Method for manufacturing optical articles

Abstract

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

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing optical articles, particularly for treating axial length-related disorders, such as for myopia control.

[0002] In particular, this disclosure relates to an injection molding method for encapsulating diffuse optical microstructures on the concave surface of a substrate. Background Technology

[0003] The eye can be defined as an optical sensor in which light from an external source is focused through the eye's lens onto the surface of the retina (an array of wavelength-dependent photoreceptors). Each of the various shapes the eye's lens can take is associated with a focal length at which external light is focused to produce an inverted image on the retinal surface corresponding to the external image observed by the eye. The eye's lens focuses light emitted or reflected by external objects located within a certain distance range from the eye; for objects located outside this range, focusing is poor or impossible.

[0004] In individuals with normal vision, the axial length of the eye, or the distance from the lens of the eye to the surface of the retina, corresponds to the focal length for near-optimal focusing on distant objects. The eye of an individual with normal vision focuses on distant objects by applying force to muscles that change the shape of the lens; this process is called "accommodation."

[0005] However, many people suffer from axial length-related disorders, such as myopia. In myopic individuals, the axial length of the eye is longer than the axial length required to focus on distant objects without accommodation. As a result, myopic individuals can see nearby objects clearly, but more distant objects are blurry. Although myopic individuals are generally able to accommodate, they can focus on objects at a shorter average distance than individuals with normal vision.

[0006] In myopic individuals, the relative axial length of the eye to the overall eye size continues to increase during development, leading to increasingly pronounced myopia.

[0007] Clinical trials have shown that achieving peripheral defocus or contrast reduction in the retina can help slow the progression of myopia. A common and known way to achieve peripheral defocus is through refraction. Some ophthalmic lenses are known to use carefully arranged arrays of microlenses with various additional refractive powers to focus light in front of the retina. Peripheral contrast reduction, on the other hand, is achieved through light scattering, where scattering centers (microstructures) at selected areas within the ophthalmic lens induce a contrast-reducing effect while maintaining visual acuity. Ophthalmic lenses with microstructures on concave surfaces to provide peripheral contrast reduction have been shown to effectively slow the progression of myopia in children and adolescents.

[0008] Light scattering and diffuse patterns can be created from microstructures of regular or random size and spatial distribution. These microstructures contribute to peripheral blurring, which is useful for helping control the progression of myopia. Scattering areas are created by using, for example, lasers to ablate materials or introduce microcracks.

[0009] Lenses with microlens arrays on convex surfaces or diffuse optical microstructures (engravings) on concave surfaces are known. In the first case, the optical refractive power of the microlenses is critical in myopia control and may be affected when a hard coating is applied. In the second case, engravings are not aesthetically pleasing; they tend to attract and retain contaminants and may be easily damaged. Furthermore, lenses with engravings are not suitable for mass production.

[0010] Injection molding methods for encapsulating optical microstructures on the concave surface of an optical substrate made of transparent thermoplastic (TP) material are known. More specifically, a TP wafer with surface microstructures on the concave surface is first prepared, and then a second transparent thermoplastic is injection molded to facilitate the encapsulation of the surface structure. Typically, to avoid compromising the benefits of the surface structure, two layers are chosen with a significant difference in refractive index and melt processing temperature. However, this leads to potential drawbacks such as thicker lenses, reduced impact resistance, adhesion problems with the hard coating, and poor aesthetics.

[0011] Figure 1 The concave surface 2 of the hard-coated lens 4 is shown, wherein the microstructure has been formed by laser engraving the concave surface 2.

[0012] Typically, the engraved microstructures have a diameter of approximately 200 µm, a depth of less than 10 µm, and a spacing of approximately 360 µm between the microstructures. These markings on lens 4 remain exposed and tend to attract and retain contaminants. Inattentive wearers may also damage the lens while cleaning it. Furthermore, the laser engraving process requires specific laser equipment in each Rx lab, which is not suitable for mass production as the volume of these lenses is expected to increase exponentially in the coming years.

[0013] Several existing technical documents propose methods, including lamination, overmolding, and injection molding, to encapsulate microstructures within the lens body, thereby eliminating coating dependence while providing protection for the microstructures. Encapsulating microstructures on the surface of a thermoplastic wafer via injection molding typically involves injecting a hot melt of another thermoplastic lens material onto the relatively cool, microstructured surface of the substrate.

[0014] Figure 2 The steps of an overmolding process for encapsulating microstructures within a lens body are illustrated. Figure 2The diagram shows an open mold 6 in which a wafer of a first thermoplastic material 8, such as a polycarbonate (PC) wafer, with microlenses (microstructures) inserted into a concave surface. The mold 6 is then closed, leaving an open space 10 between the wafer and the body of the mold 6. 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, thereby allowing the lens 14 to be obtained.

[0015] As disclosed above, the resulting microstructures will soften and deform under the high heat and pressure of the overmolding process. This leads to a loss of shape integrity and a deterioration of the optical design of the microstructures. Furthermore, careful selection of the first thermoplastic material 8 and the second thermoplastic material 12 is necessary to form a clear interface for good optical fidelity and lens sharpness, and to achieve a strong bond. The resulting lens 14 should ideally pass through subsequent Rx processing steps without issues such as delamination, cracking, and breakage; therefore, material selection is particularly challenging. A very specific property relationship is required between the two different thermoplastic materials 8 and 12. In addition, technical solutions are needed to prevent the microstructures from changing shape during injection overmolding to maintain the optical design and ensure compatibility and strong bonding between the two dissimilar materials 8 and 12.

[0016] Therefore, there are many challenges associated with encapsulating diffuse optical elements on the wafer surface via injection molding, namely maintaining optical diffuse properties (such as haze, visual acuity, and aesthetics) while also allowing for the mass production of the resulting optical products (such as lenses).

[0017] As mentioned, existing technologies have reported methods for encapsulating microstructures within the lens body through lamination, overmolding, and injection molding. Similar methods have also been proposed for the encapsulation of microstructures. Figure 3 The steps of the process for encapsulating microstructures are shown.

[0018] The first layer 20 is a wafer substrate laser-etched on a concave surface 22 using, for example, a UV laser (266 nm or 355 nm), thereby obtaining multiple microstructures 24. The molded wafer 20 is then coated with a low-refractive-index resin layer 26 (such as PMMA), thereby obtaining the final lens 28. The refractive index of the resin layer 26 is lower than that of the wafer 20, thus resulting in an increase in the overall thickness of the final lens 28. Other potential problems include incompatibility with standard coating processes and reduced impact resistance of the final lens 28.

[0019] If the wafer 20 and the resin layer 26 are made of the same material, the resulting final lens 28 will no longer maintain a haze level as the wide and shallow microstructure 24 is filled. Figure 4 This illustrates the use of the same materials in wafer 30 and resin layer 26, compared to... Figure 3 The same process steps are followed. In the final lens 28, the microstructure 24 is no longer visible.

[0020] Accordingly, there is a need to develop an innovative method for manufacturing optical products that incorporate microstructures on the concave surface of a substrate, particularly for treating axial length-related disorders, such as providing the aforementioned myopia control benefits, while being suitable for mass production, thereby overcoming the shortcomings of existing technologies. Summary of the Invention

[0021] This article provides a method for manufacturing optical products, the method comprising:

[0022] - Provide a substrate made of a predetermined first material and having a concave surface;

[0023] - Pattern the concave surface to obtain holes with a diameter less than 200 µm and a depth in the range of 10 µm to 1000 µm;

[0024] - A covering layer is obtained by applying a second material to the concave surface to coat it, thereby partially filling the pores while trapping some gas between them.

[0025] In the embodiments, the gas includes air, nitrogen, helium, argon, or another inert gas.

[0026] In this embodiment, the second material is the same as the first material of the substrate.

[0027] In one embodiment, the step of overmolding on the concave surface includes performing injection overmolding.

[0028] In one embodiment, the step of patterning the concave surface includes using a femtosecond laser to etch the concave surface.

[0029] In one embodiment, the step of patterning the concave surface includes generating a plurality of inserts on a convex support and pressing the plurality of inserts against the substrate to directly perforate the substrate, thereby obtaining the holes.

[0030] This article also provides an optical article comprising at least one of a lens, a PC wafer, and a film.

[0031] The aforementioned optical products can be designed to control an individual's myopia. Attached Figure Description

[0032] Further features and advantages of this disclosure will become apparent from the following description, provided only by way of non-limiting example and with reference to the accompanying drawings, in which:

[0033] Figure 1 The concave surface of a hard-coated lens is shown, wherein a microstructure has been created on the concave surface by laser engraving;

[0034] Figure 2 The steps of an overmolding process for encapsulating microstructures inside a lens body are shown.

[0035] Figure 3 The steps of the process for encapsulating microstructures are shown;

[0036] Figure 4 This illustrates the use of the same materials in both the wafer and the resin layer, compared to... Figure 3 The same process steps;

[0037] Figure 5 This demonstrates the application of femtosecond lasers in sculpting narrow and deep structures;

[0038] Figure 6 The steps of a method for manufacturing optical articles according to this disclosure are shown;

[0039] Figure 7 An example is shown of encapsulating a femtosecond laser-etched microstructure onto a wafer via injection molding, according to this disclosure; and

[0040] Figure 8 Alternative methods for manufacturing optical articles according to this disclosure are shown. Detailed Implementation

[0041] In the following description, the drawings are not necessarily drawn to scale, and some features may be shown in a generalized or schematic form for clarity and brevity or for informational purposes. Furthermore, although various embodiments of manufacture and use are discussed in detail below, it should be understood that many inventive concepts, as described herein, can be implemented in a wide variety of contexts. The embodiments discussed herein are merely illustrative and do not limit the scope of the invention. It will also be apparent to those skilled in the art that all technical features defined relative to the method can be transposed individually or in combination to the apparatus, and conversely, all technical features relative to the apparatus can be transposed individually or in combination to the method. To avoid unnecessary details for practicing the invention, certain information known to those skilled in the art may be omitted from this specification.

[0042] Femtosecond lasers are widely used for engraving plastics, metals, and other materials. The high-frequency pulse rate of femtosecond lasers allows for narrow and deep engravings without damaging the material. Figure 5 This demonstrates the application of femtosecond lasers in sculpting 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).

[0043] In particular, Figure 5 In the left-hand region (5a), a long-pulse laser 200 is shown applied to a substrate 202, creating a hole 204, with a damaged and heated area 206 around the hole, and leaving irregularities 208 on the surface of the substrate 202. Figure 5 In the right-hand region (5b), a femtosecond laser 210 is applied to a substrate 212 to create a hole 214, with no damaged or heated areas around the hole and no irregularities generated on the surface of the substrate 212.

[0044] Figure 6 The steps of a method for manufacturing an optical article according to this disclosure are shown.

[0045] In the first step 100, a femtosecond laser 54 is used to engrave (pattern) the concave surface 50 of the substrate 52, thereby obtaining holes 56 (engravings) with a diameter less than 200 µm and a depth ranging from 10 µm to 1000 µm. The substrate 52 is made of a predetermined first material, preferably a thermoplastic transparent resin. The substrate 52 is preferably a lens, a PC wafer, or a film. The holes 56 are obtained without thermal damage to the substrate 52.

[0046] In the next step 102, an overmolding process (preferably injection molding) is performed on the concave surface 50 by applying a second material (preferably a thermoplastic transparent resin) to the concave surface 50, thereby obtaining a cover layer 58 that partially fills the pores 56 while trapping some gas 60 between these pores. Thus, an optical article 62 is obtained, wherein the trapped gas 60 helps maintain the haze level and therefore allows for a peripheral contrast reduction effect.

[0047] Advantageously, the gas includes air, nitrogen, helium, argon, or other inert gases known to those skilled in the art.

[0048] Advantageously, the second material is the same as the first material of the substrate 52. In this case, the physical and chemical properties of the two layers (substrate 52 and capping layer 58) are identical, so the resulting optical article 62 has no compatibility issues with standard Rx processes. The impact strength of the optical article 62 is maintained, and the final thickness is unaffected because the refractive index of the optical article 62 is not reduced.

[0049] Figure 7 An example is shown of encapsulating a femtosecond laser-etched microstructure onto a PC wafer via injection molding, in accordance with this disclosure.

[0050] A PC wafer 80 with a diameter of 76 mm and a center thickness (CT) of 1.1 mm was obtained by injection molding using bisphenol A polycarbonate with a refractive index of 1.586 and a glass transition temperature of approximately 147°C, manufactured using Sabic Lexan® OQ3820. Narrow and deep holes (engravings) 82 were fabricated on the concave surface of the PC wafer 80 using a femtosecond laser (wavelength 1.06 µm, frequency 300 fs, pulse energy 0.2 mJ). The dimensions of the engraving 82 are:

[0051] - Diameter: 50 µm (diameter can range from 10 µm to 100 µm); and

[0052] - Depth: 100 µm (aspect ratio depth / diameter = 2, it can be between 1 and 10).

[0053] The engravings 82 are randomly distributed, with a center-to-center spacing of approximately 300 µm. A clear area 84 without engravings 82 is maintained at the center of the PC wafer 80.

[0054] The laser-engraved PC wafer 80 has been placed in the mold cavity and injection molding has been performed using the same PC resin as the PC wafer 80. According to Table 1 below, the resulting lens retains the light diffusion effect because air is trapped in the engraving 82.

[0055] Table 1

[0056]

[0057] A comparative example concerns a planar PC wafer with the same characteristics as the example above, where a shallow and wide engraving has been obtained on the concave surface of the PC wafer using a UV laser (355 nm wavelength) instead of the femtosecond laser cited here. The dimensions of the engraving are:

[0058] - Diameter: 200 µm, and

[0059] - Depth: 10 µm (depth / diameter aspect ratio = 0.05).

[0060] The engravings are randomly distributed, with a center-to-center spacing of approximately 300 µm. A clear 5 mm circle without engravings is maintained at the center of the wafer.

[0061] The laser-engraved PC wafer has been placed in the mold cavity and injection molding has been performed using the same PC resin as the PC wafer. Unlike the example presented above, in this case, the resulting lens exhibits no light diffusion effect because the PC resin completely fills the engraving, according to Table 2 below.

[0062] Table 2

[0063]

[0064] Figure 8 An alternative method for manufacturing optical articles according to this disclosure is shown. A plurality of inserts 90 with textured surfaces are formed on a convex support 92 and are used for direct contact with... Figure 6 The substrate 52 is perforated (the convex support 92 presses against the substrate 52) to obtain a narrow and deep hole 56. The substrate 52 is then overmolded as discussed above to obtain an optical article 62 with light diffusion properties to achieve a peripheral defocusing effect.

[0065] The method disclosed above for manufacturing optical products is specifically designed to address myopia control; however, the optical products obtained by this method are also suitable for alleviating or treating various axial length-related disorders.

[0066] Obviously, the principles of the present invention remain the same, and the embodiments and details of production may vary significantly from those described and shown only by way of non-limiting examples without departing from the scope of protection of the present invention as defined in the appended claims.

Claims

1. A method for manufacturing an optical article (62), the method comprising: - Provide a substrate (52) which is made of a predetermined first material and has a concave surface (50); - Pattern the concave surface (50) (100) to obtain a hole (56) with a diameter less than 200 µm and a depth in the range of 10 µm to 1000 µm. - A cover layer (58) is obtained by applying a second material to the concave surface (50) and overmolding (102) on the concave surface (50), which partially fills the pores (56) while trapping some gas (60) between the pores.

2. The method according to claim 1, wherein, The gas includes air, nitrogen, helium, argon, or another inert gas.

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

4. The method according to any one of the preceding claims, wherein, The step of overmolding (102) on the concave surface (50) includes performing injection overmolding.

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

6. The method according to any one of the preceding claims, wherein, The step of patterning (100) the concave surface (50) includes generating a plurality of inserts (90) on the convex support (92) and pressing the plurality of inserts (90) against the substrate (52) to directly perforate the substrate (52), thereby obtaining the hole (56).

7. An optical article, said optical article being manufactured according to any one of claims 1 to 6 for manufacturing an optical article.

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

9. The optical article according to claim 7, wherein the optical article is designed for controlling myopia in an individual.

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