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CN-122008604-A - Method for injection molding of positive power lens elements

CN122008604ACN 122008604 ACN122008604 ACN 122008604ACN-122008604-A

Abstract

A method for injection molding of a positive power lens element, the method comprising injecting a melt of a 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 are moved toward each other to define a final molding cavity having a volume that is less than the volume of the initial molding cavity. After cooling and opening the molding cavity, the positive power lens element is obtained. One of the two facing mold inserts includes a planar surface facing the initial molding cavity to form a planar surface on one 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 to form a convex surface on an opposite side of the positive power lens element.

Inventors

  • Qiu Haowen
  • D. Brassello
  • S. McDermott

Assignees

  • 依视路国际公司

Dates

Publication Date
20260512
Application Date
20180126
Priority Date
20170127

Claims (15)

  1. 1. A method for injection molding of a positive power lens element (13), the method comprising: injecting a melt of a thermoplastic material at a temperature above the glass transition temperature (Tg) of the thermoplastic material into an initial forming cavity defined by two facing mold inserts, the melt of thermoplastic material comprising at least one UV absorber; Moving the two facing mold inserts toward each other during the injection to define a final molding cavity having a volume less than the volume of the initial molding cavity, and -Obtaining said positive power lens element (13) after cooling and opening said molding cavity; One of the two facing mold inserts comprises a flat surface facing the initial molding cavity, forming a flat surface on one side of the positive power lens element (13); The other of the two facing mold inserts comprising a concave surface facing the initial molding cavity, thereby forming a convex surface on the opposite side of the positive power lens element (13), and Wherein said movement of said two facing mold inserts toward each other is effected at a speed of greater than 100 mm/s.
  2. 2. The method of claim 1, wherein the injecting is performed at a speed of greater than about 50 mm/s.
  3. 3. The method of claim 1, wherein the injecting is performed at a speed of 60-120 mm/s.
  4. 4. The method according to claim 1, wherein the rim distance between the two facing mold inserts when defining the initial molding cavity is no more than 2.5 times the rim thickness of the positive power lens element (13), and wherein the rim thickness of the positive power element is at most 1.0 mm, preferably at most 0.5 mm.
  5. 5. The method according to claim 4, wherein the edge distance between the two facing mold inserts at the time of defining the initial molding cavity is 1 to 2 times the edge thickness of the positive power lens element (13).
  6. 6. The method of claim 1, wherein said moving of said two facing mold inserts toward each other is accomplished at a speed of 150-250 mm/s.
  7. 7. The method of claim 1, wherein the thermoplastic material is a polycarbonate resin.
  8. 8. The method of claim 7, wherein the polycarbonate resin has a weight average molecular weight of less than 26,000 g/mol.
  9. 9. The method of claim 7 or 8, wherein the polycarbonate resin is injected at a speed of greater than about 50 mm/s and has a melt flow rate of at least 15 cm 3 /10 min, preferably at least 20cm 3 /10 min, at 300 ℃ per 1.2 kg, or a viscosity of less than 400 Pa at 300 ℃ for a shear rate of less than 1000 s-1, according to ISO 1133.
  10. 10. The method of claim 1, wherein the at least one UV absorber is a benzotriazole absorber.
  11. 11. The method of claim 1, wherein the at least one UV absorber is 2,2' -methylenebis (6- (2H-benzotriazol-2-yl) -4-1, 3-tetramethylbutyl) phenol).
  12. 12. The method of claim 1, wherein the at least one UV absorber is 2- (5-chloro-2H-benzotriazol-2-yl) -6- (1, 1-dimethylethyl) -4-methylphenol.
  13. 13. The method of claim 1, wherein the planar surfaces of the mold inserts of the two facing mold inserts have less than 20 fringes indicated using a flatness measurement of monochromatic light interference fringes.
  14. 14. The method of claim 1, further comprising bonding a flat side of the positive power lens element (13) to a side of a light guiding optical element.
  15. 15. A positive power lens element (13), comprising: a sheet of thermoplastic material comprising at least one UV absorber; the lamina has a planar first major surface and a convex second major surface; The flakes have a diameter in the range of 55-85 mm meters, an edge thickness of at most 0.5 mm, and a center thickness of at least 1.1 mm.

Description

Method for injection molding of positive power lens elements The present application is a divisional application of the application patent application entitled "method for injection molding of positive power lens elements" of PCT application PCT/EP2018/052001, chinese application number 201880008615.5, application date 2018, month 01, 26. Technical Field The present invention relates generally to a method for injection molding of positive power lens elements. Background Prescription augmented reality eyewear may include a lens assembly in which a light-directing optical element (LOE), such as 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. However, the front and rear lenses of such assemblies are much thinner than conventional unitary lens sheeting, which presents a significant challenge in their manufacture. It is highly desirable to produce such sheets from which such positive and negative lenses are cut by an injection molding process, as is done with lens sheets for conventional eyeglass lenses, however, the positive and negative lenses used in the three-part lens assembly of augmented reality eyeglasses are of such dimensions that they are less suitable for manufacturing using conventional injection molding techniques, such as the techniques described in commonly owned U.S. patent No. 7,854,865. Disclosure of Invention Accordingly, in one aspect, the present invention relates to a method for injection molding a positive power lens element, the method comprising injecting a melt of a 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 are moved toward each other to define a final molding cavity having a volume that is less than the volume of the initial molding cavity. After cooling and opening the molding cavity, the positive power lens element is obtained. One of the two facing mold inserts includes a planar surface facing the initial molding cavity to form a planar surface on one 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 to form a convex surface on an opposite side of the positive power lens element. The invention is characterized in that the step of moving the two facing mold inserts towards each other is carried out at a speed of less than 100 mm/s. In an exemplary embodiment of the method according to the present invention, the injection is performed at a speed exceeding about 50 mm/s. In an exemplary embodiment of the method according to the present invention, the injection is performed at a speed of about 60-120 mm/s. In an exemplary embodiment of the method according to the present invention, the edge distance between two facing mold inserts when defining the initial molding cavity is no more than 2.5 times the edge thickness of the positive power lens element. In an exemplary embodiment of the method according to the present 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 power lens element. In an exemplary embodiment of the method according to the present invention, said movement of said two facing mold inserts towards each other is effected at a speed of 150-250 mm/s. In an exemplary embodiment of the method according to the present invention, the thermoplastic material comprises one or more of polycarbonate, polyacrylate, polyol, polyamine, polyamide, polyanhydride, polycarboxylic acid, polyepoxide, polyisocyanate, polynorbornene, polysiloxane, polysilazane, polystyrene, polyolefin, polyester, polyimide, polyurethane, polythiourethane, polyallylate, polysulfide, polyvinyl ester, polyvinyl ether, polyarylene, polyoxide, polysulfone, polycycloolefin, polyacrylonitrile, polyethylene terephthalate, polyetherimide, polypentene, and cellulose triacetate. In an exemplary embodiment of the method according to the present invention, the thermoplastic material is a polycarbonate resin. In an exemplary embodiment of the method according to the present invention, the polycarbonate resin has a melt flow rate of at least 15 cm 3/10 min at 300 ℃ per 1.2 kg. In an exemplary embodiment of the method according to the present invention, the polycarbonate resin has a melt flow rate of at least 20 cm 3/10 min at 300 ℃ per 1.2 kg. In an exemplary embodiment of the method according to the present invention, the polycarbonate resin has a weight average molecular weight of less than 26,000 g/mol. In an exemplary embodiment of the method according to the present invention, the at least one UV absorber is a ben