Patent Application
20060275564
The present invention relates to thermoplastic shrink films and methods of shrinking a film.
Activating the shrink characteristic of a heat-shrinkable film may be accomplished by immersing the film in a hot-water bath or conveying the film through a hot-air tunnel. However, such exposure may heat to an undesirable extent a product (e.g., a food product) that is enclosed within the package comprising the shrink film. Such exposure method may also require extensive hot-water bath or heat tunnel equipment.
One or more embodiments of the present invention may address one or more of the aforementioned problems. One embodiment of the present invention is directed to a method of activating the shrink characteristic of a film. First, a film is provided that comprises one or more thermoplastic polymers and at least about 0.01 weight % of photothermic material based on the weight of the film. Second, the film is exposed to an amount of non-ionizing radiation effective for the photothermic material to generate heat to cause an effect selected from one or more of: 1) shrinking the film by at least about 5% in at least one direction and 2) increasing the tension in the film by at least about 50 pounds per square inch in at least one direction.
These and other objects, advantages, and features of the invention may be more readily understood and appreciated by reference to the detailed description of the invention and the drawings.
In an embodiment of the invention, a method of activating a shrink characteristic of a film comprises the following steps. First, a film is provided that comprises one or more thermoplastic polymers and at least about 0.01 weight % of photothermic material based on the weight of the film. Next, the film is exposed to an amount of non-ionizing radiation effective for the photothermic material to generate sufficient heat to cause an effect selected from one or more of: 1) shrinking the film by at least about 5% in at least one direction and 2) increasing the tension in the film by at least about 50 pounds per square inch (psi) in at least one direction.
The film comprising the photothermic material (i.e., the film), or a layer of the film, may comprise one or more thermoplastic polymers, for example, one or more of polyolefins (e.g., polyethylene, polypropylene), ethylene/vinyl alcohol copolymers, ionomers, vinyl plastics (e.g., polyvinyl chloride, polyvinylidene chloride), polyamide, and polyester. The film, or any of the film layers (e.g., any of the film layers discussed below), may comprise any of polymers discussed below in at least about, and/or at most about, any of the following weight percent values: 30, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 99 and 100% by weight of the film or by weight of the layer. The film may be a packaging film, such as a food packaging film.
Useful polyolefins include ethylene homo- and co-polymers and propylene homo- and co-polymers. The term “polyolefins” includes copolymers that contain at least 50 weight % monomer units derived from olefin. Ethylene homopolymers include high density polyethylene (“HDPE”) and low density polyethylene (“LDPE”). Ethylene copolymers include ethylene/alpha-olefin copolymers (“EAOs”), ethylene/unsaturated ester copolymers, and ethylene/(meth)acrylic acid. (“Copolymer” as used in this application means a polymer derived from two or more types of monomers, and includes terpolymers, etc.)
EAOs are copolymers of ethylene and one or more alpha-olefins, the copolymer having ethylene as the majority mole-percentage content. The comonomer may include one or more C3-C20 α-olefins, one or more C4-C12 α-olefins, and one or more C4-C8 α-olefins. Useful α-olefins include 1-butene, 1-hexene, 1-octene, and mixtures thereof.
EAOs include one or more of the following: 1) medium density polyethylene (“MDPE”), for example having a density of from 0.926 to 0.94 g/cm3; 2) linear medium density polyethylene (“LMDPE”), for example having a density of from 0.926 to 0.94 g/cm3; 3) linear low density polyethylene (“LLDPE”), for example having a density of from 0.915 to 0.930 g/cm3; 4) very-low or ultra-low density polyethylene (“VLDPE” and “ULDPE”), for example having density below 0.915 g/cm3, and 5) homogeneous EAOs. Useful EAOs include those having a density of less than about any of the following: 0.925, 0.922, 0.920, 0.917, 0.915, 0.912, 0.910, 0.907, 0.905, 0.903, 0.900, and 0.898 grams/cubic centimeter. Unless otherwise indicated, all polymer densities herein are measured according to ASTM D1505.
The polyethylene polymers may be either heterogeneous or homogeneous. As is known in the art, heterogeneous polymers have a relatively wide variation in molecular weight and composition distribution. Heterogeneous polymers may be prepared with, for example, conventional Ziegler-Natta catalysts.
On the other hand, homogeneous polymers are typically prepared using metallocene or other single-site catalysts. Such single-site catalysts typically have only one type of catalytic site, which is believed to be the basis for the homogeneity of the polymers resulting from the polymerization. Homogeneous polymers are structurally different from heterogeneous polymers in that homogeneous polymers exhibit a relatively even sequencing of comonomers within a chain, a mirroring of sequence distribution in all chains, and a similarity of length of all chains. As a result, homogeneous polymers have relatively narrow molecular weight and composition distributions. Examples of homogeneous polymers include the metallocene-catalyzed linear homogeneous ethylene/alpha-olefin copolymer resins available from the Exxon Chemical Company (Baytown, Tex.) under the EXACT trademark, linear homogeneous ethylene/alpha-olefin copolymer resins available from the Mitsui Petrochemical Corporation under the TAFMER trademark, and long-chain branched, metallocene-catalyzed homogeneous ethylene/alpha-olefin copolymer resins available from the Dow Chemical Company under the AFFINITY trademark.
Another useful ethylene copolymer is ethylene/unsaturated ester copolymer, which is the copolymer of ethylene and one or more unsaturated ester monomers. Useful unsaturated esters include: 1) vinyl esters of aliphatic carboxylic acids, where the esters have from 4 to 12 carbon atoms, and 2) alkyl esters of acrylic or methacrylic acid (collectively, “alkyl (meth)acrylate”), where the esters have from 4 to 12 carbon atoms.
Representative examples of the first (“vinyl ester”) group of monomers include vinyl acetate, vinyl propionate, vinyl hexanoate, and vinyl 2-ethylhexanoate. The vinyl ester monomer may have from 4 to 8 carbon atoms, from 4 to 6 carbon atoms, from 4 to 5 carbon atoms, and preferably 4 carbon atoms.
Representative examples of the second (“alkyl(meth)acrylate”) group of monomers include methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, hexyl acrylate, and 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, n-butyl methacrylate, hexyl methacrylate, and 2-ethylhexyl methacrylate. The alkyl(meth)acrylate monomer may have from 4 to 8 carbon atoms, from 4 to 6 carbon atoms, and preferably from 4 to 5 carbon atoms.
The unsaturated ester (i.e., vinyl ester or alkyl(meth)acrylate) comonomer content of the ethylene/unsaturated ester copolymer may be at least about 3, 6, and 8 wt. % and/or may be at most about 12, 18, and 40 wt. %, based on the weight of the copolymer. Useful ethylene contents of the ethylene/unsaturated ester copolymer include at least about, and/or at most about, any of the following: 60 wt. %, 82 weight %, 85 weight %, 88 weight %, 92 wt. %, 93 wt. %, 94 weight %, and 97 wt. %, based on the weight of the copolymer.
Representative examples of ethylene/unsaturated ester copolymers include ethylene/methyl acrylate, ethylene/methyl methacrylate, ethylene/ethyl acrylate, ethylene/ethyl methacrylate, ethylene/butyl acrylate, ethylene/2-ethylhexyl methacrylate, and ethylene/vinyl acetate.
Another useful ethylene copolymer includes ethylene/(meth)acrylic acid copolymer, which is the copolymer of ethylene and acrylic acid, methacrylic acid, or both.
Other useful ethylene copolymer includes ethylene/norbornene copolymer and ethylene/propylene/diene (EPDM) copolymer. Examples of ethylene/norbornene copolymer include those sold under the Topas™ and Zeonor™ trademarks. Exemplary EPDM copolymer include those sold under the Vistalon™ trademark.
Useful propylene copolymer includes propylene/ethylene copolymers (“EPC”) and propylene/butene copolymers, which are copolymers of propylene and ethylene, and propylene and butene, respectively, having a majority weight % content of propylene, such as those having, for example, an ethylene comonomer content of less than about 10%, less than about 6%, and/or at least about 2% by weight.
Ethylene/vinyl alcohol copolymer (“EVOH”) is another useful thermoplastic. EVOH may have an ethylene content of about 32%, or at least about any of the following values: 20%, 25%, 30%, and 38% by weight. EVOH may have an ethylene content of at most about any of the following values: 50%, 48%, 40%, 35%, and 33% by weight. EVOH may include saponified or hydrolyzed ethylene/vinyl acetate copolymers, such as those having a degree of hydrolysis of at least about any of the following values: 50% and 85%. EVOH may have an ethylene content ranging from about 20 mole percent to about 44 mole percent. Exemplary EVOH is commercially available from Evalca Corporation having ethylene contents of 29, 32, 35, 38 and 44 mole percent.
Another useful thermoplastic is ionomer, which is a copolymer of ethylene and an ethylenically unsaturated monocarboxylic acid having the carboxylic acid groups partially neutralized by a metal ion, such as sodium or zinc. Useful ionomers include those in which sufficient metal ion is present to neutralize from about 10% to about 60% of the acid groups in the ionomer. The carboxylic acid is preferably “(meth)acrylic acid”—which means acrylic acid and/or methacrylic acid. Useful ionomers include those having at least 50 weight % and preferably at least 80 weight % ethylene units. Useful ionomers also include those having from 1 to 20 weight percent acid units. Useful ionomers are available, for example, from Dupont Corporation (Wilmington, Del.) under the SURLYN trademark.
Useful vinyl plastics include polyvinyl chloride (“PVC”), vinylidene chloride polymer (“PVdC”), and polyvinyl alcohol (“PVOH”). Polyvinyl chloride (“PVC”) refers to a vinyl chloride-containing polymer or copolymer—that is, a polymer that includes at least 50 weight percent monomer units derived from vinyl chloride (CH2═CHCl) and also, optionally, one or more comonomer units, for example, derived from vinyl acetate. One or more plasticizers may be compounded with PVC to soften the resin and/or enhance flexibility and processibility. Useful plasticizers for this purpose are known in the art.
Another exemplary vinyl plastic is vinylidene chloride polymer (“PVdC”), which refers to a vinylidene chloride-containing polymer or copolymer—is, a polymer that includes monomer units derived from vinylidene chloride (CH2═CCl2) and also, optionally, monomer units derived from one or more of vinyl chloride, styrene, vinyl acetate, acrylonitrile, and C1-C12 alkyl esters of (meth)acrylic acid (e.g., methyl acrylate, butyl acrylate, methyl methacrylate). As used herein, “(meth)acrylic acid” refers to both acrylic acid and/or methacrylic acid; and “(meth)acrylate” refers to both acrylate and methacrylate. Examples of PVdC include one or more of the following: vinylidene chloride homopolymer, vinylidene chloride/vinyl chloride copolymer (“VDC/VC”), vinylidene chloride/methyl acrylate copolymer (“VDC/MA”), vinylidene chloride/ethyl acrylate copolymer, vinylidene chloride/ethyl methacrylate copolymer, vinylidene chloride/methyl methacrylate copolymer, vinylidene chloride/butyl acrylate copolymer, vinylidene chloride/styrene copolymer, vinylidene chloride/acrylonitrile copolymer, and vinylidene chloride/vinyl acetate copolymer.
Useful PVdC includes that having at least about 75, at most about 95, and at most about 98 weight % vinylidene chloride monomer. Useful PVdC (for example, as applied by latex emulsion coating) includes that having at least about any of 5%, 10%, and 15%—and/or at most about any of 25%, 22%, 20%, and 15 weight %—comonomer with the vinylidene chloride monomer.
Useful PVdC includes that having a weight-average molecular weight (Mw) of at least about any of the following 10,000; 50,000; 80,000; 90,000; 100,000; 111,000; 120,000; 150,000; and 180,000; and at most about any of the following: 180,000, 170,000; 160,000; 150,000; 140,000; 100,000; and 50,000. Useful PVdC also includes that having a viscosity-average molecular weight (Mz) of at least about any of the following: 130,000; 150,000; 170,000; 200,000; 250,000; and 300,000; and at most about any of the following: 300,000; 270,000; 250,000; and 240,000.
A layer that includes PVdC may also include a thermal stabilizer (e.g., a hydrogen chloride scavenger such as epoxidized soybean oil) and a lubricating processing aid (e.g., one or more polyacrylates).
Useful polyamides include those of the type that may be formed by the polycondensation of one or more diamines with one or more diacids and/or of the type that may be formed by the polycondensation of one or more amino acids (including those provided by the ring opening polymerization of lactams). Useful polyamides include aliphatic polyamides and aliphatic/aromatic polyamides.
Representative aliphatic diamines for making polyamides include those having the formula:
H2N(CH2)nNH2
where n has an integer value of 1 to 16. Representative examples include trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, hexadecamethylenediamine. Representative aromatic diamines include p-phenylenediamine, 4,4′-diaminodiphenyl ether, 4,4′ diaminodiphenyl sulphone, 4,4′-diaminodiphenylethane. Representative alkylated diamines include 2,2-dimethylpentamethylenediamine, 2,2,4-trimethylhexamethylenediamine, and 2,4,4 trimethylpentamethylenediamine. Representative cycloaliphatic diamines include diaminodicyclohexylmethane. Other useful diamines include heptamethylenediamine, nonamethylenediamine, and the like.
Representative diacids for making polyamides include dicarboxylic acids, which may be represented by the general formula:
HOOC-Z-COOH
where Z is representative of a divalent aliphatic or cyclic radical containing at least 2 carbon atoms. Representative examples include aliphatic dicarboxylic acids, such as adipic acid, sebacic acid, octadecanedioic acid, pimelic acid, suberic acid, azelaic acid, dodecanedioic acid, and glutaric acid; and aromatic dicarboxylic acids, such as such as isophthalic acid and terephthalic acid.
The polycondensation reaction product of one or more or the above diamines with one or more of the above diacids may form useful polyamides. Representative polyamides of the type that may be formed by the polycondensation of one or more diamines with one or more diacids include aliphatic polyamides such as poly(hexamethylene adipamide) (“nylon-6,6”), poly(hexamethylene sebacamide) (“nylon-6,10”), poly(heptamethylene pimelamide) (“nylon-7,7”), poly(octamethylene suberamide) (“nylon-8,8”), poly(hexamethylene azelamide) (“nylon-6,9”), poly(nonamethylene azelamide) (“nylon-9,9”), poly(decamethylene azelamide) (“nylon-10,9”), poly(tetramethylenediamine-co-oxalic acid) (“nylon-4,2”), the polyamide of n-dodecanedioic acid and hexamethylenediamine (“nylon-6,12”), the polyamide of dodecamethylenediamine and n-dodecanedioic acid (“nylon-12,12”).
Representative aliphatic/aromatic polyamides include poly(tetramethylenediamine-co-isophthalic acid) (“nylon-4,I”), polyhexamethylene isophthalamide (“nylon-6,I”), polyhexamethylene terephthalamide (“nylon-6,T”), poly (2,2,2-trimethyl hexamethylene terephthalamide), poly(m-xylylene adipamide) (“nylon-MXD,6”), poly(p-xylylene adipamide), poly(hexamethylene terephthalamide), poly(dodecamethylene terephthalamide), and polyamide-MXD,I.
Representative polyamides of the type that may be formed by the polycondensation of one or more amino acids (including the ring opening of lactams) include poly(4-aminobutyric acid) (“nylon-4”), poly(6-aminohexanoic acid) (“nylon-6” or “poly(caprolactam)”), poly(7-aminoheptanoic acid) (“nylon-7”), poly(8-aminooctanoic acid) (“nylon-8”), poly(9-aminononanoic acid) (“nylon-9”), poly(10-aminodecanoic acid) (“nylon-10”), poly(11-aminoundecanoic acid) (“nylon-11”), and poly(12-aminododecanoic acid) (“nylon-12”).
Representative copolyamides include copolymers based on a combination of the monomers used to make any of the foregoing polyamides, such as, nylon-4/6, nylon-6/6, nylon-6/9, nylon-6/12, caprolactam/hexamethylene adipamide copolymer (“nylon-6,6/6”), hexamethylene adipamide/caprolactam copolymer (“nylon-6/6,6”), trimethylene adipamide/hexamethylene azelaiamide copolymer (“nylon-trimethyl 6,2/6,2”), hexamethylene adipamide-hexamethylene-azelaiamide caprolactam copolymer (“nylon-6,6/6,9/6”), hexamethylene adipamide/hexamethylene-isophthalamide (“nylon-6,6/6,I”), hexamethylene adipamide/hexamethyleneterephthalamide (“nylon-6,6/6,T”), nylon-6,T/6,I, nylon-6/MXD,T/MXD,I, nylon-6,6/6,10, and nylon-6,I/6,T.
Conventional nomenclature typically lists the major constituent of a copolymer before the slash (“/”) in the name of a copolymer; however, in this application the constituent listed before the slash is not necessarily the major constituent unless specifically identified as such. For example, unless the application specifically notes to the contrary, “nylon-6/6,6” and “nylon-6,6/6” may be considered as referring to the same type of copolyamide.
Polyamide copolymers may include the most prevalent polymer unit in the copolymer (e.g., hexamethylene adipamide as a polymer unit in the copolymer nylon-6,6/6) in mole percentages ranging from any of the following: at least about 50%, at least about 60%, at least about 70%, at least about 80%, and at least about 90%, and the ranges between any of the forgoing values (e.g., from about 60 to about 80%); and may include the second most prevalent polymer unit in the copolymer (e.g., caprolactam as a polymer unit in the copolymer nylon-6,6/6) in mole percentages ranging from any of the following: less than about 50%, less than about 40%, less than about 30%, less than about 20%, less than about 10%, and the ranges between any of the forgoing values (e.g., from about 20 to about 40%).
Useful polyamides include those that are approved by the controlling regulating agency (e.g., the U.S. Food and Drug Agency) for either direct contact with food and/or for use in a food packaging film, at the desired conditions of use.
Useful polyesters include those made by: 1) condensation of polyfunctional carboxylic acids with polyfunctional alcohols, 2) polycondensation of hydroxycarboxylic acid, and 3) polymerization of cyclic esters (e.g., lactone).
Exemplary polyfunctional carboxylic acids (and their derivatives such as anhydrides or simple esters like methyl esters) include aromatic dicarboxylic acids and derivatives (e.g., terephthalic acid, isophthalic acid, dimethyl terephthalate, dimethyl isophthalate) and aliphatic dicarboxylic acids and derivatives (e.g., adipic acid, azelaic acid, sebacic acid, oxalic acid, succinic acid, glutaric acid, dodecanoic diacid, 1,4-cyclohexane dicarboxylic acid, dimethyl-1,4-cyclohexane dicarboxylate ester, dimethyl adipate). Useful dicarboxylic acids also include those discussed above in the polyamide section. As is known to those of skill in the art, polyesters may be produced using anhydrides and esters of polyfunctional carboxylic acids.
Exemplary polyfunctional alcohols include dihydric alcohols (and bisphenols) such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3 butanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 2,2-dimethyl-1,3-propanediol, 1,6-hexanediol, poly(tetrahydroxy-1,1′-biphenyl, 1,4-hydroquinone, and bisphenol A.
Exemplary hydroxycarboxylic acids and lactones include 4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, pivalolactone, and caprolactone.
Useful polyesters include homopolymers and copolymers. These may be derived from one or more of the constituents discussed above. Exemplary polyesters include poly(ethylene terephthalate) (“PET”), poly(butylene terephthalate) (“PBT”), and poly(ethylene naphthalate) (“PEN”). If the polyester includes a mer unit derived from terephthalic acid, then such mer content (mole %) of the diacid of the polyester may be at least about any the following: 70, 75, 80, 85, 90, and 95%.
Useful polyesters may be derived from lactone polymerization; these include, for example, polycaprolactone and polylactic acid.
The polyester may be thermoplastic. The polyester (e.g., copolyester) of the film may be amorphous, or may be partially crystalline (semi-crystalline), such as with a crystallinity of at least about, or at most about, any of the following weight percentages: 10, 15, 20, 25, 30, 35, 40, and 50%.
The film comprising the photothermic material (i.e., the film) may have any total thickness as long as it provides the desired properties (e.g., free shrink, shrink tension, flexibility, Young's modulus, optics, strength, barrier) for the given application of expected use. The film may have a thickness of less than about any of the following: 20 mils, 10 mils, 5 mils, 4 mils, 3 mils, 2 mils, 1.5 mils, 1.2 mils, and 1 mil. The film may also have a thickness of at least about any of the following: 0.25 mils, 0.3 mils, 0.35 mils, 0.4 mils, 0.45 mils, 0.5 mils, 0.6 mils, 0.75 mils, 0.8 mils, 0.9 mils, 1 mil, 1.2 mils, 1.4 mils, 1.5 mils, 2 mils, 3 mils, and 5 mils.
The film may be monolayer or multilayer. The film may comprise at least any of the following number of layers: 1, 2, 3, 4, and 5. The film may comprise at most any of the following number of layers: 20, 15, 10, 9, 7, 5, 3, 2, and 1. The term “layer” refers to a discrete film component which is coextensive with the film and has a substantially uniform composition. Any of the layers of the film may have a thickness of at least about any of the following: 0.05, 0.1, 0.2, 0.5, 1, 2, and 3 mil. Any of the layers of the film may have a thickness of at most about any of the following: 5, 2, 1, and 0.5 mils. Any of the layers of the film may have a thickness as a percentage of the total thickness of the film of at least about any of the following values: 1, 3, 5, 7, 10, 15, 20, 30, 40, 50, 60, 70, 80, and 90%. Any of the layers of the film may have a thickness as a percentage of the total thickness of the film of at most about any of the following values: 90, 80, 50, 40, 35, 30, 25, 20, 15, 10, and 5%.
The film may comprise one or more barrier layers, one or more tie layers, one or more heat seal layers, an outside layer, an inside layer, a shrink layer, one or more abuse layers, and/or one or more bulk or core layers. Below are some examples of combinations in which the alphabetical symbols designate the layers. Where the film representation below includes the same letter more than once, each occurrence of the letter may represent the same composition or a different composition within the class that performs a similar function.
C/D, E, D/E, C/E, C/D/E, C/D/D/E, C/A/E, C/A/E, C/B/A/E, C/B/A/B/E, C/B/A/B/D/E, C/B/A, C/A, A/E, E/B/A, C/D/B/A, E/A/E, A/B/D/E, C/B/A/B/C, C/B/A/B/E, C/B/A/B/D/E, C/D/B/A/B/E, C/D/B/A/B/D/E, C/B/A/B/C, C/B/A/B/E, C/B/A/B/D/E, C/D/B/A/B/E, C/D/B/A/B/D/E
“A” is a barrier layer, as discussed below.
“B” is a tie layer, as discussed below.
“C” is a heat seal layer (i.e., sealant layer), that is, a layer adapted to facilitate the heat-sealing of the film to itself or to another object, such as a substrate, as is known in the art.
“D” may be a core layer, a bulk layer, and/or a shrink layer. The term “shrink layer” refers to an internal layer having a composition, configuration, and thickness such that the layer has significant effect in inducing compatible shrinkage of the overall multilayer film structure. The relative thickness of a shrink layer may be selected as sufficient relative to that of the overall film thickness so that the activation of the shrink characteristic of the shrink layer may essentially control the shrinkage of the entire multilayer film.
“E” is an outside (i.e., abuse or print side) layer. The film may support a printed image on an outside layer. The film may incorporate a printed image on an internal layer, for example by trap printing as discussed below.
Useful films that may be modified to incorporate photothermic material as set forth in this Application are described in the following: U.S. Pat. No. 4,514,465 to Schoenberg; U.S. Pat. No. 4,532,189 to Mueller; U.S. Pat. No. 4,551,380 to Schoenberg; U.S. Pat. No. 4,590,124 to Schoenberg; U.S. Pat. No. 4,643,943 to Schoenberg; U.S. Pat. No. 4,724,185 to Shah; U.S. Pat. No. 4,726,984 to Shah; U.S. Pat. No. 4,755,419 to Shah; U.S. Pat. No. 5,023,143 to Nelson; U.S. Pat. No. 5,658,625 to Bradfute et al; U.S. Pat. No. 5,543,223 to Shah; U.S. Pat. No. 5,897,941 to Shah; U.S. Pat. No. 6,296,947 to Shah; U.S. Pat. No. 6,423,421 to Banaszak et al; U.S. Pat. No. 6,479,138 to Childress; and U.S. Pat. No. 6,579,621 to Shah; each of which is incorporated herein in its entirety by reference.
The film may comprise one or more barrier polymers. A “barrier polymer” is a polymer that markedly decreases the transmission rate of a specified gas through a film incorporating the polymer, relative to a comparable film not incorporating the polymer. Thus, the barrier polymer for a specified gas imparts enhanced barrier attributes to the film relative to the specified gas. When the term “barrier polymer” is used in this application without reference to a specified gas, it is understood that the term may be in reference to any of water vapor, oxygen, and/or carbon dioxide gases.
For example, an “oxygen barrier polymer” markedly decreases the oxygen gas transmission rate through a film incorporating the oxygen barrier polymer, because the oxygen barrier polymer imparts enhanced oxygen barrier attributes to the film. If the barrier polymer is effective for water vapor, then the barrier polymer may be considered a “water vapor barrier polymer.” A barrier polymer that is effective as a barrier for one type of gas may also be effective as a barrier to one or more other gases. For example, a barrier polymer that is effective for oxygen may also be effective for carbon dioxide, such that the same polymer may be considered an oxygen barrier polymer and a carbon dioxide barrier polymer.
If the film is multilayered, then the one or more layers of the film that incorporate one or more barrier polymers in an amount sufficient to notably decrease the transmission rate of a specified gas through the film may be considered “barrier layers” with respect to the specified gas. If the film is monolayer and incorporates one or more barrier polymers, then the monolayer film itself may be considered a “barrier layer.” For example, if a layer comprises an oxygen barrier polymer, then the layer may be considered an oxygen barrier layer.
The film or a barrier layer of the film may comprise one or more barrier polymers in an amount of at least about, or less than about, any of the following: 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 97%, 98%, 99%, and 99.5%, based on the weight of the film or the barrier layer, respectively.
Exemplary oxygen barrier polymers include: EVOH, PVOH, PVdC, polyalkylene carbonate, polyester (e.g., PET, PEN), polyacrylonitrile (“PAN”), and polyamide. Several of these polymers were discussed above in more detail.
The film may have an oxygen transmission rate taken at a time selected from before the non-ionizing radiation exposure step and after the non-ionizing radiation exposure step of at most about, and/or at least about, any of the following values: 20,000; 10,000; 1,000; 500; 400; 300; 200; 150; 100; 50; 45; 40; 35; 30; 25; 20; 15; 10; and 5 cubic centimeters (at standard temperature and pressure) per square meter per day per 1 atmosphere of oxygen pressure differential measured at 0% relative humidity and 23° C. All references to oxygen transmission rate in this application are measured at these conditions according to ASTM D-3985.
The film may have an oxygen transmission rate after the non-ionizing radiation exposure step that is no higher than the oxygen transmission rate of the film immediately before the radiation exposure step plus about any of the following values: 10; 50; 100; 500; 1,000; 3,000; 5,000; 8,000; 10,000; 15,000; and 20,000 cubic centimeters (at standard temperature and pressure) per square meter per day per 1 atmosphere of oxygen pressure differential measured at 0% relative humidity and 23° C. For example, the exposing step may not increase the oxygen transmission rate of the film by more than any of the values of the previous sentence.
A tie layer (e.g., a second layer) is a layer directly adhered (i.e., directly adjacent) to first and third layers, and has the primary function of improving the adherence of the first layer to the third layer. For example, the film may include one or two tie layers directly adhered to a barrier layer and/or one or two tie layers directly adhered to a layer comprising photothermic material.
A tie layer may comprise one or more polymers having grafted polar groups so that the polymer is capable of enhanced bonding to polar polymers such as EVOH. Useful polymers for tie layers include ethylene/unsaturated acid copolymer, ethylene/unsaturated ester copolymer, anhydride-modified polyolefin, polyurethane, and mixtures thereof. Further exemplary polymers for tie layers include one or more of the polyamides previously discussed; ethylene/vinyl acetate copolymer having a vinyl acetate content of at least about any of the following: 3, 6, and 15 weight %; ethylene/methyl acrylate copolymer having a methyl acrylate content of at least about 20 weight %; anhydride-modified ethylene/methyl acrylate copolymer having a methyl acrylate content of at least about any of the following: 5, 10, 15, and 20 weight %; and anhydride-modified ethylene/alpha-olefin copolymer, such as an anhydride grafted LLDPE.
Modified polymers or anhydride-modified polymers include polymers prepared by copolymerizing an unsaturated carboxylic acid (e.g., maleic acid, fumaric acid), or a derivative such as the anhydride, ester, or metal salt of the unsaturated carboxylic acid with—or otherwise incorporating the same into—an olefin homopolymer or copolymer. Thus, anhydride-modified polymers have an anhydride functionality achieved by grafting or copolymerization.
The film may comprise at least about 0.01 wt. % of one or more photothermic materials, such as any of those discussed below. A “photothermic material” as used herein is a material that is capable of absorbing non-ionizing radiation having a wavelength of from about 200 nm to about 700 nm, and as a result of the absorption, undergoing a radiationless photophysical process that results in the excited electron states reverting to ground state with the generation of heat energy. A photothermic material may also undergo a radiative photophysical process as a result of the absorption of the non-ionizing radiation, as long as the photothermic material also undergoes the radiationless photophysical process that results in the excited electron states reverting to ground state with the generation of heat energy.
The photothermic material may be capable of absorbing non-ionizing radiation having a wavelength of at least about, and/or at most about any of the following wavelengths, and as a result of the absorption, undergoing the radiationless photophysical process that results in the excited electron states reverting to ground state with the generation of heat energy: 200, 210, 250, 280, 290, 300, 310, 315, 320, 330, 340, 345, 350, 355, 360, 365, 370, 375, 380, 390, 400, 410, 470, 475, 500, 510, 560, 570, 620, 630, and 700 nm.
Additionally, the photothermic material may be incapable of absorbing non-ionizing radiation having a wavelength of at least about, and/or at most about, any of the wavelengths in the preceding sentence to undergo a radiationless photophysical process that results in the excited electron states reverting to ground state with the generation of heat energy. For example, the photothermic material may be incapable of absorbing non-ionizing radiation having wavelengths of at least about 400 nm and at most about 700 nm to undergo a radiationless photophysical process that results in the excited electron states reverting to ground state with the generation of heat energy.
If it is desirable that the film comprising the photothermic material have a colored appearance, then the photothermic material may be selected from one or more suitable dyes and/or pigments that may provide color to the film while also providing the heat to activate the shrink characteristic of the film upon exposure to an effective amount of non-ionizing radiation in the visible light spectrum.
The photothermic material may be inorganic or organic (e.g., organometallic) in nature, such as any of the inorganic or organic photothermic materials discussed below. The photothermic material may comprise a blend of inorganic and organic photothermic materials. The photothermic material may be in the form of photothermic particles, as discussed below.
Useful photothermic materials are those capable of generating sufficient heat energy to activate the shrink characteristic of the film to a desired level without requiring a radiation dose that causes an unacceptable degradation or change in a film property.
The photothermic material, for example the photothermic particles, may comprise material having a photonic band gap at 68° F. of at least about any of the following values: 3.1 eV and 3.2 eV. The photothermic material may comprise such material with any of the forgoing photonic band gap characteristics in at least about, and/or at most about any of the following amounts: 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 99, and 100 weight % based on the weight of the photothermic material or the photothermic particles. The photothermic material may consist essentially of, or consist of, material having any of the forgoing photonic band gap characteristics.
The photothermic material, for example the photothermic particles, may comprise one or more inorganic photothermic materials, such as any of those discussed below. An “inorganic photothermic material” is a photothermic material that is an inorganic chemistry material (e.g., element, compound, alloy). The photothermic material, for example the photothermic particles, may comprise inorganic photothermic material in at least about, and/or at most about any of the following amounts: 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 99, and 100 weight %, based on the weight of the photothermic material or the photothermic particles. The photothermic material may consist essentially of, or consist of, inorganic photothermic material.
Exemplary inorganic photothermic materials include titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3, Fe3O4), tin oxide (SnO2), zinc sulfide (ZnS), gallium nitride (GaN), gallium disulfide (GaS2), cuprous chloride (CuCl), copper aluminum disulfide (CuAlS2), silicon-carbide (SiC), and semiconducting fullerenes. The photothermic materials, for example the photothermic particles, may comprise any one of these materials, or any one or more of these materials, in at least about, and/or at most about any of the following amounts: 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 99, and 100 weight %, based on the weight of the photothermic material or the photothermic particles. The photothermic material may consist essentially of, or consist of, any one of these materials, or any one or more of these materials.
The photothermic material, for example the photothermic particles, may comprise semiconductor compound and/or alloy in at least about, and/or at most about any of the following amounts: 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 99, and 100 weight %, based on the weight of the photothermic material or the photothermic particles. The photothermic material may consist essentially of, or consist of, a semiconductor compound and/or alloy.
The photothermic material, for example the photothermic particles, may comprise organic photothermic material, such as any of those discussed below. An “organic photothermic material” means a photothermic material that is an organic chemistry carbon-containing compound (e.g, an organometallic material). The photothermic material, for example the photothermic particles, may comprise organic photothermic material in at least about, and/or at most about any of the following amounts: 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 99, and 100 weight %, based on the weight of the photothermic material or the photothermic particles. The photothermic material may consist essentially of, or consist of, organic photothermic material.
The photothermic material, for example the photothermic particles, may comprise any one of the organic photothermic materials, or any organic photothermic material from one of the classes of UV-absorbers listed below, in at least about, and/or at most about any of the following amounts: 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 99, and 100 weight %, based on the weight of the photothermic material or the photothermic particles. Also, the photothermic material may comprise any combination of one or more, two or more, three or more, at most four, at most three, and at most two of any of the organic photothermic materials in any of the forgoing amounts. The photothermic material may comprise organic photothermic material from any combination of one or more, two or more, three or more, at most four, at most three, and at most two of the UV-absorber classes listed below in any of the forgoing amounts.
Exemplary organic photothermic materials include compounds in the benzophenone class of UV absorbers, such as 2-Hydroxy-4-methoxy benzophenone (e.g., Cyasorb UV 9) and 2-Hydroxy-4-octoxy benzophenone (e.g., Cyasorb 531 and Ciba® CHIMASSORB® 81).
Exemplary organic photothermic materials include compounds in the benzotriazole class of UV absorbers, such as 2-(2′-Hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole, 2-(2H-hydroxy-3-5-Di-tert-Amyllphenyl)benzotriazole, 2-(2-Hydroxy-5-tert-octylphenyl)benzotriazole, 2-(2H-hydroxy-3-5-Di-tert-Butylphenyl)benzotriazole, 2-(2-Hydroxy-5-methyl phenyl)benzotriazole, and 2-[2-Hydroxy-3,5-di-(1,1-dimethylbenzyl)phenyl]-2H-benzotriazole.
Exemplary organic photothermic materials include p-Aminobenzoic acid (PABA), Avobenzone, 3-Benzylidene camphor, Benzylidene camphor sulfonic acid, Bisymidazylate, Camphor benzalkonium methosulfate, Cinoxate, Diethylamino hydroxybenzoyl hexyl benzoate, Diethylhexyl butamido triazone, Dimethicodiethylbenzal malonate (Parsol SLX), Dioxybenzone, Drometrizole trisiloxane, Ecamsule, Ensulizole, Homosalate, Isoamyl p-methoxycinnamate, 4-Methylbenzylidene camphor, Menthyl anthranilate, Octocrylene, Octyl dimethyl PABA, Octyl methoxycinnamate, Octyl salicylate, Octyl triazone, Oxybenzone, PEG-25 PABA, polyacrylamidomethyl benzylidene camphor, Sulisobenzone, bis-ethylhexyloxyphenol methoxyphenol triazine (e.g., Tinosorb S), methylene bis-benzotriazolyl tetramethylbutylphenol (e.g., Tinosorb M), and Trolamine salicylate.
Exemplary organic photothermic materials also include compounds available from Ciba Giegy under the Ciba® TINUVIN® trademarks, for example, Ciba® TINUVIN® P, Ciba® TINUVIN® 213, Ciba® TINUVIN® 234, Ciba® TINUVIN® 326, Ciba® TINUVIN® 327, Ciba® TINUVIN® 328, and Ciba® TINUVIN® 571 trademarks.
The photothermic material may have a particle configuration, that is, the photothermic material may be in the form of discrete, amassed units of the material that are larger than a single atom or molecule of the material. A particle configuration includes, for example, particles surrounded by the one or more thermoplastic polymers of the film, for example as colloidal particles in a colloid solution. In a particle configuration, the photothermic material may be referred to as “photothermic particles.” The photothermic material may comprise photothermic particles in at least about, and/or at most about, any of the following amounts: 40, 50, 60, 70, 80, 90, 95, and 100% based on the weight of the photothermic material.
The photothermic particles may have an average size in the longest dimension of at most about, and/or at least about, any of the following: 25 micron, 20 micron, 15, micron, 10 micron, 5 micron, 2 micron, 1 micron, 800 nm, 500 nm, 200 nm, 100 nm, 80 nm, 70 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm, 5 nm, 3 nm, 2 nm, and 1 nm.
The photothermic particles may have an average size in the shortest dimension of at least about, and/or at most about, any of the following values: 0.5 nm, 0.8 nm, 1 nm, 2, nm, 3 nm, 4 nm, 5 nm, 8, 10, 15, 20, 30, 50, 60, 80, 100, 105, 110, 150, 200, 500, 800, and 900 nm.
The photothermic particles may have an average size in at least one dimension (e.g., the longest dimension and/or the shortest dimension) of at least about, and/or at most about, any of the following: 0.8 nm, 1 nm, 2 nm, 3 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 50 nm, 100 nm, 200 nm, 500 nm, and 800 nm. The dimensions of the particles may be estimated from transmission electron microscope (“TEM”) images.
The photothermic particles may have an average aspect ratio (i.e., the ratio of the average largest dimension to the average smallest dimension of the particles) of from about 10 to about 30,000. The aspect ratio for the particles may be taken as the length (largest dimension) to the thickness (smallest dimension) of the particle or as the length (largest dimension) to the diameter (smallest dimension) of the particle. Useful aspect ratios for the photothermic particles include at least about any of the following values: 1, 3, 5, 8, 10; 20; 25; 200; 250; 1,000; 2,000; 3,000; and 5,000; and at most about any of the following values: 25,000; 20,000; 15,000; 10,000; 5,000; 3,000; 2,000; 1,000; 250; 200; 25; 20; 10; and 1.
The index of refraction of the photothermic particles may be substantially similar to that of the film medium (e.g., the one or more thermoplastic polymers) in which the particles are dispersed, so that the film will be optically transparent. If the index of refraction of the photothermic particles is substantially different from that of the film medium, then optical light may be scattered so that the film appears white or opaque.
However, even if the film medium and the photothermic particles have different indices of refraction, the film may nevertheless not appear white or opaque (i.e., may be transparent) if the incorporated photothermic particles are at most about 100 nm in the longest dimension, since visible light is not diffracted by the material interfaces of the photothermic particles in that size range. Accordingly, the photothermic particles may be of an average size small enough—for example, smaller than a quarter wavelength of visible light or less than 100 nm in any dimension—to maintain optical transparency of the film comprising the photothermic particles. The photothermic particles may have a size greater than 100 nm (e.g., from about 1 to about 25 microns) in at least one dimension, for example, if transparency of the film comprising the photothermic particles is not important, and, for example, if some amount of translucency or opaqueness is acceptable.
The photothermic material, for example, the photothermic particles, may be essentially non-absorptive of visible light radiation, a phrase that means that the particle absorbs less than about 20% of the visible light radiation energy to which it is exposed at 68° F.
The photothermic material may be dispersed in the film such that the material does not display a particle configuration within the film. For example, an organic photothermic material may not display a particle configuration if it is in solution in the polymer medium of the film. The photothermic material may be incorporated into the molecular structure of the one or more thermoplastic polymers of the film, for example, by grafting the photothermic material onto or copolymerizing the photothermic material with a thermoplastic polymer.
The photothermic material in the film may comprise at most about any of the following amounts of photothermic particles: 30, 20, 10, 5, 1, and 0% based on the weight of the photothermic material. The photothermic material may be substantially devoid of photothermic particles.
The photothermic material may be dispersed in the film, for example, so that the photothermic material (i.e., any of the the photothermic particles, the inorganic photothermic material, and the organic photothermic material) may be evenly dispersed throughout the film, whether monolayer or multilayer. Alternatively, one or more layers of the film may comprise photothermic material while one or more other layers of the film may be substantially devoid of photothermic material. For example, the photothermic material may be dispersed in one or more shrink layers of the film, while all layers other than the shrink layers may be essentially devoid of photothermic material. The term “dispersed” includes a molecular dispersion such as a dissolution.
Any of the film layers discussed above may comprise photothermic material, or may be essentially devoid of photothermic material.
For example, at least about, and/or at most about, any of the following numbers of film layers may comprise photothermic material: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11. Also by way of example, at least about, and/or at most about, any of the following numbers of film layers may be essentially devoid of photothermic material: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11.
The film, or a layer of the film, may comprise at least about any of the following amounts of photothermic material: 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 8%, 10%, 12%, 15%, 20%, 25%, 30%, 35%, and 40% based on the weight of the film, or the weight of the layer incorporating the photothermic material, respectively. The film, or a layer of the film, may comprise at most about any of the following amounts of photothermic material: 50%, 40%, 30%, 20%, 15%, 10%, 8%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, and 0.05% based on the weight of the film, or the weight of the layer, respectively. The film, or one or more layers of the film, may comprise one or more organic photothermic materials, and/or one or more inorganic photothermic materials, or blends or mixtures of inorganic and organic photothermic materials, in any of the forgoing amounts. The film, or one or more layers of the film, may comprise UV photothermic particles in any of the foregoing amounts.
In one embodiment, film 10 (
In another embodiment, film 20 (
In either embodiment, the one or more discontinuous regions 16 may comprise any of the types and amounts of photothermic material discussed above (but in relation to the weight of the one or more discontinuous regions). The one or more discontinuous regions 16 may comprise polymer (e.g., thermoplastic polymer), such as one or more of any of the polymers described in this application in any of the percentage amounts described in this application (but in relation to the weight of the one or more discontinuous regions). The one or more discontinuous regions 16 may comprise one or more printing inks or varnishes.
The one or more discontinuous regions 16 may be in the shape of a dot, a strip, or other arrangement to form a desired area shape on the surface 18 of the film outer layer 12. The one or more discontinuous regions 16 may be deposited onto the film outer layer, for example, by “printing” (i.e., using a print application method) to apply a mixture comprising polymer resin and photothermic material onto the film outer layer in one or more selected regions. Useful printing methods for applying the mixture include one or more of printing methods known to those of skill in the art, such as screen, gravure, flexographic, roll, metering rod coating, ink-jet, digital, and toner print techniques.
Discontinuous regions 16 that have been deposited on an outer layer may subsequently become internal to the film structure by laminating or otherwise depositing one or more additional film layers over the discontinuous regions that incorporate photothermic material. For example, just as a printed image may be “trap printed” by laminating a film over the printed image, so too can discontinuous regions 16 be trapped by an outer film layer.
The discontinuous regions 16 incorporating photothermic material may take the form of one or more bands (e.g., “stripes” or “lanes”) of polymeric resin, as described in U.S. Pat. No. 5,110,530 to Havens, which is incorporated herein in its entirety by reference. Such bands may incorporate the dispersed photothermic material rather than or in addition to pigment. Such bands may also be internal or external to the film layer structure.
A layer of the film comprising photothermic material may have a thickness of at least about, and/or at most about, any of the following percentages based on the total thickness of the film: 90, 80, 70, 60, 50, 40, 30, 20, 15, 10, 5, and 1%.
A layer comprising photothermic material may be an outer layer of the film. An outer layer may be an “outside layer” of the film (i.e., an outer layer adapted or designed to face to the outside of a package incorporating the film) or an “inside layer” of the film (i.e., an outer layer adapted or designed to face the inside of a package incorporating the film). If the film comprises only one layer, then the one layer may be considered an “outer layer.” A layer comprising photothermic material may be an inner or interior layer of the film. An inner or interior layer of the film is between two outer layers of the film.
One or more layers of the film may include one or more additives useful in thermoplastic films, such as, antiblocking agents, slip agents, antifog agents, colorants, pigments, dyes, flavorants, antimicrobial agents, meat preservatives, antioxidants, fillers, radiation stabilizers, and antistatic agents.
The film preferably exhibits a Young's modulus sufficient to withstand the expected handling and use conditions. Young's modulus may be measured in accordance with one or more of the following ASTM procedures: D882; D5026; D4065, each of which is incorporated herein in its entirety by reference. The film may have a Young's modulus—measured either before and/or after the exposing step discussed below—of at least about—or at most about—any of the following: 10,000; 15,000; 25,000; 40,000; 70,000; 80,000; 90,000; 100,000; 150,000; 200,000; 250,000; 300,000; and 350,000 pounds/square inch, measured at a temperature of 73° F. Useful ranges for Young's modulus for the film include from about 10,000 to about 300,000 psi, from about 15,000 to about 150,000 psi, and from about 15,000 to about 70,000 psi, measured at a temperature of 212° F.
The film comprising the photothermic material may have low haze characteristics. Haze is a measurement of the transmitted light scattered more than 2.5° from the axis of the incident light. Haze is measured against the outside layer of the film. As previously discussed, the “outside layer” is the outer layer of the film that will be adjacent the area outside of a package comprising the film. Haze is measured according to the method of ASTM D 1003, which is incorporated herein in its entirety by reference. All references to “haze” values in this application are by this standard. The haze of the film—measured either before and/or after the exposing step discussed below—may be at most about, and/or at least about, any of the following values: 30%, 25%, 20%, 15%, 10%, 8%, 5%, and 3%. The film may incorporate photothermic particles having a largest dimension of less than 100 nm in order that the photothermic particles avoid contributing to the haze of the film.
The film comprising the photothermic material may have a gloss (i.e., specular gloss) as measured against the outside layer—measured either before and/or after the exposing step discussed below—of at least about, and/or at most about, any of the following values: 40%, 50%, 60%, 63%, 65%, 70%, 75%, 80%, 85%, 90%, and 95%. These percentages represent the ratio of light reflected from the sample to the original amount of light striking the sample at the designated angle. All references to “gloss” values in this application are in accordance with ASTM D 2457 (45° angle), which is incorporated herein in its entirety by reference.
The film comprising the photothermic material may be transparent (at least in the non-printed regions) so that a packaged article may be visible through the film. “Transparent” means that the film transmits incident light with negligible scattering and little absorption, enabling objects (e.g., the packaged article or print) to be seen clearly through the film under typical viewing conditions (i.e., the expected use conditions of the material). The regular transmittance (i.e., clarity) of the film—measured either before and/or after the exposing step discussed below—may be at least about, and/or at most about, any of the following values: 30%, 40%, 50%, 65%, 70%, 75%, 80%, 85%, and 90%, measured in accordance with ASTM D1746. All references to “regular transmittance” values in this application are by this standard.
The total luminous transmittance (i.e., total transmittance) of the film comprising the photothermic material—measured either before and/or after the exposing step discussed below—may be at least about, and/or at most about, any of the following values: 30%, 40%, 50%, 65%, 70%, 75%, 80%, 85%, and 90%, measured in accordance with ASTM D1003. All references to “total luminous transmittance” values in this application are by this standard.
The measurement of optical properties of plastic films, including the measurement of total transmission, haze, clarity, and gloss, is discussed in detail in Pike, LeRoy, “Optical Properties of Packaging Materials,” Journal of Plastic Film & Sheeting, vol. 9, no. 3, pp. 173-80 (July 1993), of which pages 173-80 is incorporated herein by reference.
The film comprising the photothermic material may have a free shrink at 185° F. (85° C.) in at least one direction (e.g., the machine direction or the transverse direction) and/or in both the machine and transverse directions of at least about, and/or at most about, any of the following: 5%, 7%, 10%, 15%, 25%, 30%, 40%, 45%, 50%, 55%, 60%, 70%, and 80%. Further, the film may have any of the preceding free shrink values measured at a temperature selected from any of 200° F., 220° F., 240° F., 260° F., 280° F., and 300° F.
The film may have unequal free shrink in both directions, that is differing free shrink in the machine and transverse directions. For example, the film may have a free shrink (185° F.) in the machine direction of at least 40% and a free shrink (185° F.) in the transverse direction of at least 25%. The film may not have a heat shrink characteristic in both directions. For example, the film may have a free shrink at 185° F. in one direction of less than about any of the following: 5%, 4%, 3%, 2% and 1%; or the film may have 0% free shrink at 185° F. in one direction. The free shrink of the film is determined by measuring the percent dimensional change in a 10 cm×10 cm film specimen when subjected to selected heat (i.e., at a specified temperature exposure) according to ASTM D 2732, which is incorporated herein in its entirety by reference. All references to free shrink in this application are measured according to this standard.
As is known in the art, a heat-shrinkable film shrinks upon the application of heat while the film is in an unrestrained state. If the film is restrained from shrinking to some extent—for example by a packaged product around which the film shrinks—then the tension of the heat-shrinkable film increases upon the application of heat. Accordingly, a heat-shrinkable film that has been exposed to heat so that at least a portion of the film is either reduced in size (unrestrained) or under increased tension (restrained) is considered a heat-shrunk (i.e., heat-contracted) film.
The film may exhibit a shrink tension at 185° F. in at least one direction, and/or in at least both of the machine and transverse directions, of at least about, and/or at most about, any of the following: 50 psi, 75 psi, 100 psi, 125 psi, 150 psi, 175 psi, 200 psi, 225 psi, 250 psi, 275 psi, 300 psi, 325 psi, 350 psi, 400 psi, 450 psi, 500 psi, 550 psi, and 600 psi. Further, the film may have any of the preceding shrink tensions measured at a temperature selected from any of 200° F., 220° F., 240° F., 260° F., 280° F., and 300° F. The film may have unequal shrink tension in both directions, that is differing shrink tension in the machine and transverse directions. The film may not have a shrink tension in one or both directions. Shrink tension is measured at a specified temperature (e.g., 185° F.) in accordance with ASTM D 2838 (Procedure A), which is incorporated herein in its entirety by reference. All references to shrink tension in this application are by this standard.
The film may be annealed or heat-set to reduce the free shrink slightly or substantially; or the film may not be heat set or annealed once the oriented film has been quenched in order that the film will have a high level of shrink characteristic (e.g., heat shrinkability).
The film may be manufactured by thermoplastic film-forming processes known in the art. The film may be prepared by extrusion or coextrusion utilizing, for example, a tubular trapped bubble film process or a flat film (i.e., cast film or slit die) process. The film may also be prepared by applying one or more layers by extrusion coating, adhesive lamination, extrusion lamination, solvent-borne coating, print flood coating, or by latex coating (e.g., spread out and dried on a substrate). A combination of these processes may also be employed. These processes are known to those of skill in the art.
In forming the resin mixture for the one or more film layers that comprise the photothermic material, the photothermic material may be mixed with polymer before the resin mixture is heated or melted for processing to form the film. This may help to disperse the photothermic material (e.g., the photothermic particles) in the polymer. Once mixed, the blend can be extruded and processed as discussed above.
The film may be oriented in either the machine (i.e., longitudinal), the transverse direction, or in both directions (i.e., biaxially oriented), for example, to enhance the strength, optics, and durability of the film. A web or tube of the film may be uniaxially or biaxially oriented by imposing a draw force at a temperature where the film is softened (e.g., above the vicat softening point; see ASTM 1525) but at a temperature below the film's melting point. The film may then be quickly cooled to retain the physical properties generated during orientation and to provide a heat-shrink characteristic to the film. The film may be oriented using, for example, a tenter-frame process or a bubble process. These processes are known to those of skill in the art, and therefore are not discussed in detail here. The orientation may occur in at least one direction by at least about, and/or at most about, any of the following ratios: 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 12:1, and 15:1.
One or more of the layers of the film—or at least a portion of the entire film—may be cross-linked, for example, to improve the strength of the film. Cross-linking may be achieved by using chemical additives or by subjecting one or more film layers to one or more energetic radiation treatments—such as ultraviolet, or ionizing radiation such as X-ray, gamma ray, beta ray, and high energy electron beam treatment—to induce cross-linking between molecules of the irradiated material. Useful ionizing radiation dosages include at least about any of the following: 5, 7, 10, 15, 20, 25, 30, 35, 40, 45, and 50 kGy (kiloGray). Useful ionizing radiation dosages include less than about any of the following: 150, 130, 120, 110, 100, 90, 80, and 70 kGy. The dosage of the radiation utilized for crosslinking may be substantially devoid of UV light having a wavelength effective to activate the shrink characteristic of the film. The cross-linking may occur before the orientation process, for example, to enhance the film strength before orientation, or the cross-linking may occur after the orientation process.
It may be desirable to avoid irradiating a film layer comprising PVdC or a film layer comprising photothermic material. To that end, substrate layers may be extruded and irradiated, and the PVdC-containing layer and/or the photothermic particle containing layer (and subsequent layers) may then be applied to the irradiated substrate, for example, by an extrusion coating process.
All or a portion of one or two surfaces the film may be corona and/or plasma treated to change the surface energy of the film, for example, to increase the ability of print or a food product to adhere to the film. One type of oxidative surface treatment involves bringing the sealant film into the proximity of an O2- or N2-containing gas (e.g., ambient air) which has been ionized. Exemplary techniques are described in, for example, U.S. Pat. No. 4,120,716 (Bonet) and U.S. Pat. No. 4,879,430 (Hoffman), which are incorporated herein in their entirety by reference. The film may be treated to have a surface energy of at least about 0.034 J/m2, preferably at least about 0.036 J/m2, more preferably at least about 0.038 J/m2, and most preferably at least about 0.040 J/m2.
The shrink characteristic of the film may be activated by exposure of the film to an effective amount of non-ionizing radiation, for example, an effective amount of radiation having a wavelength of from about 200 to about 700 nm. “Activating the shrink characteristic of the film” means that the film is exposed to conditions that cause one or more of: 1) the film to shrink by at least about 5% of the length in at least one direction (for example, if the film or film portion is unrestrained) or 2) the tension in the film to increase by at least about 50 psi in at least one direction (for example, if the film or film portion is restrained).
Accordingly, the film comprising photothermic material may be exposed to an amount of non-ionizing radiation energy effective for the photothermic material to generate heat to cause one or more of the following effects: 1) shrink the film by at least about 5% in at least one direction, for example, if the film or film portion is in an unrestrained state and 2) increase the tension in the film by at least about 50 pounds per square inch (psi) in at least one direction, for example if the film or film portion is in a restrained state.
The film may be exposed to an amount of non-ionizing radiation effective to shrink the film in at least one direction by at least about, and/or at most about, any of the following values: 7%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 95%. The film may shrink in at least two directions (e.g., the machine and transverse directions) by any of the previous amounts. The film may shrink unequally in both directions, that is differing free shrink in the machine and transverse directions. The film may not shrink in both directions. For example, the film may shrink in one direction by less than about any of the following: 5%, 4%, 3%, 2% and 1%; or the film may not shrink in one direction as a result of the radiation exposing step.
The film may be exposed to an amount of non-ionizing radiation energy effective to increase the tension in the film in at least one direction by at least about, and/or at most about, any of the following values: 75 psi, 100 psi, 125 psi, 150 psi, 175 psi, 200 psi, 225 psi, 250 psi, 275 psi, 300 psi, 325 psi, 500 psi, 600 psi, 700 psi, 800 psi, 1,000 psi, and 1,500 psi. The film may have an unequal increase in shrink tension in both directions, that is differing shrink tension in the machine and transverse directions. The film may not have an increase in shrink tension in one or both directions.
The film may be exposed to an amount of non-ionizing radiation energy effective to shrink the film in at least one direction by at least about any of 5, 10, 15, 20, 25, 30, 40, 50, 60, and/or 80 percentage points more than the shrink value in the same direction obtainable by exposing a comparative film—which differs from the film only by lacking the photothermic material—to the same amount of non-ionizing radiation under the same conditions. For example, a film comprising a photothermic material may be exposed to an amount of radiation energy effective to shrink the film by at least about 13% (measured according to ASTM D 2732) where exposure of a comparative film (lacking the photothermic material) to the same amount of non-ionizing radiation under the same conditions shrinks in the machine direction by 8% (measured according to ASTM D 2732).
The film may be exposed to an amount of non-ionizing radiation energy effective to increase the tension in the film in at least one direction by at least about any of 50, 60, 70, 80, 100, 130, 150, 200, 250, 300, 350, and/or 400 psi more than the increase in shrink in the same direction obtainable by exposing a comparative film—which differs from the film only by lacking the photothermic material—to the same amount of non-ionizing radiation under the same conditions. For example, a film comprising a photothermic material may be exposed to an amount of radiation energy effective to increase the shrink tension in the film by at least about 100 psi (measured according to ASTM 2838) where exposure of a comparative film (lacking the photothermic material) to the same amount of non-ionizing radiation under the same conditions increases the shrink tension in the machine direction by 50 psi (measured according to ASTM 2838).
The temperature of the film at the start of the non-ionizing radiation exposure step may be below the shrink initiation temperature of the film, that is, below the minimum temperature at which the shrink characteristic of the film is activated. The temperature of the film at the start of the non-ionizing radiation exposure step may be below the shrink initiation temperature of the film by at least about, and/or at most about, any of the following: 5, 10, 15, 20, 25, 30, 50, 70, 90, 100, 120, 140, 150, 160, 170, 180, 190, 200, and 220° F. The temperature of the film at the start of the non-ionizing radiation exposure step may be at least about, and/or at most about, any of the following: −20, −10, 0, 5, 10, 15, 20, 25, 30, 50, 70, 90, 100, 120, 140, 150, 160, 170, 180, 190, 200, and 220° F. To achieve these temperatures, the film may be heated or cooled before the start of the non-ionizing radiation exposure step; for example, the film may be heated other than by radiation exposure. Such heating or cooling may occur, for example, by conduction or forced-convection, such as in a water bath or air tunnel.
The effective amount of non-ionizing radiation of the exposing step may comprise, consist of, or consist essentially of non-ionizing radiation having wavelengths of at most about, and/or at least about, any of the following: 200, 210, 250, 280, 290, 300, 310, 315, 320, 330, 340, 345, 350, 355, 360, 365, 370, 375, 380, 390, 400, 410, 470, 475, 500, 510, 560, 570, 620, 630, and 700 nm. The effective amount of non-ionizing radiation of the exposing step may be essentially devoid of non-ionizing radiation having wavelengths of at least about, and/or at most about, any of the wavelengths in the preceding sentence.
The effective amount of non-ionizing radiation energy of the exposing step may comprise radiation having wavelengths of at least about, and/or at most about, any of the wavelength ranges in the preceding paragraph in at least about, and/or at most about, any of the following amounts: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, and 95% based on the total amount of non-ionizing radiation energy of the exposing step.
The effective amount of non-ionizing radiation energy may further comprise one or more of infrared light, microwave, and radiowave radiation in at least about, and/or at most about, any of the following amounts: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, and 95% based on the total amount of non-ionizing radiation energy of the exposing step. The non-ionizing radiation of the exposing step may be essentially devoid of any one or more of the following: infrared light, microwave, and radiowave radiation. For example, the non-ionizing radiation of the exposing step may be essentially devoid of infrared light. Also, the effective amount of non-ionizing radiation energy may be essentially devoid of microwave energy in the 2.54 nm wavelength range in order to avoid exciting (heating) water or water-bearing product (e.g., food) that may be enclosed in a package comprising the film.
The radiation energy amount (e.g., the surface dosage for the non-ionizing radiation) of the exposing step may be delivered within a duration of at most about, and/or at least about, any of the following: 900, 500, 300, 100, 80, 50, 30, 25, 20, 15, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, 0.1, 0.05, 0.01, 0.005, and 0.001 seconds. The delivery of the radiation amount may be substantially continuous during the duration time period, or may occur in a discontinuous manner over the exposure duration time period, for example by at least, and/or at most, of any of the following: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, and 20 pulses of radiation.
If multiple pulses of radiation are used, then it may be beneficial for the intervals between the pulses of radiation energy to be short enough so that the multiple pulses may have cumulative effect. An individual pulse of radiation may have a duration of at least about, and/or at most about, any of the following values: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 700, and 900 milliseconds. Further, the radiation energy amount may be delivered by a pulsed source operating at from about 1 to about 120 Hz.
The duration discussed above may also be considered a residence time for a portion of the film that is in the exposure zone of a non-ionizing radiation delivery device (e.g., a UV lamp), for example, where the film is in the form of a continuous web that travels beneath a non-ionizing radiation delivery device, which may be continuously irradiating that portion of the web that travels through the non-ionizing radiation exposure zone.
The effective amount of non-ionizing radiation energy may be considered a function of the radiation intensity (i.e., the rate of radiation energy flow per unit area) and the duration of the radiation exposure, to achieve an effective surface dose (i.e., the radiation energy per unit area at the surface of the film). The relationship between these factors may be illustrated by the following equation: (intensity)×(duration)=surface dose.
The non-ionizing radiation energy exposure step may comprise a non-ionizing average radiation intensity over the duration period (measured at the surface of the film) of at least about any of the following: 10, 30, 50, 80, 100, 150, 200, 250, 300, 400, 500, 800, 1,000, 1,200, 1,500, and 1,800 mW/cm2; and at most about any of the following: 2,000, 1,800, 1,500, 1,200, 1,000, 800, 500, 450, 400, 350, 300, 250, 200, 150, and 100 mW/cm2. If the non-ionizing radiation is delivered discontinuously (e.g., as a series of pulses) over the duration period, then any of these forgoing intensity values may describe the average non-ionizing radiation intensity over the duration. Further, any of these forgoing intensities may occur during one or more pulses of radiation, if the radiation energy is delivered in a discontinuous manner. Any of these intensities may be derived solely from the amount of UV radiation energy present in the non-ionizing radiation exposure step (e.g., UV radiation in any of the UV wavelength ranges described above), or may be derived solely from UV radiation in any of the UV wavelength ranges described above.
The amount of non-ionizing radiation energy (measured at the surface of the film) of the exposing step delivered during any of the durations discussed above may include at least about, and/or at most about, any of the following surface doses: 0.1, 0.5, 1, 5, 10, 20, 50, 100, 500, 1,000, 5,000, 10,000, and 20,000 mJ/cm2 (i.e., milli-Joules/cm2). Any of these surface doses may be derived solely from the amount of UV radiation energy present in the non-ionizing radiation exposure step (e.g., UV radiation in any of the UV wavelength ranges described above), or may be derived solely from UV radiation in any of the UV wavelength ranges described above.
The radiation intensity of the non-ionizing radiation may be measured at the surface of the film utilizing the types of detectors, filters, and radiometers that are correctly calibrated and appropriate for the wavelength ranges of the radiation being measured, as is known to those of skill in the art. See, for example, A. Ryer, “Light Measurement Handbook” (1998, International Light, Inc., Newburyport, Mass.), which is incorporated herein in its entirety by reference. For example, a silicon detector type may be useful for measuring the radiation intensity for radiation wavelengths of from about 250 to about 1050 nm, in conjunction with a radiometer such as the IL 1700 (International Light Inc.).
As is also known to those of skill in the art, if a broad range of non-ionizing radiation wavelengths contributes to the radiation being measured, then one or more filters may be used to reduce or eliminate the radiation wavelengths for which a particular detector type is not appropriate or optimum, and the previously filtered radiation wavelength ranges may be subsequently measured with an appropriate detector while filtering the previously measured radiation wavelengths. The total radiation intensity may be calculated by summing the radiation intensities of the separate measurements of different wavelength ranges.
Useful equipment and methods for providing various types of non-ionizing radiation energy are known to those of skill in the art. For example, the radiation energy may be provided by a photoflash, a flashlamp (e.g., pulsed, gas-filled flashlamps), arc lamps, excimer lamps, spark-gap discharge apparatus, and solid state devices such as UV LED (Light Emitting Diodes).
For example, the radiation energy may be provided by a pulsed lamp system such as those available from Xenon Corp. (Woburn, Mass.) (e.g., model RC-740, dual lamp and model RC-747 pulsating xenon light) and Maxwell Laboratories, Inc. (e.g., Flashblast Model FB-100 pulsed light system), and those described in U.S. Pat. Nos. 5,034,235 and 6,449,923.
Also by way of example, the radiation energy may be provided by low pressure, medium pressure or high pressure mercury arc lamps. Medium pressure mercury arc lamps are available from a variety of suppliers such as Fusion UV Systems, Gaithersburg, Md.
A package (e.g., a bag or a food package system) may comprise the film comprising the photothermic material. A product (i.e., an object) may be packaged by enclosing the product in the package comprising the film. For example, the film may be wrapped around an object to be packaged (i.e., a product) and sealed around its edges. A bag may comprise the film, for example, by heat sealing the film to itself to form the bag into which an object (i.e. a product, for example, a food product) may be placed. The air pressure in the package, such as a bag, may be lowered (e.g., vacuum) and the package subsequently sealed or clipped closed.
The package may optionally be heated, for example by other than radiation exposure, so that the temperature of the film is placed within any of the temperature ranges discussed above with respect to the film temperature at the start of the non-ionizing radiation exposure step.
The package may then be exposed to the amount of non-ionizing radiation effective to activate the shrink characteristic of the film, as discussed above. Upon activation of the shrink characteristic of the film, the film may contract about the packaged object to provide a tight package appearance. The activation of the shrink characteristic of the film of the package may occur without exposing the film to an external thermal heat source such as those sources used to activate shrink characteristic by thermal conduction (e.g., a water bath or hot-air tunnel). Alternatively, the shrink characteristic of the film of the package may be activated by exposure to an external thermal heat source (such as those sources used to activate shrink characteristic by thermal conduction) at a time selected from one or more of before, during, or after the step of exposing the film to an effective amount of non-ionizing radiation to activate the shrink characteristic of the film of the package.
To facilitate the contraction of the film, a vent hole may be cut into a portion of the film to allow trapped air to escape from the package as the film shrinks.
The package may comprise a lid comprising the film comprising the photothermic material. For example, a lid may be sealed to a tray to enclose a product; see, for example, U.S. Pat. No. 6,627,273 and U.S. patent application Ser. No. 10/201,441 filed Jul. 23, 2002, each of which is incorporated in its entirety herein by reference. Such lids may be modified to incorporate the photothermic material as set forth in this Application. Upon activation of the shrink characteristic, the lid may form a tight, wrinkle-free appearance.
Products (i.e., objects) that may be packaged in a package comprising the film include food (e.g., meat, such as fresh or frozen red meat or poultry, frozen pizzas), paper products (e.g., stationery, plates, cards, calendars), toys, games, hardware, and information storage devices (e.g., cassettes, compact discs).
An article that is used to provide a protective coating, surface, cladding, or insulation may incorporate the film described in this Application comprising photothermic material. Such an article may be used, for example, to reduce the likelihood of corrosion or an electrical short at a spice, cable termination, or feed-through assembly. Such a product may be a “shrink sleeve,” a term that as used herein includes those products known in the telecommunication and power transmission fields as “heat shrink sleeves,” “splice closures,” “heat shrink tubes,” “heat recoverable tubes,” and “cable seals.” Any of these products may comprise the film of the present invention, and the shrink characteristic of the film incorporated into the shrink sleeve may be activated by the exposure to an effective amount of non-ionizing radiation as set forth in this Application. For example, a tube may be made by sealing the film to itself, or the film may be made in tubular form. The workpiece (e.g., cable or splice) to be protected may be inserted within the article, and the article may then be exposed to an amount of non-ionizing radiation effective to activate the shrink characteristic. For example, a tubing article comprising the film may form a tight enclosure to help protect the wire and splice from water exposure. Examples of shrink sleeves that may incorporate the film comprising photothermic material are described in U.S. Pat. Nos. 3,455,337; 3,593,383; 3,717,717; 3,995,964; 4,035,534; 4,085,286; 4,017,715; 4,170,296; 4,207,364; 4,219,051; 4,421,582; 4,421,945; 4,424,246; 4,586,971; 4,915,990; 5,117,094; 5,360,945; 5,479,553; 5,528,718; 5,557,073; 5,692,299; 5,736,208; 6,107,574; 6,226,435; and 6,359,226, each of which is incorporated herein in its entirety by reference.
A tamper-evident shrink band (e.g., a neckband bottle seal or closure) may also comprise the film comprising the photothermic material. The shrink band may span a container and its closure (e.g., a bottle neck and the cap) to form a tight fit after activation of the shrink characteristic. See, for example, U.S. Pat. No. 6,276,531 to Andrews; U.S. Pat. No. 5,904,266 to Tedeschi; U.S. Pat. No. 5,641,084 to Rice; U.S. Pat. No. 5,544,770 to Travisano; U.S. Pat. No. 5,292,018 to Travisano; U.S. Pat. No. 4,813,559 to Kenyon; and U.S. Pat. No. 4,782,976 to Kenyon, each of which is incorporated herein in its entirety by reference. The bottle, or the bottle and its closure, may be inserted within the shrink band. The shrink characteristic of the shrink band may then be activated by exposing the shrink band to an effective amount of non-ionizing radiation, as discussed in this Application.
A shrink label may comprise any of the films comprising photothermic material as described in this Application. The term “shrink label” as used herein refers to a shrinkable film, for example in a tube or sleeve configuration, that is adapted for placement over or around a container (e.g., a glass or plastic bottle) and then shrunk to conform to the size and shape of the container in order to label the container. The shrink label may comprise printed images and/or information. Exemplary shrink labels that may be adapted to comprise film incorporating photothermic material include those described in one or more of U.S. Pat. No. 6,875,485 to Kanai et al; U.S. Pat. No. 6,808,822 to Rajan et al; U.S. Pat. No. 6,691,439 to Miyashita et al; U.S. Pat. No. 5,070,180 to Fukuda; and U.S. Pat. No. 4,325,762 to Burmeister et al; each of which is incorporated in its entirety by reference. The shrink label may be positioned or applied to or around a container (e.g., a bottle). The shrink characteristic of the shrink label may then be activated by exposing the shrink label to an effective amount of non-ionizing radiation, as discussed in this Application.
The following examples are presented for the purpose of further illustrating and explaining one or more embodiments of the present invention and are not to be taken as limiting in any regard. Unless otherwise indicated, all parts and percentages are by weight. The following abbreviations are used in the Examples:
EVA1 is an ethylene/vinyl acetate copolymer having 12% vinyl acetate content, available from DuPont under the Elvax 3134Q trade name.
EVA2 is an ethylene/vinyl acetate copolymer having 9% vinyl acetate content, available from ExxonMobil under the Escorene LD318 trade name.
EVA3 is an ethylene/vinyl acetate copolymer having 28% vinyl acetate content, available from ExxonMobil under the Escorene LD713.93 trade name.
EVA4 is an ethylene/vinyl acetate copolymer having 28% vinyl acetate content, available from Exxon Mobil Corporation under the Escorene LD761.36 trade name.
LDPE1 is a low density polyethylene having a melt index of 12 g/10 min measured according to ASTM D1238 (Condition 190/2.16) and provided as a component of the titanium dioxide masterbatch 110858 from Ampacet Corporation
LLDPE1 is a linear low density polyethylene available from Dow Corporation under the Dowlex 2045 trade name.
LLDPE2 is a linear low density polyethylene having a melt index of 25 g/10 min measured according to ASTM D1238 Condition 190/2.16 and provided as a component of the zinc oxide masterbatch from PolyOne Corporation.
LLDPE3 is a linear low density polyethylene available from ExxonMobil Corporation under the Exceed 4518PA trade name.
LLDPE4 is a linear low density polyethylene available from ExxonMobil Corporation under the Excorene LL3003.32 trade name.
MDPE1 is a medium density polyethylene available from Dow Corporation under the Dowlex 2037 trade name.
PVDC1 is a polyvinylidene chloride copolymer available from Dow Corporation under the Saran 806 trade name.
UVB1 is an organic photothermic material that is 2-(2′-Hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole available from Ciba Geigy Corporation under the Tinuvin 326 trade name.
UVB2 is an organic photothermic material that is a benzotriazole available from Ciba Geigy Corporation under the Tinuvin T234 trade name.
VLDPE1 is a very low density polyethylene available from Dow Corporation under the ATTAIN 4203 trade name.
VLDPE2 is a very low density polyethylene available from Dow Corporation under the Affinity PL1850G trade name.
VLDPE3 is a very low density polyethylene available from Dow Corporation under the Affinity PL1280 trade name.
ZnO-1 is zinc oxide available from BASF Corporation under the Z-Cote trade name in the form of particles having an average particle size of 60 nm.
ZnO-2 is zinc oxide available from Elementis Corporation under the Decelox trade name in the form of particles having an average particle size of 50 to 55 nm.
ZnO-3 is zinc oxide available from Nanoscale Materials, Inc. under the Nanoactive ZnO trade name in the form of particles having a fully dispersed average particle size of less than 10 nm.
ZnO-4 is zinc oxide having an average particle size of 60 nm used by PolyOne Corporation in its zinc oxide masterbatch described below.
TiO2-1 is titanium dioxide having an average particle size of 23 nm.
TiO2-2 is titanium dioxide having an average particle size of 230 nm.
Three zinc oxide particle masterbatches were formed by compounding 10 weight % of each of ZnO-1, ZnO-2, and ZnO-3 with EVA1 using a Leistritz co-rotating twin screw extruder. Each of the zinc oxide masterbatches was then blended with LLDPE1 at a ratio of 85 wt. % LLDPE1 to 15 wt. % masterbatch to give a final zinc oxide particle content of 1.5 wt. %.
A titanium dioxide materbatch was formed by compounding 5 wt. % TiO2-1 with EVA2 in the same manner as above. The titanium dioxide masterbatch was blended with LLDPE1 at a ratio of 70 wt. % LLDPE1 to 30 wt. % masterbatch to give a final titanium dioxide content of 1.5 wt. %.
A zinc oxide masterbatch was procured from PolyOne Corporation containing 25% ZnO-4 and 75% EVA3. The zinc oxide masterbatch was blended with LLDPE1 at a ratio of 94 wt. % LLDPE1 to 6 wt. % masterbatch to give a final zinc oxide content of 1.5 wt. %.
Each resulting dry blend was compounded on a Leistritz co-rotating twin screw extruder, and extruded as a 1 mil thick film. Also, three unfilled 1-mil films were extruded to contain: 1) 85% LLDPE1 and 15% EVA1, 2) 70% LLDPE1 and 30% EVA2, and 3) 100% LLDPE1.
The transmission of UV and visible light was measured for each of the eight resulting films; the films that contained the particles showed preferential absorption of UV light compared to the films that did not contain the particles. Light transmission in the visible light wavelengths remained high, indicating that high optical transparency was maintained, and minimal light scattering occurred in these films.
17-mil thick plaques were also prepared using each of the above blends. Each plaque was heated to 210° F. and held at that temperature (i.e., soaked) for 60 seconds. Each plaque was then biaxially stretched at 15 inches per second so that each of the final dimensions of length and width were extended by 300% relative to the initial length and width. The final thickness for each of the resulting oriented Examples 1-4 films and the Comparisons 1-3 films was 1 mil. After stretching, each film was immediately quenched to lock shrink tension into the film. The films had a shrink initiation temperature of about 55° C.
A 3-inch by 3-inch sample of each film was placed in a chamber 1 inch from a UV light source, which was a pulsed lamp system Model RC-747 (Xenon Corp., Woburn, Mass.) pulsating xenon light having a 4.2-inch spiral lamp. The electromagnetic radiation energy distribution for this lamp for wavelengths of from 200 nm to 1,000 nm as reported by the manufacturer is shown below.
Each sample was exposed for 2 or 5 seconds in pulsing mode with a 10 pulses per second frequency and at 60 milliseconds per pulse. The surface dose for the UV radiation was calculated to have been about 354 milliJoules/cm2 for the 2 second exposure duration and about 885 mJ/cm2 for the 5 second exposure duration. The resulting linear free shrink amounts after irradiation are shown in Table 1.
The Comparison 3 and Example 5 films were also submerged in an 85° C. water bath for 8 seconds. The linear free shrink for the films is reported below in Table 1.
“—” above signifies that the sample was not tested under the referenced condition.
Further, samples of the Example 5 and Comparison 3 films were exposed for 1, 2, 3, and 5 seconds in pulsing mode with a 10 pulses per second frequency and at 60 milliseconds/pulse at a distance of either 1 inch or 2 inches from the lamp radiation source. The resulting linear shrink tensions during irradiation are shown in Table 2. The Example 5 and Comparison 3 films were also submerged in an 85° C. water bath for the exposure duration noted below The linear free shrink for the films is reported below in Table 2.
*maximum shrink force that occurred during the 2 second exposure interval.
“—” above signifies that the sample was not tested under the referenced condition.
A resin blend was formed by compounding 2.9 wt. % of UVB1 and 1 wt. % of UVB2 with MDPE1 using a Leistritz co-rotating twin screw extruder to extrude a 15 mil thick film and a 2 mil thick film. A 15 mil thick film and a 2 mil thick film of 100% MDPE1 were also extruded using the same co-rotating twin screw extruder.
The transmission of UV and visible light was measured for each of the resulting films; the films that contained the organic photothermic material showed preferential absorption of UV light compared to the films that did not contain organic photothermic material. Light transmission in the visible light wavelengths remained high, indicating that high optical transparency was maintained, and minimal light scattering occurred in these films.
Square plaques were cut from the 15-mil thick film containing UVB1 and UVB2 (Example 6) and from the 15-mil thick film of 100% MDPE1 (Comparison 4). Each plaque was heated to 230° F. and held at that temperature (i.e., soaked) for 60 seconds. Each plaque was then biaxially stretched at 15 inches per second so that each of the final dimensions of length and width were extended by 250% relative to the initial length and width. The final thickness for each of the resulting Example 6 film and Comparison 4 film was 0.5 mil. After stretching, each film was immediately quenched to lock shrink tension into the film. The films had a heat shrink initiation temperature of about 55° C.
A 2-inch by 2-inch sample of each film was placed on a tray. Each tray was placed on the conveyer belt of a Lesco C6120 UV curing conveyer, and passed under the UV light source at a selected constant speed ranging from 20 ft/min to 50 ft/min as shown in Table 3. The resulting free shrink of the films from the non-ionizing radiation exposure are shown in Table 3.
The light source of the curing conveyor was a 6,000 W Epic Lamp (Fusion) utilizing an H+ bulb. It is believed that approximately 30% of the radiation energy intensity provided by the lamp is ultraviolet radiation. The lamp radiation emission was focused into a line having a width of approximately 0.5 inches and a linear intensity of about 600 W/inch providing an average intensity of UV radiation over the exposure duration of about 2,910 mW/cm2.
A seven-layer Comparison 5 film having the structure shown in Table 4 was made by first cast extruding layers 1-3, then electronically crosslinking these layers, then extrusion coating layers 4-7 onto the crosslinked substrate layers 1-3. The resulting film was biaxially oriented using a double bubble process to form 2.5 mil thick films.
*BF = before orientation
**AF = after orientation
An Example 7 film was made using the same process, structure, and composition as the Comparison 5 film, except that the layer 1 had the composition of 80 wt % VLDPE/LLDPE blend and 20 wt % of a zinc oxide masterbatch procured from PolyOne Corporation (“ZnO-4 Masterbatch”), which contained 25% ZnO-4 and 75% LLDPE2. The ZnO-4 Masterbatch was dry-blended with the other components of layer 1. Accordingly, the total loading of ZnO-4 in the layer 1 was 5% based on the weight of layer 1; and the loading of ZnO-4 based on the weight of the entire film was 1.1%.
An Example 8 film was made using the same process, structure, and composition as the Comparison 5 film, except that ZnO-4 Masterbatch was incorporated into the layers 1, 2, and 6 in an amount of 5 wt % ZnO-4 Masterbatch, with the balance of the layer being the resin of the corresponding Comparison 5 layer. Accordingly, the total loading of ZnO-4 in each of layers 1, 2, and 6 was 1.25 wt %; and the loading of ZnO-4 based on the weight of the entire film was 0.92%.
The transmission of UV and visible light was measured for each of the Comparison 5 and Examples 7-8 films. The Examples 7-8 films, which contained the ZnO-4 photothermic particles showed preferential absorption of UV light compared to the Comparison 5 film that did not contain the particles. Light transmission in the visible light wavelengths remained high, indicating that high optical transparency was maintained, and minimal light scattering occurred in these films.
A 2-inch by 2-inch sample of each of the Comparison 5 and Examples 7-8 films was placed on a tray. Each tray was placed on the conveyer belt of the UV curing conveyor discussed above, and passed under the UV light source at a selected constant speed ranging from 20 ft/min to 50 ft/min as shown in Table 5. The resulting free shrink of the films from the non-ionizing radiation exposure are shown in Table 5. Since the transverse and machine direction shrinks were about the same for these films, the linear free shrink values below are an average of the machine and transverse direction linear free shrinkage values.
The Comparison 5 and Examples 7-8 films were also submerged in an 85° C. water bath for 8 seconds. The average of the machine and transverse direction linear free shrinks for the films is also reported below in Table 5.
A four-layer Example 9 film having the structure shown in Table 6 was made by cast extruding the film, followed by electronically crosslinking the cast film, then biaxially orienting the film using a double bubble process to form 2.0 mil thick film.
Layer 2 comprised 78 wt. % VLDPE, 11 wt % LDPE, and 11 wt % TiO2-2. The loading of TiO2-2 based on the weight of the entire film was 5.5%. The size of the TiO2 particles in layer 2 was sufficient scatter visible light, so the film was opaque to visible light. A multicolor print was applied to the surface of the bag.
*BF = before orientation
**AF = after orientation
3-inch by 3-inch samples of Example 9 film were placed on trays. Each tray was placed on the conveyer belt of the UV curing conveyor discussed in Example 6, and passed under the UV light source (as described in Example 6) at a selected constant speed ranging from 30 ft/min to 60 ft/min. The resulting free shrink of the films from the non-ionizing radiation exposure are shown in Table 7.
The Example 9 film was also submerged in an 85° C. water bath for 8 seconds. The linear free shrinks for the films is also reported in Table 7. The free linear shrink values were reported for both machine and transverse since they differed substantially in this film.
A bag configured to contain a chicken carcass was formed from the Example 8 film by heat sealing the edges of the film together. A refrigerated chicken carcass was placed in the open end of the bag, which was then vacuumed sealed closed. The packaged chicken was then placed into a chamber containing a UV light source, which was the lamp described above in Examples 1-5. The package was irradiated by the lamp in pulsing mode at a distance ranging from 2 inches to 6 inches. The package was subjected to nine consecutive UV light exposures each lasting 12 seconds. The package was rotated 30° clockwise in front of the lamp between each exposure. The total exposure time was 108 seconds. The UV light exposure caused the bag to shrink tightly around the packaged chicken carcass.
A bag configured to contain a cut of beef was formed from the Example 8 film by heat sealing the edges of the film together. A ½-inch thick refrigerated beef flank steak was placed in the open end of the bag, which was then vacuumed sealed closed. The packaged steak was then placed on a conveyor and passed under a UV light source, which was the lamp and configuration described above in Examples 6-8. The conveyor speed was 20 feet/minute. The packaged steak was passed under the UV light source two consecutive times, then flipped over and passed under the source two more times, for a total of four passes. The UV light exposure caused the bag to shrink tightly around the packaged beef steak.
Any numerical ranges recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable (e.g., temperature, pressure, time) may range from any of 1 to 90, 20 to 80, or 30 to 70, or be at least any of 1, 20, or 30 and at most any of 90, 80, or 70, then it is intended that values such as 15 to 85, 22 to 68, 43 to 51, and 30 to 32, as well as at least 15, at least 22, and at most 32, are expressly enumerated in this specification. For values that are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.
The above descriptions are those of preferred embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the claims, which are to be interpreted in accordance with the principles of patent law, including the doctrine of equivalents. Except in the claims and the specific examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material, reaction conditions, use conditions, molecular weights, and/or number of carbon atoms, and the like, are to be understood as modified by the word “about” in describing the broadest scope of the invention. Any reference to an item in the disclosure or to an element in the claim in the singular using the articles “a,” “an,” “the,” or “said” is not to be construed as limiting the item or element to the singular unless expressly so stated. The definitions and disclosures set forth in the present Application control over any inconsistent definitions and disclosures that may exist in an incorporated reference. All references to ASTM tests are to the most recent, currently approved, and published version of the ASTM test identified, as of the priority filing date of this application. Each such published ASTM test method is incorporated herein in its entirety by this reference.
