Glass manufacturing – Processes – With chemically reactive treatment of glass preform
Reexamination Certificate
2001-01-03
2004-08-10
Hoffmann, John (Department: 1731)
Glass manufacturing
Processes
With chemically reactive treatment of glass preform
C065S030130, C065S030140, C065S032100, C065S032300, C065S033100, C065S033300
Reexamination Certificate
active
06772608
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for producing UV polarizers in which polarization is effected by dichroitic absorption, and where revolution-ellipsoidal metal particles in a novel arrangement are embedded in the support material, the latter being preferably standard float glass. Said polarizers have a wide absorption range over the UV spectrum. The method uses the metal particles' dichroitic behavior, which undergoes some alterations by specific process steps to embed and treat submicroscopic metal particles within the support material.
Basically, there are several physical principles which can be used to produce plane-polarized light from non-polarized, or part-polarized light.
For instance, when utilizing the double refraction effect to produce plane-polarized light, it is the light's behavior that if in optically anisotropic media the incident light ray does not propagate along the optical axis it is divided into both an extraordinary and an ordinary light ray the polarized wave planes of which are vertically arranged to each other. Examples of application are polarizers that have been known for years such as Nicol prism, Glan Thompson prism, Wollaston prism, etc., whose structure, however, is rather solid (which makes them expensive), and they have an only limited useful surface, and they must be put very precisley into their working positions, too. Furthermore, their polarizing effect is strongly wave range dependent.
In case of inclined reflection of non-polarized light on transparent isotropic bodies the reflected light ray is part-polarized, with the component whose wave plane is arranged vertically to the plane of incidence being the preferably reflected one. If the angle of incidence is equal to the Brewster angle, the reflected light ray will be completely plane-polarized. This effected is utilized, for example, in polarizing beam splitters, the disadvantages, however, are the same as they are with polarizer prisms.
2. The Prior Art
In DE-OS 28 18 103, there is a “Method for Producing Polarizers made up of a great number of electrically conductive strips arranged all in parallel on a glass pane carrier” described, based on the so-called Hertzian polarization. Also, in EP 0416 157 A1, entitled “Polarizer”, such Hertzian polarization is used as a basis.
One of the main disadvantages in connection with these Hertzian polarizers is that they reflect the unwelcome polarization component, an effect which is found bothersome in many fields of application, especially when used in displays. While this type of polarizers is successfully utilized in the IR range, they could not yet effectively be used in the visible, or even in the UV range due to manufacturing problems in producing an exactly constant metal filament grid.
The majority of polarizers employed nowadays uses the dichroitic absorption to produce polarizing effects. The principle here is that certain molecules, or crystals, show a wave plane orientation dependent absorption effect. With the layer being sufficiently thick, and the molecules or crystals in an isotropic orientation, only a plane-polarized component exits from the polarizer.
In this context, the biggest group is represented by mechanically stretched plastic films colored by using dichroitic colorants, because such films can be produced in a very cost-efficient way. Stretching makes the colorant molecules light-absorbent in an oriented way. Despite the great progress made in producing such type of films (which has been reflected in the relatively big number of patents) the basic disadvantages such as chemical instability, sensitivity to UV rays, poor mechanical durability could not be removed. As a rule, these films can not be employed when the UV range is involved.
Dichroitic crystals, in particular non-spherical metal particle, are deemed to be most promising in compensating for those disadvantages. Especially non-spherical silver particles, 5 nm-50 nm in size, are bringing about the desired effects in the wave range from 350 nm to 1,000 nm, owing to their special electronic configuration. So, there are different starting-points from which to use this behavior.
Both U.S. Pat. No. 4,049,338 (Light polarizing material method and apparatus) and U.S. Pat. No. 5,122,907 (Light polarizer and method of manufacture) suggest using oriented revolution-ellipsoidal metal particles to be produce by precipitation on a smooth glass or plastic surface. The particles' eccentricity is controlled by said precipitation process so that maximum absorption positions can be achieved between 400 nm and 3,000 nm.
The disadvantage connected with this process is the mechanical sensitivity of the layers produced by it, which cannot be easily compensated for by applying protective coats as this would change the refractive index in the particles' environs and consequently lead to a shift in the maximum positions.
DE 29 27 230 C2 (Method for producing a polarizing glass film, glass films produced in accordance with it, and utilization of such films in liquid crystal displays) describes a process for the manufacture of a polarizer to be used in liquid crystal displays. They start from an organic, or inorganic glass melt into which pin-shaped bodies are added, and at last a glass film is drawn from. In connection with the invention to be disclosed, the above method is deemed disadvantageous in that no thin layers, i.e., no only near-surface layers can be realized.
There is a variety of suggestions made for producing polarizers having halide containing glasses as base material. Such glasses contain metal halide compounds, e.g., AgCl, AgBr, etc., out of —or in—which the metal part has precipitated. When the glass matrix is mechanically deformed, these particles receive a nonspherical shape which makes them behave in a dichroitic way.
U.S. Pat. No. 3,653,863 (Method of forming photochromic polarizing glasses) describes the manufacture of high-polarizing glasses, using phase-separated or photosensitive (i.e., silver halide containing) glass materials that must be tempered in order to produce silver halide particles of the desired size. There are two other steps to follow: firstly, at temperatures between upper cooling point and glass-transition temperature, i.e., 5000° C. to 600° C., the glass is drawn, extruded, and rolled in order to give the silver halide particles an ellipsoidal shape and the desired orientation. When the glass is subjected to radiation (i.e., by UV rays), metallic silver precipitates on the surface of the silver particles, which means that this type of glasses can be switched—by being subjected to radiation—between a clear non-polarized state and a dark-tone polarized state.
Another method of manufacturing polarizing glass by metallic silver precipitation is suggested in U.S. Pat. No. 4,304,584 (Method for making polarizing glasses by extrusion). Below its cooling point, the glass is tempered in a reducing atmosphere in order to produce metallic silver in a long-stretched out form within a surface-near layer which is at least 10 &mgr;m thick. This process includes the production of a sandwich-type glass, combining layers of polarizing and photosensitive glass into a laminated structure.
From WO 98/14409, we know a polarizer that uses glass in which metal particles showing a large size profile are embedded. In order to produce such type of polarizer, the process starts with making a specific metal compound form deposits of varying sizes inside the glass material. After that, the glass together with the precipitated matter is subjected to a single-direction stretching process, which forces the deposits into particles of a longish, revolution-ellipsoidal shape, and—as a side-effect—parallels them. The final tempering step reduces the precipitated metal compounds, which brings about metal particles of a revolution-ellipsoidal shape located in a near-surface layer of the glass. These particles show varying deformations as far as their revolution-ellipsoidal shape is concerned, depending on the si
Berger Andreas
Drost Wolf-Gernot
F.O.B. GmbH Gesellschaft Zur Fertigung Farbiger Optoelektronisch
Hoffmann John
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