Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Utilizing plasma – electric – electromagnetic – particulate – or...
Reexamination Certificate
2000-07-24
2003-06-03
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Utilizing plasma, electric, electromagnetic, particulate, or...
C264S489000, C264S492000
Reexamination Certificate
active
06572794
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a photochromic molded article through photopolymerization of a photopolymerizable composition comprising at least one photopolymerizable monomer, at least one photoinitiator and at least one photochromic compound, and in particular to such a method which allows fast photopolymerization of the composition without degrading the photochromic compound.
2. Description of the Prior Art
Photopolymerizable compositions and in particular photopolymerizable compositions for making ophthalmic lenses are usually molded by filling the cavity of a two-part mold made of transparent mineral glass with a liquid photopolymerizable monomer composition and by irradiating the composition with an appropriate UV-light for polymerizing the composition.
A mold and an apparatus typically used for molding ophthalmic lenses are disclosed in U.S. Pat. Nos. 5,547,618 and 5,662,839.
Only one lens at a time can be molded using such a mold and apparatus and therefore the lens manufacturing efficiency is highly depending upon the duration of the irradiation polymerization step, at least up to a degree of polymerization at which the composition is sufficiently cured to become self-supporting or to be safely handled.
Document U.S. Pat. No. 5,621,017 discloses a method for producing photochromic cured products which comprises irradiating a photopolymerizable monomer composition including a photopolymerizable monomer, a photoinitiator and a photochromic compound. The amount of photochromic compound that can be incorporated in the composition must be kept in a very narrow range of 0.001 to 0.2 parts by weight and, preferably, of not smaller than 0.01 part by weight but smaller than 0.1 part by weight with respect to 100 parts by weight of the polymerizable monomer.
When the amount of photochromic compound is not larger than 0.001 parts by weight, the photochromic property is not obtained with sufficient degree of color concentration.
When the amount of the photochromic compound is larger than 0.2 parts by weight, on the other hand, the polymerization with light is not completed, in a short period of time. When the polymerizable monomer is not polymerized to a sufficient degree, photochromic property tends to be deteriorated within a short period of time.
Preferably, the photoinitiator used in the compositions of U.S. Pat. No. 5,621,017 exhibits a main absorption in an ultraviolet region and a molar absorption coefficient at 400 nm of larger than 150 lit./mol.cm, i.e. the photoinitiator has preferably a sufficient absorption in the visible region.
This method has several disadvantages.
During photopolymerization, the photochromic compound is submitted to intense UV radiation, which according to the prior art and in particular to U.S. Pat. No. 5,910,516, has two consequences:
The darkening of the photochromic compound which then filters UV-visible rays consequently limits the effectiveness of the photoinitiator activation. Therefore, the time necessary for polymerizing and achieving the final degree of polymerization or a degree of polymerization sufficient for a safe handling of the molded article is lengthened.
Prolonged irradiation for completing polymerization increases the risk of degrading the photochromic compound.
In order to solve the above technical problems, U.S. Pat. No. 5,910,516 describes the use of a UV filter capable of eliminating ultraviolet light having a wavelength below 400 nm. Elimination of the shorter UV light from the irradiation beam does effectively suppress or reduce the color development of the photochromic compound.
Although this method slightly increases the polymerization rate, as the photoinitiator can be activated by UV-visible radiations having wavelengths around 400 nm, the major part of the UV irradiation does not reach the photoinitiator and consequently cannot activate it.
Thus, there is still a need to provide a faster UV polymerization method for the molding of photochromic articles and especially for compositions including higher amounts of photochromic compounds and which leads to ophthalmic lenses having excellent photochromic performance (high colorability, high speed of darkening and lightening, resistance to photodegradation, and good durability of photochromic properties).
SUMMARY OF THE INVENTION
The object of the present invention is achieved by providing a method of manufacturing a photochromic molded article, such as an ophtalmic lens, comprising the steps of:
(a) filling a mold with a photopolymerizable monomer composition containing:
at least one photopolymerizable monomer;
at least one photoinitiator exhibiting a main absorption in a UV region; and
at least one photochromic compound capable of coloring upon UV irradiation;
(b) photopolymerizing said photopolymerizable composition under irradiation with a light comprising a UV portion and UV-visible portion; wherein,
before the beginning of the photopolymerization step, said photopolymerizable composition is subjected to a pre-heating step in which the temperature of said photopolymerizable composition is increased to a temperature reducing or preventing coloration of said at least one photochromic compound during the subsequent photopolymerization step.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The pre-heating step comprises heating the photopolymerizable composition at a temperature above the ambient temperature (ambient temperature meaning ≦25° C.) at which the photochromic compound is predominantly in a non-excited state or uncolored form even at the beginning of the irradiation by the UV light. Usually, the pre-heating comprises heating the photopolymerizable composition to a temperature ranging from 30 to 90° C., preferably from 40 to 60° C. and typically around 50° C.
The pre-heating step can be performed using any classical means such as air oven heating, hot-water heating, infra-red radiation heating and microwave heating.
The photopolymerizable monomer composition can be pre-heated while in the mold cavity, before beginning photopolymerization, or it can be pre-heated before being poured in the mold cavity. In any case, the photopolymerizable composition must be at a temperature higher than ambient temperature (≦25° C.) and sufficient to at least reduce, and preferably prevent photochromic compound coloration during the photopolymerization step.
The photopolymerization step of the process of the invention is classical and generally comprises irradiating the photopolymerizable composition with a light comprising UV radiations. Preferably, the irradiation light also comprises a UV-visible portion having a wavelength spectrum around 400 nm.
Preferably also, the photopolymerization step comprises a pre-polymerization step in which the composition is irradiated with a UV light, preferably including a UV-visible portion around 400 nm, at a first intensity, followed by a further polymerization step with a UV light, preferably also including a UV-visible portion around 400 nm, at a second intensity higher than the first intensity.
By a UV-visible light portion around 400 nm, it is intended a light having a wavelength spectrum of 380 to 450 nm.
Usually, the UV light has a wavelength spectrum of 250 to 400 nm.
The pre-polymerization step, which is preferably of a short duration, generally will allow for obtaining a sufficient polymerization degree of the composition so that the pre-polymerized article is self-supporting and can be safely handled.
Generally, the pre-polymerization step can last from 1 second to 10 minutes and preferably 5 seconds to 1 minute.
The photopolymerizable monomers of the composition of the present invention may be any known monomer having a radical polymerizing group such as, for example, acrylate group, methacrylate group, vinyl group, and the like. Mixtures of such radical polymerizing monomers may be used.
A preferred class of radical polymerizing monomers are monomers of formula (I):
wherein
R
1
and R
2
, independently of each other, may represent hydrogen or a
Berzon Ronald A.
Darmes Daniel
Richard Gilles
Turshani Yassin
Weber Steve
Essilor International (Compagnie Generale d'Optique)
Fulbright & Jaworski L.L.P.
Vargot Mathieu D.
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