Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
1999-09-14
2002-05-14
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S446000, C428S448000, C428S470000, C428S472000, C428S212000, C427S162000, C427S299000, C427S407100, C427S419300, C427S515000, C106S286200, C106S287180, C525S016000
Reexamination Certificate
active
06387517
ABSTRACT:
DESCRIPTION
The invention relates to an inorganic polymer material based on tantalum oxide, notably with a high refractive index and mechanically resistant to abrasion, its method of manufacture, in particular making use of precursors based on chlorinated derivatives of tantalum, and optical materials such as anti-glare materials and reflecting materials manufactured from this material.
The anti-glare materials and the reflecting materials are made up of an organic or inorganic substrate, covered with several layers, certain of which have the specific sought for properties. More precisely, interfering dielectric mirrors comprise a substrate, covered with a dielectric film which reflects one or more desired wavelengths, while at the same time having relatively low intrinsic absorption compared with metals traditionally used to produce mirrors.
The anti-glare or reflecting materials have a multitude of applications.
Hence the organic or inorganic substrates, that is to say particularly plastic or glass substrates, coated with an anti-glare film are of interest particularly in the following fields: ophthalmic products and video or architectural applications such as glass panels placed on the outside or on the inside of buildings. Apart from this, the anti-glare materials and the interfering dielectric mirrors can also be used in high energy lasers, solar applications, heating and photovoltaic applications or in integrated optical systems.
Methods of producing these anti-glare materials or interfering dielectric mirrors are already known from the prior art. These methods are mentioned below.
Furthermore, while in the ophthalmic sector, plastics such as polycarbonates, polyacrylates, polyallylcarbonates and others are particularly interesting, glass substrates are equally interesting, notably in the field of general optics and in the field of screens such as display screens.
It can be easily understood that because of about 4% reflection loss for each air-glass interface and the mean index for glass being 1.5, the losses for a complex optical system are often high.
Consequently, opticians have been seeking for a long time to create coatings with optical properties and notably anti-glare films, using physical deposition processes under vacuum, collectively known as PVD Technology (Physical Vapor Deposition).
Among these methods, there is simple or reactive spraying, simple or reactive evaporation by electronic or ionic heating with or without assistance, etc,.
Despite the excellent optical, chemical and mechanical qualities of the deposits, these techniques require sophisticated equipment which is heavy and costly and processes which are rather long. This is even more so when the surface area of components to be treated becomes large. The result is that such processes are generally poorly suited to cheap line production.
For example, only top of the range cathode tube screens for televisions are at present being given anti-glare coatings applied by PVD.
This is the reason why deposition processes using a gentle chemical route and in particular processes of deposition by the sol-gel route appear to be an interesting alternative to the physical processes of deposition under vacuum.
The method of deposition by the sol-gel route allows one to produce films on substrates which have various optical properties. Such a process when compared with the traditional processes of deposition under vacuum offers a number of advantages among which one may mention, deposition generally carried out at ambient temperature and at atmospheric pressure without having recourse to a thermal stage at temperatures which are too high, reduced capital costs and a simple and rapid method of application that allows for great flexibility of operation.
The deposition of metal or non-metal oxides with optical properties using a sol-gel method has been widely studied. It is apparent that the sol-gel systems or methods can be classified into two categories: polymer methods or systems and colloidal methods or systems.
Each system requires different preparations and operating conditions which depend on the properties of the desired treatment solutions and the nature of the oxide concerned.
The polymer system consists of using, as precursors, monomer, oligomer or low molecular weight species, in solution, with good molecular homogeneity and which are then converted into oxide, after application onto the substrate, by a firing step. The liquid deposited possibly changes in viscosity as evaporation of the solvent progresses until a gel is formed on the substrate. The solid network obtained still containing solvent is then converted into oxide by heating the system generally to temperatures up to 500° C. One then obtains a dense, hard layer, that adheres strongly to the substrate. The conversion into oxide is generally accompanied by a large loss of mass made up of water and organic materials that brings with it a large reduction in the thickness of the layer. This induces high internal stresses, both tensile and compressive, in the deposit which can cause fine cracking of the coating in the case of thick mono- and multi-component films, that is to say films with a thickness that is greater than a few &mgr;m.
For example, German patents DE-A-736 411 and DE-A-937 913 mention the use of hydrolysable compounds for the preparation of various interfering films. The major disadvantage of these methods resides in the indispensable thermal treatment between 500 and 600° C. to convert the polymer intermediates into final dense ceramics. These high temperatures limit the choice for the nature of the substrate to be coated and complicate the industrial application.
The patent U.S. Pat. No. 2,466,119 describes a method of preparing reflecting and/or anti-glare multilayer films by hydrolysis and condensation of mixtures of halides of titanium and/or alkoxides of silicon. The control of the porosity of these layers is carried out by varying the temperature. However to obtain layers having good mechanical strength requires heating to temperatures which are very much greater than those that the usual plastics can tolerate, their thermal stability generally being 150° C. as a maximum.
The patent U.S. Pat. No. 2,584,905 deals with the preparation of reflecting thin layers from alcoholic solutions of TiCl
4
and silicon alkoxide. Here also, it is necessary to have resort to a heat treatment step that allows the oxides to be densified in a suitable way. In this method, the problems of fine cracks and spalling linked to the densification of the materials, considerably reduce the development of multi-layer build-ups with high reflection.
The patent U.S. Pat. No. 3,460,956 describes the preparation of reflecting films made of TiO
2
from hydrosylates of tetra alkyl titanates, in an alcoholic medium. However, for effective conversion of the polymeric film into dense oxide, it must be heated to heating to temperatures of about 500° C., which penalizes and can be damaging to any organic substrate.
The patents U.S. Pat. Nos. 2,768,909 and 2,710,267 describe the production of reflecting films made of TiO
2
from alcoholic sols of an alkoxide of titanium, these sols being hydrolysable by atmospheric moisture. This approach also requires strong firing of the condensed intermediates and the layers obtained are not resistant to abrasion.
The patent U.S. Pat. No. 4,272,588 is concerned with the possibility of increasing the reflectivity of mirrors made of noble metals and the possibility of making them chemically passive, by the deposition of dielectric TiO
2
and Ta
2
O
5
layers arising from molecular precursors.
Such coatings are obtained by essential heating to about 400° C.
Hence, the polymeric material generally used for thin optical layers with a high refractive index (between, for example, 1.9 and 2.1) is titanium oxide (TiO
2
). However in order to obtain layers that are mechanically resistant to abrasion, the densification must be carried out at high temperature close to 400° C. which could not be considered for plastic substrates for example.
T
Belleville Philippe
Floch Herve
Prene Philippe
Burns Doane , Swecker, Mathis LLP
Commissariat a l'Energie Atomique
Jones Deborah
Stein Stephen
LandOfFree
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