PROCESS FOR OBTAINING A TRANSPARENT COATING ON PANES OF NORMAL OR SAFETY GLASS

Abstract: The process in accordance with the invention concerns the preparation of the elastomeric coating with the direct application of one or more films made "in situ" on to the surtace of the glass by means of a special system known as "Interpenetrating Polymer Network" or "I.P.N. system". In this specific case, a solution of polyurethane poly­ mers or pre-polymers dissolved in acrylic monomers or in mixture of them, or in a solution of acrylic propolymers in acrylic monomers is applied on to the surface of the glass pane, and the as-formed layer is submitted to a strong catalytic action and/or photoinitiators capable of favouring the polymerisation of an interpenetrating polymer network, hence obtaining a particularly thin coating with good tear-­ proof and adhesion properties, with said coating combining the elastomeric and physical properties of the polyurethane polymers with the optical properties and the good resis­ tance to atmospheric agents of the glassy acrylic polymers.

Description: "PROCESS FOR OBTAINING A TRANSPARENT COATING ON PANES OF NORMAL SAFETY GLASS" This invention relates to a process for obtaining a transparent coating on normal glass panes or on safety glass panes. The most frequently used types of safety glass, are, as is well known, the laminated and toughened types. The laminated and toughened types of glass are those preferably used for windscreens of autovehicles. Many countries specifically prescribe the use of laminated glass in the automobile field, thanks to its greater resistance to penetration of solid bodies landing on its surface, thereby reducing the risk of serious injury for the driver and passengers in the vehicle. In other countries, instead, an alternative product is used, that is, toughened glass which has a lower resistance to penetration in the event of impact. The type of the more frequently used laminated glass is the one obtained by bonding two glass panes on to a thin layer of flexible polyvinyl butyral. Processes for obtaining laminated glass of satisfactory quality which is not liable to delamination or separation, are well known to those skilled in the art. However, attempts to improve such processes by varying the composition of the material of the bonded flexible film have not yet met with success, that is, attempts to obtain laminated glass which does not allow glass fragments or splinters to fly out when the glass fractures. Accidents causing facial injury have therefore urged firms operating in the field into technological research for a product which does not have the drawbacks previously complained about, or which has them to a lesser degree On the other hand, in glazing applications for the building and construction industry, above all for public buildings such as schools, gymnasiums, office blocks, etc. there is also danger of the glass fragments from falling and causing injury to persons when breakage accours of the normally used heat treated glass. In order to reduce the risk of injury also in the case of such breakages, at least one of the two glass surfaces must be coated with a transparent layer possessing strong adhesion to glass properties, and very good elasticity in order to retain the glass fragments thereby reducing the danger of injury to persons. A product which can be used for safety glass manufacture has already been prepared (German Patent No. 2.629.779 of Saint Gobain); an elastomeric film of linear polyurethane type is applied on to the glass surface, with said film being prepared from a polyol polyether or linear polyester reacted together with an aliphatic isocyanate in almost stoichiometric quantities. Another similar product has been prepared by applying on the surface of the glass pane a film based on polyurethanes which are at the same time both linear and cross linked, and obtained by partial presence of tri-isocyanates. P.P.G. (U.S.A. Patent 4.041.208) has also carried out modifications to these polyols by using chain linking members, for example diol monomers, thereby increasing the elasticity properties of the coating. The products known up till now are not altogether satisfac tory in that they have elastomeric coatings with no or nearly no cross linking bonds, that is to say essentially thermoplastic materials with low softening point, which are also susceptible to ageing and yellowing through the action of ultraviolet light and tobacco smoke. Their most advantageous feature is that of not leaving any permanent trace of surface incisions submitted by them because these incisions penetrate causing flow of the elastomeric material towards the sides of the object of impact; when the object of impact is withdrawn, there is a flowback or return of the compressed material towards the original zone, thereby determining an apparent self healing or self sealing behaviour. Currently known coatings are considered to be valid from the protection point-of-view only when the thickness of the layer lies between 200 and 800 microns. However, appli cation of films of this type and tickness on glass with concave surfaces creates problems in manufacture owing to the difficulty of obtaining products free from optical distortions and from zones with entrapped air bubbles. Moreover, the quality of the coating is such as not to permit good adhesion to the surface of the glass, hence it tends to be easily detached, nor is it easy to clean owing to its very thermoplastic nature, hence it is liable to abrasion which, in turn, causes a gradual loss of transparency of the film. After much experimenting, the Applicant has finally succee ded in eliminating the above defects as hitherto found in transparent coatings for glass panes. The process in accordance with the invention is characteri e ¯ zed in that it permits the preparation of an elastomeric coating directly on the surface of a pane of glass, and, above all, in that, for such a purpose, the process uses special formulations, described later on, which permit the formation of polymers with very good tear-proof and adhesion to glass properties. Thanks to such properties, coatings thinner than those hitherto used can be obtained, with consequent considerable improvement of the product's optical propeties. In fact, a tear-proof coating is technically and commercially valid only if it possesses very good elongation properties and high modulus of elasticity, if it adhers well to glass, if it has good abrasion resistance, and if it is not liable to deterioration through action of solvents or solar radiation, and/or moisture from defrosting and air conditioning systems. Considerable improvement of the resistance to solvents, to the loss of transparency and to abrasion can be achieved by using a coating with a cross linked polyurethane system; but, on the other hand, fully cross linked polymer systems possess poor elasticity properties and hence are not suitable for use as tear-proof coatings. A method has already been devised to overcome the limitations of the coatings based on the above cited polyurethane polymers, involving the successive applications of two coatings: - the first consists of a film of non cross linked polyure thane - the second consists of a layer of cross linked polyure thane. A final coating is obtained which is valid in that it is the result of a compensatory physical combination of the individual physical properties of both types, but which has the disadvantage of higher manufacturing costs. It is also known that mixtures can be prepared of the two previously described polyurethanes using them for tear-proof coatings; however, said mixture is fpund to have quite inferior properties to those obtained from the successive application of two types of polyurethanes. The Applicant has found that better results are, instead, achieved by directly applying on the glass surface, one or more tear-proof coatings, prepared "in situ" by a special "Interpenetrating Polymer Network system" (I.P.N. system) The I.P.N. system consist, as already known, of two or more interpenetrating polymers in which the typical structure of the macromolecules of a same type is not, or is very little altered when combined with macromolecules of other types which are formed from monomers in which the aforementioned polymers are dissolved. When the monomers of the I.P.N. system are polymerized, a polymeric system is formed in which polymers of different types are present. The Applicant has found that, by carrying out an appropria te selection of polymers and monomers in which said polymers are dissolved, surprizingly enough an Interpenetrating Polymer Network system is obtained "in situ" which gives rise to a tear-proof coating on glass, and which possesses the required mechanical and optical properties. More especially, the Applicant has found it preferable to prepare an I.P.N. system in which the polyurethane polymers are associated with acrylic, epoxy and amine polymers. In said I.P.N. system the polyurethane-fraction is preferably obtained for the required purpose, from an aliphatic polyurethane prepared from a polyol polyether or polyester having a low to medium molecular weight so as to remain highly active and not to generare free iso-cyanate groups in the resultant film, Particularly suitable for I.P.N. systems are the aliphatic iso-cyanates, either bi or tri-functional in that they can generate a linear polyurethane or a partially cross linked polyurethane respectively. The obtain said I.P.N. system, the polyester or one of its prepolymers is dissolved in an acrylic monomer or in a mix ture of suitable acrylic monomers, or in a solution of acrylic prepolymers in acrylic monomers; the solution so obtained "in situ" is then polymerized thereby giving the required protective coating. It is found that the polymerization, which, we repeat, is carried out directly on the glass pane, can be conducted under heat if radical type initiators are used, such as organic perioxides, or else by photopolymerization if ultraviolet light sensitive photoinitiators are used. It is interesting to note that if, a polyurethane prepolymer is used in the I.P.N. system, the acrylic monomers used must not have carboxyl or hydroxyl groups, in order to prevent cross linking between the various types of polymers. The proportions and type of the two main polymers generated by the I.P.N. system can be several, but one of the two polymers must always essentially possess elastomeric properties and the other glassy or semi-vitreous properties. Altough the above described polymers prepared by the I.P.N. system possess per se good adhesion to glass properties, it has been found that to optimize their adhesion, it is advisable to carry out the polymerization of the I.P.N. system on a carefully cleaned glass surface and on which has been performed a pretreatment with the application of an adhesion accelerator which creates a chemical bridge based on organo-silanes and/or organo-titanium compounds. Alternatively, the organo-silane coumpound can be added directly to the mixture of the I.P.N. system. The I.P.N. system can be prepared by using, as stated previously, the monomeric part as the polymer solvent therefore without hetrogenous solvent, or else,a non-reactive volatile organic solvent can be added. Obviously the visco sity-of the I.P.N. system to be applied on the glass will vary according to the application method chosen from the various currently valid methods for application of lacquers or fluid coatings on solid surfaces, with special preference for spray, flow and centrifugal coating methods. In view of the superior mechanical properties which can be selected and obtained with an I.P.N. system; it is possible to reduce the thickness of the tear-proof film which, generally speaking, is found to thicker in the polyurethane films obtained by other ways; hence improved optical properties are obtained. The following commercially available isocyanates are particularly useful for the preparation of the coating in accordance with the invention. - 4,4'-methylene bis (cyclohexyl isocyanate), isophorone di-isocyanate, both of bifunctional type. - Isophorone di-isocyanate cyanide, biuret hexamethylene di-isocyanate, both of bifunctional type. The ratio between the hydroxyl groups (-OH) and isocyanate groups (-NCO) must be such that an excess of hydroxyl groups remain in the polyurethane in order to improve adhesion properties of the coating to the glass surface. The theoretical stoichiometric ratio between the isocyanate and polyester can be preferably varied until having a lesser quantity of isocyanate between 5% and 15%. Suitable polyesters for the process in accordance with the invention are those having in general a molecular weight from 200 to 5000, and preferably from 1000 to 2000, both obtained from long chain acids, preferably those derived from adipic aeid. Polyesters derived from short chain acids such as sebacic acid and aromatic acids such as the phthalic acids can also be used but only in low concentrations. Diols which can be used for esterification of the polyesters are: 1,2-ethylene glycol, 1,2-propylene glycol, butane-1:4-diol, hexane-1:6-diol; polyhydric alcohols with three hydroxyl groups such as glycerine cannot be used. Moreover the polyesters used must have an acid value less than 1 and a hydroxyl number between 40 and 150, preferably between 50 and 100; as a result, the ratio between the polyols and acid in the polyester chosen will be greater than -1 in order to have an excess of polyols which will maintain the acid value less than 1 and the hydroxyl number between 50 and 100 The acrylic polymer component in the I.P.N. system is prepared both by full polymerization "in sits" of the acrylic monomers chosen, and by polimerizat-ion of the monomeric components with completion of the polymerization of the prepolymeric components whenever solutions of acrylic or methyl acrylic prepolymers dissolved in acrylic monomers are adopted. Finally acrylic monomers with certain special chemical physical properties have been found to be suitable, more especially regarding the physical properties those with low vapour pressure and with good solvent properties for polyurethane prepolymers and polymers and acrylic prepolymers. The acrylic monomers are preferably as follows: 2-ethyl hexyl acrylate, hexanediol acrylate, ethylene glycol acrylate, 2-hydroxyethyl acrylate. Alternatively, a proportional part of the acrylic monomer can be substituted with a reactive vinyl compound, such as n-vynil pyrrolidone. It has been found that for each type of I.N.P. system based on acrylic-polyurethane there is a ratio between the two polymeric components to which correponds the best elasticity properties, the best resistance to fracture and to elongation in the final product; the qptimum ratio between the two components as found by the Applicant is 1:1. The most suitable type of polymerization in the presence of acrylic monomers is that conducted under ultraviolet radiation. In this case the following additives must be incorporated in the solution to be polymerized: - a photoinitiator chosen, for example, from the following: 2,2-dimethoxy 2-acetophenone, benzoyl iso-butyl ether, benzophenone. It has been found that a mixture of two photo initiators is more efficient than using just one, such as, for example, the simultaneous use of 2,2-dimethoxy-2-phenyl acetate and benzoyl-isobutyl ether. - also an amine based accelerator, such as, for example dimethylethanolamine or dimethylaminoethanol, this lat ter being preferable on account of its activating pro perties, also in the presence of atmospheric oxygen. Should the viscosity of the solution to be used be too high for an adequate application in accordance with the method chosen, the solution can be diluted using low concentrations of solvents or mixtures of organic solvents having high vapour pressure, such as, for example, esters, ketones, hydrocarbons, tetrahydrofuran, etc. In this case, after application of the solution on the surface to be coated, the solvent used for dilution must be evaporated before proceeding to polymerization. The above described monomer-polymer or prepolymer solutions can be applied on the glass employing any of the known systems, such as: spray, curtain, flow or centrifugal coating. For glass with curved surfaces, the centrifugal system is to be preferred (U.S.A. Patent 2.632.725). The Applicant has found that the thickness of the protective coating on the inside face of the windscreen for autovehicles must be within 100 to 190 microns in order to give simultaneous assurance of the optical properties and tear resistance. A few of the solutions which are especially suitable for obtaining a transparent and tear-proof coating on a pane of normal or safety glass are given as follows. They are to be considered as an exemplification of the principales of the invention and are not intended to limit the invention. EXAMPLE I A solution was prepared as follows: Polyester with hydroxyl number 55, based on butane-1:4-diol/1,2 ethylene glycol adipate 40 parts by weight n-vinyl pyrrolidone 20 parts by weight 2-ethyl-hexyl acrylate 9 parts by weight To this solution was added: Isophoron di-isocyanate (I.P.D.I.) 4 parts by weight with stirring for 3 hours at a temperature of 600 C, following by dilution with: : Ethylene glycol diacrylate 5 parts by weight Butyl acetate 6 parts by weight 2,2-dimethoxy-2-phenyl acetophenone 5 parts by weight Dimethylaminoethanol 1 part by weight Flow agent (D.C. 193) 1 part by weight (Dow Corning) EXAMPLE II A solution was prepared as in example I but the polyester was substituted with a polyester (polytetramethyleneglycol) having a molecular weight of 650, and the iso-cyanate was replaced with 5 parts of 4,4' methylene bis (cyclohexyl isocyanate). EXAMPLE III A solution was prepared still as in example I in which 10 parts of the polyester were substituted with 10 parts of a modified polyesteracrylate, prepared from 2 mols of hexane -1:6-diol, 3 mols of adipic acid and 1,2 dihydroxylethyl acrylate. EXAMPLE IV A solution, prepared as in example I, was applied by centrifugation on a laminated glass pane, dried in a current of hot air at 600 C for 1 minute to evaporate the volatile organic solvent (butyl acetate). It was then left exposed to U.V. radiation from 4 medium pressure mercury vapour tubes with an intensity of 60 watts per centimetre. The coating obtained was found to be particularly flexible with good tear resistant properties. EXAMPLE V The solution of example II was applied using the system of example IV, and equivalent results were obtained. EXAMPLE VI The solution od example I was applied by centrifugation on a laminated glass pane, which was dried in a current of hot air at 600 C for 1 minute in order to evaporate the volatile solvent. It was then exposed to SJ,V. radiion from 4 medium pressure mercury vapour tubes with an intensity of 60 watts for a period of one minute, In this way, an incomplete polymerization of the layer applied was obtained; after cooling, a secondo layer was applied on the first layer using the solution of example IV which was polymerized as according to example IV. The coating so obtained was found to be particularly tough and flexible, with a good resistance to tearing by glass fragments, as well as good resistanc-e to abrasion and yellowing. EXAMPLE VII The procedure in examples IV and V was repeated on flat heat-treated glass. The pane of coated glass was submitted to fracture by impact; adequate controllability over the falling of glass fragments was found. EXAMPLE VIII The procedure in example IV was repeated on laminated glass which had been previously treated by spraying with an aqueous alcoholic solution containing 2% aminoethylaminopropyltrimethoxysilane, then dried at 1000 C. The solution of example IV, which was polymerized for 10 minutes at 1000 C according to the process described in example IV, gave rise to a coating with improved adhesion to the substrate.

Claims: CLAIMS OF PATENT 1. Process for obtaining a transparent coating on a pane of glass capable of guaranteeing a tear-proof protection in the event of breakage of said glass, comprising the direct application on the glass pane surface of a solution of polyurethane polymers or pre-polymers dissolved in acrylic monomers or in mixtures of acrylic monomers or in a solution of acrylic prepolymers in acrylic monomers, wherein the as-obtained layer is submitted to a strong catalytic action and/or to photoinitiators capable of favouring polymerization in a interpenetrating polymer network system so as to obtain a particularly thin tear-proof coating with good adhesion to the substrate, with said layer simultaneously possessing the typical elastomeric and physical properties of polyurethane polymers and the typical optical properties as well as good resistance to atmospheric agents of the glassy acrylic polymers. 2. Process as claimed in claim 1 in which the solution applied consists of a polyester-urethane polymer dissolved in an acrylic monomer. 3. Process as claimed in claim 1 in which the solution applied consists of a polyether-urethane polymer dissolved in an acrylic monomer. 4. Process as claimed in claim 1 in which the solution applied consists of one or more polyurethane polymers dissolved in a mixture of acrylic monomers or prepolymers and reactive vinyl monomers. 5. Process as claimed in any one of the claims from 1 to 4, characterized in that the aliphatic polyurethane polymer used is prepared from polyol polyether or polyester with a medium to low molecular weight. 6. Process as claimed in any one of the claims from 1 to 5, in which together with the polyol polyether or polyester an aliphatic isocyanate of bi- or tri-functional type was used to prepare the polyurethane polymer. 7. Process as claimed in one or more of the preceding claims, characterized in that, in order to directly polymerize the urethane prepolymer, acrylic monomers free from carboxyl or hydroxyl groups were used thereby preventing cross linking between the various types of polymers. 8. Process as claimed in one or more of the preceding claims, characterized in that a pretreatment is carried out on the carefully cleaned glass surface consisting of the application of an adhesion accelerator which creates a chemical bridge based on organo-silanes and/or organo-titanium compounds. 9. Process as claimed in claim 8 in which-the silane compound is added directly to the mixture applied on the glass pane. 10. Process as claimed in claims 6 to 9 in which an isocya nate of the bifunctional type is used consisting of 4,4' methylene bis (cyclohexyl isocyanate) or of isophoron diisocyanate. ii. Process as claimed in claims 6 to 9 in which an isocya nate of the tri-functional type is used consisting of isophoron di-isocyanate cyanide or biuret hexamethylene diisocyanate. 12. Process as claimed in one or more of the preceding claims, characterized in that the polyurethane fraction of the mixture used has an excess of hydroxyl groups with respect to the isocyanate groups. 13. Process as claimed in one or more of the preceding claims1 in which the stoichiometric ratio between the isocyanate and polyester in the polyurethane fraction of the mixture varies in the range from 1:20 to 3:20. 14. Process as claimed in claim 5 to 13 in which a polyester is used having a molecular weight between 200 and 5000, preferably between 1000 to 2000. 15. Process as claimed in one or more of the preceding claims, characterized in that the polyester used in the polyuretha ne fraction is esterified preferably with 1,2 ethylene glycol or 1,2 propylene glycol or butane-1:4-diol or hexane 1:6-diol. 16. Process as- claimed in one or more of the preceding claims in which the polyesters used in the polyurethane fraction of the mixture have an acid value lower than 1 and a hydroxil number between 40 and 150, preferably between 50 and 100. 17. Process as claimed in one or more of the preceding claims in which are used as acrylic monomers in the acrylic fraction of the mixture 2-ethyl hexyl acrylate and/or hexanedioldiacrylate and/or ethyleneglycoldiacrylate and/or 2hydroxyethylacrylate. 18. Process as claimed in claims 4 to 17 in which the reactive vinyl monomer used is n-vynil pyrrolidone. 19. Process as claimed in any one of the preceding claims characterized in that the ratio between the polyurethane and acrylic fractions in the mixture is 1:1. 20. Process as claimed in claims 1 to 19 in which the coating is obtained by superimposing more than one layer of said solutions, when a full or partial polymerization of the preceding layer has been carried out. 21. Process as claimed in claims 1 to 20 in which are applied 2 or more layers of a same type of solution. 22. Process as claimed in claims 1 to 21 in which the final layer is obtained with a different solution from that used for the preceding layers, the difference being that said solution contains more highly cross linked compounds. 23. Process as claimed from claims 1 to 22 in which the solutions are applied on the glass surfaces by centrifugal means. 24. Process as claimed from claims 1 to 23 in which the glass substrate is pretreated with an adhesion accelerator. 25. Process as claimed from claims 1 to 24 in which the solutions applied are polymerized by means of ultraviolet radiation. 26. Process as claimed from claims 1 to 24 in which the solutions applied are polymerized by means of an electronic curtain. 27. Process as claimed from claims 1 to 24 in which the solutions applied are polymerized by infrared radiation. 28. Process for obtaining a transparent coating on a glass pane designed to guarantee tear-proof protection in the event of breakage of said glass as claimed in claim 1 in .which the solution applied directly on the glass pane consists of any one of the solutions according to examples I to VIII reported in the description. 29. Process for obtaining a transparent coating on a pane of glass as claimed in claims 1 to 28 in which a quantity of solution is applied such as to obtain a coating with thickness between 100 - 190 microns. 30. Product obtained as claimed in any one of the claims from 1 to 29 in which the glass substrate consists of laminated or toughened safety glass. 31. Product obtained as claimed in any one of the claims from 1 to 29 in which the glass substrate consists of standard, normaIly heat-treated glass. 32. Windscreen for autovehicles manufactured according to a process as described in any one of the claims from 1 to 29.

Inventors: SEBASTIANO, FRANCESCO
Applicants: SOCIETA ITALIANA VETRO - SIV - S.P.A
Application year: 1981
Main classification: C03C17
IPC codes: B60J1, B32B17, C03C17, C08F283, C08G18