Optical lenses and processes of manufacture

Details Optical lenses and processes of manufacture Optical lenses and processes of manufacture

1997-11-06

1999-11-30

Marcheschi, Michael

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

501 65, 501 66, 501 68, 501 69, 501 70, 501 72, 65 66, 65 83, 65 68, 65 37, 65275, 359642, 359722, C03C 3076, C03C 400

Patent

active

059942487

DESCRIPTION:

BRIEF SUMMARY
The invention relates to lenses such as aspherical lenses and to a process for their manufacture. Although the invention is not restricted to this type of application, it will be described more particularly with reference to the production of optical lighting and signalling units for motor vehicles. More precisely still, it will be described with reference to ellipsoidal headlamps in which one of the constituent components is an aspherical lens.
Ellipsoidal headlamps at present represent a small portion of the headlamps in the motor vehicle industry, but demand for them is growing. In fact, the new vehicle shapes and the improvements, especially in the air drag coefficients of these vehicles induce motor vehicle manufacturers to choose headlamps of this type. Ellipsoidal headlamps are smaller in bulk, at least insofar as their height is concerned, and thus offer greater freedom in producing the front of the vehicles and more particularly the shape of the bonnet. It is thus possible to improve the vehicle aerodynamics and to allow the vehicle shapes to evolve according to the present proposals of the body designers. Moreover, the lighting quality of ellipsoidal headlamps is appreciably superior to that of parabolic headlamps which are used more commonly; the emitted light transmission is in fact clearly superior with ellipsoidal headlamps.
Such lenses have already been produced for motor vehicle applications and more precisely for producing ellipsoidal headlamps. To produce these lenses it is known to employ glass compositions which are usual in the case of optical applications.
One composition of this type is, for example, the extra-white glass marketed by the Schott company with reference B270, the weight contents of which are the following:
Such glasses are characterized especially by a transmission in the visible which is higher than 80% and refractive indices, at the various wavelengths, which are close to one another. The compositions differ especially in the presence of K.sub.2 O and of BaO, this latter oxide making it possible in particular to modify the refractive index without affecting the scattering coefficient, thus avoiding blurring of the images such as a chromatic aberration. These glasses are also characterized by their surface quality, having undergone a treatment of the fire-polishing type. In addition, these glasses exhibit virtually no impurities or bubbles which can give rise to scatter and hence dazzling, and the composition does not contain any iron, since the latter produces an absorption at certain wavelengths.
It turns out that the quality of these glasses, more particularly their surface quality, requires relatively costly specific treatments. Similarly, the composition of these glasses and especially the components which contribute more particularly to the optical properties are relatively costly components. Consequently, the cost of these optical glasses is very high and this in most cases limits the use of these lenses for ellipsoidal headlamps intended for top-range motor vehicles.
The inventors have set themselves the task of producing lenses exhibiting good transmission in the visible, that is to say higher than 80%, and refractive indices at the various wavelengths which are close to one another.
Another objective of the invention is to produce these lenses at a cost which is lower than that of the lenses currently produced.
These aims are attained according to the invention by a lens composed of a glass matrix including the constituents below in the following weight proportions:


______________________________________ SiO.sub.2 65-85% Al.sub.2 O.sub.3 0-10% B.sub.2 O.sub.3 0-20% Li.sub.2 O + Na.sub.2 O + K.sub.2 O 3-20% CaO + MgO + BaO 0-15% FeO + Fe.sub.2 O.sub.3 0-0.1%, ______________________________________ content remaining equal to or lower than 1%.
This glass matrix may also comprise impurities, especially those introduced by the vitrifiable raw materials, it not being permissible for the content of these to exceed 1%.
Such a glass matrix is, for exa

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