CA2018198A1

CA2018198A1 - Siloxane polymers and copolymers as barrier coatings and method of producing barrier coating properties therewith

Info

Publication number: CA2018198A1
Application number: CA 2018198
Authority: CA
Inventors: John E. Wyman
Original assignee: Energy Sciences Inc
Current assignee: EG Technology Partners LP
Priority date: 1989-04-12
Filing date: 1990-06-04
Publication date: 1991-12-04
Also published as: CA2032215A1; EP0392115B1; CN1059534A; AU634565B2; ES2104564T3; DE69030662D1; JP2667921B2; AU6096990A; JPH02286331A; DE68928031T2; EP0476202A1; DE68928031D1; EP0392115A3; US5077135A; DE69030662T2; JPH04233952A; US5096738A; ATE152750T1; EP0476202B1; EP0392115A2

Abstract

ABSTRACT

A method of imbuing polymer films as of polyethelene and polypropylene with gas, aroma, fragrance, flavor, grease and oil impermeable surface characteristics involving coating the film with appropriate silane compounds and cross-linking the same while providing physical adsorption adherence to the film, and in sufficient coating micron thickness to produce gas and related barrier characteristics; with chemical grafting, including by eb techniques, further providing improved bonding. Preferred barrier-coated polymer films with reduced haze and clarity are formed by such method.

Description

SILOXANE POLYMERS AND COPOLYMERS AS
BARRIER COATINGS AND METHOD OF PRODUCING
BARRIER COATING PROPERTIES THEREWITH

The present invention relates to novel barrier coat-ings ana ~ethoas for organic polymer films such as polye-thylene and polypropyLene f ilms and the like, wherein the coated fiIms become imbued with reduced permeability to gases, such as oxygen, air and carbon dioxiae, as well as to greases and oils.
In my earLier U.S. Patent No. 4,803,126 there is dis closed a successful technique for applying polymer coat-ings, such as late~ polymers having the desired barrier properties, to the surface of a polyolefin film which haa been treated with an organosilane primer coating, using elactron beam radiation to graft the silane to the film and to bond the polymer coating to the crosslinked silane primer coating.
~ hile earlier noted in preliminary private tests, it has now been surprisingly and repeatedly confirmed that appropriate silane primer coatings can provide remarkable : ., ~ - - .

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8~98 . , -2-barrier properties in and of themselves, and without addi~
tional coatings thereupon, to render the polymer film to which ~he coating has been applied strikingly less perme-able to gases, such as oxygen, and to aroma and flavor transmission, and to such a dègree of impermeability that the coaeed film is admirably useful for such purposes as food packaging and shelf life extension thereof and the like. In addition, improvement in the haæe reduction, clarity and appearance of the film fortuitously concurrently occurs, matching the surface quality of high grade "Mylar" film and the llke, and also providing improved dielectric performance for electrical uses, as well, as in electrical capacitors, for example.
Underlying the invention, ~herefore, is the surpris-ing discovery that appropriate polysiloxane:coatings upon such polymer films as polyethylene and polypropylene can provide for greatly decreased permeability in the fllms to gsses, including oxygen and carbon dloxide, and to oils snd greases, as well--and all as distinguished from prior u~ilizations of silane materials just to modify surfaces ' " . ~ ' , ' ~' ;, ~' ' '; '~' ,, . ' ,: . '.
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~ 3-to improve adhesion or to couple polymers-to-polymers or to mineral fibers, as described in the publications refer-enced in my said patent, or to improve surface properties for bonding as in saia patent. In "Silane Coupling Agents", by Edwin P. Plueddemann of Dow Corning Corpora-tion (Plenum Press), 19fl2, for example, the use of silane primarily as a coupling agent in mineral fillea organic resin composites and the like is taught in Chapter 8. The use of silane to couple thermoplastic polyolefins is sug-gested in the "Guide to Dow Corning Silane Coupling Agent", 1988, page 21.
The discovered remarkable oxygen barrier properties ware not only totally unexpectea from prior art experience with silane compounds, but in fact ran counter to prior expectations of those skilled in this art as to silane gas permeability. For example, it had been reported that the oxygen permeability of a silicone elastomer ta crosslinked polydimethylsiloxane) is a factor of about 80 times great-er than that of a butyl rubber ta crosslinked polyisobuty-lene).

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, -4-An object of the invention, thersfore, is to provide new and improved barrier-coated polymer films and a method of producing the same, involving the u~e of appropriate coatings of polysilo~ane, and preferably ~he grafting of the same to the film surface.
~ fllrther object is to provide food packaging materi-als of polysilo~ane-coated polymer films with improved gas impermeability, reduced aroma and flavor transmission properties and improved surface appearance and clarity, as well.
Other and further objects will be explained herein-after and are more particularly delineated in the appended claims.
In summary, the invention embodies a method of imbuing polymer films as of polyethelene and polypropylene ~ith gas, aroma, fragrancej flavor, grease and oil impermeable surface characteristics involving coating the film with appropriate silane compounds and cross-linking the same while providing physical adsorption adherence to the eilm, and ln suEEicient coaling icron ~hickn-ss to ;

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~ 5-produce gas and related barrier characteristics; with chPmical grafting, including by eb techniques, further provicing improved bonding. Preferrea barrier-coated polymer films with re~uced haze and clarity are formed by such method. Preferrec details and best mode embodiments are later presenteQ.
The invention will now be explained in connection with the accompanying drawings Fig. l of which is a graph plotting experimental results contrasting the permeability of polymer films to oxygen as a function of thickness of polysiloxane primer coating;
Fig. 2 contrasts the polysilo~ane primer coating o2-permeability characteristics as a function of temperature with present-day barrier films, the data as to the latter having been presented by H. Watanabe in "The Uqe of High Barrier Packaging Films, etc.", Future-Pax '88, Sixth International Ryder Conference on Packaging Innovations, September 14-16, 1988; and Pigs. 3A and 3B are repectively scanning electron micrographs of the surface of polyetheiene film prior and subsequent to coating with a siloxane coating of the in-ventlon.

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.. 6 Method of Preparation In accordance with the invention, the useful siloxanepolymers are prepared by hydrolysis oE silane ~onomers, and mixture of monomers when a copolymer film is desired, in an aqueous alcohol solution. The mixture is allowec to stand for about 24 hours at 25 degrees C to equilibrate the oligomeric siloxane structures, whereupon the alcohol solutLon containing the oligomeric siloxane structures is coated on the polymer film surface and is dried, preferably in a stream of warm air, to evaporate the alcohol and water to comp~ete the formation of the Si-O-Si bonds of the polymer coating, highly cross-linking the same.
Optionally, but preferably, in order to improve adhe-sion and durability by providing chemical as well as phy-sical bonding, the siloxane polymer may be grafted to the film surface whan the siloxane polymer or copolymer con-talns a double bond, by using either a conventional pro-moted peroxide cure, (of course, added to the siloxane primer prior to coating on the polymer film surface), or by electron-beam initiated grafting as described in my said prior patent.

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.. I ;~0~8~8 ! , - 7-Corona treatment of the polyolefin film prior to the siloxane coating has been founa to improve the coating adhesion, as later discussed. The further discovery of the necessary siloxane coating thicknessranges for effective gas barrier performance is also detailed hereinafter.
The structures of the silanes found useful in the practice of the present invention are shown below:

~1 .
R4 ~ R2 -. ' ' :
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9~3 The groups Rl, R2, R3 and R4 may be the same or different and they are selected from the following groups:
1. Alkoxiae groups, such as methoxy, ethoxy, pro-poxy, 2-metho~yethoxy, etc.;

2. Acid groups, such as acetoxy, propoxy, etc.;

3. Alkyl groups, such as methyl, ethyl, propyl, butyl, amyl, benzyl, cyclohexyl, and higher alkyl groups;

4. Aromatic groups, such as phenyl and alkylatea phenyl groups, naphthyl, etc.;

5. Halogenatea alkyl ana aromatic groups, such as chloropropyl, l,l,l-triflouromethyl~ triflouropropyl, pen-tafluorophenyl, 3-(heptafluoroisopropoxy)propyl, lH,lH, 2H,2H,perflourodecyl, etc.;

6. Amine containing groups, such as 3-(2-aminoethy-lamino)propyl, gamma-aminopropyl, etc.;

7. Unsaturated groups such as allyl, gammatmethacry-loxy) propyl, vinyl, gamma(acryloxy)propyl, 3-(2-vinylben-zylaminoethyl) propyl, etc.;

8. Epoxy containing groups such as 3-(2,3-epoxypro-pyloxy) propyl; and 9. Mercapto containing groups such as 3-mercapto-propyl.

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_9_ The mechanism o~ gas permeation through a plastic film is a co~plex process involving adsorption on a sur-face, migration through the bulk of the film through pores in the film, and desorption from the other side. While the total mechanism by which the siloxane polymers ana copolymers of this invention improve the barrier proper-ties of the plastic films on which they are deposited is not fully understood, and applicant does not wish to be bound by the following theoretical e~planation (it being sufficient to teach how to obtain the results of the invention), it is believed that the siloxane polymers and copolymers of the invention wet the surface of the polymer film smoothly and uniformly and mostly fill in the open-in~s of the pores on the surface of the film. This keeps the gas molecules out of the pores so that even though the pores are still there, the gas molecules cannot get into the pores to pass through the bulk of the film.
Evidence supporting this hypothesis is provided in the scanning electron micrographs of Figs. 3A and 3~
(10,000 magnification) which show respectively the coarse :: , Z018~L9~3 --1 o--rough surface of the untreated low density polyethelene film (LDPE) 125 ~icrons thick, and the leveled and smooth surEace of the siloxane coated film (vinylbenzlamine silane, Dow Corning Z6032), appro~imately six microns thick. Further support is contained in the data of later-described Table I which shows the remarkable haze reduc-tion (from 14.9% down to 2.5%) resulting from the smooth-ing and wetting of the film surface by the primer, which reduces the multiple light reflection and scatter.
It is also recognized that the more closely the chains of a polymer will pack together, the better will be the barrier properties. For example, in current-day pack-aging films sold under the trademark "SARAN' of Dow Chemi-cal Company, the chains of polyvinylidene chloride can psck together very closely and it has excellent barrier properties. Similarly, the molecular configuration of poly(ethylene-vinyl alcohol) is held very close together by hydrogen bonding between the hydroxyl groups on adja-cent polymer chains and these copolymers have good barrier properties.

' .. `
', ' "; ', ' ' ' .~ " ' ' This close packing has the disaa~antage, however, that the melt viscosity of these polymers is high and they must be extruded at high temperatues, which can lead to thermal decomposition. Generally, a comonomer is added during polymerization of polyvinylidene chloride which serves to disturb the close packing and lower the melt viscosity ana allow extrusion at lower temperatures.
Unfortunately, this also degraaes the barrier properties as well, as shown in the "SARAN" curves of later-discussed Fig. 2.
In other present-day packaging films such as those of Northern Petrochemical Company, sold under the mark "EVAL", the ethylene units included in the ethylene-vinyl alcohol copolymer tend to lower the melt viscosity of the vinyl alcohol polymer and allow extrusion at temperatues below the decomposition temperature of the polyvinyl alcohol polymer. Increasing the ethylene content of the copolymer (the upper "EVAL" curve of Fig. 2, later dis-cussed, wherein the ethylene content E is 40% as distin-guished from the lower E-~5X "EVAL" curve~, also degrades the barrier performance of the vinyl alcohol polymer.

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2~8~L98 This polymer also suffers from the disadvantage that lt is hygroscopic; and water plasticizes the polymer ana seri-ously degraaes the performance of ethylene-vinyl alcohol polymers as barrier coatings.
Clo~se packing of polymer chains to prevent gas and oil molecules from penetrating the polymer can also be achieved by crosslinking the polymer chains. However, highly crosslinked polymers are very rigid and extremely difficult to process by melt extrusion.
One of the advantages of the polymers and copoly~ers of the lnvention, on the other hand, is that the hydro-lyzed oligomers ~re soluble in alcohol solution, so they are easily applied to the surface of the base film by a simple coating technique. The polymerization and cross-linking of the siloxane coating is completed by drying the coating, preferably at a slightly elevated temperature, to remove alcohol and water. The use oE this alcohol tech-nique enables the generation of a highly cross-linked film coating structure, and no high temperzture extrusion is required. The degree of crosslinking is controlled by the ~onoters thtt are sel=cted.

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8~9~3 Exam~le 1 For example, hydrolyzeQ dimethyl di~ethoxy silane will polymerize to a linear polymer. The length of the polymer chain can be control]ea by copolymerizing with trimethyl metho~y silane. This compound has only one site which is reactive in the condensation polymerization and lt will cap' the growing polymer chain.
Example 2 On the other hand, methyl trimethoxy silane has three reactive sites during the condensatlon polymerization and will crosslink between growing polymer chains as well as branch when it Ls cohyarolyzed with dimethyl dimethoxy silane.
Example 3 Similarly, tetraethoxy silane has four reactive sites and will produca a very highly crosslinked polymer when it is lncluded in the polymerlzation mixture.
In order to practice my invëntion, it is necessary to select a monomer mixture which, subsequent to hydrolysis and application to the film surface, will smoothly and ;

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~:~18~9~3 uniformly wet the film surface. We have devised a test to select the siloxanes and mixtures of silo.canes which are useful in the practice of the invention.
Test for Useful Siloxane(s) A 10 ml quantity of a silane or a mixture of silanes is dissolved in 90 ml of methyl alcohol and 1 ml of water is added and carefully mixed in. The solution is allowed to stand at about 25 degrees C for 24 hours. A piece of test film, for example low density polyethylene film if the coating is to be used on polyolefin films, is immersed briefly in the methanol solution of the hydrolyzed silanes, and the alcohol is allowed to dry slowly in dry air. The coating is then warmed gently in a stream of air to complete the polymeriæation by driving off the water.
The silanes and mixtures of silanes that are useful in the practice of the present invention form a smooth and uniform coating on the surface of the organic film on which they are tested. These co`atings also reduce the ha2e of the film.

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2C)~ 9~3 The silanes and mixtures of silanes that are not use-ful in the practice of the invention have been found to form beads and droplets of siloxane on the surface of the film on ~hich they are testec as the alcohol dries off the surface of the film ana thus fail to weL the same. These materials thus do not form useful barrier coatings on organic polymer films.
It has been discovered that the silanes and silane mi~tures that are useful in the practice of this inven-tion, particularly on polyethylene and polypropylene films, generally contain a silane with an amino group.
Example 4 For e~ample, the vinylbenzylamine silane, Dow Corning Corp. Z-6032, when hydrolyzed in alcohol solution and a~plied to a polyethylene film surface, formed a smooth continuous film which was useful as both a barrier to oxygen and oil.
E~ample 5 In contrast, gamma-met~acryloxypropyl trimethoxy silane by itself when hydrolyzed in methanol solution anu `
applied to a polyethylene film, formed beads of material , ' ' ' ' : ' ' : :
, ' ', .

which drew away from the film surface as the alcohol driea. This indicatea that the siloxane oligomers did not wet the surface of the polyethylene film and were thus not useful as barrier coatings on polyethylene fil~.
An equal volume mixture of the ~amma-methacryloxy propyl trimetho~y silane an~ vinyl benzyl amine silane (Dow Corning Z6032) hydrolyzed together in methanol solu-tion and when applied to the polyethylene film surface was found, however, to dry out in the form of a smooth, uni-form coating. This shows that the cohydrolyzed mixture is useful in the practice of the invention.
E~ample 6 Similarly, hydrolyzed methyl trimethoxy silane in alcohol formed beads on the surface of the polyethylene film when the alcohol evaporated. However, when the methyl trimethoxy silane was cohydrolyzed with the said vinyl-benzyl amine silane and appIied to the polyethyLene film, a smooth uniform coating was obtainedO
"Wettin~"
The reason why an amine-containing silane will wet the surface of polyethylene film is not fuily known. It .:

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~17-may be due in part to a negative electrical surface charge on the surface or just unner the surface of the film which attracts the cationic amine-containing siloxane when it is in methanol solution. It is also possible that the car-boxyl groups on the film surface, particularly after it has been corona treated, attract the amine groups on the siloxane and cause it to wet the polyethylene film sur-f ace.
When mixtures of silanes which include an amino group containing siLane are to be used as barrier polymers on polyethylene or polypropylene film, it has been found that the monomers should be mixed and then cohydrolYzed in order that the resulting oligomers will wet the surface.
Thus, a mixture of equal volumes of the vinyl benzyl amine silane and the methacryloxypropyl silane hydrolyzed separately, was found to form beads on the surface of the polyethylene film as the alcohol solution evaporated.
Example 7 Similarly, a mixture of 9 parts of methyl trimethoxy silane and one part of the vinyl benzyl amine silane that had been cohydrolyzed in methanol formed a smooth, uniform coating on the surface of the polyethylene film.

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~18-In contrast, a mixture of equal parts of methanol solutions of the vinyl benzyl amine silane ana the methyl trimethoxy silane that haa been separately hydrolyzed, formea beads of material on the polyethylene as the alcohol evaporated from the mixture after it was coated on the polymer sur~ace.
Example 8 A lOml quantity of gamma aminopropyl triethoxy silane was dissolved in 90 ml of methyl alcohol and one ml of water was added and carefully mixed in. The solution was allowed to stand for about 24 hours at about 25 degrees C. A piece of polyethylene film was briefly immersed in the solution and allowed to dry slowly in dry air. The coating was warmed gently in a stream of warm air to com-plete the polymerization. A smooth, uniform coating was formed on the polyethylene film surface.
Example 9 A mixture of 2 ml of gamma-aminopropyl tri-ethoxy silane and 8 ml of vinyl triethoxy silane was dissolved in 90 ml of methanol and I ml o water was added and careful-ly mixed in. The solution was allowed to stand for 24 hours at 25 degrees C.

' ' ~ ' .

~8~.98 A piece of polyethylene film was immersed in the so-lution and allowed to ary slowly in dry air. The coating was war~ed gently in a stream of warm air to complete the polymerization. A smooth, uniform coating was for~ed on the polyethylene film ~surface.
E~am~le 10 A mi~ture of 2 ml of gamma-aminopropyl tri-ethoxy silane and 2 ml of methyl trietho~y silane was dissolved in 90 ml of methanol and 1 ml of water was added and care~
fully mixed in. The solution was allowed to stand for 24 hours at 25 degrees C.
A piece of polyethylene film was immersed in the so-lution and allowed to dry slowly in dry airO The coating was warmed gently in a stream of air to complete the poly-merization. A smooth, uniform coating was formed on the polyethylene film surface.
It has been discovered, furthermore, that the coating phqnomenon herein described is generally a surface-coating effect. Cross-sectional analysis of the LDPE coated film, for e~ample, by scanning electron microscopy and electron-dispersive X-ray spectroscopy has revealed the few micron coating to be attached to the film surface with no appar-ent penetration into the film~

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The surface and barrier properties of the barrier coating are controlled by the nature of the ~onomers that are usea to form ~he oligomers. For example, the critical surface tension of a polyethylene film that has been coat-ed with hydrolyzed vinyl benzyl amine silane is about 55 dynes/cm. In contrast, the critical surface tension of the coating on polyethylene film which was prepared by hydrolyzing a mixture of 9 parts of methyl trimethoxy silane and one part of the vinyl benzyl amine silane is only about 23 dynes/cm. A drop of hydrocarbon oil on the coated surface has a large contact angle and did not spread. In contrast, the oil spread slowly and wet the surface of the uncoated film.
If it is desired to reduce the sensitivity of the coating to moisture-, as another example, one may co-hydrolyze the vinyl ben7yl amine silane with an alkyl tri-methoxy silane in order to replace some of the amine and amlne salt groups that are hydroscopicO Similar tailoring of the selected silane compounds for desired properties can be obtained with appropriate silane selections.

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8~8 The adhesion of the coatin~ on the film can be improvea by incorporating monomers with vinyl unsaturation into the siloxane mixture before hydrolysis and grafting the resulting coating to the film surface. The grafting can be accomplishea by incorporating a conventional promo-tea free radical generator in the coating (such as dicumyl peroxide, for e~ample) that will react upon gentle heat-ing, or by use of electron beam-initiated grafting, as described in my said patent, subsequent to drying of the coating.
The improved adhesion of the barrier coating to the substrate may, as beEore expiained, be achieved by graft-ing the siloxane coating to the film. In the case of a barrier coating of a vinyl benzyl amine siloxane on a polypropylene substrate, the "Scotch tape test" (described in my said prior patent) removed some of the ungraEted coating from the polypropylene, but did not remove any of the grafted coating. This experiment demonstrates the greatly improved adhesion of the coating to the substrate that can be acheived by eb grafting.

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, -22-The graph of the before-mentioned Fig. 1, demon-strates the efficacy of siloxane coatings applieu to poly-mer films in accordance with the invention, plotting 2 permeability in cc/lOOin2/24 hours at 23C along the or-dinate, and siloxane primer thickness in microns along the abscissa for 38 micron oriented polypropylene (OPP), 135 -''t I~o micron low density polyest~r film (LDPE) and 13 ~icron polyester (PET) J with and without a coating uerived from hydrolyzed 60~ methanol and 40% Dow Corning Z-6032 silane, prepared as above-described and applied in various thicknesses to the film and electron-beam grafted with about 175KV and doses up to S Megarads as detailed in my prior patent. The uncoated films were quite permeable (approximately 70-95cc/lOOin2/24 hours); whereas coatings of from 5 eo 22 microns provided excellent 02-permeable barriers under approximately 2.5-0O5cc/lOOin2/24 hours at one atmosphere of pressure. Each of these coated Eilms provided low haze appearance as well, and outstanding aroma or fragrance retention of products packaged therewith as later described in connection with the Limonene Transmission tests of Table 2; the coated films having apparently reduced solubility of aroma and flavor compounds in such packaged food or other products--so- .called "scalpiDg" of such.

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' ~ ' :'' ' ' Gas permeability under lcc/lOOin2/24 hours at room temperature ana one atmoshpere was rPalized with primer thicknesses of the order of 10 microns. Thickness of a few microns thus provides a dramatic improvement in barrier properties. Equally impressive enhancement of oil resistance of the polyolefins has also been demonstratea by the process.
Favorable comparison of the above siloxane primer barrier system ("PRIMER") with present-day commercial food-packaging and similar film materials ln terms of 2 permeability as a function of increasing temperature, is presented in the before-mentioned Fig. 2. It will be observed that the slope or temperature coefficient of the "PRIMER" curve is more favorable than for the DO~ films known as "SARAN" (polyvinyldene chloride), and the films known as "EVAL" (Northern Petrochemical Company--ethylene vinyl alcohol), and at least comparable to "BAREX" film.
The improvement in the before-mentioned haze appear ance is shown in the following Table 1, attained for the LDPE film with 5 micron siloxane primer bilaterally applied; and the marked improvement in Limonene Transmis-sion for both the coated LDPE and OPP fil=s is presented in Table 2.

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AS _~7 ~- `T :~:r--,~CI!) 1:'~1003 . . . ~
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S~ ?E- ' ~, IP.SI`; FI'". 88.3 1~.9 ~?.I~r!:) FIL" 8~. 9 2. 5 -- ~ ._ ~ . . r _ _ _._ _ ._ _~ _ __ _ ~

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ASTN T ;)T .~1E-l~OII D-15'3 ~ 7 ~'~F ~ 35' R. H~ ) -- -- - . I . ........ . _ - _ . . .. I
S~.PLr THlCX~iESS ¦ (MG/100 IN~t2/1 HOURS~ I ~O~.M.AL;,--o VIRG N LDP~' l35 MICROI~ 8Cl b ~ 9 100. ~1 p~ lED LDP' ~?P~O~. 14i MICRO~; 6. O . 07 VIRGI~l OPP 50 MICRON 335~. 6 lOO. 0 ~INED Op ¦A~PROX. 6~ MISRON - . .- - . _ . . .

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- , The Li~onene Transmission test ~D-1653) is an acceptea measure of aroma or fragrance or flavor transmission as used in the food-packaging industry, involving gas chromatograph measurement of limolene solubility in the film. Table 2 demonstrates that for the LDPE film with the silo~ane coating ahove describea, the limonene loss was only 6mg/100in2/24 hours as contrasted with the more than thousand times greater loss (8014.9) for the uncoated or virgin LDPE. Similar tremendous fragrance retention was acheived with the coated OPP film.
While the above examples have been principally carried out with methanol, selected because of its ease of use and relatively low boiling point and because it is an e~cellent solvent for both silanes and water, other sol-vents miscible with water and of high vapor pressure for evaporation and that can dissolve a wide range of silanes may also be used, including other alcohols such as ethanol and lsopropyl alcoholO Further modifications will occur to those skilled in this art and such are considered to fall within the spirit and scope of the invention as de-fined in the appended claims.

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Claims

1. A method of rendering organic polymer films sub-stantially impermeable to gases such as oxygen, aroma, flavor and fragrance, and greases and oils, that comprises, hydrolysing silane monomers or mixtures of silane monomers in a solvent misc-ible with water and that solubilizes silanes and is evaporable, and equilibrating the same; coat-ing the same upon the polymer film; evaporating the solvent and water to complete the formation of Si-O-Si bonds and to cross-link the silane(s), thereby to produce a siloxane gas-impermeable barrier adhered to the surface of the film.

2. A method of rendering organic polymer films sub-stantially impermeable to gases such as oxygen, aroma, flavor and fragrance, and greases and oils, that comprises, hydrolysing silane monomers or mixtures of silane monomers in an aqueous alcohol solution and equilibrating the same;
coating the same upon the polymer film;

evaporating the alcohol and water to complete the formation of Si-O-Si bonds and to cross-link the silane(s), thereby to produce a siloxane gas-permeable barrier adhered to the surface of the film.

3. A method as claimed in claim 2 and in which the alcohol is methanol and the silane(s) are repre-sented by the following formula:
, where the groups R1, R2, R3 and R4 may be the same or different and are selected from the fol-lowing groups:
1. Alkoxide groups, such as methoxy, ethoxy, propoxy, 2-methoxyethoxy, etc.;
2. Acid groups, such as acetoxy, propoxy, etc.;
3. Alkyl groups, such as methyl, ethyl, propyl, butyl, amyl, benzyl, cyclohexyl, and higher alkyl groups;

4. Aromatic groups, such as phenyl and alkylated phenyl groups, naphthyl, etc.;

5. Halogenated alkyl and aromatic groups, such as chloropropyl, 1,1,1-triflouromethyl, triflouropropyl, pentafluorophenyl, 3-(deptaluoroisopropoxy)propyl, 1H,1H,2H,2H,perflourodecyl, etc.;

6. Amine containing groups, such as 3-(2-aminoethylamino)propyl, gamma-aminopropyl, etc.;

7. Unsaturated groups such as allyl, gamma-(methacryloxy) propyl, vinyl, gamma(acryloxy)propyl, 3-(2-vinylbenzylaminoethyl) propyl, etc.;

8. Epoxy containing groups such as 3-(2,3-epoxypropyloxy) propyl; and

9. Mercapto containing groups such as 3-mercaptopropyl.
4. A method as claimed in claim 2 and in which the silane comprises a vinyl benzyl amine silane.

5. A method as claimed in claim 4 and in which the vinyl benzyl amine silane is cohydrolyzed with methyl trimethoxy silane.
6. A method as claimed in claim 5 and in which the ratios of said silanes by volume range from about 9 to 1.
7. A method as claimed in claim 2 and in which the silane comprises gamma aminopropyl triethoxy-silane.
8. A method as claimed in claim 2 and in which the siloxane coating is applied in a thickness of the order of a few microns.
9. A method as claimed in claim 8 and in which the said thickness lies within the range of from about 5 to 22 microns.

10. A method as claimed in claim 2 and in which the siloxane coating is chemically grafted to the film.

11. A method as claimed in claim 10 and in which the grafting is effected by promoted peroxide.

12. A method as claimed in claim 10 and in which the grafting is effected by electron beam radiation.

13. A method of rendering organic polymer films sub-stantially impermeable to gases such as oxygen, aroma, flavor and fragrance, that comprises, wetting the film with a silane coating, and cross-linking the same while providing physical adsorption to the film.

14. A method as claimed in claim 13 and in which the further step is performed of chemically grafting the said coating to the film.

15. A method as claimed in claim 14 and in which said grafting is effected by one of peroxide cure and electron-beam-initiated grafting.

16. A polymer film constituted of an organic polymer film base to a surface of which is physically adsorbed a cross-linked siloxane coating that imbues the said surface with gas, aroma, flavor and fragrance and grease and oil impermeable surface characteristics.

17. A polymer film as claimed in claim 16 and in which said coating is chemically grafted to said film base surface.

18. A polymer film as claimed in claim 16 and in which said coating has been produced by the method of claim 2.

19. A polymer film as claimed in claim 16 and in which said coating has been produced by the method of claim 3.

20. A polymer film as claimed in claim 16 and in which the said coating is of thickness in the range of about 5 to 22 microns.

21. A polymer film as claimed In claim 16 and in which the said coating imparts haze-reduction charact-eristics and clarity.

22. A polymer film as claimed in claim 16 and in which the silane precursor of the siloxane comprises a vinyl benzyl amine silane.

23. A polymer film as claimed in claim 22 and in which the vinyl benzyl amine silane is cohydrolyzed with methyl trimethoxy silane.

24. A polymer film as claimed in claim 23 and in which the ratios of said silanes by volume range from about 9 to 1.

25. A polymer film as claimed in claim 16 and in which the silane precursor of the siloxane comprises gamma aminopropyltriethoxy silane.