Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2000-07-31
2003-10-28
Chen, Bret (Department: 1762)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C252S586000, C427S162000, C427S387000
Reexamination Certificate
active
06639039
ABSTRACT:
The present invention relates to photochromic coating compositions and to substrates provided therewith. In particular, the present invention relates to photo-chromic coating compositions which comprise, as essential components, a silicon-containing precondensate, at least one photochromic dye and at least one stabilizer (for example an antioxidant and/or a UV absorber). These coating compositions are particularly suitable for providing substrates made from (preferably transparent) plastics and mineral glasses with a hard, scratch-resistant coating having a long-term photochromic action.
Photochromic components or elements having excellent photochromic behaviour, in particular over long periods, are nowadays employed in a wide variety of areas, the best-known being the area of photochromic spectacle lenses. At present, these photochromic substrates are produced by providing corresponding plastics with organic photochromic substances by very complex and expensive processes. In general, such processes are not suitable for use on a large scale and in a wide variety of areas. Furthermore, C. Sanchez, in J. Mater. Chem. 7(1) (1997), 61-65, describes the incorporation of spiropyrans and spirooxazines into organic/inorganic matrices of diethoxydimethylsilane/zirconium propoxide and methyldiethoxysilane/triethoxysilane, but without investigating the light stability of these systems.
It has now been found, in accordance with the invention, that photochromic coating compositions which are simple and inexpensive to produce on the basis of certain silicon-containing precondensates, photochromic dyes and stabilizers are suitable for providing corresponding substrates with a remarkably hard and scratch-resistant coating which exhibits long-term photochromicity. Coating compositions of this type are suitable for a large number of applications, such as, for example, photochromic spectacle lenses, lenses for sunglasses, visors and ski goggles, but also for glazing of all types, in particular for decorative needs, buildings, automobiles and aircraft, in which a photochromic effect is desired (and which are exposed to varying irradiation with light (in particular sunlight)).
Accordingly, the present invention provides a photochromic coating composition which comprises, as essential components:
(a) a silicon-containing precondensate derived from at least one hydrolysable silane A containing at least one hydrolysis-stable radical R which has a functional group X which is capable of undergoing a thermally and/or photochemically induced (optionally catalysed) polymerization reaction, and optionally from one or more additional hydrolysable compounds of elements from the group consisting of Si, Al, Ti, Zr, Ta, Nb, Sn, Zn, W and Ge;
(b) at least one photochromic dye; and
(c) at least one stabilizer, preferably selected from antioxidants and UV absorbers.
The above silane A usually contains at least one (and preferably a single) group X, which is an epoxide, mercapto or (meth)acrylyl group.
It is furthermore particularly preferred for the silane A to be selected from compounds of the following general formula (I):
R
1
x
SiR
3
(3−x)
R (I)
in which the radicals R
1
are identical or different (preferably identical) and are selected from halogen atoms (in particular Cl and Br), (preferably C
1-4
-)alkoxy groups and (preferably C
2-6
-)acyl groups (the groups R
1
are particularly preferably methoxy or ethoxy groups); the radicals R
3
are a (preferably unsubstituted) alkyl or aryl radical (for example methyl, ethyl, propyl, butyl or phenyl), and x is 1, 2 or 3 (preferably 2 or 3).
The radical(s) R is (are) preferably selected from those of the following general formulae (II) and (III):
in which R
2
is hydrogen or methyl, and n is an integer from 1 to 6, preferably from 2 to 4, and in particular 3. However, the radical(s) R may also contain other functional groups and may optionally be fluorinated.
Specific examples of silanes A of this type are 3-glycidoxypropyltri(m)ethoxysilane and 3-(meth)acryloxypropyltri(m)ethoxysilane.
The photochromic dye (b) is preferably selected from the group consisting of the spirooxazines, spiropyrans, naphthopyrans (chromenes), fulgides and dihydroindolizines. Particular preference is given to photochromic dyes from the group consisting of the spirooxazines and naphthopyrans.
Suitable stabilizers which can be employed as component (c) in the present coating composition are all compounds which are capable of protecting the photochromic dyes (b) in a suitable manner against attack (for example decomposition) by radiation (in particular UV radiation) and/or (aggressive) chemical substances (oxygen, ozone, free radicals, etc.). Preferred examples thereof are antioxidants and UV absorbers.
The antioxidants which can be used as stabilizers in the coating composition according to the invention include the compounds known to the person skilled in the art as antioxidants. However, the antioxidant employed in accordance with the invention is preferably selected from the group consisting of phenols, hydroquinones, pyrocatechols and aromatic amines which are substituted by sterically hindered groups, and organic phosphites and phosphonates. The term “phenol” here is intended to cover not only monocyclic phenols, but also bicyclic (bisphenols), tricyclic (trisphenols) and polycyclic phenols and naphthols.
The UV absorbers which can be employed as stabilizers in the coating composition according to the invention include the compounds which are known to the person skilled in the art as UV absorbers. Preferred UV absorbers include derivatives of benzophenone, whose substituents (for example hydroxyl and/or alkoxy groups) are preferably in the 2- and/or 4-position; substituted benzotriazoles, 3-phenyl-substituted phenylacrylates (cinnamic acid derivatives) and salicylates.
Further UV absorbers which are preferred in accordance with the invention are natural products, such as 3-(5-imidazolyl)acrylic acid (urocanic acid) and ergosterol.
According to a preferred embodiment of the present invention, the coating composition according to the invention, besides the above essential components (a), (b) and (c), also comprises nanoscale particles, which are preferably selected from the group consisting of the oxides, nitrides, carbides, silicides, borides and carbo-nitrides of Al, Si, Ti, Zr, Hf, W, Ga, Nb, Ta, Sn, Zn and Ge. In the present connection, the term “nanoscale particles” is taken to mean particles having a mean particle size of not greater than 200 nm, preferably not greater than 100 nm and particularly preferably not greater than 50 nm (for example up to 30 nm). The nanoparticles can also be employed in surface-modified form in order to prevent agglomeration of the particles. The surface modification is carried out here, for example, using epoxy-, amino-, mercapto- or (meth)acrylate-functional silanes; see, for example, DE-A-195 40 623.
Particularly preferred nanoscale particles for use in the present invention are those comprising SiO
2
(for example silica sols).
Nanoscale particles of this type are preferably used, if at all, in amounts of from 2 to 100% by weight of the precondensate (a) employed, a proportion of from 5 to 50% by weight being even more preferred.
Components (a), (b) and (c) of the present coating composition are preferably present in such amounts, based on the total weight of these components, that component (b) makes up from 0.05 to 5% by weight, preferably from 0.1 to 2% by weight, and component (c) makes up from 0.1 to 5% by weight, preferably from 0.5 to 2.5% by weight.
The present invention is explained in greater detail below with reference to preferred embodiments.
As already mentioned above, the silicon-containing precondensate to be employed in the coating composition according to the invention is preferably derived from at least one hydrolysable silane A containing an epoxide, mercapto or (meth)acrylate group X.
The epoxide-based formulation comprises a precondensate derived from a silane A containing an epoxide group X, and optionally one
Fries Kira
Hou Lisong
Mennig Martin
Pietsch Marion
Schmidt Helmut
Chen Bret
Fletcher, III William Phillip
Heller Ehrman White & McAuliffe LLP
Institut für Neue Materialien gemeinnützige GmbH
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