Abstract:
A transparent thermoplastic resinous laminate film is disclosed having at least 10 very thin layers of substantially uniform thickness, said layers being generally parallel, the contiguous adjacent layers being of different transparent thermoplastic resinous materials of which one is a naphthalate-based polyester or copolyester resin, the contiguous adjacent layers differing in refractive index by at least about 0.03.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to multilayer coextruded light-reflecting films which have a narrow reflection band because of light interference and contain a layer of naphthalate-based polyester.  
         BACKGROUND OF THE INVENTION  
         [0002]    Iridescent multilayer films are composed of a plurality of generally parallel layers of transparent thermoplastic resinous material in which the contiguous adjacent layers are of diverse resinous material whose index of refraction differs by at least about 0.03. The film contains at least 10 layers and more usually at least 35 layers and, preferably, at least about 70 layers.  
           [0003]    The individual layers of the film are very thin, usually in the range of about 30 to 500 nm, preferably about 50-400 nm, which causes constructive interference in light waves reflected from the many interfaces. Depending on the layer thickness and the refractive index of the polymers, one dominant wavelength band is reflected and the remaining light is transmitted through the film. The reflected wavelength is determined by the sum of the optical thickness of a pair of layers.  
           [0004]    The quantity of the reflected light (reflectance) and the color intensity depend on the difference the two refractive indices, on the ratio of optical thicknesses of the layers, on the number of layers and on the uniformity of the thickness. If the refractive indices are the same, there is no reflection at all from the interfaces between the layers. In multilayer iridescent films, the refractive indices of contiguous adjacent layers differ by at least 0.03 and preferably by at least 0.06 or more. For first order reflections, reflectance is highest when the optical thicknesses of the layers are equal, although suitably high reflectances can be achieved when the ratio of the two optical thicknesses falls between 5:95 and 95:5. Distinct color reflections are obtained with as few as 10 layers. However, for maximum color intensity, it is desirable to have between 35 and 1000 or more layers. High color intensity is associated with a reflection band which is relatively narrow and which has high reflectance at its peak. It should be recognized that although the term “color intensity” has been used here for convenience, the same considerations apply for the invisible reflection in the ultraviolet and infrared ranges.  
           [0005]    The multilayer films can be made by a chill-roll casting technique using a conventional single manifold flat film die in combination with a feedblock which collects the melts from each of two or more extruders and arranges then into the desired layer pattern. Feedblocks are described for instance in U.S. Pat. Nos. 3,565,985 and 3,773,882. The feedblocks can be used to form alternating layers of either two components or more (e.g. ABABAB . . . , ABCABC . . . or ACBCACBC . . . ). The very narrow multilayer stream flows through a single manifold flat film die where the layers are simultaneously spread to the width of the die and thinned to the final die exit thickness. The number of layers and their thickness distribution can be changed in inserting a different feedblock module. Usually, the outermost layer or layers on each side of the sheet are thicker than the other layers. This thicker skin may consist of one of the components which makes up the optical core, may be a different polymer which is utilized to impart desirable mechanical, heat sealing, or other properties, or may be a combination of these.  
           [0006]    Examination of iridescent films of desirable optical properties revealed deficiencies in certain mechanical properties. For example, the adhesion between individual layers of the multilayer structure may be insufficient, and the film may suffer from internal delamination or separation of layers during use. The iridescent film is often adhered to paper or board for its decorative effect, and is then used for greeting cards, cartons, wrapping paper and the like. Delamination of the film is unsightly and may even lead to separation of the glued joints if carton. In addition, the solvent resistance and heat stability of such films are not as great as desired for widespread utilization.  
           [0007]    In U.S. Pat. No. 4,310,584, these deficiencies are significantly overcome by using a thermoplastic terephthalate polyester or copolyester resin as the high refractive index component of the system in which two or more resinous material form a plurality of layers. While a substantial improvement was realized, it also required the use of two polymers from significantly different polymer families. That fact, in turn, means that there are inherent significant differences between the two polymers and their relative adhesion to each other, chemical resistance, toughness, etc. As a result, the film itself is generally no better with regard to a particular characteristic than the weaker or poorer of the polymers employed. If two polymers closely related were employed in order to maximize relative adhesion to one each other, or toughness, or chemical resistance, etc., the polymers involved did not have a sufficient difference in refractive index so as to create the desired iridescent color.  
           [0008]    Schrenk and Wheatly (Co-extruded Elastomeric Optical Interference Film, Antec &#39;88, 1703-1707) have reported the preparation of a multilayer light reflecting film co-extruded from two thermoplastic elastomers. The film which had one thermoplastic elastomer based on nylon and the other based on urethane, exhibited reversible changes in reflection spectra when deformed and relaxed. That is, this very specific combination had the ability of stretching without losing appearance characteristics. This type of films has been described in more detail in U.S. Pat. No. 4,937,134.  
           [0009]    U.S. Pat. No. 5,089,318 discloses that further improvements in adhesion, solvent resistance and the like can be obtained by employing a thermoplastic elastomer (TPE) as one of the resinous materials. Such materials are copolymers of a thermoplastic hard segment such as polybutyl terephthalate, polyethylene terephthalate, polycarbonate, etc., and a soft elastomeric segment such as polyether glycols, silicone rubbers, polyetherimide and the like.  
           [0010]    While prior art structures represented significant improvement in the areas of delamination resistance and better solvent stability, there were still some limitations with regard to these properties. In addition, iridescent films of the prior art still had deficiencies relative to their temperature stability, tensile strength and UV stability. The present invention surprisingly provides significant improvements over current known structures with regard to these properties.  
         SUMMARY OF THE INVENTION  
         [0011]    It is, therefore an object of the invention to provide a transparent thermoplastic resinous laminate having good heat and solvent stability, good tensile strength, good delamination resistance, and good UV stability.  
           [0012]    In one embodiment, the present invention provides a transparent thermoplastic resinous laminate film of at least 10 very thin layers of substantially uniform thickness, said layers being generally parallel, the contiguous adjacent layers being of different transparent thermoplastic resinous materials of which one is a naphthalate-based polyester or copolyester resin, the contiguous adjacent layers differing in refractive index by at least about 0.03.  
           [0013]    In another embodiment, the present invention provides a transparent thermoplastic resinous laminate film of at least about 70 very thin layers of substantially uniform thickness, said layers being generally parallel, the contiguous adjacent layers being of different transparent thermoplastic resinous materials of which one is a polyethylene naphthalate polyester or copolyester, and the other is a polybutylene terephthalate polyester or copolyester, wherein the outermost layers are polybutylene terephthalate polyester.  
           [0014]    Other objects and advantages of the present invention will become apparent from the following description and appended claims.  
         DETAILED DESCRIPTION OF THE INVENTION  
         [0015]    It has now been found that the objectives of this invention are realized by employing a naphthalate-based polyester or copolyester resin as a component in the contiguous adjacent layers in the optical core of a transparent thermoplastic resinous laminate film. Preferably, the naphthalate-based polyester or copolyester is based on naphthalene dicarboxylate. Examples of usable polyester resin include polyethylene naphthalate and polybutylene naphthalate. Examples of usable copolyesters include copolyesters comprising ethylene naphthalate and/or butylene naphthalate. Preferably, the copolyester consists of ethylene naphthalate and butylene naphthalate.  
           [0016]    The iridescent film of the present invention can be obtained by coextruding the naphthalate-based polyester or copolyester resin with a different transparent thermoplastic resin which is selected to differ in refractive index by at least 0.03 and preferably by at least 0.06. Among the other resinous materials which can be used are transparent thermoplastic polyester or copolyester resins characterized by a refractive index of about 1.55 to about 1.61. Examples of usable thermoplastic polyester resins include polyethylene terephthalate (PET) which is made by reacting either terephthalic acid or dimethyl terephthalate with ethylene glycol; polybutylene terephthalate (PBT) which is made by the catalyzed combination of 1,4-butanediol with either terephthalic acid or dimethyl terephthalate; and the various thermoplastic copolyesters which are synthesized using more than one glycol and/or more than one dibasic acid. PETG polyester, for example, is a glycol modified PET made from ethylene glycol and cyclohexanedimethanol (CHDM) and terephthalic acid; PCTA copolyester is an acid-modified copolyester of CHDM with terephthalic and isophthalic acids. Additional other resinous materials that can be coextruded with the naphthalate-based polyester or copolyester resin are listed in Table 1.  
                           TABLE 1                                       Approximate               Refractive           Polymer name:   Index                           Poly(tetrafluoroethylene-co-hexafluoropropylene)   1.338           Poly(pentadecafluorooctyl acrylate)   1.339           Poly(tetrafluoro-3-(heptafluoropropoxy)propyl   1.346           acrylate)           Poly(tetrafluoro-3-(pentafluoroethoxy)propyl   1.348           acrylate)           Poly(tetrafluoroethylene)   1.35 (−1.38)           Poly(undecafluorohexyl acrylate)   1.356           Poly(nonafluoropentyl acrylate)   1.360           Poly(tetrafluoro-3-(trifluoromethoxy)propyl   1.360           acrylate)           Poly(pentafluorovinyl propionate)   1.364           Poly(heptafluorobutyl acrylate)   1.367           Poly(trifluorovinyl acetate)   1.375           Poly(octafluoropentyl acrylate)   1.380           Poly(pentafluoropropyl acrylate)   1.385           Poly(2-(heptafluorobutoxy)ethyl acrylate)   1.390           Poly(2,2,3,4,4,4-hexafluorobutyl acrylate)   1.392           Poly(trifluoroethyl acrylate)   1.407           Poly(2-(1,1,2,2-tetrafluoroethoxy)ethyl acrylate)   1.412           Poly(trifluoroisopropyl methacrylate)   1.4177           Poly(2,2,2-trifluoro-1-methylethyl methacrylate)   1.4185           Poly(2-(trifluoroethyoxy)ethyl acrylate)   1.419           Poly(trifluorochloroethylene)   1.42-1.43           Poly(vinylidene fluoride)   1.42           Poly(dimethylsilylene(poly(dimethyl siloxane))   1.43           Poly(trifluoroethyl methacrylate)   1.437           Poly(oxypropylene)   1.4495           Poly(vinyl isobutyl ether)   1.4507           Poly(vinyl ethyl ether)   1.4540           Poly(oxyethylene)   1.4563           Poly(vinyl butyl ether)   1.4563           Poly(vinyl pentyl ether)   1.4581           Poly(vinyl hexy ether)   1.4591           Poly(4-methyl-1-pentene)   1.459-1.465           Cellulose acetate butyrate   1.46-1.49           Poly(4-fluoro-2-trifluoromethylstyrene)   1.46           Poly(vinyl octyl ether)   1.4613           Poly(vinyl 2-ethylhexyl ether)   1.4626           Poly(vinyl decyl ether)   1.4628           Poly(2-methoxyethyl acrylate)   1.463           Poly(butyl acrylate)   1.4631           Poly(butyl acrylate)   1.466           Poly(tert-butyl methacrylate)   1.4638           Poly(vinyl dodecyl ether)   1.4640           Poly(3-ethoxypropyl acrylate)   1.465           Poly(oxycarbonyl tetramethylene)   1.465           Poly(vinyl propionate)   1.4665           Poly(vinyl acetate)   1.4665           Poly(vinyl methyl ether)   1.467           Poly(ethyl acrylate)   1.4685           Poly(ethylene-co-vinyl acetate)   1.47-1.50           (30%-20% vinyl acetate)           Cellulose propionate   1.47-1.49           Cellulose acetate propionate   1.47           Benzyl cellulose   1.47-1.58           Phenol-formaldehyde resins   1.47-1.70           Cellulose triacetate   1.47-1.48           Poly(vinyl methyl ether) (isotactic)   1.4700           Poly(3-methoxypropyl acrylate)   1.471           Poly(2-ethoxyethyl acrylate)   1.471           Poly(methyl acrylate)   1.472-1.480           Poly(isopropyl methacrylate)   1.4728           Poly(1-decene)   1.4730           Poly(propylene) (atactic, density 0.8575 g/cm 3 )   1.4735           Poly(vinyl sec-butyl ether) (isotactic)   1.4740           Poly(dodecyl methacrylate)   1.4740           Poly(oxyethyleneoxysuccinoyl)   1.4744           (poly(ethylene succinate))           Poly(teradecyl methacrylate)   1.4746           Poly(ethylene-co-propylene) (EPR-rubber)   1.4748-1.48           Poly(hexadecyl methacrylate)   1.4750           Poly(vinyl formate)   1.4757           Poly(2-fluoroethyl methacrylate)   1.4768           Poly(isobutyl methacrylate)   1.477           Ethyl cellulose   1.479           Poly(vinyl acetal)   1.48-1.50           Cellulose acetate   1.48-1.50           Cellulose tripropionate   1.48-1.49           Poly(oxymethylene)   1.48           Poly(vinyl butyral)   1.48-1.49           Poly(n-hexyl methacrylate)   1.4813           Poly(n-butyl methacrylate)   1.483           Poly(ethylidene dimethacrylate)   1.4831           Poly(2-ethoxyethyl methacrylate)   1.4833           Poly(oxyethyleneoxymaleoyl)   1.4840           (poly(ethylene maleate))           Poly(n-propyl methacrylate)   1.484           Poly(3,3,5-trimethylcyclohexyl methacrylate)   1.485           Poly(ethyl methacrylate)   1.485           Poly methacrylate)   1.4868           (2-nitro-2-methylpropyl   1.4889           Poly(triethylcarbinyl methacrylate)           Poly(1,1-diethyipropyl methacrylate)   1.4889           Poly(methyl methacrylate)   1.4893           Poly(2-decyl-1,3-butadiene)   1.4899           Poly(vinyl alcohol)   1.49-1.53           Poly(ethyl glycolate methacrylate)   1.4903           Poly(3-methylcyclohexyl methacrylate)   1.4947           Poly(cyclohexyl α-ethoxyacrylate)   1.4969           Methyl cellulose(low viscosity)   1.497           Poly(4-methylcyclohexyl methacrylate)   1.4975           Poly(decamethylene glycol dimethacrylate)   1.4990           Poly(urethanes)   1.5-1.6           Poly(1,2-butadiene)   1.5000           Poly(vinyl formal)   1.50           Poly(2-bromo-4-trifluoromethylstyrene)   1.5           Cellulose nitrate   1.50-1.514           Poly(sec-butyl α-chloroacrylate)   1.500           Poly(2-beptyl-1,3-butadiene)   1.5000           Poly(ethyl α-chloroacrylate)   1.502           Poly(2-isopropyl-1,3-butadiene)   1.5028           Poly(2-methylcyclohexyl methacrylate)   1.5028           Poly(propylene) (density 0.9075 g/cm 3 )   1.5030           Poly(isobutene)   1.505-1.51           Poly(bornyl methacrylate)   1.5059           Poly(2-tert-butyl-1,3-butadiene)   1.5060           Poly(ethylene glycol dimethacrylate)   1.5063           Poly(cyclohexyl methacrylate)   1.5066           Poly(cyclohexanediol-1,4-dimethacrylate)   1.5067           Butyl rubber (unvulcanized)   1.508           Poly(tetrahydrofurfuryl methacrylate)   1.5096           Gutta percha (5)   1.509           Poly(ethylene) ionomer   1.51           poly(oxyethylene) (high molecular weight)   1.51-1.54           Poly(ethylene) (density 0.914 g/cm 3 )   1.51           (density 0.94-0.945 g/cm 3 )   1.52-1.53           (density 0.965 g/cm 3 )   1.545           Poly(1-methylcyclohexyl methacrylate)   1.5111           Poly(2-hydroxyethyl methacrylate)   1.5119           Poly(vinyl chloroacetate)   1.512           Poly(butene) (isotactic)   1.5125           Poly(vinyl methacrylate)   1.5129           Poly(N-butyl-methacrylamide)   1.5135           Gutha percha (α)   1.514           Terpene resin   1.515           Poly(1,3-butadiene)   1.5154           Shellac   1.51-1.53           Poly(methyl α-chloroacrylate)   1.517           Poly(2-chloroethyl methacrylate)   1.517           Poly(2-diethylaminoethyl methacrylate)   1.5174           Poly(2-chlorocyclohexyl methacrylate)   1.5179           Poly(1,3-butadiene) (35% cis; 56% trans; 7%   1.5180           1,2-content)           Natural rubber   1.519-1.52           Poly(allyl methacrylate)   1.5196           Poly(vinyl chloride) + 40% dioctyl phthalate   1.52           Poly(acrylonitrile)   1.52               1.5187           Poly(methacrylonitrile)   1.52           Poly(1,3-butadiene) (high cis-type)   1.52           Poly(butadiene-co-acrylonitrile)   1.52           Poly(methyl isopropenyl icetone)   1.5200           Poly(isoprene)   1.521           Poly(ester) resin, rigid (ca, 50% styrene)   1.523-1.54           Poly(N-(2-methoxyethyl)methacrylamide)   1.5246           Poly(2,3-dimethylbutadiene) (methyl rubber)   1.525           Poly(vinyl chloride-co-vinyl acetate) (95/5-90/10)   1.525-1.536           Poly(acrylic acid)   1.527           Poly(1,3-dichioropropyl methacrylate)   1.5270           Poly(2-chloro-1-(chloromethyl)ethyl methacrylate)   1.5270           Poly(acrolein)   1.529           Poly(1-vinyl-2-pyrrolidone)   1.53           Hydrochlorinated rubber   1.53-1.55           Nylon 6: Nylon 6,6: Nylon 6, 10 (moulding)   1.53           (Nylon-6-fiber: 1.515 transverse,           1.565 in fiber direction)           Poly(butadiene-co-styrene) (ca, 30% styrene)   1.53           black copolymer           Poly(cyclohexyl α-chloroacrylate)   1.532           Poly(2-chloroethyl α-chloroacrylate)   1.533           Poly(butadiene-co-Styrene) (ca, 75/25)   1.535           Poly(2-aminoethyl methacrylate)   1.537           Poly(furfuryl methacrylate)   1.5381           Proteins   1.539-1.541           Poly(butylmercaptyl methacrylate)   1.5390           Poly(1-phenyl-n-amyl methacrylate)   1.5396           Poly(N-methyl-methacrylamide)   1.5398           Cellulose   1.54           Poly(vinyl chloride)   1.54-1.55           Urea formaldehyde resin   1.54-1.56           Poly(sec-butyl α-bromoacrylate)   1.542           Poly(cyclohexyl α-bromoacrylate)   1.542           Poly(2-bromoethyl methacrylate)   1.5426           Poly(dihydroabietic acid)   1.544           Poly(abietic acid)   1.546           Poly(ethylmercaptyl methacrylate)   1.547           Poly(N-allyl methacrylamide)   1.5476           Poly(1-phenylethyl methacrylate)   1.5487           Poly(vinylfuran)   1.55           Poly(2 -vinyltetrahydrofuran)   1.55           Poly(vinyl chloride) + 40% trictesyl phosphate   1.55           Epoxy resins   1.55-1.60           Poly(p-methoxybenyl methacrylate)   1.552           Poly(isopropyl methacrylate)   1.552           Poly(p-isopropylstyrene)   1.554           Poly(chloroprene)   1.554-1.558           Poly(oxyethylene)-α-benzoate-ω-methacrylate)   1.555           Poly(p,p′-xylylenyl dimethacrylate)   1.5559           Poly(1-phenylallyl methacrylate)   1.5573           Poly(p-cyclohexylphenyl methacrylate)   1.5575           Poly(2-phenylethyl methacrylate)   1.5592           Poly(oxycarbonyloxy-1,4-phenylene-1-Propyl   1.5602           butylidene-1,4-phenylene)           Poly(1-(o-chlorophenyl)ethyl methacrylate)   1.5624           Poly(styrene-co-maleic anhydride)   1.564           Poly(1-phenylcyclohexyl methacrylate)   1.5645           Poly(oxycarbonyloxy-1,4-phenylene-1,3-dimethyl-   1.5671           butylidene-1,4-phenylene)           Poly(methyl α-bromoacrylate)   1.5672           Poly(benzyl methacrylate)   1.5680           Poly(2-phenylsulfonyl)ethyl methacrylate)   1.5682           poly(m-cresyl methacrylate)   1.5683           Poly(styrene-co-acrylonitrile) (ca, 75/25)   1.57           Poly(oxycarbonyloxy-1,4-phenyleleneisobutylidene-   1.5702           1,4-phenylene)           Poly(o-methoxyphenyl methacrylate)   1.5705           Poly(phenyl methacrylate)   1.5706           Poly(o-cresyl methacrylate)   1.5707           Poly(diallyl phthalate)   1.572           Poly(2,3 -dibromopropyl methacryate)   1.5739           Poly(oxycarbonyloxy-1,4-phenylene-1-methyl-   1.5745           butylidene-1,4-phenylene)           Poly(oxy-2,6-dimethylphenylene)   1.575           Poly(oxyethyleneoxyterephthaloyl) (amorphous)   1.5750           (poly(ethylene terephthalate))           (crystalline fiber: 1.51 transverse;           1.64 in fiber direction)           Poly(vinyl benzoate)   1.5775           poly(oxycarbonyloxy-1,4-phenylenebutylidene-1,4-   1.5792           phenylene)           Poly(1,2-diphenylethyl methacrylate)   1.5816           Poly(o-chlorobenzyl methacrylate)   1.5823           Poly(oxycarbonyloxy-1,4-phenylene-sec-butylidene-   1.5827           1,4-phenylene)           Poly(oxypentaerythritoloxyphthaloyl)   1.584           Poly(m-nitrobenyl methacrylate)   1.5845           Poly(oxycarbonyloxy-1,4-phenyleneisopropylidene-   1.5850           1,4-phenylene)           Poly(N-(2-phenylethyl)methacrylamide)   1.5857           Poly(4-methoxy-2-methylstyrene)   1.5868           Poly(o-methylstyrene)   1.5874           Poly(styrene)   1.59-1.592           Poly(oxycarbonyloxy-1,4-phenylenecyclohexylidene-   1.5900           1,4-phenylene)           Poly(o-methoxystyrene)   1.5932           Poly(diphenylmethyl methacrylate)   1.5933           Poly(oxycarbonyloxy-1,4-phenyleneethylidene-1,4-   1.5937           phenylene)           Poly(p-bromophenyl methacrylate)   1.5964           Poly(N-benzyl methacrylamide)   1.5965           Poly(p-methoxystyrene)   1.5967           Hard rubber (32% S)   1.6           Poly(vinylidene chloride)   1.60-1.63           Poly(sulfides (“Thiokol”)   1.6-1.7           Poly(o-chlorodiphenylmethyl methacrylate)   1.6040           Poly(oxycarbonyloxy-1,4-(2,6-dichloro)phenylene-   1.6056           isopropylidene-1,4-(2,6-dichloro)phenylene))           Poly(oxycarbonyloxybis(1,4-(3,5-dichiorophenylene))   1.6056           Poly(pentachiorophenyl methacrylate)   1.608           Poly(o-chlorostyrene)   1.6098           Poly(phenyl α-bromoacrylate)   1.612           Poly(p-divinylbenzene)   1.6150                      
 
           [0017]    The iridescent film of the present invention can also be obtained by coextruding the naphthalate-based polyester or copolyester resin with a different transparent naphthalate-based polyester which is selected to differ in refractive index by at least about 0.03 and preferably at least 0.06.  
           [0018]    The outermost layers of the iridescent film of the present invention can be the same or different from resins in the optical core. For example, the outermost layers can comprise a polyester or copolyester resin such as polybutylene terephthalate polyester or glycol modified polyethylene terephthalate like PETG polyester.  
           [0019]    The number of layers in the iridescent film of the invention is at least 10 layers, preferably at least 35 layers and more preferably at least about 70 layers.  
           [0020]    A preferred combination in accordance with this invention involves an iridescent film having the contiguous adjacent layers in the optical core being of different transparent thermoplastic resinous materials of which one is polyethylene naphthalate polyester or copolyester, and the other is polybutylene terephthalate polyester or copolyester, wherein the outermost layers are polybutylene terephthalate or PETG polyester.  
           [0021]    The delamination resistance of a film is tested by restraining one surface of the film with adhesive tape. A second piece of adhesive tape is applied to the other surface of the film. This second piece of tape is then pulled away and any indications of delamination is noted. If no delamination is observed, the tape is reapplied and the test repeated until failure is noted. Different tapes with different tack levels can be used to more fully differentiate between various film structures. Additionally, the film sample being tested can be immersed in solvent prior to testing or may be scored to provide a more severe form of this test. The number of pulls to failure using a particular tape is typically recorded. A description of this test method can be found in U.S. Pat. No. 5,089,318.  
           [0022]    To test the solvent resistance of the film, samples of the film are immersed in the challenge solvent. The sample is observed for any color change, for the time at which the solvent begins to affect the iridescent color of the film and the nature of the color change. The time to initial color change and the nature of the color change at set time intervals are recorded. This test is typically run for a period of seven days with observations taken throughout the seven-day period. At the end of the seven days, the film sample is removed from the challenge solvent and allowed to dry for twenty-four hours. After the twenty-four hour drying period, the tester notes how the iridescent film color has changed. This data is referred to as the “Color Recovery”.  
           [0023]    To test the heat shrinkage of the film, a 2″×2″ piece of film is cut from the film in question. The color of this piece is measured using a spectrophotometer. Data measured include the dominant wavelength (DWL), peak wavelength (PWL), and % peak reflection of the sample. The test specimen is then placed in an oven at the test temperature for a period of fifteen minutes. The sample is then removed from the oven. The sample is measured using a ruler to determine the percentage of shrinkage experienced by the film. The color of the sample is re-measured and the changes in DWL, PWL and peak reflection are recorded. The color of the sample after heat exposure is also compared to the original color of the test material by the person performing the test. Using all of this data, the temperature at which the film color begins to change is determined. This value is referred to as the “Color Shift Temperature”.  
       
    
    
     EXAMPLE 1  
     Iridescent Films IF(1-4)  
       [0024]    Polybutylene terephthalate thermoplastic polyester was fed to the feedblock from one extruder and polymethyl methacrylate from a second extruder to form four films of varying thickness (IF(1)=1.1 mils (28 μm), IF(2)=1.2 mils (30 μm), IF(3)=1.3 mils (33 μm), IF(4)=1.4 mils (36 μm)), each consisting of a 226 optical layer film and two polyethylene terephthalate polyester skin layers (see Table 2). The films were brightly iridescent and shared the same properties. These films&#39; solvent resistance and temperature stability are described below in Tables 3 and 4.  
                                     TABLE 2                           Color and thickness of IF (1-4)                    Colors when seen                       by reflection at                   perpendicular   Dominant   Thickness           Film   incidence   Wavelength (nm)   (mils/μm)                       IF (1)   Blue/Violet   465   1.1/28           IF (2)   Blue/Green   485   1.2/30           IF (3)   Red/Green   555   1.3/33           IF (4)   Red/Red   590   1.4/36                      
 
         [0025]    [0025]                             TABLE 3                           Properties of IF (1-4)                Property   Nominal Value                       Maximum Process Temp. (° F./° C.)   180/81            (Under Tension)           Color Shift Temperature (° F./° C.)   225/107           Color Loss Temperature (° F./° C.)   425/218                        
         [0026]    [0026]                                                                                                                                             TABLE 4                           Solvent Resistance of IF (1-4)                Time to   Immersion Time                initial       24   7   Color       Challenge Solvent   change   5 min   Hours   Days   Recovery               Alcohols   N/A   N   N   N   N/A       (Ethanol, Isopropanol)       Aliphatic   N/A   N   N   N   N/A       Hydrocarbons       (Hexane, Naptha)            Aromatic   1   Hour   N   CC   CC   CL       Hydrocarbons       (Benzene, Toluene)       Ketones   &lt;5   min   CC   CC   CC   CL       (Acetone, MEK)       Esters   &lt;5   min   CS   CC   CC   CL       (Butyl Acetate,       Ethyl Acetate)            Fully Halogenated   N/A   N   N   N   N/A       Hydrocarbons       (Carbon Tet.,       Perchloroethylene)            Partially Halogenated   &lt;5   min   CC   CC   CC   CL       Hydrocarbons       (Ethylene Dichloride,       Trichloroethylene)                                                                                                                    
         [0027]    IF(1-4) were also tested for delamination using Scotch 396 pull tape according to the above-described procedure. The skin layers delaminated after the first pull while delamination of the optical core occurred after 5 pulls.  
       EXAMPLE 2  
     Iridescent Films IF(5-8)  
       [0028]    Polybutylene terephthalate thermoplastic polyester was fed to the feedblock from one extruder and ethylene vinyl acetate copolymer from a second extruder to form four films of varying thickness (IF(5)=1.1 mils (28 μm), IF(6)=1.2 mils (30 μm), IF(7)=1.3 mils (33 μm), IF(8)=1.4 mils (36 μm)), each consisting of a 226 optical layer film and two polymethyl methacrylate skin layers (see Table 5). The films were brightly iridescent and shared the same properties. These films&#39; solvent resistance and temperature stability are described below in Tables 6 and 7.  
                                     TABLE 5                           Color and thickness of IF (5-8)                    Colors when                       seen by               reflection at               perpendicular   Dominant   Thickness           Film   incidence   Wavelength (nm)   (mils/μm)                       IF (5)   Blue/Violet   465   1.1/28           IF (6)   Blue/Green   485   1.2/31           IF (7)   Red/Green   555   1.3/33           IF (8)   Red/Red   590   1.4/36                      
 
         [0029]    [0029]                             TABLE 6                           Properties of IF (5-8)                Property   Nominal Value                       Maximum Process Temp. (° F./° C.)   170/75            (Under Tension)           Color Shift Temperature (° F./° C.)   225/107           Color Loss Temperature (° F./° C.)   420/215                        
         [0030]    [0030]                                                                                     TABLE 7                           Solvent Resistance of IF (5-8)                Time to   Immersion Time                initial       24   7   Color       Challenge Solvent   change   5 min   Hours   Days   Recovery               Alcohols   N/A   N   N   N   N/A       (Ethanol, Isopropanol)            Aliphatic   15   min   N   CS   CC   None       Hydrocarbons       (Hexane, Naptha)       Aromatic   &lt;5   min   CS   CC   CC   Good       Hydrocarbons       (Benzene, Toluene)       Ketones   &lt;5   min   CS   CS   CS   Excellent       (Acetone, MEK)       Esters   &lt;5   min   CS   CS   CS   Excellent       (Butyl Acetate,       Ethyl Acetate)       Fully Halogenated   &lt;5   min   CS   CC   CC   Fair       Hydrocarbons       (Carbon Tet.,       Perchloroethylene)       Partially Halogenated   &lt;5   min   CC   CC   CC   Good       Hydrocarbons       (Ethylene Dichioride,       Trichioroethylene)                            
         [0031]    IF(5-8) were also tested for delamination using Scotch 396 pull tape according to the above-described procedure. Both the skin and the optical core delaminated after the first pull.  
       EXAMPLE 3  
     Iridescent Films IF(9-12)  
       [0032]    Polybutylene terephthalate thermoplastic polyester was fed to the feedblock from one extruder and polyethylene naphthalate polyester from a second extruder to form four films of varying thickness (IF(9)=1.1 mils (28 μm), IF(10)=1.2 mils (30 μm), IF(11)=1.3 mils (33 μm), IF(12)=1.4 mils (36 μm)), each consisting of a 226 optical layer film and two polybutylene terephthalate polyester skin layers (see Table 8). The films were brightly iridescent and shared the same properties. These films&#39; solvent resistance and temperature stability are described below in Tables 9 and 10.  
                                     TABLE 8                           Color and thickness of IF (9-12)                    Colors when                       seen by                   reflection at                   perpendicular   Dominant   Thickness           Film   incidence   Wavelength (nm)   (mils/μm)                       IF (9)   Blue/Violet   465   1.1/28           IF (10)   Blue/Green   485   1.2/31           IF (11)   Red/Green   555   1.3/33           IF (12)   Red/Green   590   1.4/36                      
 
         [0033]    [0033]                             TABLE 9                           Properties of IF (9-12)                Property   Nominal Value                       Maximum Process Temp. (° F./°C.)   N/A           (Under Tension)           Color Shift Temperature (° F./° C.)   380/193           Color Loss Temperature (° F./° C.)   450/232                        
         [0034]    [0034]                                                                                                                                             TABLE 10                           Solvent Resistance of IF (9-12)                Time to   Immersion Time                initial       24   7   Color       Challenge Solvent   change   5 min   Hours   Days   Recovery               Alcohols   N/A   N   N   N   N/A       (Ethanol, Isopropanol)       Aliphatic   N/A   N   N   N   N/A       Hydrocarbons       (Hexane, Naptha)            Aromatic   48   Hours   N   N   CS   Excellent       Hydrocarbons       (Benzene, Toluene)       Ketones   3   Hours   N   CC   CC   Excellent       (Acetone, MEK)       Esters   5   Hours   N   CC   CC   Excellent       (Butyl Acetate,       Ethyl Acetate)            Fully Halogenated   N/A   N   N   N   N/A       Hydrocarbons       (Carbon Tet.,       Perchloroethylene)            Partially Halogenated   &lt;5   min   CS   CC   CC   Fair       Hydrocarbons       (Ethylene Dichloride,       Trichloroethylene)                            
         [0035]    IF(9-12) were also tested for delamination using Scotch 396 pull tape according to the above-described procedure. Both the skin and the optical core showed no delaminated after 10 pulls.  
       EXAMPLE 4  
     Iridescent Film IF(13-18)  
       [0036]    Resin A will be fed to the feedblock from one extruder and resin B from another extruder to form five films, IF(13-18) according to Table 11. Each film will consist of 100 layers and will be about 1.1 mils (28 μm) in thickness.  
                       TABLE 11                       Film   Resin A   Resin B                   IF (13)   Fluorinated   Polymethyl           ethylene-propylene   acrylate           copolymer       IF (14)   Polybutylene   Ethylene vinyl           terephthalate   acetate       IF (15)   Polybutylene   Propylene-ethylene           terephthalate   copolymer       IF (16)   Polybutylene   Butylene           terephthalate   naphthalate               polyester       IF (17)   Polybutylene   Butylene           terephthalate   naphthalate and               ethylene               naphthalate               copolyester       IF (18)   Butylene   Butylene           naphthalate   naphthalate and           polyester   ethylene               naphthalate               copolyester                  
 
         [0037]    When compared to IF (13-15), it will be demonstrated that IF (16-18) has better delamination resistance, temperature stability and solvent resistance (with regard to at least one solvent).  
         [0038]    The invention has been described in terms of preferred embodiments thereof, but is more broadly applicable as will be understood by those skilled in the art. The scope of the invention is therefore limited only by the following claims.