Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
  • B29D11/00—Producing optical elements, e.g. lenses or prisms
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
  • B29D11/00—Producing optical elements, e.g. lenses or prisms
  • B29D11/00009—Production of simple or compound lenses
  • B29D11/00432—Auxiliary operations, e.g. machines for filling the moulds
  • B29D11/00442—Curing the lens material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
  • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
  • B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
  • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
  • B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
  • B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
  • B29C2035/0833—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation using actinic light

Definitions

• This invention relates to improved methods by which plastic resins can be cured to form ophthalmic lenses, semifinished blanks and optical preforms .
• Ophthalmic lenses often have complex geometries, with certain prescriptions having variations in thicknesses across the optic area of greater than an order of magnitude. Since the curing process is accompanied by shrinkage, a key objective of curing process development efforts is to be able to accommodate shrinkage without unduly increasing the cure time. I have developed a curing method for ophthalmic lenses that uses visible light to initiate cure, while nevertheless creating a colorless product.
• the lens does not undergo a prerelease, does not develop optical aberrations caused by the formation of local heterogeneities in the resin mass due to uneven flow, and does not develop surface defects or cracks due to resin shrinkage.
• U.S. Patent No. 4,919,850, issued to me I disclose a two stage cure process involving the use of ultraviolet polymerization initiators that allow the resin to gel under a low level of ultraviolet illumination. In this way, the initial cure rate is maintained at a low level, until the resin mass becomes a gel and mass flow ceases within the curing lens. This is important, because the risk of developing optical aberrations is highest at the initial stages of the curing process when local exotherms can induce optical aberrations through resin flow.
• the cure rate is accelerated by increasing ultraviolet light intensity. Increasing light intensity also serves to maintain the pace of curing as the initiator becomes depleted. Alternatively, the cure rate is also accelerated in the second stage by using UV light of a shorter wavelength. A commercial version of this process has now been introduced by the Rapidcast Corporation.
• a disadvantage of the two stage process, as disclosed in U.S. Patent No. 4,919,850 is that it typically uses two curing chambers for efficient implementation.
• An advantage of the present invention is that a process is provided which can be efficiently implemented using a single chamber.
• Another advantage of the invention is that the scope of the two stage curing process is expanded, rendering it applicable to resin formulations covering a wide range of chemical reactivities, functionalities, shrinkage properties, and thermal expansion characteristics.
• a curing method for ophthalmic lenses or semi-finished lens blanks wherein a curable resin is first exposed to radiation in the wavelength range of 400-800 NM. Then, the curable resin is subjected to heat or radiation of different wavelength or intensity than that used in the first step.
• the polymerizable resin preferably comprises: (1) a first photoinitiator that is activated by radiation in the wavelength range 400-800 NM and (2) a thermal initiator which is activated by heat, or a second photoinitiator which is activated by radiation of different wavelength or intensity than that used to activate the first photoinitiator.
• an ophthalmic lens, semifinished blank or optical preform is provided according to any of the methods described or claimed herein.
• a second stage of the cure process can subsequently be completed, by application of thermal energy, by application of UV light, or both.
• the initial curing stage may take place either directly under room light, or in chambers employing visible light bulbs.
• polymerization initiators which are activated by visible light are generally highly colored, it may appear at first sight that their use would be incompatible with the proposed application (i.e., to make an ophthalmic lens which is preferably colorless, or water white) .
• a new class of photopolymerization initiators has been commercialized which begin as a colored species and are activated by visible light, but upon activation form colorless photodissociation products. I discovered that .such photoinitiators can be used to develop cure processes for ophthalmic lenses and semi-finished blanks.
• a preferred photoinitiator is BAPO, available from Ciba Geigy Corp. This photopolymerization initiator is actually a mixture of two photoinitiators,
• the phosphine oxide derivative absorbs visible light in the wavelength range 400-450 NM range, and initiates polymerization of resins incorporating acrylic, methacrylic, vinylic or allylic derivatives. Under normal room illumination, the cure rate is slow. Therefore, the mold assemblies do not require cooling or other temperature control to undergo gelation. Nevertheless, precise temperature control does produce a more uniform product and improves product consistency and yield. If temperature control mechanisms are provided, they should be employed to control the temperature at or near room temperature, i.e., at about 15°C to 35°C.
• this photoinitiator works in the following fashion.
• the phosphine oxide derivative is activated and undergoes photodissociation under room light, leaving the acetophenone derivative unaffected.
• the phosphine oxide derivative undergoes bleaching on photodissociation, so that the polymerizing resin mass becomes less colored as polymerization progresses.
• the mold assembly is placed in a chamber equipped with ultraviolet light bulbs emitting radiation in the wavelength range of 300-
• the near ultraviolet radiation activates the acetophenone derivative, causing the curing process to become accelerated.
• the dissociation of the phosphine oxide derivative is completed, completing the bleaching process.
• a residual faint yellow hue can be corrected by an addition of a small amount of a bluing additive, such as TINOPAL (available from Ciba Geigy Corp.) to the resin formulation.
• the mold assembly may be heated along a preestablished temperature profile, ultimately reaching a final temperature in the range of about 90°-150°C, to complete the cure process and to obtain a final lens product with a glass transition temperature in the range of about
• the final product has a lower glass transition temperature (e.g., in the range of about 30°-50°C) .
• the cure process should be completed. The extent of the cure process can be monitored, for example, by a differential scanning calorimetric analysis of the material after cure. Whether heating is necessary to complete the cure generally depends on the monomers used in the resin formulation. Thus, if monomers used in the formulation can form homopolymers which have glass transition temperatures considerably above the room temperature
• a phosphine oxide derivative may be used which initiates cure under visible light as before.
• a thermal polymerization initiator such as a peroxide, a peracetate, a percarbonate or an azo derivative may be used to complete the second stage (post-gel cure) by placing the mold assembly in a thermal curing oven, typically a convection oven.
• the two stage polymerization process described above may be carried out in glass molds, in metal molds or in a combination thereof.
• Metal molds with reflective inner surfaces may be especially useful in reflecting radiation back into the resin mass and conducting excess heat away from the resin mass. Metal molds may also be made thinner, and thus can have a lower thermal mass than glass molds.
• glass molds with metallized surfaces may be employed for resin formulations which require a metal mold for adhesion and thus prevent prerelease during cure.
• the two stage polymerization method can be employed to produce lenses from resin formulations covering a wide range of chemical reactivities, functionalities, shrinkage properties, and thermal expansion characteristics. Both monomers and oligomers may be employed, and polymeric or small molecular weight additives can be included to alter physical properties of the resin formulation, such as viscosity and surface energy, as well as chemical properties of the formulation, such as oxidative and photothermal or hydrolytic stability.

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• Health & Medical Sciences (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Ophthalmology & Optometry (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Toxicology (AREA)
• Oral & Maxillofacial Surgery (AREA)
• Thermal Sciences (AREA)
• Casting Or Compression Moulding Of Plastics Or The Like (AREA)
• Polymerisation Methods In General (AREA)
• Eyeglasses (AREA)
• Polymerization Catalysts (AREA)

Applications Claiming Priority (3)

Publications (1)

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Family Applications (1)

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• 1996
  • 1996-09-03 AU AU69635/96A patent/AU6963596A/en not_active Abandoned
  • 1996-09-03 CA CA002230646A patent/CA2230646A1/en not_active Abandoned
  • 1996-09-03 IL IL12347896A patent/IL123478A0/xx unknown
  • 1996-09-03 WO PCT/US1996/014098 patent/WO1997009170A1/en not_active Application Discontinuation
  • 1996-09-03 BR BR9610409-0A patent/BR9610409A/pt not_active Application Discontinuation
  • 1996-09-03 CN CN96197964A patent/CN1200696A/zh active Pending
  • 1996-09-03 EP EP96930670A patent/EP0847330A1/de not_active Withdrawn
  • 1996-09-03 JP JP51132697A patent/JP2001510404A/ja active Pending
  • 1996-09-03 KR KR1019980701535A patent/KR19990044298A/ko not_active Application Discontinuation
• 1998
  • 1998-03-02 MX MX9801691A patent/MX9801691A/es not_active Application Discontinuation

Non-Patent Citations (1)

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