Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1999-01-25
2000-12-19
Dawson, Robert
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524437, 524432, 526279, 526178, 522 71, 522172, 528 32, 528 39, 26433115, 264 132, C08K 310
Patent
active
061628530
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for preparing a moulding suitable for optical purposes, for example a moulding which, possibly after appropriate machining and/or processing (for example sawing, milling, grinding, polishing, etc.), can be employed as it is (i.e. without further coating etc.) as a lens for spectacles, a camera and the like.
Mouldings which are to be employed for optical purposes are required to meet a range of highly differing requirements. They should, for example, be transparent, scratch- and abrasion-resistant, mechanically stable, free from stress and also resistant to high-energy light adjustable (e.g. high) refractive index. Furthermore, they should be homogeneous and should preferably be preparable in a simple manner from readily available (inexpensive) starting materials. Since, however, it is difficult to provide materials which meet all of these requirements, it is generally the case that one makes do with being forced to accept, or by means of additional process steps to compensate for, the lack or the paucity of one or other property. For example, materials of inadequate scratch and abrasion resistance that are to be employed for optical purposes are thus frequently provided with a coating which compensates for this deficit of the material. From an economic standpoint (additional time and expense), however, this is not a desirable state of affairs.
DE-A-32 44 877 relates to a silicone-containing contact lens material and to contact lenses produced therefrom. The contact lens material comprises oligomers or polymers of defined structure and composition that are prepared, for example, by condensing a hydrolysable silane having a free-radically polymerizable group (for example .gamma.-methacryloxypropyltrimethoxysilane) with other hydrolysable silanes and that have at least two free-radically polymerizable groups but no longer have any groups capable of further hydrolytic condensation (for example alkoxy groups attached to silicon) (and are therefore no longer capable of any inorganic crosslinking through the formation, for example, of --O--Si--O-- bonds). (Preferably hard) contact lenses are produced from these materials, referred to as organoylsiloxanes, by adding a free-radical initiator and thermally polymerizing the free-radical polymerizable groups that are present. If desired, in this polymerization, it is also possible for unsaturated monomers, for example methyl methacrylate and methacrylic acid, to be present. According to Example 5 of this document, 7 days are required to prepare a moulding which can be processed further into contact lens blanks. Nevertheless, high refractive indices, for example, can not be achieved by this route. Instead, advantageous properties cited for the resulting mouldings are good impact strength, reduced brittleness and satisfactory oxygen permeability.
EP-A-78548 describes silicic acid heteropolycondensates and their use for optical lenses, especially contact lenses. These heteropolycondensates are obtainable by subjecting (a) at least one titanium or zirconium compound which is soluble in the reaction medium and is fully hydrolysable and (b) at least one particular organofunctional silane and also (c) particular optional components to precondensation in the absence of water and in the presence or absence of an anhydrous solvent and then to further condensation by addition of water, using--based on the overall number of moles of the starting components--from 1 to 60 mol per cent of component (a) and from 20 to 99 mol per cent of component (b). Concrete examples of compounds of component (a) are titanium and zirconium tetraalkoxides, while specific examples of organo-functional silanes (b) are 3-glycidyloxypropyltrialkoxysilanes and 3-methacryloyloxypropyltrialkoxysilanes. The heteropolycondensates prepared as described are subjected, for the purpose of preparing mouldings, to thermal curing by condensation of the remaining condensable groups still present. In accordance with a specific embodiment it is also possible to polymerize het
REFERENCES:
patent: 4455205 (1984-06-01), Olson et al.
patent: 4715999 (1987-12-01), Dislich et al.
Braune Bert
Geiter Elisabeth
Krug Herbert
Mueller Peter
Schmidt Helmut
Dawson Robert
Institut fuer Neue Materialien Gemeinnuetzige GmbH
Peng Kuo-Liang
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