EP4784379A1 - Method for manufacturing an optical article - Google Patents

Abstract

1. A method for manufacturing an optical article (62) comprising: - providing a substrate (52) of a predetermined first material and having a concave surface (50); - patterning (100) said concave surface (50) so as to obtain pores (56) having a diameter lower than 200µm and a depth within the range 10µm - 1000µm; - overmolding (102) on the concave surface (50) by applying onto said concave surface (50) a second material, thus obtaining a cover layer (58) which partially fills the pores (56) while entrapping some gas (60) in between.

Description

METHOD FOR MANUFACTURING AN OPTICAL ARTICLE

DESCRIPTION

Technical field

[0001] The present disclosure relates to a method for manufacturing an optical article in particular for treating eye-length-related disorders, for example for myopia control.

[0002] In particular, the present disclosure relates to an injection molding method for encapsulating diffusive optical micro-structures on the concave surface of a substrate.

Backaround information and prior art

[0003] The eye can be defined as an optical sensor in which light from external sources is focused, by an eye lens, onto the surface of the retina, an array of wavelength-dependent photosensors. Each of the various shapes that the eye lens can adopt is associated with a focal length at which external light rays are focused to produce inverted images on the surface of the retina that correspond to external images observed by the eye. The eye lens focuses light emitted by, or reflected from external objects that lie within a certain range of distances from the eye, and less optimally focuses, or fails to focus objects that lie outside that range of distances.

[0004] In normal-sighted individuals, the axial length of the eye, or distance from the eye lens to the surface of the retina, corresponds to a focal length for near-optimal focusing of distant objects. The eyes of normal-sighted individuals focus distant objects through muscles which apply forces to alter the shape of the eye lens, a process referred to as “accommodation".

[0005] Many people, however, suffer from eye-length-related disorders, such as for example myopia. In myopic individuals, the axial length of the eye is longer than the axial length required to focus distant objects without accommodation. As a result, myopic individuals can view near objects clearly, but objects further away are blurry. While myopic individuals are generally capable of accommodation, the average distance at which they can focus objects is shorter than that of normal-sighted individuals.

[0006] In myopic individuals, the relative axial length of the eye to overall eye size continues to increase during development, thus leading to increasingly pronounced myopia. [0007] Clinical trials have shown that achieving peripheral defocus or contrast reduction in the retina helps mitigate myopia progression. The commonly known way to achieve peripheral defocus is by refraction. Ophthalmic lenses are known where carefully arranged micro-lens arrays with various added powers cause light to focus in front of the retina. On the other hand, peripheral contrast reduction is achieved by scattering of light, where scattering centers (micro-structures) at select areas in the ophthalmic lens induce the contrast reduction effect while maintaining visual acuity. Ophthalmic lenses with micro-structures on the concave surface to provide peripheral contrast reduction have been shown to effectively slow down the progression of myopia in kids and teens.

[0008] Light scattering, diffusive patterns can be made of micro-structures of regular or random distribution of sizes and spaces. The micro-structures help with peripheral blurring that is useful to help control myopia progression. The scattering region is generated using, for example, a laser to ablate materials or to introduce micro cracks.

[0009] Lenses with micro-lens arrays on the convex surface or with diffusive optical microstructures (engravings) on the concave side are known. In the first case, the optical powers of the micro-lenses are critical in myopia control and may be affected upon the application of a hard coat. In the second case, the engravings are aesthetically unappealing, they tend to attract and retain contaminants and can be easily damaged. Furthermore, lenses with engravings are not suitable for mass production.

[0010] An injection molding method for encapsulating optical micro-structures on the concave surface of an optical substrate of a transparent thermoplastic (TP) material is known. More specifically, a TP wafer with surface micro-structures on the concave side is first prepared, followed by injection overmolding of a second transparent thermoplastic to facilitate the encapsulation of the surface structures. Typically, to avoid the loss of the benefit of the surface structures the two layers need to be selected so that there is a significant difference in refractive index and melt processing temperatures. However, this leads to potential drawbacks such as thicker lenses, lowered impact resistance, hard coat adhesion issues and poor aesthetics.

[0011] Figure 1 shows a concave surface 2 of a hard coated lens 4 wherein the microstructures have been made by laser engraving the concave surface 2.

[0012] Typically, the engraved micro-structures have a diameter of about 200pm, a depth lower than 10pm and a spacing between the micro-structures of about 360pm. These markings on the lens 4 stay exposed and tend to attract and retain contaminants. They can also be damaged by wearers that do not take special care when cleaning the lenses. Additionally, the laser engraving process requires that each Rx laboratory has a specific laser equipment, and this is not suitable for mass production as the volume of these lenses is expected to grow exponentially in the next few years.

[0013] Several prior art documents propose methods including lamination, overcasting, and injection overmolding to encapsulate micro-structures inside the lens body to eliminate coating dependence while providing protection to the micro-structures. Encapsulation of microstructures on the surface of a wafer of a thermoplastic material by injection overmolding typically involves injecting a hot melt of another thermoplastic lens material over the relatively cold microstructured surface of a substrate.

[0014] Figure 2 shows the step of an overmolding process to encapsulate microstructures inside a lens body. In Figure 2 it is shown an open mold 6 wherein a wafer of a first thermoplastic material 8, such as a polycarbonate (PC) wafer, having micro-lenses (microstructures) on the concave surface is inserted. Then, the mold 6 is closed leaving on open space 10 between the wafer and the body of the mold 6. A hot melt of a second thermoplastic material 12, such as PMMA, is injected into the open space 10 through a filler 16. Finally, the mold 6 is opened, thus allowing obtaining a lens 14.

[0015] The micro-structures created as above disclosed would soften and deform under high heat and high pressure of the overmolding steps. This result in a loss of shape integrity and in a worsening of the optical design of the micro-structures. Moreover, the first thermoplastic material 8 and the second thermoplastic material 12 need to be carefully selected in order to form a well-defined clear interface for good optical fidelity and lens clarity, and in order to achieve a strong bonding. The resulting lens 14 should in fact pass subsequent Rx processing steps without issues such as delamination, cracking, and chipping, therefore, the choice of the materials is particularly challenging. Very specific property relations between the two different thermoplastics materials 8, 12 are necessary. Furthermore, it is also necessary to have a technical solution to prevent the micro-structures from changing shapes during the injection overmolding, to preserve the optical design and to guarantee compatibility and strong bonding between the two dissimilar materials 8, 12.

[0016] There are therefore many challenges associated with the encapsulation of diffusive optical elements on the surface of a wafer by injection overmolding, namely preserving the optical diffusion properties such as haze, visual acuity and aesthetics, while also allowing a mass production of the resulting optical articles such as lenses.

[0017] As mentioned, the encapsulation of micro-structures inside the body of a lens by lamination, overcasting, and injection molding has been reported in prior art. A similar approach has been proposed for the encapsulation of the micro-structures as well. Figure 3 shows the step of a process for encapsulating micro-structures.

[0018] A first layer 20 is a wafer substrate that is laser engraved on a concave surface 22 using for example a UV laser (266 nm or 355 nm), thus obtaining a plurality of micro-structures 24. The wafer 20 is subsequently overmolded with a lower refractive index resin layer 26, such as PMMA, thus obtaining a final lens 28. The refractive index of the resin layer 26 is lower than the one of the wafer 20, therefore, this leads to increased overall thickness of the final lens 28. Other potential problems include incompatibility with the standard coating processes and lowered impact resistance of the final lens 28.

[0019] If the same material is chosen for the wafer 20 and for the resin layer 26, the resulting final lens 28 no longer maintains the haze level as the wide and shallow micro-structures 24 get filled. Figure 4 shows the same process steps of Figure 3 in the case of use of a same material for the wafer 30 and for the resin layer 26. In the final lens 28 the micro-structures 24 are no more visible.

[0020] Accordingly, there is the need to develop an innovative method for manufacturing an optical article that incorporates micro-structures on the concave surface of a substrate, in particular for treating eye-length-related disorders such as, for example, to provide the myopia control benefits above-mentioned, and that is, at the same time, suitable for a mass production, thus overcoming the drawbacks of the prior art.

Summary

[0021] What is provided herein is a method for manufacturing an optical article, comprising:

- providing a substrate of a predetermined first material and having a concave surface;

- patterning said concave surface so as to obtain pores having a diameter lower than 200pm and a depth within the range 10pm - 1000pm;

- overmolding on the concave surface by applying onto said concave surface a second material, thus obtaining a cover layer which partially fills the pores while entrapping some gas in between. [0022] In an embodiment, the gas comprises air, nitrogen, helium, argon or another inert gas.

[0023] In an embodiment, the second material is the same as the first material of the substrate. [0024] In an embodiment, the step of overmolding on the concave surface comprises performing an injection overmolding.

[0025] In an embodiment, the step of patterning the concave surface comprises engraving said concave surface using a femtosecond laser.

[0026] In an embodiment, the step of patterning the concave surface comprises creating a plurality of inserts on a convex support and pressing said plurality of inserts against the substrate to directly punch the substrate, thus obtaining the pores.

[0027] Also provided herein is an optical article comprising at least one of a lens, a PC wafer and a film.

[0028] The aforesaid optical article can be designed to control myopia of an individual.

Description of the drawings

[0029] Further characteristics and advantages of the present disclosure will become apparent from the following description, provided merely by way of a non-limiting example, with reference to the attached drawings, in which:

[0030] Figure 1 shows a concave surface of a hard coated lens wherein micro-structures have been made by laser engraving the concave surface;

[0031] Figure 2 shows the step of an overmolding process to encapsulate microstructures inside a lens body;

[0032] Figure 3 shows the step of a process for encapsulating micro-structures;

[0033] Figure 4 shows the same process steps of Figure 3 in the case of use of a same material for the wafer and for the resin layer;

[0034] Figure 5 shows the application of a femtosecond laser in engraving narrow and deep structures;

[0035] Figure 6 shows the steps of a method for manufacturing an optical article according to the present disclosure;

[0036] Figure 7 shows an example of encapsulation of femtosecond laser engraved micro-structures on a wafer by injection overmolding according to the present disclosure; and [0037] Figure 8 shows an alternative method for manufacturing an optical article according to the present disclosure.

Detailed description of embodiments [0038] In the description which follows, the drawing figures are not necessarily to scale, and certain features may be shown in generalized or schematic form in the interest of clarity and conciseness or for informational purposes. In addition, although making and using various embodiments are discussed in detail below, it should be appreciated that as described herein are provided many inventive concepts that may be embodied in a wide variety of contexts. Embodiments discussed herein are merely representative and do not limit the scope of the invention. It will also be obvious to one skilled in the art that all the technical features that are defined relative to a process can be transposed, individually or in combination, to a device and conversely, all the technical features relative to a device can be transposed, individually or in combination, to a process. To avoid unnecessary details for practicing the invention, the description may omit certain information already known to those skilled in the art.

[0039] Femtosecond lasers are widely used in the engraving of plastics, metals, etc. The high frequency pulse rate of the femtosecond lasers allows obtaining narrow and deep engravings without damaging the material. Figure 5 shows the application of a femtosecond laser in engraving narrow and deep structures (see Laser Focus World, https://www.laserfocusworld.com/industrial-laser-solutions/article/14215782/femtosecond-laser- processing-of-metal-and-plastics-in-the-medical-device-industry).

[0040] In particular, in a left area (5a) of Figure 5 it is shown the application of a long- pulse laser 200 to a substrate 202 which creates a hole 204 having a damaged and heated area 206 around it and leaving irregularities 208 on the surface of the substrate 202. In a right area (5b) of Figure 5 it is shown the application of a femtosecond laser 210 to a substrate 212 which creates a hole 214 without any damaged and heated area around it and without creating irregularities on the surface of the substrate 212.

[0041 ] Figure 6 shows the steps of a method for manufacturing an optical article according to the present disclosure.

[0042] In a first step 100, a concave surface 50 of a substrate 52 is engraved (patterned) using a femtosecond laser 54, thus obtaining pores 56 (engravings) having a diameter lower than 200pm and a depth within the range 10pm-1 .000pm. The substrate 52 is made up of a predetermined first material, preferably a thermoplastic transparent resin. The substrate 52 is preferably a lens, a PC wafer or a film. The pores 56 are obtained without thermal damage of the substrate 52.

[0043] In a next step 102, an overmolding, preferably an injection overmolding, is performed on the concave surface 50 by applying onto said concave surface 50 a second material, preferably a thermoplastic transparent resin, thus obtaining a cover layer 58 which partially fills the pores 56 while entrapping some gas 60 in between. An optical article 62 is therefore obtained wherein the entrapped gas 60 helps maintaining the haze level and hence allows obtaining a peripheral contrast reduction effect.

[0044] Advantageously, the gas comprises air, nitrogen, helium, argon or other inert gas well known to a person skilled in the art.

[0045] Advantageously, the second material is the same material as the first material of the substrate 52. In such a case, the physical and chemical properties of the two layers (the substrate 52 and the cover layer 58) are the same and hence the resultant optical article 62 has no compatibility issues with the standard Rx process. The impact strength of the optical article 62 is maintained and the final thickness is also not affected as the refractive index of the optical article 62 is not lowered.

[0046] Figure 7 shows an example of encapsulation of femtosecond laser engraved micro-structures on a PC wafer by injection overmolding according to the present disclosure.

[0047] A PC wafer 80 having a diameter of 76mm and a CT (center thickness) of 1 ,1 mm has been obtained by injection molding using the Sabie Lexan® OQ3820, a bisphenol-A polycarbonate having a refractive index of 1 .586 and a glass transition temperature of about 147°C. Narrow and deep pores (engravings) 82 on the concave face of the PC wafer 80 have been fabricated using a femtosecond laser (1.06pm wavelength, 300fs frequency, pulse energy 0.2mJ). The dimensions of the engravings 82 are:

- diameter: 50pm (the diameter can be in the range 10-100pm); and

- depth: 100pm (aspect ratio depth/diameter = 2, it can be between 1 and 10).

The engravings 82 have been randomly distributed with the center-to-center spacing of around 300pm. A 5mm circle of clear zone 84 has been maintained in the center of the PC wafer 80 without engravings 82.

[0048] The laser engraved PC wafer 80 has been placed in a mold cavity and an injection overmolding with the same PC resin of the PC wafer 80 has been performed. The resulting lens retained light diffusing effect due to the trapping of air in the engravings 82, according to the following Table 1 .

Table 1 [0049] A counter-example regards a piano PC wafer having the same characteristics of the example here above wherein shallow and wide engravings have been obtained on the concave face of the PC wafer using a UV laser (355 nm wavelength) instead of the femtosecond laser here-above cited. The dimensions of the engravings are:

- diameter: 200pm, and

- depth: 10pm deep (depth/diameter aspect ratio = 0.05).

The engravings have been randomly distributed with the center-to-center spacing of around 300 pm. A 5mm circle of clear zone has been maintained in the center of the wafer without engravings. [0050] The laser engraved PC wafer has been placed in a mold cavity and an injection overmolding with the same PC resin of the PC wafer has been performed. Differently from the example here-above presented, in the present case the resulting lens had no light diffusing effect due to the complete filling of the engravings by the PC resin, according to the following table 2.

Table 2

[0051] Figure 8 shows an alternative method for manufacturing an optical article according to the present disclosure. A plurality of inserts 90 with a textured surface are created on a convex support 92 and used to directly punch the substrate 52 of Figure 6 (the convex support 92 is pressed against the substrate 52) to obtain the narrow and deep pores 56. The substrate 52 is subsequently overmolded as above discussed to get the optical article 62 with light diffusion property for peripheral defocus effect.

[0052] The above-disclosed method(s) for manufacturing an optical article are designed in particular to address the myopia control, however, the optical article obtained through such method(s) is suitable also for alleviating or treating different eye-length-related disorders.

[0053] Clearly, the principle of the invention remaining the same, the embodiments and details of production can be varied considerably from what has been described and illustrated purely by way of non-limiting example, without departing from the scope of protection of the present as defined in the attached claims.

Claims

1 . A method for manufacturing an optical article (62) comprising:

- providing a substrate (52) of a predetermined first material and having a concave surface (50);

- patterning (100) said concave surface (50) so as to obtain pores (56) having a diameter lower than 200pm and a depth within the range 10pm - 1000pm;

- overmolding (102) on the concave surface (50) by applying onto said concave surface (50) a second material, thus obtaining a cover layer (58) which partially fills the pores (56) while entrapping some gas (60) in between.

2. The method of claim 1 , wherein the gas comprises air, nitrogen, helium, argon or another inert gas.

3. The method of claim 1 or 2, wherein the second material is the same as the first material of the substrate (52).

4. The method of any of the preceding claims, wherein the step of overmolding (102) on the concave surface (50) comprises performing an injection overmolding.

5. The method of any of the preceding claims, wherein the step of patterning (100) the concave surface (50) comprises engraving said concave surface (50) using a femtosecond laser (54).

6. The method of any of the preceding claims, wherein the step of patterning (100) the concave surface (50) comprises creating a plurality of inserts (90) on a convex support (92) and pressing said plurality of inserts (90) against the substrate (52) to directly punch the substrate (52), thus obtaining the pores (56).

7. An optical article manufactured according to a method for manufacturing an optical article according to any of the claims 1 to 6.

8. The optical article according to claim 7, wherein the optical article comprises at least one of a lens, a polycarbonate (PC) wafer and a film.

9. The optical article according to claim 7, designed for controlling myopia of an individual.