PHOTO SETTING COMPOSITION FOR COATING SUBSTRATES WITH AN ABRASION-RESISTANT TRANSPARENT OR TRANSLUCENT FILM

Abstract: A photopolymerizable olefinic composition containing a mineral filler suitable for forming on a substrate an abrasion resistant protective film. The mineral filler essentially 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: PHOIO SETTING OQMPOSrriON -FOR COATING SUBSTRATES WITH AN ABRASION-RESISTANT TRANSPARENT OR TRANSLUCENT FILM Field of the invention The present invention relates to scratch-resistant surfaces and more " particularly concerns a photopolymerizable composition to be appli-ed on a substrate so as to produce thereon a transluc-ent or trans- parent coating resisting corrosion and abrasion. This coating is in¬ tended to protect said substrate against shocks, bruises and other mechanical accidents as well as against wear resulting from normal use- Such cαr ositicn is very useful in all industrial fields whe- re it is desirable to avoid, as much as possible, that sensitive ob¬ jects exposed to shcck -and wear be progressively damaged. This is particularly important when dealing with tran-sparent articles such as optical goods the surface of which must be protected by all means against scratches not to lose its desirable optical pro erties. It has been definitely established by new that the manufactu¬ re of high performance optical ware by using transparent organic ma¬ terials is possible the working of which, by casting or any other machining means, is much easier and more economical than with cor- re-sponding 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 an¬ ti-corrosion protective film but thin enough for not significantly altering the optical properties of the substrate. The Prior-Art Very many coating ccπpositions and application methods have al¬ ready been propos-ed for achieving the aforementioned object, this " being with variable success. Among all these compositions of the prior-art, seme are parti- cularly relevant that owe their properties to the presence of com¬ pounds from elements other than the usu-al constituents of organic matter and, in particul-ar, to -aluminum and silicon in the form of specific mineral or organic coπrounds. With reference to silicon, for instance, seme of the techniques used involve the build-up of a protective coating on substrate, this coating being obtained from the vapor phase deposition of glass or silica evaporated under va¬ cuum. Polysiloxane based protective coatings can also be obtained, the structure of which resembles to seme extent that of crcss-li^- -ed polysilicic acid, by the in-situ polymerization of organo-sili- con cαπpαunds previously partly hydrolyzed- During the hardening (cur¬ ing) of such coatings, polymerization occurs, either due to the form * - ation of Si-O-Si bridges (by the dehydration of sHanoi functions) , or due to the participation of polymae izable organic groups belong- ing to substituents possibly present on the silicon atoms (olefins, epoxy-, aππino- groups, etc.) , or by a combination of the said two polymerization modes. Frcm the references illustrating such techni¬ ques, the follcwings can be cited: A.J. REEDY, Ees. Disci. 1978, 171 - 6; Patents OS? 4,006,271; 4,098,840; 4,186,026 4,197,335; JP (Ko- kai) 77, 101.235; 112.698; 152.426; 154.837; __, 60.335; 62.267; 119.597; 119.599; 129.095 to 129.099; 133.600; 144.500; 148.100? 80, 05.924; and EOS 2.803.942; 2.805.552; 2.820.391? 2.831.220; 2.917.440. Eowever, despite the protection they inpart to the substrate on which they .are applied, these coatings have seme drawbacks. Qe of such disadv-antages is related to the relatively high tero-eratures need¬ ed for curing polysilicic typ ' coatings which can lead to -substra¬ te deformation. Another drawback is inherent to the expansion coef¬ ficient of the polysiloxane coatings which is often sufficiently dif¬ ferent frcm that of the substrate for causing the development of ad- hesion problems (for instance in the case of polycarbcπate or poly- ethacrylate org-anic glasses) and of cracks or crazing after alter¬ nating hot and cold periods (particularly in the case of articles sub -ected to weathering like automobile head-lights) . Adhesion pro¬ blems were partially solved by interposing an intermediate tending sublayer between the coating -and the .substrate but, more generally, it has been .sought to rem-edy the abov-e-mentionεd drawbacks by replac¬ ing the coatings frcm polymerized silicon cαrpounds by cαroositicns comprising, dispersed within -an organic or silico-organic matrix fine particles of silica or alumina. Ihus, there were used in thi context aqueous mixtures of silicon ccrrpounds, colloidal silica an hydro-compatible solvents (alcohols, glycols, etc.) , with or withou polymerizable organic monomers. Exaπples of such uses can be foun in the following references: Belgian Patents Nos. 821.403; 877.372; ϋSP 4,027,073; 4,138,451; 4,177,315; <3 2,018,621; 2,018,622; DCS 2.811.072 and JP (Kokai) 79_, 157.187. However, colloidal silica be¬ ing e.ss.entiaally hydrophilic, as are also the other types of silica such as amorphous, crystalline, micrccrystalline, precipitated and pyrcgenic silicas, it is well compatible, in general, only with hy¬ drophilic polymers, for instance or anosilicon polymer, whereas it is much less or not mi≤cible with typical hydrophobic resins such as polyolefins, which very strongly restricts its use as a filler in the film forming thermcsetting or photc-settiπg compositions. Mo¬ reover, adding hydrophilic silica to organic polyme izable monomers leads to the formation, with relatively low concentrations of solids, e.g. about 5 to 10% by weight, of highly thixotropic masses (non-New¬ tonian rheologic behaviour) which are very difficult to apply as thin layers on substrates. Hence, attempts were made to remedy this di¬ sadvantage, 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 remark¬ ed at this stage that methods for imparting hydrophobic organophil- ic properties to alumina or silica particles are already known, per se; however it -dees not appear that there exists, by now, methods for giving to silica or alumina particles sufficient organophilic properties to enable them to be incorporated at high levels (of about 40% by weight or more) into polymeric resin films, while maintain- ing suitable rheological properties for application and nearly com¬ plete transparency of the films formed. Yet, ensuring proper trans¬ parency of the protective coatings of optical goods is a fundament¬ al requirement, as will be seen hereinafter in the description of the present invention. As pertinent references regarding the methods for "treating" silica or alumina particles for rendering them orga- nophilic. South African Patent No. 72.5180 and Japanese Patent (Ko¬ kai) No. 77, 138.154 can be cited. In the first of these references, silica particles are treated with trimethylchlorcsilane which, b reaction with the silanol groups of said particles, generates hydro phobic groups of formula -ai-O-SiK≥-, whereby said particles are r-en dered compatible with a mixture of olefinic monomers (ethylenic an acrylic monomers) . These p-artides are then incorporated, to a le vel of about 5 - 10% by weight and together with a proportion of alu mina about 10 to 20 tim-es greater, into a mixture of polymerizabl resins which, after curing, provides insulators for high eletric vol tages. Such materials are however opaque and their resistance to abra sion is not indicated. In the second of the two references cited abo ve, particles of alumina are coated with -(glycidyloxy)-ρropyl-tri ethoxysilane and a mixture containing about 25% by weight of suc treated alumina and an epoxy resin is used for coating a polycarbo nate article s-o as to obtain, after polymerization, an abrasion-r-e sistant film. Moreover, in the following references, there are des cribed methods for attaching* organic groups such as vinyl, methacryl, epoxy, glycidoxy to hydrophilic silica so as to iro-art thereto hy drophobic properties: L.P. ZHMJA SKI et al, Rubber røarl 163, 1 (1970); M.W. B__1E_ et al, Sseting of the Div. of Rubber Che ., AC Meeting, Cleveland, Ohio (1971); M.W. RANEY et al, Meeting of th Div. of Rubber Qiem., ACS, Miami, Fla (1971); ΞI-SH, Bulletin 41, Jan. 1971, PPG Industries. In addition to the above mentioned prior-art, seme further U Patent references can be cited in connection with the following -sub jects pertinent to the invention: 1. Si0 2 : 3,986,997; 4,177,315; 4,188,451; 4,242,403 2A. Treated Si0 2 , e.g. to make it hydrophobic: 2 ,610 ,167; 2,818,385 ; 3,652,379 ; 4,001,128. 2. Forming SiO- in situ, e.g. hydrolyzing organic silicates: 2,404,357; 2,404,426 ; 3,971,872; 4,049,858; 4,120,992; 4,186,026 3. Using siloxanes and/or si 1 anas and the like: 2,610,167; 3,389,114; 3 ,801,361; 3,953,115 ; 3 ,986,997; 4,001,128; 4,006,271; 4,026,826; 4 ,027,073; 4 ,029,842; 4 ,049 ,868; 4 ,177,315; 4 ,186 ,026; 4,188,451; 4,197,335 ; 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 ,Q9S ,84C O P 4,120 ,992; 4,197,335; 4,242,403 4B. Prepolymers (oligomers or monomers): 3-,819,562; 4,029,842? 4,197,335 4B1. Photopolymerizable i∞nomers: 3,968,305; 3,968,309? 4,188,451 4C. Other chemicals, e.g. solvents, fillers cress-linking agents, to obtain transparent abrasicn-resistant coatings (as single or com¬ posite systems): 3,986,997 (acidic alcohol Σ^O solution); 4,001,128 (A1 2 0 3 ); 4,006,271 (solvent); 4,027,073 (acidic alcohol water solut¬ ion); 4,049,868; 4,186,026 and 4,120,992 (cross-links with formal- dehyde); 4,120,992. 5. Miscellaneous routes to such coatings: thus ISP 3,645,779 provides a vacuum vapor deposited coating of B2θ2-Siθ2 on organic glass; OSP 4,051,297 discloses a sputtered film of chromium suici¬ de on smooth surfaces; in USP 4,242,403, there is di≤-closed a coly- ethylene terephtalate sheet covered with an intermediate layer of -(3,4-epoxycyclohexyl)*^thyltrimethoxysilane and an upper layer of silica reinforced organopolysiloxane resin. In spite of the progress achieved by the above mentioned tech¬ niques, it was still desirable to have at hand a quick setting cczπ- position for providing thin tr-anslucant or transparent films very resistant to abrasion by virtue of a hig -level therein of hydrophob¬ ic silica. Thus, a first object of the invention was to provide a composition for depositing transparent protective films on substrar- tes, such films being sufficiently mechanically resistant to with- stand normal wear or accidental abuses without iir airment of the .sur¬ face properties. A second object of the invention was to provide a composition for coating protective tr-ansparent films on optical geeds, the op¬ tical properties of which will not be significantly modified by this film and which will keep such properties for a significant period of time under adverse conditions. Another object of the invention is to provide a composition for depositing thin well adhering films on substrate, such adhesion not being affected by weathering conditions even after a prolonged pe~ ricd of exposure. Another object of the invention is to provide a film forming composition that will strongly adhere to organic glass substrata and which can be cured at room temperature, i.e. much below the -soften¬ ing temperatures of the substrate. Another object of the invention is to provide a composition for making tran-sparent s-cratch-rεsistant films, such films being coat- ed on substrates as one layer films, i.e. without the need of an in¬ termediate bending layer. Still anoth-er object of the invention .is to provide a ccπposit- icn that can be stored for prolonged periods at room ta-eirerature with¬ out hardening and which can be cured on the substrates in a matter of seconds without the use of elevated temperatures. .toother object of the invention is to provide industrial optic¬ al articles made of relatively soft and easy raoldable organic glas¬ ses protected with a scratch resistant film that will withstand pro¬ longed use under severe weathering conditions without discoloration, crazing or significant -adhesion losses. Oth.er objects of the present invention will beccce apparent to people skilled in the art frcm the description, of the invention that follows and frcm the disclosed preferred embodiments thereof. Summary of the invention The present inventicn enables to achieve the aforementioned ob¬ jects. Indeed, the invention provides a photo-polymerizable coπpo- sitiαi comprising one or more photo-polymeriz-able mcnαsers, at least one phto-initiator -and Si0 2 or A^O-, particles having, grafted on ■sαπe of the oxygen atoms thereof, substituents of the formulae A***- (I) or Si -l ^A 3 (H) where.in A****** rrepresents R or OR groups, R being a saturated or unsaturated substituted or unsubstituted hydrocarbon radical and .A-2 and A-3 either represent oxygen atoms for connecting the Si atom in formula (II) to neighboring silicon or -aluminum atαπs of the silica or alumina particle, or they have the same definition as for A ** -. Naturally when, by virtue of the aforesaid definition, the Si atcra in (II) tears more than one R or OR groups, the R's can be the .sane or they can be different. The detailed nature of the R's will be explained in a πcment. One distinctive feature of the -cαπpσsiticn of the inventicn is that the total number of carbon atoms which are included in formu- lae (I) or (II) , i.e. in Al, or in A-l plus A 2 anciOr A3 in ca.se me¬ re than one of the A's on the Si atcra of (II) are R and/or OR groups, should always be four or more in order to obtain rheologicaϊ proper¬ ties of the coating compositions conta.ining high concentrations of coated particles that allow satisfactory practical application of the compositions to organic glass substrates. For example, as will be cited later, suitable coatings were not obtained with composit¬ ions containing silica treated with silicon coiηpounds having less than four carbon atoms, while other compositions involving four or more carbon atcms gave satisfactory results (see data in table Vila versus those in tables VI and VII) . Another distinctive feature of the exposition is that the re¬ fraction index "n" of the organic phase of the -coπposition should be as near as possible to that of the particles used. Furthermore, if the refraction index in the protective film of the organic matrix which is cempos-ed of the various organic constituents of the cctr o- sition is not near that of- the mineral particles, then said protect¬ iv film is not perfectly clear but only translucent, this effect being particularly significant with high levels of mineral fillers, for instance of the order of 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 pyrcgenic 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 inpossible to achieve and, for this rea¬ son, the coatings containing high proportions of alumina are tr-aπs- lucent .and not transp-arent. In general, it is preferred within the scope of the invention to use particles with 1.40 <n <1.50 and an organic phase the "n" of which lies in the same range. Preferred embodiments of the invention It should be noted that the size of the particles is iiroortant with respect to the optical properties of the present protective coat¬ ing. Thus, using relatively large particles, i.e. having a diameter of about the same order of magnitude as 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 there¬ of (undesirable light reflection and diffraction effects) -and may impart thereto a milky appearance. To be perfectly clear, the film siiould have a flawless, smcoth, mirror-like surface. Consequently, there will preferably be used particles of a size about one order of magnitude less than the coating thickπ-ess. Thus, for instance, with coatings having a thickness of the order of one micron or less, there are advantageously used particles sizes of 0-007 to 0.05 t (py- rcgt≥nic Si^: AΞRGSH. (Degussa, Germany), CAB-O-SH. (Cabot Corp. USA) ; precipitated silica: Ξi-SIL (PPG Industries, USA), etc.). For thick¬ er coatings, larger size particles are possible, for instance 0.02 to 0.1 u (precipitated silica). The same is true for alumina, cor¬ responding r-equirements for this miner-al filler being however less, since films loaded with -A^O., are usually not. tr.ansparent per se. As suitable alisπina for the present composition, there can be men¬ tioned a product called A ON (Alcan, Canada) , the particles of which have a size approximately 0.006 u. The silicas used or tried with¬ in the limits of this invention are the followings: ϊfeme and type Specific area Particle size of silica (π^/g) (-u ) Eyrcgenic silica CAB-O-SIL EΞ-5 390 + 40 0.007 Ξ-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 Hi-SIL 233 — — 215 150 0.02 STCFINE ΞF 90 0.03 Org-anophilic silica* AEROSIL R-972 120 + 30 0.016 #This silica was made organophilic by reacting with trimethyl- chlorosilane, the number of carbon atcms per grafted sili-ccn atom is thus only three which dees not corre.spond to the standards requir¬ ed for embodying the invention. Indeed, under testing, this hydro¬ phobic silica did not provide ccπpositions with properties suitable for achieving protective coatings according to the invention. Regarding the photopoly erizable monomers that fit the requi¬ rements of the present invention, one can use most monomers or ixt- ures of monomers generally kncwn to photopolymarize -and the photo- polymerization of which is fast enough under usu-al conditions to be completed shortly (i.e. with exposure tines from about a few seconds to a few minutes) and the H n" indexes of which fall within the afo- rementioned limits. Examples of such monomers (olefinic and prefe¬ rably acrylic) can be found in the following reference: UV Curing by S. Peter PAPPAS, Science & Technology, Tec±tnolcgy marketing Gsrp. , USA (1978) . Among the mcnα ers usable in the present invention, there can be mentioned also some olefinic prepolyraers with a photopolymeriza- ble 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 cur¬ ing. Such prepolymers are kncwn in practice most often under gener¬ ic ccmmerci-al n-ames such as UVITΞANΞ (Thiokol Corp.) ; ΞBΞCRYL (Union Chimique Beige) , UCAR-X (Union Carbide) , SΞEARQL (Kunstharsfabrick Syntehse NV, Holland) . The structure of such prepolyraers which fit well in the invention, provided they have the proper refraction in¬ dexes, are generally not disclosed publicly except for the fact that they are mainly pσlyol-acrylates (polyesterglycols) or polyuretha- ne-glycol_s. In practising the invention, one should use either mo¬ nomers the "n" .index of which is intrinsically close to that of the mineral filler us.ed 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 rainaral filler. By suitably varying the proportions of the two or more monomeric cons¬ tituents the- respective indexes of which axe above and below the de- sir-ed value, the latter can be approximated close enough for event¬ ually obtaining, with the c rposition according to the invention, a practically transp-arent protective film with silica contents of up to 40% by weight or more. As non limiting exaroles. Tables I and II belcw 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 there¬ of as well as viscosities under standard conditions. TABI E I Monomer Refractive index Viscosity c? -n^O" Methyl 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 T ipropyleneglycol diacrylate (TPGDA) 1.4495 max. 10 Tetraethyleneglycol diacrylate (TEGDA) 1.4616 max. 10 Bisphenol-A diacrylate (EP TRV -ISO) 1.5415 1000 + 20% Trimethylolpropane triacrylate (TMPTA) 1.4738 70 -_ 20% Pentaerythritol triacrylate (PETIA) 1.4S3T 650 ± 20% Pentaerythritol tetraacrylate (PETEA) 1.4855 800 ÷ 20% Dipentaerythritol pentaacrylate 1.4932 4400 + 20% ■ EBB2RY -210 (Acrylic prepolymer) 1.4980 125.10* ÷ 20% " -220 ( ) 1.5030 18.10 3 + 10% " -230 ( " ) 1.4646 6.1C + 30% TABIE I (Cont) * w -240 ( M ) 1.4743 3.10 4 + 50% « -270 ( " " ) 1.4755 15.10 4 ÷ 13% UVHΞANΞ-782 ( " * ) 1.5024 paste " -783 ( w w ) 1.5264 paste " -788 ( n " ) 1.5085 paste UCAR X -117 ( " ) 1.4816 135.10 2 + 1% " X -318 ( " ) 1.4898 17.10 2 + 5% π X -125 ( * π ) 1.4978 106.10 2 1% EBE2RYL-600 (epoxy-acrylate) 1.53 4-8 ,10 2 (60°C) " -601 ( " ) 1.55 2.10 5 10% ** -830 (acrylic polyester) 1.5005 45.10 3 ÷ 10% " -810 ( " ) 1.4675 500 ÷ 40% SΞTAEQL-3625 (ole inic polyester) — solid Ethylene glycol dimethacrylate (EDQSA) 1.4527(25°C) max. 10 Diethylene glycol dimethacry.late (D.EGEMA) 1.4580 (25 e C) max. 10 Triethylene glycol dimethacrylate (TRIGEMA) 1.4595 m-ax. 10 Tetraethylene glycol dimethacrylate (THiCMA) 1.4609 max. 10 Bis-phenol-A dimethacrylate 1.5412 1600 ÷ 20% 1. β-Hexanediol dimethacrylate (HDCMA) — max. 10 Trimethylolpropane trimethacrylate (Ε-5PTMA) 1.4700 (25°C) 35 + 20% Pentaerythritol tetramethacrylate solid M.P. 52-55°C TABLE II Monomers or mixtures Index Viscosity cP (% by weight) "n^Q" Ttimethylol-propane triacrylate 1.4740 75 + 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 + 10 UCAR-X 118 (31,0) Diethylene-glycol diacrylate (89.0) 1.4-570 max. 30 UCAR-X 118 (IS) Diethylene-glycol diacrylate (82) 1.4670 45 + 5 EBHSZ -600 (33,3) Diethylene-glycol diacrylate (66,6) 1.4915 75 + 5 E3ERCR2 -600 (16,7) Diethylene-glycol diacrylate (83,3) 1.4765 max. 30 EBΞ__RS 830 (33,3) Diethylene-glycol diacrylate (66,6) 1.4742 65 + 5 SΞEAEOL 3625 (16,7) Diethylene-glycol diacrylate (83,3) 1.4735 100 + 10 Methyl methacrylate (38,46) Pentaerythritol triacrylate (38 ,46) EBΞCRΩ 600 ' ' (23,08) 1.4732 max. 30 There is further noted that, especi-ally for seme applications to be described hereinafter, the adhesion of the film tcw-ard glass substrates should preferably be weak or nil and, in such cases, the mixture of photopolymerizable monom-ers will include no hydrophilic 5 monomer such as acrylic acid or glycol acrylates and methacrylates. As photopolymerization initiators, there can be used in the pre¬ sent composition most substances generally suitable for this purpo¬ se and being con-patible with the contemplated monomers and fillers. For exairple, the following photo-initiators suitable for the pre.sent j , invention can bet benzophenone, Mischler's ketone, ethyl 4-dimethyl- a ino benzoate, benzil, 2-ethylanthraquimone, diethoxyacetophen-cne, (DEftP, Uion Carbide) UVΕCBΣ ϊ>-36 (U.C.B.) , IR©CU5E-651 (Ciba) , SZacORAZ-lOOO (Saπfoz), FI-4 (Eastman Kodak) , VICUHE-1Q and -30 (Stauf- fer Chemicals) , TRIGONA -14 and P-i (Ifcury) , u^-ESRIΞR ϊfcs 1173 and ■ j c 122.6 (Merck) , 2-chlorothiox-anthone, etc. Using diethoxyacetophe.no- ne is appreciated as, being a liquid, it dissolves particularly w-ell in the present photopolymerizahle cc- position. Another excellent pho— toinitiator is UV^HSBϊER No. 1316 (frSerck) . Generally, there can be used advantag-eously from 0.5 to 5% by weight of the photo-initiat- 2 Q or depending on the selected mixture, on the amount of filler and on the polymerization rates which are desired. Using 1 to 2% by weight of diacetophenone or other initiators is advantageous. Ηs nature of the radical R which intervenes in the forn-ulae (I) and (II) can be much varied and its range is essentially dict t- 25 ed by the requirement of mutual- compatibility with the organic pha¬ se components. In general, alkyl, alkenyl, cycloalkyl and cyclo-al- kenyl of about 1 to about 12 carbon atoms are suitable, provided of course that the total nuπber of C's in (I) or (II) is 4 or more, i.e. for instance, if only one organic radical per grafting site is in- 3 Q volv d, then it should be at least a four carbon radical while if more than one organic radical are involved, say three for instance, two of such radicals can be methyl and the third be ethyl or the li¬ ke. The organic radicals can be unsubstituted or substituted with functions containing oxygen or heteroato s (N, S, etc.) . Cxygen funct- 2 ions can be hydroxy, keto, ester, ether functions and the like. Un- .substituted radicals can include photopolymerizable functions that will participate to the overall photopolymerization of the composit¬ ion and provide thus photo-copolymers -in which seme of the copoly- m-ariz-ed groups will actually bond to the silica particles by virtue of the fact that the photopolymerizable R was included in the ccm- pounds of formulae (I) or (II) for grafting to said silica particles. Other definitions for the R radicals will appear from further details hereinafter. Preferably, for optimal properties of the scratch-re¬ sistant coatings of this invention, the weight of the organic subs- tituents used for grafting the silica particles relative to the weight of the Si0 2 of said particles will be at least 20% and can be more. Ihe methods which can be advantageously used for rendering or¬ ganophilic the particles of the mineral fillers that are incorporat¬ ed into the coroosition of the invention are selected among the known methods the references of which are listed in the intrcducticn. Among these meth-eds, the four methods (A to D) described hereinafter suit the invention to various extents. In the following schemes the sign -Si-OH represents one of the peripheral silicon atcms (with a- sila- nol function) of a hygrophilic silica particle which is to be made hydrop-hobic. It will remain understood that the free Si bonds repre- sented in the schemes mean that this Si atom is bonced to the gene¬ ral polysilicic acid network of the particle as follows: It should be further remarked that the particles of silica thus treated, even the .smallest, each have a relatively large nuirber of oxygen and silicon atoms. For instance, a particle of 0.02 u diame¬ ter has a weight of about ICT 17 g assuming a value of 2.3.for the average density which corresponds to about 10~3-8/6 mole of SiO-. Sin- ' . ce the number of molecules in a mole is 6.10 23 , said particle will have about 10 5 atoms of Si. The particles are therefore aggregates of relatively high molecular weight and the mixtures therefrom in liquid media are indeed icεllar dispersions or colloidal solutions and not true solutions of αrgano-silicon cαπoounds as in the majo¬ rity of prior-art compositions mentioned hereinbefore. It is thus all the more remarkable that the composition of the invention dees 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 ap¬ ply by analogy since peripheral alumina molecules also bear react¬ ive OH functions. The gr-afting methods which were experimented in the scope of the invention are listed below schematically. They a.re given for il¬ lustration -and evidently they do not limit the invention as other method could be contemplated or even preferred as far as they may be more economical or more ef icient. A. The conversion of some OH functions of the mineral particles (silanol functions in the case of silica particles) into reactive functionsj e.g. by chlorination as in the schemes below: 1. -έiOH ÷ SCCl^ ■ -SiCl + ΞC1 ÷ 30 2 2. -SiOH + SiCl 4 - -SiO-SiCl 3 + HC1 Ihen alkylation of the inverroediate product thus obtained: 3. -SiCl + ROH - -SiOR + HC1 4. -SiO-SiO^ + 3RCB -SiO-Si(OR) 3 + 3HC1 B. A reaction with organosubstituted halcgenosilanes: t ci 5. -SiOH + Cl^SiRR' ^ -SiO-Si-R + HC1 R * ' Then alkylation of the silicon atom with elimination of the chio- rine atom: Cl R'' 6. ^ .SiO-Sii--RR ++ RR « "'OOHH \*>--SSiiOO--SSii-R + HC1 I II II if R * R' In the above schemes, R 1 and R'' (organic radicals) can be the same as R or be different frcm R. Ihey can have (taken individual¬ ly) less than four carbon atoms since for having the grafting con¬ ditions within the sccpe of the invention to be satisfied, it is suf- ficient to have only one of the organic substitu-ents brought up dur¬ ing grafting at one site with at least four C atcms or, otherwise, the total of the carbon atoms of substituents R, R' and R" put to¬ gether in accordance with the definition of the aforesaid formula (II) should be at least four. C. The condensation promoted by heat with silanols (R-Si(OH),) : OH 7. -SiOH + (ΞO) 3 SiR 5>-SiQ-Si-R + H^O 1 OH It should be noted with reg-ard to reaction 7 that the remain¬ ing OH functions c-an still react after grafting by further dehydrat¬ ion with other silanol molecules (chain extension by grafting) or with an OH on a neighbor Si atom in the polysilicic acid backbone of the particle und-er reaction* (cross-link bridges) . It should al¬ so be noted that the silanols used generally result frcm the hydro¬ lysis of trial oxysilanes according to reaction 8: 8. BSi(0Me) 3 + 3H 2 0 ^SSi(0H) 3 + 3 eOH D. A reaction of "physisorption" with trialkoxysilanes. Ibis route is a "complexaticn" reaction providing a product in which the bends to the silicon atom to be gr-afted -are not cov-alent. It is car- ried out by boiling in an organic solvent like xylene: 9. -SiOH + (MeO) 3 SiR - j-SiOH.(MeO) 3 Si - IB - — " It should be remarked that the "cαrølex" thus obtained (e trostatic type of bonds) is not v-ery stable and that a dispers made frσπ particles grafted as such has characteristics differ frαn that of dispersiαis made from particles grafted by raethed to C above. In particular, dispersions obtained from particles tre ed according to 9 have a rheologic behavior that is scsistimes non- tαiian in ch-aracter and are more difficult to use in the present position. In the above described grafting methods, the group R will ferably be a radical such as n-butyl, n-hexyl, n-heptyl, n-cc oleyl, 3-butenyl, decanyl, etc. Also functional groups are suit that result frαn the use, when alkylating activated mineral partic of glycol acrylates or methacrylates. Thus, in the substituent mulae R can be where n can be for instance an teger between 1 and 6. V5hen the group R has an olefinic moiety, function can copolymerize with the other monomers of the ccπpo ion when under irradiation, in which case the particles are then mobilized by chemical bonds within the coating organic matrix. Grafting method C is preferred in the methods described h inabove because it is relatively single .and because no halogen intermediates are necessary, the handling and the di.sposal of w are undesirable regarding safety and environmental problems. Furt cαπpounds of the formula R-Si(OR') 3 where R 1 is an easily hydr zable lower alkyl are cαrsπercially available, the range of the rious us-able R groups being relatively large. For instance, the R with reactive functions can be the fol ingsj CH 2 -CH * -<3L 2 -0-(CΞ 2 ) 3 (glycidoxypropyl rest) (CH 2> 2 (3 ,4-epoxycyclohexyl-ethyl rest) In the case where R contains a reactive function, such as oxirane function as above, it is evident that the latter can contri¬ bute' by its cwn polymerization reaction to the overall curing of the protective film of the invention. • On the practical a-speet, or achieving the coπposition of the invention, the mineral particles made organophilic as mentioned abo¬ ve are dispersed into the photopolymerizable monomer or the mixture of monomers and the photoinitiator. This dispersion is carried out by usual means (blendor, ultra-sonics, mixer, ball-mill, etc.) un¬ til the coπposition is well homogeneous. Then, after allowing the mixture to stand for enabling the air bubbles (or gas bubbles if the operation is done under an inert gas) to escape, it is applied to a substrate to be coated -so as to form a thin film thereon. Tor this, standard tools .and methods can be us-ed such as brush, rod, doctor blade, spraying, dipping, etc. With regard to the protection of oρ- tical gcods, lenses, mirrors, etc., the following procedure is pre¬ ferably followed: on the surface to be protected, there is put a few drops of the photopolymerizable coπ osition, after which th-ere is applied thereon, in order to well spread it and make it even, a ne¬ gative counter-plate or mold made of optical glass, the uncured ro- tective layer being squeezed (and molded) between it and the gccd and consecutive spreading of the mixture taking place leading to the formation of a rs≥gular film ov-er said good. The surface of the mold has a finish which is such as to confer we.ll defined optical proper¬ ties to the outside surface of the coating such properties being that, in fac-simile, of said mold (replica molding) . After irradiation of the piece and photo setting of the coating, the mold is removed which step is effected with no effort as the adhesion between the mold and the film is weak or practically negligible. This unexpected result is due to the hydrophobic properties of the coating and of the part- ides therein; indeed, the monomers used are not hydrophilic (they contain no significant amount of hydrccoπpatible c-arboxylic or hy- droxy groups such that of acrylic acid or the hydroxyacrylates) and also the mineral particles have no more affinity for the glass af¬ ter being grafted with organic radicals as described above. In this connection, it should be said that if, instead of the corrpcsition- of the invention, another cαrpositicn were used having the same or¬ ganic coirponent but containing in lieu of 20 - 40% hydrophobic si- lica, only 2 - 3% of ordinary (non grafted) pyrogenic or precipitat¬ ed silica, there is obtained a film that strongly adheres to a glass substrate so that it is difficult, if not impossible, to remove it th-erefrom. With regard to photo-setting of the film on the substrate to be protected, usual means are employed, i.e. aSubj-ecting the f-ilrn on the substrate to a suitable irradiation operation, such irrjsdiation taking place either directly on the film or through a tran.sparent layer applied ov-er the coating (plastic membrane for avoiding dust falling on the fresh film or negative glass counter-form as describ¬ ed above) . Also, the substrate -can be turned up side dσ-vn relative to the irradiation -source, the exposure being done thc-ugh the trans- parent body of the substrate itself if desired. As an irradiation ■source, one preferably uses a ccmmercial type UV light giving flu- xes of about 10 - 100 W/cm and suitable for photopolymerizing a film " at a distance of 5 - 30 cm for a few seconds (2 - 60 sec) at room temperature. Other means and techniques for photopolymerization kncwn to these skilled in the art may be used in photocur ng the coating. Exanples may be found in Swiss Patent Application No. 101.91 79-6. The photopolymerized film thus obtained is in form of a thin smooth layer perfectly transparent in the ca-se when hydrophobic si¬ lica is pr-ssent and tr-anslucent if hydrophobic alumina is present. When clear, this thin layer dees not signific-antly modify the optic¬ al properties of the substrate and it offers an exceptional resis- tance to abrasion, weathering and accidental abuses as seen herein¬ after in the special part of this ■ disclosure. It can thus be used advantageously for coating optical apparatus lenses made of organ¬ ic glasses such as PVC, polycarbonates and polymethacrylates -as well as many other transparent articles such as clear panels, head-lights and other lighting appliances in automotive or still equipment. In summary, the resulting advantages frcm embodying the present invention are as listed below: a) Thin layers (fran -about 0.5 to 20 or 50 urn) , smcoth, trans¬ parent (with 3i0 2 ) and very resistant to wear by abrasion (the ccm- position of the invention lends itself h-cwever to the preparation of thicker layers in special cases) . b) Solventless compositions requiring no evaporation step when - curing the coating. The absence of solvents al-so removes the risks that the substrate be attacked (organic glass) by such solvents. c) Very quick h-ardening of the film at room tei perature which is -technically and ■econcmic-ally advantageous, the production rate being high and the risks of damaging the coating before curing be¬ ing strongly reduced. d) Low cost of the raw materials by virtue of the fact that the mineral fillers and the monomers are easily available and relative¬ ly cheap and that the fillers- load percent is quite high. e) Excellent physical properties such as abrasion resistance and very low friction index. This last property is mostly unexpect¬ ed 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 -eco- nonical iπplementatiαn raetheds, ncn-standard equipment being unneces¬ sary. The coatings of the invention as far as described up to now con¬ tain no stabilizers against weathering and against degradation by daylight exposure. If such stabilizers (a description of which will be found hereinafter in section II) are incorporated in the compo¬ sition of the invention at concentration of about 0.5 to 5% by weight of coπposition, the resistance against oxidation, discoloration and other damages caused by external exposure conditions is greatly in- creased. This will be described in section II of this disclosure. There will be new described in detail in the experimental part that follows how the invention can be put to application practical¬ ly. Reduction to practice of the invention 1. Preparation of hydrophobic silica and alumina A. Chlorination of silica th-en alkylation of the chlorinated product: In a 1 liter flask were placed 500 ml of .anhydrous benzene, 240 ml of thionyl chloride and 30 g of pyrogenic silica (AΞRCSIL-380) . ϊhe mixture was refl xed for 5 hrs after which the solvent and ex¬ cess of SOCI2 were distilled off. The residue was further left for 2 hrs at 50°C under 10 T rr (13.3 irbar) so as to complete the eva¬ poration 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 (ac¬ tually, temperatures of 60 - 90°C were already sufficient for 2 hrs reaction periods) . Tϊie HC1 formed was removed under reduced pressu¬ re (20 - 28 bar) and an excess of dry ether was added. The suspen¬ sion was centrifugated and, after separating the liquid phase, the 10 solid was washa-ed twice with ether. There were thus obtained 11.1 g of silica the particles of which bore, grafted on the silicon atαπs, O-n-Butyl rests. The same procedure was followed but replacing in the above pre¬ paration the nr-butanol by -equivalents of the following alcohols: n-he- * - * " * ' xanol, n-heptanol, nr- ctanol, oleyl alcohol and 1,2-prcpanediol o- noacrylate. There were thus obtained silica products with correspond¬ ing grafted substituents. A'. Treating with tetrachlorcsilane then alkylaticn of the ob¬ 20 tained chlorinated product: This reaction corresponds to the following sch-e e: l . t ROH . -SiOH ÷ SιCl 4 ^ -SiO-SiCl 3 -SiO-Si(0R) 3 • " In a 1 liter flask there was boiled for 5 hrs a mixture of 500 ml . of anhydrous benzene, 240 ml of SiCl and 30 g of AΞRCSIL-38σ (De¬ gussa) . Then, the .solvent and the excess SiCl, were distilled off and evaporation was completed by heating 2 hrs at 50°C under 14 πfaar for fully removing volatile materials. Then 70 g of n-decanol were 30 added to 10 g of the silica thus modified and, after 2 - 3 hrs at 70 - 90 β C, the pressure was dropped to 20 - 30 mbar for coroletely expelling the B 1 formed. After cooling, ether was added as describ¬ ed before (see under part A) and the product was centrifugated and washed twice with ether. After drying in air 10.7 g of grafted si- 35 lica were collected. With n-hexyl -and oleyl alcohols, corresponding results were ob¬ tained. B. Reaction with chlorosi.lanes: ' Tw-enty five g of AEECSIL-380 were heated to ref.lux for 5 hrs with 500 ml of anhydrous chloroform and 25 ml of trichlorovinylsi- lane or dichloromethylvinylsilane. Then, the solvents and excess vo¬ latile reagents were evaporated under vacuum. Alkylation of the re¬ sidue was achieved by heating for 2 hrs with 200 ml of ethanol. Then the reaction mixture was centrifugated -and the residue was purifi¬ ed by extracting with ether (5 hrs) . This method provided a graft- ed silica of excellent whiteness, analogous results were obtained by replacing trichlorovinylsilane by trichlorαnethylsilane. C. Condensation with sil-anols: Forty g of y-methaeryloxypropyl-trimethoxysilane (product A-174, Union Carbide) were stirred at room teiroerature in one liter of wa¬ ter acidified with dilute acetic acid to i 3.5. An eπiαlsion which first appeared in the flask dissolved progressively during hydroly¬ sis. After 1 - 2 hrs stirring, there were added, when the solution became clear, 40 g of silica aerosil 380 and the mixture was stir¬ red for an additional 15 hrs at room temperature. The suspension which had become thicker with time was centrifugated and the solid was dried overnight at 80 - 100"C under vacuum. Then the roedified silica was milled in a Waring blendor and heated another 2 hrs a * t 110 β C under 14 - 20 mbar in order to complete dehydration and condensation of the remaining free silanol groups of the grafts with neighbour si¬ lanol groups of the particle network. The organic content of the graft¬ ed 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 org-anophilic silica from the following grades: AEROSIL 130,200, 300,380 and CAB-Q-SIL M-5 and H-5. By this method, 40 g of starting silica furnished 54 - 57 g of silica grafted with oxy-silicc-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-methacrylo«ypropyl-ethoxy-dimethoxysilane (No. A-175, Union C≥rbidε); -^lycidoxypropyl-trimethoxysilane (No. A-187, Union Carbide); (3,4-epoxy-_yclc*exyl)*^thyl-trimethoxysilane (No. A-186, Union Carbide); i-sobu * tyl-trimethoxysilane (DϊNASILANE, IBIMO) and octyl-triethoxysilane (DYNASILANΞ, OCEEO) . D. "Physisorption" with trialkoxysilanes. In a 1 liter flask, there was heated 5 hrs to the boil a mixt¬ ure of pyrcgenic silica (Aerosil 380) (25 g) , A-174 (Union Carbide) (25 ml) and anhydrous xylene (500 ml) . Ωie mixture was centrifugat¬ ed and the solid residue was taken into fresh xylene and again cen- trifugat.ed. 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 following tri- alkoxysilane products (defined above): A-175, A-186 and A-187, as well as with γ-aminopropyltriethoxysilane (A-1100) all from Union Carbide. Results were similar except for the color of the treated silica (brα with A-175 and pale yellow with A-1100) . The other mo¬ dified silicas were colorless. A sample of silica modified with A-174 (methycryloxypropyl group) (10 g) was mixed with 3 g of methyl methacrylate, 60 g of xylene and 0.05 g of lauroyl peroxide after which the mixture was refluxed for 4 hrs. Thereafter, the doubly modified silica was purified by .suc¬ cessively centrifugating with xylene thr-ee times. 2. Preparation of coπpositions according to the invention ' A. B_r means of silica grafted by chlorination and alkylation. There were used several types of organophilic silica obtained according to the procedure described hereinbefore under paragraph l.A. which were dispersed as indicated in the first part of this spe- cification, to various solid concentrations into tri____ethylol-propa- ne triacrylate (TKPTA) containing 2% of diethoxyacetophenone (DEAP) . Compositions having different viscosities were obtained the rheolo- gical properties of which were either Newtonian or thixotropic de¬ pending on the ca-ses. The data about such cαipositions are gather¬ ed ift Table HI below. In this Table, the following data are provid¬ ed: the type of alkylating alcohol used, the concentration of the silica in parts by weight relative to the MPTA (the total of the parts being 100) , the refraction index of the organic mixture of the coirpositions, the viscosities and the rheologic-al properties. TABLE III Table IV gives indi-cations similar to that of Table III regard¬ ing silica activated by SiCl..than .alkylated by method A' or by means of silica grafted with tetrachlorosilane then -alkylation of th " e chic— r.inated intermediate. TABLE IV Cαroosi-f -alcohol Silica (A-380) "n 20" Viscosity (Properties tion no. (parts by (cP) weight) Decanol 16 1.4715 830-930 Fluid Oleyl alcohol 13 Thixotropic B. By means of silica grafted with chlorosilanes th<≥n alkylat¬ ion of the chlorinate intermediate. There was proceeded as disclosed in paragraph 2.A. and ccπ o- siticns were prepared by mixing various lots of silica (made hydro¬ phobic by method l.B.) in TMPTA with 2% DEAP. Table V summarizes the tested compositions and indicates, in turn, the type of chlorosila- ne used foe modifying the silica, the allylating alcohol, the levels of silica fillers in the coπpositions, the refraction index, visco¬ sities and properties of the coπpositions. TABLE V Composi¬ ' Chloro- Alcohol Silica "n 20" Visco¬ ' Properties tion No. silanes (parts sity by (cP) weight] 1 trichlo- ethanol A 380 1.4525 260-270 Fluid rovinyl (40) silane 2 trichlc- ethanol A 380 1.4634 1150-1490 Fluid rovinyl + (33) silane water 3 trichlo- ethanol A 200 1.4730 1150-1600 Fluid rovinyl + (18,4) silane water 4 dichlo- ethanol A 380 1.4636 240-230 Fluid rαnethyl (20) vinyl s: Llane 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 ^-metha- cryloxypropyl-trimethoxysilane (A-174) . Table VT hereinafter summa¬ rizes the various parameters relative to such compositions and in¬ dicates 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 properties of the cαnpositicns which also contained 2% by weight of diethoxyacetophenone photoinitiatσr. The three first compositions of this ' Table distinguish themselves frαπ each other by the hydrophilic mcdificatiαn conditions: composition 1 contains a silica treated with a 1 percent aqueous solution of a-174, ccπpo- sitϊcπ. 2 contains a silica treated with a 4 percent aqueous solut¬ ion of a-174 after 18 hours of hydrolysis, and composition 3 a si¬ milarly treated silica except that hydrolysis was for only 20 in. TABLE VI TABLE VI (Cont) 13 . 210-215 Newtonian 14 140 Newtonian 15 Very fluid and Newtonian 16 Very fluid and Newtonian D. Silica grafted by "physisorpticn": Preparation of the corre.sponding coπposition was carried out exactly as for ' the previous compositions of Tables III to VI. The various parameters pertaining to these coirpositions are greuped in Table VII hereinafter. These parameters ccπprise, in turn, the ty¬ pes of organosilanes used for the "physisorption", the amount of si¬ lica (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 of moncmers used, the refraction index V, the viscosity of the mixture -and its rhec— logical behavior. All the ccπpositions also contained 2% by weight of diethoxyacetophencne -as the photoinitiator. The four first cαroositions of Table VII differ frcm each other by the following points: In the first (No. 1) , silica has been ma¬ de organophilic siπply by the indicated treatment (all the other sam¬ ples starting frcm the fifth were also treated likely) . Goπposition No. 2 -contains silica which, after physisorption, was subjected to a second activating modification by thermal ccpolymerization with methyl ethacrylate as indicated in the last paragraph of section I.D.* hereinabove- Coroositions 3 and 4 contained silica products that were similarly doubly modified with the A-174 monomer and butyl acry- late, respectively. TABLE VII Cαipositions represented in Tables III to VII have, depending on the cases, a Newtonian (fluid) or thixotropic behavior . For em¬ bodying the invention, composition with newtoni-an properties are pre- ferred since they more easily form thin films with well controlled characteristics. Generally, the .smaller the silica particles (or alu¬ mina particles) and the greater the organophilic properties there¬ of * (in proportion to the degree of grafting and to the length and the number 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 cαipositions in¬ creases with increasing size of the particl≤s and increasing solid concentration in the mixture. With respect to the clarity of the -compositions containing or¬ ganophilic silica, it is advantageous to use mixtures of monomers with .an index of refraction as near as possible to that of said si¬ lica. It should be pointed out in this connection that the organo¬ philic modifying treatments used in this invention do not necessa- rily lead to silica products with every time the same refraction in¬ dex. However, this index remains most of the tins reasonably close to the 1.4740 - 1.4750 range. Thus, it may happen to be useful to adapt, from case to case, the refraction of the organic mixture to that of the selec ^ silica. In this regard, it is reminded that if the difference between the indices (that of the organic phase and that of the silica) becomes too great, the coπposition becomes mil¬ ky and the ooatings obtained therefrαn are not perfectly clear. Quan¬ titatively speaking, if cne uses 20 parts by weight of organophil¬ ic silica (n - *** 1.4746} with 80 parts by weight of TMPTA (n = 1.4732) or a 1:1 mixture of PETIA and DΞ53A (n = 1.4746} , cne obtains a clear mixture. Contrariwise, in the same conditions but with either pure HDDA (n a 1.-4574) or DB3DA (1.4621), transluc-ent mixture will be ob¬ tained. The results in table Vila below obtained with the use of a si- lica, a-972, treated with a silicone coating coπpound containing less than four carbon atoms shew that this silica treatment dees not gi¬ ve satisfactory coating application behavior, even with low silica loading. TABLE Vila 3. Goiroositicns with alumina If, in the various methods for treating silica* described until new and in the methods for preparing the coating oorπpcsitions of the present invention with said organophilic particles, the silica part¬ icles are replaced by alumina of equivalent mesh size, similar re¬ sults are experienced except for the transparency parameter as al- ready explained. 4. Qbtention of abrasion resisting coatings For the coating experiments, organic glass plates ( 2 x 10 cm) were used namely of polymethylmethacrylate (ϊMMa) , polycarbonate (PC) , polyvinyl chloride (PVC) and CR-3^ (poly(diethyleneclycol) . -bis-al- lylcarbonate) . The plates were first washed with iscpropanol, then, thin layers (thickness 1 to 50 Aim) of the compositions listed in Ta¬ bles III to VII were applied on the plates by the ire-≥ns already en- tioned hereinbefore. Then, the saπples were irradiated with a 80 w/cm UV source for periods of 5 to 30 sec or more. Best optical proper¬ ties were obtained by pressing on the freshly coated plates a per- *^t)R£ fectly -smooth glass plate, i.e. by performing a "replica molding" of the coating by means of a glass mold. In this case, the exposu¬ re is done through the glass, the latter being eventually easily de¬ tached from the hardened film after cooling. 5. Measurements of the optical properties Bie 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 parameters were the percent transmission and reflectance (relative to a corre.sponding non-coated plate) bet- wean 800 and 400 nm with a PYE-UNI-CSM -spectrophoto eter. Results are provided in the following Tables: Table vm for the PC substrates ( AKROLO^ ; Table IX for the PMMa substrates " (PLΞXIGLA^ and Ta¬ ble X for the PVC substrates (T HU ^) . In the tables, there are provided, successively, the following data: a control sample uncoat- • ed, then saπples identified by the number given to the corre.spond- ing coπposition from Tables III to VII, the % of transmission at 800, 590 and 400 nm for said coatings (plus the substrate) , respective¬ ly, and the gain or the less relative to said control sample. TABLE VIII Table IX further lists a saπple, X, coated with a translucent film containing alumina. This film was prepared with a coπposition containing TMPTA and 16 parts by weight of A1 2 0 3 (total 100 p.b.w.), the latter having been made organophilic by the process disclos-ed under section A.l. + hexanol (analogy with composition 111-6} ; vis¬ cosity: '255 - 277 cP. A similar behavior was observed for a corres¬ ponding saπple containing silica activated by the process describ- ed under section C. TABLE IX TABLE X Composition Transmission (%) Gain or loss (%) No. at 590 nm 5 Control PVC TA IEQN® 83.2 - 83.3 0 10 VI 2 83.8 - 83.9 + 0.6 VI 4 82.5 - 82.6 - 0.6 VI 5 84.1 - 84.2 + 0.7 l VI 6 83.6 - 83.7 + 0.4 VI 7 83.3 - 83.4 ÷ 0.1 20 It is interesting to note frαr. the results of Tables VIII ?nd IX that the clarity of the coatings containing silica rendered or¬ ganophilic by "chemiaSorpticn", i.e. by the techniques described in sections A to C is better than the clarity of the coating contain¬ 5 ing silica modified by "Physisorpticn". 6. Measurements of abrasion resistance . For the abrasion resistance measurements, the same plates we- 0 re used which are described in Section 4 with a protective coating according to the invention. Ihe abrading device (Creusot- ire Ins¬ trumentation, Adamel-Ihσmargy, France) comprised a rubbing shoe (1 x 1 cm; 2 kg) moving alternatively forward and backward on the sam¬ ple by means of a crankdrive and the rubbing surface of which was " 5 provided (stuck with tape) with a patch of steel wool (Taπpon GΞX) . The operating parameters of this testing were: displacement aπpli- tude: 4 cm; frequency: 1.4 HZ; nurcber of cydes: up to 500. Table XI provides the results obtained for saπples of polycarbonate (MAK- PO CS^ , PMMa (PLEXIGLASS) , CR-39& (PPG) , Polyurethane (SE2URIFLΞ of St. Gbbain) and 5LQAT glass as w-ell as for the coatings of the invention applied on seme of the above substrates (thicknesses 5 - 20 urn) . de abrasion effect is expressed as the loss of optical trans¬ mission (less of gloss) after a number of abrading cydes. TABLE XI The results of Table XI show that> with the exception of com¬ position VI-9, all coatings according to the invention provide an excellent protection against scratches. The protection offered by the coating containing alumina (sample X *^^0 3 ) is even better sin¬ ce no optical tr-aπaSmission loss was evidenced after 100 rubbing cy¬ cles. However, account should be taken that silica hardness is on¬ ly 820 Kπoop whereas that of alumina is 2,100 Kncop. 7. Resistance to corrosion by org-anic solvents ■ For testing the resistance of the present coatings to solvent attack, the steel wool used in the device of the previous test was replaced with a porous plug soaked in the solvent to be tried. Af¬ ter 100 rubbing cydes, the possible transmission less of the sam- pie was coπpared to that of the same coating saπple not subjected to an attack by the solvent. The following solvents were tried and none had any effect on a PIΞXIGLA≤iS^ saπple protected by films from the coπpositicπs HI-2 and 5, VI-2 and VII-1, 5, 6 and 7. In contrast, a nak- a ≤d PIΞXIGLAS© plate suffered a 47.6% loss under the same ccn- diticns when subjected to chloroform. Solvents tried: heptane/tolue¬ ne (70/30); toluene, acetone chloroform; tetra-chlorcethylene/trichlo- rcethylene (60/40) ; heptane/trichlorethylene/toluene (1550 35) . 8. Resistan-ce to surfactants solutions Saπples to be tested were ' iiππersed for variable periods into 1% aqueous TΞEPOlC (an alkyl-aryl-sulfonats) at 20 - 30 β C, then they were left to dry in air after which they were deaned with a moist doth. It was noted that the same saπples mentioned above under sect- ion 7 had only a 0.8% optical transmission loss after 864 hrs of im¬ mersion and that the films had no taidency to loosen frcm the sup¬ port. 9. Resistance to heat For this test, the saπple is subj-ected to conditions reproduc¬ ing normal operating conditions for vehide head-lights cover glas¬ ses: 1 day in a moist atmosphere at 18 - 28°C and 16 hrs in a dr atmosphere at 115°C. In the present case a polycarbonate projector glass (type Ξ-2, SEV Marchal) was protected with a film frcm compo¬ sition VII-1. After 16 hrs in the oven at 115°C the coating was not cracked, nor flaked off and had no visible deformation. 10. Resistance to shock A steel ball (13.6 g, 015 mm) was dropped from a height of 9 m on a projector glass protected as descr bed in the previous section. The velocity at the hitting point was 13.28 m/sec. After the shcck, the coating did not crack or peel off (composition VTI-1) . 11. Resistance to weathering A photopolymerizable anti-abrasive cαrposition was prepared by mixing together 333 parts of ΞBEC HJ^ 220 (see Table I) and 666 parts of diethylene glycol diacrylate (DΞΞDA) . Tb this mixture were added, and all ingredients were milled t-cgether overnight in a glass jar with glass beads, variable amounts of grafted silica (prepared ac¬ cording to the method described under section l.C) , variable amounts of a photo-initiator (DV-Harter-1116 from Merck) and variable quan- titles of a range of OV stabilizers. Suc stabilizers were select¬ ed from commercially available stabilizers as listed below: the TI- -NϋvTlI stabilizers made by the ttBA-GEIGX Company and induding the TΩTO EP^OO, -P,-328. The D I DI^ stabilizers sold by the BASF-Svyan- dotte Company; the ϋVINDL stabilizers are mostly benzcphencne deri- vatives and are detailed in a Data sheet frm the BASF WΪAND3ITE COEP. , Parsippany, N.J. 07054 called "WINUlID DV Absorbers for cos¬ metics, Plastics, Coatings and Textiles". The absorbers tested in¬ cluded the following types of N-539; D-49. Phenyl salicy- late was also included in the UV ab-sorbers tested. Ihe respective quantities of grafted silica, photo-initiator and the various sta-~ bilizers are given in % by weight with respect to the above coπpo- sitiαn. After filtering the coπpositiαi on a nick-el mesh (25 si) , films of such expositions (10 - 50^α thick) were applied on standard po¬ lycarbonate plates (7.5 x 15 cm) and irradiated with a 60 W/cm W light source placed 30 cm frαn the film. IXiring irradiation, a 4 mm 5 thick glass plate was interposed between the -source and the s-aπple plates to evenly distribute the light energy. Irradiation times we¬ re 30 sec ( - j -and 60 sec (T 2 ) ♦ The coated saπples were then subjected to an accelerated weather¬ ing test in a "Q-ϋV accelerated Weathering Tester (the Q-Panel Gom- 10 pany, Cleveland OHIO) . This test consists in subjecting the saπples to very strong DV irradiation from fluorescent UV lanes under alter¬ nating cαnditins of dry and humid heat (1 cyde = 8 hrs under W at 70°C dry followed by 4 hrs UV at 50 β C under condensating hurtidi- ty -conditions 100% r-elative humidity) . After intervals, the samples ■15 were examined for the advent or formation of crazing (cracks) , de- wetting (separation of the film from substrate) , chalking and other gener-al 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 20 knife so as to provide cri-ss-cross stripes about 1 mm wide thus de¬ fining a plurality of little film squares like a chequer bo-ard; the- n a piece of scotch adhesive tape i≤ press-ed over che test area and therea ter lifted whereby sαπe of the little -squares will be remov¬ ed if adhesion of the film on the substrate is low. The conditions •25 for passing the -above weath-ering test were that no trace of any de¬ ficiency (in connection with the 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 saπples had failed at the 30 end of the 168-hour -exposure period. The first column of the weather¬ ing test data (table XII) shows -an x for each coating that was rat¬ ed failed at the end of the 336-hr. period, the second column simi¬ larly shows which coatings were rated failed at the end of the 504-hr. period, and the third column likewise shews those rated failed at 35 the end of the 672-hr. period. Only one coating was considered to have pass-ed the 672-hr test no.658 gg't2. The other columns of the Table pertain to the other aforεdescribed composition parameters^ TABLE XII Saπple sio 2 Photoiniti Stabilizer Weathering test - ϊ .EA C-MPI TABLE XII (Cant) * Coating considered to have passed the 672 hrs test. 12. Cαroarative testinσs Further testings were dene with films (about 5 . to 30 μ thick of the coπposition disclosed in the previous Exaπple deposited on polymethacrylate (IMMA) and polycarbonate (PC) organic glasses. The coπposition contained 20% by weight of the grafted silica, 2% of the photoinitiator (DV-Harter-1116) and 2% of a ϋVINUL** weathering sta- bili2er. Ihe tests to which the samples were submitted are listed below. i: Adhesion after c-uring; cross-hatch scotch-tape test (tech¬ nique and passing criteria were described in the previous Ξxaπple) , ii: Pencil hardness: pencil lines are drawn by hand on the sam¬ ple by holding the pencil at 45° angle and pushing forward. Pencil hardness grades 2 H to 9 H. No mark should be visible for passing, iii: Flexion (GIB test) : In this test, the saπple (150 x 25 mm) is supported horizontally on two blocks (with -rounded corners) se¬ parated by a distance of 125 mm. Then a force is applied in the cen¬ ter of the .saπple that produces a bending the central extent of which (relative to the horizontal) is measured. Ihe 25 ram and 50 mm deform¬ ation are recorded in terms of the coating asp-ect after returning to horizontal i.e. the look for creases, crazing, peel-off, opales- cence, etc. No such defect should be visible for passing. iv: Heat resistance: the saπple is heated in an oven for one hour at 115°C. Then surface examination is done as above. v: 'Bnermoforming: A coated plate saπple (75 x 140 mm, 1 mm thick) is heated in an oven to its softening point (glass tr-ansition tem¬ perature) , then it is bent until forming a cylinder with the oppo¬ site shorter edges touching. After cooling, the surface of the ri- gid 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 saπple is layed on the table and a diamond point with a 270 g load is fixedly applied on it by its cwn weight. The saπple is then gently pulled so that the point will dig a groove in the saπple surface the width of which is inversely proportional to the surface resistance to scratching. T £ O PI ' The width of the groove is recorded vii: Taber abrasion test (ASTM) : The test saπple is placed o a horizontal turn-tahle and two free spinning flat edge abrasive rol lers held on a fixed horizontal axle are applied on the saπple i a manner such that, upon rotation of the table, the rollers will b driven to spin by friction with the saπple surface. The rollers ar loaded with a 500 g weight and since they are radially symmetrical¬ ly disposed with reg-ard to the turn-table center, they will provi de an annular abraded zone cn the sample after seme time of operat ion. The number of cydes is 500 after which the less of tran.sp.aren cy of the abraded area is measured in an apparatus for measuring dif fusion of light and expressed as a percent attenuation of visibili ty by diffusion. viii: GIB abrasion test: In this test, a seven inch di-amete org-anic glass lens protected by a scratch-resistant coating to be tested (such kind of lens is used in automotive light equipment) i subjected to rubbing with an alternatively moving shoe applying o the horizontally layed anti-scratch surface. The contact surfa-ce o the shoe is provided with a cloth dusted with quartz powder (UTA powder) . The load on the shoe is 2N απ 2 .and the nisόer of rubbin cycles is 100. She abraded area is then examined for diffusion (4D) and light tr-an-smisson (ΔT) as above. Results are expressed in "di git units" being known that the lewer the "digits" value, the mor abrasion resistant the saπple is ix: Water iπmersicn test: The saπples were iπmersed in 1% TEE POL a.queous solution at 65°C. Ihey were remove at intervals and tεst d for adhesion (cross-hatc__h) . The number of hours before failur is re-corded as the merit index in this test. x: Accelerated weathering resistance: This is the Q-UV test des cribed in the previous Example. -The aforedescribed tests were applied to the sasgl.es of the in vention and, simultaneously, to saπples of PC protected by a cαrrcner cially available anti-s-cratch ccπposition labelled G5/SHC-1000. Th data pertaining to that coπparable material and to the saπples o 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 EMMA -and EC unless separately mentioned. TABLE XIII Data & Tests Coatings of ' GΞ/SΞC-1000 the invention an PC Composition before curing resin content 80% 20% solvent none methanol-isobutanol flash-point > 130°C 26°C (PenskeH^rkens) density (g/cπr*") 1.1 - 1.3 • 0.91 pH neutral to mildly alcaline shelf-life >6 months at 2 months at 4°C 23°C in the dark viscosity 100 - 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, flo or spay air dry¬ ing 30 min scratch resistant spray, brush. dip, flow, spray layer roll, doctor air drying 20 min blade replica coating curing 30 - 60 sec UV 60 min 120 - 12S°C . no heat Film data density 1.2 - 1.5 g/cm 1.45 g/cm-ai thickness 5 - 30 ^ 5.1 U ..C PI TABLE XIII (Cant) e.sts i passed pass-ed ii PC< 6 H < 6 H 11 PMMA> 8H<9H > 6 H iii (25) pass pass (50) pass pass iv PC pass pass V -?b2 J Α pass 7 vi PC 50-75/2 150 - 200/α vii 18 - 19 20 - 21 viii Δ Ώ = 30 - 40 ΛO = 50 - 80 _ _ = 8 - 16 < 4 =^7Q ix PC > 600 hrs PC passed 500 hrs X 500 - 672 hrs up to 500 hrs The results of T&ble .XIII show that the scratch resistant films obtained from the cαrposition behave equally or better than coπpar rable ccπmercially available material. However, being applicable as a one layer coating the .σcπposition of the invention is more siπple to use than the two layers commercial coπposition.

Claims: What is claimed is: " 1. A photopolymerizable coπposition to be applied on a substra¬ te to provide thereon a translucent or transparent abrasion and weath- er and solvent resistant coating, this ccπposition containing essen¬ tially an organic phase consisting of one or more photopolymeriza¬ ble monomers or prepolymers, one or more photoinitiators and a mi¬ neral charge of finely divided silica or alumina, the particles of which are carrying, grafted on seme of the oxygen atoms thereof, subs- tituents of the formulae A-l (I) or Si -iA 2 (H) , wherein A-l repre¬ sents R or OR groups with R being a saturated or unsaturated subs¬ tituted or uπsubstituted hydrocarbon radical and 2 and 3 either represent oxygen atom bridges for connecting the Si atom of formu¬ la II to neighbor silicon or aluminum atαπs of 'the silica or alumi- na particles or they correspond to the same definition given for A* 1 , the R or OR groups in formula II being identical or different, whe¬ rein the total number of carbon atoms ccnprised by formulae I or II is four or more and wherein the refractive index "n" of the organ¬ ic phase is as close as possible to the refractive index of said part- icles of the mineral charge. 2. The ccπposition of claim 1, wherein the "n" value of the or¬ ganic phase is in the range + 2% from the value of the refraction index of the silica used. 3. The coπposition of claim 2, wherein "n" is between 1.45 and 1.48. 4. The coπposition of claim 1, wherein the size of the particles 5. The composition of claim 1, wherein R .is selected frcm the radicals n-hexyl, n-heptyl, n-cctyl, 3-butenyl, oleyl, acryloxy-al- kyl and methacryloxyalkyl in which the alkyl moiety has 2 to 6 C atoms, glycidoxypropyl, epoxycyclohexyl-ethyl and isobutyl. 6. The ccπposition of claim 5, wherein R is a methacryloxypro- pyl group which is further polymerized with an acrylic ester. 7. The coπposition of claim 1, wherein the percent weight of the organic substituents used for grafting the particles of the mi¬ neral charge relative to the weight of the particles themselves is 20% or more. 8. The composition of claim 1 coπprising, 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 ccπpo- 5 sition of claim 1, coπprising applying said coπposition as a thin film over said substrate and subjecting it to irradiation for caus¬ ing photocuring of said film. 10. The ethcd of claim 9, wherein the substrate is an organ¬ ic glass article. 0 11. A photopolymerized protective coating resisting abrasion which results frcm the irradiation of films made on substrates with the composition of claim 1, comprising 10 to 40% by weight of orga¬ nophilic silica and the visible light absorption of which does not exceed 10% of the light tr.ansmitted by the substrates protected by 5* said coating. 12. The coating of claim 11, the thickness of which is 1 to 50 / um. 13. An optical article coated with a protective film of the com¬ position of claim 8 the resistance of which, after photocuring, to 0 accelerated weathering is more than 672 hours.

Inventors: BELLMANN GUENTER, NGUYEN TAO VAN
Applicants: BATTELLE DEVELOPMENT CORP, BELLMANN GUENTER, NGUYEN TAO VAN, BATTELLE DEV CORP
Application year: 1982
Main classification: C09D3
IPC codes: C08F2, C08J7, C08K9, C09C1, C09C3, C09D4, C09D5, C09D151