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`U.S. Patent
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`Oct. 4, 1994
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`Sheet 2 of 11
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`5,353,154
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`POLYMERIC REFLECTIVE MATERIALS
`UTILIZING A BACK LIGHT SOURCE
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`BACKGROUND OF THE INVENTION
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`The present invention generally relates to a multi-
`layer reflective polymeric body or film which, when
`illuminated by means of a back light source, transmits
`such light. The invention also relates to articles pro-
`duced therefrom which include decorative trim, light-
`ing lenses for automotive, commercial and residential
`lighting applications, and structural parts such as refrig-
`erator doors, and the like. The present invention also
`relates to a method by which such articles can be pro-
`duced from the multilayer reflective polymeric body or
`film without causing undesirable iridescent colors.
`By way of example, in the automotive industry, auto-
`mobile stylists and designers are always seeking ways in
`which a particular vehicle’s appearance can be differen-
`tiated. Most recently, automobiles have been approach-
`ing very similar designs in view of the rather limited
`number of ways in which automobiles bodies can be
`aerodynamic as well as fuel efficient. Consequently,
`stylists and designers are faced with the formidable task
`of differentiating such vehicles.
`To the extent that vehicle headlights, taillights and
`the like are required for functional purposes, designs of
`the vehicle adjacent to areas where lights are needed
`have been limited since the associated lighting lenses
`disrupt the styling contours on the vehicle and exhibit
`color mismatches. Thus, it is desirable to be able to
`render vehicle lights indiscerriible by blending the vehi-
`cle body lines, colors, and/or decorative trim with a
`reflective and/or colored surface which conceals the
`lighting, and yet conforms to standard lighting require-
`ments when the lights are illuminated.
`Such a design option would also find utility in a wide
`variety of other areas in addition to the automotive
`industry. For example, in the area of consumer appli-
`ances, the housings on such appliances could be made to
`exhibit one color or appearance when viewed and yet
`permit internal items to become visible when illumi-
`nated. For example, a refrigerator door or portion
`thereof could be reflective and/or colored to match,
`blend, or contrast with the reminder of the appliance
`and yet become transparent when illuminated by a light
`inside the refrigerator so as to expose its contents to
`view without opening the door.
`Additionally, in the areas of commercial and residen-
`tial lighting, it would be desirable to be able to provide
`lights which would blend in with the chosen decor, and
`yet illuminate a room when turned on. This would
`expand on the variety of options available for interior
`decoration and the styles of lamps and lighting. For
`example, in restaurants, nightclubs and the like, hand
`rails, floor tiles, panels, etc., it would be desirable to
`have such items reflective in appearance yet appear
`differently when back lit.
`Conventional methods for fabricating reflective sur-
`faces include forming such surfaces of highly polished
`metals. Such polished metal surfaces are useful to re-
`flect light but such surfaces are opaque and they cannot
`be used to hide lamps or other lighting from view. Be-
`cause of the high costs, weight, environmental con-
`cerns, and fabricating problems involved in using met-
`als, there has been a shift to use plastic surfaces which
`contain thin coatings of metal thereon.
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`Thus, metal coated plastic articles are now com-
`monly found as both decorative and functional items in
`a number of industries. Such articles are used as bright
`work for consumer appliances such as refrigerators,
`dishwashers, washers, dryers,
`radios, and the like.
`These types of articles are also used by the automotive
`industry as head lamp reflectors, bezels, radio knobs,
`automotive trim, and the like. Again, however, such
`reflective surfaces are designed to be substantially
`opaque and cannot be used to conceal lamps or other
`lighting from view.
`There have been a wide multitude of lighting designs
`in several areas such as the automobile industry. For
`example, Goldbaum et al, U.S. Pat. No. 3,321,618 dis-
`close an automotive vehicle lamp assembly with a snap-
`in lens and Kirsch, U.S. Pat. No. 4,020,338 discloses an
`automobile lighting lens which provides an adaptor for
`styling headlights. Further, Egawa et al, U.S. Pat. No.
`5,005,949, discloses an anti—glare covering for illumi-
`nated lights which substantially reduces perceived glare
`from lighting. However, none of these attempts in the
`art provide a lighting lens or covering which possesses
`the desired feature of reflectivity and yet transmissivity
`upon exposure to a back light source.
`Multilayer articles of polymers are known, as are
`methods and apparatus for making such articles. For
`example, such multilayered articles may be prepared
`utilizing multilayer coextrusion devices as described in
`commonly-assigned U.S. Pat. Nos. 3,773,882 and
`3,884,606 to Schrenk. Such devices are capable of si-
`multaneously extruding diverse thermoplastic poly-
`meric materials in substantially uniform layer thick-
`nesses. The number of layers may be multiplied by the
`use of a device as described in commonly-assigned U.S.
`Pat. No. 3,759,647 to Schrenk et al.
`Alfrey, Jr. et al, U.S. Pat. No. 3,711,176, teach a
`multilayered highly reflective thermoplastic body fabri-
`cated using thin film techniques. That is, the reflective
`thin film layers of Alfrey, Jr. et al relied on the con-
`structive interference of light to produce reflected visi-
`ble, ultraviolet, or infrared portions of the electromag-
`netic spectrum. Such reflective thin films have found
`use in decorative items because of the iridescent reflec-
`tive qualities of the film. See also, Cooper, U.S. Pat. No.
`Re. 31,780.
`However, the films of Alfrey, Jr. et al are extremely
`sensitive to thickness changes, and it is characteristic of
`such films to exhibit streaks and spots of nonuniform
`color. Further, color reflected by such films is depen-
`dent on the angle of incidence of light impinging on the
`film. Thus, such films are not practical for uses which
`require uniformity of reflectivity. Moreover, such films
`are not practical to thermoform into articles since local-
`ized thinning of the layers during thermoforming causes
`alterations in the reflective characteristics of the films.
`More recently, reflective multilayer polymeric films
`and sheets formed of optically thick layers (optical
`thickness of greater than about 0.45 pm), a combination
`of optically thick and optically very thin layers (optical
`thickness of less than about 0.09 pm), or combinations
`of optically thick, optically thin, and optically very thin
`layers have been taught which exhibit a substantially
`colorless uniform silvery reflective appearance. See,
`Wheatley etal, U.S. Pat. No. 5,122,905; Wheatley, U.S.
`Pat. No. 5,122,906; and Wheatley etal, U.S. Pat. No.
`5,126,880. Wheatley et al teach using these reflective
`films and sheets for many of the same uses as polished
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`metal and metallized plastic sheets have been heretofore
`used.
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`Accordingly, the need still exists in this art for a
`polymeric body or film which is reflective, and yet is
`capable of transmitting light upon exposure to a back
`light source for a variety of applications including auto-
`motive, commercial, and residential applications. There
`is also a need for a method of forming such a polymeric
`body or film into a variety of useful shapes.
`SUMMARY OF THE INVENTION
`
`invention meets the above-described
`The present
`needs by providing a polymeric body which is reflec-
`tive in appearance, and yet which transmits light upon
`exposure to a back light source and by providing a
`method for forming such a polymeric body into useful
`shapes. The terms “reflective”, “reflectivity”, “reflec-
`tion”, and “reflectance” as used herein refer to total
`reflectance (i.e., ratio of reflected wave energy to inci-
`dent wave energy) sufficiently specular in nature such
`that the polymeric body has a metallic appearance. The
`use of these terms is intended to encompass serni-specu-
`lar or diffuse reflection such as that of brushed metal,
`pewter, and the like. In general, reflectance measure-
`ment refers to reflectance of light rays into an emergent
`cone with a vertex angle of 15° centered around the
`specular angle.
`A specific intensity of reflectance, when used herein,
`is the intensity of reflection which occurs at a wave-
`length where negligible absorption occurs. For exam-
`ple, a silver appearing article reflects substantially all
`visible wavelengths, whereas the introduction of a dye
`to achieve other metallic hues will necessarily lower
`reflectivity of the body at the absorbing wavelengths.
`Wavelengths unaffected by the dye will be reflected at
`essentially the same intensity as a non-dyed sample, and
`it is at these unaffected wavelengths to which the inten-
`sity of reflection pertains. With respect to transmission
`of light through the body, the specific percentages re-
`ported are with respect to nonabsorbing wavelengths.
`In accordance with one aspect of the invention, a
`multilayer reflective polymeric body of at least first and
`second diverse polymeric materials arranged in substan-
`tially parallel alternating layers is provided. The body
`has first and second major surfaces, wherein the first
`and second polymeric materials differ from each other
`in refractive index by at least 0.03. The body includes a
`sufficient number of layers such that the body reflects at
`least 40% of light impinging on the first major surface
`thereof while transmitting at least 5% of light directed
`through the body from the second major surface. Pref-
`erably, the body includes a coloring agent incorporated
`in or present On at least one of the first and second
`major surfaces such that when the body is illuminated,
`the body exhibits the color of the coloring agent.
`The reflective polymeric body of the invention may
`take a variety of forms. For example, in a preferred
`embodiment, the polymeric body may be in the form of
`a film or sheet. In addition, the polymeric body may be
`in the form of a lighting lens for a vehicle. Further, the
`reflective polymeric body can be in the form of a deco-
`rative trim part for a vehicle or in the form of a housing
`or part of a housing for a consumer appliance such as a
`door or portion thereof for a refrigerator. Additionally,
`the reflective polymeric body of the invention may
`have at least one of the first and second major surfaces
`of the body comprising first and second portions,
`wherein the first portion has the coloring agent incor-
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`4
`porated in or present thereon and the second portion is
`substantially transparent upon exposure to light di-
`rected through the body from the second major surface
`thereof.
`Further, one color on the first surface and a different
`color on the second surface is possible. For example, a
`red coloring agent can be present in or on the first sur-
`face while the second surface includes a green coloring
`agent resulting in the polymeric body appearing red in
`reflection and neutral or gray upon exposure to a back
`light source. Similarly, different color combinations on
`the first and second surfaces of the polymeric body,
`respectively, can interact to produce a third color when
`back lit.
`
`A number of substantially transparent polymers are
`suitable for use in the present invention. In a preferred
`embodiment, the first polymeric material may be a poly-
`urethane and the second polymeric material may be
`polymethylmethacrylate. Alternatively, the first poly-
`meric material can be a polyurethane while the second
`polymeric material is a polyether imide. Other combina-
`tions of polymers include the combination of a polycar-
`bonate with a miscible blend of polyvinylidene fluoride
`and polymethylmethacrylate, the combination of poly-
`styrene with a copolymer of ethylene and at least one
`unsaturated monocarboxylic acid, the combination of
`polystyrene with polymethylmethacrylate, and the
`combination of a polycarbonate with polymethylmeth-
`acrylate.
`In certain embodiments of the invention, to obtain
`high reflectivity, it is desirable to form the reflective
`polymeric body to comprise at least 500 or more layers.
`Increasing the total number of layers in the polymeric
`body has been found to increase its reflectivity (i.e., the
`percentage of incident light reflected from the body).
`Thus, by controlling the number of layers, the degree of
`reflectivity of the article may be controlled. Preferably,
`the reflectivity should not be too high so as to maintain
`the preferred level of transmissivity, namely, at least
`5%. It should be understood, however, that an intense
`light source, such as a light-emitting diode (LED), can
`be used as the back light source resulting in transmission
`of light even with a polymeric body which is 95% re-
`flective.
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`The coloring agent used in the polymeric body is
`preferably selected from the group consisting of pig-
`ments and dyes. Metallic colors such as gold, bronze, or
`copper may be used. Other colors such as black, blue,
`red, yellow, white, and the like may also be used. Addi-
`tionally, the polymeric body may contain a second
`coloring agent incorporated into at least one of the
`layers between the first and second major surfaces of
`the body. In this way, coloring agents may be used in
`combination to provide desirable coloring and optical
`properties. For example, a gold or other bright metallic
`trim or lens can be produced from the polymeric body
`that can be illuminated to create an illuminated gold,
`copper, bronze decorative trim or lens. Further, a white
`coloring agent may be used in an interior surface while
`a colored dye, such as blue, yellow, red, or green, may
`be included on one or more surface layers to provide a
`unique reflective colored effect.
`Further, while the normal surface of the polymeric
`body is smooth to give a highly reflective specular
`silver appearance, in some instances it may be desirable
`to give the surface of the polymeric body a roughened,
`grained or brushed appearance to simulate a brushed
`metallic appearance. Further, a solvent may be used to
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`etch the surface of the multilayer body to provide a
`matte or pewter look to the polymeric body. Addition-
`ally, the polymeric body may be embossed with a vari-
`ety of patterns to provide desirable optical effects.
`In addition, at least one surface of the polymeric body
`may have indicia printed thereon to illuminate informa-
`tion upon exposure to a back light source and to conceal
`such information when not exposed to light. In that
`regard, the polymeric body of the invention may be
`used in the interior of a vehicle, for example, to illumi-
`nate controls with the appearance of a chrome knob
`with a green label or printed indicia indicating “vol-
`ume” when traveling during the night. Further, a bright
`exterior vehicle door trim can include text printed in or
`on one of the layers of the polymeric body which forms
`the trim so as to illuminate the keyhole.
`In all of the aforedescribed embodiments, the particu-
`lar polymers and the optical thicknesses of the layers are
`preferably chosen such that there is an absence of visi-
`bly perceived iridescence. To that end, suitable polymer
`combinations and the manner in which the optical
`thicknesses are chosen to provide a substantially noni-
`ridescent polymeric body is set forth in Wheatley etal,
`U.S. Pat. No. 5,122,905, Wheatley, U.S. Pat. No.
`5,122,906, and Wheatley etal, U.S. Pat. No. 5,l26,880.
`Additionally,
`the multilayer
`reflective polymeric
`bodies of the present invention may be formed by a
`variety of ways. For example, the polymeric body can
`be formed using the extrusion die, i.e., profile extrusion
`as described in Wheatley et al, U.S. Pat. No. 5,126,880.
`Additionally, post-forining operations can be used
`which include thermoforming, vacuum forming and
`pressure forming. In a preferred embodiment, the poly-
`meric body is therrnoformable. Further, through the use
`of forming dies, the polymeric body may be initially
`formed into a variety of useful shapes including parts
`for automotive, commercial and residential
`lighting
`applications. In addition, component fabrication tech-
`niques including insert injection molding, ultrasonic
`welding, adhesive bonding, and other attachment and
`welding methods can be used to fabricate the present
`polymeric body into the desired part.
`Another aspect of the invention is directed to the
`polymeric body having an image projected on a surface
`thereof and which can be back lit with, for example a
`LED (light emitting diode), to be used as a pointer or
`the like. Further, an array of light sources such as LEDs
`can be used in, for example, display panels, automotive
`decorative lamps, centered high-mounted stop lamps
`and the like. Preferably, this embodiment comprises a
`multilayer reflective polymeric body of at least first and
`second diverse polymeric materials arranged in substan-
`tially parallel alternating layers wherein the first and
`second polymeric materials differ from each other in
`refractive index by at least 0.03. The body has first and
`second major surfaces wherein an image is projected
`onto the first major surface of the body. The body in-
`cludes a sufficient number of layers such that the body
`reflects at least 40% of light impinging on the first
`major surface thereof while transmitting at least 5% of 60
`light directed through the body from the second major
`surface so as to illuminate the image on the first major
`surface. It should be understood that high intensity light
`sources such as LEDs are sufficient to penetrate poly-
`meric bodies capable of transmitting only 5% of light
`directed through the body.
`In another aspect of the invention, a colored light
`source is provided. A light source is enclosed by a mul-
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`tilayered reflective polymeric sheet or film having first
`and second major surfaces wherein the second major
`surface faces the light source and the first major surface
`faces opposite the second major surface. The sheet or
`film has at least first and second diverse polymeric ma-
`terials arranged in substantially parallel alternating lay-
`ers, the sheet or film including a coloring agent incorpo-
`rated in or present on at least one of the first and second
`major surfaces, wherein the first and second polymeric
`materials differ from each other in refractive index by at
`least 0.03. The sheet or film includes a sufficient number
`of layers such that the film reflects at least 40% of light
`impinging on the first major surface thereof while trans-
`mitting at least about 5% of light directed through the
`body from the second major surface such that when the
`body is illuminated, the polymeric body exhibits the
`color of the coloring agent.
`Further, the present invention may find use in a lamp
`assembly comprising a light source mounted in a hous-
`ing having at least one surface in the form of a lighting
`lens. The lighting lens comprises at least first and sec-
`ond diverse polymeric materials arranged in substan-
`tially parallel alternating layers. The lighting lens has
`first and second major surfaces wherein the second
`major surface faces the light source and the first major
`surface faces opposite the second major surface. Prefer-
`ably, the lighting lens has a coloring agent incorporated
`in or present on at least one of the first and second major
`surfaces, wherein the first and second polymeric materi-
`als differ from each other in refractive index by at least
`0.03. The lighting lens includes a Sufficient number of
`layers such that the lighting lens reflects at least 40% of
`light impinging on the first major surface thereof while
`transmitting at least 5% of light directed through the
`body from the second major surface such that when the
`body is illuminated, the polymeric body exhibits the
`color of the coloring agent.
`In accordance with another aspect of the invention, a
`multilayer reflective polymeric body of at least first and
`second diverse polymeric materials arranged in substan-
`tially parallel alternating layers which define at least
`one edge of the body is provided. The body has first and
`second major surfaces substantially parallel to the lay-
`ers, and includes a coloring agent incorporated in or
`present on at least one of the layers. The first and sec-
`ond polymeric materials differ from each other in re-
`fractive index by at least 0.03, the body including a
`sufficient number of layers such that the body reflects at
`least 40% of light impinging on the first major surface
`thereof while transmitting at least 5% of light directed
`through the edge of the body. Preferably, at least one of
`the first and second major surfaces includes irregular-
`ities thereon such that when the edge is illuminated, the
`body exhibits the color of the coloring agent. As used
`herein, irregularities encompasses notches, conical dots
`or indentations, conical protrusions, embossments, sur-
`face abrasions or any other shaped indentation or pro-
`trusion which would render the surface other than uni-
`formly smooth.
`Another aspect of the invention is directed to a
`method for forming a reflective multilayer polymeric
`body having essentially no visually perceived irides-
`cence. The method comprises the step of providing a
`molding assembly including a mold having a face half
`and a corresponding core half together which define the
`contour of the product. The face half and the core half
`of the mold each have a press platen adapted to com-
`press the face half and the core half against one another.
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`The molding assembly includes means for cushioning
`the mold when the face half and the core half are com-
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`FIG. 11 is a fragmentary perspective view of the
`automobile shown in FIG. 10 in which the indicia dis-
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`5,353,154
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`pressed together by the press platens to mold the prod-
`uct. The method further comprises the steps of inserting
`between the face half and the core half of the mold a
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`formable multilayer reflective polymeric sheet having
`essentially no perceived iridescence, and compressing-
`each of the press platens in the molding assembly such
`that the face half and the core half of the mold are
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`the sheet while the cushioning
`compressed against
`means cushions the mold to prevent uneven flowing and
`thinning of the layers in the sheet or film to produce .the
`product. Such uneven flowing and thinning in the sheet
`or film causes iridescence in the resulting product.
`In a preferred embodiment, the cushioning means
`comprises an elastomeric blanket inserted between the
`face half and the core half of the mold. Additionally, or
`alternatively, the cushioning means may comprise an
`elastomeric blanket inserted between at least one of the
`
`press platens and the mold. Another embodiment of the
`present method includes the step of forming at least one
`of the core half and the face half from an elastomeric
`material to serve as the cusluoning means.
`Accordingly, it is an object of the invention to pro-
`vide a polymeric body or film which is reflective, and
`yet transmits light upon exposure to a back light source
`for a variety of applications including automotive, com-
`mercial, and residential applications; and, it is also an
`object of the invention to provide a method for making
`such a polymeric body or film. Other objects and ad-
`vantages of the invention will be apparent from the
`following detailed description,
`the accompanying
`drawings and the appended claims.
`BRIEF DESCRIPTION THE DRAWINGS
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`FIG. 1 is a fragmentary perspective view of an auto-
`mobile in which the polymeric body of the invention is
`used in its lighting system;
`FIG. 2 is a fragmentary view of the automobile
`shown in FIG. 1 in which the front lighting system is
`illuminated;
`FIG. 3 is a cross-sectional view taken along view line
`3-3 in FIG. 1 of one headlight of the automobile de-
`picted in FIGS. 2;
`FIG. 4 is a partial cross-sectional View taken along
`view line 4-4 in FIG. 3 of the lighting lens in the head-
`light shogun in FIG. 3;
`FIG. 5 is a cross-sectional view of the headlight
`shown in FIG. 3 in which the light source is illumi-
`nated;
`FIG. 6 is a fragmentary perspective View of the rear
`portion of an automobile in which the rear lighting
`system incorporates the polymeric body of the inven-
`t10n;
`FIG. 7 is a fragmentary perspective view of the auto-
`mobile as shown in FIG. 6 wherein the rear lighting
`system is illuminated;
`FIG. 8 is a cross-sectional view taken along view line
`8-8 in FIG. 6 of one half of the rear lighting system on
`the automobile depicted FIGS. 6-7;
`FIG. 9 is a rear elevational view of the rear lights
`shown in FIG. 8 in which the lights are illuminated;
`FIG. 10 is a fragmentary perspective view of the rear
`portion of an automobile similar to FIGS. 6 and 7 with
`the addition of a centrally located rear indicia display
`light;
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`45
`
`50
`
`55
`
`60
`
`65
`
`play light is illuminated;
`FIG. 12 is a fragmentary perspective view of an auto-
`mobile having a body side molding formed of the poly-
`meric body wherein a light source is mounted adjacent
`an edge thereof for illuminating the molding;
`FIG. 13 is a plan view of the molding depicted in
`FIG. 12 in which the light source is illuminated;
`FIG. 14 is a fragmentary perspective view of a room
`ceiling in which a colored or uncolored (silvery) lens
`formed from the polymeric body is mounted;
`FIG. 15 is a fragmentary perspective view as shown
`in FIG. 16 in which the colored lens is illuminated;
`FIG. 16 is a perspective view of a refrigerator which
`includes a freezer door and a refrigerator formed from
`the polymeric body of the invention;
`FIG. 17 is a perspective view of the refrigerator
`shown in FIG. 16 wherein an internal light has been
`illuminated to permit viewing of the refrigerator con-
`tents;
`FIG. I8 is a perspective view of another embodiment
`in which the polymeric body has an image casted upon
`it while also being back lit;
`FIG. 19 is a side elevational view of a molding assem-
`bly which is used to forth the polymeric body of the
`invention into the desired product; and
`FIG. 20 is an enlarged fragmentary side elevational
`view of the molding assembly shown ‘in FIG. 18 in
`which the mold is compressed together to form the
`desired product.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`The present invention provides a polymeric body
`which is reflective, and yet transmits light upon expo-
`sure to a back light source. A method for forming the
`polymeric body is also provided and will be discussed in
`detail below. Such a polymeric body finds use in a wide
`variety of applications including but not limited to auto-
`motive, residential and commercial applications. Those
`skilled in the art will appreciate the multitude of ways in
`which a polymeric body, which is reflective and yet
`transmits light upon exposure to a back light source, can
`be applied in various areas other than those explicitly
`described herein.
`As stated above, the preferred polymeric body is a
`multilayered, reflective material comprising at least two
`diverse polymeric materials arranged in substantially
`parallel alternating layers which, in most applications,
`has at least two major surfaces with a coloring agent
`incorporated in or present on one of the major surfaces.
`The polymeric materials differ in refractive index by at
`least 0.03. Preferably, the polymeric body should com-
`prise a sufficient nun%her of layers such that the body
`reflects at least 40% of light impinging one of the major
`surfaces thereof while transmitting at least 5% of light
`directed through the polymeric body when illuminated
`with a back light source.
`For most applications, it is preferred that the poly-
`meric body has an absence of visually perceived irides-
`cence. In fact, it is an object of the method of the inven-
`tion to form polymeric film or sheet material which
`does not exhibit iridescence into a product which also
`does not display such iridescence. Consequently, the
`polymeric body of the invention should specifically
`avoid layer thicknesses which would result in substan-
`tial iridescent color. On the other hand, alternating
`
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`Page 16 of 21
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`5,353,154
`
`9
`layers too thick to cause iridescence, in combination
`with layers too thin to cause iridescence, result in a
`body which exhibits an essentially uniform silver and
`non-iridescent appearance. This silvery appearance,
`which is desired for the invention, is due to higher order
`reflections from the optically thick layers being so
`closely spaced that the human eye perceives the reflec-
`tion to be essentially non-iridescent.
`There are an unlimited number of ways in which the
`alternating layers of the polymeric body can be de-
`signed to provide this silvery appearance along with the
`other desired properties for use with a back light
`source. For example, reflective multilayer polymeric
`films and sheets can be formed of optically thick layers
`(optical thickness of greater than about 0.45 pm) or a
`combination of optically thick and optically very thin
`layers (optical thickness of less than about 0.09 pm), or
`a combination of optically thick, optically thin (optical
`thickness of between 0.09 and 0.45 pm), and optically
`very thin layers which exhibit a substantially colorless
`uniform silvery reflective appearance. Specifically, the
`manner in which the optical thicknesses are chosen is
`set forth in Wheatley et al, U.S. Pat. No. 5,122,905,
`Wheatley, U.S. Pat. No. 5,122,906, and Wheatley et al,
`U.S. Pat. No. 5,126,880, all of the disclosures of which
`are incorporated herein by reference. Furthermore, by
`introducing large layer thickness gradients into the
`layers, a broad band substantially uniformly reflective
`body may be produced as taught in commonly assigned
`copending U.S. application Ser. No. 07/969,710, filed
`Oct. 29, 1992.
`Preferably, the polymers chosen have a refractive
`index mismatch of at least 0.03 at the visible wave-
`lengths 380-680 run. Typically, refractive indices of
`materials, including polymers, are measured at a conve-
`nient wavelength in the visible range such as 589 nm
`sodium vapor. As briefly stated above, several substan-
`tially transparent polymers are suitable for use in the
`present invention. A number of substantially transpar-
`ent polymers are suitable for use in the present inven-
`tion. In a preferred embodiment, the first polymeric
`material may be a polyurethane and the second poly-
`meric material may be polymethylmethacrylate. Alter-
`natively, the first polymeric material can be a polyure-
`thane while the second polymeric material is a poly-
`ether imide.
`
`Other combinations of polymers include the combi-
`nation of a polycarbonate with a miscible blend of poly-
`vinylidene fluoride and polymethylmethacrylate,
`the
`combination of polystyrene with a copolymer of ethyl-
`ene and at least one unsaturated monocarboxylic acid,
`the combination of polystyrene with polymethylmeth-
`acrylate, and the combination of a polycarbonate with
`polymethylmethacrylate. Further, polymers and their
`respective refractive indices, which are useful in the
`practice of the present invention include all of the poly-
`mers listed in the aforementioned Wheatley et al, U.S.
`Pat. No. 5,122,905, Wheatley, U.S. Pat. No. 5,122,906,
`and Wheatley et al, U.S. Pat. No. 5,126,880, all of the
`disclosures of which are incorporated herein by refer-
`ence.
`
`In accordance with another aspect of the invention, a
`multilayer reflective polymeric sheet and film are pro-
`vided. The sheet and f