Title of Invention	UV CURABLE METHACRYLATE SILICA BASED NANOCOMPOSITE SOL USEFUL FOR ANTI SCRATCH COATINGS AND A PROCESS THEREOF
Abstract	The present invention provides UV curable "methacrylate-silica" hybrid nanocomposite sol derived from tetraalkoxysilane and methacryloxyalkylalkoxy silanes and acrylate polymerization photoinitiator useful for the deposition of anti-scratch coatings. This invention also provides a process for the preparation of "methacrylate-silica" hybrid nanocomposite sol having longer shelf life and is useful for the deposition of anti-scratch coatings on the substrate like PMMA and other related plastics. Conveyorised UV curing machine was used to cure the coating materials. The high hardness of the cured coatings is due to the generation of glass-like dense silica nanoparticles in situ in the sol which remain bonded with the organic-silica polymer network after UV-curing.

Title of Invention

UV CURABLE METHACRYLATE SILICA BASED NANOCOMPOSITE SOL USEFUL FOR ANTI SCRATCH COATINGS AND A PROCESS THEREOF

Abstract

The present invention provides UV curable "methacrylate-silica" hybrid nanocomposite sol derived from tetraalkoxysilane and methacryloxyalkylalkoxy silanes and acrylate polymerization photoinitiator useful for the deposition of anti-scratch coatings. This invention also provides a process for the preparation of "methacrylate-silica" hybrid nanocomposite sol having longer shelf life and is useful for the deposition of anti-scratch coatings on the substrate like PMMA and other related plastics. Conveyorised UV curing machine was used to cure the coating materials. The high hardness of the cured coatings is due to the generation of glass-like dense silica nanoparticles in situ in the sol which remain bonded with the organic-silica polymer network after UV-curing.

Full Text	FIELD OF THE INVENTION The present invention relates to UV curable methacrylate silica based nanocomposite sol useful for anti scratch coatings. More particularly the present invention relates to 'methacrylate-silica' based nanocomposite inorganic-organic hybrid sol. The present invention further relates to a process for the preparation of methacrylate-silica' based nanocomposite inorganic-organic hybrid sol useful for the deposition of anti-scratch coating on a substrate like plastics. This invention provides an alternative process for making an inorganic-organic hybrid sol having glass-like dense silica nanoparticles generated in situ in the sol, and having a pH 0.8 - BACKGROUND OF THE INVENTION Transparent plastic materials are promising materials for optical applications. Some important properties are: (i) excellent optical clarity (ii) UV cut off (iii) light in weight (iv) can withstand much greater impact than glass etc. Such qualities offer a lot of industrial applications of plastics and presently glasses (including ophthalmic) are being replaced by transparent plastics (e.g. PMMA, PC, CR39® etc.). One of the main disadvantages of these plastics is that they are not scratch resistant enough; as a result their optical properties are being deteriorated very quickly due to surface damage. This problem may be alleviated by coating the plastic surfaces (in the form of sheets, ophthalmic lenses or other shapes) with an abrasion and stain resistant thin film that commonly is known as a hardcoat. Present published literature shows that some sol-gel hybrid materials exhibit abrasion resistance in addition to optical clarity: Schmidt and co-workers reported thick films of ORMOSILS (organically modified silica) on plastic substrates as a abrasion resistant coatings (H. Schmidt, B. Seiferling, G. Philipp, K. Deichmann, in Ultrastructure Processing of Advanced Ceramics, III, eds. J. D. Mackenzie, D. R. Ulrich, Wiley, New York, 1988, p 651; H. Schmidt, G. Rinn, R. Nass and D. Sporn, in Better Ceramics Through Chemistry III, eds. C. J. Brinker and D. R. Ulrich Mat. Res. Soc., Pittsburgh, Pa, 1988, p 743; R. Nass, E. Arpac, W. Glaubitt, H. Schmidt, J. Non-Cryst. Solids 1990, 121, 370; H. Schmidt, J. Non-Cryst. Solids, 1994, 178, 302). These films were prepared by a combination of silicon alkoxide like tetraethyl orthosilicate (TEOS) and epoxy functional group containing organic chain bonded with silicon alkoxides like 3-glycidoxypropyl-trimethoxysilane (GLYMO). They cured the coatings at temperatures 120° and 130°C for 3 h, which are not suitable for CR-39®, PC or PMMA substrates because at this temperature either yellowing (CR-39® /PMMA/PC) or softening (PC) results. The hardness and abrasion resistance of organic polymer coatings is improved by mixing an inorganic oxide, such as silica, boehmite nanoparticles etc. with the composition that is used to form the coating. These compositions may be thermally cured or may be cured by ultraviolet radiation depending on the polymer that is used. Film coatings produced with such compositions are clear provided the individual silica/boehmite particles are well dispersed and smaller than the visible wavelengths of light. Etiente et al also reported preparation of coatings from similar systems and also containing colloidal silica. They also used relatively high temperature (100°C) and time (3h) to cure the coatings. Schmidt and co-workers developed boehmite nanoparticle incorporated inorganic-organic hybrids (epoxy-silica-boehmite or methacrylate-silica-boehmite) to enhance the scratch resistant property of the coatings (see for examples H.K. Schmidt, J. Sol-Gel Sci. and Tech. 1997, 8, 557; S. Sepeur, N. Kunze, B. Werner, H. Schmidt, In Coatings on Glass 1998. Pulkar, H.; Schmidt, H.; Aegerter, M. A. Eds. Proc. 2nd International Conference on Coatings on Glass, 1998 (Saarbruecken, Germany) pp 319-322, H. K. Schmidt, E. Geiter, M. Mennig, H. Krug, C. Becker R.-P. Winkler, J. Sol-Gel Sci. and Technol., 1998, 73, 397; M. Mennig, P. W. Oliveira H. Schmidt, In Coatings on Glass 1998. Pulkar, H.; Schmidt, H.; Aegerter, M. A. Eds. Proc. 2nd International Conference on Coatings on Glass, 1998 (Saarbruecken, Germany) pp 328-332. In these works also no data regarding the stability of the sols with respect to time is reported. In another work Schmidt pointed out that a curing temperature in the range 130-150°C is necessary for obtaining ultra hard coatings, which is not at all suitable for PC or CR-39® substrates. Reference may also be made to our co-pending Indian patent application no. 744Del2003, wherein we have reported preparation of UV curable hard coatings on polycarbonate substrates using boemite nanoparticle incorporated epoxy-methacryloxy silanes and described that the composition is stable for the deposition of coating for longer time period. However this composition is not very suitable for PMMA or CR-39® substrates. The amount of silica / boehmite nanoparticles that can be added to a coating material for ophthalmic lenses is limited by the requirements of avoiding agglomeration of silica / boehmite particles and ensuring good dispersion so that the silica / boehmite particles will not be visible in the protective film. Polymer compositions that include colloidal silica are disclosed in many U.S. patents, several of which are mentioned hereafter by way of example. U.S. Pat. No. 4,499,217 discloses a dispersion of colloidal silica in a thermosetting polymer. U.S. Pat. Nos. 4,973,612, 5,075,348 and 5,188,900 disclose blends of multifunctional acrylates, unsaturated organic compounds and colloidal silica. U.S. Pat. No. 5,104,929 discloses a blend of colloidal silica in ethylenically unsaturated aliphatic and/or cycloaliphatic monomers. The compositions in the above refered U.S. patents do not have chemical bonding between the silica / boehmite nanoparticles and the polymer, and protective thin film coatings formed with such compositions tend to fail in a relatively short time. U.S. Pat. No. 5,426,131 discloses a composition that includes acrylic monomers, functionalized colloidal silica and acrylated urethane. U.S. Pat. No. 4,177,315 discloses the generation of silica within the composition by hydrolyzing tetraethyl orthosilicate and aging the composition followed by the addition of organic silanol compounds to modify the preformed silica. Abrasion resistant coatings derived from UV-curable organic monomer group (acrylic, methacrylic) bonded with alkoxy silane (e.g. 3-methacryloxypropyl-trimethoxysilane also known as MEMO, 3-acryloxypropyltrimethoxysilane etc.) and colloidal silica were also reported. Reference may be made to US patent 4,348,462, September 1982, R.H. Chung, 'Abrasion resistant ultraviolet light curable hard coating compositions' and US patent 5,086,087, February 4, 1992, A. Tosko Misev, 'composition containing UV curable unsaturated monomers and/or oligomers, a photoinitiator and colloidal silica with an oragnosilane compound, and the application of this composition in coatings'. The main disadvantage of these works is poor adhesionability of the coatings with polycarbonate substrates and a primer coat prior to this coating is necessary. Preformed colloidal silica particles are very porous and have a density that usually is in the range of 1.0-1.5 g/cm3 depending on the process used to form the particles where as fused silica has a density of 2.2 g/cm3. Because of the low density and porous nature of colloidal silica particles, thin film coatings formed from such compositions are not hard enough. For the above reasons, it would be desirable to have a film forming composition wherein a dense glass-like silica component is self-generated in situ within the solution during preparation of the composition, and is chemically bonded with the silica- organic polymer network of the solution on a molecular level to provide an essentially single phase state that has no interface problems. U.S. boehmite Pat. Nos. 4,173,490, 4,186,026 and 4,229,228 disclose compositions wherein tetraethyl orthosilicate, methyltrimethoxysilane and glycidoxypropyltrimethoxysilane are cohydrolized with water and acid, and wherein the amount of methyltrimethoxysilane is very high, such as about 50 weight percent. However, methyl is an inert organic group that dramatically reduces the possible degree of crosslinking bonds. Large amounts of methyl or phenyl groups commonly are included in these types of film forming compositions to reduce brittleness and minimize cracking at the sacrifice of film hardness. Decreased crosslinking reduces the density of a film formed by the composition so that it remains relatively porous and does not have optimum hardness. The absence of any curing compound also reduces the possible crosslinking reactions by silanol condensation and by ring opening polymerization of epoxy groups. Therefore, these compositions form thin films having a porosity such that the films also are readily tintable by conventional organic dyes. U.S. Pat. No. 4,547,397 also discloses a coating composition that includes tetraethyl orthosilicate, methacryloxytrimethoxy and/or vinyltriethoxysilane. Thin film coatings formed by this composition also do not provide optimum abrasion resistance to the surface. Recently US patent application no. 20020127330 discloses a thermally curable coating composition that includes tetraalkyl orthosilicate, epoxyalkylalkoxy silanes in combination with mathacryloxyalkoxy silanes having a pH range 4-6. They did not mention the stability of sol useful for the deposition of coatings and it is expected that at the above pH range silanol condensation reaction would be faster and stability of sol would be less. Furthermore two organic functionalities have been used in this composition, one of which (mathacryloxyalkoxy silanes) is commonly cured by UV light. So there is a possibility of existing monomeric methacryloxy groups in the coatings cured at 90-120°C. Furthermore, in this composition acetic acid has been used which may be entrapped in the coating after curing. Recently we observed glass-like silica particles could be generated in solution by hydrolysis and condensation reactions of tetraethyl orthosilicate (TEOS) in presence of any acid (inorganic or organic) at room temperature (G. De, B. Karmakar and D. Ganguli, J. Mater. Chem., 2000, 10, 2289-2293; B. Karmakar, G. De and D. Ganguli, J. Non-Cryst. Solids, 2000, 272, 119-125). We also noticed that dense silica nanoparticles formed first and then grow into larger glass-like dense silica particles. We also found that about one-third mole% of total TEOS has been transformed into dense silica glass nanoparticles and rest remains as soluble silica and growth of the particle occurs through deposition of soluble silica on the silica nanoparticles those are formed initially through acid hydrolysis of TEOS. Such dense silica nanoparticles bonded with silica network in combination with organic polymer-silica network should produce very hard and dense coatings on plastics after curing. Using this concept we were able to develop a composition (patent no. 346Del2003) based on 'epoxy-silica' hybrids where the in-situ generated SiO2 nanoparticles of diameter 3-26 nm are chemically bonded with the hybrid network. This composition is very suitable on CR39® grade plastics and hardness value of the coatings of the order of >6H was obtained. Although this composition is applicable on PMMA and PC, the adhesion characteristics of this composition with these surfaces are relatively weak. Further, we reported (Indian patent no 744Del2003) preparation of UV curable hard coatings on PC substrates using boemite nanoparticle incorporated epoxy-methacrylate-silica composites. This composition is stable for the deposition of coating for longer time period. Using this sol we have developed scratch resistant coatings on PC sheets of dimensions 2 feet x 2 feet using conveyorised UV curing machine. The hardness of the coatings deposited on PC is of the order of 4H. Both the adhesion and abrasion resistance properties of the coatings have passed following international standards. The coated PC substrates also resistant to 10 cycles of boiling salt solution test and thermal test. So this epoxy-methacrylate-silica-boehmite composite is very suitable for PC. However, this composition is not very suitable when applied on PMMA or CR39® grade plastics considering the hardness values of the coatings. The main drawbacks of the processes are: (i) The curing temperature is in higher side (ii) The 'epoxy-silica', 'methacryloxy-silica', 'epoxy-methacryloxy-silica' and 'methacryloxy-silica-boehmite' systems used by different workers did not mention the viscosity of the sol up to which it can be usable and also stability of the sol. (iii) The direct incorporation of porous silica nanoparticles could not produce high hardness of the coating. (iv) UV curable 'epoxy-methacrylate-silica-boemite' composite materials reported by us is stable with time and good quality abrasion resistant coatings could be obtained on PC substrates. This composition deposited on PMMA showed relatively poor hardness value, (v) Thermal curable good abrasion resistant 'epoxy-silica bonded with nano-SiO2' composition also reported by us is very suitable for CR39® grade plastics which shows relatively poor adhesion characteristics when applied on PC and PMMA. (vi) Colloidal silica incorporated acrylate or methacrylate-silica composite materials could not have good adhesion on PMMA and PC substrates, (vii) The thermal curable (90-120°C) composition 'epoxy-methacryloxy-silica' recently reported in a US patent application no. 20020127330 claims high hardness of the coating due to the generation of silica molecules in-situ in the sol. However, higher pH range shortens the shelf life of the sol. Furthermore, dual organic functionalities have been used in this composition, one of which (methacryloxy) is usually cured by UV light. Therefore, a hard coating composition that can be useful to prepare protective coatings on PMMA would be desirable. Considering the compatibility of PMMA, a methacrylate-silica based composition having glass-like dense silica nanoparticles chemically bonded with the hybrid network could provide an essentially a single phase state that has no interface problems when applied on PMMA resulting in a hard-coating with good adhesion and abrasion properties. OBJECTIVES OF THE INVENTION The main object of the present invention is to provide UV curable methacrylate silica based nanocomposite sol useful for anti scratch coatings. Another object of the present invention is to provide a sol having longer shelf life at least 40 days, at room temperature (25-35 °C), which could be increased further if the sol is stored in normal refrigerating condition. Yet another object of the present invention is to provide a simpler inorganic-organic hybrid composition suitable for UV curing. Yet another object of the present invention is to provide in-situ generation of glass-like dense silica nanoparticles in the sol, which are bonded and embedded in the polymethacrylate-silica network. Yet another object of the present invention is that the optical transmission of the coated PMMA does not deteriorate after curing. Yet another object of this present invention is that the sol could also be applied onto the other plastics like PC and CR39® Still another object of this present invention is to provide a process for the preparation of UV curable methacrylate silica based nanocomposite sol useful for anti scratch coatings. SUMMARY OF THE INVENTION Accordingly the present invention provides an UV curable methacrylate silica based nano-composite sol comprising methacrylate alkyl trialkoxysilane (MATAS) and tetraalkoxysilane (TAS) in a molar ratio of 7:3 to 3:7. In an embodiment of the present invention the methacrylate alkyl trialkoxysilane used is selected from the group consisting of 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane 2-methacryloxypropyltrimethoxysilane, 2-methacryloxypropyltriethoxysilane, 2-methacryloxyethyltrimethoxysilane, 2-methacryloxyethyltriethoxysilane and 2-methacryloxypropylmethyldiethoxysilane. In yet another embodiment the tetraalkoxysilane used is selected from the group consisting of tetra methyl orthosilicate, tetraethyl orthosilicate, tetra propyl orthosilicate and tetra butyl orthosilicate. In yet another embodiment the nanocomposite sol has the following characteristics: a) average particle size distribution is in the range of 27-50 nm, b) shelf life is about 45 days, c) viscosity is ranging between 8-40 cps. In yet another embodiment the nanocomposite sol as claimed in claim 1 is useful for the preparation of anti-scratch coatings. In yet another embodiment the an anti-scratch nanocomposite coating comprises 38-63 weight percentage of silica (TAS) and 37-62 weight percentage of polymethyacrylate (MATAS). The present invention further provides a process for the preparation of UV curable nanocomposite coating using nanocomposite inorganic-organic sol and the said process comprising the steps of: a) preparing nanocomposite inorganic-organic sol by mixing methacrylate alkyl trialkoxysilane (MATAS) with tetraalkoxysilane (TAS) in a molar ratio of 7:3-3:7 in an organic solvent, under stirring, for a period of about 15 minutes, b) adding a mixture of 0.5-0.9 mole water per mole of alkoxy group and 4.4 - 5.2 X 10™4 mole mineral acid (HCL) per mole of alkoxy group, under stirring, at a temperature of about 25-30°C to obtain a clear solution, followed by refluxing to obtain the hydrolyzed product, c) cooling the above said hydrolysed product to a temperature of about 25-30° C, followed by ageing for a period of about 20 hours, d) adding a polymerizing initiator into the above said ageing solution, under stirring, till the complete dissolution of the initiator and keeping it at a temperature of about 25-30° C, for a period of 2-3 days, followed by evaporation up to 10-12 wt. % with respect to the total sol, filtering the above said sol, followed by ageing at a temperature of about 25-30 0 C, for a period of about 4-6 days to obtain the desired coating sol, e) depositing the above said coating sol over a substrate and drying it, at a temperature of about 60-70° C, for a period of about 1 hour, followed by curing it under UV radiation, at energy of 2.6-2.7 J/cm2 and further curing it for a period of 40-60 minutes to obtain the desired coating on a substrate. In yet another embodiment the methacrylate alkyl trialkoxysilane used in step (a) is selected from the group consisting of 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane 2-methacryloxypropyltrimethoxysilane, 2-methacryloxypropyltriethoxysilane, 2-methacryloxyethyltrimethoxysilane, 2-methacryloxyethyltriethoxysilane and 2-methacryloxypropylmethyldiethoxysilane. In yet another embodiment the tetraalkoxysilane used in step (a) is selected from the group consisting of tetra methyl orthosilicate, tetraethyl orthosilicate, tetra propyl orthosilicate and tetra butyl orthosilicate. In yet another embodiment the the organic solvent used in step (a) is selected from the group consisting of n-propanol, n-butanol, ethanol, and methanol. In yet another embodiment the pH of the coating sol is ranging between 0.8 to In yet another embodiment the the acrylate polymerizing initiator used in step (d) is selected from the group consisting of benzoyl peroxide (Bz2O2), 1-hydroxycyclohexyl phenyl ketone (HCPK), Irgacure184, azobisisobutryro nitrile (AIBN) and a,a'-dimethoxyphenylacetophenone (Irgacure 651). In still another embodiment the the substrate used in step (e) is selected from the group consisting of polymethyl methacrylate (PMMA), polycarbonate (PC), plastic sheets and ophthalmic lenses. Detail description of the invention An optically clear protective thin film for polymeric sheets, lenses and other polymeric substrate surfaces (PMMA, PC, and other related plastics) has glass-like dense silica nanoparticles bonded with silica - polymethacrylate network. The improved film is formed from a coating solution that includes tetraalkyl orthosilicate, methacrylatealkylalkoxy silanes and solvents having a pH values 0.8- Glass-like silica nanoparticles have been generated in a silicon alkoxide -methacrylatealkylalkoxysilane combined sol. It is expected that these glass-like dense silica nanoparticles would remain chemically bonded with the silica-organic polymer network because a fraction of silicon alkoxide (about one third) is transforming to silica nanoparticles. Accordingly, in the present invention glass-like silica nanoparticles of a few nanometer size ranges are generated in the tetraalkoxysilane - methacrylatealkyl-trialkoxysilane derived sol and these silica nanoparticles remain bonded with the silica - methacrylate network formed during hydrolysis and condensation of alkoxy groups. In this process, the silica particles could not grow in to larger sizes because of the low pH of sol and presence of long chain organic moiety (methacrylatealkyl chain) which are not allowing the generated silica nanoparticles to agglomerate. This may also be noted here that MEMO:TEOS mole ratio has an effect in controlling the size of the silica nanoparticles in the sol (Table 1). As for example, the composition MEMO:TEOS = 7:3 (MT73 sol) generates SiO2 nanoparticles of mean particle diameter 49.5 nm where as the 5:5 (MT55 sol) and 3:7 (MT37 sol) mole compositions produce SiO2 nanoparticles of mean diameter 38 and 27.7 nm respectively. The particle size distribution was measured in a Malvern particle size analyser model ZETASIZER 1000 HS. The pH of the sol is lying in the range 0.8 to The important features of the invention are as follows: (a) obtaining a sol having a pH values 0.8- provide a better scratch resistant coatings by UV curing on PMMA substrate. (b) generation of nanometer sized glass-like dense silica particle from hydrolysis- condensation reactions of tetraalkoxy silane in presence of methacrlatealkyltrialkoxy silanes in situ in the sol. (c) use of one UV curable organic functionality group (methacrylate) remains in monomeric form in the sol, polymerizes only after exposition of UV-light on it. (d) maintaining of sol pH 0.8 to silica to slow down the -Si-O-Si- condensation, which controls the viscosity and increases further the shelf life of the sol. (e) no deterioration of optical transmission property of coated PMMA after UV curing. (f) compatibility of PMMA surface and the coating composition based on methacrylate organic functionality which gives better adhesion through vander Waal's force of attraction. (g) hardness of the coating is due to the presence of glass-like dense nanoparticles bonded and embedded in a highly cross-linked polymethacrylate- silicon oxide network. Other features, which have been realized by the present invention, are: (i) using tetraalkoxy silane and methacrlatealkyltrialkoxy silanes for making the hybrid sol and having a pH of 0.8 - (ii) In the sol in-situ generation of glass-like dense nano-silica particles in side the MATAS and TAS originated methacrylate (monomeric)-silica network at low pH which remain bonded with silica network and do not grow in size due to the presence of methacrylate (monomeric or polymeric) alkyl organic chains; (iii) final sol pH value close to the isoelectric point (IEP) of silica minimizes the rate of -Si-O-Si- condensation which increases the shelf life of sol; (iv) simultaneous polymerization of methacrylate unsaturation and further silanol condensation reactions during UV photo-curing helps in generating hard coatings having highly cross-linked polymethacrylate-silica network covalently bonded with silica nanoparticles. The process steps of the present invention are given below: (i) Mixing of methacrylatealkyltrialkoxysilane (MATAS) and tetraalkoxysilane (TAS) in organic solvent(s) with stirring (ii) Hydrolysis and condensation of alkoxy groups of MATAS and TAS by adding HCI - H2O mixture dissolved in organic solvents. (iii) Generation of glass-like dense nano-silica particles in side the MATAS and TAS originated methacrylate (monomeric)-silica network. (iv) Refluxing the above mixture for 30 - 90 min in the temperature range 78-81 °C (Table 2) at normal atmospheric condition. (v) Addition of methacrylate polymerization initiator with stirring at room temperature. (vi) After 2-3 days ageing at room temperature, 10-12 wt% solvent is evaporated out from the sol followed by another 4-6 days aging at room temperature. (vii)Deposition of coating on cleaned plastic (PMMA, PC, and other related plastics) ophthalmic lenses, sheets and other shapes by dip-coating technique. (viii)Drying the coating at 60 - 70°C for 60 min followed UV photo-curing (energy 2.6-2.7 J/cm2) 1-4 times each side and finally by curing at 90 - 100°C for 40-60 min. The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention. EXAMPLE-I Preparation of sol (MT-55 sol): UV curable hybrid coating solution was prepared by mixing 76.13 gm of 3-(methacryloxypropy)-trimethoxy silane, 63.84 gm of tetraethoxy orthosilicate and 35 gm of 1-butanol were mixed and stirred for 15 min. To this water (9.73 gm), HCI 0.1N, (10.30 gm), 1-butanol (14.0 gm) and methanol (14.0gm) mixture was added under stirring condition and stirring was continued for 3-5 min at room temperature (25±2 °C). The above solution was then refluxed for 90 min. and cooled down to room temperature, and this was kept at RT for 20 hours aging (over night). Then 0.160 gm of solid benzoyl peroxide (Bz2O2) was added directly into the sol with stirring. The complete dissolution of the initiator took 120 min. Then the sol was kept at room temperature for 2-3 days followed by the sol was evaporated 10-12 wt% with respect to the sol The sol was then filtered through whatman no. 1 filter paper and aged room temp (25-35°C) for about 4-6 days before coating deposition. EXAMPLE-II MT-73 sol: UV curable hybrid coating solution was prepared by mixing 103.00 gm of 3-(methacryloxypropy)-trimethoxy silane, 37.00 gm of tetraethoxy orthosilicate and 35 gm of 1-butanol were mixed and stirred for 15 min. To this water (8.89 gm), HCI 0.1N, 9.40 gm), 1-butanol (14 gm) and methanol (14 gm) mixture was added under stirring condition and stirring was continued for 3-5 min at room temperature (25+2 °C). This partially hydrolyzed alkoxide group's derived solution was then refluxed for 90 min. The solution was then cooled at room temperature, and this was kept at RT for 20 hours aging (over night). Then 0.2086 gm of solid benzoyl peroxide (62262) was added directly into the sol with stirring. The complete dissolution of the initiator took 120 min. Then the sol was kept at room temperature for 2-3 days followed by the sol was evaporated 10-12 wt% with respect to the sol The sol was then filtered through whatman no. 1 filter paper and aged room temp (25-35°C) for about 4-6 days before coating deposition. Coatings preparation/deposition: Cleaning of the substrates: Prior to coatings deposition, PMMA substrates are cleaned with neutral detergent followed by washing with tap water and rinsing with distilled water and finally wiping with soft tissue paper (Lotus® brand) soaked with ethanol. For polycarbonate sheets and related plastics are cleaned with neutral detergent, followed by washing with tap water and rinsing with distilled water and ethanol and finally 5 min in warm isopropanol. Coating deposition: Cleaned PMMA, PC and CR-39® are immersed into the coating sol and withdrawn at a rate of 10-20 cm/min from the sol perpendicular to the solution surface. Coating thickness was measured by surface profilometer (Kosaka, Japan). Curing of the coatings: As deposited coatings were first dried at temperature 60 - 70°C for 1h followed by UV cured 1-4 times each side using a conveyorized UV curing machine. Conveyor speed was adjusted in such a way that energy 2.6 - 2.7 J/cm2 each time on the sample is received. After UV curing the samples were kept at 90 - 100°C for 40-60 min. There are several standard tests that are used in the ophthalmic lens industry to quantify the abrasion resistance and adhesion of lens coatings, and a brief description of each test follows. (i) Abrasion test using a lens coating hardness tester This standard procedure is for evaluating the abrasion resistance of coated plastic sheets or lens. This test was performed using a US military specification lens coating hardness tester kit in accordance with MIL-F-48616. The kit contains one brass instrument with a spring that was calibrated for 2.5 Ibs of pressure. The eraser (rubber-pumice composite) inserts provided with the instrument are manufactured and certified to conform to US federal specification MIL-E-12397B. The test consists of rubbing across the coated surface with the eraser bearing 2.5 Ibs of pressure. The specification of this test is that the coated surface should withstand 20 cycles of rubbing (one way) with the eraser bearing 2.5 Ibs of pressure without any visual scratch. Isopropanol was used to clean the coated surface before and after tests. After tests the surface was cleaned and examined visually and with a profilometer (Kosaka, Japan). Tests were also performed on the uncoated substrate. (ii) Pencil hardness test (ASTM D 3363) The purpose of this standard scratch hardness tests is to determine the resistance of coating materials to scratch effect on the surface. Generally, scratch hardness is measured by moving a sharp object under a known pressure over the surface. The result may be either pressure require to scratch through the test materials if a scratching tool of constant hardness is used , or the hardness is used of the scratching tool is varied while constant pressure is applied. Value is given according to grade of pencil such as 9B-9H. For testing the sample, first pencil is inserted then it must touch the test surface, and is tighten the lamping screw. Then pencil is moved over the surface about 6-12 mm under a fixed load of 750 gm and a fixed angle of 45 degrees. The test is repeated using successive grade pencils where one does not scratch and next one does scratch. The pencil grade for which it does not scratch the sample is the value of hardness. (iii) Cross cut and adhesive tape test following DIN 53151 or ASTM D 3359 This standard procedure is for evaluating the adhesion of a hardcoat on a substrate like sheet or lens. Using a cutting device such as a razor blade, six parallel cuts 1.5 mm ± 0.5 mm apart and approximately 15 to 20 mm in length are made in the coating on the front or convex surface of the lens. Another six parallel cuts 1.5 mm ± 0.5 mm apart are made in the coating perpendicular to the first set. This forms a cross-hatched pattern of squares over which tape is applied, such as Birla 3M Scotch Magic Tape #810. The tape then is pulled rapidly as close to an angle of 180° as possible, and the percent adhesion is quantified by the amount of coating removed from the squares in the cross-hatched pattern. The 180° reference means that the tape is pulled back over itself in a direction that is nearly parallel to the substrate surface. (iv) Boiling Salt Water Test This standard procedure evaluates the ability of a hardcoat to adhere to a substrate (sheet, lens or other shape) and the susceptibility of the coating to crazing. A coated lens is subjected to three to ten cycles of thermal shock by submersing the coated lens for two minutes in a boiling salt water solution which comprises 3.5 litres of deionized water, 157.5 grams of sodium chloride, and 29.2 grams of sodium dihydrogen orthophosphate, followed by submersing the coated lens for one minute in water at 24±2°C Coating performance is quantified by whether or not coating layer detachment or complete delamination from the substrate occurs, and by whether or not crazing of the coating occurs. The resultant coatings of 4-10 µm in thickness are optically transparent having refractive index of 1.489 - 1.492 and showed good abrasion and other properties as follows: (i) Optical transmission The optical transmission of the coated PMMA does not deteriorate after UV curing. Similar result is obtained in case of coated CR-39® grade plastics whereas the optical transmission of PC is increased to 2-3% after deposition of the coating followed by UV curing. (ii) Adhesion property (DIN 53151 orASTM D 3359) Adhesion test by adhesive tape test shows no peeling off in any coatings deposited on PMMA, PC and CR39 grade plastics. The results of adhesion test by cross-cut and adhesive tape following DIN 53151 orASTM 3359 specification are as follows: the coatings deposited on PMMA shows no peeling off in cases of sols containing higher amount of MEMO (e.g. MT73) and it can be classified as ASTM class 5B (highest quality). But in case of coatings obtained from higher silica content in the sol (e.g. MT55 composition) it is classified as ASTM Class 4B. In cases of coated PC and CR-39® no peeling off result and therefore classified as ASTM Class 5B. Detailed results are given in Table 6. (iii) Pencil hardness value (ASTM D 3363) Coated PMMA shows pencil hardness value in the ranges 3H-5H depending upon the sol composition. The hardness value is increased with increasing the SiOa content of the sol. Similar result is also found in cases of PC substrates where hardness value is varied from 2H-5H. In case of CR-39® lenses a pencil hardness value close to 5H is achieved using MT55 sol. The detailed results are given in Table 7. (iv) Abrasion test (specification MIL-E-12397B) Uncoated PMMA is suffering from damage even after 1-5 times of abrasion whereas 20 abrasion cycles is the specification of this test. The coated PMMA showed resistant towards damage after 20 abrasion cycles. A very few scratches are however observed in case of coatings obtained from the sols containing higher amount of MEMO (e.g. MT73 composition. Similar result is also obtained in case of CR-39® lenses. Where as the coated PC showed resistance towards damage even after more than 50 times of abrasion. The detailed results are given in Table 8. (v) Boiling salt solution test Coated PMMA could resist up to 4 cycles of boiling salt solution test. After this few cracks are observed. Coated CR-39 could resist up to 3 cycles of such test. The coated PC sheet is however passed 10 cycles of boiling salt solution test. Table I: Particle diameter in size of different sols (measured Malvern particle size analyser ZETASIZER1000HS). (Table Removed) Table II: Refluxed temperature of the sol for different sol composition. . (Table Removed) Table III: Change in viscosity of the MT55 sol aged at room temperature (25-35°C). .(Table Removed) Table IV: Change in coating thickness with lifting speed (inches/min) at given viscosity for MT55 sol. . (Table Removed) Table V: Change of coating thickness with lifting speed (inches/min) at different viscosities for MT73 sol. . (Table Removed) Table VI: Cross cut adhesive tape test of the coated samples (ASTM 3359 or DIN 53151 specification). . (Table Removed) Table VI I: Pencil hardness test (ASTM D 3363) results obtained from uncoated and coated PMMA, PC and CR-39 grade plastic substrates. . (Table Removed) Table VIII: Results after 20 abrasion cycles (one way) using lens coating hardness tester following US specification MIL-F-48616 using eraser with specification MIL-E-12397B. . (Table Removed) The main advantages of the present invention are: (i) A UV curable coating sol suitable for deposition of anti scratch coatings on plastic substrates (PMMA, PC and related plastics) (ii) The shelf life of sol is at least 45 days (Table 1) when kept at room temperature (25-35°C) in closed condition. In this period of time the viscosity lies within 30 cps which suitable for obtaining good quality coatings. The coating can be done up to 40 cps of viscosity, however in such condition, lower withdraw speed is recommended in order to obtain coating thicknesses in the ranges 5-7 jam. Some representative results are given in Tables 2 and 3. Shelf life could be increased further if the sol is stored in normal refrigerator. (iii) Only two common types of precursor chemicals, silicon alkoxide and methacrylatealkylalkoxysilane are required. (iv) Incorporation of surfactants is not necessary. (v) Coating can be applied on different types of plastics. (vi) Highly dense, anti scratch coatings can be obtained on plastic ophthalmic lenses and sheets. (vii) Complicated shaped plastic ophthalmic lenses (e.g. bifocal D- or O-shaped lenses) can also coated without any problem. (viii) Still another advantage of the process is that the % transmission of coated PMMA and CR-39® does not deteriorate compared to that of uncoated substrates where as the % transmission of the coated PC is found to be increased by 2-3 %. We claim 1. A UV curable methacrylate silica based nano-composite sol comprising methacrylate alkyl trialkoxysilane (MATAS) and tetraalkoxysilane (TAS) in a molar ratio of 7:3 to 3:7. 2. A nanocomposite sol as claimed in claim 1 wherein methacrylate alkyl trialkoxysilane used is selected from the group consisting of 3- methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane 2- methacryloxypropyltrimethoxysilane, 2-methacryloxypropyltriethoxysilane, 2- methacryloxyethyltrimethoxysilane, 2-methacryloxyethyltriethoxysilane and 2- methacryloxypropylmethyldiethoxysilane. 3. A nanocomposite sol as claimed in claim 1 wherein tetraalkoxysilane used is selected from the group consisting of tetra methyl orthosilicate, tetraethyl orthosilicate, tetra propyl orthosilicate and tetra butyl orthosilicate. 4. A nanocomposite sol as claimed in claim 1 has the following characteristics: a) average particle size distribution is in the range of 27-50 nm; b) shelf life is about 45 days; c) viscosity is ranging between 8-40 cps. 5. A nanocomposite sol as claimed in claim 1 is useful for the preparation of anti- scratch coatings. 6. An anti-scratch nanocomposite coating as claimed in claim 5 comprises 38-63 weight percentage of silica (TAS) and 37-62 weight percentage of polymethyacrylate (MATAS). 7. A process for the preparation of UV curable nanocomposite coating using nanocomposite inorganic-organic sol and the said process comprising the steps of: a) preparing nanocomposite inorganic-organic sol by mixing methacrylate alkyl trialkoxysilane (MATAS) with tetraalkoxysilane (TAS) in a molar ratio of 7:3-3:7 in an organic solvent, under stirring, for a period of about 15 minutes, b) adding a mixture of 0.5-0.9 mole water per mole of alkoxy group and 4.4 - 5.2 X 10~4 mole mineral acid (HCL) per mole of alkoxy group, under stirring, at a temperature of about 25-30°C to obtain a clear solution, followed by refluxing to obtain the hydrolyzed product, c) cooling the above said hydrolysed product to a temperature of about 25-30° C, followed by ageing for a period of about 20 hours, d) adding a polymerizing initiator into the above said ageing solution, under stirring, till the complete dissolution of the initiator and keeping it at a temperature of about 25-30° C, for a period of 2-3 days, followed by evaporation up to 10-12 wt. % with respect to the total sol, filtering the above said sol, followed by ageing at a temperature of about 25-30 0 C, for a period of about 4-6 days to obtain the desired coating sol, e) depositing the above said coating sol over a substrate and drying it, at a temperature of about 60-70° C, for a period of about 1 hour, followed by curing it under UV radiation, at energy of 2.6-2.7 J/cm2 and further curing it for a period of 40-60 minutes to obtain the desired coating on a substrate. 8. A process as claimed in claim 7, wherein the methacrylate alkyl trialkoxysilane used in step (a) is selected from the group consisting of 3- methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane 2- methacryloxypropyltrimethoxysilane, 2-methacryloxypropyltriethoxysilane, 2- methacryloxyethyltrimethoxysilane, 2-methacryloxyethyltriethoxysilane and 2- methacryloxypropylmethyldiethoxysilane. 9. A process as claimed in claim 7, wherein the tetraalkoxysilane used in step (a) is selected from the group consisting of tetra methyl orthosilicate, tetraethyl orthosilicate, tetra propyl orthosilicate and tetra butyl orthosilicate. 10. A process as claimed in claim 7, wherein the organic solvent used in step (a) is selected from the group consisting of n-propanol, n-butanol, ethanol, and methanol. 11. A process as claimed in claim 7, wherein the pH of the coating sol is ranging between 0.8 to 12. A process as claimed in claim 7 wherein the acrylate polymerizing initiator used in step (d) is selected from the group consisting of benzoyl peroxide (Bz2O2), 1-hydroxycyclohexyl phenyl ketone (HCPK), Irgacure184, azobisisobutryro nitrile (AIBN) and ά,ά-dimethoxyphenylacetophenone (Irgacure 651). 13. A process as claimed in claim 7, wherein the substrate used in step (e) is selected from the group consisting of polymethyl methacrylate (PMMA), polycarbonate (PC), plastic sheets and ophthalmic lenses. 14. A UV curable methacrylate silica based nano-composite sol useful for the preparation of anti-scratch coatings and a process for the preparation thereof, substantially as herein described with reference to the examples.

Full Text

FIELD OF THE INVENTION
The present invention relates to UV curable methacrylate silica based nanocomposite sol useful for anti scratch coatings. More particularly the present invention relates to 'methacrylate-silica' based nanocomposite inorganic-organic hybrid sol. The present invention further relates to a process for the preparation of methacrylate-silica' based nanocomposite inorganic-organic hybrid sol useful for the deposition of anti-scratch coating on a substrate like plastics. This invention provides an alternative process for making an inorganic-organic hybrid sol having glass-like dense silica nanoparticles generated in situ in the sol, and having a pH 0.8 - BACKGROUND OF THE INVENTION
Transparent plastic materials are promising materials for optical applications. Some important properties are: (i) excellent optical clarity (ii) UV cut off (iii) light in weight (iv) can withstand much greater impact than glass etc. Such qualities offer a lot of industrial applications of plastics and presently glasses (including ophthalmic) are being replaced by transparent plastics (e.g. PMMA, PC, CR39® etc.). One of the main disadvantages of these plastics is that they are not scratch resistant enough; as a result their optical properties are being deteriorated very quickly due to surface damage. This problem may be alleviated by coating the plastic surfaces (in the form of sheets, ophthalmic lenses or other shapes) with an abrasion and stain resistant thin film that commonly is known as a hardcoat.
Present published literature shows that some sol-gel hybrid materials exhibit abrasion resistance in addition to optical clarity: Schmidt and co-workers reported thick films of ORMOSILS (organically modified silica) on plastic substrates as a abrasion resistant coatings (H. Schmidt, B. Seiferling, G. Philipp, K. Deichmann, in

Ultrastructure Processing of Advanced Ceramics, III, eds. J. D. Mackenzie, D. R. Ulrich, Wiley, New York, 1988, p 651; H. Schmidt, G. Rinn, R. Nass and D. Sporn, in Better Ceramics Through Chemistry III, eds. C. J. Brinker and D. R. Ulrich Mat. Res. Soc., Pittsburgh, Pa, 1988, p 743; R. Nass, E. Arpac, W. Glaubitt, H. Schmidt, J. Non-Cryst. Solids 1990, 121, 370; H. Schmidt, J. Non-Cryst. Solids, 1994, 178, 302). These films were prepared by a combination of silicon alkoxide like tetraethyl orthosilicate (TEOS) and epoxy functional group containing organic chain bonded with silicon alkoxides like 3-glycidoxypropyl-trimethoxysilane (GLYMO). They cured the coatings at temperatures 120° and 130°C for 3 h, which are not suitable for CR-39®, PC or PMMA substrates because at this temperature either yellowing (CR-39® /PMMA/PC) or softening (PC) results.
The hardness and abrasion resistance of organic polymer coatings is improved by mixing an inorganic oxide, such as silica, boehmite nanoparticles etc. with the composition that is used to form the coating. These compositions may be thermally cured or may be cured by ultraviolet radiation depending on the polymer that is used. Film coatings produced with such compositions are clear provided the individual silica/boehmite particles are well dispersed and smaller than the visible wavelengths of light.
Etiente et al also reported preparation of coatings from similar systems and also containing colloidal silica. They also used relatively high temperature (100°C) and time (3h) to cure the coatings. Schmidt and co-workers developed boehmite nanoparticle incorporated inorganic-organic hybrids (epoxy-silica-boehmite or methacrylate-silica-boehmite) to enhance the scratch resistant property of the coatings (see for examples H.K. Schmidt, J. Sol-Gel Sci. and Tech. 1997, 8, 557; S. Sepeur, N. Kunze, B. Werner, H. Schmidt, In Coatings on Glass 1998. Pulkar, H.; Schmidt, H.; Aegerter, M. A. Eds. Proc. 2nd International Conference on Coatings on Glass, 1998 (Saarbruecken, Germany) pp 319-322, H. K. Schmidt, E. Geiter, M. Mennig, H. Krug, C. Becker R.-P. Winkler, J. Sol-Gel Sci. and Technol., 1998, 73, 397; M. Mennig, P. W. Oliveira H. Schmidt, In Coatings on Glass 1998. Pulkar, H.; Schmidt, H.; Aegerter, M. A. Eds. Proc. 2nd International Conference on Coatings on Glass, 1998 (Saarbruecken, Germany) pp 328-332. In these works also no data

regarding the stability of the sols with respect to time is reported. In another work Schmidt pointed out that a curing temperature in the range 130-150°C is necessary for obtaining ultra hard coatings, which is not at all suitable for PC or CR-39® substrates.
Reference may also be made to our co-pending Indian patent application no. 744Del2003, wherein we have reported preparation of UV curable hard coatings on polycarbonate substrates using boemite nanoparticle incorporated epoxy-methacryloxy silanes and described that the composition is stable for the deposition of coating for longer time period. However this composition is not very suitable for PMMA or CR-39® substrates.
The amount of silica / boehmite nanoparticles that can be added to a coating material for ophthalmic lenses is limited by the requirements of avoiding agglomeration of silica / boehmite particles and ensuring good dispersion so that the silica / boehmite particles will not be visible in the protective film. Polymer compositions that include colloidal silica are disclosed in many U.S. patents, several of which are mentioned hereafter by way of example. U.S. Pat. No. 4,499,217 discloses a dispersion of colloidal silica in a thermosetting polymer. U.S. Pat. Nos. 4,973,612, 5,075,348 and 5,188,900 disclose blends of multifunctional acrylates, unsaturated organic compounds and colloidal silica. U.S. Pat. No. 5,104,929 discloses a blend of colloidal silica in ethylenically unsaturated aliphatic and/or cycloaliphatic monomers. The compositions in the above refered U.S. patents do not have chemical bonding between the silica / boehmite nanoparticles and the polymer, and protective thin film coatings formed with such compositions tend to fail in a relatively short time. U.S. Pat. No. 5,426,131 discloses a composition that includes acrylic monomers, functionalized colloidal silica and acrylated urethane. U.S. Pat. No. 4,177,315 discloses the generation of silica within the composition by hydrolyzing tetraethyl orthosilicate and aging the composition followed by the addition of organic silanol compounds to modify the preformed silica.
Abrasion resistant coatings derived from UV-curable organic monomer group (acrylic, methacrylic) bonded with alkoxy silane (e.g. 3-methacryloxypropyl-trimethoxysilane also known as MEMO, 3-acryloxypropyltrimethoxysilane etc.) and

colloidal silica were also reported. Reference may be made to US patent 4,348,462, September 1982, R.H. Chung, 'Abrasion resistant ultraviolet light curable hard coating compositions' and US patent 5,086,087, February 4, 1992, A. Tosko Misev, 'composition containing UV curable unsaturated monomers and/or oligomers, a photoinitiator and colloidal silica with an oragnosilane compound, and the application of this composition in coatings'. The main disadvantage of these works is poor adhesionability of the coatings with polycarbonate substrates and a primer coat prior to this coating is necessary.
Preformed colloidal silica particles are very porous and have a density that usually is in the range of 1.0-1.5 g/cm3 depending on the process used to form the particles where as fused silica has a density of 2.2 g/cm3. Because of the low density and porous nature of colloidal silica particles, thin film coatings formed from such compositions are not hard enough.
For the above reasons, it would be desirable to have a film forming composition wherein a dense glass-like silica component is self-generated in situ within the solution during preparation of the composition, and is chemically bonded with the silica- organic polymer network of the solution on a molecular level to provide an essentially single phase state that has no interface problems.
U.S. boehmite Pat. Nos. 4,173,490, 4,186,026 and 4,229,228 disclose compositions wherein tetraethyl orthosilicate, methyltrimethoxysilane and glycidoxypropyltrimethoxysilane are cohydrolized with water and acid, and wherein the amount of methyltrimethoxysilane is very high, such as about 50 weight percent. However, methyl is an inert organic group that dramatically reduces the possible degree of crosslinking bonds. Large amounts of methyl or phenyl groups commonly are included in these types of film forming compositions to reduce brittleness and minimize cracking at the sacrifice of film hardness. Decreased crosslinking reduces the density of a film formed by the composition so that it remains relatively porous and does not have optimum hardness. The absence of any curing compound also reduces the possible crosslinking reactions by silanol condensation and by ring opening polymerization of epoxy groups. Therefore, these compositions form thin films having a porosity such that the films also are readily tintable by conventional

organic dyes. U.S. Pat. No. 4,547,397 also discloses a coating composition that includes tetraethyl orthosilicate, methacryloxytrimethoxy and/or vinyltriethoxysilane. Thin film coatings formed by this composition also do not provide optimum abrasion resistance to the surface.
Recently US patent application no. 20020127330 discloses a thermally curable coating composition that includes tetraalkyl orthosilicate, epoxyalkylalkoxy silanes in combination with mathacryloxyalkoxy silanes having a pH range 4-6. They did not mention the stability of sol useful for the deposition of coatings and it is expected that at the above pH range silanol condensation reaction would be faster and stability of sol would be less. Furthermore two organic functionalities have been used in this composition, one of which (mathacryloxyalkoxy silanes) is commonly cured by UV light. So there is a possibility of existing monomeric methacryloxy groups in the coatings cured at 90-120°C. Furthermore, in this composition acetic acid has been used which may be entrapped in the coating after curing.
Recently we observed glass-like silica particles could be generated in solution by hydrolysis and condensation reactions of tetraethyl orthosilicate (TEOS) in presence of any acid (inorganic or organic) at room temperature (G. De, B. Karmakar and D. Ganguli, J. Mater. Chem., 2000, 10, 2289-2293; B. Karmakar, G. De and D. Ganguli, J. Non-Cryst. Solids, 2000, 272, 119-125). We also noticed that dense silica nanoparticles formed first and then grow into larger glass-like dense silica particles. We also found that about one-third mole% of total TEOS has been transformed into dense silica glass nanoparticles and rest remains as soluble silica and growth of the particle occurs through deposition of soluble silica on the silica nanoparticles those are formed initially through acid hydrolysis of TEOS. Such dense silica nanoparticles bonded with silica network in combination with organic polymer-silica network should produce very hard and dense coatings on plastics after curing.
Using this concept we were able to develop a composition (patent no. 346Del2003) based on 'epoxy-silica' hybrids where the in-situ generated SiO2 nanoparticles of diameter 3-26 nm are chemically bonded with the hybrid network. This composition is very suitable on CR39® grade plastics and hardness value of the coatings of the order of >6H was obtained. Although this composition is applicable on

PMMA and PC, the adhesion characteristics of this composition with these surfaces are relatively weak.
Further, we reported (Indian patent no 744Del2003) preparation of UV curable hard coatings on PC substrates using boemite nanoparticle incorporated epoxy-methacrylate-silica composites. This composition is stable for the deposition of coating for longer time period. Using this sol we have developed scratch resistant coatings on PC sheets of dimensions 2 feet x 2 feet using conveyorised UV curing machine. The hardness of the coatings deposited on PC is of the order of 4H. Both the adhesion and abrasion resistance properties of the coatings have passed following international standards. The coated PC substrates also resistant to 10 cycles of boiling salt solution test and thermal test. So this epoxy-methacrylate-silica-boehmite composite is very suitable for PC. However, this composition is not very suitable when applied on PMMA or CR39® grade plastics considering the hardness values of the coatings. The main drawbacks of the processes are:
(i) The curing temperature is in higher side
(ii) The 'epoxy-silica', 'methacryloxy-silica', 'epoxy-methacryloxy-silica' and
'methacryloxy-silica-boehmite' systems used by different workers did
not mention the viscosity of the sol up to which it can be usable and
also stability of the sol.
(iii) The direct incorporation of porous silica nanoparticles could not
produce high hardness of the coating.
(iv) UV curable 'epoxy-methacrylate-silica-boemite' composite materials reported by us is stable with time and good quality abrasion resistant coatings could be obtained on PC substrates. This composition deposited on PMMA showed relatively poor hardness value, (v) Thermal curable good abrasion resistant 'epoxy-silica bonded with nano-SiO2' composition also reported by us is very suitable for CR39® grade plastics which shows relatively poor adhesion characteristics when applied on PC and PMMA.

(vi) Colloidal silica incorporated acrylate or methacrylate-silica composite
materials could not have good adhesion on PMMA and PC substrates, (vii) The thermal curable (90-120°C) composition 'epoxy-methacryloxy-silica' recently reported in a US patent application no. 20020127330 claims high hardness of the coating due to the generation of silica molecules in-situ in the sol. However, higher pH range shortens the shelf life of the sol. Furthermore, dual organic functionalities have been used in this composition, one of which (methacryloxy) is usually cured by UV light.
Therefore, a hard coating composition that can be useful to prepare protective coatings on PMMA would be desirable. Considering the compatibility of PMMA, a methacrylate-silica based composition having glass-like dense silica nanoparticles chemically bonded with the hybrid network could provide an essentially a single phase state that has no interface problems when applied on PMMA resulting in a hard-coating with good adhesion and abrasion properties.
OBJECTIVES OF THE INVENTION
The main object of the present invention is to provide UV curable methacrylate silica based nanocomposite sol useful for anti scratch coatings.
Another object of the present invention is to provide a sol having longer shelf life at least 40 days, at room temperature (25-35 °C), which could be increased further if the sol is stored in normal refrigerating condition.
Yet another object of the present invention is to provide a simpler inorganic-organic hybrid composition suitable for UV curing.
Yet another object of the present invention is to provide in-situ generation of glass-like dense silica nanoparticles in the sol, which are bonded and embedded in the polymethacrylate-silica network.
Yet another object of the present invention is that the optical transmission of the coated PMMA does not deteriorate after curing.
Yet another object of this present invention is that the sol could also be applied onto the other plastics like PC and CR39®

Still another object of this present invention is to provide a process for the preparation of UV curable methacrylate silica based nanocomposite sol useful for anti scratch coatings.
SUMMARY OF THE INVENTION
Accordingly the present invention provides an UV curable methacrylate silica based nano-composite sol comprising methacrylate alkyl trialkoxysilane (MATAS) and tetraalkoxysilane (TAS) in a molar ratio of 7:3 to 3:7.
In an embodiment of the present invention the methacrylate alkyl trialkoxysilane used is selected from the group consisting of 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane 2-methacryloxypropyltrimethoxysilane, 2-methacryloxypropyltriethoxysilane, 2-methacryloxyethyltrimethoxysilane, 2-methacryloxyethyltriethoxysilane and 2-methacryloxypropylmethyldiethoxysilane.
In yet another embodiment the tetraalkoxysilane used is selected from the group consisting of tetra methyl orthosilicate, tetraethyl orthosilicate, tetra propyl orthosilicate and tetra butyl orthosilicate.
In yet another embodiment the nanocomposite sol has the following characteristics:
a) average particle size distribution is in the range of 27-50 nm,
b) shelf life is about 45 days,
c) viscosity is ranging between 8-40 cps.
In yet another embodiment the nanocomposite sol as claimed in claim 1 is useful for the preparation of anti-scratch coatings.
In yet another embodiment the an anti-scratch nanocomposite coating comprises 38-63 weight percentage of silica (TAS) and 37-62 weight percentage of polymethyacrylate (MATAS).
The present invention further provides a process for the preparation of UV curable nanocomposite coating using nanocomposite inorganic-organic sol and the said process comprising the steps of:

a) preparing nanocomposite inorganic-organic sol by mixing methacrylate
alkyl trialkoxysilane (MATAS) with tetraalkoxysilane (TAS) in a molar
ratio of 7:3-3:7 in an organic solvent, under stirring, for a period of about
15 minutes,
b) adding a mixture of 0.5-0.9 mole water per mole of alkoxy group and
4.4 - 5.2 X 10™4 mole mineral acid (HCL) per mole of alkoxy group,
under stirring, at a temperature of about 25-30°C to obtain a clear
solution, followed by refluxing to obtain the hydrolyzed product,
c) cooling the above said hydrolysed product to a temperature of about
25-30° C, followed by ageing for a period of about 20 hours,
d) adding a polymerizing initiator into the above said ageing solution,
under stirring, till the complete dissolution of the initiator and keeping it
at a temperature of about 25-30° C, for a period of 2-3 days, followed
by evaporation up to 10-12 wt. % with respect to the total sol, filtering
the above said sol, followed by ageing at a temperature of about 25-30
0 C, for a period of about 4-6 days to obtain the desired coating sol,
e) depositing the above said coating sol over a substrate and drying it, at a
temperature of about 60-70° C, for a period of about 1 hour, followed by
curing it under UV radiation, at energy of 2.6-2.7 J/cm2 and further
curing it for a period of 40-60 minutes to obtain the desired coating on a
substrate.
In yet another embodiment the methacrylate alkyl trialkoxysilane used in step (a) is selected from the group consisting of 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane 2-methacryloxypropyltrimethoxysilane, 2-methacryloxypropyltriethoxysilane, 2-methacryloxyethyltrimethoxysilane, 2-methacryloxyethyltriethoxysilane and 2-methacryloxypropylmethyldiethoxysilane.
In yet another embodiment the tetraalkoxysilane used in step (a) is selected from the group consisting of tetra methyl orthosilicate, tetraethyl orthosilicate, tetra propyl orthosilicate and tetra butyl orthosilicate.
In yet another embodiment the the organic solvent used in step (a) is selected from the group consisting of n-propanol, n-butanol, ethanol, and methanol.

In yet another embodiment the pH of the coating sol is ranging between 0.8 to In yet another embodiment the the acrylate polymerizing initiator used in step (d) is selected from the group consisting of benzoyl peroxide (Bz2O2), 1-hydroxycyclohexyl phenyl ketone (HCPK), Irgacure184, azobisisobutryro nitrile (AIBN) and a,a'-dimethoxyphenylacetophenone (Irgacure 651).
In still another embodiment the the substrate used in step (e) is selected from the group consisting of polymethyl methacrylate (PMMA), polycarbonate (PC), plastic sheets and ophthalmic lenses.
Detail description of the invention
An optically clear protective thin film for polymeric sheets, lenses and other polymeric substrate surfaces (PMMA, PC, and other related plastics) has glass-like dense silica nanoparticles bonded with silica - polymethacrylate network. The improved film is formed from a coating solution that includes tetraalkyl orthosilicate, methacrylatealkylalkoxy silanes and solvents having a pH values 0.8- Glass-like silica nanoparticles have been generated in a silicon alkoxide -methacrylatealkylalkoxysilane combined sol. It is expected that these glass-like dense silica nanoparticles would remain chemically bonded with the silica-organic polymer network because a fraction of silicon alkoxide (about one third) is transforming to silica nanoparticles. Accordingly, in the present invention glass-like silica nanoparticles of a few nanometer size ranges are generated in the tetraalkoxysilane - methacrylatealkyl-trialkoxysilane derived sol and these silica nanoparticles remain bonded with the silica - methacrylate network formed during hydrolysis and condensation of alkoxy groups. In this process, the silica particles

could not grow in to larger sizes because of the low pH of sol and presence of long chain organic moiety (methacrylatealkyl chain) which are not allowing the generated silica nanoparticles to agglomerate. This may also be noted here that MEMO:TEOS mole ratio has an effect in controlling the size of the silica nanoparticles in the sol (Table 1). As for example, the composition MEMO:TEOS = 7:3 (MT73 sol) generates SiO2 nanoparticles of mean particle diameter 49.5 nm where as the 5:5 (MT55 sol) and 3:7 (MT37 sol) mole compositions produce SiO2 nanoparticles of mean diameter 38 and 27.7 nm respectively. The particle size distribution was measured in a Malvern particle size analyser model ZETASIZER 1000 HS.
The pH of the sol is lying in the range 0.8 to The important features of the invention are as follows:
(a) obtaining a sol having a pH values 0.8- provide a better scratch resistant coatings by UV curing on PMMA substrate.
(b) generation of nanometer sized glass-like dense silica particle from hydrolysis-
condensation reactions of tetraalkoxy silane in presence of methacrlatealkyltrialkoxy
silanes in situ in the sol.
(c) use of one UV curable organic functionality group (methacrylate) remains in
monomeric form in the sol, polymerizes only after exposition of UV-light on it.
(d) maintaining of sol pH 0.8 to silica to slow down the -Si-O-Si- condensation, which controls the viscosity and
increases further the shelf life of the sol.
(e) no deterioration of optical transmission property of coated PMMA after UV
curing.

(f) compatibility of PMMA surface and the coating composition based on
methacrylate organic functionality which gives better adhesion through vander Waal's
force of attraction.
(g) hardness of the coating is due to the presence of glass-like dense
nanoparticles bonded and embedded in a highly cross-linked polymethacrylate-
silicon oxide network.
Other features, which have been realized by the present invention, are:
(i) using tetraalkoxy silane and methacrlatealkyltrialkoxy silanes for making the hybrid
sol and having a pH of 0.8 - (ii) In the sol in-situ generation of glass-like dense nano-silica particles in side the
MATAS and TAS originated methacrylate (monomeric)-silica network at low pH which
remain bonded with silica network and do not grow in size due to the presence of
methacrylate (monomeric or polymeric) alkyl organic chains;
(iii) final sol pH value close to the isoelectric point (IEP) of silica minimizes the rate of
-Si-O-Si- condensation which increases the shelf life of sol;
(iv) simultaneous polymerization of methacrylate unsaturation and further silanol
condensation reactions during UV photo-curing helps in generating hard coatings
having highly cross-linked polymethacrylate-silica network covalently bonded with
silica nanoparticles.
The process steps of the present invention are given below:
(i) Mixing of methacrylatealkyltrialkoxysilane (MATAS) and tetraalkoxysilane (TAS) in organic solvent(s) with stirring
(ii) Hydrolysis and condensation of alkoxy groups of MATAS and TAS by adding HCI - H2O mixture dissolved in organic solvents.
(iii) Generation of glass-like dense nano-silica particles in side the MATAS and TAS originated methacrylate (monomeric)-silica network.
(iv) Refluxing the above mixture for 30 - 90 min in the temperature range 78-81 °C (Table 2) at normal atmospheric condition.

(v) Addition of methacrylate polymerization initiator with stirring at room temperature.
(vi) After 2-3 days ageing at room temperature, 10-12 wt% solvent is evaporated out from the sol followed by another 4-6 days aging at room temperature.
(vii)Deposition of coating on cleaned plastic (PMMA, PC, and other related plastics) ophthalmic lenses, sheets and other shapes by dip-coating technique.
(viii)Drying the coating at 60 - 70°C for 60 min followed UV photo-curing (energy 2.6-2.7 J/cm2) 1-4 times each side and finally by curing at 90 - 100°C for 40-60 min.
The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention.
EXAMPLE-I
Preparation of sol (MT-55 sol):
UV curable hybrid coating solution was prepared by mixing 76.13 gm of 3-(methacryloxypropy)-trimethoxy silane, 63.84 gm of tetraethoxy orthosilicate and 35 gm of 1-butanol were mixed and stirred for 15 min. To this water (9.73 gm), HCI 0.1N, (10.30 gm), 1-butanol (14.0 gm) and methanol (14.0gm) mixture was added under stirring condition and stirring was continued for 3-5 min at room temperature (25±2 °C). The above solution was then refluxed for 90 min. and cooled down to room temperature, and this was kept at RT for 20 hours aging (over night). Then 0.160 gm of solid benzoyl peroxide (Bz2O2) was added directly into the sol with stirring. The complete dissolution of the initiator took 120 min. Then the sol was kept at room temperature for 2-3 days followed by the sol was evaporated 10-12 wt% with respect to the sol The sol was then filtered through whatman no. 1 filter paper and aged room temp (25-35°C) for about 4-6 days before coating deposition.
EXAMPLE-II MT-73 sol:
UV curable hybrid coating solution was prepared by mixing 103.00 gm of 3-(methacryloxypropy)-trimethoxy silane, 37.00 gm of tetraethoxy orthosilicate and 35 gm of 1-butanol were mixed and stirred for 15 min. To this water (8.89 gm), HCI 0.1N, 9.40 gm), 1-butanol (14 gm) and methanol (14 gm) mixture was added under stirring condition and stirring was continued for 3-5 min at room temperature (25+2 °C). This partially hydrolyzed alkoxide group's derived solution was then refluxed for 90 min. The solution was then cooled at room temperature, and this was kept at RT for 20 hours aging (over night). Then 0.2086 gm of solid benzoyl peroxide (62262) was added directly into the sol with stirring. The complete dissolution of the initiator took 120 min. Then the sol was kept at room temperature for 2-3 days followed by the sol was evaporated 10-12 wt% with respect to the sol The sol was then filtered through whatman no. 1 filter paper and aged room temp (25-35°C) for about 4-6 days before coating deposition.
Coatings preparation/deposition: Cleaning of the substrates:
Prior to coatings deposition, PMMA substrates are cleaned with neutral detergent followed by washing with tap water and rinsing with distilled water and finally wiping with soft tissue paper (Lotus® brand) soaked with ethanol. For polycarbonate sheets and related plastics are cleaned with neutral detergent, followed by washing with tap water and rinsing with distilled water and ethanol and finally 5 min in warm isopropanol.
Coating deposition:
Cleaned PMMA, PC and CR-39® are immersed into the coating sol and withdrawn at a rate of 10-20 cm/min from the sol perpendicular to the solution surface. Coating thickness was measured by surface profilometer (Kosaka, Japan).
Curing of the coatings:
As deposited coatings were first dried at temperature 60 - 70°C for 1h followed by
UV cured 1-4 times each side using a conveyorized UV curing machine. Conveyor
speed was adjusted in such a way that energy 2.6 - 2.7 J/cm2 each time on the
sample is received. After UV curing the samples were kept at 90 - 100°C for 40-60
min.
There are several standard tests that are used in the ophthalmic lens industry to quantify the abrasion resistance and adhesion of lens coatings, and a brief description of each test follows.
(i) Abrasion test using a lens coating hardness tester
This standard procedure is for evaluating the abrasion resistance of coated plastic sheets or lens. This test was performed using a US military specification lens coating hardness tester kit in accordance with MIL-F-48616. The kit contains one brass instrument with a spring that was calibrated for 2.5 Ibs of pressure. The eraser (rubber-pumice composite) inserts provided with the instrument are manufactured and certified to conform to US federal specification MIL-E-12397B. The test consists of rubbing across the coated surface with the eraser bearing 2.5 Ibs of pressure. The specification of this test is that the coated surface should withstand 20 cycles of rubbing (one way) with the eraser bearing 2.5 Ibs of pressure without any visual scratch. Isopropanol was used to clean the coated surface before and after tests. After tests the surface was cleaned and examined visually and with a profilometer (Kosaka, Japan). Tests were also performed on the uncoated substrate.
(ii) Pencil hardness test (ASTM D 3363)
The purpose of this standard scratch hardness tests is to determine the resistance of coating materials to scratch effect on the surface. Generally, scratch hardness is measured by moving a sharp object under a known pressure over the surface. The result may be either pressure require to scratch through the test materials if a scratching tool of constant hardness is used , or the hardness is used of the scratching tool is varied while constant pressure is applied. Value is given
according to grade of pencil such as 9B-9H. For testing the sample, first pencil is inserted then it must touch the test surface, and is tighten the lamping screw. Then pencil is moved over the surface about 6-12 mm under a fixed load of 750 gm and a fixed angle of 45 degrees. The test is repeated using successive grade pencils where one does not scratch and next one does scratch. The pencil grade for which it does not scratch the sample is the value of hardness.
(iii) Cross cut and adhesive tape test following DIN 53151 or ASTM D 3359
This standard procedure is for evaluating the adhesion of a hardcoat on a substrate like sheet or lens. Using a cutting device such as a razor blade, six parallel cuts 1.5 mm ± 0.5 mm apart and approximately 15 to 20 mm in length are made in the coating on the front or convex surface of the lens. Another six parallel cuts 1.5 mm ± 0.5 mm apart are made in the coating perpendicular to the first set. This forms a cross-hatched pattern of squares over which tape is applied, such as Birla 3M Scotch Magic Tape #810. The tape then is pulled rapidly as close to an angle of 180° as possible, and the percent adhesion is quantified by the amount of coating removed from the squares in the cross-hatched pattern. The 180° reference means that the tape is pulled back over itself in a direction that is nearly parallel to the substrate surface.
(iv) Boiling Salt Water Test
This standard procedure evaluates the ability of a hardcoat to adhere to a substrate (sheet, lens or other shape) and the susceptibility of the coating to crazing. A coated lens is subjected to three to ten cycles of thermal shock by submersing the coated lens for two minutes in a boiling salt water solution which comprises 3.5 litres of deionized water, 157.5 grams of sodium chloride, and 29.2 grams of sodium dihydrogen orthophosphate, followed by submersing the coated lens for one minute in water at 24±2°C Coating performance is quantified by whether or not coating layer detachment or complete delamination from the substrate occurs, and by whether or not crazing of the coating occurs.
The resultant coatings of 4-10 µm in thickness are optically transparent having refractive index of 1.489 - 1.492 and showed good abrasion and other properties as follows:
(i) Optical transmission
The optical transmission of the coated PMMA does not deteriorate after UV curing. Similar result is obtained in case of coated CR-39® grade plastics whereas the optical transmission of PC is increased to 2-3% after deposition of the coating followed by UV curing.
(ii) Adhesion property (DIN 53151 orASTM D 3359)
Adhesion test by adhesive tape test shows no peeling off in any coatings deposited on PMMA, PC and CR39 grade plastics. The results of adhesion test by cross-cut and adhesive tape following DIN 53151 orASTM 3359 specification are as follows: the coatings deposited on PMMA shows no peeling off in cases of sols containing higher amount of MEMO (e.g. MT73) and it can be classified as ASTM class 5B (highest quality). But in case of coatings obtained from higher silica content in the sol (e.g. MT55 composition) it is classified as ASTM Class 4B. In cases of coated PC and CR-39® no peeling off result and therefore classified as ASTM Class 5B. Detailed results are given in Table 6.
(iii) Pencil hardness value (ASTM D 3363)
Coated PMMA shows pencil hardness value in the ranges 3H-5H depending upon the sol composition. The hardness value is increased with increasing the SiOa content of the sol. Similar result is also found in cases of PC substrates where hardness value is varied from 2H-5H. In case of CR-39® lenses a pencil hardness value close to 5H is achieved using MT55 sol. The detailed results are given in Table 7.
(iv) Abrasion test (specification MIL-E-12397B)
Uncoated PMMA is suffering from damage even after 1-5 times of abrasion whereas 20 abrasion cycles is the specification of this test. The coated PMMA showed resistant towards damage after 20 abrasion cycles. A very few scratches are however observed in case of coatings obtained from the sols containing higher amount of MEMO (e.g. MT73 composition. Similar result is also obtained in case of CR-39® lenses. Where as the coated PC showed resistance towards damage even after more than 50 times of abrasion. The detailed results are given in Table 8.
(v) Boiling salt solution test
Coated PMMA could resist up to 4 cycles of boiling salt solution test. After this few cracks are observed. Coated CR-39 could resist up to 3 cycles of such test. The coated PC sheet is however passed 10 cycles of boiling salt solution test.
Table I:
Particle diameter in size of different sols (measured Malvern particle size analyser ZETASIZER1000HS).
(Table Removed)

Table II:
Refluxed temperature of the sol for different sol composition. .
(Table Removed)
Table III:
Change in viscosity of the MT55 sol aged at room temperature (25-35°C).
.(Table Removed)

Table IV:
Change in coating thickness with lifting speed (inches/min) at given viscosity for MT55 sol. .
(Table Removed)
Table V:
Change of coating thickness with lifting speed (inches/min) at different viscosities for MT73 sol. .
(Table Removed)

Table VI:
Cross cut adhesive tape test of the coated samples (ASTM 3359 or DIN 53151 specification). .
(Table Removed)
Table VI I:
Pencil hardness test (ASTM D 3363) results obtained from uncoated and coated
PMMA, PC and CR-39 grade plastic substrates. .
(Table Removed)

Table VIII:
Results after 20 abrasion cycles (one way) using lens coating hardness tester following US specification MIL-F-48616 using eraser with specification MIL-E-12397B. .
(Table Removed)

The main advantages of the present invention are:
(i) A UV curable coating sol suitable for deposition of anti scratch coatings on plastic substrates (PMMA, PC and related plastics)
(ii) The shelf life of sol is at least 45 days (Table 1) when kept at room temperature (25-35°C) in closed condition. In this period of time the viscosity lies within 30 cps which suitable for obtaining good quality coatings. The coating can be done up to 40 cps of viscosity, however in such condition, lower withdraw speed is recommended in order to obtain coating thicknesses in the ranges 5-7 jam. Some representative results are given in Tables 2 and 3. Shelf life could be increased further if the sol is stored in normal refrigerator.
(iii) Only two common types of precursor chemicals, silicon alkoxide and methacrylatealkylalkoxysilane are required.
(iv) Incorporation of surfactants is not necessary.
(v) Coating can be applied on different types of plastics.
(vi) Highly dense, anti scratch coatings can be obtained on plastic ophthalmic lenses and sheets.
(vii) Complicated shaped plastic ophthalmic lenses (e.g. bifocal D- or O-shaped lenses) can also coated without any problem.
(viii) Still another advantage of the process is that the % transmission of coated PMMA and CR-39® does not deteriorate compared to that of uncoated substrates where as the % transmission of the coated PC is found to be increased by 2-3 %.

We claim
1. A UV curable methacrylate silica based nano-composite sol comprising
methacrylate alkyl trialkoxysilane (MATAS) and tetraalkoxysilane (TAS) in a
molar ratio of 7:3 to 3:7.
2. A nanocomposite sol as claimed in claim 1 wherein methacrylate alkyl
trialkoxysilane used is selected from the group consisting of 3-
methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane 2-
methacryloxypropyltrimethoxysilane, 2-methacryloxypropyltriethoxysilane, 2-
methacryloxyethyltrimethoxysilane, 2-methacryloxyethyltriethoxysilane and 2-
methacryloxypropylmethyldiethoxysilane.
3. A nanocomposite sol as claimed in claim 1 wherein tetraalkoxysilane used is
selected from the group consisting of tetra methyl orthosilicate, tetraethyl
orthosilicate, tetra propyl orthosilicate and tetra butyl orthosilicate.
4. A nanocomposite sol as claimed in claim 1 has the following characteristics:
a) average particle size distribution is in the range of 27-50 nm;
b) shelf life is about 45 days;
c) viscosity is ranging between 8-40 cps.

5. A nanocomposite sol as claimed in claim 1 is useful for the preparation of anti-
scratch coatings.
6. An anti-scratch nanocomposite coating as claimed in claim 5 comprises 38-63
weight percentage of silica (TAS) and 37-62 weight percentage of
polymethyacrylate (MATAS).
7. A process for the preparation of UV curable nanocomposite coating using
nanocomposite inorganic-organic sol and the said process comprising the
steps of:

a) preparing nanocomposite inorganic-organic sol by mixing methacrylate
alkyl trialkoxysilane (MATAS) with tetraalkoxysilane (TAS) in a molar
ratio of 7:3-3:7 in an organic solvent, under stirring, for a period of about
15 minutes,
b) adding a mixture of 0.5-0.9 mole water per mole of alkoxy group and
4.4 - 5.2 X 10~4 mole mineral acid (HCL) per mole of alkoxy group,

under stirring, at a temperature of about 25-30°C to obtain a clear solution, followed by refluxing to obtain the hydrolyzed product,
c) cooling the above said hydrolysed product to a temperature of about
25-30° C, followed by ageing for a period of about 20 hours,
d) adding a polymerizing initiator into the above said ageing solution,
under stirring, till the complete dissolution of the initiator and keeping it
at a temperature of about 25-30° C, for a period of 2-3 days, followed
by evaporation up to 10-12 wt. % with respect to the total sol, filtering
the above said sol, followed by ageing at a temperature of about 25-30
0 C, for a period of about 4-6 days to obtain the desired coating sol,
e) depositing the above said coating sol over a substrate and drying it, at a
temperature of about 60-70° C, for a period of about 1 hour, followed by curing it under UV radiation, at energy of 2.6-2.7 J/cm2 and further curing it for a period of 40-60 minutes to obtain the desired coating on a substrate.
8. A process as claimed in claim 7, wherein the methacrylate alkyl trialkoxysilane
used in step (a) is selected from the group consisting of 3-
methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane 2-
methacryloxypropyltrimethoxysilane, 2-methacryloxypropyltriethoxysilane, 2-
methacryloxyethyltrimethoxysilane, 2-methacryloxyethyltriethoxysilane and 2-
methacryloxypropylmethyldiethoxysilane.
9. A process as claimed in claim 7, wherein the tetraalkoxysilane used in step (a)
is selected from the group consisting of tetra methyl orthosilicate, tetraethyl
orthosilicate, tetra propyl orthosilicate and tetra butyl orthosilicate.
10. A process as claimed in claim 7, wherein the organic solvent used in step (a)
is selected from the group consisting of n-propanol, n-butanol, ethanol, and
methanol.
11. A process as claimed in claim 7, wherein the pH of the coating sol is ranging
between 0.8 to 12. A process as claimed in claim 7 wherein the acrylate polymerizing initiator
used in step (d) is selected from the group consisting of benzoyl peroxide

(Bz2O2), 1-hydroxycyclohexyl phenyl ketone (HCPK), Irgacure184, azobisisobutryro nitrile (AIBN) and ά,ά-dimethoxyphenylacetophenone (Irgacure 651).
13. A process as claimed in claim 7, wherein the substrate used in step (e) is
selected from the group consisting of polymethyl methacrylate (PMMA),
polycarbonate (PC), plastic sheets and ophthalmic lenses.
14. A UV curable methacrylate silica based nano-composite sol useful for the
preparation of anti-scratch coatings and a process for the preparation thereof,
substantially as herein described with reference to the examples.

Documents:

1416-del-2007-Abstract-(28-07-2014).pdf

1416-del-2007-abstract.pdf

1416-del-2007-Claims-(28-07-2014).pdf

1416-del-2007-claims.pdf

1416-del-2007-Correspondence Others-(28-07-2014).pdf

1416-del-2007-correspondence others.pdf

1416-DEL-2007-Correspondence-Others-(14-05-2009).pdf

1416-del-2007-description (complete).pdf

1416-del-2007-form-1.pdf

1416-DEL-2007-Form-18-(14-05-2009).pdf

1416-del-2007-form-2.pdf

1416-del-2007-Form-3-(28-07-2014).pdf

1416-del-2007-form-3.pdf

1416-del-2007-form-5.pdf

« Previous Patent

Next Patent »

Patent Number

264741

Indian Patent Application Number

1416/DEL/2007

PG Journal Number

04/2015

Publication Date

23-Jan-2015

Grant Date

19-Jan-2015

Date of Filing

03-Jul-2007

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN, RAFI MARG NEW DELHI-110 001,India

Inventors:

#	Inventor's Name	Inventor's Address
1	GOUTAM DE	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, P.O.JADAVPUR UNIVERSITY, KOLKATA 700 032
2	SAMAR KUMAR MEDDA	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, P.O.JADAVPUR UNIVERSITY, KOLKATA 700 032

PCT International Classification Number

C08J7/04

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA