Microporous sheets with barrier coatings
Microporous sheets coated with barrier coatings are disclosed.
This application claims priority to provisional application Ser. No. 60/550,491, filed Mar. 5, 2004.
FIELD OF THE INVENTIONThe present invention relates to microporous sheets having a barrier coating.
BACKGROUND INFORMATIONMicroporous sheets can comprise a matrix of thermoplastic organic polymer with interconnecting pores and optional filler particles. Examples of microporous sheets comprising polyethylene and silica filler particles are sold under the designation TESLIN by PPG Industries, Inc. Microporous sheets are useful in many applications such as cards, tags, labels, menus, in-mold graphics, commercial printing and specialty printing.
Conventional microporous sheets are typically gas permeable. Microporous sheets with improved gas barrier properties are desired for various applications such as printed labels and packaging materials. Other barrier properties are also desired.
SUMMARY OF THE INVENTIONThe present invention provides a coated microporous sheet comprising a microporous sheet and a barrier coating over at least a portion of the microporous sheet. The coated microporous sheets are flexible and possess desirable barrier properties. The present invention further provides a method of coating a microporous sheet, comprising applying a gas barrier coating composition to at least a portion of the microporous sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention provides microporous sheets coated over at least a portion with a barrier coating. The coated sheets can be flexible and/or elastic, generally have good printability, and/or provide desirable barrier properties.
As used herein, “barrier coating” refers to a coating that imparts vapor barrier, gas barrier and/or chemical barrier to a substrate. “Vapor barrier” refers to a barrier and/or low permeability to liquid and/or its vapor. “Gas barrier” refers to a barrier and/or low permeability to oxygen, nitrogen, carbon dioxide and other gases. “Chemical barrier” refers to a barrier and/or low permeability to the migration of a molecule from one substrate to another, and/or from within one substrate to its surface. Any resistance to permeation of vapor, gas and/or chemical(s) is sufficient to qualify the coating as a “barrier coating” according to the present invention. The gas barrier properties of a substrate, and any coatings thereon, are typically described in terms of the oxygen permeability constant (“P(O2)”). The “P(O2)” number quantifies the amount of oxygen that can pass through a substrate and/or coating under a specific set of circumstances and is generally expressed in units of cm3-mil/100 inches2/atmosphere/day. This is a standard unit of permeation measured as cubic centimeters of oxygen permeating through one mil (25.4 micron) thickness of a sample, 100 square inches (654 square centimeters) in an area, over a 24-hour period, under a partial pressure differential of one atmosphere at a specific temperature and relative humidity (R.H.) conditions.
The barrier coatings used according to the present invention may possess a permeability co-efficient P(O2) of less than 2 or 3 cm3-mil/100 inches2/atmosphere/day. In certain nonlimiting embodiments, the barrier coatings have a P(O2) of less than 1, or even less than 0.6, or less than 0.1 cm3-mil/100 inches2/atmosphere/day. In certain nonlimiting embodiments, the present barrier coatings, when applied to microporous sheets, reduce the permeance of the sheet by at least 10 times, by at least 100 times, or in some nonlimiting embodiments by at least 1,000 times, as compared with the permeance of the uncoated microporous sheet.
The barrier coating 20, when cured on the microporous sheet, may have a dry film thickness of from about 1 to about 50 microns, such as from about 5 or 10 microns to about 20 or 25 microns.
The barrier coating compositions may comprise resins such as polyurethanes, polyureas, polyamides, polyvinylidene chlorides epoxy amines, poly(meth)acrylates, polyvinyl ethers, polyvinyl alcohols, polyesters and the like, and combinations thereof. Any resin that forms a suitable polymeric barrier film can be used in accordance with the present invention, absent compatibility problems. In certain nonlimiting embodiments, polyurethane resins may be used, including those prepared using polyester diol(s) and/or aromatic diol(s).
In certain nonlimiting embodiments the barrier coating comprises a polyurethane comprising at least 30 weight percent of meta-substituted aromatic material. The weight percent is based on the total solid weight of the resin. The meta-substituted aromatic material can be introduced through components of the polyurethane pre-polymer, or through chain extenders reacted with the polyurethane pre-polymer. In certain embodiments, the polyurethane can comprise 50 weight percent or higher of meta-substituted aromatic material, such as 60 weight percent or higher. “Polyurethane” as used herein refers to compounds having urethane linkages and/or urea linkages.
In one embodiment of the present invention, the polyurethane comprises a polyester polyol. In another embodiment of the present invention, the polyester polyol has a Molar Permachor Number of at least 35, such as 39 or higher. “Molar Permachor Number” and like terms refer to the number calculated from the chemical structure of the polymer; each atom or group of atoms in side chains or the backbone has a value from the Master Table of Segmental Permachor Values, which Table can be found, for example, in “Properties of Polymers” by D. W. Van Krevelan, 3rd Ed., Elsevier, (1990). The values are then used to get the Permachor Number, according to methods known to those skilled in the art, which are also discussed in “The Use of Barrier Polymers in Packaging” by Morris Salame, Polysultants Co.
In certain nonlimiting embodiments of the invention, the polyester polyol Molar Permachor Number of at least 35 is achieved by preparing a polyester polyol from a polyol comprising an ether moiety and a carboxylic acid or anhydride. Suitable ether polyols include, for example, diethylene glycol, ethylene glycol and lower oligomers of ethylene glycol including diethylene glycol, triethylene glycol and tetraethylene glycol; propylene glycol and lower oligomers of propylene glycol including dipropylene glycol, tripropylene glycol and tetrapropylene glycol; also poly(tetrahydrofuran). Suitable dicarboxylic acids include but are not limited to glutaric acid, succinic acid, malonic acid, oxalic acid, phthalic acid, isophthalic acid, hexahydrophthalic acid, adipic acid, maleic acid, and mixtures thereof. Anhydrides of these and any other carboxylic acids can also be used. In certain nonlimiting embodiments, the polyester polyol has greater than eight carbon atoms.
The polyester polyol can be prepared according to any method known in the art. For example, the polyol and carboxylic acid/anhydride can be heated together while removing the water generated by esterification until a desired acid number is achieved.
The polyester polyol can then be reacted with isocyanate to form a polyurethane. The polyurethane can be formed according to any method known in the art, such as by heating the polyol with an isocyanate until a desired NCO equivalent weight is achieved. Any isocyanate can be used according to the present invention; examples include, but are not limited to, isophorone diisocyanate (IPDI), dicyclohexylmethane 4,4′-diisocyanate (H12MDI), cyclohexyl diisocyanate (CHDI), m-tetramethylxylylene diisocyanate (m-TMXDI), p-tetramethylxylylene diisocyanate (p-TMXDI), ethylene diisocyanate, 1,2-diisocyanatopropane, 1,3-diisocyanatopropane, 1,6-diisocyanatohexane (hexamethylene diisocyanate or HDI), 1,4-butylene diisocyanate, lysine diisocyanate, 1,4-methylene bis-(cyclohexyl isocyanate), toluene diisocyanate (TDI), m-xylylenediisocyanate (MXDI) and p-xylylenediisocyanate, 4-chloro-1,3-phenylene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, 4,4′-dibenzyl diisocyanate, and 1,2,4-benzene triisocyanate, xylylene diisocyanate (XDI), and combinations thereof.
The polyurethane can then be chain extended to build molecular weight using, for example, any chain extension agent having more than one reactive functional group. Examples include polyols, polyamines, polythiols, or other compounds having reactive functional groups, such as hydroxy groups, thiol groups, amine groups, carboxylic acids, and acetylacetonate protons. Suitable polyol chain extenders include, but are not limited to: 1,6-hexanediol; cyclohexanedimethanol; 2-ethyl-1,6-hexanediol; 1,4-butanediol; ethylene glycol and lower oligomers of ethylene glycol including diethylene glycol, triethylene glycol and tetraethylene glycol; propylene glycol and lower oligomers of propylene glycol including dipropylene glycol, tripropylene glycol and tetrapropylene glycol; 1,3-propanediol; 1,4-butanediol; neopentyl glycol; dihydroxyalkylated aromatic compounds such as the bis (2-hydroxyethyl) ethers of hydroquinone and resorcinol (HER); p-xylene-α, α′-diol; the bis (2-hydroxyethyl) ether of p-xylene-α, α′-diol; m-xylene-α, α′-diol and the bis (2-hydroxyethyl) ether, trimethylol propane, 1,2,6-hexantriol, glycerol, and mixtures thereof. Suitable polyamine extenders include, but are not limited to, p-phenylenediamine, m-phenylenediamine, benzidine, 4,4′-methylenedianiline, 4,4′-methylenibis (2-chloroaniline), ethylene diamine, m-xylylenediamine (MXDA) and combinations of these. Other typical chain extenders are amino alcohols such as ethanolamine, propanolamine, and butanolamine. Acidic chain extenders include 2,2-bis(hydroxymethyl)propionic acid (DMPA), 2,2-bis(hydroxymethyl)butyric acid, and diphenolic acid. Other suitable chain extenders and combinations of chain extenders are also within the scope of the present invention.
Isocyanates can also be used, such as any of those listed above, to further chain extend the molecule and/or impart desired properties.
Chain extension can be accomplished by means standard in the art. For example, the chain extenders can be heated in a flask and the polyurethane added thereto. In certain nonlimiting embodiments, it may be desired to neutralize a chain extended polyurethane having acidic functionality to increase stability of the polyurethane when it is dispersed in water. Any amine or other neutralizing agent can be used; certain chain extenders may also provide neutralization. Examples include but are not limited to MXDA and dimethylethanol amine (DMEA); the neutralizing agent can also contribute to the barrier properties of the coating. In certain nonlimiting embodiments, the polyurethane is in solvent, and neutralization of any acid in the polyurethane molecule is not desired.
As noted above, the polyurethanes used in the coatings of the present invention comprise at least 30 weight percent of meta-substituted aromatic material. Weight percent is based on the total solid weight of the resin (i.e. polyurethane) itself. The meta-substituted aromatic material can be introduced in the polyester polyol, the isocyanate reacted with the polyester polyol to form the urethane, and/or any of the various chain extenders.
The polyurethane prepolymer of the present invention will typically have a weight average molecular weight in THF of 5000 to 30,000, such as 7000 to 25,000 or 10,000 to 15,000. The polyurethane when dispersed in water (i.e. the “polyurethane dispersion”) will typically have a weight average molecular weight (in DMF) of8000 to 200,000, such as 10,000 to 130,000 or 20,000 to 60,000. In certain nonlimiting embodiments, the polyurethane will have a Molar Permachor Number of at least 50.
In certain nonlimiting embodiments, it may be desired to use a meta-substituted aliphatic isocyanate, such as TMXDI, as a chain extender.
In certain nonlimiting embodiments, the polyurethane dispersion is comprised of a blend of two or more different polyurethanes. In these embodiments, there will be at least 30 weight percent of meta-substituted aromatic material based on the overall weight of polyurethane in the blend, but each polyurethane added to the blend may or may not have at least 30 weight percent of meta-substituted aromatic material. For example, a first polyurethane dispersion, having approximately 35 weight percent TDI and approximately 20 weight percent HER can be blended with a second polyurethane dispersion comprising approximately 20 weight percent TDI and zero percent HER.
In accordance with certain nonlimiting embodiments of the present invention, the barrier coating composition applied on the microporous sheet may comprise from about 10 to about 50, such as 25 to 40, weight percent resin, such as those listed above, based on the total weight of the coating composition. The coating composition may comprise a suitable solvent, such as water and/or organic solvents that will not cause embrittlement of the microporous sheet.
In certain nonlimiting embodiments, the barrier coating composition may be substantially solvent-free. The term “substantially solvent-free” as used herein when referring to the barrier coating composition means that the gas barrier coating composition contains less than about 15 or 20 weight percent organic solvents, such as less than 5 or 10 weight percent, with weight percent being based on the total weight of the coating composition to be applied to the microporous sheet. For example, the barrier coating composition may contain from zero to 2 or 3 weight percent organic solvents. In a particular example, the composition comprises less than 0.1 or 0.01 weight percent MEK, and less than 2 or 3 weight percent DMEA.
The barrier coating compositions may be water based, e.g., in the form of an aqueous dispersion. The term “water-based” as used herein to describe the barrier coating 20 composition means compositions in which the carrier fluid of the composition is predominantly water on a weight percent basis, i.e., more than 50 weight percent of the carrier comprises water. The remainder of the carrier comprises less than 50 weight percent organic solvent, typically less than 25 weight percent, such as less than 15 weight percent. Based on the total weight of the barrier coating composition (including the carrier and solids), the water may comprise from up to about 90 weight percent, although the weight percent of water will typically be lower.
In certain nonlimiting embodiments, the barrier coating of the present invention further comprises one or more additional polymers. The polymer(s) can be chosen to impart various properties and/or effects to the coating. For example, a polymer known to impart barrier can be used, such as polyvinylidene chloride (PVDC), copolymers of vinylidene chloride, EVOH, polyamides, and the like. Other polymers that function as adhesion promoters, flexibilizers, plasticizers and the like can also be used.
In certain nonlimiting embodiments, the present barrier coatings further comprise a pigment or other colorant. As used herein, the term “colorant” means any substance that imparts color and/or other opacity and/or other visual effect to the composition. The colorant can be added to the coating in any suitable form, such as discrete particles, dispersions, solutions and/or flakes. A single colorant or a mixture of two or more colorants can be used in the coating of the present invention.
Example colorants include pigments, dyes and tints, such as those used in the paint industry and/or listed in the Dry Color Manufacturers Association (DCMA) as well as special effect compositions. A colorant may include, for example a finely divided solid powder that is insoluble but wettable under the conditions of use. A colorant can be organic or inorganic and can be agglomerated or non-agglomerated.
As noted above the colorant can be in the form of a dispersion including, but not limited to, a nanoparticle dispersion. Nanoparticle dispersions can include one or more highly dispersed nanoparticle colorants or colorant particles that produce a desired visible color and/or opacity and/or visual effect. Nanoparticle dispersions can include colorants such as pigments or dyes having a particle size of less than about 150 nm, such as less than 70 nm, or less than 30 nm. Example nanoparticle dispersions and methods for making them are identified in U.S. Application Publication No. 2003/0125417, which is incorporated herein by reference. Nanoparticle dispersions can also be produced by crystallization, precipitation, gas phase condensation, and chemical attrition (i.e., partial dissolution). In order to minimize re-agglomeration of nanoparticles within the coating, a dispersion of resin-coated nanoparticles can be used. As used herein, a “dispersion of resin-coated nanoparticles” refers to a continuous phase in which is dispersed discreet “composite microparticles” that comprise a nanoparticle and a resin coating on the nanoparticle. Example dispersions of resin-coated nanoparticles and methods for making them are identified in U.S. application Ser. No. 10/876,315 filed Jun. 24, 2004, which is incorporated herein by reference, and U.S. Provisional Application Ser. No. 60/482,167 filed Jun. 24, 2003, which is also incorporated herein by reference.
Example special effect compositions that may be used in the coating of the present invention include pigments and/or compositions that produce one or more appearance effects such as reflectance, pearlescence, metallic sheen, phosphorescence fluorescence, photochromism, photosensitivity, thermochromism, goniochromism and/or color-change. Additional special effect compositions can provide other perceptible properties, such as opacity or texture. In a non-limiting embodiment, special effect compositions can produce a color shift, such that the color of the coating changes when the coating is viewed at different angles. Example color effect compositions are identified: in U.S. Patent Application Publication No. 2003/0125416, incorporated herein by reference. Additional color effect compositions can include transparent coated mica and/or synthetic mica, coated silica, coated alumina, a transparent liquid crystal pigment, a liquid crystal coating, and/or any composition wherein interference results from a refractive index differential within the material and not because of the refractive index differential between the surface of the material and the air.
In certain non-limiting embodiments, a photosensitive composition and/or photochromic composition, which reversibly alters its color when exposed to one or more light sources, can be used in the coating of the present invention. Photochromic and/or photosensitive compositions can be activated by exposure to radiation of a specified wavelength. When the composition becomes excited, the molecular structure is changed and the altered structure exhibits a new color that is different from the original color of the composition. When the exposure to radiation is removed, the photochromic and/or photosensitive composition can return to a state of rest, in which the original color of the composition returns. In one non-limiting embodiment, the photochromic and/or photosensitive composition can be colorless in a non-excited state and exhibit a color in an excited state. Full color-change can appear within milliseconds to several minutes, such as from 20 seconds to 60 seconds. Example photochromic and/or photosensitive compositions include photochromic dyes.
In a non-limiting embodiment, the photosensitive composition and/or photochromic composition can be associated with and/or at least partially bound to, such as by covalent bonding, a polymer and/or polymeric materials of a polymerizable component. In contrast to some coatings in which the photosensitive composition may migrate out of the coating and crystallize into the substrate, the photosensitive composition and/or photochromic composition associated with and/or at least partially bound to a polymer and/or polymerizable component in accordance with a non-limiting embodiment of the present invention, have minimal migration out of the coating. Example photosensitive compositions and/or photochromic compositions and methods for making them are identified in U.S. application Ser. No. 10/892,919 filed Jul. 16, 2004 and incorporated herein by reference. Composite polyester/nylon pigments, for example, can be incorporated into the present coatings and provide, for example, a good appearance without affecting flexibility; such pigments can also contribute to barrier. Suitable polyester/nylon pigments are commercially available from Teijin Fiber Limited, Osaka, Japan.
In certain nonlimiting embodiments, the pigment can be one having a high aspect ratio. Suitable high aspect ratio pigments include, for example, vermiculite, mica, talc, metal flakes platy clays and platy silicas. High aspect ratio platelets or pigments may be present in coatings in amounts from above 0.1 to 20 weight percent of the barrier coating, such as from 1 to 10 weight percent, with weight percent based on the total solid weight of the coating. The high aspect ratio pigments may form a “fish-scale” arrangement within the coating, which provides a tortuous path for gases to pass through from one side of the coating to the other. Such platelets typically have diameters of from about 1 to about 20 microns, such as about 2 to 5 or 10 microns. The aspect ratio of the platelets is typically at least 5:1, such as at least 10:1 or 20:1. As particular examples, mica flakes may have an aspect ratio of about 20:1, talc may have an aspect ratio of about 10:1 to about 20:1 and vermiculite may have an aspect ratio of from about 200:1 to about 10,000:1. While high aspect ratio pigments contribute to barrier properties, if used in quantities that are too great, flexibility and/or elasticity may be sacrificed. Accordingly, the user will need to determine the appropriate amount of high aspect ratio pigment to use to get the desired properties of barrier and flexibility/elasticity. In certain nonlimiting embodiments, a high aspect pigment will be ground and added directly to the polyurethane.
The barrier coating composition of the present invention may optionally include other ingredients such as fillers, other than the pigments described above, extenders, UV absorbers, light stabilizers, plasticizers, surfactants and wetting agents. These optional ingredients, if used, may comprise up to 10 weight percent, with weight percent being based on the total solid weight of the barrier coating composition.
The barrier coating compositions may form a film by drying, as the coating may be cured at ambient or elevated temperature. Alternatively, the coating compositions may comprise crosslinkers that render the coatings thermosetting. Suitable crosslinkers include carbodiimides, aminoplasts, aziridines, zinc/zirconium ammonium carbonates and isocyanates. Water-based carbodiimides and isocyanates may be particularly suitable in some applications because they do not add a significant amount of organic solvent to the barrier coating composition. Aziridines might be particularly suitable in other applications. When a crosslinker is used, it is typically present in an amount of up to about 10 weight percent, such as 1 weight percent, based on the total solid weight of the barrier coating. In certain nonlimiting embodiments, use of a crosslinker can result in better barrier. It will be appreciated that when a crosslinker is used, the coating in the present invention may be thermoset, and when a crosslinker is not used, the coating of the present invention will be a thermoplast.
In accordance with the present invention, the barrier coating composition is applied to a microporous sheet. The barrier coating 20 may be applied on the microporous sheet 10 by any suitable technique. For example, the barrier coating 20 may be applied directly on the microporous sheet 10 in liquid form by spraying, painting, rolling, dipping or the like.
As used, herein, the term, “microporous sheet” means a sheet comprising a polymer matrix, an interconnecting network of pores and, optionally, filler particles. The matrix of the microporous sheet may comprise substantially water-insoluble thermoplastic organic polymer. Many kinds of such polymers are suitable for use as the matrix. In general; any substantially water-insoluble thermoplastic organic polymer which can be extruded, calendered, pressed or rolled into film, sheet, strip or web may be used. The polymer may be a single polymer or it may be a mixture of polymers. The polymers may be homopolymers, copolymers, random copolymers, block copolymers graft copolymers, atactic polymers isotactic polymers, syndiotactic polymers, linear polymers or branched polymers. When mixtures of polymers are used, the mixture may be homogeneous or it may comprise two or more polymeric phases.
Examples of classes of suitable substantially water-insoluble thermoplastic organic polymers of the microporous sheets include the thermoplastic polyolefins, poly(halo-substituted olefins), polyesters polyamides, polyurethanes, polyureas, poly(vinyl halides); poly(vinylidene halides) polystyrenes poly(vinyl esters), polycarbonates, polyethers, polysulfides, polyimides, polysilanes, polysiloxanes, polycaprolactones, polyacrylates, and polymethacrylates. Hybrid classes, for example, thermoplastic poly(urethane-ureas), poly(ester-amides), poly(silane-siloxanes), and poly(ether-esters) are within contemplation. Examples of specific substantially water-insoluble thermoplastic organic polymers include thermoplastic high density polyethylene, low density polyethylene, ultrahigh molecular weight polyethylene, polypropylene (atactic, isotactic, or syndiotactic), poly(vinyl chloride), polytetrafluoroethylene, copolymers of ethylene and acrylic acid, copolymers of ethylene and methacrylic acid, poly(vinylidene chloride), copolymers of vinylidene chloride and vinyl acetate, copolymers of vinylidene chloride and vinyl chloride, copolymers of ethylene and propylene, copolymers of ethylene and butene, poly(vinyl acetate), polystyrene, poly(omega-aminoundecanoic acid) poly(hexamethylene adipamide), poly(epsilon-caprolactam), and poly(methyl methacrylate).
The microporous sheets also comprise a network of interconnecting pores that communicate substantially throughout the material. The pores typically constitute from 30 to 95 volume percent of the microporous material. For example, the pores may constitute from 60 to 75 percent by volume of the microporous material. On a coating-free basis, the volume average diameter of the pores may be at least 0.02 micrometers, typically at least 0.04 micrometers. The volume average diameter of the pores is also typically less than 0.5 micrometer.
The finely divided, substantially water-insoluble particulate fillers which may optionally be added to the microporous sheets of the present invention may comprise, for example, siliceous and/or non-siliceous particles. The filler particles may comprise at least30 or 40 weight percent of the microporous material up to about 70 or 80 weight percent. In one embodiment, the filler particles are the predominant component of the sheet in comparison with the polymer matrix on a weight percent basis. Thus, the filler particles may comprise greater than 50 weight percent of the combined total of the polymer matrix and filer particles. For example, the filler particles may comprise greater than 60 weight percent.
A suitable particulate filler is finely divided substantially water-insoluble siliceous particles. Examples of suitable siliceous particles include particles of silica, mica, montmorillonite, kaolinite, asbestos, talc, diatomaceous earth, vermiculite, natural and synthetic zeolites, cement, calcium silicate, aluminum silicate, sodium aluminum silicate, aluminum polysilicate, alumina silica gels, and glass particles. Of the silicas, precipitated silica, silica gel or fumed silica may be particularly suitable.
Examples of non-siliceous filler particles include particles of titanium oxide, zinc oxide, antimony oxide, zirconia, magnesia, alumina, zinc sulfide, barium sulfate, strontium sulfate, calcium carbonate, magnesium carbonate, magnesium hydroxide, and finely divided substantially water-insoluble flame retardant filler particles such as particles of ethylenebis(tetra-bromophthalimide), octabromodiphenyl oxide, decabromodiphenyl oxide, and ethylenebisdibromonorbornane dicarboximide.
The filler particles typically have an average particle size of less than 40 micrometers. In the case of precipitated silica, the average ultimate particle size (irrespective of whether or not the ultimate particles are agglomerated) may be less than 0.1 micrometer.
Minor amounts, usually less than 5 percent by weight, of other materials used in processing such as lubricant, processing plasticizer, organic extraction liquid, water and the like may optionally also be present. Additional materials introduced for particular purposes may optionally be present in the microporous material in small amounts, usually less than 15 percent by weight. Examples of such materials include antioxidants, ultraviolet light absorbers, reinforcing fibers such as chopped glass fiber strand and the like.
Some examples of microporous sheets are disclosed in U.S. Pat. Nos. 4,833,172; 4,861,644 and 6,114,023, which are incorporated herein by reference. Commercially available microporous sheets are sold under the designation TESLIN by PPG Industries, Inc.
The microporous sheets of the present invention may be flexible and/or elastic “Flexible substrate”, “flexibility”, and like terms refer to a microporous sheet that can undergo mechanical stresses, such as bending, stretching and the like, without significant irreversible change. “Elastic” and like terms refer to a substrate that will become distorted when it undergoes mechanical stresses, such as bending, stretching and the like, and will substantially return to its original shape when the mechanical stress is removed. Thus, it will be appreciated that a flexible microporous sheet may or may not also be an elastic microporous sheet.
A primer or other intermediate layer may optionally be provided in certain nonlimiting embodiments between the microporous sheet and the gas barrier coating. For example, an acrylic primer, such as a water-based styrenic/acrylic copolymer, may be used. When a primer is used, it typically has a dry film thickness of from about 1 to about 25 microns. Some or all of the primer may pass into the pores of the microporous sheet upon application. Thus, the primer does not necessarily form a film on the surface of the sheet but may, in some cases, be absorbed into the pores of the sheet. It will be appreciated that the primer itself does not typically function as a barrier coating. For example, the primer coating in certain nonlimiting embodiments does not minimize the P(O2) to a point at which P(O2) can even be determined using a Mocon Octran 2/20. That is, P(O2) of the microporous sheet cannot be determined because it is too permeable; even application of an acrylic primer does not allow such reading to be made.
In certain nonlimiting embodiments, one or more additional coatings may be applied on top of at least a portion of the one or more barrier coatings, which may or may not have one or more primer(s) or other intermediate layer(s) thereunder. It has been observed that the barrier coatings used herein impart greater barrier typically significantly greater barrier, to microporous sheets as compared with uncoated microporous sheets or microporous sheets having a coating that does not function as a barrier coating or does not offer significant barrier (i.e. coatings that do not allow permeance to even be measured).
In certain nonlimiting embodiments, the microporous sheet has good printability; that is, printing on the sheet is clear and of relatively high definition. In certain nonlimiting embodiments, the present coated microporous sheets provide a substrate that has both printability and barrier. A particular application is in the production of labels for plastic substrates, many of which are gas permeable. The present microporous sheets therefore make suitable labels that offer barrier protection to, for example, polyester, polyolefin, polyamide, cellulosic, polystyrene, polyacrylics, polycarbonates, poly(ethylene terephthalate) and/or poly(ethylene naphthalate) substrates. Packaging for food, beverages, medical supplies, and the like that are sensitive to, for example, oxidation, is a particular application of the present invention.
As used herein, unless otherwise expressly specified, all numbers such as those expressing values, ranges, amounts or percentages may be read as if prefaced by the word “about”, even if the term does not expressly appear. Any numerical range recited herein is intended to include all sub-ranges subsumed therein. Also, as used herein, the term “polymer” is meant to refer to prepolymers, oligomers and both homopolymers and copolymers; the prefix “poly” refers to two or more. Plural encompasses singular and vice versa. Thus, while the present invention has been described in terms of “a” barrier coating, “a” polyurethane, and the like, one or more of these things can be used.
EXAMPLESThe following examples are intended to illustrate various aspects of the present invention and are not intended to limit the disclosure or claims of the invention.
Example 1 Hydroxyl-functional polyesters were prepared using the following procedure. The ingredients listed in Table 1a were charged to a round-bottomed glass flask equipped with a mechanical stirrer, nitrogen inlet tube, thermometer, steam jacket column, fractionating column, and a distillation head connected to a condenser and a receiver. The resultant mixture was heated to react in a nitrogen atmosphere. At about 160° C., water generated by the esterification process began to be collected. With continuous removal of water, heating continued to 210° C. The reaction was allowed to continue until the acid value was below 3.0 mg KOH/gram, at which time the reaction product was cooled and collected. Table 1a lists the polyester prepared by the foregoing procedure (Polyester Sample No. 1), as well as several other polyesters prepared by a similar procedure. The determined acid value in mg KOH/gram, and hydroxyl value in mg KOH/gram for each sample was determined and is shown in Table 1b, as are the Mw, Mn and Mw/Mn values as determined by GPC (using linear polystyrene standards).
Polyurethane prepolymers were prepared in a similar manner. The diols were combined (including HER and DMPA) and heated until dissolved. This mixture was then added to isocyanate in an appropriate solvent and held until a specific NCO equivalent weight was reached. Specifically, a polyurethane prepolymer in the form of an isocyanate-functional polymer was prepared in the following manner. Polyester diol Sample No. 1 from Example 1 and Table 1a, 162.9 g, DMPA (2,2-bis(hydroxymethyl)propionic acid), 56.4 g and HER (hydroxyethyl ether of resorcinol), 233.7 g, were charged to a round bottomed glass flask equipped with a mechanical stirrer, nitrogen inlet, condenser and thermometer. The contents of the flask were slowly heated to 110° C. to dissolve the solids. To a separate round-bottomed glass flask equipped with a mechanical stirrer, nitrogen inlet, condenser and thermometer was added MEK, 420 g and TDI (toluene diisocyanate), 327 g. The contents of this flask were heated to 60° C. with constant stirring. The heated mixture of diols was then added slowly to the isocyanate solution to form the polyurethane prepolymer. The diols were added at a rate such that the temperature of the reaction did not exceed 80° C. The reaction was held at 80° C. until the NCO equivalent weight was greater than 3000. The resultant, polymer had a non-volatile content of 62.2%, the acid value was 17.5 mg KOH/gram and the NCO equivalent weight was 3380. GPC analysis gave Mw=14229, Mn=4478 with Mw/Mn=3.2.
Example 3The isocyanate-functional prepolymer of Example 2 was chain extended and dispersed in water in the following manner. To a round-bottomed glass flask equipped with a mechanical stirrer, nitrogen inlet, condenser and thermometer was added deionized water, 1533 g, MXDA (m-xylylenediamine), 23.0 g, and DMEA (dimethylethanol amine), 33.4 g. The contents of the flask were heating with stirring to 50° C. The polyurethane prepolymer of Example 2 was then dropped into the aqueous mixture over about 15 minutes followed by an MEK rinse, 60 g, resulting in a milky-white dispersion. The dispersion was then put under vacuum to remove MEK to a level of less than 0.1% by weight. The resultant dispersion had a non-volatile content of 35.8%, the pH was 8.9, meq acid was 0.195 and meq base was 0.197. GPC analysis (dmf) yielded Mw=40360, Mn=10802 with Mw/Mn=3.7.
Table 2 lists the ingredients of the polyurethane dispersion prepared in the foregoing example (Dispersion Code No. 1), as well as ingredients of several other polyurethane dispersions prepared in a similar manner using polyester diols. The values listed in Table 2 represent grams of each listed ingredient.
*TMXDI was used in place of TDI.
MICROLITE 923 and 963 are supplied at 7.5% solids in water. MICROLITE is a dispersion of vermiculite sold by W. R. Grace.
HEEU—hydroxyethyl ethylene urea.
MEK—methyl ethyl ketone.
Table 3 lists additional polyurethane dispersions prepared without polyester. These polyurethane prepolymers and dispersions were prepared in substantially the same way as described in Examples 2 and 3.
TEG—tetraethylene glycol.
Coating materials having compositions listed below in Table 5 were spray-applied to TESLIN SP700. or TS1000 microporous sheets to form gas barrier coatings on the microporous sheets. Each of the coatings was subjected to oxygen barrier testing with Mocon's Oxtran 2/20 at 23° C. and 50% R.H. Oxygen permeability results are listed in Table 5.
The oxygen permeability properties of the above-listed coated microporous sheets were compared With both un-coated microporous sheets and microporous sheets coated with primer materials using the following procedure: Spray applied (multiple passes)using a Binks 62 siphon spray gun, 60 p.s.i. and baked 8 minutes at 82° C. Primer is a waterborne styrene acrylic with no waxes 4-8 microns in thickness (0.16-0.31 mil). For comparison purposes, primed TESLIN microporous sheets were masked to reduce the area from 50 in2 to 5 in2on Mocon Company's Oxtran -1000. Temperature was 26.5° C. and R.H. was approximately 30 percent for primed TESLIN without the barrier coating the Oxtran 1000 over-ranged, which indicates that permeance is greater than 1289 cm3/100 inch2/day.
The gas barrier coatings applied on the microporous sheets (such as those shown in Table 5) have permeance values well below those of un-coated and primer-coated microporous sheets.
Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.
Claims
1. A coated microporous sheet comprising:
- a microporous sheet; and
- a barrier coating over at least a portion of the microporous sheet.
2. The coated microporous sheet of claim 1, wherein the barrier coating has an oxygen permeability of less than 3 cm3-mil-/100 inches2/atmosphere/day.
3. The coated microporous sheet of claim 1, wherein the barrier coating has an oxygen permeability of less than 1 cm3-mil/100 inches2/atmosphere/day
4. The coated microporous sheet of claim 1, wherein the barrier coating comprises a polyurethane.
5. The coated microporous sheet of claim 4, wherein the polyurethane comprises at least 60 weight percent of meta-substituted aromatic material.
6. The coated microporous sheet of claim 5, wherein the polyurethane dispersion comprises a polyester polyol.
7. The coated microporous sheet of claim 5, wherein the polyurethane has a Molar Permachor Number of at least 50.
8. The coated microporous sheet of claim 1, wherein the coating further comprises one or more polymers.
9. The coated microporous sheet of claim 8, wherein one or more polymers imparts additional barrier to the coating.
10. The coating microporous sheet of claim 9, wherein one of the polymers is polyvinylidene chloride and/or copolymers comprising polyvinylidene chloride.
11. The coated microporous sheet of claim 1, wherein the barrier coating further comprises high aspect ratio platelets.
12. The coated microporous sheet of claim 1, further comprising an intermediate layer between the barrier coating and the microporous sheet.
13. The coated microporous sheet of claim 1, wherein the microporous sheet comprises a polymer matrix.
14. The coated microporous sheet of claim 1, wherein the microporous sheet comprises a polyethylene matrix and from about 30 to about 95 volume percent pores.
15. The coated microporous sheet of claim 1, wherein the microporous sheet is flexible.
16. The coated microporous sheet of claim 1, wherein the microporous sheet is elastic.
17. A method of coating a microporous sheet, comprising applying a gas barrier coating composition on the microporous sheet.
18. The method of claim 17, wherein the gas barrier coating composition comprises a polyurethane.
19. The method of claim 18, wherein the polyurethane comprises at least 30 weight percent of meta-substituted aromatic material.
20. The coated microporous sheet of claim 1, wherein the barrier coating is over substantially all of the sheet.
Type: Application
Filed: Mar 4, 2005
Publication Date: Sep 8, 2005
Inventors: Lawrence Fitzgerald (Gibsonia, PA), Brian Woodworth (Pittsburgh, PA), Walter Kasper (Gibsonia, PA), John Zern (Cheswick, PA), Ken Niederst (Allison Park, PA)
Application Number: 11/072,833
