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Process for transferring coatings onto a surface of a lens substrate with most precise optical qualityRelated Patent Categories: Adhesive Bonding And Miscellaneous Chemical Manufacture, Methods, Surface Bonding And/or Assembly Therefor, Optically Transparent Glass Sandwich Making (e.g., Window Or Filter)Process for transferring coatings onto a surface of a lens substrate with most precise optical quality description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060219347, Process for transferring coatings onto a surface of a lens substrate with most precise optical quality. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an improved process or method for transferring at least one coating onto at least one geometrically defined surface of a lens substrate, which can be implemented in a short period of time without any risk of deformation of the lens substrate, which avoids the use of a liquid curable adhesive composition for adhesion of the coating to the lens substrate and results in the coating adhering to the lens substrate through an adhesive layer of uniform thickness. [0003] 2. Description of Related Art [0004] It is a common practice in the art to coat at least one main surface of a lens substrate, such as an ophthalmic lens or lens blank, with several coatings for imparting to the finished lens additional or improved optical or mechanical properties. These coatings are designated in general as functional coatings. [0005] Thus, it is usual practice to coat at least one main surface of a lens substrate, typically made of an organic glass material, with successively, starting from the surface of the lens substrate, an impact-resistant coating (impact resistant primer), an abrasion- and/or scratch-resistant coating (hard coat), an anti-reflection coating and, optionally, an anti-fouling top coat. Other coatings such as a polarized coating, a photochromic or a dyeing coating may also be applied onto one or both surfaces of the lens substrate. [0006] Numerous processes and methods have been proposed for coating a surface of an ophthalmic lens and are disclosed. [0007] U.S. Pat. No. 6,562,466 describes one process or method for transferring a coating from at least one mold part onto at least a geometrically defined surface of a lens blank comprising: [0008] providing a lens blank having at least one geometrically defined surface; [0009] providing a support or mold part having an internal surface bearing a coating and an external surface; [0010] depositing on said geometrically defined surface of said lens blank or on said coating a pre-measured amount of a curable adhesive composition; [0011] moving relatively to each other the lens blank and the support to either bring the coating into contact with curable adhesive composition or bring the curable adhesive composition into contact with the geometrically defined surface of the lens blank; [0012] applying a sufficient pressure onto the external surface of the support so that the thickness of a final adhesive layer once the curable composition cured is less than 100 micrometers; [0013] curing the layer of adhesive composition; and [0014] withdrawing the support or mold part to recover the lens blank with the coating adhered onto the geometrically defined surface of said lens blank. [0015] U.S. Pat. No. 6,562,466 uses a liquid light or thermal curable adhesive composition to transfer the coating layers from the carrier to the surface of the lens substrate. The liquid curable adhesive composition is required to stick both to the exposed coating on the carrier and the geometrically defined surface of the lens substrate. The process requires to precisely dropping the liquid adhesive composition, either too much or too less of the liquid adhesive needs to be avoided, which renders the process more complicated and less cost effective. Furthermore, this process may cause optical distortions when the liquid adhesive composition is not spread out very evenly on the lens curved surface. In particular, when the liquid adhesive composition is spread using air pressure (inflatable membrane apparatus) applied on a flexible coating carrier, the applied pressure may not usually be uniform over the whole carrier surface, resulting in an uneven spreading of the liquid adhesive composition and a final cured adhesive layer having some variations in thickness. SUMMARY OF THE INVENTION [0016] Therefore, one object of the invention is to provide a process or method for transferring at least one coating from a carrier onto a geometrically defined surface of a lens substrate, which avoids the drawbacks of the prior art processes and in particular avoids the use of a flowable liquid curable adhesive composition. [0017] A further object of the invention is to provide a process or method as above, which results in a coated lens substrate in which the coating(s) adhere(s) to the lens substrate surface through an adhesive layer of very uniform thickness. [0018] According to the invention, there is provided a process for transferring at least one coating onto at least one geometrically defined surface of a lens substrate, which comprises the steps of: [0019] (a) obtaining a carrier having a main surface bearing at least one functional coating; [0020] (b) obtaining a lens substrate having at least one geometrically defined surface; [0021] (c) depositing, either on said at least one functional coating or said at least one geometrically defined surface of the lens substrate, a layer of a transparent adhesive composition; [0022] (d) bringing said layer of transparent adhesive composition to a state at which the layer becomes unflowable under the process conditions if said layer is not already in such a state at the end of step (c); [0023] (e) moving the carrier and the lens substrate relatively to each other to bring the layer of transparent adhesive composition into direct contact with either said at least one geometrically defined surface of the lens substrate or said at least one functional coating; [0024] (f) pressing together the layer of transparent adhesive composition and either said at least one functional coating or said at least one geometrically defined surface of the lens substrate; [0025] (g) optionally, applying heat during pressing step (f); [0026] (h) stopping pressing step (f); and [0027] (i) withdrawing the carrier to recover the lens substrate coated with said at least one functional coating adhering to said at least one geometrically defined surface through the layer of transparent adhesive composition. [0028] In one embodiment of the process of the invention, the main surface of the carrier, preferably a flexible carrier, bears a stack of several functional coatings. Of course, the coatings are then applied on the surface of the carrier in the reverse order with regard to the desired order of the coating stack on the lens substrate. [0029] Preferably, the at least one functional coating is transferred on a geometrically defined surface of the rear surface of the lens substrate. In such a case, the coating transfer process is referred to as a BST (back side transfer) process. Of course, geometrically defined surfaces of front surface or both rear and front surface of the lens substrate can be coated using the process of the invention. The rear surface (generally the concave surface) of the lens substrate is the surface of the lens substrate which, in use, is the closest to the wearer's eye. The front surface (generally the convex surface) of the lens substrate is the surface of the lens substrate which, in use, is the farthest from the wearer's eye. [0030] The ophthalmic articles which can be treated by the process of the invention are finished or semi-finished articles preferably comprising a transparent polymer substrate. [0031] The geometrically defined surface of the lens substrate to be coated in this invention may be a spherical, toric or progressive surface, provided that an adequate spherical flexible carrier is employed. [0032] The present invention also encompasses the case in which the transparent adhesive composition layer is pre-deposited and brought to a state at which the layer is unable to flow, either on a functional coating borne by a carrier or on a geometrically defined surface of a lens substrate, which may be stored and later used in the process steps e) to i) of the invention. [0033] In a preferred embodiment of the process of the invention, the transparent adhesive composition is selected from the group consisting of pressure-sensitive adhesives (PSA) and hot-melt adhesives (HMA). [0034] Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. BRIEF DESCRIPTION OF THE DRAWINGS [0035] The foregoing and other objects, features and advantages of the present invention will become readily apparent to those skilled in the art from a reading of the detailed description hereafter when considered in conjunction with the accompanying drawings wherein: [0036] FIGS. 1A to 1C are schematic views of the main steps of a first embodiment of the process of the invention for transferring at least one coating onto at least one geometrically defined surface of a lens substrate, in which the layer of a transparent adhesive composition is deposited on at least one functional coating; [0037] FIGS. 2A to 2C are schematic views of the main steps of a second embodiment of the process of the invention wherein the layer of a transparent adhesive composition is deposited on at least one geometrically defined surface of the lens substrate; Continue reading about Process for transferring coatings onto a surface of a lens substrate with most precise optical quality... 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