Lamellar polymeric body

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The present invention relates to a multilayered polymeric body of optically thick, thin, and/or very thin plate-like or ribbon-like layers of one or more polymers within a matrix of another polymer, which body reflects light and can be fabricated to have a silvery or hued (i.e., gold, copper, etc.) metallic appearance, or a nonconventional hued (i.e., blue, green) appearance, or even an iridescent appearance, and to methods of producing such a polymeric body.

Conventional methods for fabricating reflective surfaces include forming such surfaces of highly polished metals. Because of the high costs and fabricating problems involved in using metals, more recently fabricators have used plastic surfaces which contain thin coatings of metal thereon. Thus, metal coated plastic articles are now commonly 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.

Typically, such metal coated plastic articles are formed by electroplating or by the vacuum, vapor, or chemical deposition of a thin metal layer on the surface of the article. Additionally, such coatings are subject to 45 the chipping and flaking of the metal coatings as well as corrosion of the metal over time. If additional protective layers must be applied over the metal coating to protect it, additional labor and materials costs are involved. Further, there may be environmental disposal problems with some metal deposition processes.

One such vacuum metallized deposition system to produce bright work and automotive decorative trim is taught by Eisenfeller in U.S. Pat. Nos. 4,713,143, 4,431,711, and 4,407,871. That system deposits minute specular islands of indium metal on a dielectric substrate. The metal is then encapsulated in a clear polymer.

The preparation of multilayer articles of polymers are known, as are methods and apparatuses for making such articles. For example, such multilayered articles may be prepared utilizing multilayer coextmsion devices as described in commonly-assigned U.S. Pat. Nos. 3,773,882 and 3,884,606 to Schrenk. Such devices are capable of simultaneously extruding diverse thermoplastic polymeric materials in continuous layers having substantially uniform layer thicknesses. The number of layers may be multiplied by the use of a device as de

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scribed in commonly-assigned U.S. Pat. No. 3,759,647 to Schrenk et al.

Im et al, U.S. Pat. No. 4,540,623, teaches a multilayer laminated article which includes a polycarbonate as one of the alternating continuous layers. The articles of Im, however, are intended to be transparent rather than reflective and to exhibit optical properties comparable to a pure polycarbonate polymer.

Alfrey, Jr. et al, U.S. Pat. No. 3,711,176, teaches a multilayered highly reflective thermoplastic body fabricated using thin film techniques. That is, the reflective thin film layers of Alfrey, Jr. et at relied on the constructive interference of light to produce reflected visible, ultraviolet, or infrared portions of the electromagnetic spectrum. Such reflective thin films have found use in decorative items because of the iridescent reflective qualities of the film.

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 dependent 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 where uniformity of light reflectance is needed as localized thinning of the layers during thermoforming causes alterations in the reflective characteristics of the films.

Moreover, both the Alfrey, Jr. et al films and the multilayer films and articles made up of substantially continuous layers, such as those described in commonly-assigned U.S. Pat. Nos. 5,122,905 and 5,122,906 have some limiting characteristics inherent in their construction. The continuous layers must adhere to themselves to hold the film together. This may necessitate the use of intervening adhesive layers which could adversely affect the optical properties of the film and certainly add to the overall thickness of the film. Further, no gas or other fluid can be permitted at the interface between any of the layers as this may contribute to the delamination of the layers. Additionally, each of the materials used in the layers exerts an effect on the overall mechanical properties of the film. For example, if one of the polymers used is brittle, the layers of brittle material will have an effect on the overall properties of the multilayer film.

Accordingly, there remains a need in the art for a polymeric reflective film, sheet or body which can be fabricated into a variety of parts and which can exhibit a uniform reflective appearance or a silvery iridescent appearance over a range of processing conditions and part geometry. There is also a need for a polymeric reflective film or body which will hold together even if some or all of the individual layers do not, there is a need for a body in which gas or other fluid can be present at layer interfaces without adversely affecting the optical and mechanical properties of the body, and there is a need for a multilayer reflective body which has mechanical properties which are substantially independent of the mechanical properties of at least some of the layers in the body.

SUMMARY OF THE INVENTION

The present invention meets those needs by providing a lamellar reflective polymeric body containing no metals, and a method of making that body which polymeric body can be fabricated and/or post-formed into a variety of parts. In one embodiment of the invention, such fabrication and/or post-forming can be accomplished without alteration of its uniform reflective appearance. The body comprises discontinuous layers of at least one polymeric material within a matrix of an- 5 other polymeric material which polymers differ in refractive index. The layers of the polymeric material may be either optically thick, optically thin (i.e., iridescent interference layers) or optically very thin. The optically thick layers are too thick to cause visible iri- 10 descent effects (visually perceived as a variety of colors), while the very thin layers are too thin to cause such effects. The resulting multilayered lamellar polymeric body, depending upon the layer thicknesses selected, may reflect substantially white light and exhibit 15 a silvery, metallic appearance, or may have bands of iridescent color.

In another embodiment of the invention, where optical properties are not important, the discontinuous multilayer construction provides a number of advantageous 20 mechanical properties. Such properties include high tensile properties in one direction but lower in a direction transverse to the discontinuous ribbon-like layers, the ability to tailor flexibility and ductility into the body, and the ability to include overlapping gas barrier 25 layers into the multilayer construction.

The terms "reflective", "reflectivity", "reflection", and "reflectance" as used herein refer to total reflectance (i.e., ratio of reflected wave energy to incident wave energy) sufficiently specular in nature such that 30 the polymeric body has a metallic appearance. The use of these terms is intended to encompass semi-specular or diffuse reflection such as that of brushed metal, pewter, and the like. In general, reflectance measurement refers to reflectance of light rays into an emergent cone with 35 a vertex angle of 15 degrees centered around the specular angle.

A specific intensity of reflectance, when used herein, is the intensity of reflection which occurs at a wavelength where negligible absorption of light occurs. For 40 example, 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 45 reflected at essentially the same intensity as a non-dyed sample, and it is at these unaffected wavelengths to which the intensity of reflection is referring. Likewise, where optically thin (i.e., iridescent) layers are present, the reflectance referred to is the peak reflectance ob- 50 served.

In accordance with one aspect of the present invention, a lamellar reflective polymeric body of at least first and second diverse polymeric materials is provided, the body having at least first and second major surfaces. 55 The body includes a plurality of layers of the first polymeric material within a matrix of the second polymeric material, with layers of the first polymeric material having their major interfaces aligned substantially parallel to the major surfaces of the body. 60

The number of layers of the first polymeric material in the body is sufficient such that at least 30% of light incident on the body is reflected. The individual layers of the first polymeric material in the body and those portions of the second polymeric material sandwiched 65 between the individual layers of the first polymeric material, have an optical thickness of not more than 0.09 micrometers (i.e., are optically very thin), between 0.09

micrometers and 0.45 micrometers (i.e., are optically thin), or not less than 0.45 micrometers (i.e., are optically thick).

In a preferred embodiment of the invention, at least 75% of the individual layers of first polymeric material and those portions of second polymeric material sandwiched between the individual layers of first polymeric material have at least an optical thickness of 0.45 micrometers or greater or 0.09 micrometers or less to produce a uniformly reflective, metallic appearing body. Alternatively, the individual layers of first polymeric material and portions of second polymeric material sandwiched therebetween should have an optical thickness such that no visibly perceived iridescence is reflected from the body. In another embodiment of the invention, a portion or all of the individual layers of first polymeric material and second polymeric material sandwiched therebetween have optical thicknesses in the range of from 0.09 micrometers to 0.45 micrometers to produce a body which has a colored and/or silvery iridescent appearance.

The first and second polymeric materials differ from each other in refractive index by at least about 0.03. To increase the refractive index mismatch at the layer interfaces, and thus increase the reflectance of the body, a fluid such as air may be present at a plurality of the major interfaces of the first and second polymeric materials.

In a preferred embodiment of the invention, the body may comprise from less than one hundred to several thousand layers of the first polymeric material with alternating portions of the second polymeric material therebetween. Increasing the 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.

The reflective body of the present invention may be made up of two or more generally transparent polymer resins. The polymers used in the practice of the present invention may be rigid or elastomeric, or have varying degrees of flexibility. Preferred are thermoplastic resins which are capable of being post formed into a variety of shapes. For example, in one embodiment of the invention, the first polymeric material may be polymethyl methacrylate and the second polymeric material may be polystyrene.

Where the reflective body is used in a situation requiring gas impermeability, the first polymeric material may be a gas barrier material. The many overlapping layers in the body create an effective barrier to the passage of gases. For example, suitable barrier layer materials such as copolymers of ethylene and vinyl alcohol, polyvinylidene chloride, nitrile polymers, and nylons may be used in the multilayer body.

The layers of the first polymeric material may be present in the form of elongated, flat, ribbon-like layers which are substantially continuous in a first plane parallel to one of the major surfaces of the body and discontinuous in a second plane transverse to the first plane. Alternatively, the layers of the first polymeric material may be present in the form of platelet-like layers which are substantially discontinuous along planes' generally parallel and transverse to one of the major surfaces of the body.

In some embodiments of the invention it may be desirable to incorporate coloring agents such as dyes or 5

pigments into one or more of the individual interior layers of the polymeric body or into the continuous polymeric matrix of the body. The coloring agents may be selected to give the polymeric body a metallic appearance other than its normal silvery appearance such 5 as bronze, copper, or gold, for example.

Different colors such as black, blue, red, yellow, white, and the like may also be used. Typically, it is most desirable to use pigmented coloring agents in the interior layers to provide opaqueness and a two-sided 10 mirror-like reflective quality and to use dyes for the continuous matrix portion of the body. Coloring agents may be used in combination to provide desirable coloring and optical properties. For example, a pigmented white coloring agent may be used in an interior layer 15 while a colored dye, such as blue, yellow, red, or green may be included in the continuous polymeric matrix to provide a unique reflective colored effect.

Further, while in certain embodiments of the invention the surface of the body is smooth to give a highly 20 reflective appearance, in some instances it may be desirable to give the surface of the body a roughened or brushed appearance to simulate a brushed metallic appearance. Further, a solvent may be used to etch the surface of the multilayer body to provide a matte or 25 pewter look to the body. Additionally, the body may be embossed with a variety of patterns to provide desirable optical effects.

In another embodiment of the invention, the interior layers of the reflective body may include layers of two 30 or more different polymers in a matrix of a third polymer. Thus, a lamellar reflective polymeric body of at least first and second diverse polymeric materials is provided, the body having at least first and second major surfaces. The body comprises a plurality of indi- 35 vidual layers within a matrix of a third polymeric material, with each individual layer comprising at least three or more alternating layers of the first and second polymeric materials within the matrix.

The alternating layers of the first and second poly- 40 meric materials have their major interfaces aligned substantially parallel to the major surfaces of the body, with the number of alternating layers of the first and second polymeric materials being sufficient such that at least 30% of light incident on the body is reflected. In a 45 preferred embodiment, the individual layers of the first and second polymeric materials have optical thicknesses of not more than 0.09 micrometers (i.e., are optically very thin), between 0.09 micrometers and 0.45 micrometers (i.e., are optically thin), or not less than 50 0.45 micrometers (i.e., are optically thick). The first and second polymeric materials differ from each other in refractive index by at least about 0.03.

In one alternative construction, at least 75% of the individual layers of the first and second polymeric mate- 55 rials have an optical thickness of at least 0.45 micrometers to produce a uniformly reflective, metallic-appearing body. In another embodiment of the invention, a portion or all of the individual layers of first polymeric material and second polymeric material sandwiched 60 therebetween have optical thicknesses in the range of from 0.09 micrometers to 0.45 micrometers to produce a body which has a colored and/or silvery iridescent appearance.

Again, the polymers making up the various layers of 65 the body may be chosen to give the body specific mechanical or optical properties. For example, the third polymeric material which makes up the continuous

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matrix may be elastomeric to produce a flexible reflective body. Polymers may be selected to provide a reflective body which is post formable and/or thermoformable. Also, coloring agents such as pigments or dyes may be incorporated into one or more of the polymeric materials as previously described. Reflectivity of the body may be controlled by controlling the number of layers of polymers in the body. Preferably, the body comprises from less than one hundred to several thousand layers of the first and second polymeric materials.

Again, in one variation of this embodiment of the invention, the layers of the first and second polymeric materials are substantially continuous in a first plane parallel to one of the major surfaces of the body and discontinuous in a second plane transverse to the first plane to form elongated ribbon-like elements. In another variation, the layers of the first and second polymeric materials are substantially discontinuous along planes parallel and transverse to one of the major sur-. faces of the body to form platelet-like elements.

The reflective polymeric body of the present invention may also be fabricated to act as a birefringent light polarizer which polarizes a broad band of the electromagnetic spectrum. The polarizer is fabricated of at least first and second diverse polymeric materials, with the body having at least first and second major surfaces. The body includes a plurality of layers of the first polymeric material within a matrix of the second polymeric material, with the layers of the first polymeric material having their major interfaces aligned substantially parallel to the major surfaces of the body.

The number of layers of the first polymeric material is sufficient such that at least 30% of light incident on the polarizer is reflected in the plane of polarization. The individual layers of the first polymeric material and those portions of the second polymeric material sandwiched between individual layers of the first polymeric material have an optical thickness of not more than 0.09 micrometers or at least 0.45 micrometers, with the first and second polymeric materials differing from each other in refractive index by at least about 0.03 in one plane of the polarizer. In a preferred embodiment, the difference in refractive index between the first and second polymeric materials is caused by selecting polymers having differing stress optical coefficients and then stretching those materials in a uniaxial direction to orient the polymeric materials.

The unique arrangement of layers of diverse polymeric materials may also provide a useful body even where reflective properties are not required. The arrangement of discontinuous layers of one polymer in a continuous matrix of another polymer permits the fabrication of bodies which have physical properties which are controllable and substantially independent of the materials used for the discontinuous layer. Additionally, because of the continuous matrix of the second polymer surrounding the layers, delamination of the first and second polymers at their respective interfaces does not adversely affect the overall body; catastrophic delamination of the body does not occur.

Accordingly, for this embodiment of the invention, a lamellar polymeric body of at least first and second diverse polymeric materials is provided, with the body having at least first and second major surfaces. The body includes a plurality of layers of the first polymeric material within a matrix of the second polymeric material. Further, the layers of the first polymeric material are substantially discontinuous along planes parallel