AU735361B2

AU735361B2 - Primer for plastic films

Info

Publication number: AU735361B2
Application number: AU61528/98A
Authority: AU
Inventors: Dennis Emmett Mcgee
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1997-02-10
Filing date: 1998-02-06
Publication date: 2001-07-05
Anticipated expiration: 2018-02-06
Also published as: EP0960159A1; CA2280050A1; AR011658A1; KR20000070911A; EP0960159A4; JP2001511211A; WO1998034982A1; BR9807569A; ID23409A; CN1246879A; AU6152898A

Description

WO 98/34982 PCT/US98/02498 PRIMER FOR PLASTIC FILMS Field of the Invention The invention relates to a primer for plastic films which comprises a blend of poly(vinyl alcohol) and an adhesion promoter, specifically poly(ethylene imine) and/or a hardened epoxy resin. The invention provides plastic films with excellent oxygenbarrier properties.

Background of the Invention Oriented plastic film, specifically poly(vinyl alcohol), has been widely used for packaging products, particularly foods. Poly(vinyl alcohol) is a water-soluble synthetic polymer made by alcoholysis of polyvinyl acetate. Among other things, it is known for utility as a laminating adhesive. When used in packaging films, poly(vinyl alcohol) has been described as providing a film which is impervious to oils, fats and waxes and to be an excellent oxygen barrier. For this reason, poly(vinyl alcohol) is often used as barrier coatings on thermoplastic films. No single unmodified polymeric film, however, has the gas and moisture barrier characteristics and adhesion property needed for packaging.

Attempts have been made in the past to provide polymeric films which have high oxygen, oil, and moisture barrier. Furthermore, some polymeric film can have a metal layer firmly bonded thereto. In U.S. Patent No. 5,330,831 to Knoerzer et al., a multilayer film was disclosed. The multilayer film ofKnoerzer et al. includes a polymeric substrate having a primer coating on at least one surface of the substrate, a layer of cross-linked poly(vinyl alcohol) on the coating, and a layer of a blend of a poly(vinyl alcohol) homopolymer or copolymer and an ethylene acrylic acid copolymer on the cross-linked layer. This reference also discloses that an optional metal layer can be deposited on the blend layer. In addition, U.S. Patent No.

4,214,039 to Steiner et al. is directed to thermoplastic films which include a film substrate having a primer coating layer applied to it, and a vinylidene chloride polymer as a top coat applied on the primer coating layer. These films, however, require two separate layers of primer and polymer in order to obtain both chemical barrier and adhesion properties. Many coaters only have two stations for applying coating to one side of a film at a time.

The above discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this application.

Accordingly, there is a need in the art of packaging materials to provide a oo* s15 precoating layer that has excellent oxygen barrier and adhesion to plastic films.

It would therefore be desirable to provide a primer layer with excellent oxygen barrier for packaging materials. By combining barrier and adhesion properties into a o *single layer, this frees a coating station that can be used to supply addition barrier and/or other properties such as sealability.

20 Throughout the description and claims of the specification the word "comprise" and variations of the word, such as "comprising" and "comprises", is not intended to exclude other additives, components, integers or steps.

Summary of the Invention The present invention relates to a primer for plastic films and the use of the primer in packaging materials. In one aspect the present invention provides a primer for plastic film comprising a blend of poly (vinyl alcohol) and an adhesion promoter and a hardened epoxy resin. The invention is useful to improve the oxygen-barrier properties of a plastic film.

In a preferred aspect hardened epoxy resin is in an amount of about 15 to about 35 parts per hundred poly(vinyl alcohol). The primer can further comprise an glyoxal in an amount of about 10 to about 20 parts per hundred poly(vinyl alcohol). In addition, the primer can further include choline chloride. The adhesion promoter is RA/ preferably polyethyleneimine.

The packaging material of the present invention comprises a packaging -0 J substrate that has a first surface layer and a second surface layer; a precoating layer Y 'rI\Nl K\Spccs\6 152Hdoc WO 98/34982 PCTIUS98/02498 3 having a primer coated on at least one surface layer of the substrate, wherein the primer is a blend of poly(vinyl alcohol), an adhesion promoter and/or an epoxy resin; and optionally a top coat layer and/or a metallic layer deposited thereon the precoating layer.

Advantageously, as the result of the present invention, packaging films having a unique primer layer are produced. The unique blend of the primer layer of the present invention provides excellent oxygen barrier properties.

The primer layers of the present invention can have a coating layer and/or a metallic layer deposited thereon, and thus offer greater barrier properties and sealant strength. For example, an unexpected synergy between the primer and top coats provides additional barrier enhancement.

For a better understanding of the present invention, reference is made to the following description and figures, and its S.scope will be pointed out in the appended claims.

Description of the Drawings 99.* Figure 1 is a plot showing the concentration of primer ingredients vs. oxygen barrier properties of the uncoated film; Figure 2 is a plot showing the concentration of primer ingredients vs. oxygen barrier properties for the coated films; Figure 3 is a plot showing the concentration of primer ingredients vs. oxygen barrier properties for the metallized film.

Figure 4 is a plot showing the concentration of primer ingredients vs. crimp-seal strength for coated films for seals formed at 127°C.; and Figure 5 is another plot showing the concentration of primer ingredients vs.

-crimp-seal strength for coated films for seals formed at about 104 0

C.

WO 98/34982 PCT/US98/02498 4 Description of the Invention The invention comprises a primer for plastic film and the use of the primer in packaging materials. The primer is a blend ofpoly(vinyl alcohol) and an adhesion promoter and/or a hardened epoxy resin.

The primer of the invention can be used as a primer layer for coatings and/or metallization of a substrate such as oriented polypropylene or other plastic film. The primed and coated or primed and metallized film has enhanced oxygen barrier properties. Synergistic oxygen barrier properties have been found in that the barrier properties are better than expected based on the oxygen barrier contribution of the individual layers.

The poly(vinyl alcohol) in the blend of the present invention refers to any commercially available poly(vinyl alcohol), EVANOL 71-30, an E.I. DuPont product.

Examples of the adhesion promoter include, but are not limited to,hardened epoxy as described by U.S. Patent No. 4,214,039 to Steiner which is incorporated herein by refemce and polyethyleneimine, in which polyethyleneimine is preferred.

The amount of the epoxy resin can range from between about 15 and about parts per hundred parts poly(vinyl alcohol). Higher epoxy levels are found to degrade barrier properties, 25 parts per hundred parts poly(vinyl alcohol) result in good oxygen barrier properties.

The primer coating can further contain a cross-linking agent in an amount ranging from about 10 and 20 parts per hundred parts poly(vinyl alcohol). A higher level is useful to promote cross-linking of the PVOH primer. Suitable examples of the cross-linking agent in the present invention include, but are not limited to, glyoxal, melamine formaldehyde, glutaraldehyde, with glyoxal being preferred.

WO 98/34982 PCT/US98/02498 It is contemplated that sealable coatings such as acrylic coatings and low temperature sealable coatings will adhere well to the primer of this invention.

The coating weight of the primer of this invention is most easily controlled by the solids level. It is preferred to apply the primer at about 6% solids, which with our application method provides a primer coat weight of about 0.4 g/1000 square inches (g/msi). Lower levels favor adhesion to other coatings but must be balanced with barrier properties. Higher solids levels can adversely impact operability because the primer becomes too viscous.

The coating weights of coatings applied to the primer of this invention are typical to those used in the film coating industry. Examples in this disclosure range between about 0.6% to about 1.3% solids which provides about 0.6 to about 1.3 g/msi, coating weight, depending upon the coating applied. However, this range should not be construe as limiting.

Choline chloride can also be added to the primer formulation in amounts of about 0.25 parts per hundred poly(vinyl alcohol).

:Evaluation of static levels indicates that with the primer of this invention, acrylic-based coatings exhibit an acceptably low tendency to develop a static charge.

The packaging material of the present invention comprises a packaging 0substrate that has a first surface layer and a second surface layer; a precoating layer 20 having a primer coated on at least one surface layers of the substrate, wherein the primer is a blend of poly(vinyl alcohol), an adhesion promoter and/or an epoxy resin; and optionally a top coat layer and/or a metallic layer deposited thereon the precoating layer. The blend in the primer can further include a cross-linking agent and/or choline chloride.

The packaging substrate of the present invention includes any polymeric film substrate which inherently permits the transmission of oxygen and water vapor, and WO 98/34982 PCT/US98/02498 6 wherein the utility of such film for packaging purposes would call for a minimization of such transmission. Suitable examples of the polymeric materials include, but are not limited to, nylon, polyethylene teraphthaplate, polycarbonate, and polyolefins.

Preferably, the substrate is a polyolefin including, but not limited to polyethylene, polypropylene, polybutylene, terpolymers, copolymers, and blends thereof. More preferably, the substrate is an oriented polypropylene.

Examples of the packaging substrate of the present invention can also include paperboards and fiberboard. Suitable examples of the paperboards and fiberboards can include, but are not limited to, glassine papers and clay coated papers.

The packaging substrate of the present invention can be of any desired thickness. Generally, to ensure good machinability on high speed packaging equipment, the thickness of the substrate is from about 10 to about 50 microns, preferably, from about 10 to about 35 microns, and more preferably from about 12 to about 25 microns.

At least one surface of the packaging substrate of the present invention is coated with a precoating layer by any coating method known in the art, gravure coating.

The polymeric substrate can be pretreated to enhance the adhesion of the precoating layer to the polymeric substrate by any pretreatment known in the art. Pretreatments well known in the art include, but are not limited to, flame treatment, plasma treatment, chemical treatment and corona discharge treatment that are well known in the art.

Flame treatment and corona discharge treatment are preferred with corona discharge treatment being particularly more preferred.

As previously described, the primer coating of the present invention is a blend ofpoly(vinyl alcohol), an adhesion promoter and/or an epoxy resin. The blend in the primer coating can further include a cross-linking agent and/or choline chloride.

The thickness of the precoating layer is from about 0.5 to about 2.0 microns, preferably, from about 0.7 to about 1.5 microns, and more preferably from about to about 1.5 microns.

The weight ratio of the adhesion promoter and/or epoxy resin and polyvinyl alcohol is preferably from about 0.15 to about 0.35, more preferably from about 0.20 to about 0.30, and even more preferably from about 0.22 to about 0.28.

The weight ratio of the cross-linking agent and polyvinyl alcohol is from about 0.05 to about 0.4, preferably from about 0.10 to about 0.30, and more preferably from about 0.11 to about 0.12.

The precoating layer of the present invention can optionally have a top coat layer and/or a metallic layer deposited thereon. The top coat layer can be applied on top of the precoating layer by any manner known in the art, gravure coating.

The function of the top coat layer is to provide additional barriers and/or sealability and/or machinability and/or printability.

15 Examples of coating materials to be used as a top coat layer are described in *o U.S. Patent No. 4,214,039 to Steiner which is incorporated herein by reference.

Preferred examples of the coating materials include, but are not limited to, emulsions •or solutions comprising poly(vinylidene) chloride, poly(vinyl chloride), poly(vinyl alcohol), ethylene acrylic acid copolymer, and acrylic. The thickness of the coating 20 layer is up to 5.0 microns.

The metal layer is deposited on the top layer by a manner known in the art, vacuum metallisation or plasma deposition. The metal layer provides the packaging material with extra barrier and sealant properties.

Suitable examples of metals for the metal layer can include, but are not limited to, aluminium and aluminium oxide.

Y:\fionl\NKl\Spccics\(,j 52 doc WO 98/34982 PCT/US98/02498 8

EXAMPLES

The following non-limiting examples illustrate the chemical barrier and adhesive properties of the films of the conventional packaging films and the packaging films of present invention.

EXAMPLE 1 PACKAGING FILMS OF THE PRESENT INVENTION This example illustrates the chemical barrier and adhesion properties of the packaging films of the present invention. Chemical barrier and adhesion tests were performed on eight film substrates having various coating compounds.

Each of the eight film substrates was coated with eight different precoating layers of primer blends. The primer blends were applied utilizing a reverse direct gravure coating. The coated films were passed through a dry-air oven at about 125 ft/min. and at a temperature of 200°F. The primer blends include PVOH, epoxy primer, and glyoxal. The primer blends are illustrated in Table 1.

TABLE 1 Sample Roll No. PVOH Epoxy Glyoxal Coat wt.

No. at 12% solids 1 PC-06186-01 100 phr 15 phr 10 phr 0.2 g/msi 2 PC-06186-02 100 phr 25 phr 10 phr 0.2 g/msi (0.25 phr Choline Chloride was also included) 3 PC-06186-03 100 phr. 15 phr 15 phr 0.2 g/msi 4 PC-06186-04 100 phr 25 phr 15 phr 0.2 g/msi PC-06186-0 100 phr 15 phr 10 phr 0.4 g/msi 6 PC-06186-06 100 phr 25 phr 10 phr 0.4 g/msi 7 PC-06186-07 100 phr 15 phr 15 phr 0.4 g/msi 8 PC-06186-08 100 phr 25 phr 15 phr 0.4 g/msi WO 98/34982 PCT/US98/02498 9 Each of the eight precoating layer was then coated with a top coating layer of an EAA formulation. The EAA formulation was applied utilizing a reverse direct gravure coater. The coated films were passed through a dry air oven at a temperature of200 F. The EAA formulation included 100phr M4983 (Michemprime manufactured by Michelman), NaOH; 4phr carnaube wax emulsion (obtained from Michelman), 0.3phr silloid and 0.4phr talc.

The resulting films were tested for oxygen transmission. The dried films were then tested in an oxygen-permeability device in which a stream of dry oxygen was passed through an aqueous salt solution-permeated pad to control the gas moisture content and then through the films, disposed at right angles to the stream with the top coating layer upstream. The oxygen transmitted was determined and the amount of oxygen passed per unit area of film per time period was calculated. The results of oxygen barrier tests are shown in Table 2.

TABLE 2 Sample TO 2 Askco Askco Crimp Crimp Crimp No. (cm 3 /100in 2 /day) 230-260 Retained 220 260 Retained (g/in) (g/in) (g/in) (g/in) (g/in) 1 5.02 169 166 100 140 145 2 1.64 186 163 125 200 255 3 2.41 134 129 105 150 170 4 2.12 144 171 150 160 180 0.33 373 168 160 190 190 6 0.15 515 541 265 220 360 7 0.20 261 230 260 220 215 8 0.16 421 411 400 415 310 WO 98/34982 PCT/US98/02498 From Table 2, it is observed that the packaging films of the present invention have low gas transmission and excellent adhesion property. Thus, the unique blend of the precoating layer of the present invention provides both chemical barrier and adhesion properties offer by the conventional packaging films. However, the blend of the precoating layer of the packaging films of the present invention eliminates the required primer layers of the conventional films.

EXAMPLE 3 METALLIZED PACKAGING FILMS This example illustrates the chemical barrier and adhesion properties of conventional metallized packaging films and metallized packaging films of the present invention. Chemical barrier and adhesion tests were performed on nine MC550 film substrates (made by Mobil) having various coating compounds.

Each of the nine film substrates was coated with nine different precoating layers of primer blends. The primer blends include PVOH, EAA, epoxy primer, and glyoxal.

The primer blends are illustrated in Table 3.

WO 98/34982 PCT/US98/02498 11 TABLE 3 Sample No. PVOH Solids EAA Epoxy Glyoxal 1 100 phr 1 100 phr 0 phr 0 phr 2 100 phr 1 200 phr 0 phr 0 phr 3 100 phr. 4 100 phr 0 phr 0 phr 4 100 phr 4 200 phr 0 phr 0 phr 100 phr 1 0 phr 100 phr 20 phr 6 100 phr 1 Ophr 200 phr 20 phr 7 100 phr 4 0 phr 100 phr 20 phr 8 100 phr 4 0 phr 200 phr 20 phr 9 100 phr 4 0 phr 100 phr 20 phr Each of the precoating layers was then metallized with a metal.

The resulting films were tested for water vapor transmission, oxygen transmission, and adhesion properties. The results of the tests are illustrated in Table WO 98/34982 PCT/US98/02498 12 TABLE 4 Sample T02 WVTR Scuff Adhesion No.

1 2.64 0.03 Poor Good 2 3.09 0.03 Poor Good 3 0.42 0.03 Poor Good 4 1.03 0.02 Poor Good 3.34 0.04 Poor Good 6 2.01 0.05 Poor Good 7 0.89 0.04 Medium Good 8 1.22 0.04 Medium Good 9 0.95 0.02 Poor Good From Table 4, it is observed that Sample Nos. 5 to 9, the metallized packaging films of the present invention, have both chemical barrier and adhesion properties offer by Sample Nos. 1 to 4 of the conventional packaging films. However, the metallized packaging films of the present invention have excellent adhesion properties and thus do not require the additional primer layers of the conventional films.

Example 4 Oriented polypropylene film samples (Samples 1-21) were primed with primer formulations described in the following table. M4983 is Michemprime manufactured by Michelman. M215 is a carnaube wax emulsion obtained from Michelman. SR344 is Tospearl 145 obtained by Toshiba Silicone Co. ML71513 is a synthetic wax obtained from Michelman. D8500 is Daran 8500 obtained from Hampshire Chemical.

WO 98/34982 PCT/US98/02498 Each of the samples were tested for oxygen barrier properties and for sealability and the results of the testing are reported in Table 5 and Figures 1 to 0 TABLE TABLE ACN.8 I TABLE5 LABCOATER RIJN 8ASE FILM FPM 1 0 CHILROLL 92MC550S PIIMING so50 220 130 60. TREAIMENT LEVEL 2 50 220 130 Boo DISPERSE SYI OID 421NA WARING BLENDER FOR LABEL SAPLES AS'ACN XX. SUBMaIT FOR PHIYSCAL TESTING UNDER 11701 SAMPIES WITHII PRIMER ONLY SHOULD BE LABELLED AS ACNSOXA" PREPARE STANDARD EPOXY PRIMER AND DILUTE TO 20% SOLIDS FOR USE IN BLENDS 9% TOTALCOAT 10 20 40 1 I LESS SLDS LTX ST0 GLY- SYLD CHOL.... IEXYL IIEX o STD GLY- SYLD CHOL.

ROLL LATEX LOTS SLDS LATEX TALC EPOXY OXAL 42 Cl 120 CELL. P&II LTX TALC EPOXY OXAL 42 Cl TOTAL 9 9 9 9 0 0 0 9 9 PIR PiR PtIR PIIR PHIl Pin PtII PART I:PRIMING.NEEDENOIIGII TOMAKE SOFT.SAMPLES OF TOP.COAIED FILtMPLUS IOFEE T OF PIIIMEDFILMFOII BARRIER TESTS ACNB ELVANOL 9050 80 998 000 60 2.0 00 2.0 902 20 5 100 0 15 10 0 025 125.3 ACNB 2ELVANOL 9050 80 1070 000 107 32 00 2.1 770 20 200 6 100 0 25 15 0 025 140.3 ACN8 3ELVANL 950 80B 1127 000 15.8 45 00 2.3 64.7 20 200 7 100I 0 35 20 0 025 1553 ACNB 4ELVANOL 9050 80 1190.8 000 72 24 00 2.4 683 20 200 6 In 0 s15 to10 0 025 125.3 ACNI SELVANOL 9050 80 1248 000 125 37 00 25 565 20 200 7 100 0 25 15 0 025 1403 ACU8 6 ELVAINOL 9050 80 805 000 11.3 3.2 00 1.6 1034 20 2001 5 100 0 35 20 0 025 155.3 ACN8 7ELVANOL 9050 80 960 000 58 2.9 00 1.9 935 20 200 5 100 0 15 15 0 025 130.3 ACN8 BELVANOL 950 80 1033 000o 103 4.1 00 2.1 80.2 20 2o 6 100 0 25 20 0 025 1453 ACN8 9ELVANOL 9050 80 1205 000 169 2.4 00 2.4 578 20 200 7 100 0 35 o10 0 025 1453 ACHO I0ELVANOL 9050 00 1294 000 78 52 00 26 55.1 20 200 7 100 0 IS 20 0 025 135.3 ACN8 II ELVANOL 9050 80 92.4 000 92 18 00 1B 94.6 20 200 5 100 0 25 10 0 0.25 135.3 ACN8 12ELVANOL 9050 80 998 000 140 30 00 2.0 81.2 20 20 6 tm 0 35 15 0 025 150.3 ACIIS 13ELVANOL 9050 80 1344 000 01 4.0 00 2.7 509 20 2(0 7 100 0 15 15 0 025 1303 ACNB 14EIVANOL 9050 80 661 000 86 34 00 17 100. 20 2(0 5 100I 0 25 20 0 025 145.3 ACtJ8 15 ELVANOL 9C50 80 1033 000 145 2.1 00 2.1 781 20 2(X) 6 IO 0 35 10 0 025 1453 ACN8 16ELVANOL 90/50 80 1109 000 67 4.4 00 2.2 75.8 20 200 6 100 0 s15 20 0 025 135.3 ACNB 17ELVANOL 9050 80 129.4 000 12.9 2.6 00 26 52.5 20 2E 7 IE 0 25 10 0 0.25 135.3 ACN8 IELVANOL 90150 80 83.2 000 116 2.5 00 1.7 1010 20 200 5 too100 0 35 IS 0 0.25 1503 ACN8 19 STD PEIPRIMER IO.10%SOLIDSI) TOPCOAT WITH M4983FROMMASIER BATCH ACN 20 ST ID PEIPRIMER (0.10% SOLIDSI- TOPCOAT WITH STANDARD ACRYLICFROMMASTER BA CII ACNB 21 ST0 EPOXYPRIMER 13%SOLOSI.- TOPCOAT WilT DARAN 8500FFIOMMASIER BATCII AFIER PRIMING TOP COATROI LS WITII COATINGS FROM IlE FOLLOWING MAST BATCIIES M215 5102 M215 SIO2 ACN 13.1012 M4983 CUTRL 250 (6113 611 36 -0O 45.8 00 3062 00 1(1) 16 10) 04 4 O0 0.3 0 104.7 SRS44 SR344 ACN846.1315 ACRYLIC CNIRL 22.0 497.1 2.73 32.8 109.4 0.0 352.5 00 1000) 16 100 0.25 6 40 0 146.3 ML1113 ACNB 7-9.1618 DO8500 CNTRL 49.0 641.5 9.43 23.8 00 00 0.0 325.5 0.0 10o0 32 100 0.3 1.5 0 0 0 101.8 00 WO 98/34982 PCT/US98/02498 Figure 1 is a plot showing the concentration of primer ingredients vs. oxygen barrier properties of the uncoated film. Figures 1 shows that high concentrations of poly(vinyl alcohol), which correspond to lower concentrations of epoxy, provide better oxygen barrier properties as does an increased coating weight.

Figure 2 is a plot showing the concentration of primer ingredients vs. oxygen barrier properties for the coated film. Figure 2 shows that, after top coating, all samples demonstrated better oxygen barrier properties than could be expected on the basis of the barrier contribution of the individual components. For example, when coated over polyethylene imine, the low temperature sealable coating gave an oxygen barrier of 117 cm 3 /100 in 2 /day, which is approximately the barrier given by this gauge of polypropylene coated with polyethylene imine (129 cm 3 /100 in 2 /day).

As shown in the graph of Figure 1, the mean barrier for the samples that were coated with the low temperature sealable coating was about 3.7 cm 3 /100 in 2 /day.

The barrier contribution of the low temperature sealable coating layer is about 1300 cm 3 /100 in 2 /day. Therefore, the expected oxygen transmission of the primed and coated film combination is expected to be no better than 3.69 cm 3 /100 in2/day. The expected value was calculated from the approximate barriers of the component layers: (1/3.69) The value includes the barrier of the oriented polypropylene and the primer.

The value (1/300) was arrived at by subtracting the reciprocal of the barrier for polyethylene imine primed oriented polypropylene (1/117) from the reciprocal of the observed barrier of low temperature sealable coated polyethylene imine on the same gauge of oriented polypropylene (1/129).

WO 98/34982 PCT/US98/02498 16 However, the actual mean value for the six samples was about 2.1 cm 3 /100 in 2 /day. This value is lower than the mean value for any group of samples that only had the primer. It is about two-times as good as expected.

When an acrylic coating was applied to the film, the results were even better.

Assuming that the oxygen transmission value for oriented polypropylene film is about 129 cm 3 /100 in 2 /day, then the barrier of the acrylic layer over polyethylene imine should contribute about 610 cm 3 /100 in 2 /day (1/107 1/129 1/610).

Therefore, it is expected that from the mean values in Figure 1, the acrylic-coated polyethylene imine should have a barrier of 2.99 cm 3 /100 in 2 /day (1/3 1/610 1/2.99). Yet Figure 2 shows that the mean oxygen transmission was about six times better than expected cm 3 /100 in 2 /day).

When a polyvinylidene chloride coated was applied to the primed film, at a relatively low coating weight the polyvinylidene chloride provided an oxygen barrier of about 0.85 cm 3 /100 in 2 /day on epoxy-primed film which without the coating provided an oxygen barrier of 124 cm 3 /100 in 2 /day. Therefore, the polyvinylidene chloride layer contributed 0.86 cm 3 /100 in 2 /day to the barrier. If this coating is applied to a base sheet with a barrier of 2.6 cm 3 /100 in 2 /day, then the expected oxygen barrier should be about 0.81 cm 3 /100 in 2 /day. For the six polyvinylidene chloride coated samples, the mean value was 0.05 cm 3 /100 in 2 /day.

This is sixteen times better than expected.

These data show that the primer layer of the invention provides an unexpected and synergistic improvement in oxygen barrier properties when used with any top coat. Moreover, the better the inherent barrier properties of the top coat, the better the synergistic effect.

Figure 3 is a plot showing the concentration of primer ingredients vs. oxygen barrier properties for the metallized film. Unlike the coated film samples, the metallized films show better barrier properties at low poly(vinyl alcohol) coating weights. When polyethylene imine or epoxy primed film was metallized the WO 98/34982 PCT/US98/02498 17 oxygen barrier values ranged from 1.5 to cm 3 /100 in 2 /day. Switching to the poly(vinyl alcohol) primer, the mean oxygen transmission value was about 0.13 cm 3 /100 in 2 /day. However, some samples (for example the primed film in example ACN8-16) provided an oxygen barrier value of 0.01 cm 3 /100 in 2 /day after metallization. This is comparable to oriented polypropylene made with an ethylene-vinyl alcohol copolymer skin which provides an oxygen transmission range of 0.03 cm 3 /100 in 2 /day after metallization. Since films made with ethylenevinyl alcohol copolymer skins are difficult to make, the invention provides a significant advantage.

Figure 4 is a plot showing the concentration of primer ingredients vs. crimpseal strength for coated films for seals formed at 127"C. the best results were achieved with a low temperature sealable coating but good effects were achieved with polyvinylidene chloride (Daran 8500) which performed better than acrylic.

The improvement appears to relate to adhesion to primer. Higher epoxy levels in the primer improved the adhesion to the coatings.

Figure 5 is another plot showing the concentration of primer ingredients vs.

crimp-seal strength for coated films for seals formed at about 104 0 C. Similar results are achieved at lower temperatures. Surprisingly the low temperature sealable coating achieved improved seals at lower temperatures. At 82 0 C the low temperature sealable coating still had seals of)400 g/in.

Claims

1. A primer for plastic film comprising a blend of poly (vinyl alcohol) and an adhesion promoter and a hardened epoxy resin.

2. A primer according to claim 1 in which the amount of the epoxy resin is in an amount of about 15 to about 35 parts per hundred parts poly(vinyl alcohol).

3. A primer according to claim 1 or claim 2 which further comprises glyoxal in io an amount of about 10 to about 20 parts per hundred parts poly(vinyl alcohol).

4. A primer according to any one of the preceding claims which further comprises choline chloride. 15 5. A primer according to any one of the preceding claims in which the adhesion promoter is polyethyleneimine.

6. A primer according to claim 1 in which the plastic film is coated with a polymeric coating layer and/or metallised with a metallic layer, the substrate 20 having a primer beneath the polymeric coating layer or metallic layer. oooo 7. A primer according to claim 6 in which the amount of the epoxy resin is in an amount of about 15 to about 35 parts per hundred parts poly(vinyl alcohol).

8. A primer coating according to claim 6 or claim 7 which further comprising glyoxal in an amount of about 10 to about 20 parts per hundred parts poly(vinyl alcohol).

9. A primer according to any one of claims 6 to 8 which further comprises choline chloride. y RA 10. A primer according to any one of claims 6 to 9 in which the adhesion promoter is polyethyleneimine. Y:\llon\NKI\Spccics\152K doc

19- 11. A primer according to claim 1 substantially as hereinbefore described with reference to any of the examples. DATED: 3 November, 1999 PHILLIPS ORMONDE FITZPATRICK Attorneys for: MOBIL OIL CORPORATION 0 00 0 0 CAWy D. ,,.IsAFl~n,SpOcki3628.d.