METHOD FOR MAKING LAMINATED OPHTHALMIC LENSES

Abstract: A laminated lens assembly consists of a glass lens (9) and a composite, integral, optically transparent organic poly­ meric sheet (1) bonded thereto. The polymeric sheet (1) is composed of a thin thermoplastic polyurethane ply (1A) and a thick thermosetting polyurethane ply (1B). The thermoplastic ply (1A) is bonded to glass lens (9) after the surface of each has been properly cleaned via a blast of deionized air and anti­ static brushing. The lens assembly is particularly suitable for eyeglasses.

Description: Title : LAMINATED OPHTHALMIC LENSES AND METHOD FOR MAKING METHOD FOR MAKING For more than 50 years, research in the manufacture of laminated glass structures for use as safety glass has been relatively continuous. In general, the previous safety glass structure has comprised two sheets or layers of glass bonded together through a plastic interlayer material, customarily a plastic sheet, which is optically transparent and flexible. This latter property of the interlayer is important to inhibit the fragmentation of the glass and to minimize the dispersion of particles thereof when the glass structure is subjected to an impact of sufficient force to cause breakage. Laminated safety glasses have been used for such diverse applications as eyeglasses, instrument lenses, vehicle windows, and building windows. Nevertheless,the' use of the conventional, trilayer safety glass structure consisting of two glass sheets bonded together through an organic plastic interlayer has been subject to a particular problem, which is that when subjected to an impact sufficient to fracture the structure, sharp glass fragments may be projected rearwardly. This problem has been especially acute in the fields of vehicle windshields and eyeglasses where the sharp pieces of broken glass have sometimes induced severe lacerations and loss of sight. The use of a bilayer laminated structure, i.e., an outer sheet or ply of glass and an inner ply of an organic plastic material, has been suggested to provide an answer to this problem. In such a configuration, the plastic is designed to hold the glass fragments resulting from the breakage. However, because the inner plastic ply is exposed to the ambient environment, it must demonstrate good resistance to chemical agents and the effects of radiation so as to maintain the required mechanical and optical properties. The most widely-used plastic interlayer material utilized in the trilayer safety glass structures, viz, polyvinyl butyral, cannot be employed in applications where it will be exposed to moisture. Nevertheless, numerous organic plastics have been prepared which are relatively unaffected by the ambient atmosphere. Such materials include cellulose acetate, cellulose triacetate, cellulose acetate butyrate, cellulose propionate, polyvinyl chloride, copolymers of vinylidene chloride, e.g. vinyl chloride, polycarbonates, polyphenylene ethers, and nylons, polyethylene terephthalate (MYLAR - Registered Trade Mark), and certain urethane polymers. For example, United States Patent No. 4,103,070 describes bilayer laminated glass structures wherein the outer layer comprises a glass ply and the inner lamina is a polycarbonate urethane which is the reaction product of: (1) an organic diisocyanate; (2) an organic compound having two isocyanate reactive hydrogens and a molecular weight less than 250; and (3) a polycarbonate diol prepared from a mixture of linear aliphatic and cycloaliphatic diols wherein the aliphatic diol has at least four carbon atoms comp rising (a) at least 30 mole percent linear aliphatic diol and (b) at least 10 mole percent cycloaliphatic diol. In forming a bilayer structure, the urethane polymer used in the above patent is cast as a 30-35 mil (approximately 750-900 microns) film and the film is assembled between two glass sheets, one of which is coated with a release agent on the surface in contact with the film. The assembly is placed into a plastic bag which after being introduced into an oven, is evacuated to about 26-28 inches of mercury (130-165 millibars absolute pressure), and the oven heated to 2150-3000F (approximately 1000-1500C). The vacuum and heat are continued for a sufficient length of time to remove all the air between the plies of glass, the plastic interlayer material, and the release material. Thereafter, the assembly is transferred to an oil autoclave or other suitable high pressure equipment and exposed to a temperature of about 2500-3000F (approximately 120 - 1900C) and a pressure between about 50-500 psi (approximately 3.5-35 bars) for a sufficient length of time to laminate the structure. The temperature of the autoclave is then reduced, the pressure released, the assembly withdrawn from the autoclave, and the glass ply coated with the release agent stripped away from the assembly, thereby leaving a glass-polycarbonate urethane bilayer laminate. No reference is made to a three-ply laminate composed of an outer glass layer and two organic plastic inner laminae. United States Patent No. 3,867,235 is directed to the production of trilayer laminated glass structures consisting of an outer glass ply weakly bonded to a tough, flexible, optically transparent, organic plastic lamina. A weak bond between the glass and the tough, flexible plastic layer is required to effect partial delamination of the flexible layer from the glass when the latter is subjected to an impact of sufficient force to cause breakage thereof. The strength of the bond is measured in accordance with ASTM D903-49, "Peel or Stripping Strength of Adhesive Bonds". The preferred strengths are stated to range about 0.1-0.5 lbs/linear inch (0.18-0.9N/cm). The preferred intermediate bonding materials are cited as polyvinyl acetate, polyvinyl butyrate, and polystyrene. Although not explicitly stating this to be a required characteristic, the preferred bonding materials will exhibit thermoplasticity. The term polyurethane is mentioned only once and that in a working example where a layer of "polyurethane" is bonded directly to a surface of a glass lens. The resulting structure was deemed unsatisfactory for the desired application. The polymer employed was not identified as being thermoplastic or thermosetting. British Patent No. 1,576,394 discloses the production of a composite, two-layer, preformed polymeric sheet for use in fabricating glass-plastic laminates, the sheet consisting of one ply of a thermoplastic polyurethane having adhesive properties and another ply of a thermosetting polyurethane. The thermoplastic material is optically transparent and essentially non-tacky at room temperature, but will strongly adhere to glass at temperatures of 400C and higher. The thickness of the thermoplastic film is stated to range between about 0.01-0.8 mm and is formed from an aliphatic diisocyanate and a diol of an aliphatic diacid polyester or a diol of a polyglycol ether, each of said diols having a molecular weight between 500-4000. The thermosetting layer is optically transparent, is stated to have a thickness ranging between about 0.2-0.8 mm, and is the reaction product of: (a) a polyglycol ether resulting from the condensat ion of 1,2-propylene oxide with 2,2 bis(hydroxymethyl) l-butanol and containing 10.5-12% by weight free hydroxyls; with (b) a biuret 1,6-hexamethylene diisocyanate having 21-22% by weight of isocyanate groups, the weight of said biuret being between 0.9-1.1 times the weight of said polyglycol ether. The patent discloses preparing trilayer laminates utilizing a glass ply as the outer layer and the inventive two-layer, preformed sheet adhesively attached thereto by means of the thermoplastic lamina. The thermosetting plastic provides anti-lacerative properties and demonstrates self-healing. The desired, three-ply laminated product is fabricated through the following three steps: (1) the outer glass layer is heated to a temperature of at least 400C, preferably 500-800C; (2) a sheet of the inventive composite layer is pressed onto the glass surface while at that temperature with the thermoplastic lamina being in contact with the glass surface, a pressure ranging about 0.5-2 bars above atmospheric pressure being suggested as operable; and (3) the laminate is introduced into an autoclave and heated to higher temperatures and pressures, e.g., temperatures of about 100 -140 C and pressures of about 3-15 bars above atmospheric pressure. The patent also observed that tinting of the plastic sheet may be effected prior to or subsequent to its being applied to the glass ply, but no details were provided as to the dye compositions used or the process for carrying out the tinting. An objective of one aspect of the present invention is to provide a process for making a three-layer, laminated lens structure suitable for eyeglass wear, i.e., prescription and non-prescription lenses, including sunglasses, said lens consisting of an outer ply of glass and an inner layer of an optically transparent, thermosetting polyurethane bonded to the glass through a thin layer of an optically transparent, thermoplastic polyurethane. According to the invention there is provided a method for making a laminated lens assembly consisting of an outer glass lens and a composite, integral, optically transparent organic polymeric sheet bonded thereto, said polymeric sheet being composed of a thin thermoplastic polyurethane ply and a thick thermosetting polyurethane ply, said thermoplastic polyurethane being bonded to said glass lens and being formed from an aliphatic diisocyanate and a diol of an aliphatic diacid polyester or a diol of a polyglycol ether, each of said diols having a molecular weight of 500-4000, and said thermosetting polyurethane being the product of (a) a polyglycol ether resulting from the combination of epoxy-1,2 propane with 2,2-bisChydroxymethyl) l-butanol and containing 10.5-12% by weight free hydroxyls, and (b) a biuret of 1,6-hexamethylene diisocyanate having 21-22% by weight isocyanate groups, the weight of said biuret being from 0.9-1.1 times the weight of said polyglycol ether, said method being characterised in that it comprises the steps of: (1) firmly holding said polymeric sheet composed of a thin ply of thermoplastic urethane and a thick ply of thermosetting polyurethane, said thin ply being exteriorly exposed; (2) cleaning the surfaces to be b-onded together; (3) positioning said glass lens and said polymeric sheet in such a manner that said thermoplEtic polyurethane ply is in contact with the facing side of glass lens; ; (4) pressing said polymeric sheet against said side of said glass lens at room temperature or at a slightly elevated temperature and at slightly elevated pressures to produce a wrinkle-free and uniformly progressive spreading of said sheet on said side of said glass lens and to effect adherence of said sheet to said glass lens to form a laminate; and thereafter (5) subjecting said laminate to elevated temperatures and pressures for a time sufficient to strengthen the bond between said polymeric sheet and said glass lens and to eliminate gaseous inclusions therein. This process can be used to form an optical quality lens free from dust and other foreign particles, air or other gaseous inclusions, and optical distortions resulting from film deformation in the lamination process. In addition, the process provides uniform adhesion of the film to glass lenses of different compositions and contours, such adhesion being essential for the successful edging, framing, and, optionally, tinting of the plastic after lamination. The preferred thermoplatic and thermosetting polyurethanes are those described in British Patent No.1,576,394, supra. Utilizing the multilayer films disclosed in that patent in overall thicknesses of about 0.4 mm with negative power lenses having centre thickness not less than about 0.5 mm and positive power lenses having overall thicknesses not less than about 1 mm, a laminated product with an annealed glass outer layer will withstand the impact of a 5/8" (about 16 mm) steel ball dropped from a height of 50" (about 1.27 m). Whereas the glass will fracture, the fragments resulting therefrom will not penetrate through the organic layers. Where measured in the above -described peel test, the adhesive force demonstrated by the inventive lenses averages about 10 N/cm (approximately 5.68 lbs/in), with values varying about 2 to 25 N/cm. Such peel strength levels permit edging of the laminate whereas the adhesive forces displayed in the laminates of Patent No. 3,867,235 are too weak to ensure a sound product after edging. Commonly, the overall combined thickness of the composite, integral polyurethane sheet utilized will range between about 0.25 to 0.55 mm with the thermoplastic layer varying over the range of about 0.04 to 0.06 mm, the preferred thickness being about 0.05 mm, and the thickness of the thermosetting lamina varying over the range of about 0.2 to 0.5 mm, the preferred thickness being about 0.35 mm. In a preferred form of the invention the method comprises four general steps: (a) cleaning of the glass lens and polymeric sheet surfaces to be joined together, the cleaning step involving, for example, a blast of deionized air, and, at least for the polymer layer, an antistatic brushing operation; (b) positioning the glass lens and polymeric sheet such that the thermoplastic layer is in contact with the glass surface; (c) pressing the sheet against the glass surface at room temperature or at slightly elevated temperatures (about 400 to 800C) and at slightly elevated pressures (about 3 to 5 bars above atmospheric pressure) in such a manner to promote the wrinkle-free and uniformly progressive spreading of the sheet on the glass surface Åand to effect adherence of the sheet to the glass, thereby forming a laminate; and, finally, (d) subjecting the laminate to elevated temperatures (about 750 to 1500C) and to high pressures (about 5 to 25 bars above atmospheric pressure) for times ranging from about 0.5 to 4 hours to strengthen the bond between the sheet and glass and to eliminate inclusions therein. In another of its aspects the invention provides a laminate lens assembly consisting of an outer glass lens and a composite, integral, optically transparent organic polymeric sheet bonded thereto such that, when subjected to the peeling test according to ASTM D903-49, the assembly demonstrates an adhesive forte ranging between about 2-25 N/cm, said lens having a centre thickness not less than about 0.5 mm with a negative power lens and an overall thickness not less than 1 mm with a positive power lens, characterised in that said polymeric sheet consists of a thin thermoplastic polyurethane ply bonded to said glass lens and a thick thermosetting polyurethane ply, the total thickness of said polymeric sheet ranging from about 0.250.55 mm with said thermoplastic polyurethane ply varying from about 0.04-0.06 mm and said thermosetting polyurethane ply ranging from about 0.2-0.5 mm, said thermoplastic polyurethane being formed from an aliphatic diisocyanate and a diol of an aliphatic diacid polyester or a diol of a polyglycol ether, each of said diols having a molecular weight of 500-4000, and said thermosetting polyurethane being the product of (a) a polyglycol ether resulting from the combination of expoxy-1,2 propane with 2 ,2-bis (hydroxymethyl), l-butanol containing 10.5-12% by weight free hydroxyls, and (b) a biuret of 1,6-hexamethylene diisocyanate having 21-229s by weight isocyanate groups, the weight of said biuret being from 0.9-1.1 tires the weight of said polyr3ly- col ether. In the accompanying drawings: FIGURE 1 schematically represents an apparatus for cleaning the surface of the polymeric sheet; FIGURE 2 schematically illustrates an apparatus for cleaning the surface of the lens; FIGURE 3 is a top plan view of the foraminous top surface of the apparatus depicted in FIGURE 1; FIGURES 4 and 5 are schematic side views of the apparatus of FIGURE 1 demonstrating means for positioning the polymeric sheet on the surface of the glass lens; and FIGURE 6 schematically portrays an apparatus for pressing the polymeric sheet against the surface of the glass lens. In the embodiment shown in the drawings, an optically transparent, unitary, polymeric composite sheet 1 is prepared composed of a thin layer of thermoplastic polyurethane 1A and a thick layer of thermosetting polyurethane lB. As illustrated in FIGURES 1 and 3, polymeric sheet 1 is positioned with thermosetting layer 1B resting upon the top surface 2 of the apparatus which had previously been treated with anti-adhesive and anti-reflective materials 3. Polymeric sheet 1 is applied with its thermosetting layer 1B against the top surface 2 of the apparatus by a vacuum through small holes 4 connected for this purpose to a vacuum source 10 of about 50 mm mercury (approximately 67 millibars). The size of the holes 4 and extent of the vacuum are regulated such that the force exerted on sheet 1 by the vacuum will not induce any permanent deformation of the sheet 1 in the holes 4. Valve 8 permits a vacuum to be drawn or compressed air to be introduced from pressure source 11 through holes 4. Particles which may be resting upon the thermoplastic layer 1A of polymeric sheet 1 are illuminated under low incidence light 5. Deionized air is blown through pipes 6 onto thermoplastic layer 1A of sheet 1 to remove such particles which are aspirated through suction holes 7 located around ther perimeter of sheet 1. The cleaning operation with deionized air is advantageously completed by means of light antistatic brushing utilizing a brush made of long haired velvet and connected to an aspirator (not shown). Immediately prior to bringing glass lens 9 and polymeric sheet 1 into contact with each other, a blast of deionized air is directed onto the inner surface 9A of lens 9 through pipe 12 (FIGURE 2) to remove any possible dust. Then, referring to FIGURE 4, glass lens 9 is placed upon polymeric sheet 1, the thermosetting layer 1B thereof resting on the top surface 2 of the cleaning apparatus. In FIGURE 5, a partial vacuum which holds sheet 1 to the top surface 2 is interrupted by actuating valve 8 and, instead, compressed air is blown through holes 4. As a consequence, sheet 1 is removed from the top surface 2 and forced against side 9A of lens 9. The position of the holes 4 and the force of the compressed air applied from source 11 are controlled in such a manner that sheet 1 is moved against side 9A of lens 9 without irregular distortion or stresses. Sheet 1 adheres sufficiently well to lens 9 to prevent the entrance of loose particles therebetween. FIGURE 6 represents an apparatus which has been found to be very effective in pressing sheet 1 into uniform contact with the surface of lens 9 while simultaneously eliminating large gaseous inclusions from the laminated structure. The apparatus basically consists of a pneumatic cylinder 13, a plunger 14, and a lens holder 15 whose function is to hold lens 9 securely. The contour of plunger 14 and the hardriess of the material are selected to effect a wrinkle-free and uniformly progressive movement of polymeric sheet 1 over the surface of side 9A of lens 9. An elastomer material having A Shore hardness of 45 has functioned very well to provide films of uniform thickness over lenses within the range of -18 to +20 diopters, i.e., having surface radii ranging from 175 mm to 20 mm. After this pressing step, the laminated structure may be stored indefinitely under normal conditions and ambient temperature. Heating the laminate at elevated temperatures and pressures to strengthen the bonding and to remove any gaseous inclusions can be carried out in an air autoclave or other high pressure equipment. With the thermoplastic and thermosetting films used herein, the preferred operating procedure involves exposure times of about 2 to 3 hours, temperatures varying over the interval of about 100-120 C, and pressures ranging between about 12-18 bars above atmospheric pressure. Most advantageously, the laminate will be subjected to the elevated temperatures and pressures at relatively the same time, for example using an autoclave with the laminate contained therewithin can be heated to a predetermined temperature and the pressure raised in conjunction therewith. A dwell time of about two hours within the preferred ranges of temperatures and pressures has been deemed especially suitable to ensure strong, substantially bubble-free laminates. Also, to inhibit thermal deformation, it is strongly recommended that the laminated structure be cooled under pressure at least down to a temperature of about 400C.

Claims: CLAIMS: 1. A method for making a laminated lens assembly consisting of an outer glass lens (9) and a composite, integral, optically transparent organic polymeric sheet (1) bonded thereto, said polymeric sheet (1) being composed of a thin thermoplastic polyurethane ply (IA) and a thick thermosetting polyurethane ply (1B), said thermoplastic polyurethane (1A) being bonded to said glass lens (9) and being formed from an aliphatic diisocyanate and a diol of an aliphatic diacid polyester or a diol of a polyglycol ether, each of said diols having a molecular weight of 500-4000, and said thermosetting polyurethane being the product of (a) a polyglycol ether resulting from the combination of epoxy-1,2 propane with 2,2-bis(hydroxymethyl) 1-butanol and containing 10.5-12% by weight free hydroxyls, and (b) a biuret of 1,6-hexamethylene diisocyanate having 21-22% by weight isocyanate groups, the weight of said biuret being from 0.9-1.1 times the weight of said polyglycol ether, said method being characterized in that it comprises the steps of: (1) firmly holding said polymeric sheet (1) composed of a thin ply (1A) of thermoplastic urethane and a thick ply (1B) of thermosetting polyurethane, said thin ply (1A) being exteriorly exposed; (2) cleaning the surfaces (9A,lA)to be bonded together; (3) positioning said glass lens (9) and said polymeric sheet (1) in such a manner that said thermoplastic polyurethane ply (1A) is in contact with the facing side (9A) of glass lens (9); ; (4) pressing said polymeric sheet (1) against said side (9A) of said glass lens (9) at room temperature or at a slightly elevated temperature and at slightly elevated pressures to produce a wrinkle-free and uniformly progressive spreading of said sheet (1) on said side (9A) of said glass lens (9) and to effect adherence of said sheet (1) to said glass lens (9) to form a laminate; and thereafter (5) subjecting said laminate (1,9) to elevated temperatures and pressures for a time sufficient to strengthen the bond between said polymeric sheet (1) and said glass lens (9) and to eliminate gaseous inclusions therein. 2. A method according to claim 1 characterized in that said polymeric sheet (1) is pressed against side (9A) of said lens (9) at temperatures from about 400-800C and at pressures ranging from about 3-5 bars above atmospheric pressure. 3. A method according to claim 1 characterized in that said laminate (1,9) is exposed to temperatures from about 75 0-1500C and pressures from about 5-25 bars above atmospheric pressure for time intervals ranging from about 0.5-4 hours. 4. A method according to claim 3 characterized in that said laminate is exposed to temperatures from about 100 - 125"C, pressures from about 12-18 bars above atmospheric pressure, for time intervals ranging from about 2-3 hours. 5. A laminate lens assembly consisting of an outer glass lens (9) and a composite, integral, optically transparent organic polymeric sheet (1) bonded thereto such that, when subjected to the peeling test according to ASTM D903-49, the assembly demonstrates an adhesive force ranging between about 2-25 N/cm, said lens (9) having a centre thickness not less than about 0.5 mm with a negative power lens and an overall thickness not less than 1 mm with a positive power lens, characterized in that said polymeric sheet (1) consists of a thin thermoplastic polyurethane ply (1A) bonded to said glass lens (9) and a thick thermosetting polyurethane ply (1B), the total thickness of said polymeric sheet (1) ranging from about 0.25-0.55 mm with said thermoplastic polyurethane ply (1A) varying from about 0.04-0.06 mm and said thermosetting polyurethane ply (1B) ranging from about 0.2-0.5 mm, said thermoplastic polyurethane (1A) being formed from an aliphatic diisocyanate and a diol of an aliphatic diacid polyester or a diol of a polyglycol ether, each of said diols having a molecular weight of 500-4000, and said thermosetting polyurethane being the product of (a) a polyglycol ether resulting from the combination of expoy-1,2 propane with 2,2-bis(hydroxymethyl) l-butanol containing 10.5-12% by weight free hydroxyls, and (b) a biuret of 1, 6-hexamethylene diisocyanate having 21-22% by weight isocyanate groups, the weight of said biuret being from 0.9-1.1 times the weight of said polyglycol either. 6. A laminated lens assembly according to claim 5 characterized in that the total thickness of said polymeric sheet (1) is about 0.4 mm. 7. A laminated lens assembly according to claim 6 characterized in that said thermoplastic polyurethane (1A) has a thickness of about 0.05 mm and said thermosetting polyurethane ply (1B) has a thickness of about 0.35 mm.

Inventors: BOGNAR, LEWIS LEE, GOEPFERT, SERGE, ROGER, FRANCOISE, VACHET, ANDRE
Applicants: CORNING GLASS WORKS
Application year: 1982
Main classification: B29D11
IPC codes: B32B17, B29C39, C08G18, B29C61, B29C65, B29D11, G02B1