In the food packaging and similar industries flexible films with barrier properties are used in large amounts to resist the transmission of water vapor and oxygen through the film. These barrier films typically have a base layer of a structurally strong material which is not very resistant to water vapor and oxygen transmission. Such films generally also include a barrier layer of a more water vapor and oxygen transmission resistant material.
Conventional barrier layers have a matrix phase of composition having an intrinsically high transmission resistance. To increase transmission resistance properties, a phase of discrete, fine particles are dispersed in the matrix phase. The dispersed phase particles are inorganic composition, such as clay, kaolin, vermiculite, silicates, and the like. It is generally understood that the dispersed phase particles are not particularly non-transmissive to water vapor and oxygen in and of themselves. However, they function to improve overall barrier film transmission resistance by providing discontinuities in the matrix and thus blocking the direct path of water and/or oxygen molecules migrating directly across the film. This causes such migrating molecules to take a tortuous, longer path which slows their flow from one side of the film to the other.
Use of inorganic particles in barrier films has certain drawbacks. Of some concern is an adverse effect observed in the process of making barrier films with an inorganic particle dispersed phase. The matrix phase is quite often a crosslinked polymeric composition of an intrinsically transmission resistant component. Polyvinyl alcohol (PVOH) and ethylene vinyl alcohol copolymer (EVOH) are preferred polymers. Usually the inorganic particles are dispersed in a liquid coating solution that is deposited onto the base layer and dried to form the barrier layer, A preferred solvent is water. A thermally activated crosslinking agent can be included to promote the crosslink reaction of the polymers which are dissolved substantially uncrosslinked in the solvent.
A problem arises when the inorganic particles are dispersed in the polymer matrix. A sharp rise in viscosity occurs at very low inorganic particle concentrations due to ionic charges that are inherent in inorganic mineral particles such as mica and vermiculite. This significant viscosity increase inhibits handling of the solution and the formation of a uniform and desirably thin barrier layer. High viscosity is particularly problematic when coating the wet barrier layer composition onto the base layer with gravure coating technology. There is a need to provide an effective moisture vapor and oxygen barrier transmission resistant coating and barrier film that does not suffer from excessive viscosity buildup using existing production equipment and process techniques.
U.S. Pat. No. 7,737,200 relates to a stable, aqueous barrier composition which comprises prolamine; cold water insoluble polymer; water; water-soluble co-solvent; and stabilizer. The composition, when applied to a substrate, produces an article having a high surface energy and resistance to oil and grease penetration.
U.S. Pat. No. 7,521,103 discloses a coating comprised of a first polymer reacted with a second polymer optionally using a crosslinker. For example, the first polymer may comprise a copolymer of polyvinyl alcohol and a vinylamine. The second polymer may comprise a copolymer of a maleic acid and an acrylic acid. The coating is present on the polymer film in an amount sufficient to increase the oxygen barrier properties of the film.
U.S. Pat. No. 7,501,471 describes a blend comprising a poly(vinyl alcohol) stabilized vinyl acetate-ethylene polymer emulsion and a paraffin wax emulsion. A dried coating of the blend on a substrate has a hydrostatic head barrier sufficient to prevent passage of fluids but allows passage of water vapor through it. The vinyl acetate-ethylene polymer emulsion comprises a polymer containing 70 to 95 wt % vinyl acetate and 5 to 30 wt % ethylene, based on the total weight of monomers in the polymer. The paraffin wax in the paraffin wax emulsion has an average particle size of at least 0.3 microns.
U.S. Pat. No. 7,473,729 describes an article comprising an acrylic nanocomposite film adhered to a substrate. The acrylic nanocomposite film comprises (a) a non-elastomeric acrylic polymer; and (b) an acid-treated, layered silicate filler material which has an aspect ratio of at least about 25.
U.S. Pat. No. 7,303,797 discloses a coating layer for increasing the gas barrier performance of rigid shaped containers and films. The coating layer includes a water-borne composition comprising a water-soluble or water dispersible organic binder in the optional presence of a cross-linking agent. The organic binder includes from 10% up to less than 90% by weight, based on the dry weight of the coating layer, of an inorganic laminar mineral selected from montmorillonite, laponite, organo-modified montmorillonite and mixtures thereof.
U.S. Pat. No. 5,981,029 describes a gas barrier film with a barrier coating. The film that provides high gas barrier ability at high humidity and under elongation, and also has durability of gas barrierability, and also with adhesiveness and post-lamination gas barrierability. The film is suggested for packaging material highly reliable in preservability. The barrier coating has inorganic stratified particles that may be provided by inorganic particles formed by overlapping one to several very thin unit crystal layers. Among them, especially, a clay is preferably used.