Stock material or miscellaneous articles – Composite – Of inorganic material
Patent
1986-09-18
1988-04-05
Lusignan, Michael R.
Stock material or miscellaneous articles
Composite
Of inorganic material
350166, 427165, 427169, 427299, G02B 528, B05D 506, B32B 900, B32B 1900
Patent
active
047358696
DESCRIPTION:
BRIEF SUMMARY
This invention relates to optical films on articles and especially to a process of forming a titanium dioxide optical film by aqueous solution reaction, in particular to a process to make titanium dioxide films which exhibit controlled interference colors. The optical film is a thin film whose optical thickness, defined by the product "nd" of the refractive index "n" and the actual dimensional thickness "d" is in the order of magnitude of the visible light wave lengths. As commonly known, it is used for such optical purposes as antireflection coatings and interference filters, as well as for ornamental purposes to impart decorative effect to glassware, porcelain or plastics where such substances having high refractive indices, such as zinc sulfide, bismuth oxichloride, stannic oxide or titanium dioxide, are used in thin films, exploiting the irridescent effect (colors produced by interference of light) which the thin films of these substances produce.
Among these substances, titanium dioxide is widely used in various ornamental purposes such as luster glaze for china because of its very high refractive index and chemical stability. This invention can be applied not only for the above ornamental purposes but also for optical purposes and ornamental multilayer films which require more strict control of optical thickness (hereinunder to be referred to as "nd"). Thin films of titanium dioxide are also used for preparing nacreous pigments by coating the surface of mica (muscovite) flakes for decorative purposes.
The known methods for making a thin film of titanium dioxide are classified into four groups. The first is a vacuum deposition process which is the surest for obtaining a uniform film thickness in principle, but due to the fact that titanium dioxide cannot readily be vacuum-evaporated ion-spattering methods are employed. For example, Japanese Patent Prepublication Showa No. 58-12564 describes a process under a vacuum of 5.times.10.sup.-5 Torr with an oxygen partial pressure of 10.sup.-4 Torr, wherein titanium dioxide is vaporized by means of an electron gun and deposited onto the substrate surface heated to 100.degree.-350.degree. C.
As seen in this example, the vacuum deposition process requires special equipment and accordingly the size of objects is limited by its capacity, which must have certain economic limitation, and the process costs are high.
The second method is a vapor decomposition which is characterized by thermal decomposition of titanium tetrachloride vapor on the heated surface of substrate in a vapor mixture with steam. Its process control is complex and reproducibility is low, so that film formation with uniform thickness is difficult. The iridescent effect cannot be distributed uniformly over a wide surface area of this method.
The third group are solution-coating or melt-coating methods. A solution of titanium compound is either coated at room temperature to form a surface film and then heated for thermal decomposition, or such solution, or otherwise a pulverized solid titanium compound, is sprayed over a heated substrate surface to realize the film formation and thermal decomposition simultaneously. In the Japanese Patent Publication Showa No. 52-1406, for example, a solution of organic titanium compound is sprayed over a heated glass surface. Iridescent films obtained by this method have fine spots of different colors, which spoil the color effect of the whole surface and the performance expected from the high refractive index of titanium dioxide cannot be attained. A further example of Japanese Patent Prepublication Showa No. 58-49645 describes that window panes exhibiting reflection of 31-39% for the range of the visible light are obtained by spraying pulverized tetramethoxy titanium over the heated surface of glass panels. The obtained titanium dioxide films, however, are colorless and uniformity of optical thickness is not mentioned. In any case, these coating methods have the intrinsic drawback that formation of a film with uniform "nd" over an undulated surface is impossible
REFERENCES:
patent: 3619235 (1971-11-01), Furuuchi et al.
patent: 3984591 (1976-10-01), Plumat et al.
patent: 4272588 (1981-06-01), Yoldas et al.
patent: 4596745 (1986-06-01), Chao
Lusignan Michael R.
Merck Patent Gesellschaft mit beschrankter Haftung
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