POLYMERIC REFLECTIVE BODIES WITH
MULTIPLE LAYER TYPES
BACKGROUND OF THE INVENTION 5
The present invention relates to a multilayered polymeric body comprising multiple optical thickness layer types which reflects light and which can be fabricated to have a silvery or hued (i.e., copper, gold, etc.) metallic or nonconventional hued (i.e., blue, green, etc.) ap- 10 pearance, and to articles produced therefrom which may find use as mirrors, reflectors, lenses, polarizers, and the like.
Highly reflective articles (i.e., articles having a reflectance of 70-85% or greater) are generally sought by 15 industry for a number of uses. 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 20 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, 25 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 30 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 the chipping and flaking of the metal coatings as well as corrosion of the metal over time. If additional protec- 35 tive 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.
Multilayer articles of polymers are known, as are 40 methods and apparatuses 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- 45 multaneously extruding diverse thermoplastic polymeric materials in substantially uniform or varying layer thicknesses. The number of layers may be multiplied by the use of a device as described in commonlyassigned U.S. Pat. No. 3,759,647 to Schrenk et al. 50
Im et al, U.S. Pat. No. 4,540,623, teach a multilayer laminated article which includes a polycarbonate as one of the alternating layers. The articles of Im et al, however, are intended to be transparent rather than reflective and to exhibit optical properties comparable to a 55 pure polycarbonate polymer.
Alfrey, Jr. et al, U.S. Pat. No. 3,711,176, teach a multilayered highly reflective thermoplastic body fabricated using thin film techniques. That is, the reflective optically thin film layers of Alfrey, Jr. et al rely on the 60 constructive interference of light to produce reflected visible, ultraviolet, or infrared portions of the electromagnetic spectrum. Such reflective optically thin films have found use in decorative items because of the iridescent reflective qualities of the film. 65
Although the film of Alfrey, Jr. et al exhibits a high reflectance, the iridescent qualities of the film cause it to reflect multiple colors, resulting in a "rainbow" effect.
In addition, the optically thin 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. Because the color reflected by such films is dependent on the angle of incidence of light impinging on the film, such films are not practical for uses which require uniformity of reflectivity. Moreover, such films are not practical to thermoform into articles as localized thinning of the layers during thermoforming causes alterations in the reflective characteristics of the films.
Accordingly, there remains a need in the art for a highly reflective polymeric sheet or body in which there is an absence of visibly perceived iridescent color. Further, there is a need for a highly reflective polymeric sheet or body which can be fabricated into a variety of parts without alteration of the uniform reflective appearance of the material over a range of processing conditions and part geometry, and which can be post formed without alteration of the uniform reflective appearance of the material. Still further, there is a need for silvery or metallic appearing articles which do not use metal.
SUMMARY OF THE INVENTION
The present invention meets those needs by providing a multilayered polymeric reflective body comprising multiple types of layers having differing optical thicknesses which has substantially no visibly perceived iridescent color, is highly reflective, post formable, and capable of being fabricated into a variety of parts while maintaining a uniform reflective appearance. 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 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 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 occurs. For example, a silver appearing article reflects substantially all visible wavelengths (white light), 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 nondyed sample, and it is at these unaffected wavelengths to which the intensity of reflectance is referring.
According to one aspect of the present invention, a reflective polymeric body of at least first and second diverse polymeric materials is provided in which the first and second polymeric materials differ from each other in refractive index by at least about 0.03. The body should comprise a sufficient number of layers of the first and second polymeric materials such that at least 30% of light incident on the body is reflected. As used herein, the term "light" is meant to encompass not only visible light but also electromagnetic radiation in both the infrared and ultraviolet regions of the spectrum. The term "at least 30% of light incident on the body" refers, as discussed above, to reflected light at wavelengths where negligible absorption occurs.