Patent Application
20070264426
1. Technical Field
The present invention relates to a method for coating an optical lens, and in particular, to an improved system and method for coating a segmented multifocal lens.
2. Description of Related Art
Optical lenses are typically manufactured from polycarbonate due to the myriad of advantages such material offers which makes it ideally suited for optical use. Namely, polycarbonate possesses a high index of refraction, blocks all UVA and UVB radiation, is an ideal candidate for injection molding processes, is easily drilled (e.g., for securing to eye frames), and is lightweight and highly impact resistant. However, polycarbonate in untreated form is a relatively soft material vulnerable to scratches and other surface insults. When a lens is scratched or otherwise damaged, the optical properties of the lens are negatively affected. Various methodologies for imparting scratch resistance to polycarbonate lenses are known, among them the application or integration of scratch-resistant coatings to the lens itself.
With lenses having uniform, smooth surfaces, application of such coatings is typically effectively achieved via straightforward methods such as dip coating the lens into a coating composition. Uniform coating distribution may accordingly be achieved on such lenses in a relatively simple manner with satisfactory results.
Certain lenses having irregular surfaces, e.g., typically lenses designed to offer more than one focal point or lens power (multifocal lenses) within each lens, are often configured such that the area of the lens that offers a separate focal distance is segmented and projects away from at least one major optical surface of the lens. Such segmented lenses may include, e.g., a raised or protruding area (segment) which is elevated from the rest of the lens area, and thus have a segment line or ridge separating the powers. Segmented lenses thus have a non-uniform surface profile. Straight top bifocal lenses are one example, having a “D” shaped segment dedicated to a particular focal distance with a straight top protruding edge. Currently, straight top lenses are coated by means of, e.g., dip coating or a complex process of centering the straight top edge in the middle of a spin coater while dispensing a coating material at a precise location and time during the spin process.
Coating solutions applied to these optical surfaces must flow around and over these segments. However, both dip coating and spin coating methods when used with segmented lenses often produce undesirable results, namely, the occurrence of drip lines, flow marks, or bubbling at the protruding edges. In addition, such methods do not allow for a thicker hard coating. Lack of sufficient coating thickness tends to lead to poorer mechanical values and reduced durability.
U.S. Pat. No. 4,544,572 describes coating of ophthalmic lenses via application of a coating solution to a mold surface. It specifically mentions wherein if a mold is designed for the production of multifocal lenses having a straight segment line (e.g., a flat top lens), the face containing the multifocal portion is positioned so that the straight segment line is parallel to the vertical, such that the outline of the segment forms the letter “D”.
U.S. Pat. No. 6,884,292 and U.S. Patent Application Publication No. 2005/0208212 discuss methods for applying a coating to optical lenses via dipcoating. U.S. Pat. No. 6,077,569 describes a coating method for a plastic lens substrate via plasma ion beam deposition and bombarding with energetic atoms.
Accordingly, an efficient and effective coating technique for lenses having a non-uniform surface profile, in particular, for segmented multifocal (e.g., bifocal or trifocal) lenses, is highly desirable.
It is an object of the present invention to provide an improved coating technique for lenses having non-uniform or irregular surface profiles.
It is a further object of the invention to provide an improved coating technique for multifocal segmented lenses, namely, straight top multifocal lenses.
According to an aspect of the present invention, a method for providing an optically uniform coating to an optical non-uniform surface profile of an ophthalmic lens is provided comprising the steps of providing the lens having a straight edge in a first orientation relative to at least one stationary ultrasonic spray nozzle, and positioning the nozzle a predetermined height above the optical surface of the lens. The lens is moved at a predetermined speed in a direction towards the nozzle and a coating composition is simultaneously applied in atomized form during traveling of the lens surface beneath the nozzle. The first orientation comprises wherein a length of the straight edge is substantially perpendicular to the direction of travel of the lens towards the nozzle.
According to another aspect of the present invention, a method for coating a segmented straight top ophthalmic lens is provided comprising the steps of providing the straight top lens having a straight edge in a first orientation relative to at least one stationary ultrasonic spray nozzle, and applying a coating material in atomized form during traveling of the lens surface beneath the nozzle, the first orientation comprising a length of the straight edge being substantially perpendicular to the direction of travel of the lens.
These and other aspects, features and advantages of the present invention will be described or become apparent from the following detailed description of the preferred embodiments, which is to be read in connection with the accompanying drawings.
The advantages, nature, and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments now to be described in detail in connection with accompanying drawings. In the drawings wherein like reference numerals denote similar components throughout the views:
The present invention provides a system and method for coating optical lenses having inherently uneven, non-uniform surface topographies (e.g., segmented multifocal lenses) which achieves improved optical uniformity and evenness in coating distribution. According to an aspect of the present invention, a coating composition may be uniformly and precisely applied to, e.g., a segmented multifocal lens having a raised portion, with minimal to non-existent coating build-up and/or bubbling at ridges, and with minimal coating waste. Advantageously, these features may be achieved despite the challenging mechanical properties presented by segmented lenses having non-uniform surface profiles and the resultant difficulty in uniformly coating same. Namely, the objectives of the present invention are achieved through a novel lens positioning and coating methodology described herein with reference to the Figures.
Referring now to the Figures,
Spray device 107 preferably comprises an ultrasonic atomizer, and includes an ultrasonic spray nozzle 109 through which an atomized liquid coating composition is projected.
Surprisingly, it was found that the positioning of a straight top lens 201 in a specific orientation (“first orientation”) compounded with the specially adapted use of an ultrasonic atomizer produced unexpected and improved segmented lens coating results. Namely, the lens 201 is preferably oriented such that the straight line portion 304 of the segment 203 is substantially perpendicular to the direction of movement 305 of the lens 201 towards nozzle 301. During coating application, the lens 201 is moved at a predetermined speed towards the nozzle 301, preferably from about 1 to about 3 mm/sec, and the coating composition is ejected from the nozzle 301 preferably at a predetermined flow rate, e.g., from about 1 to about 2 ml/min. During coating, the nozzle 301 is preferably held stationary (e.g., is mounted on a fixed mounting structure) as the lens 201 is caused to travel (e.g., via moving tray 302) at a predetermined speed beneath the spray.
An ultrasonic spray nozzle typically operates at a specific resonant frequency, determined primarily by the length of the nozzle. Both free ends of the nozzle should be anti-nodes (points of maximum vibrational amplitude). The nozzle produces standing, sinusoidal longitudinal waves. A critical amplitude is ultimately reached at which the height of the capillary waves exceeds that which is required to maintain their stability. The result is that the capillary waves collapse and tiny drops of liquid are ejected from the tops of the degenerating waves to the atomizing surface of the nozzle.
Ultrasonic atomization as employed according to an aspect of the present invention advantageously has been found to assist in imparting improved process control and precise, uniform thin film coatings for segmented lenses. Existing and known ultrasonic atomizers (e.g., ultrasonic spray devices used in the electronics industry, namely, devices having an ultrasonic spray nozzle including piezoelectric transducers, ground and active electrodes and an atomizing surface) may be utilized in the present invention Various types of ultrasonic nozzles may be utilized, e.g., a Vortex™ nozzle, e.g., a Sono-Tek™ nozzle Model 8700-60 A2 (which sprays in about a 3.0″-8.0″ diameter conical pattern) or a widetrack nozzle, e.g., a Sono-Tek™ nozzle Model 8700-120 A2 (which provides up to about 24.0″ of coverage). The power of the ultrasonic spray is preferably at a setting of 25 KHz to 120 KHz.
Representative exemplary coating compositions used according to the present invention may comprise any coating material desired to be imparted onto a polycarbonate lens (e.g., for imparting increased durability), such as, e.g., glycidoxypropyltrimethoxysilane based coatings, latex (polyurethane) coatings, polyphasic acrylic coatings, etc. A preferred viscosity range of a coating to be applied according to an aspect of the present invention is from about 1.0 cps to about 10.0 cps, preferably from about 1.0 cps to about 3.0 cps. Preferred coating compositions comprise coatings with solvents having a viscosity of about 2.0 cps.
In step 403, a multifocal segmented lens having an optical surface area desired to be coated is provided. Such a segmented lens may comprise bifocal, trifocal lens, etc., and namely, may comprise a lens having a straight-top or D-shaped segment which provides a different focal point from the rest of the lens. For example, the D-shaped segment may be reserved for near-vision correction, while the remaining lens area may assist in distance correction or have no power at all. The segmented lens is positioned in a particular orientation relative to the spray nozzle (a “first orientation”); for example, the lens 201 is preferably oriented such that the length of straight line edge 304 of the segment 203 is substantially perpendicular to the direction of movement 305 of the lens 201 along the guide rod 103.
A spray nozzle 301 is positioned overhead a predetermined height above the lens surface 202 to direct an atomized spray in a downwards direction 303 onto the lens 201 (step 405). The predetermined distance between the nozzle tip and lens surface may comprise, e.g., about 40 to about 60 mm, and preferably comprises about 55 mm. The plane of surface 202 is substantially perpendicular to the downwards direction 303 of the coating spray.
During coating application, the lens to be coated is moved along the rod 103 at a predetermined speed and passed under the stationary nozzle 301 while the coating composition is simultaneously ejected from the nozzle at a predetermined flow rate onto the area of the lens surface to be covered (steps 407, 409). The predetermined speed preferably comprises, e.g., about 1 to about 10 mm/sec, most preferably from about 5 to about 10 mm/sec. The predetermined flow rate preferably comprises, e.g., about 1 to about 2 ml/min.
It is to be noted that, e.g., coating flow rates as well as the power of the ultrasonic spray are parameters which may be adjusted as necessary depending, e.g., on the density and/or viscosity of coating material used. Further, one or more ultrasonic spray nozzles may be mounted in series during coating according to an aspect of the present invention. For example, multiple spray nozzles may be set up in parallel and/or may be set up in series to coat, e.g., in multiple passes over the same lens and/or for applying different coating materials.
Experimental data:
Representative data results are presented in the following Table 1.
For optimal results and most satisfactory coverage of the segmented lens undergoing a coating process according to the present invention, in a preferred embodiment, the following parameters were used:
Flow rate: 2 ml/min
Height of lens from nozzle: 55 mm
Speed of lens travel: 5-10 mm/sec
Following ultrasonic spray application of coating material, the applied coating layer is cured via thermal and/or UV curing, etc. to obtain a coated lens.
Key advantages of the present invention include the capability to now provide significantly improved uniform coating of segmented lenses with minimal drip lines or bubbling at line edges in a most efficient manner, with minimal coating waste and overspray. The present invention provides such advantages while permitting flexibility in the types of coatings used and coating parameters employed. Moreover, the present invention enables the production of thicker hard coatings (e.g., coatings in excess of 3-20 μm) on segmented lenses with minimal drip lines and/or bubbling. Uniform thicker coatings may be achieved according to an aspect of the present invention via e.g., increasing the viscosity of the coating fluid, decreasing application speed, and/or running the lens through multiple passes.
Overall, the present invention provides, in one embodiment, a significantly improved coating process for segmented multifocal lenses, namely, the virtual elimination of coating defects, characterized by bubbling, drip lines, etc. at the segment line.
Having described preferred embodiments for lens coating, materials used therein and methods for processing same (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as outlined by the appended claims. Having thus described the invention with the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.
