Optical: systems and elements – Extended spacing structure for optical elements – Extension of tubular element adjustable
Reexamination Certificate
1998-07-31
2001-07-03
Shafer, Ricky D. (Department: 2872)
Optical: systems and elements
Extended spacing structure for optical elements
Extension of tubular element adjustable
C359S599000, C359S900000, C359S494010, C359S492010, C252S585000, C264S001340, C264S001900, C264S002700, C427S163100
Reexamination Certificate
active
06256146
ABSTRACT:
The present invention relates to post-forming of optical bodies containing structures suitable for controlling optical characteristics, such as reflectance and transmission.
BACKGROUND
Optical films are known to the art which are constructed from inclusions dispersed within a continuous matrix. The characteristics of these inclusions can be manipulated to provide a range of reflective and transmissive properties to the film. These characteristics include inclusion size with respect to wavelength within the film, inclusion shape and alignment, inclusion volumetric fill factor and the degree of refractive index mismatch with the continuous matrix along the film's three orthogonal axes.
Other films, such as those disclosed in U.S. Pat. No. 4,688,900 (Doane et. al.), include a clear light-transmitting continuous polymer matrix, with droplets of light modulating liquid crystals dispersed within. Stretching of the material reportedly results in a distortion of the liquid crystal droplet from a spherical to an ellipsoidal shape, with the long axis of the ellipsoid parallel to the direction of stretch. U.S. Pat. No. 5,301,041 (Konuma et al.) make a similar disclosure, but achieve the distortion of the liquid crystal droplet through the application of pressure. A. Aphonin, “Optical Properties of Stretched Polymer Dispersed Liquid Crystal Films: Angle-Dependent Polarized Light Scattering,
Liguid Crystals
, Vol. 19, No. 4, 469-480 (1995), discusses the optical properties of stretched films consisting of liquid crystal droplets disposed within a polymer matrix. He reports that the elongation of the droplets into an ellipsoidal shape, with their long axes parallel to the stretch direction, imparts an oriented birefringence (refractive index difference among the dimensional axes of the droplet) to the droplets, resulting in a relative refractive index mismatch between the dispersed and continuous phases along certain film axes, and a relative index match along the other film axes. Such liquid crystal droplets are not small as compared to visible wavelengths in the film, and thus the optical properties of such films have a substantial diffuse component to their reflective and transmissive properties. Aphonin suggests the use of these materials as a polarizing diffuser for backlit twisted nematic LCD's. However, optical films employing liquid crystals as the disperse phase are substantially limited in the degree of refractive index mismatch between the matrix phase and the dispersed phase. Furthermore, the birefringence of the liquid crystal component of such films is typically sensitive to temperature.
U.S. Pat. No. 5,268,225 (Isayev) discloses a composite laminate made from thermotropic liquid crystal polymer blends. The blend consists of two liquid crystal polymers which are immiscible with each other. The blends may be cast into a film consisting of a dispersed inclusion phase and a continuous phase. When the film is stretched, the dispersed phase forms a series of fibers whose axes are aligned in the direction of stretch. While the film is described as having improved mechanical properties, no mention is made of the optical properties of the film. However, due to their liquid crystal nature, films of this type would suffer from the infirmities of other liquid crystal materials discussed above.
Other optical films have been made by incorporating a dispersion of inclusions of a first polymer into a second polymer, and then stretching the resulting composite in one or two directions. U.S. Pat. No. 4,871,784 (Otonari et al.) is one example of this technology. The polymers are selected such that there is low adhesion between the dispersed phase and the surrounding matrix polymer, so that an elliptical void is formed around each inclusion when the film is stretched. Such voids have dimensions of the order of visible wavelengths. The refractive index mismatch between the void and the polymer in these “microvoided” films is typically quite large (about 0.5), causing substantial diffuse reflection. However, the optical properties of microvoided materials are difficult to control because of variations of the geometry of the interfaces, and it is not possible to produce a film axis for which refractive indices are relatively matched, as would be useful for polarization-sensitive optical properties. Furthermore, the voids in such material can be easily collapsed through exposure to heat and pressure.
There thus remains a need in the art for methods of manufacturing diffusely reflective articles from an optical body including a continuous and a dispersed phase, wherein the refractive index mismatch between the two phases along the material's three dimensional axes can be conveniently and permanently manipulated to achieve desirable degrees of diffuse and specular reflection and transmission, wherein the optical material is stable with respect to stress, strain, temperature differences, and electric and magnetic fields, and wherein the optical material has an insignificant level of iridescence. All of these characteristics are also preferably met by the post-formed articles manufactured from the optical bodies.
SUMMARY OF THE INVENTION
The present invention provides diffusely reflective articles manufactured from optical bodies including continuous and disperse phases, methods of manufacturing such articles, and optical bodies including continuous and disperse phases that are particularly well-suited to post-forming operations. The articles, methods and optical bodies of the present invention allow for post-forming of the optical bodies while retaining the desired diffuse reflectivity in the articles formed from the optical bodies.
Because optical bodies including continuous and disperse phases rely on refractive index differentials developed at least in part by drawing, post-forming of the optical bodies may pose a number of problems. The additional strain caused during the post-forming processes can affect the refractive index differentials between the continuous and disperse phases in the optical bodies, thereby affecting the optical properties of the optical bodies. For example, an optical body designed to diffusely reflect light of one polarization orientation and transmit light of the orthogonal polarization orientation may be altered during post-forming such that it diffusely reflects light with both polarization orientations. In addition, many post-forming processes involve the use of heat during forming, and that heat may alter the refractive index differentials in many of the optical bodies.
As discussed in more detail below, post-forming of diffusely reflective optical bodies in accordance with the present invention involves additional deformation, typically strain-induced, of the optical bodies while retaining desired levels of diffuse reflectivity in the articles so produced. It is preferred that the diffuse reflectivity of the articles be at least as high as the diffuse reflectivity of the optical bodies used to produce the articles and, in some cases, the diffuse reflectivity of the articles may be improved over the diffuse reflectivity of the optical bodies used to produce them.
As used in connection with the present invention, post-forming may involve additional deformation of an optical body provided in film or sheet form along one or more in-plane axes. The optical body being post-formed will preferably have some desired level of diffuse reflectivity for light of at least one polarization orientation before post-forming, and after post-forming the post-formed article will preferably exhibit diffuse reflectivity for light of at least one polarization that is at least as high as the optical body used to manufacture the article. Because the deformation caused during post-forming is along in-plane axes, the resulting post-formed article will also be a sheet or film form. Furthermore, the post-forming may produce a film or sheet article that has increased diffuse reflectivity as compare to the diffuse reflectivity of the optical body used to produce the article.
The addi
Allen Richard C.
Benson, Jr. Olester
Condo Peter D.
Merrill William W.
3M Innovative Properties
Pechman Robert J.
Shafer Ricky D.
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