Patent Publication Number: US-5840825-A

Title: Gas barrier coating compositions containing platelet-type fillers

Description:
BACKGROUND OF THE INVENTION 
     The technical field of the present invention relates to gas barrier coating compositions and multilayer packaging materials made therewith. 
     Plastics have found increasing use as replacements for glass and metal containers in packaging. Advantages of such plastic packaging over glass packaging include lighter weight, decreased breakage and potentially lower costs. Moreover, an advantage of plastic packaging over metal packaging is that the former can more easily be designed as re-closable. Notwithstanding the above, shortcomings in the gas-barrier properties of common plastic packaging materials (e.g., polyesters, polyolefins and polycarbonates) present major problems to those in the packaging industry when used to package oxygen-sensitive items and/or carbonated beverages. 
     Specifically, gases such as oxygen and carbon dioxide can readily permeate through most of the plastic materials commonly used by the packaging industry. The oxygen permeability constant (herein referred to as &#34;OPC&#34;) of such plastic materials, which quantifies the amount of oxygen which can pass through a film or coating under a specific set of circumstances, is generally expressed in units of cubic centimeter-mil/100 square inches /atmosphere/day. This is a standard unit of permeation measured as cubic centimeters of oxygen permeating through 1 mil (25.4 micron) thickness of a sample, 100 square inches (645 square centimeters) in area, over a 24-hour period, under a partial pressure differential of one atmosphere at specific temperature and relative humidity (R.H.) conditions. As used herein, OPC values are reported at 30° C. and 50% R.H. unless otherwise stated. 
     Since many foods, beverages, chemicals, medicines, medical supplies and the like are sensitive to oxidation, they typically must be protected from the ingress of oxygen into the sealed container so as to prevent the discoloration and/or spoilage of the item contained therein. Moreover, carbonated beverages should be stored in sealed containers which prevent the egress of carbon dioxide therefrom so as to keep the beverage from going flat. As used herein, the term &#34;flat&#34; refers to a carbonated beverage losing at least about 10% of its carbonation, typically at least about 15% of its carbonation, and more typically at least about 20% of its carbonation. Accordingly, since oxygen and carbon dioxide can readily permeate through most plastic materials used by the packaging industry, the shelf-life of items stored in conventional plastic containers is reduced when compared to their shelf-life when stored in glass or metal containers. 
     Some examples of oxygen sensitive items whose shelf life would be greatly reduced if stored in conventional plastic containers are perishable foods and beverages such as tomato-based products (e.g., ketchup, tomato sauces and tomato pastes), juices (e.g., fruit and vegetable juices) and malt beverages (e.g., beer, ale, malt liquor). In these instances, exposure to minute amounts of oxygen over a relatively short period of time adversely affects their taste. Some examples of carbonated beverages whose shelf life would be greatly reduced if stored in conventional plastic containers are soft drinks, malt beverages, sparkling water, sparkling wines, champagne, and the like. 
     One of the common packing materials used today in the food and beverage industry is poly(ethylene teraphthalate) (&#34;PET&#34;). Notwithstanding its widespread use, PET has a relatively high OPC value (i.e., 6.0). As such, although it has been used for making many types of food and beverage containers, the food and beverage industry has sought ways to improve the OPC value of such packaging materials. It should be noted that, typically, oxygen permeates through a film and/or coating more readily than does carbon dioxide. Accordingly, although OPC values pertain to the permeability of oxygen through a film and/or coating, lowering a coating&#39;s OPC value not only improves its oxygen barrier properties, but also improves its carbon dioxide barrier properties. 
     One of the methods disclosed in the literature as a means of improving a plastic packaging material&#39;s OPC value pertains to chemically and/or physically modifying the plastic. This method is typically expensive and can create recycleability problems. Another method disclosed in the literature as a means of improving a plastic packaging material&#39;s OPC value pertains to coating the plastic material with a gas barrier material (e.g., a gas barrier coating composition or a gas-barrier film). This method is typically less expensive than the method set out above and creates fewer, if any, recycleability problems. 
     Numerous gas barrier coating compositions have been disclosed in the prior art. For example, polyepoxide-polyamine based gas barrier coating compositions having very low OPC values are the subject of commonly-owned U.S. Pat. Nos. 5,006,381; 5,008,137 and 5,300,541 and WO 95/26997. These coatings have found commercial acceptance as barrier coatings for polymeric containers. However, further improvements are still desirable by certain segments in the packaging industry. An example of such desired improvements would include the development of gas barrier coatings which have OPC values of not more than 0.05 and a smooth and glossy appearance. 
     One specific approach which has been disclosed as a means for improving the gas barrier properties of resin-based coating compositions, in general, is to incorporate therein the use of platelet shaped inorganic fillers (hereinafter referred to as &#34;platelet-type&#34; fillers). Without being bound to theory, it is believed that such blends of platelet-type fillers and resins function, at least in part, by forming tortuous paths for diffusion of permeating gases there through. 
     There are a number of examples in the patent literature on the use of inorganic platelet-type fillers to improve the gas barrier properties of coating compositions. For example, WO 95/26997 states that the use of pigments in the polyepoxide-polyamine based gas barrier coating compositions disclosed therein may further reduce the gas permeability of the resultant barrier material. Examples of preferred pigments listed therein include micas, aluminum flakes and glass flakes due to their platelet-type structure. There is, however, no disclosure therein as to which platelet-type particles, if any, can be used in order to produce a gas barrier coating having not only an OPC value of not more than 0.05, but also a smooth and glossy appearance. 
     U.S. Pat. Nos. 4,528,235 and 1,018,528 disclose thin polymer films containing small sized platelet-type fillers. The preferred polymer is polycaprolactam or high density polyethylene. According to those patents, there is from 10 to 50 percent of a platelet-type filler present therein which has an average equivalent diameter of from 1 to 8 micrometers, a maximum equivalent diameter of about 25 micrometers, and an average thickness of less than 0.5 micrometers. The preferred filler is talc. Ground mica, platelet silicas, flaked metal and flaked glass are also disclosed as being suitable fillers. 
     In some instances, the use of platelet-type fillers in coating compositions significantly improves the coatings&#39; gas barrier properties. However, in other instances, the use of platelet-type fillers has little, if any, effect on the coating&#39;s gas barrier properties and/or reduces the resulting coating&#39;s gloss and smoothness. In the packaging industry, while it is often desirable for a coating to have excellent gas barrier properties, it is also often equally desirable for the coating to have a smooth and glossy appearance. 
     Therefore, when the use of platelet-type fillers improves a coating&#39;s gas barrier properties, the resulting OPC values are oftentimes either still too high to be used when making plastic packaging materials for foods, beverages, chemicals, medicines, medical supplies and the like which are highly sensitive to oxidation, or too rough and dull to satisfy appearance requirements. Accordingly, notwithstanding the many advantages associated with the polymeric packaging materials, some items are still stored in glass or metal containers due to the gas permeability problems of polymeric packaging materials. 
     The extensive prior art in this area shows the unfilled need for a specific combination of a filler and a gas barrier coating which would have a very low OPC value (i.e., an OPC value of not more than 0.05) and a smooth and glossy appearance. 
     SUMMARY OF THE INVENTION 
     The present invention provides a gas barrier coating composition which includes: a polyamine (A), a polyepoxide (B), and a filler (C). Polyamine (A) includes at least one of the following: (a) an initial polyamine, or (b) an ungelled polyamine adduct. Polyepoxide (B) includes a polyepoxide having a plurality of glycidyl groups linked to an aromatic member. Filler (C) is characterized as a platelet-type filler with the following particle size distribution: (a) a number mean particle diameter ranging from about 5.5 to about 15 microns, and (b) a volume mean particle diameter ranging from about 8 to about 25 microns. When cured, the gas barrier coatings of this invention have an OPC value of not more than 0.05, and a 20° gloss of at least 60% reflected light. 
     The present invention also provides smooth and glossy, multilayer packaging materials which include: (a) at least one layer of a substrate material, and (b) at least one layer of the gas barrier material described above. 
     DETAILED DESCRIPTION OF THE INVENTION 
     As used herein, the term &#34;glossy&#34; refers to a cured coating having a gloss, as measured at an angle of 20° using a Gardner Glossgard IIa 20° Glossmeter from Gardner Instruments, of at least 60% reflected light. 
     As used herein, the term &#34;ungelled polyamine adduct&#34; refers to an amine-functional polymeric resin which is soluble and/or dispersible in a liquid medium. 
     As used herein, the term &#34;number mean particle diameter&#34; refers to the sum of the equivalent circle diameter of all the particles in the sample that were analyzed (Σd) divided by the total number of the particles that were analyzed. 
     As used herein, the term &#34;equivalent circle diameter&#34; refers to the diameter of a circle having a projected area equal to the projected area of the particle in the sample being analyzed. 
     As used herein, the term &#34;volume mean particle diameter&#34; refers to the cube root of the sum of the cube of the equivalent spherical diameter of all the particles in the sample that were analyzed ((Σd 3 ) 1/3 ) divided by the total number of the particles that were analyzed. 
     As used herein, the term &#34;equivalent spherical diameter&#34; refers to the diameter of a sphere having a volume equal to the volume of the particle being analyzed. 
     All particle size measurements pertaining to the filler used when practicing this invention are as determined by a HORIBA LA-900 laser scattering particle size distribution analyzer from Horiba Instruments, Inc. in Irving, Calif. The HORIBA LA-900 works off the same principle as many conventional laser scattering particle size distribution analyzers. 
     For example, light traveling in a homogeneous medium travels in straight lines. However, when light travels through a medium containing particles of a material, the particles cause the light to scatter. For a single particle, the amount of scattering in a particular direction depends upon the size, shape, and composition of the particle and the wavelength of the incident light. For a collection of particles, light scattered from all of the particles contributes to the total intensity of light scattered in a particular direction relative to the incident light. By measuring the amount and/or intensity of light scattered throughout a number of angles relative to the incident light, it is possible to infer properties of the particles that induce the scattering. In particular, for particles of small size and similar composition, the pattern of scattered light is indicative of the sizes of the scattering particles. 
     Many conventional analyzers have used the aforementioned technique of analyzing the scattered light intensity to determine the spectrum of particle sizes for a mixture of small particles of varying sizes. Particle size analyzers using this technique typically sample the angular distribution of the intensity of the light scattered from the mixture, process the data, and produce numerical values and possibly a graph or a histogram as output. The analyzer output represents the number or volume fraction of scattering particles in the mixture as a function of the size of the particles and is usually called a particle size distribution. 
     For classical light scattering analysis, the problem of relating the angular distribution of scattered light to the size of the scattering particle has been solved mathematically for the case of a spherical particle illuminated by a beam of unpolarized light. The mathematical solution is given by a theory proposed by Gustav Mie. The Mie theory is set forth in Chapter 4 of the book, Absorption and Scattering of Light by Small Particles, by Craig F. Bohren and Donald R. Huffman (John Wiley &amp; Sons, 1983). Some particle size analyzers employ the Mie theory to determine particle size distributions from the observed pattern of scattered light. 
     Although such analyzers are not limited to the analysis of only samples containing particles of spherical shape, the particle sizes are reported as radii of spheres that are equivalent to the actual particles in terms of light scattering. For most applications, the equivalent-sphere specification of a particle size distribution is sufficient to characterize the actual particle size distribution. Mathematical models have also been derived for particular particle shapes other than spherical, but they have been found to have limited value since, for scattering, only the average behavior of a large number of particles is of interest. 
     Since scattering is also a function of the wavelength of the incident light, some analyzers use incident light of a single wavelength. For this purpose, a laser has been the typical light source. Lasers have been used which produce light in the visible and near-visible wavelength range. 
     In many typical particle size distribution analyzers, a source of unpolarized light is projected in a beam to impinge upon a sample. The sample contains the particles whose sizes are under investigation. The particles are dispersed in the region of the sample that is illuminated by the incident light beam. The particles scatter light in patterns that are dependent on the ratio of the size of the particle to the wavelength of the light, and on the refractive index of the particle material. The refractive index, a complex function of wavelength, is a measure of how much the light is refracted, reflected, and absorbed by the material. For a beam of unpolarized light incident on a random mixture of small particles, the scattering pattern is symmetric about the axis of the incident beam. The scattering is the result of the refraction, reflection, and absorption by the particles, as well as diffraction at each particle surface where a light ray in the incident beam is tangent to the particle surface. 
     Light that scatters at a particular angle with respect to the incident beam may be rotated about the beam axis without changing the scattering angle. A large number of rays scattering from a single particle at a given scattering angle will fill all rotational orientations and thus form a cone of light, with the apex at the scattering particle and with the generating angle (one-half the apex angle) of the cone equal to the scattering angle. The pattern of light rays scattering at all angles from a single particle may thus be thought of as made up of a continuous series of open cones of light, with the generating angle for a given cone corresponding to the scattering angle for the light comprising the surface of that cone. The axes of all of the cones are collinear with the line defined by the incident beam, and the apexes of the cones are located at the scattering particle. At a distance from the scattering particle, a plane perpendicular to the incident beam will intersect a given cone in a circle. Planes not perpendicular to the incident beam will intersect a given cone in a curved line comprising a conic section (i.e., an ellipse, a parabola, or a hyperbola), depending upon the orientation of the plane. Regardless of form, the curved line of intersection represents a single scattering angle. 
     In particle size analyzers, it is not necessary to measure the scattering angle with infinite precision. Nevertheless, better angular resolution in the analyzer provides better particle size resolution. In order to address angular precision effects directly, the set of all scattering angles falling between a precise lower angular limit and a precise upper angular limit will be referred to as an &#34;angle class&#34; of some intermediate angle. Light scattered within an angle class scatters into the region between two cones of slightly different size. The smaller (inner) of the two cones is generated by the lower angular limit of the angle class and the larger (outer) cone is generated by the upper angular limit. The apexes of both cones are located at the scattering particle. 
     The inner and outer cones of an angle class define a circular annular region on a plane perpendicular to the incident beam and a more complex shaped region (corresponding to a conic section) on a plane not perpendicular to the incident beam. Scattered light rays intersecting the interior of such a region are rays which have scattered through an angle between the two generating angles of the cones. Thus any light ray intersecting such a region belongs to the angle class defined by that region. Some conventional analyzers employ ring-shaped light detectors to measure the amount of light that scatters in an angle class determined by the radius and width of the ring and its distance from the scattering region. To correlate correctly the detected light with a scattering angle, these ring-shaped detectors are typically mounted and aligned precisely perpendicular to the incident beam. 
     Since the interaction region of the incident beam with the particles generally has a finite extent, multiple particles at different locations in the incident beam will each contribute multiple overlapping cones of scattered light, with the apexes of the cones offset by the distance between the particles. Particles of the same size will have overlapping scattered-light cones of similar intensity variations, whereas particles of different sizes will have overlapping scattered-light cones of different intensity variations. 
     When the light beam illuminates a sample volume of finite extent, a converging lens may be used to direct parallel rays of light, each by definition scattered through the same scattering angle (by different particles), to a single point on a light detector in the focal plane of the lens. A lens that functions in this manner performs a Fourier transform, so that all light arriving at a given point on the detector is known to have been scattered by the sample through a particular scattering angle, regardless of the location of the scattering particle in the sample volume. 
     The effect of the converging lens is to transform the spatial distribution of the scattered light it receives to that of an equivalent virtual system in which the light distribution in the focal plane of the lens is the same as if all the scattering particles were located at a point coincident with the optic center of the lens. The light detectors are placed in the focal plane of the lens. The line from the optic center of the lens to the focal point of the lens is usually called the optic axis. 
     If a scattered ray passes through different refracting media, such as air and a sample suspension fluid, before detection, then an appropriate correction is typically applied to the ray&#39;s apparent angle of scatter to determine its true angle of scatter. Use of a lens and recognition of the virtual scattering system simplifies the correction. 
     The intensity of light scattered as a function of scattering angle, when experimentally determined as above for a sample composed of many particles of a range of different sizes, consists of the summation of the scattered light from all the particles. If it is assumed that each size particle in the sample scatters light according to a given mathematical theory and in proportion the relative number of such size particles present, then it is mathematically possible to determine from the experimental data the relative numbers of each size particle constituting the sample (i.e., to determine the size distribution of the sample. The well-known mathematical process by which the size distribution may extracted from the composite data is called an inversion process, or sometimes a deconvolution process. 
     In the usual convention, a scattering angle of zero degrees coincides with unscattered light, and a scattering angle of 180 degrees represents light reflecting directly back into the incident beam. Scattering angles between 90 and 180 degrees are termed back scattering. 
     Similar to these conventional particle size distribution analyzers, the HORIBA LA-900 works by irradiating particles dispersed in a solution with a red light beam and a blue light beam which is obtained by filtering a tungsten lamp in parallel with an He-Ne laser. The particles cause the light to scatter at various angles. A condenser lens is used with an array detector at the focal point of the lens. There are also detectors positioned in the front, side and rear of the sample. From the angular measurement of the scattered light by all the detectors, the particle size distribution of the sample is calculated. These computations are made by the particle size distribution analyzer by using the Mie scattering light theory. Using the technique set out above, the HORIBA LA-900 laser scattering particle size distribution analyzer can provide an accurate, reproducible assessment of particle sizes in the range from 0.04 microns to 1,000 microns. 
     To measure particles having a diameter less than 0.1 microns, the HORIBA LA-900 uses three separate detectors--one for the front, side and rear scattering. As the light source for detecting scattering on the side and rear, the HORIBA LA-900 uses a tungsten lamp. In the HORIBA LA-900, the small angle forward scattered light is conventionally given by an He-Ne laser and detected by the ring detector and the large angle and rear scattered light is given by the tungsten lamp and detected by a photodiode. For a complete description of how the HORIBA LA-900 works, see U.S. Pat. No. 5,4278,443. 
     The gas barrier coating compositions of the present invention include: a polyamine (A), a polyepoxide (B), and a filler (C). Polyamine (A) can be an initial polyamine, an ungelled polyamine adduct, or a mixture thereof. 
     The initial polyamine used as, or in the making of, polyamine (A) is typically characterized as having a substantial aromatic content. Specifically, at least 50 percent of the carbon atoms in the initial polyamine are in aromatic rings (e.g., phenylene groups and/or naphthylene groups). Preferably the number of the initial polyamine carbon atoms in aromatic rings is at least 60 percent, more preferably at least 70 percent, and even more preferably at least 80 percent. This initial polyamine can be represented by the structure: 
     
         Φ-(R.sup.1 NH.sub.2).sub.k 
    
     where: 
     k is 1.5 or greater, 
     Φ is an aromatic-containing organic compound, and 
     R 1  is an allyl group having between 1 and 4 carbon atoms. 
     Preferably, k is 1.7 or greater, more preferably 1.9 or greater, and even more preferably, 2.0 or greater. Preferably, R 1  is not larger than C 3 , more preferably not larger than C 2 , and even more preferably not larger than C 1 . Typically, Φ comprises an aryl group, preferably a benzyl and/or a naphthyl group. 
     The gas barrier coating compositions of the present invention can be produced without having to form an ungelled polyamine adduct. In instances where a polyamine adduct is not formed, all of the epoxide required for curing the gas barrier coating composition (i.e., polyepoxide (B)) is blended with the initial polyamine (i.e., polyamine (A)). 
     When an initial polyamine is pre-reacted to form an adduct, sufficient active amine hydrogen groups must be left unreacted so as to provide reaction sites for reacting during the final curing step. Typically, about 10 to about 80 percent of the active amine hydrogens of the polyamine are reacted with epoxy groups. Pre-reacting fewer of the active amine hydrogens reduces the effectiveness of the pre-reaction step and provides little of the linearity in the polymer product that is one of the advantages of forming the adduct. 
     In accordance with one embodiment, a polyamine adduct is formed by reacting the initial polyamine with epichlorohydrin. By carrying out the reaction at polyamine to epichlorohydrin molar ratios greater than about 1:1 in the presence of an alkali, a primary reaction product is polyamine groups joined by 2-hydroxypropylene linkages. The reaction of m-xylylenediamine (&#34;MXDA&#34;), a preferred polyamine, with epichlorohydrin is described in U.S. Pat. No. 4,605,765, and such products are commercially available as GASKAMINE 328® and GASKAMINE® 328S from Mitsubishi Gas Chemical Company. 
     In accordance with another embodiment, a polyamine adduct is formed by reacting the initial polyamine with polyepoxides in which a plurality of glycidyl groups are linked to an aromatic member. As used herein, the term &#34;linked&#34; refers to the presence of an intermediate linking group. Such polyepoxides can be represented by Formula (I): ##STR1## where: R 2  is phenylene or naphthylene; 
     X is N, NR 3 , CH 2  N, CH 2  NR 3 , O, and/or C(O)--O, where R 3  is an alkyl group containing 1 to 4 carbon atoms, a cyanoethyl group or cyanopropyl group; 
     n is 1 or 2; and 
     m is 2 to 4. 
     Examples of such polyepoxides include: N,N,N&#39;,N&#39;-tetrakis (oxiranylmethyl)-1,3-benzene dimethanamine (e.g., that which is commercially available as TETRAD X epoxy resin from Mitsubishi Gas Chemical Co.), resorcinol diglycidyl ether (e.g., that which is commercially available as HELOXY® 69 epoxy resin from Shell Chemical Co.), diglycidyl esters of phthalic acid (e.g., that which is commercially available as EPI-REZ® A-100 epoxy resin from Shell Chemical Co.), and triglycidyl para-aminophenol (e.g., that which is commercially available as Epoxy Resin 0500 from Ciba-Geigy Corporation). 
     Optionally, if a polyamine adduct is formed, it may also include up to about 20 weight percent a novolac epoxy resin or a bisphenol F epoxy resin. This percentage is based upon the total resin solids of the adduct. 
     Notably excluded from the types of epoxides that can be reacted with the initial polyamine to form a polyamine adduct are bisphenol A type epoxy resins. Alternatives for such bisphenol A type epoxides which can be reacted with the initial polyamine in accordance with the present invention include novolacs with higher glycidyl functionality (e.g., those commercially available from Dow Chemical Co. as DEN-438 and/or DEN-439). 
     The reaction of the epoxide and the initial polyamine to produce the ungelled adduct is carried out at temperatures and concentrations of reactants sufficient to produce the desired ungelled product. These temperatures and concentrations will vary depending upon the selection of starting materials. Typically, however, reaction temperatures will range from about 40° C. to about 140° C., with lower temperatures (e.g., from about 40° C. to about 110° C.) being preferred for those systems that are more susceptible to gellation. Similarly, concentrations of reactants will typically range from about 5 to about 100 percent by weight of reactant in an appropriate solvent depending upon the particular molar ratio and type of reactants. Lower concentrations of reactants are generally preferred for those systems that are more susceptible to gellation. 
     Specific reaction conditions can readily be chosen by one skilled in the art guided by the disclosure and the examples herein. Moreover, preparation of an ungelled amine-functional polymeric adduct is also described in commonly-owned U.S. Pat. No. 5,006,381, columns 2 through 7. The description in U.S. Pat. No. 5,006,381, of the preparation of such amine-functional polymeric adducts, is incorporated herein by reference. 
     In most instances, when compared to the non adduct producing approach, forming the polyamine adduct has the advantage of increasing molecular weight while maintaining linearity of the resin, thereby avoiding gellation. This can be achieved by using an initial polyamine having no more than two primary amino groups. 
     Typically, the initial polyamines react relatively slowly with polyepoxide (B). On the other hand, the aforementioned polyamine adduct reacts relatively quickly with polyepoxide (B). Accordingly, another advantage of forming the polyamine adduct is that the reaction period necessary to form the resulting gas barrier coating is significantly reduced. 
     Polyepoxide (B) used when practicing this invention may be any epoxide known to those of skill in the art which can react with polyamine (A) to form gas barrier coating compositions. Preferably, polyepoxide (B) includes those polyepoxides in which a plurality of glycidyl groups are linked to an aromatic member are represented by Formula (I) described earlier. Specific examples of such a group of polyepoxides are also the same as those described earlier which can be reacted with the initial polyamine to form the ungelled polyamine adduct. 
     When polyepoxides are employed in both the formation of a polyamine adduct, they may be the same or different as those used as polyepoxide (B). Typically, if a polyamine adduct is used in the formation of the gas barrier coatings of this invention, the epoxides used in forming the polyamine adduct and those used as polyepoxide (B) have epoxy functionality of at least about 1.4, and preferably at least about 2.0 The presence of small amounts of monoepoxides may not, however, be objectionable. 
     Polyepoxide (B) may include polyepoxides that are saturated or unsaturated, aliphatic, cycloaliphatic, aromatic, or heterocyclic, and may be substituted with non-interfering substituents such as hydroxyl groups or the like. Generally, such polyepoxides may include polyglycidyl ethers of aromatic polyols, which may be formed by etherification of aromatic polyols with epichlorohydrin or dichlorohydrin in the presence of an alkali. Specific examples of such include: bis(2-hydroxynaphthyl)methane, 4,4&#39;-dihydroxylbenzophenone, 1,5-dihydroxy-naphthalene and the like. Also included in the category of a suitable polyepoxide (B) are polyglycidyl ethers of polyhydric aliphatic alcohols including cyclic and polycyclic alcohols. 
     The epoxy group equivalent weight of polyepoxide (B) is preferably minimized so as to avoid unnecessarily introducing molecular groups into the cured polymeric network that are not the preferred groups of this invention. Generally, polyepoxide (B) has a molecular weight above about 80. Preferably, the molecular weight of polyepoxide (B) is in the range from about 100 to about 1,000, and more preferably from about 200 to about 800. Moreover, polyepoxide (B) generally has an epoxy equivalent weight above about 40. Preferably, the equivalent weight of polyepoxide (B) is in the range from about 60 to about 400, and more preferably from about 80 to about 300. 
     The diglycidyl ethers of an aromatic polyol such as bisphenol A or an aliphatic alcohol such as 1,4-butanediol are not preferred when practicing the present invention. However, they may be tolerated when used to cure preferred embodiments of the polyamine adduct. Diglycidyl ethers of bisphenol F are preferred over bisphenol A based epoxides for the sake of low oxygen permeability. It is theorized that the presence of methyl groups in bisphenol A has a detrimental effect on oxygen barrier properties. Thus, isopropylidene groups are preferably avoided. Other unsubstituted alkyl groups are believed to have a similar effect, and constituents containing such groups are preferably avoided in the present invention. 
     In addition to polyamine (A) and polyepoxide (B), the gas barrier coating compositions of this invention further include filler (C). It has been discovered that, in order for the presence of filler (C) to lower the OPC value of the gas barrier coating composition disclosed herein to not more than 0.05, and to maintain a smooth appearance having a 20° gloss of at least 60% reflected light, filler (C) is characterized as a platelet-type filler having the following particle size distribution: (a) a number mean particle diameter ranging from about 5.5 to about 15 microns, and (b) a volume mean particle diameter ranging from about 8 to about 25 microns. Preferably, the platelet-type filler included in filler (C) has the following particle size distribution: (a) a number mean particle diameter ranging from about 7.5 to about 14 microns, and (b) a volume mean particle diameter ranging from about 10 to about 23 microns; and more preferably the following particle size distribution: (a) a number mean particle diameter ranging from about 9.5 to about 13 microns, and (b) a volume mean particle diameter ranging from about 14 to about 20 microns. In addition to the above, in preferred embodiments of this invention, the platelet-type filler included in filler (C) further has the following particle size distribution: (a) at least about 55 percent by number of its particles having a diameter greater than 7 microns, and (b) less than about 15 percent by number of its particles having a diameter greater than 30 microns; preferably: (a) at least about 75 percent by number of its particles having a diameter greater than 7 microns, and (b) less than about 10 percent by number of its particles having a diameter greater than 30 microns; and more preferably: (a) at least about 95 percent by number of its particles having a diameter greater than 7 microns, and (b) less than about 5 percent by number of its particles having a diameter greater than 30 microns. 
     It has been observed that the incorporation of a sufficient amount of a platelet-type filler having a particle size distribution within these parameters into a barrier coating comprising polyamine (A) and polyepoxide (B) as described herein results in a gas barrier coating composition which, when cured, has an OPC value of not more than 0.05 and a 20° gloss of at least 60% reflected light. However, it has also been observed that, when a platelet-type filler is used which has a particle size distribution outside of the aforementioned parameters, or if an insufficient amount of a platelet-type filler is used which has a particle size distribution within the aforementioned parameters, the resulting gas barrier coating may not have an OPC value of not more than 0.05 and/or a 20° gloss of at least 60% reflected light. 
     When filler (C) has the following particle size distribution: (a) a number mean particle diameter ranging from about 9.5 to about 15 microns, and (b) a volume mean particle diameter ranging from about 14 to about 25 microns, in order for the resulting gas barrier coating to have an OPC value of not more than 0.05 and a 20° gloss of at least 60% reflected light, filler (C) is preferably present in an amount ranging from about 5 to about 50 weight percent, more preferably in an amount ranging from about 6 to about 45 weight percent, and even more preferably from about 7 to about 40 weight percent. These weight percentages are based upon the total solids weight of the gas barrier coating composition. 
     However, when the number mean particle diameter of filler (C) ranges from about 5.5 to less than 9.5 microns, and/or when the volume mean particle diameter ranges from about 8 to less than 14 microns, in order for the resulting coating composition to have an OPC value of not more than 0.05, filler (C) is preferably present in an amount ranging from about 12 to about 50 weight percent, more preferably in an amount ranging from about 15 to about 45 weight percent, and even more preferably from about 18 to about 40 weight percent. These weight percentages are based upon the total solids weight of the gas barrier coating composition. 
     Any suitable platelet-type filler which has the aforementioned particle size distribution and which is compatible with the barrier coating composition described above can be used when practicing this invention. Examples of such suitable fillers include: mica, vermiculite, clay, talc, micaeous iron oxide, silica, flaked metals, flaked graphite, flaked glass, flaked phthalocyanine, and the like. The preferred filler for the purposes of this invention is mica due to its commercial availability. 
     Micas which can be used when practicing this invention include natural micas and synthetic micas. Examples of natural micas include: muscovite (K 2  Al 4  (Al 2  Si 6  O 20 )(OH) 4 ), phlogopite (K 2  (Mg,Fe 2+ ) 6  (Al 2  Si 6  O 20 )(OH,F) 4 ), and biotite (K 2  (Fe 2 ,Mg) 6  (Al 2  Si 6  O 20 )(OH) 4 ). Examples of synthetic micas include: fluorophlogopite (K 2  Mg 6  Al 2  Si 6  O 20  F 4 ) and barium disilicic (Ba 2  Mg 6  Al 2  Si 6  O 20  F 4 ). Of the micas which have the aforementioned particle size distribution, the preferred, for the purposes of this invention, is muscovite mica due to its commercial availability. 
     The polymers that comprise the chief film-forming resin of the gas barrier coating composition of the present invention are cured in situ when polyamine (A) and polyepoxide (B) are mixed together. Each amine hydrogen of polyamine (A) is theoretically able to react with one epoxy group and is considered as one amine equivalent. Thus, a primary amine nitrogen is considered as difunctional in the reaction with epoxides to form the gas barrier material. 
     For the purposes of this invention, these two components are typically reacted in a ratio of the equivalents of active amine hydrogens in polyamine (A) to equivalent of epoxy group in polyepoxide (B) of at least about 1:1.5. In order to produce a gas barrier material which is strong, flexible, moisture resistant and solvent resistant, the ratio of the equivalents of active amine hydrogens in polyamine (A) to equivalent of epoxy group in polyepoxide (B) is preferably in the range from about 1:1.5 to about 1:3.0, more preferably from about 1:1.7 to about 1:2.8, and even more preferably from about 1:2.0 to about 1:2.5. 
     Preferably, the cured reaction product of polyamine (A) and polyepoxide (B) contains a substantial number of unreacted amine hydrogens. However, although maximizing the amount of polyamine reactant is generally desirable for the sake of maximizing gas barrier properties, insufficient numbers of epoxy groups may not provide enough crosslinking to yield a film which is strong, moisture resistant and solvent resistant. On the other hand, the use of more epoxy than the preferred amounts may provide excessive crosslinking to yield a film that is very brittle. 
     As the amount of amine nitrogen in the gas barrier coating increases, the coating&#39;s OPC value decreases. When practicing this invention, the amine nitrogen content in the cured gas barrier coating is typically at least about 6.0 weight percent. Preferably, the cured gas barrier coatings of this invention have an amine nitrogen content of at least about 6.5 weight percent, and more preferably of at least about 7.0 weight percent. Typically, for economical reasons, the maximum amount of amine nitrogen content in the cured gas barrier coating of this invention is generally less than about 20 weight percent, more typically less than about 17 weight percent, and even more preferably less than about 15 weight percent. These weight percentages are based upon total resin solids weight of the gas barrier coating. 
     Cured films of the gas barrier coating compositions prepared in accordance with the present invention have a molecular network that consists predominantly of two molecular groups: 
     (1) aminoalkyl substituted aromatic groups of the type 
     
         &lt;NR.sup.4 ΦR.sup.4 N&lt; 
    
     where, R 4  is an alkyl group containing not more than 4 carbons, preferably not more than 3, more preferably not more than 2, and even more preferably not more than 1 carbon atom), and 
     (2) --CH 2  CH(OH)CH 2  -- (2-hydroxypropylene groups) groups. 
     Typically, the amount of the aminoalkyl substituted aromatic groups present in the cured gas barrier coating is at least about 50 weight percent, more preferably at least about 55 weight percent, and even more preferably at least about 60 weight percent. The amount of the 2-hydroxy-propylene groups present in the cured gas barrier coating is typically at least about 20 weight percent, more preferably at least about 30 weight percent, and even more preferably at least about 40 weight percent. These weight percentages are based upon the total weight of resin solids of the gas barrier coating. Examples of these embodiments include m-xylylenediamine adducted with epichlorohydrin or with N,N,N&#39;,N&#39; tetrakis (oxiranylmethyl)-1,3-benzene dimethanamine (TETRAD X epoxy resin) and cured with TETRAD X epoxy resin. 
     It has been discovered that excellent gas barrier properties can be attained when the cured film network of the gas barrier coating contains at least about 70 weight percent of aminoalkyl substituted aromatic groups and/or 2-hydroxypropane groups. For the purposes of this invention, the gas barrier coating preferably contains at least about 80 weight percent of these two molecular groups, more preferably at least about 90 weight percent, and even more preferably at least about 95 weight percent. These weight percentages are based upon the total weight of resin solids of the gas barrier coating. 
     As stated above, in one preferred embodiment, at least 50 percent of the carbon atoms in the initial polyamine used as, or in the making of, polyamine (A) are in an aromatic ring(s). In a particularly useful embodiment, R 4  in the &gt;NR 4  ΦR 4  N&lt; group contains a single carbon atom. Accordingly, when Φ is benzene, at least seventy percent of the carbon atoms are in aromatic rings. 
     It should be understood, however, that excellent gas barrier properties may still be attained without the optimum levels of the aminoalkyl substituted aromatic groups and/or the 2-hydroxypropane groups molecular groups described above. For example, in addition to the aforementioned preferred groups, some of the aminomethyl substitutions can be replaced with oxy substitutions, (i.e., --O--Φ--O-- groups). These may be introduced into the network by adducting the initial polyamine with the polyglycidyl ethers of polyphenols (e.g., diglycidyl ether of resorcinol) or by curing one of the preferred adducts with such a polyglycidyl ether of a polyphenol. Additionally, some of the aminomethyl substitutions can also be replaced with mixed substitutions such as --O--Φ--N&lt; groups. These particular groups could be the residue of adducting or curing the initial polyamine with triglycidyl para-aminophenol. 
     Although not exhibiting performance properties which may be characterized as preferred for the purposes of this invention, the cured polymer network of the gas barrier coating can also include: --O--Φ--CH 2  --Φ--O-- groups, which are the residues of novolac epoxy resins or bisphenol F epoxy resins; and --O--C(O)--Φ--C(O)--O groups, which are derived from diglycidyl esters of aromatic acids. 
     While maximizing the content of the aminoalkyl substituted aromatic groups and/or the 2-hydroxypropane groups present in the cured gas barrier coating composition is generally desirable, it has also been found to be additionally advantageous that the content of certain molecular groups be minimized in, or even essentially absent from, the gas barrier&#39;s cured polymer network. For example, the groups that are preferably avoided include unsubstituted alkyl chains, particularly alkylene polyamine groups, as well as isopropylidene groups (i.e., as in bisphenol A). 
     It should be apparent from the description herein that the desired molecular groups may be introduced into the cured polymeric network of the gas barrier coating composition by the initial polyamine, the polyamine adduct or the epoxide curing component (i.e., polyepoxide (B)). It should also be apparent that the various substitutions on the aromatic members described above may be provided in combination with each other on the same molecule in the reactants. 
     The gas barrier coatings of the present invention are thermoset polymers. This is desired feature for the packaging industry since containers often rub together during processing and shipping. Since the gas barrier coatings of this invention are thermosetting polymers, any such rubbing together of adjacent containers will be less likely to cause localized softening of the barrier coatings when compared to thermoplastic gas barrier coatings. 
     The OPC value of the cured gas barrier coating compositions prepared in accordance with this invention is not more than 0.05. If even lower OPC values are desired, the cured gas barrier coating composition of this invention can have OPC values of not more than 0.04, and even of not more than 0.03. 
     When practicing this invention, the gas barrier coating composition can be applied over a substrate as either a solvent-based or an aqueous-based thermosetting coating composition. If solvents are used, they should be chosen so as to be compatible with the substrate being coated, and also provide desirable flow properties to the liquid composition during application. Suitable solvents which can be used include: oxygenated solvents, such as glycol ethers (e.g., 2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, 2-butoxyethanol, 1-methoxy-2-propanol and the like); or alcohols such as methanol, ethanol, propanol and the like. Glycol ethers, such as 2-butoxyethanol and 1-methoxy-2-propanol, are more preferred with 1-methoxy-2-propanol being most preferred. The use of 1-methoxy-2-propanol is preferred for its rapid evaporation rate, which minimizes solvent retention in the cured film. In order to obtain desired flow characteristics in some of the embodiments using a pre-reacted adduct, use of 2-butoxyethanol may be preferred. Moreover, in embodiments not requiring slow evaporating solvents for the sake of flow properties, the solvents listed here may be diluted with less costly solvents such as toluene or xylene. The solvent may also be a halogenated hydrocarbon. For example, a chlorinated hydrocarbon, such as methylene chloride, 1,1,1-trichloroethane and the like (usually considered fast evaporating solvents), may be especially useful in obtaining cured barrier films. Mixtures of such solvents may also be employed. Non-halogenated solvents are preferred where the resultant barrier material is desired to be halide-free. 
     The resin may also be in an aqueous medium (i.e., the ungelled amine-functional polymeric resin may be an aqueous solution or dispersion). For example, when polyepoxide (B) is water-soluble (e.g., the polyglycidyl ether of an aliphatic diol), the ungelled amine-functional polymeric resin can be utilized as an aqueous solution. Otherwise, with water-insoluble polyepoxides, the ungelled amine-functional polymeric resin can have sufficient amine groups neutralized with an organic acid (e.g., formic acid, lactic acid or acetic acid), or with an inorganic acid (e.g., hydrochloric acid or phosphoric acid), to allow solubilization of the ungelled amine-functional polymeric resin in an aqueous medium. For such aqueous-based systems, an organic acid is typically preferred. 
     Generally, for embodiments employing the pre-reacted adduct approach, the solution of the amine-functional polymeric coating ready for application will have a weight percent of resin solids in the range of from about 15 weight percent to about 50 weight percent, and preferably from about 25 weight percent to about 40 weight percent. Higher weight percent solids may present application difficulties, particularly with spray application, while lower weight percentages will typically require removal of greater amounts of solvent during the curing stage. For the embodiments using direct reaction of the initial polyamine and the epoxide, solids contents above 50 weight percent can be applied successfully. 
     Gas barrier coating composition of the present invention can further include other additives known to those skilled in the art. Some of the more common additives which can be present include: pigments, silicones, surfactants, and/or catalysts for coating compositions which involve an epoxy-amine reaction. Each of these specific optional components will be discussed below. 
     With regard to the use of pigments, in addition to imparting color and/or tint to the gas barrier material, their use can also even further reduce the amount of gas that permeates there through. If employed, the weight ratio of pigment to binder is typically not more than about 1:1, preferably not more than about 0.3:1, and more preferably not more than about 0.1:1. The binder weight used in these ratios is the total solids weight of the polyamine-polyepoxide resin in the gas barrier coating composition. 
     With regard to the use of silicones, they may be included in the gas barrier coating composition to assist in wetting the substrate over which the barrier material will be applied. Generally, silicones which can be used for this purpose include various organosiloxanes such as polydimethylsiloxane, polymethylphenylsiloxane and the like. Specific examples of such include: SF-1023 silicone (a polymethylphenylsiloxane available from General Electric Co.), AF-70 silicone (a polydimethylsiloxane available from General Electric Co.), and DF-100 S silicone (a polydimethylsiloxane available from Mazer Chemicals, a division of PPG Industries, Inc.). If employed, such silicones are typically added to the gas barrier coating composition in amounts ranging from about 0.01 to about 1.0 percent by weight based on total resin solids in the gas barrier coating composition. 
     With regard to the use of surfactants, they are typically included in the aqueous-based versions of the gas barrier coating composition. Examples of surfactants that can be used for this purpose include any suitable nonionic or anionic surfactant. If employed, such surfactants are typically present in an amount ranging from about 0.01 to about 1.0 percent by weight based on the total weight of the gas barrier coating composition. 
     With regard to the use of catalysts, they may be included in the gas barrier coating composition to aid in the reaction between polyamine (A) and polyepoxide (B). Generally, any suitable catalyst that is used for epoxy-amine reactants can be employed when practicing this invention. Examples of such suitable catalysts include: dihydroxy aromatics (e.g., resorcinol), triphenyl phosphite, calcium nitrate and the like. 
     Typically, when applying the gas barrier coating composition to a substrate, the components of an gas barrier coating composition (i.e., polyamine (A), polyepoxide (B) and filler (C)) are first thoroughly mixed together. After mixing, the gas barrier coating composition can be immediately applied to the substrate, or held for a period of time typically ranging from about 1 minutes to about 60 minutes prior to application to improve cure and/or clarity. This holding time can be reduced and/or eliminated when the initial polyamine is a pre-reacted adduct or when the solvent employed is 2-butoxyethanol. 
     When practicing this invention, the gas barrier coating composition can be applied by any conventional means known to those skilled in the art (e.g., spraying, rolling, dipping, brushing and the like). Preferred methods of application include spray and/or dipping processes. 
     After application of the gas barrier coating composition, it may be cured at temperatures as low as ambient temperature by allowing for a gradual cure over several hours to several days. However, such low temperature curing is generally slower than desired for commercial production lines. It is also not an efficient means of removing solvent from the cured barrier material. Therefore, in one preferred embodiment, the oxygen barrier material is cured by heating it at elevated temperatures as high as possible without distorting the substrate over which it is applied. 
     For a relatively &#34;slow&#34; solvent (i.e., a solvent having a relatively low evaporation rate), curing temperatures typically range from about 55° C. to about 110° C., and preferably from about 70° C. to about 95° C. At such curing temperatures, curing times will typically range from about 1 minute to about 60 minutes. 
     For a relatively &#34;fast&#34; solvent (i.e., a solvent having relatively high evaporation rate), curing temperatures typically range from about 35° C. to about 70° C., and preferably from about 45° C. to about 65° C. At such curing temperatures, curing times will typically range from about 0.5 minute to about 30 minutes. 
     The cured gas barrier coatings of the present invention can have any suitable dry film thickness. Although thicker coatings typically provide greater gas protection, the packaging industry typically prefers thinner coating for economic reasons. As such, the cured gas barrier coatings of this invention generally have a dry film thickness of not more than about 1.0 mil (25.4 microns). If even thinner films are desired, the cured gas barrier coating of the present invention can have a dry film thickness of not more than about 0.5 mil (12.7 microns), and even of not more than about 0.3 mil (7.6 microns). 
     In addition to having OPC values of not more than 0.05, the cured gas barrier coatings of this invention are also relatively smooth, transparent and glossy. Specifically, the cured gas barrier coatings prepared in accordance with this invention have a 20° gloss of at least 60% reflected light. Preferably, the cured gas barrier coatings have a 20° gloss of at least 70% reflected light, and more preferably of at least 80% reflected light. 
     The gas barrier coating composition may be applied over a substrate as a single layer or as multiple layers with multiple heating stages to remove solvent from each subsequent layer. Both are referred to herein as &#34;multilayer&#34; packaging materials. 
     The present invention also provides a multilayer packaging material which has improved gas barrier properties. The multilayer packaging material of the present invention includes at least one layer of a substrate material and at least one layer of a gas barrier material which is the filler-containing, cured reaction product of polyamine (A) and polyepoxide (B) as described above. 
     When making a multilayer packaging material in accordance with this invention, the gas barrier coating composition of the present invention can be applied over any suitable substrate. Typically, however, it is applied over a gas-permeable substrate, and more typically, it is applied over a polymeric, gas-permeable packaging material. 
     Gas-permeable materials over which the gas barrier coating composition can be applied typically include any suitable polymeric material through which gases can pass and which can be used as a packaging material. Examples of such suitable gas-permeable materials which can be used in the packaging of food, beverages, chemicals, medicines, medical supplies, and the like include: polyesters, polyolefins, polyamides, cellulosics, polystyrenes, and polyacrylics, and the like. Due to their physical properties, the preferred polymeric packaging materials for use in making food and beverage containers for such types of oxygen-sensitive products typically include a polyester. Examples of polyesters which can be used for this purpose include: PET, poly(ethylene napthalate) (&#34;PEN&#34;), and/or combinations thereof. 
     In one embodiment of a multilayer packaging material encompassed by the present invention, a laminate is formed which includes a layer of the gas barrier material. Here, the gas barrier material is applied onto a first layer of a suitable substrate material. Thereafter, a second layer of a similar or dissimilar substrate material is applied over the layer of the gas barrier material to form a laminate. 
     In embodiments of the present invention wherein a polyolefin (e.g., polypropylene) is the gas-permeable packaging material, the surface of the polyolefin is preferably treated to increase surface tension and promote better adhesion of the oxygen barrier material to the polyolefin material. Examples of treating techniques which can be used for this purpose include: flame-treating, corona-treating and the like. 
     Specific examples of such treating techniques are described in detail by Pinner et al. in Plastics: Surface and Finish, Butterworth &amp; Co. Ltd. (1971), Chapter 3. The description of the surface treatments described in Pinner et al is herein incorporated by reference. 
     In another embodiment of a multilayer packaging material encompassed by the present invention, a sheet or film stock, which is subsequently formed into containers by conventional plastic processing techniques, is coated with the gas barrier coating composition disclosed herein. Thereafter, the coated film or sheet is formed into articles such as: wrappers, bags, containers and the like. 
     In still another embodiment of a multilayer packaging material encompassed by the present invention, pre-formed containers (e.g., malt beverage bottles), are coated with at least one layer of the gas barrier coating composition disclosed herein. 
     The multilayer packaging materials of the present invention are ideally suited for packaging of food, beverages, chemicals, medicines, medical supplies, and the like. Their very low OPC values make them especially suited for packaging malt beverages such as beer and ale. 
     Specifically, the malt beverage industry has established very strict quality standards for small beverage containers (e.g., 12 ounce (355 milliliter) bottles made out of PET having an average wall thickness of 15 mils (381 microns)). Specifically, according to this shelf-life standard typically, not more than 5 ppm of oxygen should pass through the walls of the sealed container over a 90-day storage period at ambient temperatures and 50% R.H. Parts per million of oxygen is based upon the weight of oxygen to the weight of the beverage (1 cubic centimeter of oxygen weighs 0.0014 gram). For example, one cubic centimeter of oxygen in 12 ounces of beverage would be 4.0 ppm ((0.0014 grams per cubic centimeter of oxygen/355 cubic centimeters in a 12 ounce bottle)×10 6 ). Preferred levels of performance for the malt beverage industry would entail that, over the 90-day storage period at ambient temperatures and 50% R.H., not more than 4 ppm oxygen, more preferably not more than 3 ppm oxygen, and even more preferably not more than 2 ppm of oxygen pass through the walls of the sealed container. In order to meet these desired objectives, the cured gas barrier coating layer of a multilayer packaging material should have an OPC value of not more than 0.05, preferably, not more than 0.04, more preferably not more than 0.03, and even more preferably not more than 0.02. As stated above and demonstrated in the examples which follow, the gas barrier coatings of this invention meet these strict standards. 
     As used herein, desired OPC values are calculated by Equation (A): 
     
         t=O.sub.i (3a).sup.-1 (L.sub.1 /P.sub.1 +L.sub.2 /P.sub.2 +. . . +L.sub.n /P.sub.n)                                                 (A) 
    
     where: 
     t=desired storage time in days; 
     O i  =desired maximum level of oxygen ingress through the walls of a sealed multilayer container, in ppm; 
     a=ratio of exterior surface area of the multilayer container, in square inches, to internal volume ratio of the container, in cubic centimeters; 
     L=average thickness of each layer of the multilayer container, in mils; and 
     P=OPC value of each individual layer of the multilayer container. 
     For example, if a 0.3 mil (7.6 micron) thick gas barrier coating is to be coated over a typical 12 ounce (355 milliliter) beverage bottle made out of PET, and if it is desired that not more than 5 ppm of oxygen permeate through the walls of the sealed, coated bottle after 90 days of storage at 30° C. and 50% R.H., the necessary minimum OPC value of the gas barrier coating to achieve this desired result can be calculated by using Equation A. Specifically, in this example, a typical 12 ounce (355 milliliter) beverage bottle made out of PET has an internal volume of 355 cubic centimeters, a surface area of 49 square inches (35.6 square centimeters) and an average wall thickness of 15 mils (381 microns). Moreover, uncoated PET has an OPC value of 6.0. When plugging this data into Equation A: t is 90 days; O i  is 5 ppm; a is 49 square inches/355 cubic centimeters; L 1  is 15 mils; L 2  is 0.3 mil; and P 1  is 6.0. Accordingly, solving Equation A for P 2  (i.e., the OPC value for the gas barrier coating needed to achieve the desired result at 30° C. and 50% R.H.) yields 0.06. 
     It has been observed that OPC values of gas barrier coatings made in accordance with this invention can be even further improved by treating them with carbon dioxide (CO 2 ). If it is desired to even further lower the OPC value of the gas barrier coatings of this invention, this can be achieved by treating them with CO 2 . The CO 2  treatment, if used, typically occurs after the coatings have been applied over a substrate. The extent of CO 2  treatment necessary for the gas barrier coating to obtain the desired OPC value depends upon the duration, temperature and CO 2  pressure during the CO 2  treatment process. 
     In one embodiment of treating a gas barrier coating of this invention with CO 2 , the gas barrier coating is applied over a packaging material. Thereafter, the coating is exposed to a CO 2  atmosphere at an elevated pressure and temperature. During such a treatment process, CO 2  pressures typically range from about 30 to about 1,000 pounds per square inch (about 2 bar to about 70 bar); treatment temperatures typically range from about 32° F. (0° C.) to about 200° F. (93° C.); and treatment duration typically ranges from about 1 minute to about 6 weeks. Preferably, during the treatment process CO 2  pressures range from about 30 to about 100 pounds per square inch (about 2 bar to about 7 bar); treatment temperatures range from about 40° F. (14° C.) to about 150° F. (65° C.); and treatment duration is typically range from about 1 hour to about 3 weeks. 
     In another embodiment of treating a gas barrier coating of this invention with CO 2 , the gas barrier coating is applied over a gas-permeable packaging material in the form of a sealable container. Thereafter, the container is at least partially filled with a carbonated beverage and sealed. Since the packaging material is gas-permeable, CO 2  can pass there through. As such, the carbonated beverage is being used as the CO 2  treating medium. In this embodiment of treating a gas barrier coating of this invention with CO 2 , the gas-permeable material should have an OPC value greater than about 0.5. 
     The multilayer packaging materials of the present invention are ideally suited for packaging of food, beverages, chemicals, medicines, medical supplies, and the like. However, their very low OPC values makes them especially suited for packaging malt beverages. 
     It is known that malt beverages are not stable in light with wavelengths of electromagnetic radiation ranging from 300 nanometers (nm) to 500 nm (hereinafter referred to as &#34;product damaging light&#34;). It is also known that brown or dark amber-tinted glass substantially blocks most of this product damaging light. As used herein, the term &#34;substantially blocks&#34; means that less than about 10%, preferably less than about 7%, more preferably less than about 5% and even more preferably less than about 3% of this product damaging light passes therethrough. Accordingly, if the multilayer packaging materials of the present invention are used for packaging malt beverages, the gas barrier coating and/or the gas-permeable substrate should be tinted so as to substantially block the transmission of this product damaging light. 
     If the gas-permeable material is tinted so as to substantially block product damaging light, this can be done by any suitable means known to those in the art. However, from a recycling standpoint, it is undesirable to recycle tinted plastics since this often requires manual sorting. It would greatly reduce recycling time and costs if all of the plastic being recycled was clear and un-tinted. Accordingly, since the gas barrier coating of this invention are easily removable by a recycler, the use of a tinted gas barrier coating over an un-tinted gas-permeable polymeric material is preferred. 
     When tinting the gas barrier coating so as to substantially block the aforementioned product damaging light, the weight ratio of pigment to binder is typically not more than about 1:1, preferably not more than about 0.3:1, and more preferably not more than about 0.1:1. The binder weight used in these ratios is the total solids weight of the polyamine-polyepoxide resin in the gas barrier coating. 
     The pigments typically used in tinting gas barrier coatings for use in multilayer packaging materials for the malt beverage industry can be any suitable particulate pigment and/or dye which has the following properties: it substantially blocks the aforementioned product damaging light; it results in a glossy, transparent gas barrier coating; and it does not significantly adversely affect the gas barrier properties of the resulting gas barrier coating. Examples of dyes which can be used for this purpose include brown dyes, amber dyes and/or a blend of red and yellow dyes. Examples of pigments which can be used for this purpose include brown pigments, amber pigments and/or a blend of red and yellow pigments. Preferably, pigments are used since they typically improve the OPC value of the resulting tinted coating. A preferred pigment is iron oxide since it imparts a dark amber color which closely matches the color of most conventional glass beer bottles. 
    
    
     EXAMPLES 
     The present invention is more particularly described in the following examples which are intended as illustration only and are not intended to limit the scope thereof. Unless otherwise indicated, all weight percentages are based upon the total weight of the resin solids of the gas barrier coating composition. Filler equivalent particle size measurements set out in TABLE 1 were performed with a HORIBA LA-900 laser scattering particle size distribution analyzer. 
     SAMPLE PREPARATION FOR DETERMINING PARTICLE SIZE DISTRIBUTION 
     The preparation of samples for determining particle size distribution by the HORIBA LA-900 laser scattering particle size distribution analyzer was as follows: 1 to 2 grams of the particular platelet-type filler was added to a beaker containing 10 to 15 milliliters of 1-methoxy-2 propanol which was used as the dispersing agent for all samples. This mixture was then stirred vigorously for approximately 1 minute to form a dispersion. Thereafter, the beaker containing the dispersion was placed in an ultrasonic bath for approximately 1 minute to disperse any air trapped between the particles and dispersing agent. 
     The HORIBA LA-900 laser scattering particle size distribution analyzer was then calibrated by filling a fraction cell supplied with the apparatus with 1-methoxy-2 propanol, placing the filled fraction cell in the appropriate analyzing chamber of the HORIBA LA-900 laser scattering particle size distribution analyzer, and analyzing the sample. Thereafter, an identical fraction cell used to calibrate the machine was filled with a sample of the dispersion containing the platelet-type filler. The fraction cell was then placed in the appropriate analyzing chamber of the HORIBA LA-900 laser scattering particle size distribution analyzer and analyzed. The analyzing chamber is equipped with an ultrasonic bath which is designed the keep the dispersed particles in motion during their analysis. The results of this analysis are set out in TABLE 1. 
     
                                           TABLE 1                                 
__________________________________________________________________________
          Example in                                                      
                No. Mean                                                  
                     Vol. Mean                                            
                          Number Percent                                  
                                  Number Percent                          
Platelet- Which Particle                                                  
                     Particle                                             
                          of Particles                                    
                                  of Particles                            
Type      Filler Was                                                      
                Diameter                                                  
                     Diameter                                             
                          Greater Than 7                                  
                                  Greater Than 30                         
Filler    Used  (Microns)                                                 
                     (Microns)                                            
                          Microns Microns                                 
__________________________________________________________________________
Magna Pearl 2000.sup.1                                                    
          I/II  9.3  13.3 92      0.5                                     
Mica M RP.sup.2                                                           
          III/IV                                                          
                9.8  14.6 95      1.5                                     
Mearl Mica SVA.sup.3                                                      
          V/VI  10.7 16.8 98      4.0                                     
EM Fine Mica.sup.2                                                        
          VII/VIII                                                        
                11.6 18.7 98      2.5                                     
Afflair 110.sup.4                                                         
          IX/X  6.1  8.5  65      0                                       
Magna Pearl 3000.sup.1                                                    
          XI/XII                                                          
                5.8  8.0  55      0                                       
Miro-Mica C-4000.sup.5                                                    
          XIII/XIV                                                        
                11.2 27.6 98      35                                      
WG 325.sup.5                                                              
          XV/XVI                                                          
                9.8  68.2 90      22                                      
ASP-NC.sup.6                                                              
          XVII/XVIII                                                      
                3.4  7.8  50      0                                       
Micro Talc MP12-52.sup.7                                                  
          XIX/XX                                                          
                3.7  7.3  65      0.5                                     
__________________________________________________________________________
 .sup.1 White pearlescent muscovite mica coated with TiO.sub.2 available  
 from Mearl Corp.                                                         
 .sup.2 Gray powder muscovite mica filler from EM Industries, Inc.        
 .sup.3 White waterground muscovite mica treated with lauroyl lysine      
 available from Mearl Corp.                                               
 .sup.4 White pearlescent muscovite mica coated with TiO.sub.2 available  
 from EM Industries, Inc.                                                 
 .sup.5 Muscovite mica filler available from KMG Minerals, Inc.           
 .sup.6 Aluminum silica clay available from Engelhard Corp.               
 .sup.7 Platy Montana talc available from Pfizer Minerals, Pigments &amp;     
 Metals.                                                                  
 
    
     EXAMPLES I-XXI 
     Examples I through XX are gas barrier coating compositions containing fillers, and Example XXI is a gas barrier coating composition which does not contain a filler. Examples I through XII demonstrate gas barrier coating compositions encompassed by this invention, while Examples XII through XXI are provided for comparison. A comparison of Examples I through XII with Examples XIII through XXI demonstrates the importance of selecting a platelet-type filler having particle size distribution within the scope of the present invention. 
     For each of Examples I-XX, filler pastes were prepared by slowly sifting and blending 34.0 weight percent of one of the dry fillers set out in TABLE 1 into a liquid resin mixture consisting of: 33.0 weight percent of GASKAMINE® 328S (the reaction product of MXDA and epichlorohydrin with any excess MXDA stripped therefrom, commercially available from Mitsubishi Gas Chemical Co.), and 33.0 weight percent of 1-methoxy-2-propanol (commercially available from Dow Chemical Co. as DOWANOL® PM solvent). Each of the blends were then subjected to high speed Cowles mixing until a smooth, uniform paste was formed (i.e., 15 to 30 minutes). 
     Filler-containing gas barrier coatings were then prepared containing 10% filler and 20% filler for each of the fillers in TABLE 1 using the filler pastes made above. These percentages are based upon the total solids weight of all the ingredients in the filler-containing gas barrier coating. 
     The filler-containing gas barrier coatings containing 10% filler were prepared by blending together the following ingredients: 11.6 weight percent of GASKAMINE® 328S, 8.4 weight percent of N,N,N&#39;,N&#39;-tetrakis (oxiranylmethyl)-1,3-benzene dimethanamine (commercially available from Mitsubishi Gas Chemical Co. as TETRAD-X epoxy resin), 68.1 weight of DOWANOL® PM solvent, 7.3 weight percent of the filler paste prepared above, 4.5 weight percent of ethyl acetate, and 0.1 weight percent of SF-1023 silicone (a polymethylphenylsiloxane commercially from General Electric Co.). 
     The filler-containing gas barrier coatings containing 20% filler were prepared by blending together the following ingredients: 7.7 weight percent of GASKAMINE® 328S, 7.5 weight percent of TETRAD-X epoxy resin, 66.3 weight of DOWANOL® PM solvent, 14.4 weight percent of the appropriate filler paste prepared above, 4.0 weight percent of ethyl acetate, and 0.1 weight percent of SF-1023 silicone. 
     For Example XXI, a barrier coating composition which did not contain any filler was prepared by blending together the following ingredients: 17.7 weight percent GASKAMINE® 328S, 10.6 weight percent of TETRAD-X epoxy resin, 64.7 weight percent of DOWANOL® PM solvent, 5.7 weight percent of ethyl acetate, 1.2 weight percent of deionized water, and 0.1 weight percent of SF-1023 silicone. 
     All of the resulting gas barrier coating compositions were allowed to stand for about 15 minutes prior to use. Thereafter, each coating composition was spray applied to samples of a 2-mil thick PET film and baked for about 30 minutes at 145° F. (63° C.) to produce a dry coating having a thickness ranging from of 0.3 to 0.5 mil. All of the coated films were allowed to age for four days at 70° F. (21° C.) and 50% R.H. prior to testing. 
     TESTING OF COATING SAMPLES 
     Oxygen transmission rates were measured using an OXTRAN 20/20 at 30° C. and 50-55% R.H. and at 30° C. and 70-75% R.H.. OPC values of the gas barrier layer for each of the coated samples were then calculated by using the following equation: 
     
         1/R.sub.1 =1/R.sub.2 +DFT/PO.sub.2 
    
     where: 
     R 1  =coated PET transmission rate in cc/100 in 2  /atmosphere/day; 
     R 2  =PET film transmission rate in cc/100 in 2  /atmosphere/day; 
     DFT=coating dry film thickness in mils; and 
     PO 2  =OPC value of coating in cc-mil/100 in 2  /atmosphere/day. 
     The gloss of each of the coating samples was measured at an angle of 20° using a Gardner Glossgard IIa 20° Glossmeter from Gardner Instruments. Roughness and clarity of the coating was determined by a visual rating on a scale of 0 to 10, with 0 being very smooth and clear and 10 being extremely rough and hazy. The results of these tests are set out in TABLE 2. 
     
                                           TABLE 2                                 
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                                Oxygen Permeability Constant of           
                                the Gas Barrier Material Layer            
     Filler       Roughness                                               
                       20° Gloss                                   
                                at 50-55%                                 
                                       at 70-75%                          
Example                                                                   
     (Wt. % - Type)                                                       
                  Index                                                   
                       (% Reflected Light)                                
                                R.H.   R.H.                               
__________________________________________________________________________
I    10% - Magna Pearl 2000                                               
                  0    94       0.061  0.11                               
II   20% - Magna Pearl 2000                                               
                  0    74       0.025  0.05                               
III  10% - Mica M RP                                                      
                  0    84       0.049  0.22                               
IV   20% - Mica M RP                                                      
                  0    83       0.017  0.11                               
V    10% - Mearl Mica SVA                                                 
                  1    83       0.044  0.16                               
VI   20% - Mearl Mica SVA                                                 
                  2    91       0.030  0.09                               
VII  10% - EM Fine Mica                                                   
                  1    87       0.042  0.19                               
VIII 20% - EM Fine Mica                                                   
                  2    63       0.033  0.07                               
IX   10% - Afflair 110                                                    
                  1    74       0.039  0.11                               
X    20% - Afflair 110                                                    
                  1    66       0.029  0.08                               
XI   10% - Magna Pearl 3000                                               
                  0    98       0.085  0.17                               
XII  20% - Magna Pearl 3000                                               
                  0    94       0.045  0.1                                
XIII 10% - C-4000 5    34       0.043  0.12                               
XIV  20% - C-4000 8    2        0.038  0.08                               
XV   10% - WG 325 10   5        0.052  0.19                               
XVI  20% - WG 325 10   1        0.037  0.09                               
XVII 10% - ASP-NC 2    78       0.052  0.13                               
XVIII                                                                     
     20% - ASP-NC 4    53       0.038  0.09                               
XIX  10% - Micro Talc MP-12-52                                            
                  4    53       0.063  0.14                               
XX   20% - Micro Talc MP-12-52                                            
                  5    23       0.076  0.16                               
XXI  None         0    100      0.085  0.27                               
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     As can be seen from the data in TABLE 2, the filler-containing gas barrier coatings of Examples XII-XVI and XVIII-XX were rough and hazy (i.e., each had a roughness index of greater than 4) and had a 20° gloss of less than 60 percent reflected light. Moreover, the filler-containing gas barrier coatings of Examples XVII, XIX-XXI each had an OPC value, at 50%-55% R.H. and 30° C., of greater than 0.05. Accordingly, the use of platelet-type fillers having a particle size distribution of those used in Examples XIII through XX did not result in a gas barrier coating which had a 20° gloss of at least 60 percent reflected light as well as an OPC value, at 50%-55% R.H. and 30° C., of not more than 0.05. 
     Although the fillers used in Examples I and XI had a particle size distribution that resulted in gas barrier coatings which had an OPC value, at 50%-55% R.H. and 30° C., of greater than 0.05, this only occurred when the amount of filler employed was 10 weight percent. However, when these fillers were present in an amount greater than 10 weight percent (e.g., Examples II and XII), they had an OPC value, at 50%-55% R.H. and 30° C., of not more than 0.05. Accordingly, the use of platelet-type fillers having a particle size distribution as those employed in Examples I/II and XI/XII (e.g., those which have a number mean particle diameter in the range from about 5.5 to less than 9.5 microns, and/or a volume mean particle diameter in the range from about 8 to less than 14 microns), are within the scope of this invention when present in an amount of greater than 10 weight percent. 
     The fillers used in Examples III and X had a particle size distribution which resulted in gas barrier coatings which had an OPC value, at 50%-55% R.H. and 30° C., of greater than 0.050 and a 20° gloss of at least 60% reflected light. Accordingly, the use of platelet-type fillers having a particle size distribution as those employed in Examples III thorough X is within the scope of the present invention regardless of whether they were present in an amount of 10 or 20 weight percent. 
     It is evident from the foregoing that various modifications, which are apparent to those skilled in the art, can be made to the embodiments of this invention without departing from the spirit or scope thereof. Having thus described the invention, it is claimed as follows.