CS258942B1 - A method of producing dispersion dispersion filters of the type crystal-air - Google Patents

Abstract

Crystal-air type dispersion filters are made of a transparent substrate in the form of a foil on which a layer of sorted powder is fixed, the grain size of which is tied to the range of wavelengths in which the filter is to transmit light. The solution relates to a method of manufacturing these filters, according to which a sticky surface is created on the transparent substrate, onto which, after drying, the sorted powder is applied by spraying. For example, the transparent substrate is made of high-pressure polyethylene and the sticky surface is created by applying a 10% solution of amorphous polypropylene to the transparent substrate.

Description

The present invention relates to a process for the production of crystal-air dispersion filters using light scattering processes. Dispersion dispersion filters are usually composed of thin layers of transparent medium with refractive index forming a matrix with dispersed particles (filler) with refractive index n ₂ · Both substances used, ie matrix and filler, must be light transmissive in the required spectral range, both components used are selected so that the difference of refractive indices Δ n = n ₂ - n ₂ decreases to zero at the wavelength Λ _{max of the} required maximum filter throughput. For this wavelength of light (Λ _ax , the transmittance of dispersion dispersion filters will be greatest, since the light scattering on the dispersed particles disappears (Δ _n = 0) and the filter material (matrix + filler) behaves as an optically homogeneous environment. the transmitted light will scatter the dispersed particles, and the more the Δη for a given wavelength.

High-quality dispersion dispersion filters are commonly prepared so; that the screened powder is allowed to sediment directly from the slurry onto a transparent substrate or a liquid. window, such as NaCl,

KCl, and the like, to obtain a uniform powder layer. After removal of the liquid residue by vacuum drying, the powder layer had to be mechanically fixed by means of another through window preventing the powder from falling off (see N.A. Borisevich, V.G. Bereschagin, M.A. Validov "Infrakrasnye filtr Izdatelstvo" Nauka i technika Minsk 1971). This method of manufacture requires the use of two transparent windows which are mechanically additionally rigid in order to allow sufficient mechanical fixation of the powder, i.e. windows of crystalline materials or glass. In this process, the use on a transparent backing of transparent flexible films, e.g. polymeric films, is practically avoided. The existing technology is therefore very complicated, lengthy and expensive.

Nevertheless, it represents a classic and hitherto used procedure.

These drawbacks are overcome by the dispersion filter manufacturing process according to the invention, in which a layer of sorted powder whose grain size is bound to the wavelength range over which the filter is to pass light is fixed on a transparent film-shaped substrate. It is an object of the present invention to provide an adhesive surface on a transparent substrate on which, after partial drying, the screened powder is applied by dusting.

It is advantageous to use a high-pressure polyethylene film on which the adhesive surface is formed by applying a 10% amorphous polypropylene solution as a transparent substrate. The transparent substrate is then dusted with a sorted crystalline lithium fluoride powder.

Method of preparation resp. The production of dispersion dispersion filters according to the present solution allows for use on the base material resp. flexible film windows, for example polymeric. The spectral characteristics of the crystal-air dispersion dispersion filters produced in this way are comparable with the spectral characteristics of the dispersion dispersion filters produced by the classical method. The present method of manufacturing dispersion dispersion filters substantially reduces labor, is simple and the costs associated with implementation are relatively low.

An exemplary embodiment of the invention is described in the following example of a possible dispersion dispersion filter having a maximum transmittance at a wavelength of = _max = 10.8 µm crystal-air type, on a transparent substrate with high-pressure polyethylene in the shape of 45 µm thick with 80% at a wavelength λ _max = 10.8 µm, 10 wt. % of a solution of amorphous polypropylene and after evaporating the excess solvent at room temperature, a screened crystalline lithium fluoride powder having a grain size in the range of 45 to 80 .mu.m is sprayed into the adhesive layer thus formed. Dusting can be carried out either by compressed air or electrostatically.

The crystal-air dispersion dispersion filters thus produced exhibited a transmittance of approximately 66% at a wavelength of Λ _max = 10.8, with a transmittance bandwidth of Δ Λ = 2 µm and a residual transmittance in the vicinity of 5 µm of less than 5%. The two basic dispersion dispersion filters arranged in series have a transmittance at Λ _max = 10.8 µm of about 40% and a residual permeability outside the permeability band of the order of 0.1%.

Claims (2)

OBJECT OF THE INVENTION A method of making crystal-air dispersion dispersion filters, in which a layer of graded powder, the grain size of which is bound to a wavelength range within which the filter is intended to transmit light, is fixed to a transparent film-like substrate. forms a sticky surface to which the dried powder is sprayed onto the sorted powder. 2. A method according to claim 1, characterized in that on a transparent substrate of high-pressure polyethylene, a sticky surface is formed by applying a 10% amorphous polypropylene solution and the transparent substrate is dusted with a sorted crystalline lithium fluoride powder (LiF).