US20020041942A1 - Gas-impermeable, chemically inert container structure for food and volatile substances and the method and apparatus producing the same - Google Patents

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.

Description

FIELD OF THE INVENTION
• This invention deals with a gas-impermeable, chemically inert container product and the method and apparatus for producing that product.[0001]
BACKGROUND OF THE INVENTION
• 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.[0002]
• 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.[0003]
• 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.[0004]
• 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.[0005]
• 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.[0006]
• 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.[0007]
SUMMARY OF THE INVENTION
• 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.[0008]
• 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.[0009]
• 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.[0010]
• Another object of the invention is to provide a container having the above properties which can be shaped as desired.[0011]
• Still another object of the invention is to provide a method of producing a container possessing one or more of the above properties.[0012]
• 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.[0013]
• Other objects will, in part, be obvious and will, in part, appear hereinafter.[0014]
• 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.[0015]
• 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.[0016]
• 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.[0017]
• 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.[0018]
• 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.[0019]
• 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.[0020]
• 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[0021]_xIn_1-xN or Al_xIn_1-xN can be used. The mole fraction x determines the cutoff wavelength.
• 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.[0022]
• 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.[0023]
• 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.[0024]
• 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.[0025]
• 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.[0026]
• 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.[0027]
BRIEF DESCRIPTION OF THE DRAWINGS
• 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:[0028]
• FIG. 1 is a sectional view of a container incorporating our invention;[0029]
• FIGS. 2A to[0030]2C are fragmentary sectional views taken along line2-2 of FIG. 1 showing different wall structures that may be present in the FIG. 1 container;
• FIGS.[0031]3 to5 are graphical diagrams showing the radiation and reflection properties of certain wall structures embodying the invention;
• FIG. 6 is a longitudinal sectional view of apparatus for making the FIG. 1 container;[0032]
• FIG. 7 is a vertical section on a larger scale showing a portion of the FIG. 6 apparatus in greater detail;[0033]
• FIG. 8 shows the wall temperature of a FIG. 1 container during the operation of the FIG. 6 apparatus;[0034]
• FIG. 9 is a fragmentary sectional view taken along[0035]2-2 of FIG. 1 showing a container wall structure having an internal barrier layer, and
• FIG. 10 is a view similar to FIG. 6, of apparatus for making a container having the FIG. 9 wall structure.[0036]
DESCRIPTION OF THE PREFERRED EMBODIMENTS
• FIG. 1 of the drawings shows a[0037]container10 having awall12 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.
• As shown in FIG. 2A, usually[0038]wall12 comprises atransparent base layer14 of a polymeric material such as polypropylene, but it may also be of an opaque material such as fiberglass—reinforced epoxy. Typically,layer14 has a thickness in the order of 300 μm. The outer andinner surfaces14aand14bofbase layer14 may be subjected to a plasma to render those surfaces chemically pure as shown by the hatching. These enable theouter surface14ato be printed on with a hot melt ink (not shown) and makes the inner surface14bchemically receptive so that it provides an excellent bonding surface for ablocking layer16 applied to layer14bby vapor deposition in the presence of a plasma.
• Depending upon the particular application,[0039]layer16 may consist of any one of a variety of inorganic materials such as aluminum oxide (AL₂O₃), silicon dioxide (SiO₂), boron nitride (BN), silicon nitride (Sl₃N₄) which are chemically inert and fluid impermeable. Thebarrier layer16 for a container such asbottle12 may have a thickness in the order of 100-1000 Å. Thewall structure12 is suitable for a container intended to hold solvents, acids or other such fluids which would otherwise react chemically with thebase layer14 material. That wall structure would also be suitable for containers whose contents might be adversely affected by oxygen or moisture that would penetrate through thebase layer14 but for thebarrier layer16.
• FIG. 2B illustrates another[0040]container wall structure12′ which is similar towall12 in that it is composed of apolymeric base layer14′ whose pretreated interior surface14bis covered by abarrier layer16 so that it has all of the attributes of thewall structure12. In addition, however, thebase layer14′ ofwall12′ contains tiny, monodispersed, inorganic,radiation blocking particles18 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 ofsilicon particles18, thebase layer14′ can be designed to provide good radiation blocking for short wavelengths, but good transmission for longer wavelengths. Therefore, thewall structure12′ in FIG. 2B will protect the contents ofcontainer10 from external UV radiation, while allowing one to see the contents of the container throughwall12, assuming that thebarrier layer16 is of a material such as aluminum oxide which is transparent to visible light.
• A[0041]container10 having thewall structure12′ would be suitable for packaging foods, pharmaceuticals and the like which degrade upon being exposed to sunlight.
• FIG. 2C illustrates another[0042]wall structure12″ forcontainer10 which comprises several layers that are applied to the pre-treated inner surface14bof abase layer14 similar to the one in FIG. 2A. Thewall structure12″ includes a relatively thick, e.g., 1000 Å,underlayer22 of a somewhat softer material that is compatible with thebarrier layer16. For example,layer22 may be silicon dioxide with some residual free radicals of CH₂or CH₃or siloxane, i.e., a transitional material or the like which provides stress relief for abarrier layer16 and whose chemical resistance to alcohols, acids, solvents or the like is optimal, but which derives its hardness from a top oroutermost layer26 of an abrasion-resistant material such as silicon dioxide or aluminum oxide. Thewall structure12″ 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.
• 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[0043]base layer14. 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.
• Refer now to FIGS.[0044]3 to5 which illustrate the radiation transmission and reflection properties of three different-thickness dual function barrier layers16 such as depicted in FIG. 2. In FIG. 3, thelayer16 is a film of crystalline silicon, in FIG. 4, thelayer16 is of amorphous silicon and in FIG. 5, thelayer16 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, alayer16 of crystalline silicon 1.0 μ thick (FIG. 3) has a cutoff of about 0.4 μm, while an equally thick layer of amorphous silicon (FIG. 4) has a cutoff of about 0.6 μm
• Refer now to FIG. 6 which illustrates apparatus for fabricating the wall structures illustrated in FIGS. 2A to[0045]2C. The apparatus processes thecontainers10 in batches. It includes an antechamber32 into which a plurality ofuntreated containers10′ in arack34 may be transported on atray36. Chamber32 communicates with alock38 by way of a vertically reciprocable gate44 which may be opened and closed by conventional means (not shown).
• The[0046]lock38 contains anelevator46 which may be moved up and down within that chamber by apiston rod48 reciprocated by a standard double-acting pneumatic or hydraulic cylinder (not shown). When gate44 is open, and theelevator46 as in its lower position, atray36 carrying a batch ofuntreated containers10′ may be slid into thelock38 as shown in phantom in FIG. 6. Then, theelevator46 may be moved to its upper position inlock38 shown in solid lines in FIG. 6. This liftsrack34 and the containers therein to acoating chamber52 abovelock38. When theelevator46 is in its upper position, thetray36 which it supports forms the lower wall of thecoating chamber52.
• The[0047]coating chamber52 also hasside walls54 and a top wall or hood56 which communicates by way of abaffle58 with anexhaust duct62 leading to avacuum source63 such as turbomolecular pumps and Root pumps. Preferably, these walls are surrounded by or contain coolingconduits63 through which cold water may be circulated to coolchamber52.
• A plurality of[0048]RF generators64 are positioned adjacent tochamber52. Energy from the generators is coupled intochamber52 through ports56 in thechamber side wall54. 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, theRF generators64 may operate at 900 MHZ with a power output in the order of 40 KW which fills thechamber52 with various shifting intense modes of resonating energy.
• Positioned on the opposite side of the[0049]lock38 is anexit chamber72 which communicates withchamber38 by way of a verticallyreciprocable gate76 which may be moved between its open and closed positions by any suitable means (not shown). When theelevator46 is in its lower position shown in phantom in FIG. 6 and thegate76 is open, thetray36 and the containers supported thereon may be moved fromlock38 to theexit chamber72.
• When both[0050]gates44 and76 are closed andelevator46 is in its raised position, thevacuum source63 draws a high vacuum, e.g., 10⁻³Torr, in coatingchamber52; a lesser vacuum, e.g., 10⁻²Torr, may exist inlock38. Also, an inert gas such as argon may be introduced intochamber52 through apipe78 leading into that chamber, the flow of gas through the pipe being controlled by avalve80.
• Referring now to FIGS. 6 and 7, when the[0051]elevator46 is raised to position the array ofuntreated containers10′ incoating chamber52, the open mouths of the containers are positioned opposite a corresponding array ofheads82 mounted inside the chamber. Eachhead82 is shaped like a stopper so that it closes the mouth of the underlying container. Eachhead82 is designed to introduce a plurality of gases into and draw gas from the corresponding container. For this, eachhead82 is equipped with five tubes which extend down into the container whose mouth is closed by that head. There is a tube84 which is connected by asolenoid valve86 to a source of plasticizer P. Asimilar tube88 is connected by a solenoid valve92 to a source of inert gas such as argon A. A pair of longer tubes94 and96 are connected byvalves98 and102, respectively, to sources of different reactive gases R₁and R₂to be described later. Finally, there is atube104 connected by a valve106 to a vacuum source V which may be theduct62 or a separate vacuum pump (not shown).
• All of the[0052]valves80,86,92,98,102 and106 are controlled by acontroller110 shown in FIG. 6 which also controls the operation of thelock gates44 and76,piston48 and theRF generators64.Controller110 also receives temperature information fromtemperature sensors112 inside thecoating chamber52. In response to these signals, the controller regulates the power output ofgenerators64 so as to control within precise limits the temperature of the containers inchamber52.
• During operation of the FIG. 6 apparatus, with gate[0053]44 in its open position andelevator46 in its lower position, a batch ofuntreated containers10′ may be moved from antechamber32 into thelock38,gate76 being closed.Controller110 may then close gate44 and raise the elevator to position the batch of containers inside coatingchamber52 so that the open mouths of those containers are closed by the array ofheads82 in that chamber. Next,controller110 controls thevacuum source63 and valves106 so as to provide a low pressure, e.g., 2×10⁻³Torr, insidecontainers10′ as well asinside chamber52 as a whole so that there is essentially no pressure differential across thecontainer walls12.
• Next,[0054]valves80 and92 are opened so that an inert gas such as argon is flowed intochamber52 and into thecontainers10′. At this point, thecontroller110 activates theRF generators64. Thecontainers10′ being of a dielectric material are essentially transparent to the microwave radiation. Therefore, intense microwave energy produced inchamber52 is transmitted to the interiors of the containers and ionizes the argon gas therein producing a plasma within thecontainers10′. The gas inchamber52 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.
• To meet extreme impermeability requirements, it may also be desirable to seal the just-cleaned interior surfaces of the[0055]containers10′. For this,controller110 closesvalve80 so that the argon gas present in the chamber is removed viaduct62 and closes the exhaust valves106. It then momentarily opensvalves86 to inject a plasticizer into thecontainers10′. 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 thecontainer walls12, the plasticizer will be sucked into any pores or micro-voids in the container walls. Next, thecontroller110 activates theRF generators64. The resulting microwave energy inside the containers crosslinks the polymer skin on the container interior walls thereby sealing those surfaces with a coherent skin.
• Following the[0056]container10′ surface preparation steps just described, a new type of plasma is ignited inside the containers whose constituents are selected reactant gases. More particularly, aftercontroller110 opens exhaust valve106 momentarily to remove any residual gases fromcontainers10′, it opensvalves98 and102 to allow measured amounts of the reactant gases R₁and R₂into the containers. For example, if the barrier layers16 being applied to the container interior walls is silicon dioxide, the reactant gases R₁and R₂may be silane and oxygen. On the other hand, if the barrier layers are boron nitride, the reactant gases may be boron trichloride and ammonia.
• 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-[0057]line gas analyzer116 which monitors the gas contents ofexhaust tubes104 viabranch lines104a(FIG. 7) and which is linked tocontroller110.
• At this point,[0058]controller110 turns on theRF generators64 so that the gases R₁and R₂insidecontainers10′ 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 layers16 that results from the reaction of the two gases, e.g., silicon dioxide or boron nitride.Controller110, responding to the outputs of thetemperature sensors112, monitors the temperature of thecontainer walls12 and regulates the power output ofgenerators64 to assure an amorphous build up, without micro-crystallization, of the barrier layers16 on thecontainer walls12.
• As a result of the chemical vapor condensation of the reacting gases on the[0059]container walls12, 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 thebarrier layer16 through poor adhesion of the barrier layers16 to the base layers14 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 thecontainer base layer14 consists of an epoxy or a polymer. This is accomplished by applying the barrier layers16 to the base layers14 ofcontainers10′ in a succession of deposition events rather than all at once.
• More particularly,[0060]controller110 controls thereactant gas valves98 and102 and the exhaust valve106 so that the reactant gases are injected into thecontainers10′ 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.
• In addition, while pulsing the gas injection,[0061]controller110 also pulses theRF generators64 in synchronism so that microwave energy is also pulsed into thecoating chamber52. 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 ofchamber52.
• Thus, referring to FIG. 8, while the temperature of the[0062]container walls12 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 thewall12 material, below e.g., 50° C. In a typical example, the coating time needed for growing sufficient andeffective barrier coatings16 on the container interior surfaces may be in the order of 5 seconds. During that time, thegenerators64 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 layers16 having a thickness in the order of 200 Å. While being coated, the interior skin of the containers may reach a temperature of 120° C. However, the average temperature at the outside of the container may be only 100° C.
• 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[0063]containers10.
• After[0064]barrier coatings16 of the desired thickness have been deposited on the container walls,controller110 turns off all of the valves, lowerselevator46 to the position shown in phantom in FIG. 6 and opensgate76 so that the just-processed batch offinished containers10 can be moved to theexit chamber72.
• A[0065]container10 with thewall structure12′ 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 thepolymeric base layer14 of thecontainer wall12′ contains theradiation blocking particles18. Alayer14 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.
• To fabricate a[0066]container10 having thewall structure12″ depicted in FIG. 2C, thesurfaces14aand14bof thebase layer14 of thecontainer wall12 are pre-conditioned as described above. Then, prior to applying thebarrier coating16 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 surfaces14bof the base layers14. 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 thatuniform layers22 of the requisite thickness, e.g., 500 Å, are deposited on the base layers14 of the various containers.
• Then,[0067]controller110 initiates the purging of thecoating chamber52 and of the containers and commences the next stage of the coating process which is the deposition of the barrier layers16. 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 theinterlayers22 instead of on the base layers14. Since thelayers22 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.
• After purging the[0068]coating chamber52 and the containers of residual gases left from the deposition of the barrier layers16,controller110 initiates the final stage of the process which is the application of the abrasion-resistant protectivetop coating26. 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 thelayer26 has built up to the desired thickness, e.g., 200 Å,controller110 initiates a final purge ofchamber52 and of thefinished containers10 and then lowers the batch of containers so that they can be removed from the apparatus by openinggate76 and advancing thetray36 into theexit chamber72.
• 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[0069]web120 composed of several layers. The web includes apolymeric base layer122 containingradiation blocking particles124. Thus, the base layer is similar to thebase layer14′ described in connection with FIG. 2B. Deposited on one of the surfaces ofbase layer122 is a relatively thininorganic barrier layer126 which is impervious to gas and moisture despite its thinness.Barrier layer126 may be of the same material as thelayers16 described in the FIGS. 2A to2C wall structures. Covering thebarrier layer126 is a relatively thickprotective layer128. This layer prevents direct mechanical contact with thethin barrier layer126 by keeping that layer sealed inside a sandwich structure to protect thatlayer126 from damage during handling when theweb120 is subsequently formed into a container such as a pouch or package. Furthermore, because thelayer126 is thin and confined between the twolayers122 and128, it is flexible allowing theweb120 to be formed into many different shapes while still maintaining the integrity of the barrier layer. Generally,layer128 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, thelayer128 may also perform a welding function for containers that have to be heat-sealed along their edges.
• The FIG. 9 three-[0070]layer web120 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 theweb120 are readily observable. Yet, the structure performs a radiation blocking function to protect the contents of a container or package formed of theweb120 from UV radiation.
• Refer now to FIG. 10 which illustrates apparatus for making the FIG. 9[0071]web120. 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 apreparation chamber132 with anairlock134 at its entrance end and asecond airlock136 at its exit end. AnRF generator137 is mounted abovechamber132 and delivers microwave energy to the chamber by way of aport138. An inert gas such as argon may be introduced intochamber132 through a pair ofpipes142 with the flows of gas being controlled byvalves144.
• The outlet airlock[0072]136 fromchamber132 leads to acoating chamber146 which is also a resonant cavity, receiving microwave energy from anRF generator148 through aport152 at the top of the chamber. Reactive gases R₁and R₂are introduced intochamber146 by way of afirst pipe154 controlled by avalve156 and asecond pipe158 controlled by a valve162.Temperature sensors163 monitor the temperature in that chamber.
• The[0073]coating chamber146 has anoutlet airlock164 which leads to alaminating chamber166 containing a pair of heated laminating rolls168 and172, with the nip of the rolls being aligned with theairlock164. Beyond those rolls is asecond airlock174 located at the exit end ofchamber166 and athird airlock176 is present at the top ofchamber166.
• All of the airlocks are connected by way of[0074]pipes178 to avacuum pump182 at the bottom of the apparatus.Pump182 is also connected directly to thecoating chamber146 by way of aduct184 containing afilter186 to prevent backstreaming intochamber146.
• A[0075]sheet122 of the base layer material is drawn from a roll R₁and guided by aguide roll couple192 into theairlock134 ofchamber132.Sheet122 passes, via air locks134,136 and164, throughchamber132 andchamber146 intochamber166 where it is fed into the nip of the laminating rolls168 and172. Also, fed to that nip is asheet128 of the protective material which is drawn from a roll R₂and enterschamber166 throughairlock176. The twolaminated sheets122 and128leave chamber166 throughairlock174 and are guided by aguide roll couple194 to aturn roll196 which directs the webs to a driven take up roll R₃. A controller198, which receives temperature signals fromsensors163, controls the operations of theRF generators137 and148, pump182, the various valves and the rotation of the take up roll R₃to carry out the steps of the process described above.
• More particularly, as the[0076]base layer sheet122 passes throughchamber132,controller198 releases argon gas into the chamber while exposing the gas to microwave radiation from thegenerator136. Resultantly, a plasma is formed which bombards both surfaces of thesheet122 with ions thereby cleaning those surfaces and making them receptive to CVD coating in thecoating chamber146.
• As the[0077]sheet122 passes through thecoating chamber146,controller198controls valves156 and162 so that the reactant gases R₁and R₂are injected into the chamber in high frequency pulses. At the same time, thecontroller198 controls themicrowave generator148 so that microwave energy is pulsed into the chamber in synchronism with the gas pulses. Resultantly, the pre-treated upper surface ofsheet122 is exposed to a compound vapor of precise stoichiometry which vapor becomes deposited uniformly on that surface without the sheet becoming overheated to form thebarrier layer126.Controller198 controls the transit time of the sheet through thechamber146 so that abarrier layer126 of the desired thickness is deposited onsheet122.
• The thus[0078]coated sheet122 then passes into thelaminating chamber166 where it is fused to thesheet128 of protective material by the heated laminating rolls168 and172. Upon leaving thelaminating chamber166, the thus-formedmulti-layer web120 cools and is wound up on the take up roll R₃.
• 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[0079]laminating chamber166 may be replaced by a second coating chamber similar tochamber146 so as to apply two functional coatings or layers to thesheet122 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.
• 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.[0080]

Claims (33)

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 inclaim 1 wherein the heating step is accomplished by exposing said gases and said surface to microwave radiation.

3. The method defined inclaim 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 inclaim 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 inclaim 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 inclaim 1 including the step of forming the base layer into a container before the conducting step.

7. The method defined inclaim 1 including the step of forming said structure into a container after the continuing step.

8. The method defined inclaim 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 inclaim 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 inclaim 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 inclaim 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 inclaim 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 inclaim 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 inclaim 15 and further including a crosslinked plasticizer between said surface and said barrier layer.

17. The wall structure defined inclaim 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 inclaim 15 and further including a relatively thin top layer of a hard, abrasion-resistant material covering said barrier layer.

19. The wall structure defined inclaim 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 inclaim 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 inclaim 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 ofclaim 22 wherein the particulate material is spherical and exhibits an imaginary refractive-index component K which decreases substantially with wavelength.

24. The material ofclaim 23 wherein K is at least 0.5 at a wavelength of 0.4 μm and is less than 0.005 μm at a wavelength of 0.7 μm.

25. The material ofclaim 23 wherein the density per unit of surface area varies inversely with K.

26. The material ofclaim 22 wherein the particle size is chosen to minimize scattering of visible radiation.

27. The material ofclaim 22 wherein the particulate material consists of uniformly sized spheres having a diameter that ranges from 0.005 μm to 0.04 μm.

28. The material ofclaim 22 wherein the particulate material consists of spheres of diameter less than 0.04 μm.

29. The material ofclaim 22 wherein the density per unit of surface area is approximately 10⁻⁴to 10⁻⁵g/cm².

30. The material ofclaim 22 wherein the silicon is crystalline silicon.

31. The material ofclaim 22 wherein the silicon is amorphous silicon.

32. The material ofclaim 22 wherein the silicon is hydrogenated amorphous silicon.

33. The material ofclaim 22 wherein the silicon is alloyed with germanium.

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