Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-11-29
2003-09-30
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S446000, C428S697000, C428S702000, C427S523000, C427S525000, C427S527000, C427S529000, C427S576000, C427S162000, C427S163100, C427S164000, C106S286800
Reexamination Certificate
active
06627320
ABSTRACT:
The present invention relates to a method for producing a composition for vapor deposition to form an antireflection film, to a composition for vapor deposition, and to a method for producing an optical element with an antireflection film. In particular, the invention relates to a method for producing a composition for vapor deposition and to a composition for vapor deposition capable of forming a high-refraction layer even in low-temperature vapor deposition, and therefore ensuring an antireflection film having good scratch resistance, good chemical resistance and good heat resistance, of which the heat resistance decreases little with time; and also relates to a method for producing an optical element having such an antireflection film.
BACKGROUND OF THE INVENTION
For improving the surface reflection characteristics of an optical element that comprises a synthetic resin, it is well known to form an antireflection film on the surface of the synthetic resin. To enhance the antireflectivity of the film, a laminate of alternate low-refraction and high-refraction is generally used. In particular, for compensating for the drawback of synthetic resins that are easy to scratch, silicon dioxide is often used for the vapor source to form low-refraction layers on the substrates, as the film formed is hard. On the other hand, zirconium dioxide, tantalum pentoxide and titanium dioxide are used for the vapor sources to form high-refraction layers on the substrates. Especially for forming an antireflection film of lower reflectivity, substances of higher refractivity are selected for the high-refraction layers of the antireflection film. For this, titanium dioxide is generally used.
However, the vapor source prepared by sintering titanium dioxide powder, when heated with electron beams for vaporizing it to be deposited on substrates, is decomposed into TiO
(2-x)
and generates oxygen gas. The thus-formed oxygen gas exists in the atmosphere around the vapor source, and oxidizes the vapor of TiO
(2-x)
from the source before the vapor reaches the substrates. Therefore, a film of little light absorption is formed on substrates from the vapor source. On the other hand, however, the oxygen gas interferes with the vapor component that runs toward the substrates, and therefore retards the film formation on the substrates. In addition, when the vapor source, prepared by sintering titanium dioxide powder, is heated with electron beams, it melts, and is therefore generally used as a liner. At this stage, the electroconductivity of the TiO
(2-x)
vapor increases, and the electrons of the electron beams applied to the vapor source therefore escape to the liner. This causes electron beam loss, and the vapor deposition system therefore requires higher power which is enough to compensate for the loss. On the other hand, when pellets only made of titanium dioxide are used for vapor deposition, the speed of film formation is low. When electron beams are applied, it was problematic in that the pellets are readily cracked.
The problem with optical elements comprising a synthetic resin is that the heating temperature in vapor deposition for the structures cannot be increased. Because of this limitation, therefore, the density of the film formed from titanium dioxide in such optical elements cannot be made satisfactory, and the film refractivity is not satisfactorily high. In addition, the scratch resistance and the chemical resistance of the film are also not satisfactory. To compensate for the drawbacks, ion-assisted vapor deposition is generally employed, but the ion gun unit for it is expensive, therefore increasing the production costs.
Optical elements comprising a synthetic resin, especially lenses for spectacles, are generally planned so that an organic hard coat film is formed on a plastic lens substrate for improving the scratch resistance of the coated lenses, and an inorganic antireflection film is formed on the hard coat film. For spectacle lenses, new optical elements having an antireflection film of superior antireflectivity are now desired, in which the antireflection film is desired to have superior abrasion strength and good heat resistance, and its heat resistance is desired not to lower with time.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method for producing a composition which is suitable for vapor deposition and to provide a composition which is suitable for vapor deposition. The advantages are such that the composition can form a high-refraction layer even on synthetic resin substrates that must be processed for vapor deposition thereon at low temperatures, within a short period of time and without using an ion gun unit or a plasma unit; not detracting from the good physical properties intrinsic to the high-refraction layer formed, that the high-refraction layer formed has high refractivity; that the antireflection film comprising the high-refraction layer formed on such synthetic resin substrates has good scratch resistance, good chemical resistance and good heat resistance, and that the heat resistance of the antireflection film decreases little with time.
Another object of the invention is to provide an optical element comprising a synthetic resin substrate with an antireflection film formed thereon, in which the antireflection film has good scratch resistance, good chemical resistance and good heat resistance, and the heat resistance of the antireflection film decreases little with time.
In our efforts to develop plastic lenses for spectacles having the above-mentioned desired properties, we have found that, when an antireflection film is formed through vapor deposition on a plastic lens substrate from a vapor source prepared by sintering a mixture of titanium dioxide and niobium pentoxide, we can attain the above-mentioned objects. Specifically, the invention provides a method for producing a composition, which comprises sintering a vapor source mixture prepared by mixing vapor sources that contain titanium dioxide and niobium pentoxide; and provides a composition that contains titanium dioxide and niobium pentoxide.
The invention also provides a method for producing an optical element with an antireflection film, which comprises vaporizing the composition and depositing the generated vapor on a substrate to form thereon a high-refraction layer of an antireflection film.
DETAILED DESCRIPTION OF THE INVENTION
A method for producing a composition for vapor deposition of the invention comprises sintering a vapor source mixture prepared by mixing vapor sources that contain titanium dioxide and niobium pentoxide. The composition of the present invention contains titanium dioxide and niobium pentoxide. The method for producing an optical element of the invention comprises vaporizing the composition and depositing the generated vapor on a substrate to form thereon a high-refraction layer of an antireflection film.
The method of the invention for preparing a composition comprises sintering a mixture containing titanium dioxide powder and niobium pentoxide powder. The powder particles may be of any suitable size, and are generally in the range of 500 nm to 4000 nm. The composition containing titanium dioxide and niobium pentoxide can be prepared by mixing titanium dioxide powder and niobium pentoxide powder. In this method, niobium pentoxide melts first as its melting point is low, and thereafter titanium dioxide melts. In the melting and vaporizing process, since the vapor pressure of the molten titanium dioxide is higher than that of the molten niobium pentoxide, the amount of titanium dioxide vapor that reaches the substrate is generally higher than that of the niobium pentoxide vapor. In addition, since the oxygen gas partial pressure resulting from the titanium dioxide decomposition is low, rapid film formation on the substrate is possible even if the power of electron beams applied to the vapor source is low. Preferably, the compositional ratio of titanium dioxide to niobium pentoxide is such that the amount of titanium dioxide (calculated in terms of TiO
2
Kamura Hitoshi
Kobayashi Akinori
Mitsuishi Takeshi
Shinde Ken-ichi
Takahashi Yukihiro
Dawson Robert
Feely Michael J
Finnegan Henderson Farabow Garrett & Dunner LLP
Hoya Corporation
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