CA2179960A1 - Controlled barrier film structure - Google Patents

Abstract

The barrier properties of a packaging film may be modified by applying an admixture containing a nonvolatile barrier extender such as an acrylic copolymer and a barrier coating such as polyvinylidene chloride (PVDC) to a substrate such as a polyethylene. The gas permeability of the resulting film may be controlled by adjusting the percentages of barrier coating and barrier extender in the admixture.
The invention includes a film comprising a substrate having a coating applied thereon, the coating comprising a barrier coating and a barrier extender.

Description

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BACKGROI~D OF THE INVENTION
Thi6 application claims priority on provisional patent application Attorney Docket Number 81,335 entitled "Controlled --Barrier Film Structure, " by Wayne Robert Osgood, Jr., filed June 27, 1995.
This invention relates to the production of f ilms having increased barrier properties. More particularly, this invention --relates to the production of film using a barrier coating which is diluted such that the barrier properties of the film can be .:
readily varied to prepare a film having a desired gas permeability .
The production of films is well known. Such films may be prepared f rom a wide variety o materials commonly used in packaging, including the packaging of food products such as fruits and vegetables. Depending on the food product, the desired level of oxygen barrier of the packaging f ilm may vary .
In the past, oxygen barrier polymeric coatings such as polyvinylidene chloride (PVDC) have typically been used to provide very high barrier properties when applied as the straight polymer. While the oxygen barrier can be varied by varying the application amount of PVDC (i.e., varying the grams PVDC per = -~-cubic centimeter of film), this has several problems.
One problem with varying PVDC application amount is that it is generally difficult to control such application such that less =~
than a 1096 swing in coating weight is achieved. Furthermore, it is i~lown that the decreaae in oxygen permeabil_ty of a barrier coated ilm is nonlinear relative to the application amount.
While at low application levels a small increase in PVDC coverage on the film produces a small decrease in oxygen permeability, at higher coating levels there is a dramatic decrease in oxygen permeability and at even higher levels the decrease in oxygen permeability flattens out. Hence, permeability is difficult to control since a small change in amount (in the range where _ = -perm~ability changes dramatically) pr~duces a large change in , 9 g6 ~
permeability. Thus, due to the variability of the application and the dlfficulty in controliing permeahility at higher co~ting levels, there is no practice method to accurately control permeability over a wide range of permeability. . In view of 5 these two significant problems, it can be seen that the problem of controlling the oxygen permeability of a film by applying a barrier coating is made compoundedly difficult.
Owing to these difficulties, in order to provide controlled medium and low range barriers, suppliers have heretofore used ~ :
10substrate selection and film gauge changes to affect oxygen permeability. In this regard, substrates (film types) intrinsically have varying degrees of oxygen permeability.
Combinations of substrates can also be employed. Also,~ the thickDess of the substrate film can be manipulated. Combinations 15of these techniques have been used to produce f ilms having a -~~~
variety of barrier properties.
While it has been possible to obtain f ilms having a range of barrier properties, it can be seen that a need exists for a method to simply and accurately control the oxygen transmission 20 rate through fllm. Such a method, if available, would advantageously be capable of being practiced using conventional film manufacturing apparatus. ~uch a method, if available, would also be able to produce films having accurately contrl~lled barrier properties without the need to vary substrate type or ~ =: -25gauge. Accordingly, such a method would be able to accurately vary the oxygen permeability of the same film having the same = = -- -f i na l thicknes~
~U~RY OF THE INVENTION
The present invention provides a solution to one or more of the problems discussed above.
In one broad respect, this invention is a process wherein a film is produced by applying a barrier coating to a substrate thereon in an amount effective to decrea~;e the gas permeability -- 3 -- .

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of the substrate, the improvement comprising employing a barrier extender in admixture with the barrier coating.
In a second broad respect, this invention is a process --~
useful for modifying the barrier properties of a film, 5 comprising: applying a coating composition, the coating composition comprising a barrier coating and a barrier extender, to a substrate, wherein the coating composition is applied in an amount efiective to decrease the gas pertneability of the substrate .
As used herein, "admixture" and "coating composition" have the same meaning. A coating composition is a solution or suspension r~n~A;n;ng a volatile solvent and a barrier coating and a barrier extender. The solvents are typically water, alkanes such as heptanes and hexanes, acetates such as ethyl acetate and propyl acetate, alcohols such as methanol, ethanol or propanol, or combinations thereof As used herein, the phrase "barrier coating" means a composition which has less oxygen permeability than the substrate film. Advantageously, conventional barrier coatings such as PVDC
can be employed in the practice of this invention.
As used herein, the phrase "barrier extender" means a compound or composition which forms a stable admixture with the selected barrier coating, such as an admixture of PVDC and acrylic copolymer. The barrier ex~ender has a higher permeability than the barrier coating. Also, the barrier ~Y~ r5 used in this lnvention are commonly referred to as low barrier or non-barrier materials. By stable it iP meant ~hat no --pr~cipitation or coagulation of barrier coating and extender occurs when the admixture is prepared. Such stability can be tested by trial and error using well known techniques as would be readily apparent to one of skill in the art. As used herein, the phrase ~barrier r~-nrl~r'~ has the same meaning as barrier filler or barrier diluent.

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After applying the coating composition the resulting film is dried to drive off the volatile solvent. If the barrier coating ~-or extender 80 requires, the resulting film can also be cured Also contemplated within the scope of thie invention are films treated in accordance with the practice of this invention.
In this respect, the present invention includes a film comprising~
a substrate having an admixture applied thereon, wherein the ~lmi ~tllre compri8eg a barrier coating and a barrier extender.
Advantageously, the present invention provides a process to control the barrier properties of film such that the resulting f ilm may have barrier properties individually tailored to the items to be packaged with the resulting film Additionally, the films produced in accordance with the practice of this invention enjoy enable more flexibility in substrate selection, the ability to reduce gauge independently of barrier, and the ability to modify barrier over a wide range without modifying gauge or substrate type While the films produced in accordance with this invention are advantageously suited for used in packaging food products, such films can be used in a wide variety of applications.
It has been iound, surprisingly, that the decrease in oxygen permeability of a substrate film coated with a barrier/extender admixture of this~ invention (e g., diluted PVDC), relative to the amount of the coating applied, is less sensitive than the decrease in oxygen permeability caused by varying a coating of the barrier (e.g., PVDC) alone. Thus, it has been found that changing t'~le relative amountP of ~arrier and P~'Pn~1Pr in the coating composition, the oxygen permeability can be cDntrolled without changing the coating weight, thereby enabling the operator to stay in the flatter portions of the curve defined by oxygen permeability versus PVDC coating weight. This property of the admixture is highly desirable because the gas permeability of the ~ilm to be treated can be accurately varied, as opposed to the relatively inaccurate variance of gas permeability by - ~ 2l7s~a application of a barrier coating in the absence Df a barrier extender of the present invention.
The present invention can be employed to vary the barrier properties of a wide variety of films, including films made from 5 materials such as polyethylene, polypropylene, polyester, polyamides such as nylon, polystyrene and laminaEes thereof.
Advantageously, the present invention can be practiced using well known, conventional film manufacturing apparatus.
DETAII-ED DES~RIPTION OF THE PREFERRED EMBODIMENTS ~._ The substrate which can be treated in the practice of this invention include any conventional substrate f ilm with the proviso that the admixture of barrier coating and barrier -extender must be compatible with (e . g. adhere to) the substrate 15 film to be treated. The substrates are commonly used as packaging f ilms . Representative examples of such substrate f ilms include polyethylene, polypropylene, polyester such as polyethylene terephthalate (PET), polyamides such as nylon, polystyrene and laminates thereof . Such substrate f ilms may have 20 a wide variety of thicknesses (gauges), typically in the range from about 10 microns to about 150 microns and more commonly from about 25 microns to about 150 microns. Substrate films to be treated in accordance with this invention may vary widely and are readily available commercially. It is believed such substrate f ilms are commonly produced using methods well known to those of skill in the art as by, for example, extrusion, coextrusibn, - ~
lamination and extrusiGn-lam,nation. Su-h packaging films ~:
typically may have an oxygen transmission rate which is undesirably high for certain depending on end use Substrates with high rates allow for a greater range of controlled permeability when treated in accor~ance with this invention.
Polyethylene film has been found to be particularly suitable as a substrate film to be treated in accordance with the practice of this invention. It is also contemplated that flexible substrates including paper, paper derivatives and laminates o~ paper and ~ ~179960 plastic may also be treated in accordance with the practlce of this invention to reduce the oxygeri permeability thereof.
The barrier cDatings used in the practice of this invention may vary widely depending on the desired level of oxygen 5 permeability of the resulting film. It is preferred that barrier coatings conventionally used by skilled artisans be employed in the practice of this invention. Representative examples of barrier coatings that may be used in the practice of this invention include polyvinylidene chloride (~VDC), polyvinyl 1~ alcohol (PVOH), polyethylenevinyl alcohol (EVOH), nylons and acrylonitrile-methylacrylate copolymers (6uch as those available under the name BAREX from Sohio Chemical Co. ) . Barrier coatings and extenders available commercially typically are sold~ as a suspension cnnt~;ninr~ a given percentage of solids. PVDC is 15 preferred in the practice of this invention.
Barrier coatings of this invention are capable of entering solution or forming a suspension in the coating composition which rnnt~;n~ a volatile solvent.
The barrier P~rt~nri~rS of the present invention may vary 20 depending, ~for example, on the stability of the barrier extender with the selected barrier coating. The barrier extenders of this invention are nonvolatile at working standard pre~sure and temperature. It should be appreciated that commercially available barrier extenders may contain volatile components which 25 volatili~e after or during coating of the film with t~e mixture of barrier coating and barrier P~ctPnAPr, ~t should also be .
appreciated that volatile, liquid inert diluents such as water and alcohol can be used to in the preparation of the admixture cont~inln~ barrier coating and barrier extender to thereby 30 provide a solution or a tsolids-rnn~Aining slurry and to thereby reduce the concentration of solids in the mixture and to in some instances reduce the viscosity of the mixture. The diluted mixture can be applied to the substrate film to be treated. It i8 believed that, generally, as the ratio of barrier coating to :
35 barrler extender lncreases in a mixture inrll-rling an inert, .: 2~7gg~
liquld diluent, the coating weight has as increasing influence cn~
oxygen transmission ra~es. Representative examples of such barrier extenders include acrylic polymers and copolymers, polyurethanes, polyester and polyamides. It should be 5 appreclated that compounds such as polyesters and polyamides, which are also used to make films, have a subst~nt;~11y lower molecular weight when used as barrier extenders, as would be readily apparent to one of ekill in the art. Likewise, the barrier coating is of relatively low molecular weight. A barrier ~ -`
10 e~tf~nrl~r which has been found to particularly useful in the practice of this invention is an acrylic copolymer made by Morton International and distributed under the product number "24-102".
The stable admixtures of the invention containing barrier ~ - ~~-~
coating and nonvolatile barrier e~:tender compIise less than lO0~
by weight of the barrier coating and less than lO0~6 by weight of the barrier extender. Advantageously, the gas permeabiiity of the film treated in accordance with this invention can be varied by adjusting the relative percentages of barrier coating and barrier eXtender in the admixture. In this regard, that the amount of barrier`P~t~n~f~r may be increased in an amount approximately equal to the decrease in the amount of }~arrier coating such that the thickness of the admixture applied to the f ilm may re~ain approximately constant . Accordingly, no adjustment of the manufacturing apparatus need be made to vary gas permeability; instead, the admi~ture may alone be varied to :
vary gas permeability.
The admixture may be applied to a film using conventionaI
apparatus designed for such purpose. Such apparatus are well known to those of skill in the art. Representative examples of such applicators include gravure applicators including direct, reverse and offset gravure applicators, flexographic applicators, air knife and Meyer rod applicators. Gravure applicators are ~ ~ -preferred in the practice of this invention.
The thickness of the admixture applied may vary widely depending-on the desired gauge thickness of the resulting film ~ 21~60 and particular barrier coating selected, which is generally dependent on end use. As used herein, "coating weight~' means the weight of dried coating per area of film Generally, the coating weight may vary from about 1 to about 10 grams of solids per 1000 square inches of substrate film ( "g/1000 sq. inch" ), and more ~ :-typically from about 3 to about 4 g/1000 sq. inch. Generally, the average thickness of a coating i~ less than about 10 microns and more commonly iB less than about 7 microns. The average thickness of the coating is the thickness of a dry coating after i .:
the volatile solvent in the admixture evaporates from the -resulting f ilm .
The t_ickness of the treated film resulting from the practice of this invention may vary depending on the desired end use of the film. Generally, the th; ,-kn~s ranges from about lQ
to about 150 microns. For single packages or consumer units, about 45 to about 75 micron thick film is commonly used.
Oxygen transmission of a coated f ilm made in the practice of the present invention can be measured using conventional techniques and using conventional measuring apparatus.
Generally, such measurements are conducted in accordance with ASTM D-3985. Typically, the oxygen transmission rate of the final films of this invention is lower than that of the substrate. Generally, the rate of the final film is greater than about 4 cc~100 square inches/24 hours.
In the practice of this invention, the admixture can be applied to a single web of film to provide the treated film Moreover, it is cGntemplated that in the practice of this invention, that multilayer films having one or more layers of the substrate may be prepared. For instance, it is contemplated that a three layer treated film may be produced in accordance with this invention such as a three layer film composed of a layer of admixture containing the barrier coating disposed between two layers o~ polyethylene substrate film. The number of film layers ~ ~
will merely be limited by the thickness of individual layers, by the compatibility o~ the layers to one another and by the design =~

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of the manufacturing apparatus, all as would be readily apparent to one of skill in the art.
The following examples are illustrative of the pr-esent invention and are not to be construed as limiting the scope of 5 the invention ~r claims thereto. Unles6 otherwise denoted, all percentages are by weight and all measurements of oxygen transmiss~on are expressed in terms of cc/100 square inches 24 hours .
Polyethylene film is treated in accordance with the present 10 invention using a Gravure applicator. The mixture that is applied to the film contains polyvinylidene chlQride and an acrylic copolymer obtained from Morton International under the name "24-102~. The properties of such treated films are ~
described in the~following table. In the table, "Serfene 701" is 15 a polyvinylidene chloride, available from Morton.

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TABI,E
No. t ',; t Gauge CWgm- CWlb OTR OTR
~3arrier Bxtender Dilution avg. ~i ream avg/4 range 50 0 50.0 7.5 2.42 3.79 3.61 209.7 8.0 52 14.6 85.4 2.2 2 42 3.85 3.66 227.8 13.9 3 85.4 14.6 2.2 2.37 4.00 145.3 4 14.6 85.4 12.8 2.40 3.78 3.60 225.7 12.0 5 85.4 14.6 12.8 2.47 3.70 148.1 6 50.0 50.0 7.5 2.40 3.al 3.63 207.0 6.1 10 7 85.4 14.6 23.4 2.37 3.37 149.2 8 50.0 50.0 16.2 2.34 3.50 3.33 212.9 9.0 9 100.0 0.0 16.2 2.33 3.59 89.0 10 0.00 100.0 16.2 2.41 3.62 .3.45 225.8 2.6 11 14.6 85.4 23.4 2.36 3.32 3.16 229.6 16.1 15 12 50.0 50.0 26.3 2.52 3.24 3.08 198.8 7.4 13 50.0 50.0 0.00 2.62 3.66 3.48 191.2 - 13.8 14 50.0 50.0 16.2 2.50 3.53 3.36 19~9.3 18.8 15 76.8 23.2 20 . 2.43 3.28 167.7 16 76.8 23.2 20 2.54 3.16 161.3 20 17 92.5 7.5 20 2.45 3.04 131.7 18 65.0 35.0 20 2.48 3.08 184.3 19 76.8 23.2 20 2.45 3.11 175.6 20 65.0 35.0 20 2.41 3.05 196.6 21 100.0 0.0 20 2.44 77.6 25 22 98.0 2.0 14 2.40 3.40 85.4 23 99.0 1.0 2 2.42 4.08 75.1 24 99 . 0 1 . 0 26 2 . 38 3 . 31 85 . 9 2s 97.0 3.0 2 ~.41 3.58 90.9 26 97 . 0 3 . 0 26 2 . 43 3 . 19 91 . 8 30 27 98.~) 2.0 14 2.41 3.63 82.9 28 76 . 5 23 . 5 14 2 . 44 3 . 46 176 . 4 29 78 . 5 21 . 5 2 2 . 53 3 . 95 162 . 6 30 74.5 25.5 2 2.46 3.76 179.5 31 74.5 25.5 26 2.46 3.12 174.3 35 32 76.5 23.s 14 2.43 3.41 180 5 33 30.a 70.0 20 2.42 3.43 211.4 - 11 ,-.

' ~' 21~g~6~
No. % % % Gauge CWgm- CWlb OTR OTR
Barrier Bxtender Dilution avg si ream avg/4 range 34 50.0 50.0 20 2.38 3.4L 205.9 35 50.0 50.0 20 2.27 3.27 219.3 36 78.5 21.5 26 2.29 2.99 161.1 Barrier s Morton Seri~ene 701 barrier coating (45~ solids as received) .
E:xtender = Morton 24-102 (50" solids as received) .
Dilution = " of a 50t50 water/alcohol mixture added to the barrier/extender mixture.
Gauge = OTR sample gauge, mils. base i~ilm = 2.25 mils, nominal (about 57 microns~.
CWgmsi .. coating weight, g~l000 gquare inches.
CWlb/ream = coating weight, pounds/ream.
0~ ..... O~ ~r/~n~m~ ion ~a_, cc/10~ ~oua~e ~ q hou~s - lZ - ~

Claims (21)

1. In a process wherein a film is produced by applying a barrier coating to a substrate in an amount effective to decrease the gas permeability of the substrate, the improvement comprising employing a barrier extender in admixture with the barrier coating.

2. The process of claim 1 wherein the barrier coating is polyvinylidene chloride.

3. The process of claim 1 wherein the barrier extender is an acrylic copolymer.

4. The process of claim 1 wherein the film is a polyethylene film.

5. In a process wherein a polyethylene film is produced by applying polyvinylidene chloride to polyethylene substrate in an amount effective to decrease the gas permeability of the polyethylene substrate, the improvement comprising employing an acrylic copolymer in admixture with the polyvinylidene chloride.

6. A process useful for modifying the barrier properties of a film, comprising: applying a coating composition, the coating composition comprising a barrier coating and a barrier extender, to a substrate, wherein the coating composition is applied in an amount effective to decrease the gas permeability of the substrate.

7. The process of claim 6 wherein the barrier coating is polyvinylidene chloride.

8. The process of claim 6 wherein the barrier extender is an acrylic copolymer.

9. The process of claim 6 wherein the film is a polyethylene film

10. A film comprising a substrate having a coating applied thereon, wherein the coating comprises a barrier coating and a barrier extender.

11. The film of claim 10, wherein the coating has a thickness less than about 10 microns.

12. The film of claim 11 wherein the substrate is polyethylene and the barrier coating is polyvinylidene chloride.

13. A laminated packaging material comprising a substrate film coated with an admixture of a barrier coating and a barrier extender.

14. A packaging material as defined in claim 13, wherein the admixture coating decreases the permeability of the film to oxygen.

15. A packaging material as defined in claim 13, wherein the barrier coating comprises polyvinylidene chloride.

16. A packaging material as defined in claim 15, wherein the barrier extender comprises an acrylic polymer or copolymer.

17. A laminated packaging material comprising a film coated with a quantity of an admixture of a polymeric barrier coating material and a polymeric barrier extender material sufficient to decrease the permeability of the film to oxygen.

18. A laminated packaging material as defined in claim 17, wherein changing the proportion of barrier extender in the coating causes generally corresponding changes in said permeability.

19. A laminated packaging material as defined in claim 17, wherein the film comprises a polyalkylene, polyester or polyamide.

20. A laminated packaging material as defined in claim 19, wherein the barrier coating material comprises polyvinylidene, a polyvinyl alcohol, a polyamide or an acrylonitrile-methacrylate copolymer

21. A laminated packaging material as defined in claim 20, wherein the barrier extender material comprises an acrylic or methacrylic polymer or copolymer, a polyurethane, a polyester or a polyamide.