[001] The present invention relates to a method for demolding the polymerized lens from its glass-mold assembly. Particularly, the present invention relates to a method for demolding convex bulk ophthalmic lens of refractive index 1.56 without applying manual mechanical force.

BACKGROUND OF THE INVENTION

[002] The phenomenal growth of the industry which is engaged in the manufacture of the evermore popular bulk ophthalmic lenses, especially the aspects of the industry which pertains to the supplying of lenses in spectacles which are intended for frequent periodic replacement by a wearer, has dramatically increased the need for the mass-production of immense quantities of such lenses which are of a consistently high quality while being inexpensive to produce. Consequently, commensurate with the foregoing needs of the industry, this has necessitated manufacturers of such lenses to strive for the development of automated methods and apparatuses which are particularly adaptable to high-speed automated production practices, and which perform with consistency at adequate degrees of accuracy or precision in a highly cost-effective and consequently economically viable manner.

[003] Casting is a most economical and popular technology in mass production to manufacture bulk ophthalmic stock lenses. Manufacturing process of the said lenses involves depositing a curable mixture of polymerizable monomers in a mold cavity formed by two mold sections, curing the monomer mixture, and disassembling the mold assembly and removing the lens. During casting process, both male-mold and female-mold are taped together with appropriate airgap to form the glass-mold cavity. The said cavity is filled with polymerizable-resin. After polymerization process, the thermally cured lens is held tightly together with mold-surfaces. Demolding is the process of separating the cured-lens from the pair of bulk-glass-molds.
[004] In the existing technology, demolding of 1.56 refractive-indexed bulk ophthalmic lenses are done manually by applying undue force at the circumferential surface of the either or both male or female mold using mechanical leverage. Since glass-molds are brittle so ‘the mold separation force’ may increase the likelihood of breakage or damage of either or both glass-molds and cured-lens thereby reducing the shelf-life of glass-molds, reducing the yield, and increasing the cost of production.

[005] Further manual demolding of 1.56 Index Convex (plus power) lenses are relatively circumferential thickness (edges) of convex-lens is thinner compared to its center-thickness. So, in manual demolding likelihood of breakage/damage of either or both glass-molds and cured-lens are higher for the said lenses.

[006] Particularly, for convex lenses (plus power lens) the damage of molds while demolding are relatively higher than the concave lenses due to its geometry. Manual demolding process is time-consuming and there are chances of obtaining scratch or crack at working surfaces of molds/lenses. Therefore, it leads to reduce the shelf-life of the molds, lower the yield, and also increasing manufacturing-cost of the product.

[007] In order to overcome the above issues, and reduce the adhesion between the molds and lens, convex lens-mold assemblies are dipped into hot-water-bath typically for 3 to 5 minutes, and proceed with manual demolding.

[008] For lenses having refractive index of 1.49, a peeling method of plastic lens and glass molds separation is disclosed in Japanese Patent No. JPS55123428. This patent is related to the method, wherein glass mould is peeled off from plastic lens after cast polymerisation method. It deals with the peeling method of plastic lens of refractive index of 1.49 and glass mould, wherein glass mould and plastic lens after cast polymerization, are passed through more than 2 liquid vessels in the presence of the ultrasound and the temperature difference between the tank is maintained between 50? to 70?. The lowest value of processing temperature is less than ambient temperature, typically -10? to 5?.

[009] In the existing technology, partially automated and semi-automated processes are used in the production of ophthalmic lenses, however, high production rates are not achievable, partly due to the strict process controls and tight tolerances necessary in the production of high quality ophthalmic lenses.

[010] The present invention provides a means for removing an ophthalmic lens from the lens-mold assembly. This invention greatly simplifies this portion of the lens making process by saving cost of electric power due to absence of ultrasound in a processing tank, thereby increasing throughput and allowing for automation.

OBJECTIVES OF THE INVENTION

[011] The primary objective of the present invention is to provide a method for removing an ophthalmic lens from the glass mold assembly.

[012] Another object of the invention is to reduce number of processing tanks by utilizing ultrasound to minimize thermal shock on mold-lens assembly, and also reduced cost of the demolding machine, particularly for plus power lenses.

[013] Another objective of the present invention is to provide only two processing tank and no ultrasound in the second processing tank for thermally cured convex lens of index 1.56.

[014] Yet another object of the invention is to provide a method for releasing adhesion bond at the interface of convex mold-lens surfaces without applying mechanical force.

[015] Yet another objective of the present invention is to improve shelf-life of the glass molds.

[016] Yet another objective of the present invention is to provide a fast, efficient and precise method of demolding.

[017] Yet another objective of the present invention is to reduce the ultrasound exposure time per batch.

[018] Still another object of the invention is to provide a processing tray designed to accommodate more number of pieces of convex lens-glass-mold assembly, which reduces scratches in functional area of both lens and glass-mold during processing.

SUMMARY OF THE INVENTION
[019] The present invention provides method and apparatuses which are utilized for the production of ophthalmic lenses, and more particularly, pertains to a method for the removal or demolding of molded bulk ophthalmic lenses from the individual glass-molds in which they are produced. The method utilizes a two-step process, wherein in the first step, bonding between the convex-lens and glass-mold assembly is reduced in the first processing tank followed by thermal contraction of lens-glass mold assembly in second processing tank weakening the interface bonding. Therefore, so that the lens-glass mold assembly is easily separated without any mechanical force.

DETAILED DESCRIPTION OF INVENTION
[020] The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. The detailed description of the appended drawings is construed as a description of the currently preferred embodiment of the present invention and does not represent the only form in which the present invention may be practiced. This is to be understood that the same or equivalent functions may be accomplished, in any order unless expressly and necessarily limited to a particular order, by different embodiments that are intended to be encompassed within the scope of the present invention.

[021] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[022] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[023] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention.

[024] It is to be understood that the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.

[025] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[026] The present invention is applicable to a convex lens but may also be applied to a concave lens. However, an embodiment in which the spirit of the present invention is applied to a convex lens is hereinafter described in detail.

[027] In accordance with the present invention, a demolding method is provided which utilizes at least two processing tanks, at least one processing tray, at least one tray holder and a device for automated movement of the processing tray. In a specific embodiment, the demolding method utilizes two tanks i.e. tank 1 and tank 2, a processing tray with ‘convex-lens-glass-mold assembly’, a Basket/ Zig to hold the processing tray, and a robotic arm for automatic tray movement. Lesser number of processing tank are utilized to reduce repetitive thermal shock on mold-lens assembly, hence preferably only two tanks are utilized for the demolding process.

[028] In a specific embodiment of the present invention, two dimensionally identical process tanks are used. Both the processing tanks i.e. tank 1, and tank 2 have an outer dimension of 20 x 20 x 12 inches (length x width x height), and internal dimension of 500 x 500 x 300 mm (length x width x height) with effective volume of 75 litres or 19.80 US GAL. However, the dimensions of both the tanks may be varied and thereby increasing or decreasing the effective volume. Further for the said dimension, twenty ultrasound transducers have been fixed within the transducer box, and each transducer has a power rating of 60W to achieve a power output of 3.5 W/inch2 to 5 W/inch2. The number of ultrasound transducers may increase or decrease depending upon the size of the tanks. Both the tanks are filled with water which is maintained at a temperature below the boiling point of water, specifically between 85? to 96? in order to protect the molds. Further, the processing time depends on the power of the lens.

[029] In accordance with the present invention, in tank 1, the interface bonding between the glass-molds and lens is reduced. In order to improve the shelf-life of mold there is no ultrasound used in tank 2. Further in tank 2, temperature of water is maintained just above the ambient temperature allowing the lens-glass mold assembly to contract thermally. Operating temperatures of tank 2 is 25oC to 40oC. The processing tray and handling-zig /basket are designed to accommodate more number of pieces of convex-lens-glass-mold assembly thereby reducing scratches in functional area of both lens and glass-mold during processing. The said tray facilitates in improving the ‘impact of ultrasonic effect’ on said assembly. Further the said tray is placed inside the handling-zig/basket wherein the robotic arm handles the zig/ tray-movement automatically.

[030] As per a preferred embodiment, demolding method of the present invention for separating the mold halves and removing the lens is explained below:
[031] First Stage of de-molding:
Firstly, the processing tray is positioned with tape-removed convex ‘glass-mold-lens assembly’. Secondly, the said tray is immersed in a tank 1 having hot water with a temperature in the range of 80? to 98? to produce differential thermal expansion between the glass-molds and lens. The said thermal expansion aids in reducing the strength of the bonding at the interface of cured-lens and glass-molds.

[032] In the aforementioned process, the ultrasonic waves at a frequency range of 20KHz to 50KHz is made incident along the direction of the perimeter of lens and glass mold assembly, and power is launched simultaneously to release the grip at the interface.

[033] Since, the angle of incidence of ultrasonic wave at the said assembly decides the amount of reflection and transmission of wave between the media for the given material. Therefore, to reduce the amount of reflection and transmission of wave, the tray is designed such that the angle of incidence of the ray formed by said wave is zero. This results in maximum amount of wave being transmitted into lens-mold assembly which develops the de-bonding force at the interface, and also reduces the processing time.

[034] The time taken in demolding of 1.56 refractive indexed lenses depends upon the following properties:
(a) adhesion property of cured-resin with glass-molds,
(b) geometrical size of the lens,
(c) geometry of the mold,
(d) operating temperature of process tank, and
(e) power and frequency of ultrasound.

[035] In tank 1, the processing time is associated with Ultrasonic Power, ultrasonic frequency, temperature of water, and power of the lens-mold assembly. The typical processing time for single tank for the said tank specification varies from 100 seconds to 140 seconds. Further a single tray can accommodate upto 126 pieces of convex-lens-mold assembly. The processing tray also improves the effect of ultrasound at circumferential surface of lens-glass-mold assembly.

[036] Second Stage of de-molding:
In second stage with absence of ultrasound, the input step-temperature of tank 2 is reduced to 25? - 40?. In the aforementioned condition the mold-lens assembly undergoes differential contraction which also improves the shelf-life. The bonding between the lens and glass-mold is released. Thereafter the lens is separated from the molds gently by hands without applying undue stress at the circumferential surface of molds. Further, a holding time of 2 minutes to 5 minutes at ambient temperature is required to release the grip at the interface between lens and glass molds. Hence, the second processing tank (tank 2) is only used for cooling the said assembly to detach the lens from glass molds easily.
[037] The proposed method is suitable for bulk demolding process of convex lens by reducing the process time, and physical damage in molds which improves the shelf-life of the mold. In an exemplary embodiment, a convex lens of power +0.25 to +4.00 is successfully demolded from a 73 mm mold lens assembly.

[038] In accordance with the present invention the advantages of the proposed method are enlisted below:
1. Convex bulk ophthalmic lens of index 1.56 is demolded without applying manual mechanical force.
2. Shelf-life of convex-glass-molds is improved by suitable operating temperature in tank 1 and tank 2 and also the temperature difference between them.
3. Since no pressure is induced on lens-mold assembly due to absence of ultrasound in tank 2, the shelf-life of molds can be improved.
4. Processing-Tray is designed to accommodate relatively more number of convex lens-mold assembly as compared to concave lens-mould assembly.
5. Processing tray also facilitates to improve the effect of ultrasound at circumferential surface of lens-glass-mold assembly.

[039] During manual demolding, reduction of shelf-life of convex/plus power molds are significantly higher than the minus power molds. Hence, the present invention is also more effective for increasing shelf life of the plus power mold. However, the method disclosed in the present invention is applicable for demolding of both convex and concave lens from the glass mold assembly.

[040] While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

We Claim:

1.A method for demolding lens from a glass mold assembly, comprising the steps of:
a. positioning the glass mold-lens assembly on a processing tray;
b. immersing the processing tray from step (a) in a first type of tank filled with hot fluid;
c. projecting ultrasonic waves along the direction of perimeter of the lens and glass mold assembly; and
d. immersing the processing tray obtained from step (c) in a second type of tank filled with warm fluid,
wherein,
differential thermal expansion reduces the strength of bonding at interface of lens and glass-molds in the first type of tank;
the ultrasonic waves release the grip at said interface; and
glass mold-lens assembly undergoes differential contraction in the second type of tank to release said bond between the lens and glass mold.

2. The method for demolding lens from glass mold assembly as claimed in claim 1, wherein the hot fluid in the first type of tank is water with temperature between 80? to 98?.

3. The method for demolding lens from glass mold assembly as claimed in claim 1, wherein frequency of the ultrasonic waves transmitted is in a range of 20 KHz to 50 KHz.

4. The method for demolding lens from glass mold assembly as claimed in claim 1, wherein the ultrasonic waves is incident with a power of 3.5W/inch2 to 5W/inch2.

5. The method for demolding lens from glass mold assembly as claimed in claim 1, wherein processing time in both the types of tank is up to 110 seconds.

6. The method for demolding lens from glass mold assembly as claimed in claim 1, wherein the warm fluid in the second type of tank is water with temperature between 25? to 40?.

7. The method for demolding lens from glass mold assembly as claimed in claim 1, wherein angle of incidence of the ultrasonic waves with the lens-glass mold assembly is zero.

8. The method for demolding lens from glass mold assembly as claimed in claim 1, wherein the processing tray can accommodate up to 126 pieces of lens-glass mold assembly.

9. The method for demolding lens from glass mold assembly as claimed in claim 1, wherein the lens is separated from the glass molds by hands without applying any undue stress after processing in the second type of tank.

10. The method for demolding lens from glass mold assembly as claimed in claim 1, wherein shelf life of glass molds is increased by regulating temperature of fluids in both the tanks.