it provides an
excellent bonding surface for a blocking layer 16 applied to layer
14b by vapor deposition in the presence of a plasma.
[0039] Depending upon the particular application, layer 16 may
consist of any one of a variety of inorganic materials such as
aluminum oxide (AL.sub.2O.sub.3), silicon dioxide (SiO.sub.2),
boron nitride (BN), silicon nitride (Sl.sub.3N.sub.4) which are
chemically inert and fluid impermeable. The barrier layer 16 for a
container such as bottle 12 may have a thickness in the order of
100-1000 .ANG.. The wall structure 12 is suitable for a container
intended to hold solvents, acids or other such fluids which would
otherwise react chemically with the base layer 14 material. That
wall structure would also be suitable for containers whose contents
might be adversely affected by oxygen or moisture that would
penetrate through the base layer 14 but for the barrier layer
16.
[0040] FIG. 2B illustrates another container wall structure 12'
which is similar to wall 12 in that it is composed of a polymeric
base layer 14' whose pretreated interior surface 14b is covered by
a barrier layer 16 so that it has all of the attributes of the wall
structure 12. In addition, however, the base layer 14' of wall 12'
contains tiny, monodispersed, inorganic, radiation blocking
particles 18 described in detail in the above-identified pending
application, the contents of which is hereby incorporated by
reference herein. For example, for modest mass loadings of silicon
particles 18, the base layer 14' can be designed to provide good
radiation blocking for short wavelengths, but good transmission for
longer wavelengths. Therefore, the wall structure 12' in FIG. 2B
will protect the contents of container 10 from external UV
radiation, while allowing one to see the contents of the container
through wall 12, assuming that the barrier layer 16 is of a
material such as aluminum oxide which is transparent to visible
light.
[0041] A container 10 having the wall structure 12' would be
suitable for packaging foods, pharmaceuticals and the like which
degrade upon being exposed to sunlight.
[0042] FIG. 2C illustrates another wall structure 12" for container
10 which comprises several layers that are applied to the
pre-treated inner surface 14b of a base layer 14 similar to the one
in FIG. 2A. The wall structure 12" includes a relatively thick,
e.g., 1000 .ANG., underlayer 22 of a somewhat softer material that
is compatible with the barrier layer 16. For example, layer 22 may
be silicon dioxide with some residual free radicals of CH.sub.2 or
CH.sub.3 or siloxane, i.e., a transitional material or the like
which provides stress relief for a barrier layer 16 and whose
chemical resistance to alcohols, acids, solvents or the like is
optimal, but which derives its hardness from a top or outermost
layer 26 of an abrasion-resistant material such as silicon dioxide
or aluminum oxide. The wall structure 12" would be suitable for
containers requiring an abrasion-resistant interior surface for
protection against mechanical attack from container contents such
as particles P or from cleaning brushes and the like. It would also
be suitable for fuel tanks which are exposed to vibration and shock
forces during normal use.
[0043] Instead of, or in addition to, having the mechanical and
radiation barrier functions in different layers of the container
walls as described in connection with FIG. 2A, those functions may
be incorporated into a surface layer applied to the base layer 14.
This is accomplished by applying to the plain polymeric base layer
films or layers consisting of the polycrystalline or amorphous
phase of silicon in the proper thickness. Such films are impervious
to liquids and gases. They also provide a cutoff effect so that all
wavelengths of incident radiation shorter than the selected cutoff
wavelength are absorbed by the surface films or layers, while
wavelengths above the cutoff may pass through the container walls.
Thus, for example, the cutoff wavelengths may be chosen to exclude
UV light from the container interior while allowing one to see the
container contents. Thus, those films behave in a manner similar to
the small silicon particle-filled films or layers described in the
above application.
[0044] Refer now to FIGS. 3 to 5 which illustrate the radiation
transmission and reflection properties of three different-thickness
dual function barrier layers 16 such as depicted in FIG. 2. In FIG.
3, the layer 16 is a film of crystalline silicon, in FIG. 4, the
layer 16 is of amorphous silicon and in FIG. 5, the layer 16 is of
hydrogenated amorphous silicon. As seen from those figures, the
different layers have very different radiation transmission
characteristics that may suit different applications for the wall
structure disclosed herein. For example, a layer 16 of crystalline
silicon 1.0 .mu. thick (FIG. 3) has a cutoff of about 0.4 .mu.m,
while an equally thick layer of amorphous silicon (FIG. 4) has a
cutoff of about 0.6 .mu.m
[0045] Refer now to FIG. 6 which illustrates apparatus for
fabricating the wall structures illustrated in FIGS. 2A to 2C. The
apparatus processes the containers 10 in batches. It includes an
antechamber 32 into which a plurality of untreated containers 10'
in a rack 34 may be transported on a tray 36. Chamber 32
communicates with a lock 38 by way of a vertically reciprocable
gate 44 which may be opened and closed by conventional means (not
shown).
[0046] The lock 38 contains an elevator 46 which may be moved up
and down within that chamber by a piston rod 48 reciprocated by a
standard double-acting pneumatic or hydraulic cylinder (not shown).
When gate 44 is open, and the elevator 46 as in its lower position,
a tray 36 carrying a batch of untreated containers 10' may be slid
into the lock 38 as shown in phantom in FIG. 6. Then, the elevator
46 may be moved to its upper position in lock 38 shown in solid
lines in FIG. 6. This lifts rack 34 and the containers therein to a
coating chamber 52 above lock 38. When the elevator 46 is in its
upper position, the tray 36 which it supports forms the lower wall
of the coating chamber 52.
[0047] The coating chamber 52 also has side walls 54 and a top wall
or hood 56 which communicates by way of a baffle 58 with an exhaust
duct 62 leading to a vacuum source 63 such as turbomolecular pumps
and Root pumps. Preferably, these walls are surrounded by or
contain cooling conduits 63 through which cold water may be
circulated to cool chamber 52.
[0048] A plurality of RF generators 64 are positioned adjacent to
chamber 52. Energy from the generators is coupled into chamber 52
through ports 56 in the chamber side wall 54. Also, the chamber is
dimensioned so that it constitutes a resonant cavity. Thus, the
chamber functions as a microwave heating source, similar to a
microwave oven, for heating the contents of the chamber. Typically,
the RF generators 64 may operate at 900 MHZ with a power output in
the order of 40 KW which fills the chamber 52 with various shifting
intense modes of resonating energy.
[0049] Positioned on the opposite side of the lock 38 is an exit
chamber 72 which communicates with chamber 38 by way of a
vertically reciprocable gate 76 which may be moved between its open
and closed positions by any suitable means (not shown). When the
elevator 46 is in its lower position shown in phantom in FIG. 6 and
the gate 76 is open, the tray 36 and the containers supported
thereon may be moved from lock 38 to the exit chamber 72.
[0050] When both gates 44 and 76 are closed and elevator 46 is in
its raised position, the vacuum source 63 draws a high vacuum,
e.g., 10.sup.-3 Torr, in coating chamber 52; a lesser vacuum, e.g.,
10.sup.-2 Torr, may exist in lock 38. Also, an inert gas such as
argon may be introduced into chamber 52 through a pipe 78 leading
into that chamber, the flow of gas through the pipe being
controlled by a valve 80.
[0051] Referring now to FIGS. 6 and 7, when the elevator 46 is
raised to position the array of untreated containers 10' in coating
chamber 52, the open mouths of the containers are positioned
opposite a corresponding array of heads 82 mounted inside the
chamber. Each head 82 is shaped like a stopper so that it closes
the mouth of the underlying container. Each head 82 is designed to
introduce a plurality of gases into and draw gas from the
corresponding container. For this, each head 82 is equipped with
five tubes which extend down into the container whose mouth is
closed by that head. There is a tube 84 which is connected by a
solenoid valve 86 to a source of plasticizer P. A similar tube 88
is connected by a solenoid valve 92 to a source of inert gas such
as argon A. A pair of longer tubes 94 and 96 are connected by
valves 98 and 102, respectively, to sources of different reactive
gases R.sub.1 and R.sub.2 to be described later. Finally, there is
a tube 104 connected by a valve 106 to a vacuum source V which may
be the duct 62 or a separate vacuum pump (not shown).
[0052] All of the valves 80, 86,92, 98,102 and 106 are controlled
by a controller 110 shown in FIG. 6 which also controls the
operation of the lock gates 44 and 76, piston 48 and the RF
generators 64. Controller 110 also receives temperature information
from temperature sensors 112 inside the coating chamber 52. In
response to these signals, the controller regulates the power
output of generators 64 so as to control within precise limits the
temperature of the containers in chamber 52.
[0053] During operation of the FIG. 6 apparatus, with gate 44 in
its open position and elevator 46 in its lower position, a batch of
untreated containers 10' may be moved from antechamber 32 into the
lock 38, gate 76 being closed. Controller 110 may then close gate
44 and raise the elevator to position the batch of containers
inside coating chamber 52 so that the open mouths of those
containers are closed by the array of heads 82 in that chamber.
Next, controller 110 controls the vacuum source 63 and valves 106
so as to provide a low pressure, e.g., 2.times.10.sup.-3 Torr,
inside containers 10' as well as inside chamber 52 as a whole so
that there is essentially no pressure differential across the
container walls 12.
[0054] Next, valves 80 and 92 are opened so that an inert gas such
as argon is flowed into chamber 52 and into the containers 10'. At
this point, the controller 110 activates the RF generators 64. The
containers 10' being of a dielectric material are essentially
transparent to the microwave radiation. Therefore, intense
microwave energy produced in chamber 52 is transmitted to the
interiors of the containers and ionizes the argon gas therein
producing a plasma within the containers 10'. The gas in chamber 52
is also ionized producing a plasma around the containers. These
plasmas result in intense ionic bombardment of the inside and
outside walls of the containers which removes adsorbed gases,
particulate matter such as dust and any condensed moisture from
those walls. Resultantly, the wall surfaces become chemically pure
and quite receptive to chemical vapor deposition coating, in the
case of the inside surfaces, and to later printing with hot-melt
ink, in the case of the outside surfaces. The surfaces may also
acquire a surface treatment which aids the deposition or printing
process.
[0055] To meet extreme impermeability requirements, it may also be
desirable to seal the just-cleaned interior surfaces of the
containers 10'. For this, controller 110 closes valve 80 so that
the argon gas present in the chamber is removed via duct 62 and
closes the exhaust valves 106. It then momentarily opens valves 86
to inject a plasticizer into the containers 10'. The plasticizer
enters the containers as a vapor cloud raising the pressure therein
somewhat and becomes deposited on the inner surfaces of the
containers. Moreover, due to the pressure differential now present
across the container walls 12, the plasticizer will be sucked into
any pores or micro-voids in the container walls. Next, the
controller 110 activates the RF generators 64. The resulting
microwave energy inside the containers crosslinks the polymer skin
on the container interior walls thereby sealing those surfaces with
a coherent skin.
[0056] Following the container 10' surface preparation steps just
described, a new type of plasma is ignited inside the containers
whose constituents are selected reactant gases. More particularly,
after controller 110 opens exhaust valve 106 momentarily to remove
any residual gases from containers 10', it opens valves 98 and 102
to allow measured amounts of the reactant gases R.sub.1 and R.sub.2
into the containers. For example, if the barrier layers 16 being
applied to the container interior walls is silicon dioxide, the
reactant gases R.sub.1 and R.sub.2 may be silane and oxygen. On the
other hand, if the barrier layers are boron nitride, the reactant
gases may be boron trichloride and ammonia.
[0057] To maintain precise stoichiometry of the reactant gases used
in this step of the process, the gas content of the containers may
be measured using an on-line gas analyzer 116 which monitors the
gas contents of exhaust tubes 104 via branch lines 104a (FIG. 7)
and which is linked to controller 110.
[0058] At this point, controller 110 turns on the RF generators 64
so that the gases R.sub.1 and R.sub.2 inside containers 10' respond
reactively to the microwave energy and form a compound chemical
vapor which, due to diffusion pressure, becomes deposited uniformly
on the container interior walls to form the barrier layers 16 that
results from the reaction of the two gases, e.g., silicon dioxide
or boron nitride. Controller 110, responding to the outputs of the
temperature sensors 112, monitors the temperature of the container
walls 12 and regulates the power output of generators 64 to assure
an amorphous build up, without micro-crystallization, of the
barrier layers 16 on the container walls 12.
[0059] As a result of the chemical vapor condensation of the
reacting gases on the container walls 12, those walls will heat up
and could reach excessive temperatures. This could result in
structural softening of the walls, outgassing and the formation of
exudates such as plastisizer micro-spheroids, all of which would
negatively affect the quality of the barrier layer 16 through poor
adhesion of the barrier layers 16 to the base layers 14 and the
formation of pin holes in the barrier layers. Thus, it is essential
that the containers be maintained at a moderate, non-critical
temperature, particularly if the container base layer 14 consists
of an epoxy or a polymer. This is accomplished by applying the
barrier layers 16 to the base layers 14 of containers 10' in a
succession of deposition events rather than all at once.
[0060] More particularly, controller 110 controls the reactant gas
valves 98 and 102 and the exhaust valve 106 so that the reactant
gases are injected into the containers 10' at high frequency
intervals. That is, during each injection, the stoichiometry of the
gases in the containers is maintained at exact proportions. On the
other hand, during the pulse interval time, the residual gas left
from the previous injection pulse and not yet deposited on the
container walls is pumped out of the containers to maintain the
purity and stoichiometric balance of the internal environment in
the containers.
[0061] In addition, while pulsing the gas injection, controller 110
also pulses the RF generators 64 in synchronism so that microwave
energy is also pulsed into the coating chamber 52. This allows the
container walls to maintain thermal equilibrium by dissipating,
during the power pulse intervals, the deposition heat by radiation
and convection to the water-cooled walls of chamber 52.
[0062] Thus, referring to FIG. 8, while the temperature of the
container walls 12 may become quite high momentarily as shown by
the waveform W, the mean temperature of the walls, while increasing
during the coating process, remains below the softening temperature
of the wall 12 material, below e.g., 50.degree. C. In a typical
example, the coating time needed for growing sufficient and
effective barrier coatings 16 on the container interior surfaces
may be in the order of 5 seconds. During that time, the generators
64 may be pulsed at a frequency in the order of 100 Hz to apply,
say, 500 power pulses to the containers, each pulse being in the
order of 1 ms long. This may deposit barrier layers 16 having a
thickness in the order of 200 .ANG.. While being coated, the
interior skin of the containers may reach a temperature of
120.degree. C. However, the average temperature at the outside of
the container may be only 100.degree. C.
[0063] In accordance with the invention, then, temperature
stabilization of the containers being processed is achieved through
a combination of interacting events, namely the pulsing of the
microwave energy, the brevity of the successive reactive gas
deposition events and the length of the interval between the power
pulses which allows for the dissipation of heat and hence the
cooling of containers 10.
[0064] After barrier coatings 16 of the desired thickness have been
deposited on the container walls, controller 110 turns off all of
the valves, lowers elevator 46 to the position shown in phantom in
FIG. 6 and opens gate 76 so that the just-processed batch of
finished containers 10 can be moved to the exit chamber 72.
[0065] A container 10 with the wall structure 12' shown in FIG. 2B
having a selected UV radiation blocking capability may be formed in
the same way described above. The only difference is that the
polymeric base layer 14 of the container wall 12' contains the
radiation blocking particles 18. A layer 14 such as this and the
process for making it are described in detail in the
above-identified application, and therefore, will not be detailed
here.
[0066] To fabricate a container 10 having the wall structure 12"
depicted in FIG. 2C, the surfaces 14a and 14b of the base layer 14
of the container wall 12 are pre-conditioned as described above.
Then, prior to applying the barrier coating 16 as described above,
reactive gases such as tetraethyloxysilane (TEOS) and oxygen are
introduced into the containers while they are exposed to microwave
energy as described above. These gases will react to form a
relatively flexible layer of silicon dioxide on the interior
surfaces 14b of the base layers 14. The injection of the gases and
the application of the microwave energy are pulsed as described
above to maintain precise control over the stoichiometry of the
reacting gases and the temperature of the container walls so that
uniform layers 22 of the requisite thickness, e.g., 500 .ANG., are
deposited on the base layers 14 of the various containers.
[0067] Then, controller 110 initiates the purging of the coating
chamber 52 and of the containers and commences the next stage of
the coating process which is the deposition of the barrier layers
16. This is carried out in the same way described above for the
FIGS. 2A and 2B wall structures except that the barrier layers are
laid down on the interlayers 22 instead of on the base layers 14.
Since the layers 22 have just been applied, their surfaces are
chemically pristine and quite receptive to the barrier layer
deposits. Resultantly, there is very intimate bonding of those
layers.
[0068] After purging the coating chamber 52 and the containers of
residual gases left from the deposition of the barrier layers 16,
controller 110 initiates the final stage of the process which is
the application of the abrasion-resistant protective top coating
26. This coating, which may be of silicon dioxide or aluminum
oxide, is applied by injecting reactant gases into the containers
in the presence of a plasma as described above. For the former
material, the reactive gases may be TEOS and oxygen; for the latter
material, those gases could be trimethylaluminum or
tripropyloxyaluminum and oxygen. Preferably, the pulsing technique
described above is used to maintain the proper stoichiometry of the
reacting gases and to prevent overheating of the containers. After
the layer 26 has built up to the desired thickness, e.g., 200
.ANG., controller 110 initiates a final purge of chamber 52 and of
the finished containers 10 and then lowers the batch of containers
so that they can be removed from the apparatus by opening gate 76
and advancing the tray 36 into the exit chamber 72.
[0069] While we have described our process in the context of
coating the interior surfaces of an already formed container, the
invention is also applicable to coating a polymeric base layer in
sheet or strip form to form a plural-layer web which may then be
formed into a container. FIG. 9, shows in crossection, a web 120
composed of several layers. The web includes a polymeric base layer
122 containing radiation blocking particles 124. Thus, the base
layer is similar to the base layer 14' described in connection with
FIG. 2B. Deposited on one of the surfaces of base layer 122 is a
relatively thin inorganic barrier layer 126 which is impervious to
gas and moisture despite its thinness. Barrier layer 126 may be of
the same material as the layers 16 described in the FIGS. 2A to 2C
wall structures. Covering the barrier layer 126 is a relatively
thick protective layer 128. This layer prevents direct mechanical
contact with the thin barrier layer 126 by keeping that layer
sealed inside a sandwich structure to protect that layer 126 from
damage during handling when the web 120 is subsequently formed into
a container such as a pouch or package. Furthermore, because the
layer 126 is thin and confined between the two layers 122 and 128,
it is flexible allowing the web 120 to be formed into many
different shapes while still maintaining the integrity of the
barrier layer. Generally, layer 128 will provide the inside surface
of the container. Therefore, that layer should be of a relatively
inert aseptic thermoplastic material such as polyethylene or
polyester. Also, being thermoplastic, the layer 128 may also
perform a welding function for containers that have to be
heat-sealed along their edges.
[0070] The FIG. 9 three-layer web 120 is much simpler than the six
or seven layer laminates currently being used in the packaging
industry. It is lighter in weight and should be less expensive and
more readily disposable and recyclable than conventional
multi-layer sheet structures. Furthermore, it may be transparent so
that the contents of packaging made of the web 120 are readily
observable. Yet, the structure performs a radiation blocking
function to protect the contents of a container or package formed
of the web 120 from UV radiation.
[0071] Refer now to FIG. 10 which illustrates apparatus for making
the FIG. 9 web 120. Unlike the FIG. 6 apparatus, the FIG. 10
apparatus employs two different resonant cavities to first prepare,
and then coat, the base layer. More particularly, the FIG. 10
apparatus includes a preparation chamber 132 with an airlock 134 at
its entrance end and a second airlock 136 at its exit end. An RF
generator 137 is mounted above chamber 132 and delivers microwave
energy to the chamber by way of a port 138. An inert gas such as
argon may be introduced into chamber 132 through a pair of pipes
142 with the flows of gas being controlled by valves 144.
[0072] The outlet airlock 136 from chamber 132 leads to a coating
chamber 146 which is also a resonant cavity, receiving microwave
energy from an RF generator 148 through a port 152 at the top of
the chamber. Reactive gases R.sub.1 and R.sub.2 are introduced into
chamber 146 by way of a first pipe 154 controlled by a valve 156
and a second pipe 158 controlled by a valve 162. Temperature
sensors 163 monitor the temperature in that chamber.
[0073] The coating chamber 146 has an outlet airlock 164 which
leads to a laminating chamber 166 containing a pair of heated
laminating rolls 168 and 172, with the nip of the rolls being
aligned with the airlock 164. Beyond those rolls is a second
airlock 174 located at the exit end of chamber 166 and a third
airlock 176 is present at the top of chamber 166.
[0074] All of the airlocks are connected by way of pipes 178 to a
vacuum pump 182 at the bottom of the apparatus. Pump 182 is also
connected directly to the coating chamber 146 by way of a duct 184
containing a filter 186 to prevent backstreaming into chamber
146.
[0075] A sheet 122 of the base layer material is drawn from a roll
R.sub.1 and guided by a guide roll couple 192 into the airlock 134
of chamber 132. Sheet 122 passes, via air locks 134,136 and 164,
through chamber 132 and chamber 146 into chamber 166 where it is
fed into the nip of the laminating rolls 168 and 172. Also, fed to
that nip is a sheet 128 of the protective material which is drawn
from a roll R.sub.2 and enters chamber 166 through airlock 176. The
two laminated sheets 122 and 128 leave chamber 166 through airlock
174 and are guided by a guide roll couple 194 to a turn roll 196
which directs the webs to a driven take up roll R.sub.3. A
controller 198, which receives temperature signals from sensors
163, controls the operations of the RF generators 137 and 148, pump
182, the various valves and the rotation of the take up roll
R.sub.3 to carry out the steps of the process described above.
[0076] More particularly, as the base layer sheet 122 passes
through chamber 132, controller 198 releases argon gas into the
chamber while exposing the gas to microwave radiation from the
generator 136. Resultantly, a plasma is formed which bombards both
surfaces of the sheet 122 with ions thereby cleaning those surfaces
and making them receptive to CVD coating in the coating chamber
146.
[0077] As the sheet 122 passes through the coating chamber 146,
controller 198 controls valves 156 and 162 so that the reactant
gases R.sub.1 and R.sub.2 are injected into the chamber in high
frequency pulses. At the same time, the controller 198 controls the
microwave generator 148 so that microwave energy is pulsed into the
chamber in synchronism with the gas pulses. Resultantly, the
pre-treated upper surface of sheet 122 is exposed to a compound
vapor of precise stoichiometry which vapor becomes deposited
uniformly on that surface without the sheet becoming overheated to
form the barrier layer 126. Controller 198 controls the transit
time of the sheet through the chamber 146 so that a barrier layer
126 of the desired thickness is deposited on sheet 122.
[0078] The thus coated sheet 122 then passes into the laminating
chamber 166 where it is fused to the sheet 128 of protective
material by the heated laminating rolls 168 and 172. Upon leaving
the laminating chamber 166, the thus-formed multi-layer web 120
cools and is wound up on the take up roll R.sub.3.
[0079] Using an apparatus similar to the one depicted in FIG. 10,
webs having a variety of different functional layers may be
fabricated. For example, the laminating chamber 166 may be replaced
by a second coating chamber similar to chamber 146 so as to apply
two functional coatings or layers to the sheet 122 of base layer
material. Accordingly, it should be understood that certain changes
may be made in carrying out the above process, in the described
product and in the apparatus set forth without departing from the
scope of the invention. Therefore, it is intended that all matter
contained in the above description or shown in the accompanying
drawings, shall be interpreted as illustrative and not in a
limiting sense.
[0080] It is also to be understood that the following claims are
intended to cover all of the generic and specific features of the
invention described herein.
* * * * *