CA1207932A - Photocuring composition for coating substrates with an abrasion-resistant transparent or translucent film - Google Patents

Abstract

ABSTRACT

A photopolymerizable olefinic composition containing a mineral filler suitable for forming on a substrate an abra-sion resistant protective film. The mineral filler essen-tially consists of silica or alumina particles having been made organophilic and compatible with olefinic monomers by grafting organic groups on the surface thereof. When the filler is silica thus modified and when the refraction indexes of the organic phase and of the particles are near to each other, the anti-abrasive film is transparent.

Description

1 ~Z~7~

PHOTOCURING COMPOSITION FOR COATING SUBSTRATES WITH

AN ABRASION-RESISTANT TRANSPARENT OR TRANSLUCENT FILM

Field of the invention The present invention relates to scratch-resistant sur-faces and more particularly concerns a photopolymerizable composition to be applied on a substrate so as to produce thereon a translucent or transparent coating resisting cor-rosion and abrasion. This coating is intended to protect said substrate against shocks, bruises and other mechanical accidents as well as against wear resulting from normal use. Such composition is very useful in all industrial fields where it is desirable to avoid, as much as possible, that sensitive objects exposed to shock and wear be progres-sively damaged. This is particularly important when dealing with transparent articles such as optical goods the surface of which must be protected by all means against scratches so as not to lose its desirable optical properties.
It has been definitely established by now that the manu-facture of high performance optical ware by using transparent organic materials is possible, the working of which by cast-ing or any other machining means, is much easier and more economical than with corresponding articles of ordinary glasses from metal oxides. On the other hand, such articles of "organic glass" are relatively soft and poorly resist abrasion, wear and corrosion by external agents. Thus, it is desirable to cover such articles with an anti-abrasion and anti-corrosion protective film but thin enough for not sig-nificantly altering the optical properties of the substrate.

The prior art Very many coating compositions and application methods have already been proposed for achieving the aforementioned objectives, this being with variable success.
Among all these compositions of the prior art, some are particularIy relevant that owe their properties to the pres-ence of compounds from elements other than the usual con-stitutents of organic matter and, in particular, to aluminum and silicon in the form of specific mineral or organic com-pounds. With reference to silicon, for instance, some of the techniques used involve the buildup of a protective coating on substrate, this coating being obtained from the vapor phase deposition of glass or silica evaporated under vacuum.
Polysiloxane based protective coatings can also be obtained,

2 :~2~7~3;2 the structure of which resembles to some extent that of crosslinked polysilicic acid, by the in situ polymerization of organo-silicon compounds previously partly hydrolyzed.
During the hardening (curing) of such coatings, polymeriza-tion occurs, either due to the formation of Si-O-Si bridges (by the dehydration of silanol functions), or due to the participation of polymerizable organic groups belonging to substituents possibly present on the silicon atoms (olefins, epoxy-, amino- groups, etc.), or by a combination of the said two polymerization modes. From the references illustrating such techniques, the followings can be cited: A.J. REEDY, Res. Discl. 1978, 171-6; Patents USP 4,006,271; 4,098,840;
4,186,026; 4,197,335; JP (Kokai) 77, 101,235; 112,698;
152,426; 154,837; 79, 60,335; 62,267; 119,597; 119,599;
129,095 to 129,099; 133,600; 144,5G0; 148,100; 80, 05,924;
and DOS 2,803,942; 2,805,552; 2,820,391; 2,831,220;
2,917,440. However, despite the protection they impart to the substrate on which they are applied, these coatings have some drawbacks. One of such disadvantages is related to the relatively high temperatures needed for curing polysilicic type coatings which can lead to substrate deformation. An-other drawback is inherent to the expansion coefficient of the polysiloxane coatings which is often sufficiently differ-ent from that of the substrate for causing the development of adhesion problems (for instance in the case of polycarbonate or polymethacrylate organic glasses) and of cracks or crazing after alternating hot and cold periods (particularly in the case of articles subjected to weathering like automobile headlights). Adhesion problems were partially solved by interposing an intermedlate bonding sublayer between the coating and the substrate but, more generally, it has been sought to remedy the above-mentioned drawbacks by replacing the coatings from polymerized silicon compounds by composi-tions comprising, dispersed within an organic or silico-organic matrix, fine particles of silica or alumina. Thus, there were used in this context aqueous mixtures of silicon compounds, colloidal silica and hydrocompatible solvents (alcohols, glycols, etc.), with or without polymerizable or-ganic monomers. Examples of such uses can bè found in the following ~eferences: Belgian Patents Nos. 821.403; 877.372;
USP 4,027,073; 4,188,451; 4,177,315; GB 2,018,621; 2~018,622;
DOS 2.811.072 and JP (Kokai) 79, 157,187. However, colloidal silica being essentially hydrophilic, as are also the other types of silica such as amorphous, crystalline, microcrystal-line, precipitated and pyrogenic silicas, it is well compati-ble, in general, only with hydrophilic polymers, for instance organosilicon polymer, whereas it is much less or not

3 ~ 7~3Z

miscible with typical hydrophobic resins such as polyolefins, which very strongly restricts its use as a filler in the film forming thermosetting or photocuring compositions. rloreQverl adding hydrophilic silica to organic polymerizable monomers leads to the formation, with relatively low concentrations of solids, e.g., about 5 to 10% by weight, of highly thixotropic masses (non-Newtonian rheologic behaviour) which are very difficult to apply as thin layers on substrates. Hence, attempts were made to remedy this disadvantage, i.e., to increase the level of silica in organic resin coatings, while overcoming such application problems, by treating the particles so as to make them organophilic. It should be re-marked at this stage that methods for imparting hydrophobic organophilic properties to alumina or silica particles are already known, per se; however, it does not appear that there exist, up to now, methods for giving to silica or alumina particles sufficient organophllic properties to enable them to be incorporated at high levels (of more than about 40~ by weight) into polymeric resin films, while maintaining suit-able rheological properties for application and nearly com-plete transparency of the films formed. Yet, ensuring proper transparency of the protective coatings of optical goods is a fundamental requirement, as will be seen hereinafter in the description of the present invention. As pertinent refer-ences regarding the methods for "treating" silica or alumina particles for rendering them organophilic, South African Pat-ent No. 72,5180 and Japanese Patent (Kokai) No. 77, 138,154 can be cited. In the first of these references~ silica par-ticles are treated with trimethylchlorosilane which, by reac-tion with the silanol groups of said particles, generates hy-drophobic groups of formula -Si-O-Si~e3, whereby said par-ticles are rendered compatible with a mixture of olefinic monomers (ethylenic and acrylic monomers). These particles are then incorporated, to a level of about 5 - 10% by weight and together with a proportion of alumina about 10 to 20 times greater, into a mixture of polymerizable resins which, after curing, provides insulators for high electric voltages.
Such materials are, however, opaque and their resistance to abEasion is not indicated. In the second of the two refer-ences cited above, particles of alumina are coated with y-(glycidyloxy)-propyl-trimethoxysilane and a mixture contain-ing about 25% by weight of such treated alumina and an epoxy resin is used for coating a polycarbonate article so as to obtain, after polymerization, a translucent abrasion-resis-tant film. rloreover, in the following references, there are described methods for attaching organic groups such as vinyl, methacryl, epoxyr glycidoxy to hydrophilic silica so as to

4 ~ 3~

impart thereto hydrophobic properties: L.P. ZIEMJANSKI et al, Rubber ~orld 163, 1 (1970); rl.w. RANEY et al, Meeting of the Div. of Rubber Chem., Paper No. 71, ACS ~eeting, Cieve-land, Ohio (1971); M.W. RANEY et al, Meeting of the Div. of Rubber Chem., ACS, Miami, Fla (1971); and Rubher Chem. and Tech. 44, 1080-142 (1971); HI-SIL Bulletin 41, Jan. 1971, PPG
Industries.
In addition to the above mentioned prior art, some fur-ther United States Patent references can be cited in connec-tion with the following subjects pertinent to the invention:
1. SiO2: 3,986,997; 4,177,315; 4,188,451; 4,242,403.
lA. Treated SiO2, e.g., to make it hydrophobic:
2,610,167; 2,818,385; 3,652,379; 4,001,128.
2. Forming SiO2 in situ, e.g., hydrolyzing organic silicates: 2,404,357; 2,4~4,426; 3,971,872; 4,049,868;
4,120,992; 4~186J026.
3.Using siloxanes and/or silanes and the like:
2,610,167; 3,389,11~; 3,801,361; 3,953,115; 3,986,997;
4,001,128; 4,006,271; 4,~26,826; 4,027,073; 4,029,842;
4,049,868; 4,177,315; 4,186,026; 4,188,451; 4,1g7,335;
4,242,403.
4. Combination of any of the above items with:
4A. Polymers: 2,404,357; 2,404,426; 2,610,167;
3,652,379; 3,801,361; 3,971,872; 4,001,128; 4,026,826;
4,049,868; 4,098,840; 4,120,992; 4,197,335; 4,242,403 4B. Prepolymers (oligomers or monomers): 3,819,562;
4,029,842; 4,197,~35.
4Bl~ Photopolymerizable monomers: 3,968,305;
3,968,309; 4,188,451.
4C. Other chemicals, e.g., solvents, fillers cross-linking agents, to obtain transparent abrasion-resistant coatings (as single or composite systems): 3,986,997 (acidic alcohol H2O solution); 4,001,128 (A12O3); 4,006,271 (sol-vent); 4,027,073 (acidic alcohol water solution); 4,049~868;
4,186,026 and 4,120,992 (crosslinks with formaldehyde);
4,120,992.

5. Miscellaneous routes to such coatings: thus USP
3,645,779 provides a vacuum vapor deposited coating of B2O3-SiO2 on organic glass; USP 4,051,297 discloses a sputtered film of chromium silicide on smooth surfaces; in USP
4,242,403, there is disclosed a polyethylene terephthalate sheet covered with an intermediate layer of ~-(3,4-epoxycy-clohexyl)-ethyltrimethoxysilane and an upper layer of silica reinforced organopolysiloxane resin.
In spite of the progress achieved by the above mentioned techniques, it was still desirable to have at hand a quick setting composition for providing thin translucent or _ 5 _ ~Z~7~3~

transparent films very resistan-t to abrasion by virtue of a high level therein of hydrophobic silica. Thus, a first object of the invention was to provide a composition for depositing transparent protective films on substrates, such films being sufficiently mechanically resistant to withstand normal wear or accidental abuses without impairment of the surface proper-ties.
A second object of the invention was to provide a composition for coating protective transparent films on optical goods, the optical properties of which will not be significant-ly modified by this film and which will keep such proper-ties for a significant period of time under adverse conditions.
Another object of the invention is to provide a com-position for depositing thin well-adhering Eilms on subs-trate, such adhesion not being affected by weathering conditions even after a prolonged period of exposure.
Another object of the invention is to provide a film forming composition that will strongly adhe~e to organic glass substrate and which can be cured at room temperature, i.e., much below the softening temperatures of the substrate.
Another object of the invention is to provide a com-position for making transparent scratch-resistant films, such films being coated on substrates as one layer films, i.e., without the need oE an intermediate bonding layer.
Still another object of the invention is to provide a composition that can be stored for prolonged periods at room temperature without hardening and which can be cured on the substrates in a matter of seconds without the use of elevated temperatures.
Another object of the invention is to provide indus-trial optical articles made of relatively soft and easy mold-able organic glasses protected with a scratch-resistant film that will withstand prolonged use under severe weathering con-ditions without discoloration, crazing, or significant adhesion losses.
Other objects of the present invention will become apparent to people skilled in the art from the description of the invention that follows and from the disclosed preferred embodiments thereof.

. ~' .~.. ~ ,.~....

- 5a -'75~3z Summary of the Invention The present invention enables achievement of the aforementioned objects. Indeed, the invention provides a photo-polymerizable composition comprising one or more pho-to-polymerizable monomers, at least one photo-initiator and parti-cles of pyrogenic or precipitated SiO2 or ~.~..,

6 ~l2~93Z

A12O3 particles having, grafted on some of the oxygen atoms thereof, substituents of the formulae Al (I) or siAlA2A3 (II) wherein Al represents R or OR groups, R being a saturated or unsaturated substituted or unsubstituted hydrocarbon radical and A2 and A3 either represent oxygen atoms for connecting the Si atom in formula (II) to neighboring silicon or alumi-num atoms of the silica or alumina particle, or they have the same definition as for Al. Naturally when, by virtue of the aforesaid definition, the Si atom in ~II) bears more than one or OR groups, the R's can be the same or they can be dif-ferent. The detailed nature of the R's will be explained in a moment.
One distinctive feature of the composition of the inven-tion is that the total number of carbon atoms which are in-cluded in formulae (I) or (II), i.e., in Al, or in Al plus A2 and/or A3 in case more than one of the A's on the Si atom of (II) are R and/or OR groups, should always be four or more in order to obtain rheological properties of the coating compo-sitions containing high concentrations of coated particles that allow satisfactory practical application of the composi-tions to organic glass substrates. For example, as will be cited later, suitable coatings were not obtained with compo-sitions containing silica treated with silicon compounds hav-ing less than four carbon atoms, while other compositions in-volving four or more carbon atoms gave satisfactory results Table VIIa vs those in Tables VI and VII).
Another distinctive feature of the composition is that the refraction index "n" of the organic phase of the composi-tion should be as near as possible to that of the particles used. If the refraction index in the protective film of the organic matrix which is composed of the various organic con-stituents of the composition is not near that of the mineral particles, then said pxotective film is not perfectly clear but only translucent, this effect being particularly signifi-cant with high levels of mineral fillers, for instance of the order o 10 or 20 to 40% by weight. Thus, it was noticed that if the index "n" of the organic mixture is between 1.45 and 1.48, there is obtained with for instance a pyrogenic silica of index "n" = 1.475, even at high concentration levels, excellent clear coatings even for thicknesses thereof of the order of several microns. In the case of alumina (n =
1.70 - 1.76), such index values for the organic phase are nowadays impossible to achieve and, for this reason, the coatings containing high proportions of alumina are translu-cent and not transparent. In general, it is preferred within the scope of the invention to use partlcles with refractive ~7~3;2 index values between 1.40 and 1.50 and an organic phase the "n"
of which lies in the same range.
The inven-tion also comprises a process for producing a UV-cured photopolymerizable composition for applying onto substrates to provide thereon a transparent abrasion resistant coating. The process comprises: hydrolyzing a trialkoxysilane in an aqueous acidic solution; dispersing the hydrolyzed trial-koxysilane into intimate contact with finely divided pyrogenic or precipitated silica or alumina having a particle size of less than 0.1 microns to form a dispersion; chemisorbing the hydrolyzed trialXoxysilane on-to the finely divided pyrogenic or precipitated silica or alumina by effecting dehydration of the dispersion by heating to 80-110C to yeild organophillic parti-cles; and dispersing the organophillic particles into intimate contact wi-th one or more photopolymerizable monomers and one or more photoinitiators.
_ eferred Embodiments of the Invention It should be noted that the size of the particles is important with respect to the optical properties of the present protective coating. Thus, using relatively large particles, i.e., having a diameter of about the same order of magnitude as that of the thickness of the film, produces at the surface thereof microscopic prominences not visible with the eye but being detrimental to the optical properties thereof (undesir-able light reflection and diffraction effects) and may impart thereto a milky appearance. To be perfectly clear, the film should have a flawless, smooth, mirror-like surface. Conse-quently, there will preferably be used particles of a size about one order of magnitude less than the coating thick-ness. Thus, for instance, with coa-tings having a thickness of the order of one micron or less, there are advantageously used particle sizes of 0.007 to 0.05 ~ (pyrogenic SiO2: AEROSIL*
(Deguc,sa, Germany), CAB-O-SIL* (Cabot Corp. USA); precipitated silica: Hi-SIL* (PPG Industries, USA), etc.). For thicker coatings, larger size particles are possible, for instance 0.02 to 0.1 ~L (precipitated silica). The same is true for alumina, * Trade Mark ~,...~

3~
corresponding requiremen-ts for this mineral filler being however less, since films loaded with ~12O3 are usually not transparent per se. As suitable alumina for the present compo-sition, there can be mentioned a product called ALON (Alcan, Canada), the particles of which have a size approximately 0.006~. The silicas used or tried within the limits of this invention are the following:
Name and type Specific area Particle size of silica (m2/g) s~/m) _ 10 Pyrogenic silica CAB-O-SIL*EH-5 390 + 40 0.007 H-5 325 + 25 0.007 M-5 200 + 25 0.012 L-5 50 0.05 AEROSIL*-380 380 + 30 0.007 -300 300 ~ 30 0.007 -200 200 + 25 0.012 ~130 130 + 25 0.016 Precipitated silica ~li-SIL* 233 -- --215 150 0.02 SILENE* EF 90 0-03 Organophillic silica*
~EROSIL* R-972 120 + 30 0.016 *This silica was made organophillic by reacting with trimethylchlorosilane, the number of carbon atoms per grafted silicon atom is thus only three which does not correspond to the standards required for embodying the invention. Indeed, under testing, this hydrophobic silica did not provide composi-tions with properties suitable for achieving protective coatings according to the invention, as shown in Table IIIa.
Regarding the photopolymerizable monomers that fit the requirements of the present invention, one can use most monomers or mixtures of monomers generally known to photopoly-* Trade Mark ~,~

~Z~7~Z
merize and the photopolymerization of which is fas-t enough under usual conditions to be completed shortly (i.e., with exposure times from about a few seconds to a few minutes) and the "n" indexes of which fall within the aforementioned limits.
Examples of such monomers (olefinic and preferably acrylic) can be found in the following reference: ~V Curing by S. Peter PAPPAS, Science & Technology, Technology Marketing Corp., USA
(1978).
Among the monomers usable in the present invention, there can be mentioned also some olefinic prepolymers with a photopolymerizable function which possess, at the start, a significant intrinsic viscosity. This feature is valuable when it is wished to deposit with the present composition a relatively thick film but with sufficient flow stability during the period before the photopolymerization not to collapse and spread out or run away from the substrate before curing. Such prepolymers are known in practice most often under generic commercial names such as UVITHANE* (Thiokol Corp.), EB~RYL*
~Union Chimique Belge), UCAR-X* (Union Carbide), SETAROL*
(Kunstharsfabrick Syntehse MV, Holland). The structure of such prepolymers which fit well in the invention, provided they have the proper refraction indexes, are generally not disclosed publicly except for the fact that they are mainly polyol-acrylates (polyesterglycols) or polyurethane-glycols.
In practising the invention, one should use either monomers the "n" index of which is intrinsically close to that of the mineral filler used or, and this is the most frequent case, mixtures of photopolymerizable monomers and/or prepolymers the mixture index of which comes as near as possible to that of said mineral filler. By suitably varying the proportions of the two or more monomeric constituents the respective indexes of which are above and below the desired value, the latter can be approximated close enough for eventually obtaining, with the composition according to the invention, a practically transparent protective film with silica contents of up to 40%

* Trade Mark _, ~ ~, ...

- 9a 1;~ ~7~432 by weight or more. As non-limiting examples, Tables I and II
below give a list of such possible monomeric ingredients in the form of individual constituents or of mixtures (proportions of cons-tituents in the mixtures are given), the refraction indexes thereof as well as viscosities under standard conditions.

2~ .~J,: ...

3L%~7~13;~

TABLE I

~lonomer Refractive index Viscosity nD20 cP

.. . . ..
~5ethyl acrylate 1.4040 max. 10 Methyl methacrylate 1.4142 max. 10 Ethylene glycol diacrylate (EGDA) 1.4550 max. 10 1-6-Hexanediol diacrylate (HDDA) 1.4574 max. 10 1,4-Butanediol diacrylate (BUDA) 1.4567 max. 10 Neopentylglycol diacrylate (NPGDA) 1.4515 max. 10 Diethyleneglycol diacrylate (DEGDA) 1.4621 max. 10 Tripropyleneglycol diacrylate (TPGDA) 1.4495 max. 10 Tetraethyleneglycol diacrylate (TEGDA) 1.4616 max. 10 Bisphenol A diacrylate (EBECRYL-150) 1.5415 1000 + 20%
Trimethylolpropane triacrylate (TMPTA) 1.4738 70 ~ 20%
Pentaerythritol triacrylate (PETIA) 1.4871 650 ~ 20%
Pentaerythritol t~traacrylate (PETEA) 1.4855 800 + 20%
Dipentaerythritol pentaacrylate 1.4932 4400 + 20%
EBECRYL 210 (Acrylic prepolymer) 1.4980 25.10 + 20%

" 220 ( " " ) 1.5030 18.10 + 10%
" 230 ( " " ) 1.4646 6.10 + 30%
" 240 ( " " ) 1.4743 3.10 + 50%
" 270 ( " " ) 1.4755 15.10 + 13%
VVITHANE 782 ( " " ) 1.5024 paste " 783 ( " " ) 1.5264 'paste " 788 ~ " " ) 1.5085 paste ~CAR X 117 ( " " )1.4816 135.10 + 1%
" X 118 ( " " ) 1.4898 17.10 + 5%
" X 125 ( " " ) 1.4978 106.10 + 1 EBECRYL 600 (epoxy-acrylate)1.53 4-8.10 (60C) n 601 ( " " ) 1.55 2.10 + 10~
" 830 (acrylic polyester) 1.5005 45.10 + 10%
" 810 ( " " ) 1.4675 500 + 40 ~%q}~3~

TARLE I (Cont.) SETAROL 3625 (olefinic polyester) -- solid Ethylene glycol dimethacrylate (EDGMA) 1.4527 max. 10 .
(25C) Diethylene glycol dimethacrylate (DEGDMA) 1.4580 max. 10 (25C) Triethylene glycol dimethacrylate (TRIGDMA) 1.4595 max. 10 Tetraethylene glycol dimethacrylate (TEGDMA) 1.4609 max. 10 Bis~phenol-A dimethacrylate 1.5412 1600 i 20%
1.6-Hexanediol dimethacrylate (HDDMA) -- maxO 10 Trimethylolpropane trimethacrylate (TMPTMA3 1.4700 35 ~ 20%
(25C) Pentaerythritol tetramethacrylate solid M.P. 52-55C

12 ~ z~7~3Z

TABLE II

Monomers or mixtures IndexViscosity cP
(% by weight) "nD20"

Trimethylol-propane triacrylate 1.474075 ~ 15 ( 100 ~
Pentaerythritol triacrylate (50) Diethylene glycol diacrylate (50) 1.4742 70 + 15 UCAR X 118 (49,2) Diethylene-glycol diacrylate (50,8) 1.4748 290 i 10 UCAR X 118 (11,0) Diethylene-glycol diacrylate (89.0) 1.4670 max. 30 UCAR X 118 (18) Diethylene-glycol diacrylate (82) 1.4670 45 ~ 5 EBECRYL 600 (33,3) Diethylene-glycol diacrylate (66,6) 1,4915 75 + 5 EBERCRYL 600 (16,7) Diethylene-glycol diacrylate (83,3) 1.4765 max. 30 EBECRYL 830 (33,3) Diethylene-glycol diacrylate (66,6) 1.4742 65 i 5 SETAROL 3625 (16,7) Diethylene-glycol diacrylate (83,3) 1.4735 100 i 10 r~ethyl methacrylate (38,46) Pentaerythritol triacrylate (38,46) EBECRYL 600 (23,08) 1.4732max~ 30

7~32 There is further noted that, especially for some applications to be described hereinafter, the adhesion of the film toward glass substrates should preferably be weak or nil and, in such cases, the mixture of photopolymerizable monomers will include no hydrophillic monomer such as acrylic acid or glycol acrylates and methacrylates.
~ s photopolymerization initiators, there can be used in the present composition most substances generally suitable for this purpose and being compatible with the contemplated monomers and fillers. For example, the following photo-initi-ators suitable for the present invention can be; benzophenone, Michler's ketone, ethyl 4-dimethylamino-benzoate, benzil, 2-ethylanthraquinone, diethoxyacetophenone, (DEAP, Union Carbide) UVECRYL*P-36 (U.C.B.), IRGACURE* 651 (Ciba), SANDORAY*1000 (Sandoz), FI-4 (Eastman Kodak), Vicure*10 and 30 (Stauffer Chemicals), TRIGONAL* 14 and P-l (Noury), UV-Harter Nos. 1113 and 1116 (Merck), 2-chlorothioxanthone, etc. Using diethoxy-acetophenone is appreciated as, being a liquid, it dissolves particularly well in the present photo-polymerizable composi-tion. Another excellent photo-initiator is UV-HARTER No. 1116 (Merck). Generally, there can be used advantageously from 0.5 to 5% by weight of the ~hoto-initiator depending on the selected mixture, on the amount of filler and on the polymeri-zation rates which are desired. Using 1 to 2% by weight of diacetophenone or o-ther initiators is advantageous.
The nature of the radical R in -the formulae (I) and (II) can be much varied and its ranye is essentially dictated by the requirement of mutual compatibility with the organic phase components. In general, alkyl, alkenyl, cycloalkyl, and cycloalkenyl of about 1 to about 12 carbon atoms are suitable, provided of course that the total number of C's in (I) or (II) is 4 or more, i.e., for instance, if only one organic radical per grafting site i9 involved then it should be at least a four-carbon radical while if more than one organic radical is * Trade Mark ?~

~Z~. ~793;~:

involved, say three for instance, two of such radicals can be methyl and the third be ethyl or the like. The organic radi-cals can be unsubstituted or substituted with functions containing oxygen or heteroatoms (N, S, etc.). Oxygen functions can be hydroxy, keto, ester, ether functions, and the like. Unsubstituted radicals can include photopolymerizable functions that will participate to the overall photopolymeriza-tion of -the composition and provide thus photocopolymers in which some of the copolymerized groups will actually bond to the silica particles by vir-tue of the fact that the photopoly-merizable R was included in the compounds of formulae (I) or (II~ for grafting to said silica 7~3~
particles. Other definitions for the R radicals will appear from further details hereinafter. Preferably, for optimal properties of the scratch-resistant coatings of this inven-tion, the weight of the organic substituents used for graft-ing the silica particles relative to the weight of the SiO2 of said particles should be at least 20%~
The methods which can be advantageously used for render-ing organophilic the particles of the mineral fillers that are incorporated into the composition of the invention are selected among the known methods the references of which are listed in the introduction. Among these methods, the four methods (A to D? described hereinafter suit the invention to various extents~ In the following schemes the structure -Si-OH represents one of the peripheral silicon atoms (with a silanol function) of a hydrophilic silica particle which is to be made hydrophobic. It will remain understood that the free Si bonds represented in the schemes mean that this Si atom is bonded to the general polysilicic acid network of the particle as follows:

-o-s i-o-s i-oH

-Si-o-Si-oH

-Si-oH

It should be further remarked that the particles of sil-ica thus treated, even the smallest, each has a relatively large number of oxygen and silicon atoms. For instance, a particle of 0.02 ~ diameter has a weiyht of about 10 17 g assuming a value of 2.3 for the average density which corre-sponds to about 10 18/6 mole of SiO2. Since the number of molecules in a mole is 6.1023, said particle will have about 105 atoms of Si. The particles are therefore aggregates of relatively high molecular weight and the mi~tures therefrom in liquid media are indeed micellar dispersions or colloidal solutions and not true solutions of organo-silicon compounds as in the majority of prior art compositions mentioned here-inbefore. It is thus all the more remarkable that the compo-sition of the invention does provide, in the case of silica particles, transparent films even with very high levels of such mineral fillers.
In the case of alumina particles, the above discussion will apply by analogy since peripheral alumina molecules also bear reactive OH functions.
The grafting methods which were experimented with in the scope of the invention are listed below schematically~ They ~ 2~t~ 3 z are given for illustration and evldently they do not limit the invention as other methods could be contemplated or even preferred as far as they may be more economical or more efficient.
A. The conversion of some OH functions of the mineral particles (silanol functions in the case of silica particles) into reactive functions; e.g., by chlorination as in the schemes below:

~ iOH + soC12 . ~ iCl + HCl + SO2 2. -liOH + SiC14 ~ -$iO-SiC13 + HCl Then alkyla ion of the intermediate product thus ob-tained:

3. -SiCl + ROH ~ -SioR + HCL

4. -SiO-SiC13 + 3ROH ~ slo-si(oR)3 + 3HC1 B. A reaction with organosubstituted halogenosilanes:

Cl 5. -SioH ~ C12SiRR' ~ SiO-Si~R + HCl R' Then alkylation of the silicon atom with elimination of the chlorine atom:

Cl R"
6. -SiO-Si-R ~ R''OH D -Sio-si-R + HC1 R' R' In the above schemes, R' and R" (organic radicals) can be the same as R or be different from R. They can have ~taken individually) less than four carbon atoms since for having the grafting conditions within the scope of the inven-tion to be satisfied, it is sufficient to have only one of the organic substituents brought up during grafting at one site with at least four C atoms or, otherwise, the total of the carbon atoms of substituents R, R' and R'' put together in accordance with the definition of the aforesaid formula tII) should be at least four.
C. The condensation promoted by heat with silanols (R-Si(OH)3):

16 ~ 7~

o~
7. -SiOH + (HO)3SiR - D -SlO-Si-R + H20 OH

It should be noted with regard to reaction 7 that the remaining OH functions can still react after grafting by further dehydration with other silanol molecules tchain ex-tension by grafting) or with an OH on a neighbor Si atom in the polysilicic acid backbone of the particle under reaction (cross-link bridges). It should also be noted that the sila-nols used generally result from the hydrolysis of trialkoxy-silanes according to reaction 8:

8. RSi(OMe)3 ~ 3H20 ~ RSi(OH)3 + 3~1eOH

D. ~ reaction of "physisorption" with trialkoxysilanes.
This route is a "complexation" reaction providing a product in which the bonds to the silicon atom to be grafted are not covalent. It is carried out by boiling in an organic solvent like xylene:
I ~ I

9. -SioH ~ tMeo)3siR - ~ -sioH.(rleo)3siR

It should be remarked that the "complex" thus obtained (electrostatic type of bonds) is not very stable and that a dispersion made from particles grafted as such has character-istics different from those of dispersions made from parti-cles grafted by methods A to C above. In particular, disper-sions obtained from particles treated according to 9 have a rheologic behavior that is sometimes non-Newtonian in charac-ter and are more difficult to use in the present composition.
In the above described grafting methods, the group R
will preferably be a radical such as n-butyl, n-hexyl, n-heptyl, n-octyl, oleyl, 3-butenyl, decanyl, etc. Also func-tional groups are suitable that result from the use, when alkylating activated mineral particles, of glycol acrylates or methacrylates. Thus, in the substituent formulae R can be -(CH2~nOCO-CH=CH2 where n can be for instance an integer between l and 6. ~hen the group R has an olefinic moiety, that function can copolymerize with the other monomers of the composition when under irradiation, in which case the parti-cles are then immobilized by chemical bonds within the coat-ing organic matrix.
Grafting method C is preferred in the methods described hereinabove because it is relatively simple and because no halogenated intermediates are necessary, the handling and the disposal of which are undesirable regarding safety and 17 ~LZ~37~3Z

environmental problems. Further, compounds of the formula R-Si(OR')3 where R' is an easily hydrolyzable lower alkyl are ¢ommercially available, the range of the various usable R
groups being relatively large.
For instance, the R with reactive functions can be the following: ' CH2-C(CH3)-COO-(CH2)3 (methacryloylpropyl radical) CH2-cH-cH2-o-(cH2)3 (glycidoxypropyl radical) O~ .
O -(CH2)2 ~3,4-epo~ycyclohexyl-ethyl radical) In the case where R contains a reactive function, such as the oxirane function as above, it is evident that the lat-ter can contribute by its own polymerization reaction to the overall curing of the protective film of the invention.
On the practical aspect, for achieving the composition of the invention, the mineral particles made organophilic as mentioned above are dispersed into the photopolymerizable monomer or the mixture of monomers and the photo-initiator.
This dispersion is carried out by usual means (blender, ul-trasonics, mixer, ball-mill r etc.) until the composition is suitably homogeneous. Then, after the mixture is allowed to stand for escape of the alr bubbles (or gas bubbles if the operation is done under an inert gas), it is applied to a substrate to be coated so as to form a thin film thereon.
Generally, standard tools and methods can be used such as brush, rod, doctor blade, spraying, dipping, etc~ However, for the protection of the all important optical goods, lens-es, mirrors, etc., the following procedure is preferably fol-lowed- on the surface to be protected, there is put a few drops of the photopolymerizable composition, after which there is applied thereon, in order to wel'l spread it and make it even, a negative counter-plate or mold made of optical glass, the uncured protective layer being squeezed (and mold-ed) between it and the substrate and consecutive spreading of the mixture taking place leading to the formation of a regu-lar film over said substrate. The surface of the mold has a finish which is such as to confer well defined optical prop-erties to the outside surface of the coating such properties being that, in facsimile, of said mold (replica molding).
After irradiation of the piece and photosetting of the coat-ing, the mold is removed which step is effected with no effort as the adhesion between'the mold and the film is weak 7~3;:
or practically negligible. This unexpected result is due -to the hydrophobic properties oE the coating and of the particles therein; indeed, the monomers used are not hydrophillic (they contain no significant amount of hydrocompatible carboxylic or hydroxy groups such as those of acrylic acid or the hydroxyac-rylates) and also the mineral particles have no more affinity for the glass after being grafted with organic radicals as described above. In this connection, it should be said that if, instead oE the composition of the invention, another compo-sition were used having the same organic component but contain-ing in lieu of 20 - 40% hydrophobic silica, only 2 - 3~ of ordinary (non grafted) pyrogenic or precipitated silica, there is obtained a film that strongly adheres to a glass subs-trate so that it is difficult, if not impossible, to remove it there-from.
With regard to photocuring of the film on the sub-strate to be protected, usual means are employed, i.e., subjecting the film on the substrate to a suitable irradiation operation, such irradiation taking place either directly on the film or through a transparent layer applied over the coating (plastic membrane for avoiding dust falling on the fresh film or negative glass counter-form as described above). Also, .
the substrate can be turned upside down relative to the irradiation source, the exposure being done -through the transparent body of the substrate itself if desired. As an irradiation source, one preferably uses a commercial type UV
light giving fluxes of about 10 - 100 W/cm and suitable for photo-polymerizing a film at a distance of 5 - 30 cm for 2 to 60 seconds at room temperature. Other means and techniques for photopolymerization known to those skilled in the art may be used in photocuring the coating.
The photopolymerized film thus obtained is in the foxm of a thin smooth layer perfectly transparent in the case where hydrophobic silica is present and translucent if hydrophobic alumina is present. When clear, this thin layer does not significantly modify the optical properties of the substrate and it offers an exceptional resistance to abrasion, weathering, and accidental abuses as seen hereinafter in the special part of this disclosure. It can thus be used advan-,~-t - 18a - ~2~7~32 tageously for coating optical apparatus lenses made of organic glasses such as PVC, polycarbonates and polymethacrylates as well as many other transparent articles such as clear panels, headlights, and other lighting appliances.
In summary, the resulting advantages from embodying the present invention are as listed below:

19 ~7~3~

a) Thin layers (from about O.S to 20 or 50 ~m), smooth, transparent (with SiO2) and very resistant to wear by abra-sion (the composition of the invention lends itself however to the preparation of thicker layers in special cases).
b) Solventless compositions requiring no evaporation step when curing the coating. The absence of solvents also removes the risks that the substrate be attacked (organic glass) by such solvents.
c) Very quick hardening of the film at room temperature which is technically and economically advantageous, the pro-duction rate being high and the risks of damaging the coating before curing being strongly reduced.
d) Low cost of the raw materials by virtue of the fact that the mineral fillers and the monomers are easily availa-ble and relatively cheap and that the fillers load percent is quite high.
e) Excellent physical properties such as abrasion re-sistance and very low friction index. This last property is mostly unexpected in connection with such a high proportion of mineral filler and constitutes a highly surprising element of the present invention.
f) Simple application techniques and well experimented and economical implementation methods, non-standard equipment being unnecessary.
The coatings of the invention, as far as described up to now, contain no stabilizers against weathering and against degradation by daylight exposure. If such stabilizers (a de-scription of which will be found hereinafter in section II) are incorporated in the composition of the invention at con-centration of about 0.5 to 5% by weight of composition, the resistance against oxidation, discoloration, and other dam-ages caused by external exposure conditions is greatly in-creased. This will be described in section II of this disclosure.
There will be now described in detail in the experimen-tal part that follows how the invention can be put to appli-cation practically, Reduction to practice of the invention 1. Preparation of hydrophobic silica and alumina A. Chlorination of silica then alkylation of the chlo-rinated product:

In a 1 liter flask were placed 500 ml of anhydrous ben-zene, 240 ml of thionyl chloride and 30 g of pyrogenic silica ~2~793;~
~AEROSIL 380). The mixture was refluxed for 5 hrs after which the solvent and excess of SOC12 were distilled off.
The residue was further left for 2 hrs at 50C under 10 Torr (13.3 mbar) so as to complete the evaporation and 31~3 g of chlorinated silica were collected. Ten g of this were then alkylated by boiling 2 hrs with 60 g of n-butanol (actually, temperatures of 60 - 90C were already sufficient for 2 hrs reaction periods). The HCl formed was removed under reduced pressure (20 - 28 mbar) and dry ether was added. The suspen-sion w~s centrifugated and, after separating the liquid phase, the solid was washed twice with ether. There were thus obtained 11.1 g of silica the particles of which bore, grafted on the silicon atoms, n-butoxy radicals.
The same procedure was followed but replacing in the above preparation the n-butanol by equivalents of the follow-ing alcohols: n-hexanol, n-heptanol, n-octanol, oleyl alco-hol, and 1,2-propanediol monoacrylate. There were thus obtained silica products with corresponding grafted substituents.

A'. Treating with tetrachlorosilane then alkylation of the obtained chlorinated product:
This reaction corresponds to the following scheme:

-lioH + SiC14 ~ -liO-SiC13 ~ -SiO-Si(OR)3 In a 1 liter flask there was boiled for 5 hrs a mixture of 500 ml of anhydrous benzene, 240 ml o~ SiC14 and 30 g of AEROSIL 380 (Degussa). Then, the solvent and the excess SiC14 were distilled off and evaporation was completed by heating 2 hrs at 50C under 14 mbar for fully removing vola-tile materials. Then 70 g of n decanol were added to 10 g of the silica thus modified and, after 2 - 3 hrs at 70 - 90C, the pressure was dropped to 20 - 30 mbar to completely expel the HCl formed. After cooling, ether was added as described beore (see under part A~ and the product was centrifugated and washed twice with ether. After drying in air, 10.7 g of grafted silica were collected.
With n-hexyl and oleyl alcohols, corresponding results were obtained.

B. Reaction with chlorosilanes: ' Twenty-five g of AEROSIL 380 were heated to reflux for 5 hrs with 500 ml of anhydrous chloroform and 25 ml of tri-chlorovinylsilane or dichloromethylvinylsilane. Then, the solvents and excess volatile reagents were evaporated under ~Z~793Z
vacuum. Alkylation of the residue was achieved by heating for 2 hrs with 200 ml of ethanol. Then the reaction mixture was centrifugated and the residue was purified by extracting with ether (5 hrs). This method provided a grafted silica of excellent whiteness. Analogous results were obtained by re-placing trichlorovinylsilane by trichloromethylsilane.

C. Condensation with silanols:

Forty g of y-methacryloxypropyl-trimethoxysilane (prod-uct A-174, Union Carbide) were stirred at room temperature in one liter of water acidified with dilute acetic acid to pH
3.5. An emulsion which first appeared in the flask dissolved progressively during hydrolysis. After 1 - 2 hrs stirring, there were added! when the solution became clear, 40 g of silica (AEROSIL 380) and the mixture was stirred for an addi-tional 15 hrs at room temperature. The suspension which had become thicker with time was centrifugated and the solid was dried overnight at ~0 - 100C under vacuum. Then the modi-fied silica was processed in a Waring blender and heated an-other 2 hrs at 110C under 14 - 20 mbar in order to complete dehydration and condensation of the remaining free silanol groups of the grafts with neighbour silanol groups of the particle network. The organic content of the grafted silica was determined thermogravimetrically to be 33 parts by weight of organic matter for 100 ppw of silica, i.e., 33%.
This grafting process is the preferred method in the present invention~ It was used successfully to provide or-ganophilic silica from the following grades: AEROSILS 130, 200, 300, and 380, and CAB-O-SIL rl-5 and H-5. By this method, 40 g of starting silica furnished 54 - 57 g of silica grafted with oxy-silico-y-methacryloxypropyl groups. The organic content of said grafted silica lots varied between about 25~ and 33%.
In the above preparation, the following trialkoxysilanes were also used: y-methacryloxypropyl-ethoxy-dimethoxysilane tNo. A-175, Union Carbide); y-glycidoxypropyl-trimethoxy-silane ~No. A-lB7, Union Carbide); (3,4-epoxy-cyclohexyl)-ethyl-trimethoxysilane (No~ A-186, Union Carbide); isobutyl-trimethoxysilane (DYNASILANE, IBIMO) and octyl-triethoxy-silane (DYNASILANE, OCTEO).

D. "Physisorption" with trialkoxysilanes:

In a 1 liter flask, there was heated 5 hrs to the boil a mixture of pyrogenic silica (AEROSIL-380) (25 g), A-174 (Union Carbide) (25 ml) and anhydrous xylene (500 ml). The ~Z~7~3~, mixture was centrifugated and the solid residue was taken into fresh xylene and again centrifugated. After repeating once more such purification step, the resulting powder was collected and dried in air.
The above procedure was also carried out with the fol-lowing trialkoxysilane products (defined above): A-175, A-186, and A-187, as well as with ~-aminopropyltriethoxy-silane (A-llO0) all from Union Carbide. Results were similar except for the color of the treated silica--brown with A-175 and pale yellow with A-llO0. The other modified silicas were colorless.
A sample of silica modified with A-174 (methycryloxy-propyl group) (10 g) was mixed with 3 9 of methyl methacry-late, 60 g of xylene and 0.05 g of lauroyl peroxide after which ~he mixture was refluxed for 4 hrs. Thereafter, the doubly modified silica was purified by successively centrifu-gating with xylene three times.

2._ Preparation of compositions according to the invention A. By means of silica grafted by chlorination and alky-lation: ' Several types of organophilic silica were used, obtained according to the procedure described hereinbefore under para-graph l.A. which were dispersed as indicated earlier in this specification, to various solid concentrations into tri-methylol-propane triacrylate (TMPTA) containing 2% of di-ethoxyacetophenone (D~AP). Compositions having different viscosities were obtained the rheological properties of which were either Newtonian or thixotropic depending on the cases.
The data about such compositions are gathered in Table III
below. In this table, the following data are provided: the type of alkylating alcohol used, the concentration of the silica in parts by weight relative to the TMPTA (the total of the parts being 100), the refraction index of the organic mixture of the compositions, the viscosities, and the rheo-logical properties.

~793~
TABLE III

Silica (A-380) Rheo-Composi- (parts Viscosity logical tion No. Alcohol by weight) "nD20" (cP) properties . .

1 Butanol 20 1.4705 670-710 Thixotropic 2 Heptanol 20 1.4691 340-360 Newtonian 3 Glycidyl acrylate 20 -- -- Thixotropic 4 Octanol 20 -- -- Thixotropic Decanol 20 ~ Thixotropic 6 Hexanol 16 1.4708 240-250 Newtonian 7 " 20 1.4701 320-325 Newtonian 8 " 25 -- 810-950 Fluid 9 " 27 -- 950-1450 Fluid Table IV gives information similar to that of Table III
regarding silica activated by SiCl~ then alkylated by method A' or by means of silica grafted with tetrachlorosilane then alkylation of the chlorinated intermediate.

TABLE IV

Silica (A-380) Rheo-Composi- (parts Viscosity logical tion No. Alcohol by weight) "nD20" (cP) Properties _ ................. . . .

1 Decanol 16 1.4715 830-930 Fluid 2 . Oleyl alcohol 13 -- -- Thixotropic B. By means of silica grafted with chlorosilanes then alkylation of the chlorinated intermediate:

The procedure used was as disclosed in paragraph 2.A.
and compositions were prepared by mixing various lots of sil-ica (made hydrophobic by method l.B) in TMPTA with 2% DEAP.
Table V summarizes the tested compositions and indicates, in turn, the type of chlorosilane used for modifying the silica, the alkylating alcohol, the levels of silica fillers in the compositions, the refraction index, viscosities, and rheolog-ical properties of the compositions~

24 ~LZC~793 ~

TABLE V

Rheo-SilicaVi5- logical Composi- Chloro- (partscosity proper-tion No. silanes Alcohol by weight) "nD20" (cP) ties . . . . . . _ _ 1 Trichloro~ ethanol A 380 (40) 1.4525 260-270 Fluid vinyl silane 2 Trichloro-ethanol A 380 ~33) 1.4634 1150-1490 Fluid vinyl silane water 3 Trichloro-ethanol A 200 1.4730 1150-1600 Fluid vinyl ~ (18.4) silane water 4 Dichloro-ethanol A 380 (20) 1.4636 240 280 Fluid methyl vinyl silane .

C. Silica treated by condensing with silanols:

Several types of silica were used and made organophilic by the method described above under paragraph l.C with hydrolyzed y-methacryloxypropyl-trimethoxysilane (A~174).
Table VI summarizes the various parameters relative to such compositions and indicates the type of monomer or monomer mixture used, the amount of silica filler in parts by weight (the total of said parts and the parts of monomers being 100 parts), the refraction index "n", and the rheological proper-ties of the compositions which also contained 2% by weight of diethoxyacetophenone photo-initiator. The first three compo-sitions of this table distinguish themselves from each other by the hydrophilic modification conditions: Composition 1 contains a silica treated with a 1% aqueous solution of A-174, Composition 2 contains a silica treated with a 4% aque-ous solution of A-174 after 18 hrs of hydrolysis, and Compo-sition 3 a similarly treated silica except that hydrolysis was for only 20 minutes.

TABLE VI

Silica type Composi- Monomer or (parts by Viscosity Rheolo~ical tion No. mixture weight)"nD20" (cP) properties 1 TMPTA A-380 (20)1.4735 -- Thixotropic 2 " " (20)1.4740 530-535 Newtonian 3 ~ n ( 20)1.4743 990-1040 Newtonian 4 " A-300 (20)1.4738 445-455 Newtonian " A-200 (20)1.4739 570-590 Newtonian 6 " H-5 (20)1.4738 425-440 Newtonian 7 " M-5 (20)1.4736 520-570 Newtonian 8 . " H-5 (28.5)1.4758 1020-1050 Newtonian (49.2) H-5 (13.6)1.4748 -- Pseudo-DEGDA (50.8) plastic UCAR ~-118 (18) DEGDA (82) H-~ (20)1.4698 230-228 Newtonian .' (11) 1 DEGDA (89) H-5 (20)1.4682 150-155 Ne~tonian (33.3) DEGDA (66.7) H-5 (20) 1.4745 430-450 Newtonian 13 E~ECRYL 600 (16.7) DEGDA (83.3) H-5 (20) 1.4762 210-215 Newtonian 14 Methyl ~-5 (20)1.4755 140 Newtonian methacrylate (38.5) PETEA (38.5) (23) Methyl H-5 (43.7) -- -- Very fluid methacrylate and Newtonian 16 Butyl H-5 ~43.7) -- -- Very fluid acrylate and Newtonian D. Silica grafted by "physisorption":

Preparation of the corresponding composition was carried out exactly as for the previous compositions of Tables III to VI. The various parameters pertaining to these compositions 26 ~2~7932 are grouped in Table VXI. These parameters comprise, in turn, the types of organosilanes used for the "physisorp-tion", the amount of sllica (A-380) used in the compositions (parts by weight in relation to the weight of the organic matter, the total of the ingredients being 100 parts), the types of monomers or mixtures o~ monomers used, the refrac-tion index "n", the viscosity of the mixture and its rheolog-ical behavior. All the compositions also contained 2% by weight of diethoxyacetophenone as the photo-initiator.
The first ~our compositions of Table VII differ from each other by the following points: In the first (No. 1), silica has been made organophilic simply by the indicated treatment (all the other samples starting from the fifth were also trea~ed similarly). Composition No. 2 contains silica which, after physisorption, was ~ubjected to a second acti-vating modification by thermal copolymerization with methyl methacrylate as indicated in the last paragraph of section l.D hereinabove. Compositions 3 and 4 contained silica products that were similarly doubly modified with the A-174 monomer and butyl acrylate, respectively.
TABLE VII
., Silica Composi- Silane (parts Monomers Viscosity Rheological tion No. used by weight) used (%) "nD20" (cP) properties .

1 A-174 20 TMPTA1.4730 650-800 Fluid 2 " " " 1.47741100-1200 Fluid 3 " " " 1.47422000-2400 Fluid 4 " " " 1.47502250-2750 Fluid " " HDDA 1.4595 205-207 Newtonian 6 " " DEGDA1.4S84 205-210 Newtonian 7 " " DEGDA1~4732 510-570 Fluid (50) PETRIA
(50) 8 " 24.5 DEGDA1.4732 800-900 Fluid (50) PETRIA
(50) 9 A-174 + 17 T~lPTA -- -- Thixotropic 1~ SOC12 A-175 20 " 1.47341300-1700 --11 A-1120 20 " 1.4775 Thixotropic ~Zg:~793Z
Compositions represented in Tables III to VII have, de-pending on the cases, a Newtonian (fluid) or thixotropic be-havior. For embodying the invention, composition with New-tonian properties are preferred since they more easily form thin films with well-controlled characteristics. Generally, the smaller the silica par~icles ~or alumina particles) and the greater the organophilic properties thereof (in propor-tion to the de~ree of grafting and to the length and the num-ber of carbon atoms of the grafted radicals), the more the composition will behave as a Newtonian liquid and the easier it can be handled. Moreover, the overall viscosity of the compositions increases with increasing size of the particles and increasing solid concentration in the mixture.
With respect to the clarity of the compositions contain-ing organophilic silica, it is advantageous to use mixtures of monomers with an index of refraction as near as possible to that of said silica. It should be pointed out in this connection that the organophilic modifying treatments used in this invention do not necessarily always lead to silica prod-ucts with the same refraction index. However, this index remains most of the time reasonably close to the 1.4740 -1.4750 range. Thus, it may be useful to adapt, from case to case, the refraction of the organic mixture to that of `the selected silica. In this regard, it is to be remembered that if the difference between the indices (that of the organic phase and that of the silica) becomes too great, the composi-tion becomes milky and the coatings obtained therefrom are not perfectly clear. For example, if one uses 20 parts by weight of organophilic silica (n = 1.4746) with 80 parts by weight of TMPTA (n = 1.4732) or a 1:1 mixture of PETIA and DEGDA (n = 1.4746), one obtains a clear mixture. Contrari-wise, in the same conditions but with either pure HDDA (n =
1.4574) or DEGDA (1.4621), translucent mixture will be ob-tained.
The results in Table VIIa obtained with the use of a silica, A-972, treated with a silicone coating compound con-taining less than four carbon akoms show that this silica treatment does not give satisfactory coating application be-havior, even with low silica loading.

~Z~793~
TABLE VIIa Composition Concentration No. of A-972 Polymer Viscosity and Observations 12 11 TMPTA 89 Strongly thixotropic mass 121 8 TMPTA 92 550-840, liquid, developed thixotropy after storage for a day 7.4 DEGDA 92.6 195-205, nD20 1.4615 slow-ly developed thixotropic properties 3. Compositions with alumina .
If, in the various methods for treating silica described in the prior art and in the methods for preparing the coating compositions of the present invention with said organophilic particles, the silica particles are replaced by alumina of equivalent mesh sizel similar results are experienced except for the transparency parameter as already explained.

4~ Preparation of abrasion resisting coatings For the coating experiments, organic glass plates (2 x

10 cm) of polymethylmethacrylate (PMMa), polycarbonate (PC), polyvinyl chloride (PVC), and CR-39~ (poly(diethyleneglycol)-bis-allylcarbonate) were used as substrates. The plates were first washed with isopropanol, then, thin layers (thickness 1 to 50 ~m) of the compositions listed in Tables III to VII
were applied on the plates by the means already mentioned previously. Then, the samples were irradiated with a 80 w/cm W source for periods o~ 5 to 30 sec or more. Best optical properties were obtained by pressing on the freshly coated plates a perfectly smooth glass plate, i.e., by performing a "replica molding" of the coating by means of a glass mold.
In this case, the exposure is done through the glass, the latter being eventually easily detached from the hardened film after cooling to room temperature.

5. Measurements of the optical properties The optical properties of the coatings (obtained by "replica molding" as above) from the various compositions listed in Tables III to VII were measured. Coatings with about 15 25 ~m thickness were selected. The measured 29 ~ 75~3~

parameters were the percent transmission and reflectance (relative to a corresponding non-coated plate) between 800 and 400 nm measured with a PYE-UNICAM spectrophotometer. Re-sults are provided in the following tables: Table VIII for the PC substrates (MAKROLON~); Table IX for the P~lMa sub-strates (PLEXIGLAS~) and Table X for the PVC substrates (TAKIRON~). In the tablesr there are provided, successively, the following data: a control sample uncoated, then samples identified by the number given to the corresponding composi--tion from Tables III to VII, the percent of transmission at 800 ~ 590 ~ and 400 nm for said coatings (plus the substrate), respectively, and the gain or the loss relative to said con-trol sample.

- TABLE VIII

Composition Transmission (%) at nm Gain or loss (%) at No. 800 590 400 590 nm . .
Control (MAKROLON) 89~7 86.5 74~4 0 III 2 92 ~ 2 86. 8 76 ~ 8+ 0 ~ 35 III 5 91.5 88~2 76~8 + la96 III 6 94 ~ 2 87 ~ 5 73 ~ 4 ~ 1.16 VI 2 89~7 86~7 74~4 + 0~02 VI 3 89 ~ 5 86 ~ 5 73 0 VII 1 93~4 86~4 76~8 ~ 0~01 VII 7 88~2 84~2 70~0 ~ 2~54 Table IX further lists a samplel X, coated with a trans-lucent film containing alumina. This film was prepared with a composition containing TMPTA and 16 parts by weight of A12O3 (total 100 p.b.w.), the latter having been made organo-philic by the process disclosed under section A.l + hexanol (analogous to Composition III-6); viscosity: 255 ~ 277 cP~
A similar behavior was observed for a corresponding sample containing silica activated by the process described under section C.

~2~7~3Z
TABLE IX

Composition Transmission (%) at nmLoss (%) at nm No. 400 590 800 590 Control (PLEXIGLAS) 93.2 91.7 88.2 o III 2 93.5 91.0 85.5 0.76 III 5 93.2 90.4 84.5 1.4 III 6 93.2 91.0 87.0 0.76 VI 2 92.0 89.7 83.5 2.18 VI 3 90.0 87.0 79.0 5.12 VII l 91.8 89.5 84.0 2.4 VII 5 91.0 88.0 83.5 4.03 VII 6 88.5 84.5 76~0 7.85 VII 7 92.8 89.5 84.0 2.40 X (A12O3) 75.0 66.5 49.5 27.5 TABLE X

Composition Transmission (%) No. at 590 nm Gain or loss `(%) Control PVC TAKIRON~ 83.2 - 83.3 0 VI 2 83.8 - 83~9 ~ 0.6 VI 4 82.5 - 82.6 - 0.6 VI 5 84.1 - 84.2 ~ 0.7 VI 6 83.6 - 83.7 + 0.4 VI 7 83.3 - 83.4 + 0.1 It is interesting to note from the results of Tables VIII and IX that the clarity of the coatings containing sil-ica rendered organophilic by "chemisorption" r i.e., by the techniques described in sections A to C is better than the clarity of the coating containing silica modified by "Physi-sorption".

6 Measurements of abrasion resistance _ For the abrasion resistance measurements, the same plates were used which are described in Section 4 with a pro-tective coating according to the invention. The abrading de-vice (Creusot-Loire Instrumentation, Adamel-Lhomargy, France) 31 12~793~

comprised a rubbing shoe (1 x 1 cm; 2 kg) moving alternative-ly forward and backward on the sample by means of a crank-drive and the rubbing surface of which was provided with a patch of steel wool (Tampon GEX). The operating parameters of this testing were: displacement amplitude: 4 cm; fre-quency: 1.4 HZ; number of cycles: up to 500. Table XI
provides the results obtained for samples of polycarbonate (MAKROLON~), PMMa (~LEXIGLAS~), CR-39~ (PPG), Polyurethane (SECURIFLEX~ of St. Gobain) and FLOAT glass as well as for the coatings of the invention applied on some of the above substrates (thicknesses 5 - 20 ~m). The abrasion effect is expressed as the loss of optical transmission (loss of gloss) after a number of abrading cycles.

32 ~z~793;:

TABLE XI
~ ~ = ....

Loss of Coated sample Coating compo- Cycles transmission or substrate sition No. ~number of) at 590 nm (%) MAKROhON~ (1 mm) - O O.O
" - 100 34.1 " III 2, 5 and 6 " 0.67 " VI 2 and 3 " 0.67 " VII 1 and 7 " 0.67 " X (A1203) " -PLEXIGLAS~ (1 mm) - O O.O
" - 50 29.0 " - 100 32.9 " III 2 " 0.52 " III 5 " 0.67 " VI 2 " 0.52 " VI 9 " 8.0 " VI 10 " 1.0 " VI 11 " 0.6 VI 12 " 0-5 " VI 13 " 1.7 " X (A12O3 " 0.0 " VII 1, 5 and 6 " 0.52 " VII 7 " 0.57 PLEXIGLAS0 (1 mm) III 2 500 0.80 " III 5 500 0.80 " VI 2 500 0.80 SECURIFLEX~ - 0 0.0 " - 100 5.4 " - 200 9.1 CR-39~ PPG - 0 0.0 " - 50 7.8 " - 100 8.9 " - 200 10.8 Glass ~1 mm) - 100 0.O

33 ~2~793~
The results of Table XI show that, with the exception of composition VI-9, all coatings according to the invention provide an excellent protection against scratches. The pro-tection offered by the coating containing alumina (sample X
A12O3) is even better since no optical transmission loss was evidenced after 100 rubbing cycles. However, account should be taken that silica hardness is only 820 Knoop whereas that of alumina is 2,100 Knoop.

7. Resistance to organic solvents For testing the resistance of the present coatings to solvent attack, the steel wool used in the device of the pre-vious test was replaced with a porous plug soaked in the 501-vent to be tried. After 100 rubbing cycles, the possible transmission loss of the sample was compared to that of the same coating sample not subjected to an attack by the sol-vent. The following solvents were tried and none had any effect on a PLEXIGLAS~ sample protected by films from the compositions III-2 and 5, VI-2 and VII-l, 5, 6, and 7. In contrast, a noncoated PLEXIGLAS~ plate suffered a 47.6~ loss under the same conditions when subjected to chloroform. Sol-vents tried heptane/toluene (70/30); toluene, aceto'ne, chloroform; tetrachloroethylene/trichloroethylene (60~40);
heptane/trichlorethylene/toluene (15/50/35).

8. Resistance to surfactants solutions .

Samples to be tested were immersed for various periods in 1~ aqueous TEEPOL~ (an alkyl-aryl-sulfonate) at 20 - 30C, then they were left to dry in air after which they were cleaned with a moist cloth. It was noted that the same sam-ples mentioned above under section 7 had only a 0.8~ optical transmission loss after 864 hrs of immersion and that the films had no tendency to loosen from the substrate.

9. Resistance to heat For this 'test, the sample was subjected to conditions reproducing normal operating conditions for vehicle head-lights cover glasses: 1 day in a moist atmosphere at 18 -28C and 16 hrs in a dry atmosphere at 115C. In the present case a polycarbonate projector glass (type E-2, SEV Marchal) was protected with a film from composition VII-l. After 16 hrs in the oven at 115C the coating was not cracked, nor flaked off and had no visible deformation.

~LZ~;P79;~2 10. Resistance to shock -A steel ball (13.6 g, 0 15 mm) was dropped from a height of 9 m on a projector glass protected as described in the previous section. The velocity at the hitting point was 13.28 m/sec. After the shock, the coating did not crack or peel off (composition VII-l).

11. Resistance to weathering A photopolymerizable anti-abrasive composition was pre-pared by mixing together 333 parts of EBECRYL~ 220 (see Table I) and 666 parts of diethylene glycol diacrylate (DEGDA). To this mixture were added, and all ingredients were milled to-gether overnight in a glass jar with glass beads, various amounts of grafted silica (prepared according to the method described under section l.C), various amounts of a photo-initiator (UV-Harter-1116 from Merck) and various quantities of W stabilizersO Such stabilizers were selected rom com-mercially available stabilizers as listed below: th~
TINUVIN~ stabilizers made by the CIBA-GEIGY Company and in-cluding the TINUVIN~-900, -P, ~328. The WIN~L~ stabilizers sold by the BASF-Wyandotte Company; the UVINUL~ stabiliz'ers are mostly benzophenone derivatives and are detailed in a data sheet from the BASF-Wyandotte Corp., Parsippany, N.J.
07054 called "UVINUL~ UV Absorbers for Cosmetics, Plastics, Coatings and Textiles". The absorbers tested included the following types of WINUL~: N-539; D-49. Phenyl salicylate was also included in the W absorbers tested. The respective quantities of grafted silica, photo-initiator and the various stabilizers are given in % by weight with respect to the above composition.
After filtering the composition on a nickel mesh (25 ~), films of such compositions (10 - 50 ~ thick) were applied on standard polycarbonate plates (7.5 x 15 cm) and irradiated with a 60 W~cm W light source placed 30 cm from the film.
During irradiation cure, a 4 mm thick glass plate was inter-posed between the source and the sample plates to evenly dis-tribute the light energy. Irradiation times were 30 sec (Tl) and 60 sec (T2).
The coated samples were then subjected to an accelerated weathering test in a "Q-UV Accelerated Weathering Tester"
(the Q-Panel Company, Cleveland, Ohio). This test consists in subjecting the samples to very strong W irradiation from fluorescent W lamps under alternating conditions of dry and humid heat (1 cycle = 8 hrs under W at 70C dry followed by 4 hrs W at 50C under condensating humidity conditions 100 ~lZ~793z relative humid'ty). After intervals, the samples were examined for the advent or formation of crazing (cracks), dewetting (separation of the film from substrate), chalking and other general degradation signs. The "cross-hatch"
testing was applied to determine the residual adhesion of the film over the substrate. This test consists in cross-cutting the film at right angles with a sharp knife so as to provide criss-cross stripes about 1 mm wide thus defining a plurality of little film squares like a checkerboard; then a piece of scotch adhesive tape is pressed over the test area and there-after lifted whereby some of the little squares will be removed if adhesion of the film on the substrate is low. The conditions for passing the above weathering test were that no trace of any deficiency (in connection with th.e aforesaid criteria) is found; for instance, in the cross-hatch test, the lifting of even one of the little squares is failing.
In the weathering test none of the samples had failed at the end o~ the 168-hour exposure period. The first column of the weathering test data (Table XII) shows an X for each coating that was rated failed at the end of the 336-hour per-iod, the second column similarly shows which coatings were rated failed at the end of the 504-hour period, and the third column likewise shows those rated failed at the end of 'the 672-hour period. Only one coating was considered to have passed the 672-hour test--No. 658gg'T2. The other columns of the table pertain to other aforedescribed composition parameters.

TABLE XII

Sample SiO2 Photo-initiator Stabilizer Weathering test (No) (%) (%) type and (%) 1 2 3 Cure(T) .. . . _ _ _ _ _ , TINUVIN~9OQ
658 c Tl 20 1 0.5 X
658 c T2 " " " X
658 d T2 " " 1 X
658 Tl " 2 0.5 X
658 T2 " " " X
658 a Tl " " 1 X
658 a T2 " " " X
658 b Tl " 4 0.5 X
658 b T2 " 4 " X
658 kkTl 27.7 2 " X
658 kkT2 " " " X

~2~7~
_ BLE XII (Cont) l 2 3 UVINUL~N-539 658 bb'T2 27.i l l X
658cc''T2 " " 2 X
658 aaTl " 2 0.5 X
658 aaT2 " " " X
658 bbTl " " 1 X
658 llTl ~ 1- 0.5 X
658 llT2 " " " X
658 ll'T2 " " 2 X
658 bbT220 2UVINUL~-539 X

658 ccT2 " " 2 X
658 cc'T2 " " 3 X
658 ddTl " 4 1 X
658 ddT2 " " l X

658 V T2 lS " " X
UVINUL~D-49 658 iiT2 " 1 l X
658 eeTl " 2 0.5 X
658 eeT2 " " " X
658 ffTl " " l X
658 ffT2 " " " X
658 ggT2 " " Z X
658 gg'T2 " " 3 *
658 hhTl " " l X
658 hhT2 " " " X
658 mmTl27.7 " 0.5 X
658 mmT2 " " " X
658 mm'T2 " " 2 X
TINUVIN~-P
658 p T220 " 2 X
TINUVIN~-328 658 g T2 " " 2 X
Phenyl saly-658 r T2 " " cylate 2 X

658 xlT2 " " (l:l) 2 X

658 x2T2 " " (l:l) 2 X
UVINULæ ~1-40/
658 x3T2 " "TIN~-328 (l:) 2 X

~2e~7~3;~
TABLE XII (Cont) ,_ TIN~-P/Phenyl 658 x4T2 " "salicylate(l:l) X

;*Coating considered to have passed the 672~hour test.
... i,- .. , . . . \
The data of Table XII show that the best results were ` ~ obtained with films containing 20% grafted silica and the UVINUL0 W stabilizers.

- 12 Comparative testin~s -Further tests were done with films (about 5 ~ to 30 ~
thick) of the composition disclosed in the previous Example deposited on polymethacrylate (PMMA) and polycarbonate (PC) organic glasses. The composition contained 20% by weight of the grafted silica, 2% of the photo-initiator (UV-H-arter-1116) and 2% of a UVINUL~ weathering stabilizer. The tests to which the samples were submitted are listed below. ~
i: Adhesion after curing; cross-hatch scotch-tape test (technique and passing criteria were described in the pre-vious Example), ii: Pencil hardness: pencil lines are drawn by hand on the sample by holding the pencil at 45 angle and pushing forward. Pencil hardness grades 2 H to 9 H were used. No mark should be visible for passing, iii: Flexion (GTB test): In this test, the sample (150 x 25 mm) is supported horizontally on two blocks twith rounded corners) separated by a distance of 125 mm~ Then a force is applied in the center of the sample that produces a bending the central extent of which (relative to the hori-zontal) is measured. The 25 mm and 50 mm deformation are recorded in terms of the coating aspect after returning to horizontal, i.e., the inspection for creases, crazing, peel-off, opalescence, etc. No such defect should be visible for passing.

iv: Heat resistance: the sample is heated in an oven for one hour at 115C. Then surface examination is done as in iii above.

~2~7~3Z
v: Thermoforming: A coated plate sample (75 x 140 mm, 1 mm thick) is heated in an oven to its softening point (glass transition temperature), then it is bent until forming a cylinder with the opposite shorter edges touching. After cooling, the surface of the rigid cylinder is examined for any of the defects outlined under iii. No defect should be visible for passing.

vi: Scratch width (French standards): A flat sample is placed on the table and a diamond point with a 270 g load is fixedly applied on it by its own weight. The sample is then gently pulled so that the point will dig a groove in the sample surface the width of which is inversely proportional to the surface resistance to scratching. The width of the groove is recorded in ~m.

vii: Taber abrasion test (ASTM): The test sample is placed on a horizontal turntable and two free spinning flat edge abrasive rollers held on a fixed horizontal axle are applied on the sample in a manner such that~ upon rotation of the table, the rollers will be driven to spin by friction with the sample surface. The rollers are loaded with a 500 g weight and since they are radially symmetrically disp~sed with regard to the turntable center, they will provide an annular abraded zone on the sample after some time of opera-tion. The number of cycles is 500 after which the loss of transparency of the abraded area is measured in an apparatus for measuring diffusion of light and expressed as a percent attenuation of visibility by diffusion.

viii: GTB abrasion test: In this test, a seven inch diameter organic glass lens protected by a scratch-resistant coating to be tested (such as a lens is used in automotive light equipment) is subjected to rubbing with an alterna-tively moving shoe applying on the horizontally layed anti-scratch surface. The contact surface of the shoe is provided with a cloth dusted with quartz powder (UTAC powder)~ The load on the shoe is 2N/cm2 and the number of rubbing cycles is 100. The abraded area is then examined for diffusion (~D) and light transmission (~T) as above. Results are expressed in "digit units"; the lower the "digits" value, the more abrasion resistant the sample is.

ix: Water immersion test: The samples were immersed in 1% TEEPOL aqueous solution at 65C. They were removed at intervals and tested for adhesion (cross-hatch). The number 39 ~Z¢~7932 of hours before failure is recorded as the merit index in this test.

x: Accelerated weathering resistance: This is the QUV
~est described in the previous Example.
.

The aforedescribed tests were applied to the samples of the invention and, simultaneously, to samples of PC protected by a commercially available anti-scratch composition labelled GE/SHC-1000. The data pertaining to that comparable material and to the samples of the invention as well as the results to the aforementioned tests are recorded in Table XIII. In the middle column, the results are for both coated PMMA and PC
unless separately mentioned.

- TABLE XIII

Data & tests Coatings of GE/SHC-1000 the invention on PC

.
Composition before curing resin content 80~ 20% ~
solvent none methanol-isobutanol flash-point >130C 26C ~Penske-Markens) density tg/cm3) 1.1 - 1.3 0.91 pH -- neutral to mildly alkaline shelf-life >6 months at 2 months at 4C
23C in the dark viscosity lO0 - 200 cP 4 - 10 cStokes handling care fluid (no vapor) flammable liquid toxicity skin irritant skin and eye irritant Application procedure primer none primer SHP-200 dip, flow or spray air drying 30 min scratch-resistant spray, brush, dip, flow, spray layer roll, doctor air drying 20 min blade replica coating curing 30 - 60 sec W 60 min 120 - 125C
no heat 40 ~2q~793;~ ~

TABLE XIII (Cont) Film data density 1.2 - 1.5 g/cm 1.45 g/cm3 thickness 5 - 30 ~ 5.1 Tests i passed passed ii PC <6H <6H
ii pMrlA >8H <9H >6H
iii ~25) pass pass (50) pass pass iv PC pass pass v prlrlA pass ?
vi PC 50-75 ~ 150 - 200 ~ .
vii 18 - 19 20 - 21 .
viii ~D = 30 - 40 ~D = 50 - 80 ~T = 8 - 16 QT = ~70 .
ix PC ~600 hrs PC passed 500 hrs x 500 - 672 hrs up to 500 hrs The xesults of Table XIII show that the scratch-resistant films obtained from the composition behave equally or better than a comparable commercially available material.
However, being applicable as a one layer coatin~ the composi- .
tion of the invention is more simple to use than two layers .
commercial composition.

Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A photo-polymerizable composition to be applied on a substrate to provide thereon a translucent or transparent abra-sion and weather and solvent resistant coating, this composi-tion containing essentially an organic phase consisting of one or more photopolymerizable monomers or prepolymers, one or more photo-initiators and a mineral charge of finely divided parti-cles of pyrogenic silica or precipitated silica or alumina, the particles of which are carrying, grafted on some of the oxygen atoms thereof, substituents of the formulae A1 (I) or SiA1A2A3 (II), wherein A1 represents R or OR groups with R being a saturated or unsaturated substituted or unsubstituted hydrocar-bon radical and A2 and A3 either represent oxygen atom bridges for connecting the Si atom of formula II to neighbor silicon or aluminum atoms of the silica or alumina particles or they cor-respond to the same definition given for A1, the R or OR groups in formula II being identical or different, wherein the total number of carbon atoms comprised by formulae I or II is four or more and wherein the refractive index "n" of the organic phase is as close as possible to the refractive index of said parti-cles of the mineral charge.

2. The composition of claim 1, wherein the "n" value of the organic phase is in the range + 2% from the value of the refraction index of the silica used.

3. The composition of claim 2, wherein "n" is between 1.45 and 1.48.

4. The composition of claim 1, wherein the size of the particles is 0.001µm to 0.1µm.

5. The composition of claim 1, wherein R is selected from the radicals n-hexyl, n-heptyl, n-octyl, 3-butenyl, oleyl, acryloxy-alkyl and methacryloxy-alkyl in which the alkyl moiety has 2 to 6 C atoms, glycidoxy-propyl, epoxy-cyclohexyl-ethyl and isobutyl.

- 41a-

6. The composition of claim 5, wherein R is a methacryl-oxy-propyl group which is further polymerized with an acrylic ester.

7. The composition of claim 1, wherein the percent weight of the organic substituents used for grafting the parti-cles of the mineral charge relative to the weight of the parti-cles themselves is 20% or more.

8. The composition of claim 1 comprising, in addition, about 0.5 to about 5% of a light and weathering stabilizer.

9. A method for protecting a substrate by means of the composition of claim 1, comprising applying said composition as a thin film over said substrate and subjecting it to irradia-tion for causing photocuring of said film.

10. The method of claim 9, wherein the substrate is an organic glass article.

11. A photopolymerized protective coating resisting abrasion which results from the irradiation of a film of the composition of claim 1 on a substrate, comprising 10 to 40% by weight of organophilic said particles of silica and the visible light absorption of which does not exceed 10% of the light transmitted by the substrates protected by said coating.

12. The coating of claim 11, the thickness of which is 1 to 50 µm.

13. A process for producing a UV-cured photopolymerizable composition for applying onto a substrate to provide thereon a transparent abrasion resistant coating comprising:
hydrolyzing a trialkoxysilane in an aqueous acidic solution, dispersing said hydrolyzed trialkoxysilane into intimate contact with finely divided pyrogenic or precipitated silica or alumina having a particle size of less than 0.1 microns to form a dispersion, chemisorbing said hydrolyzed trialkoxysilane onto the finely divided pyrogenic or precipitated silica or alumina by effecting dehydration of said dispersion by heating to 80° to 110°C to yield organophillic particles, dispersing said organophillic particles into intimate contact with one or more photopolymerizable monomers and one or more photoinitiators.

14. The process according to claim 13, wherein said trialkoxysilane is selected from the group consisting of .gamma.-methacryloxypropyl-trimethoxysilane, .gamma.-methacryloxypropyl-ethoxy-dimethoxysilane, .gamma.-glycidoxypropyl-trimethoxysilane, (3,4-epoxy-cyclohexyl)-ethyl-trimethoxy silane, isobutyl-trimethoxysilane, and octyl-triethoxysilane.

15. The process according to claim 13, wherein said photopolymerizable monomer is selected from the group consisting of methyl acrylate, methyl methacrylate, ethylene glycol diacrylate, 1,6-hexanediol diacrylate, 1,4-butanediol diacrylate, neopentylglycol diacrylate, diethyleneglycol diacrylate, tri-propyleneglycol diacrylate, tetraethyleneglycol diacrylate, bisphenol-A diacrylate, trimethylolpropane triacrylate, penta-erythritol triacrylate, pentaerythritol tetra acrylate, dipenta-erythritol pentaacrylate, epoxy-acrylate, acrylic prepolymer, acrylic polyester, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, bisphenol-A dimethacrylate, 1,6-hexanediol dimethacrylate trimethylolpropane trimethacrylate pentaerythritol tetra-methacrylate, trimethylolpropane triacrylate, and pentaery-thritol triacrylate.

16. The process according to claim 13, wherein said photoinitiator is selected from the group consisting of benzophenone, Mischler's ketone, ethyl 4-dimethyl-amino benzoate, benzil, 2-ethylanthraquinone, diethoxyacetophenone, and 2-chlorothioxanthane.