Method for injection molding of a positive position lens element

Abstract

A method for injection molding of a positive power lens element, the method comprising injecting a melt of thermoplastic material at a temperature above the glass transition temperature (Tg) of the thermoplastic material into an initial molding cavity defined by two facing mold inserts, the melt of thermoplastic material comprising at least one UV absorber. During injection, the two opposing mold inserts move toward each other to define a final molding cavity having a volume smaller than that of the initial molding cavity. And after cooling and opening the forming cavity, obtaining the positive-power lens element. One of the two facing mold inserts includes a flat surface facing the initial molding cavity, thereby forming a flat surface on a side of the positive power lens element, and the other of the two facing mold inserts includes a concave surface facing the initial molding cavity, thereby forming a concave surface on a side of the positive power lens element. Thereby forming a convex surface on an opposite side of the positive power lens element.

Description

[0001] This application is a divisional application of Chinese patent application PCT / EP2018 / 052001, filed on January 26, 2018, with application number 201880008615.5 and application date of January 26, 2018, entitled "Method for Injection Molding of Positive Focus Lens Elements". Technical Field

[0002] This invention generally relates to a method for injection molding of positive focal lens elements. Background Technology

[0003] Prescription augmented reality glasses may include a lens assembly in which a light-guiding optics (LOE), such as that described in U.S. Patent No. 7,457,040, is sandwiched between a front plano-concave (positive) lens and a rear plano-convex (negative) lens, wherein the front and rear lenses correct the wearer’s vision.

[0004] However, the front and rear lenses of this assembly are much thinner than conventional one-piece lens sheets, which presents significant challenges in their manufacture. Ideally, such sheets would be produced by cutting the positive and negative lenses from them using an injection molding process, as is done for lens sheets used in conventional eyeglasses; however, the positive and negative lenses used in the three-piece lens assembly of augmented reality glasses are of such a size that they are not well-suited for manufacture using conventional injection molding techniques, such as those described in jointly owned U.S. Patent No. 7,854,865. Summary of the Invention

[0005] Therefore, in one aspect, the present invention relates to a method for injection molding a positive-focus lens element, the method comprising injecting a melt of a thermoplastic material at a temperature above its glass transition temperature (Tg) into an initial molding cavity defined by two opposing mold inserts, the melt of the thermoplastic material comprising at least one UV absorber. During injection, the two opposing mold inserts move toward each other to define a final molding cavity, the volume of which is smaller than the volume of the initial molding cavity. After cooling and opening the molding cavity, the positive-focus lens element is obtained. One of the two opposing mold inserts includes a flat surface facing the initial molding cavity, thereby forming a flat surface on one side of the positive-focus lens element, and the other of the two opposing mold inserts includes a concave surface facing the initial molding cavity, thereby forming a convex surface on the opposite side of the positive-focus lens element. A feature of the invention is that the step of moving the two opposing mold inserts toward each other is performed at a speed of less than 100 mm / s.

[0006] In an exemplary embodiment of the method according to the invention, the injection is performed at a speed of more than approximately 50 mm / s.

[0007] In an exemplary embodiment of the method according to the invention, the injection is performed at a speed of approximately 60-120 mm / s.

[0008] In an exemplary embodiment of the method according to the invention, the edge distance between two facing mold inserts when defining the initial molding cavity does not exceed 2.5 times the edge thickness of the positive focal lens element.

[0009] In an exemplary embodiment of the method according to the invention, the edge distance between the two facing mold inserts when defining the initial molding cavity is 1 to 2 times the edge thickness of the positive focal lens element.

[0010] In an exemplary embodiment of the method according to the invention, the movement of the two facing mold inserts toward each other is achieved at a speed of 150-250 mm / s.

[0011] In an exemplary embodiment of the method according to the present invention, the thermoplastic material includes one or more of polycarbonate, polyacrylate, polyol, polyamine, polyamide, polyanhydride, polycarboxylic acid, polyepoxide, polyisocyanate, polynorbornene, polysiloxane, polysilazane, polystyrene, polyolefin, polyester, polyimide, polyurethane, polythiocarbamate, polyallyl, polysulfide, polyethylene ester, polyethylene ether, polyaryl, polyoxide, polysulfone, polycyclic olefin, polyacrylonitrile, polyethylene terephthalate, polyetherimide, polypentene, and cellulose triacetate.

[0012] In an exemplary embodiment of the method according to the present invention, the thermoplastic material is polycarbonate resin.

[0013] In an exemplary embodiment of the method according to the invention, the polycarbonate resin has a density of at least 15 cm at 300°C / 1.2 kg. 3 Melt flow rate per 10 min.

[0014] In an exemplary embodiment of the method according to the invention, the polycarbonate resin has a density of at least 20 cm at 300°C / 1.2 kg. 3 Melt flow rate per 10 min.

[0015] In an exemplary embodiment of the method according to the invention, the polycarbonate resin has a weight-average molecular weight of less than 26,000 g / mol.

[0016] In an exemplary embodiment of the method according to the present invention, the at least one UV absorber is a benzotriazole absorber.

[0017] In an exemplary embodiment of the method according to the present invention, the at least one UV absorber is 2,2'-methylenebis(6-(2H-benzotriazol-2-yl)-4-1,1,3,3-tetramethylbutyl)phenol.

[0018] In an exemplary embodiment of the method according to the present invention, the at least one UV absorber is 2-(5-chloro-2H-benzotriazol-2-yl)-6-(1,1-dimethylethyl)-4-methylphenol.

[0019] In an exemplary embodiment of the method according to the invention, the flat surface of the mold insert in the two facing mold inserts has fewer than 20 fringes as indicated by a flatness measurement using monochromatic light interference fringes.

[0020] In an exemplary embodiment of the method according to the invention, the flat surface of the mold insert in the two facing mold inserts has fewer than 10 fringes as indicated by a flatness measurement using monochromatic light interference fringes.

[0021] In an exemplary embodiment of the method according to the invention, the positive focal lens element has an edge thickness of up to 1.0 mm and a center thickness of at least 1.1 mm.

[0022] In an exemplary embodiment of the method according to the invention, the flat side of the positive focal length lens element is coupled to one side of the light guide optical element.

[0023] In an exemplary embodiment of the method according to the invention, a negative focal length lens element is incorporated to the opposite side of the light-guiding optical element.

[0024] In another aspect, the present invention relates to a positive-focal lens element comprising a sheet made of a thermoplastic material, the sheet containing at least one UV absorber. The sheet has a flat first primary surface and a convex second primary surface. The sheet has a diameter in the range of 55-85 mm, an edge thickness of at most 1.0 mm, and a center thickness of at least 1.1 mm. Attached Figure Description

[0025] Other objects, features, and advantages of the invention will become clearer after reading the following detailed description of exemplary embodiments of the invention given with reference to the accompanying drawings, in which:

[0026] Figure 1a This is a schematic side view of a light-guiding optical element suitable for use in prescription augmented reality glasses lens assemblies;

[0027] Figure 1bThis is a schematic side view of a plano-concave lens suitable for use in prescription augmented reality glasses lens assemblies, produced according to the method of the present invention;

[0028] Figure 1c This is a schematic side view of a plano-concave lens produced according to the method of the present invention, to which a light-guiding optical element has been bonded;

[0029] Figure 1d This is a schematic side view of a plano-convex lens in a prescription augmented reality glasses lens assembly;

[0030] Figure 1e yes Figure 1c A schematic side view of a sub-component, to which a plano-convex lens has been attached;

[0031] Figure 1f yes Figure 1e A schematic side view of the sub-component, to which the micro-display projector has been integrated; and

[0032] Figure 2 yes Figure 1f A schematic side view showing the components already installed in the eyeglass frame. Detailed Implementation

[0033] Now for reference Figure 1a The light guide optic (LOE) 11 can be manufactured as described, for example, in U.S. Patent No. 7,457,040. To provide prescription augmented reality glasses, Figure 1b The front plano-concave (positive) lens 13 shown is combined with LOE 11, as follows Figure 1c As shown. Figure 1d The rear plano-convex (negative) lens 15 shown is then attached to the rear side of LOE 11, as... Figure 1e As shown. Next, as Figure 1f As shown, the microdisplay projector 17 is integrated into the edge of the LOE 11, and then the lens assembly is mounted into a pair of eyeglass frames 19, as follows. Figure 2 As shown.

[0034] The thin film used to manufacture the positive lens 13 includes a flat side and a curved side, and preferably meets the very stringent geometric, optical, and performance requirements shown below. Specifically, this lens should have an edge thickness (ET) of at most 0.5 mm and a center thickness (CT) of at least 1.3 mm. This lens should also allow for lens assemblies with a power distribution (spherical, cylindrical, prism), wherein the spherical and cylindrical powers are within ±0.06 diopters (D), and the prism is within ±(0.25 + 0.1 * diopters) / 2. The lens has a diameter of 16 × 16 mm at its center. 2The power uniformity, determined by a dual-lens mapper (DLM, manufactured by Automation & Robotics SA) measuring the area, preferably has a spherical-cylindrical peak-to-valence (PtV) value of less than 0.15 D. The warpage of the flat surface of the positive lens 13, determined by Automation & Robotics SA using the Focovision SR-2, preferably results in spherical and cylindrical lens values ​​within ±0.06 D (while in typical lens products, warpage up to 0.50 D is permissible). Furthermore, the warpage evolution of the coated flat surface, measured by the SR-2, preferably results in changes in spherical and cylindrical lens values ​​within ±0.03 D. The assembly should also pass FDA / CEN, thermal shock, pressure resistance, and UV aging tests.

[0035] These requirements present significant challenges to injection molding. Injection molding of thin films (or lenses) is accomplished by filling the molding cavity from one side to the other. However, for thin films, the center thickness is relatively thick, while the edge thickness is much thinner. The very thin edges exhibit very high flow resistance, causing the edge region to freeze before the molding cavity is filled.

[0036] A further challenge is that the high flow resistance at the periphery of the thin film requires very high injection pressure to fill the cavity, which can generate high residual stress in the molded part, ultimately leading to high warpage before and after coating.

[0037] The aforementioned difficulties have hindered the use of existing polycarbonate lens injection process configurations (including machines and high-viscosity ophthalmic grade PC resin) in the production of films that meet LOE assembly requirements.

[0038] The method according to the invention provides an injection molding technique for producing positive focal length sheets (preferably made of polycarbonate) that meet the above-mentioned performance criteria, particularly those concerning thickness and warpage.

[0039] In particular, it has been found that combining injection molding with a high-flow-rate thermoplastic resin (preferably polycarbonate), rather than with conventional ophthalmic-grade resin, reduces flow resistance and thus residual stress. High-speed injection molding is particularly effective in preventing premature freezing in the periphery of the sheet and in promoting cavity filling. This paper describes a process for injection molding positive sheets (preferably made of polycarbonate) using a high-speed injection molding process with specific process parameters and a high-flow-rate preferred polycarbonate resin with a specific viscosity range.

[0040] Example

[0041] Generally, the molding cavity for injection molding of sheet metal is formed by two opposing inserts, one flat and the other concave. The injection molding process is typically characterized by the formation of a cavity with an opening greater than the target part thickness at the start of the injection cycle. This increased cavity thickness significantly reduces flow resistance and thus reduces the pressure required to fill the cavity. Subsequently, before the injection ends, the cavity opening is rapidly closed by the movement of the inserts and / or the mold platen to the final part thickness. However, careful determination of the injection speed, the initial opening of the cavity, and the closing speed according to the invention is necessary to ensure that the cavity is filled and the cavity pressure is evenly distributed, thereby minimizing sheet warpage. It has been found that the injection speed is preferably greater than about 50 mm / s, and the movement of the two opposing mold inserts toward each other is advantageously performed at a speed greater than 100 mm / s. The initial edge distance of the cavity opening should not exceed 2.5 times the target sheet edge thickness, preferably between 1 and 2 times.

[0042] However, it was also found that when using high-viscosity ophthalmic-grade polycarbonate (PC) resins (such as Sabic Lexan RL7220), high-speed injection molding alone is often insufficient to produce positive films that meet optical requirements. These films must have a weight-average molecular weight of less than 26,000 and a minimum thickness of 15 cm³ at 300°C / 1.2 kg according to ISO 1133. 3 / 10 min, preferably at least 20 cm 3 Melt flow rate of / 10 min, or for less than 1000 s at 300°C. -1 High-flowability PC resins with a shear rate of less than 400 Pa and viscosity help overcome high flow resistance, reduce residual stress, and minimize warpage.

[0043] In addition, a very flat insert with fewer than 20 fringes, and preferably fewer than 10 fringes, as indicated by a flatness measurement using monochromatic interference fringes, should be used to ensure that the flat side of the sheet meets the flatness requirements of the LOE assembly process.

[0044] Finally, since most commercially available high-flow optical-grade PC resins are used for indoor applications (such as the production of CD / DVD or Blu-ray discs), they typically do not contain UV absorbers (UVA), which are necessary to prevent UV aging of LOE components and to provide UV protection for the wearer's eyes. An internal formulation was developed consisting of 0.1 wt% BASF Tinuvin 360 benzotriazole UV absorber mixed with high-flow PC resin. The formulation showed a UV cutoff of 380 nm, effectively preventing UV aging of the resulting film, as indicated by zero increase in yellowness index after 80 hours of QSun testing.

[0045] The thin sheets produced in this way will include gate marks, which are an aftereffect of the injection molding process.

[0046] Using the aforementioned standards, a combination of high-speed injection molding with carefully selected process parameters, flat inserts with specific flatness, and high-flow PC resin containing UVA within a specific viscosity range has been used to injection mold positive LOE PC sheets that meet very stringent geometric, optical, and performance requirements.

[0047] The table below compares the injection molding results of positive LOE PC sheets produced according to the present invention (shown in the right column) with those of conventionally produced sheets (shown in the left column):

[0048]

[0049] As the data above shows, this method successfully produced +1.00 sheets that met optical and geometric requirements. Furthermore, birefringence analysis revealed that the residual stress of the sheets produced according to this invention was significantly lower compared to conventionally produced sheets. On the other hand, sheets with poorer optical properties were produced using conventional ophthalmic-grade PC and direct injection processes. The achievable minimum center thickness was 2.0 mm, and the edge thickness was 0.95 mm, which is significantly higher than the expected maximum edge thickness of 0.5 mm.

[0050] It should be understood that this method allows the use of existing injection molding machines and concave inserts, so that no new machines are needed, while producing positive sheets that meet all performance requirements.

[0051] Although the invention has been described in conjunction with various exemplary embodiments thereof, it should be understood that these embodiments are provided merely for illustrative purposes and should not be used as an excuse to limit the scope of protection conferred by the true scope and spirit of the appended claims.

Claims

1. A method for injection molding of a positive-focus lens element (13), the method comprising: A melt of the thermoplastic material at a temperature above the glass transition temperature (Tg) of the thermoplastic material is injected into an initial molding cavity defined by two facing mold inserts, the melt of the thermoplastic material containing at least one UV absorber. During the injection process, the two facing mold inserts are moved toward each other to define a final molding cavity, the volume of which is smaller than the volume of the initial molding cavity; as well as After cooling and opening the molding cavity, the positive focal length lens element (13) is obtained. One of the two facing mold inserts includes a flat surface facing the initial forming cavity, thereby forming a flat surface on one side of the positive focal lens element (13). The other of the two facing mold inserts includes a concave surface facing the initial forming cavity, thereby forming a convex surface on the opposite side of the positive focal lens element (13). as well as The movement of the two facing mold inserts toward each other is achieved at a speed greater than 100 mm / s.

2. The method according to claim 1, wherein, The injection was performed at a speed greater than approximately 50 mm / s.

3. The method according to claim 1, wherein, The injection is performed at a speed of 60-120 mm / s.

4. The method according to claim 1, wherein, When defining the initial forming cavity, the edge distance between the two facing mold inserts does not exceed 2.5 times the edge thickness of the positive focal lens element (13), and wherein the edge thickness of the positive focal element is at most 1.0 mm, preferably at most 0.5 mm.

5. The method according to claim 4, wherein, When defining the initial molding cavity, the edge distance between the two facing mold inserts is 1 to 2 times the edge thickness of the positive focal lens element (13).

6. The method according to claim 1, wherein, The movement of the two facing mold inserts toward each other is achieved at a speed of 150-250 mm / s.

7. The method according to claim 1, wherein, The thermoplastic material is polycarbonate resin.

8. The method according to claim 7, wherein, The polycarbonate resin has a weight-average molecular weight of less than 26,000 g / mol.

9. The method according to claim 7 or 8, wherein, The polycarbonate resin is injected at a speed greater than about 50 mm / s and has a minimum thickness of 15 cm at 300°C / 1.2 kg according to ISO 1133. 3 / 10 min, preferably at least 20 cm 3 Melt flow rate of / 10 min, or viscosity of less than 400 Pa at a shear rate of less than 1000 s⁻¹ at 300°C.

10. The method according to claim 1, wherein, The at least one UV absorber is a benzotriazole absorber.

11. The method according to claim 1, wherein, The at least one UV absorber is 2,2'-methylenebis(6-(2H-benzotriazol-2-yl)-4-1,1,3,3-tetramethylbutyl)phenol.

12. The method according to claim 1, wherein, The at least one UV absorber is 2-(5-chloro-2H-benzotriazol-2-yl)-6-(1,1-dimethylethyl)-4-methylphenol.

13. The method according to claim 1, wherein, The flat surface of one of the two facing mold inserts has fewer than 20 fringes as indicated by a flatness measurement using monochromatic light interference fringes.

14. The method of claim 1, further comprising attaching the flat side of the positive focal lens element (13) to one side of the light guide optical element.

15. A positive focal length lens element (13), comprising: A sheet of thermoplastic material, said thermoplastic material comprising at least one UV absorber; The sheet has a flat first main surface and a convex second main surface; The sheet has a diameter in the range of 55-85 mm, an edge thickness of up to 0.5 mm, and a center thickness of at least 1.1 mm.

Images