Gas barrier structures

A gas barrier structure is disclosed which comprises a base synthetic thermoplastic polymeric layer, e.g. nylon, polyethylene, having two coatings on one side of the base layer. The first coating is a solvent-based urethane primer and the second coating comprises a polyvinyl alcohol gas barrier material. The primer is present in the range of 0.3 to 3.0 g/m.sup.2 and the polyvinyl alcohol is present in an amount of up to 2.0 g/m.sup.2. The polyvinyl alcohol is deposited from solution or dispersion.

The present invention relates to so-called high gas barrier structures, 
especially films. Such structures are sought after in order to provide 
long shelf life for foodstuffs which tend to spoil through oxidation. 
It is known to use aluminum foil, vacuum-deposited aluminium, polyvinyl 
alcohol, saponified copolymers of ethylene and vinyl acetate and 
polyvinylidene chloride as gas barriers for food packaging, usually as a 
part of a composite structure. European Publication No. 132 565 to De 
Antonis et al., published Feb. 13, 1985, discloses a film laminate 
comprising a polyamide layer and an ethylene/vinyl alcohol copolymer 
layer. The laminate may include other compatible polymeric film layers and 
adhesives. The laminate is expanded to an area of less than four times the 
original, and is preferably drawn to a draw ratio of 1.5:1 to 4:1 in one 
direction. The ethylene/vinyl alcohol copolymer is preferably hydrolysed 
with a degree of hydrolysis of 85 to 99.5% and contains 15 to 65 mole per 
cent of ethylene. The laminate is disclosed as having good oxygen barrier 
properties, which are greater than would be expected from separate films 
of oriented polyamide and ethylene/vinyl alcohol copolymer layers. 
Japanese Patent No. 59 182 714 to Kido Shigyo KK, published Oct. 17, 1984, 
discloses a process comprising extruding an ethylene/vinyl alcohol film 
and laminating other films onto both surfaces of the extruded film. Films 
having water-vapor resistance, e.g., polyethylene, polypropylene, 
polyvinyl chloride, polyvinylidene chloride, polyester and nylon, are 
preferably coated with an adhesive and applied onto the extruded film. The 
laminated film is reported to have good gas barrier properties, which 
decrease as the ethylene/vinyl alcohol copolymer absorbs moisture. 
West German Patent No. 3 207 740 to Dahms et al., published Sept. 15, 1983, 
discloses a multi-layer synthetic film, consisting of a middle gas 
diffusion barrier layer, covered on both sides with polymer layers. Such 
multi-layer film is used as a jacket layer for synthetic water pipes. The 
laminated jacket films are of polyethylene/polyamide/polyethylene, 
polyethylene/polyvinylidene chloride/polyethylene, polyethylene/polyvinyl 
alcohol/polyethylene. The inner barrier layer may also be a laminate, 
e.g., polyamide/polyvinyl alcohol, polyvinylidene 
chloride/polyamide/polyvinylidene chloride or polyvinylidene 
chloride/polyester/polyvinylidene chloride. The thickness of the barrier 
layer is 3-150 microns (.mu.m) and the thickness of the two outer layers 
is at least that of the barrier layer. Diffusion of oxygen into the pipe, 
when such a multi-layer film is used as a jacket for the pipe, is reported 
as being negligible. 
Japanese Patent No. 57 061 025 to Kuraray KK, published Apr. 13, 1982 
discloses a transparent film, without fish-eyes and having excellent 
gas-barrier and anti-dewing properties. The film comprises a thermoplastic 
film, e.g., polypropylene, polystyrene, polyester, nylon, regenerated 
cellulose, polyethylene, polyvinyl chloride, coated with a solution of 
ethylene/vinyl alcohol copolymer resin of saponification value of at least 
96%, and ethylene content of 25-60 wt percent containing 0.1 to 3 wt 
percent of a nonionic surfactant having a hydrophilic-lipophilic balance 
of 4 to 16. The solvent for the ethylene/vinyl alcohol copolymer may be 
mixtures of water and n-propanol, iso-propanol, t-butyl alcohol, methanol, 
ethanol, dioxane and the like. After coating the surface of the film, 
drying same and removing the solvent, the coated film is preferably heated 
at 80.degree.-170.degree. C. to improve the anti-dewing, gas barrier 
property, mechanical strength and slip. The film is useful as a packaging 
material, especially for foods. 
Japanese Patent No. 57 059 720 to Unitika KK, published Apr. 10, 1982 
discloses production and biaxial oriention at a draw ratio of more than 
500% of a composite film comprising an amorphous polyamide film and a 
completely saponified polyvinyl alcohol film. The film produced is useful 
for packaging materials and in industrial applications, e.g., mould 
release films. Such film is reported as having excellent clouding proof 
properties, mould release properties, oxygen barrier and perfume retention 
properties. In an example, a polyvinyl alcohol film having a thickness of 
110 microns and a moisture content of 7.5%, a polymerization degree of 
1680 and a saponification degree of 99.4 mol percent was laminated with a 
polyamide film having a thickness of 70 microns (.mu.m) using a 
urethane-based adhesive. The resulting laminate film (nylon 6) was 
simultaneously biaxially oriented at a draw ratio of 3 in the machine and 
transverse directions at 135.degree. C. and then heat treated at 
195.degree. C. for 5 sec. kg/.mu.m.sup.2 and had excellent folding 
endurance and abrasion resistance. 
Japanese Patent No. 55135659 to Toray Industries Inc. published Oct. 22, 
1980 discloses a laminate film comprising many layers of saponified 
ethylene/vinyl acetate copolymer (EVOH) and many layers of polyamide. The 
two kinds of polymer layers are alternately laid on top of each other. The 
number of pairs of layers is from 7 to 150. Typically, ten 1 micron thick 
sheets of EVOH and ten 1 micron (.mu.m) thick sheets of polyamide is 
superior in gas permeability, impact strength and dimensional stability to 
a double layered film made of a 10 micron (.mu.m) thick sheet of EVOH and 
a 10 micron (.mu.m) thick sheet of polyamide. 
Japanese Patent No. 54 104 988 to Toppan Printing KK, published Aug. 17, 
1984 discloses a container consisting of 
(a) an inner layer made from an ethylene/vinyl alcohol copolymer which 
contains 20-50 mol. percent of ethylene and has a saponification degree of 
greater than 95 mol. percent, 
(b) an intermediate layer made from a grafted and modified polyolefin and 
an unsaturated carboxylic acid, or derivative thereof, or an unsaturated 
glycidyl compound, and 
(c) an outer layer of a polyamide. The container may be an extruded tube. 
Japanese Patent No. 54 047 776 to Gunze KK, published Apr. 16, 1979 
discloses a film comprising outer hydrophobic resin layers of a polyamide 
resin and an ethylene/vinyl acetate saponified copolymer, in which the 
ethylene content is 25-50 mole percent and the degree of saponification is 
at least 90 percent. When laminating a composite film of a hydrophobic 
resin layer and an ethylene/vinyl acetate saponified copolymer layer to a 
composite film of a hydrophobic resin layer and a polyamide resin layer, 
with the polyamide resin layer adjacent the copolymer layer, the copolymer 
layer is laminated at 230.degree.-270.degree. C. and immediately pressed 
under linear pressure of at least 5 kg/cm.sup.2. When the bonding between 
the polyamide and the hydrophobic resin layers or the hydrophobic resin 
and the copolymer layers is not adequate, an adhesive layer, e.g., a 
modified polyolefin, may be used. The films are reported to have good gas 
impermeability, transparency strength and hot water resistance, which do 
not cause curling thus making them especially useful for automatic 
packaging. 
Japanese Patent No. 53 035 778 to Nippon Synthetic Chemical Industries, 
published Apr. 13, 1978 discloses a laminate comprising a heat sealing 
layer, a biaxially-stretched layer obtained by drawing a film of 
saponified ethylene/vinyl acetate copolymer, and a biaxially stretched 
film of polypropylene, polyester or nylon. The saponified ethylene/vinyl 
acetate copolymer has 15-45 mole percent ethylene content and a degree of 
saponification of greater than 95 mole percent and the film made therefrom 
has been drawn at least 1.5 times in the machine and transverse directions 
and has a fusing temperature of greater than 95.degree. C. in water. 
Japanese Patent No. 60 052 337 to Toyobo KK, published Mar. 25, 1985 
discloses a film comprising 
(a) a polyester film having a film density of up to 1.355 g/cm.sup.3 and a 
maximum refractive index of up to 1.590 to the direction parallel to the 
surface, 
(b) a soft polymer material laminated to at least one surface of the 
polyester film, and 
(c) a sparingly gas permeable material laminated to the soft polymer and 
having an oxygen permeability of 30 ml/m.sup.2.24 hr. atm. at 20.degree. 
C. under the dried condition of the laminated film and peel strength of at 
least 1000 g/15 mm at 20.degree. C. when the laminated film is heat 
sealed. The soft polymer is preferably polyethylene, polyurethane or 
polyester elastomer. The sparingly gas permeable material is preferably 
polyvinyl alcohol, saponified ethylene/vinyl acetate copolymer polyamide, 
aluminium foil, or metallized polyester or polyamide. 
Japanese Patent No. 60 019 525 to Toppan Printing KK, published Jan. 31, 
1985 discloses a film obtained by bonding hydrophilic films to an 
arbitrary material using a moisture-curing type adhesive to laminate the 
material with the films. Water content of the hydrophilic films is 1-5%. 
The adhesive is preferably a urethane-containing adhesive, the hydrophilic 
film is preferably nylon, polyvinyl alcohol or an ethylene/vinyl acetate 
copolymer and the arbitrary film is preferably polyolefin, polyester, 
polystyrene or cellulose film. 
U.S. Pat. No. 4,544,698 to Roullet et al. which issued Oct. 1, 1985 
discloses coating thermoplastic material, e.g., polyolefins, polyamides, 
polyesters, with an aqueous solution of a polyvinyl alcohol and a water 
insensitive polymer latex. The implication of the disclosure appears to be 
that for polyvinyl alcohol alone the gas permeability increases in 
proportion to its moisture content, and stains due to moisture. Apparently 
any kind of polyvinyl alcohol is suitable for use in combination with the 
water insensitive latex. Preferably the polyvinyl alcohol may be 
hydrolyzed polyvinylacetates having more than about 90 percent vinyl 
alcohol moieties, or may be hydrolyzed ethylene/vinyl acetate copolymers 
containing less than 10 percent ethylene units. Suitable water insensitive 
polymer latexes include styrene-butadiene or styrene alkyl acrylate 
latexes, vinyl halogenide latexes such as vinyl chloride and vinylidene 
chloride. The composition is characterized by forming a two-phase coating 
upon drying, such that the latex polymer forms the continuous phase and 
the polyvinyl alcohol forms the discontinuous phase. 
Coating thicknesses, of the polyvinyl alcohol and polymer latex layers, of 
2.9-4.3 microns (.mu.m) are exemplified, giving oxygen permeabilities at 
45 percent relative humidity and 40.degree. C. of between 0.8 and 2 
cm.sup.2.s.sup.-1.cmHg.sup.-1 .times.10.sup.12. 
U.S. Pat. No. 4,416,938 to Haskell, which issued Nov. 27, 1986 discloses a 
transparent gas barrier, for retortable pouches made from a 
dialdehyde-treated polyvinyl alcohol. Haskell indicates that films made 
from polyvinyl alcohol, chemically hardened or not, have been used in 
packaging materials but have been found to exhibit moisture sensitivity 
inconsistent with good barrier properties. This problem is overcome by 
using a coating composition comprising a homogenous combination of metal 
orthophosphate and dialdehyde treated polyvinyl alcohol. The metal is 
primarily iron or aluminium, but may contain small quantities of tin, 
titanium or zirconium. Elvanol.TM. 71-30 is disclosed as being a suitable 
type of dialdehyde treatable polyvinyl alcohol. The coatings are described 
as being substantially glassy or non-crystalline, and may be placed on 
shaped substrates such as fibres, films and containers prepared from 
polyesters, polyamides, polyolefins and other polymers. 
U.S. Pat. No. 4,418,119 to Morrow et al., which issued Nov. 29, 1983 
discloses an ovenable board made of paperboard, having coatings of 
polyvinyl alcohol and silicone. The polyvinyl alcohol, e.g., Elvanol 
brand, is coated at a weight of about 3 to 12 lb/ream and the silicone 
release coating, e.g., General Electric SS 4191 brand, is coated at a 
weight of about 0.7 to 0.9 lb/ream. The silicone coating is cured using a 
catalyst and an accelerator. The polyvinylalcohol may be selected from any 
commercially available product. Morrow et al. disclose that such an 
ovenable board can withstand temperatures of from 0.degree. to 350.degree. 
F. (-18.degree. to 177.degree. C.). 
U.K. Patent No. 2 115 770, published Aug. 7, 1985 to A. N. Ferrar et al. 
discloses the manufacture of film composites which include gas barrier 
materials. In this patent, it is disclosed that multiply structures of 
ionomer/gas barrier/ionomer, ionomer/gas barrier/polyester or ionomer/gas 
barrier/nylon layers can be made by adhesive combination of several plies 
of single layers, adhesive combination of composite plies or by a 
coextrusion process. Suitable gas barrier layers are indicated as being 
made from polyvinylidene chloride, polyvinyl alcohol or an ethylene/vinyl 
acetate copolymer which may be partly hydrolysed. Specifically disclosed 
are the manufacture of multiply structures by coating an ionomer base 
layer with a layer of polyvinylidene chloride and then adhesively bonding 
a further layer, viz of nylon, polyester or ionomer, to the polyvinylidene 
chloride. 
In many of the prior art structures, the gas barrier layer is in film form 
or part of a coextrusion. The thickness of each gas barrier layers is such 
that it usually affects the physical properties of the structure, e.g., 
flex crack resistance, impact resistance. The gas barrier properties could 
be attained with significantly thinner layers of polyvinyl alcohol or 
ethylene vinyl alcohol copolymer, but such thin coextrusions or films 
thereof tend to pinhole, thus making such an approach impractical. Coating 
a base film with a thin coating of such gas barrier materials would 
provide the necessary gas barrier properties while essentially maintaining 
the structural properties of the base film. Heretofore polyvinyl alcohol, 
applied as a coating from solution or dispersion, has been used as a 
sizing agent and adhesive for hydrophilic, porous materials, e.g., paper. 
It has been demonstrated that commercially functional flexible packaging 
material, even employing hydrophilic films such as nylon, cannot be 
prepared from direct application of wet polyvinyl alcohol, i.e., from 
dispersion or solution. In particular, the bond between the gas barrier 
layer and the base layer seems to disintegrate, especially when the film 
composite is subjected to moisture. 
A structure and a method of making such a structure which overcomes the 
foregoing difficulty has now been found.

Accordingly, the present invention provides a composite structure 
comprising a synthetic thermoplastic polymeric base layer having two 
coatings on one side of said base layer, the first coating being adjacent 
the base layer and being a solvent-based urethane primer, which when dry 
allows an aqueous dispersion or solution of polyvinyl alcohol to "wet out" 
the primer, in an amount in the range of from about 0.3 to about 3.0 
g/m.sup.2 of the base layer, and the second coating being placed on the 
exposed dried surface of the first coating and being a polyvinyl alcohol 
gas barrier material in an amount up to about 2.0 g/m.sup.2 of said base 
layer, said second coating having been formed from a dispersion or 
solution. 
In an embodiment the surface free energy of the dried primer is at least 36 
mN/m. 
In a preferred embodiment the first coating is a two component urethane 
primer. 
In another embodiment the second coating has a saponification value of at 
least about 90 mole percent, preferably at least about 99 mole percent. 
In yet another embodiment the polyvinyl alcohol gas barrier material is in 
an amount of from 0.15 to 2.0 g/m.sup.2, especially from 0.5 to 1.0 
g/m.sup.2. 
Depending upon the end use for the composite structure, the base layer may 
be formed from nylon, ethylene/vinyl alcohol copolymer, polyolefin, 
polyester, or olefin copolymers, e.g., ionomers, ethylene/vinyl acetate 
copolymers. The base layer may be in film form or in a moulded form. For 
example, for packaging meats and the like, a preferred base layer is nylon 
in film form. For food tray lidding material, preferred base layers are 
polyester or nylon, as film or in a preformed state. 
The base layers useful in the present invention particularly include 
polypropylene, polyester, high density polyethylene, low density 
polyethylene nylon 6 and nylon 66. 
In further embodiments the composite structure has a heat-sealable layer, 
e.g., polyethylene or ionomer film adhesively laminated to the gas barrier 
layer or a heat-sealable layer, e.g., polyethylene or ionomer film 
laminated coated on the gas barrier layer. 
The invention also provides a process for forming a composite film 
comprising: 
(a) coating a base synthetic polymeric film with a solvent-based urethane 
primer, which when dry allows an aqueous dispersion or solution of 
polyvinyl to "wet out" thereon and drying said primer to form a primer 
coating in an amount in the range of about 0.5 to about 3.0 g/m.sup.2 of 
the base film; 
(b) coating the dried primer with an aqueous dispersion or solution of 
polyvinyl alcohol and drying said dispersion or solution to form a gas 
barrier coating in an amount in the range of up to about 2.0 g/m.sup.2 of 
the base film. 
In an embodiment the surface free energy of the dried primer is at least 36 
mN/m. 
In yet another embodiment the polyvinyl alcohol gas barrier material is in 
an amount of from 0.15 to 2.0 g/m.sup.2, especially from 0.5 to 1.0 
g/m.sup.2. 
In a preferred embodiment the gas barrier coating of the composite film is 
subsequently adhesively laminated to a heat sealable film. 
Surprisingly it has also been found that a composite film comprising a 
unoriented synthetic thermoplastic polymeric base film having a urethane 
primer coating thereon in an amount of about 0.5 to about 3.0 g/m.sup.2 of 
the base film, and a polyvinyl alcohol or gas barrier coating applied to 
the primer coating in an amount of up to about 2.0 g/m.sup.2 of the base 
film may be oriented without destroying the gas barrier properties of the 
composite film. The orientation may be monoaxial biaxial. 
The invention also provides a food package comprising food enveloped in a 
film composite, said film composite comprising a base synthetic 
thermoplastic polymeric film on the outside of the package, a primer 
coating, in a amount of about 0.5 to about 3.0 g/m.sup.2 of the base film 
on the inner side of the base film, a gas barrier coating adjacent to the 
primer coating, in an amount of up to about 2.0 g/m.sup.2 of the base 
film, and a heat-sealable layer adhered to the gas barrier coating by 
adhesive lamination or extrusion coating, said primer coating being a 
urethane primer, and the gas barrier layer comprising polyvinyl alcohol, 
said gas barrier layer having been coated from an aqueous dispersion or 
solution thereof. 
The term "primer" as used herein will be understood by those skilled in the 
art to mean those coatings which are formulated to promote adhesion 
between layers of two materials but which will not, in the coating 
process, adhere or transfer in part or in whole to surfaces contacted by 
the coating prior to the application of the top coat. Primers useful in 
the present invention are known. Primers which may be used include 
polyester or polyether-based polyurethane liquid resins. 
Solvent-based urethane primers include those which are soluble in 
substantially non-polar organic solvents, e.g. methyl ethyl ketone, ethyl 
acetate and toluene, and exclude those which are soluble in relatively 
polar solvents, e.g. water, alcohols. 
As used herein "polyvinyl alcohol" is the product formed by hydrolysing 
(saponifying) polyvinyl acetate. It is sometimes referred to in the trade 
as PVAL. Those polyvinyl alcohols which are highly saponified, e.g., 
90-99.99 mole percent, are most useful as gas barrier materials, and are 
particularly preferred in the present invention. 
In the present invention, the PVAL materials are not first formed into film 
nor are they melt extruded onto the base synthetic thermoplastic polymeric 
layer. The PVAL is coated onto the base layer from a dispersion or 
solution. 
With respect to the film composite, the following describes a typical 
process and product of the present invention. Although reference is only 
made to a nylon base film, it will be understood that it is for 
exemplification only. 
Nylon film is pulled from a roll and transported past two coating stations. 
Typically, the nylon film is about 20-80 .mu.m in thickness but may be 
from 8-125 .mu.m, and depending on the end use may be unoriented or 
oriented. For most food packaging applications, unoriented film is 
preferred. The linear speed of the nylon film, past the coating stations 
is typically about 90 m/min-300 m/min, using commercial apparatus. 
The urethane primer may be, for example, a reaction product of a polyester 
or a polyether component and a diisocyanate component. It is often 
supplied in solution form in an organic solvent, e.g., acetone, ethyl 
acetate or toluene. The urethane primer may be applied using a gravure 
cylinder. The primer-coated nylon film is then dried in order to remove 
the solvent. The urethane primer is applied in a manner such that, when 
dry, the amount applied is from about 0.5 to about 1.5 g/m.sup.2 of the 
nylon film. Typically, the amount is about 0.6 to 0.8 g/m.sup.2. A 
suitable urethane primer is available from Morton Chemical Company under 
the trade mark Adcote 503H. As indicated hereinbefore, it is important 
that the primer has substantially no "green tack". Otherwise, when the 
primer-coated film passes through the roller assembly of the laminator, 
the primer may be picked off, and the PVAL subsequently applied will be in 
direct contact with the base film and subject to being poorly bonded to 
the base film. It is important that the primer, when dry, can be "wetted 
out" by the PVAL solution (or dispersion). The term "wetted out" refers to 
an even coating of PVAL solution forming on the primer, without any 
formation of holes or puddles in the coating. It has been found that, for 
best results the primer, when dry should have a high free surface energy, 
e.g. above about 36 mN/m. Free surface energy is measured by the procedure 
ASTM No. D2578. 
The PVAL is applied at the second coating station. Isopropyl alcohol or 
ethanol may be added to the solution, in an amount up to 50 wt. percent, 
e.g. from 5 to 35 wt percent of the solution, to minimize foaming of the 
solution and to assist in drying the PVAL coating. Other compounds may be 
added in minor amounts to improve wettability of the primer, decrease 
moisture sensitivity of the dried topcoat, as well be understood by those 
skilled in the art. The PVAL solution may be applied using a gravure or 
reverse gravure roll. The PVAL is applied in a manner such that when dry, 
the amount applied is up to about 2.0 g/m.sup.2 of the nylon film, 
especially from 0.15 to 2.0 g/m.sup.2. Typically, the amount is about 0.5 
to 1.0 g/m.sup.2, especially from 0.8 to 0.9 g/m.sup.2. Suitable PVALs are 
available from E. I. du Pont de Nemours and Company under the trade marks 
ELVANOL 71-30 and ELVANOL 90-30. The PVAL-coated structure is then passed 
through a dryer in order to remove the water. Drying may be provided by 
known means, e.g., in a so-called roll support oven or in a floater oven. 
With respect to the PVAL coating, the small quantity of PVAL laid down on 
the base sheet and the high bond strength between the primer and the PVAL 
means that the PVAL coating thickness cannot be measured accurately using 
classical unit weight measuring techniques. The coating weights are based 
upon the theoretical lay-down capability of the coating technique and the 
concentration of the PVAL dispersion or solution. 
The PVAL-coated base layers show excellent oxygen barrier properties. For 
example, a 25 um thick nylon film coated with about 0.7 g/m.sup.2 urethane 
primer and 0.9 g/m.sup.2 Elvanol 71-30 PVAL showed an oxygen permeability 
of less than 15.5.times.10.sup.-6 ml O.sub.2 /cm.sup.2 film/24 h at 0% 
relative humidity (R.H.). 
The gas barrier-coated film of the present invention is not normally used 
without being bonded to another film. For example, the PVAL-coated nylon 
film referred to above may be adhesively laminated or extrusion coated 
with a heat sealable film or layer. The heat sealable layer is typically a 
low density polyethylene, linear low density polyethylene, an 
ethylene/vinyl acetate copolymer or a mixture thereof, or an ionomer. The 
four-or-five layer structure, e.g., nylon film-primer-PVAL-extrusion 
coated heat sealable film or nylon film-primer-PVAL-adhesive-heat sealable 
film, may then be used to package, for example, wieners, bacon, which are 
sensitive to spoilage by oxygen. 
The following examples are used to illustrate the present invention. 
EXAMPLE 1 
This example does not fall within the scope of the present invention and is 
included for purposes of comparison. 
A 7 wt percent aqueous solution of Elvanol 71-30 polyvinylalcohol, 
containing 5 wt percent isopropyl alcohol was coated onto a 25 um thick 
unoriented nylon 66 film, using a Faustel.TM. coater with a gravure roll. 
The "line speed" was 12 m/min and the drying oven temperature was set at 
150.degree. C. The solution "wetted out" well on the nylon film, and the 
temperature of the PVAL-coated film at the exit from the oven was 
52-60.degree. C. The coated film was extremely clear. The oxygen 
permeability, as measured by the procedure of ASTM F-372 was about 
7.8.times.10.sup.-6 ml/cm.sup.2 /24 h at 23.degree. C. and 0% R.H. 
The PVAL-coated film so produced was adhesively laminated to a 76 um thick 
film of low density polyethylene film. The bond strength of this laminate 
was tested by pulling the nylon and polyethylene films apart with a Suter* 
tester, according to the procedure of ASTM D-1876. The bond strength was 
found to be about 20 g/cm, with the PVAL coating being pulled from the 
nylon film. 
EXAMPLE 2 
Example 1 was repeated, except that the nylon film was first coated with 
Adcote.TM. 503-H two-component urethane primer (with Catalyst F) in an 
amount of about 0.7 g/m.sup.2. The bond strength was measured. The bond 
strength over the entire range of relative humidities (0-100% R.H.) was at 
least 390 g/cm. Oxygen permeabilites, in ml/cm.sup.2 /24 h at 23.degree. 
C., were 15.5.times.10.sup.-6 at 0% R.H., 34.1.times.10.sup.-5 at 53% 
R.H., 52.7.times.10.sup.-4 at 75% R.H., and 27.9.times.10.sup.-3 at 100% 
R.H. This example falls within the scope of the present invention. 
EXAMPLE 3 
Adcote 503-H urethane primer was coated onto a 25 um nylon 66 film in an 
amount of about 0.7 g/m.sup.2 and the primer dried. The surface free 
energy on the primer coating was 40 mN/m. A 5 wt percent of aqueous 
solution of Elvanol 71-30 polyvinyl alcohol containing 9 wt percent 
isopropyl alcohol was coated onto the primer coating in an amount of about 
0.8 g/m.sup.2, and dried. The thus-coated film exhibited an oxygen 
permeability of less than 15.6.times.10.sup.-6 ml/cm.sup.2 /24 h at 
23.degree. C. and 0% R.H. The line speed was 90 m/min. This example falls 
within the scope of the present invention. 
EXAMPLE 4 
Example 2 was repeated except that the nylon base film was replaced by 12 
.mu.m oriented polyester film and the primer coating weight was increased 
to 2.44 g/m.sup.2. The bond strength was measured at at least 275 g/cm at 
0 and 100% R.H. The oxygen transmission was less than 3.1.times.10.sup.-5 
ml/cm.sup.2 /24 h at 23.degree. C. and 0% R.H. 
EXAMPLE 5 
Example 2 was repeated except that the nylon base film was replaced by 51 
.mu.m unoriented linear low density polyethylene film. The bond strength 
was measured at at least 275 g/cm at 0 and 100% R.H. The oxygen 
transmission was less than 77.5.times.10.sup.-6 ml/cm.sup.2 /24 h at 
23.degree. C. and 0% R.H. 
EXAMPLE 6 
A 25 .mu.m unoriented nylon 66 film was coated with a Adcote 503H two 
component urethane primer in an amount of 2.44 g/m.sup.2. The primer was 
dried. A 5 wt % aqeous solution of Elvanol 90-50 polyvinyl alcohol 
containing 25 wt % isopropyl alcohol was coated onto the primer coating in 
an amount of about 0.81 g/m.sup.2 at a line speed of 12 m/min. The 
polyvinyl produced was adhesively laminated to a 51 .mu.m thick film of 
low density polyethylene film. The bond strength of this laminate was 
tested by pulling the nylon and polyethylene films apart with an Instron* 
tester, at 0% R.H. The bond strength was found to be at least 275 g/cm. 
The oxygen transmissions, in ml/cm.sup.2 /24 h at 23.degree. C., were 
46.5.times.10.sup.-6 at 0% R.H., 109.times.10.sup.-6 at 59% R.H., 0.002 
434 at 75% R.H., 0.003 472 at 80% R.H. and 0.014 353 at 100% R.H. 
EXAMPLE 7 
Example 2 was repeated except that the unoriented nylon film was 76 .mu.m 
thick. The coated film was then oriented in the machine direction. The 
draw ratio was 3.1 to 1. The thickness of the coated film was then about 
25. The oxygen permeability was measured as 31.times.10.sup.-6 ml/cm.sup.2 
/24 h at 0% R.H. and as 0.0062 ml/cm.sup.2 /24 h at 100% R.H. The oriented 
coated film was then adhesively laminated to linear low density 
polyethylene film. The bond strength was measured at greater than 158 
g/cm. 
EXAMPLE 8 
Example 2 was repeated except that the polyvinyl alcohol was deposited from 
a 1.25 wt % aqueous solution of Elvanol.TM. 71-30. The coating weight, 
when dry, was estimated to be 0.16 g/m.sup.2. The oxygen permeability of 
the coated film was measured as 77.5.times.10.sup.-6 ml/cm.sup.2 /24 h. 
EXAMPLE 9 
About 333 single component urethane primer was coated onto a 25 .mu.m nylon 
66 film. The coating weight of the primer was 2.44 g/m.sup.2. The coating 
was dried. The surface free energy of the dried primer was 34 mN/m. The 
primer did not "wet" using a 5 wt % aqueous solution of Elvanol 71-30 
polyvinyl alcohol and 35 wt % ethanol. This example does not fall within 
the scope of the present invention. 
EXAMPLE 10 
A number of aqueous primers, outside the scope of the present invention 
were coated onto 25 .mu.m unoriented nylon 66 film using a gravure roll. 
The primers were dried and then coated with a 5 wt % aqueous solution of 
Elvanol 71-30 polyvinyl alcohol containing 25 wt % isopropyl alcohol. The 
PVAL coating, after drying had a weight of about 0.81 g/m.sup.2. The PVAL 
coating films were adhesively laminated to 51 .mu.m thick low density 
polyethylene films. The bond strengths and oxygen transmissions were 
determined. The results are shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
COATING BOND g/cm 
PRIMER wt (g/m.sup.2) 
OPTICS 
0 TRANSM..sup. 
0% RH 
80% RH 
__________________________________________________________________________ 
SPENBOND*650 
3.74 poor 0.001 64 
&gt;275 67 
2 part epoxy 
AD77T670* 
5.37 poor 0.001 27 
&gt;275 84 
1 part acrylic 
AD77T660* 
5.37 poor 0.000 20 
240 43 
2 part acrylic 
SERFENE*2060 
5.37 poor 0.000 02 
30 -- 
PVdC emulsion 
__________________________________________________________________________ 
.sup. ml/cm.sup.2 /24 h 
* trademark 
The above experiments show that aqueous primers seem to either have good 
oxygen permeabilities or good bond strengths, but not both.